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  • 2701.
    Ahmadian, Afshin
    et al.
    KTH, School of Biotechnology (BIO), Gene Technology.
    Ren, Z P
    Williams, Cecilia
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.
    Pontén, F
    Odeberg, Jacob
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.
    Pontén, J
    Uhlén, Mathias
    KTH, School of Biotechnology (BIO), Proteomics and Nanobiotechnology.
    Lundeberg, Joakim
    KTH, School of Biotechnology (BIO), Gene Technology.
    Genetic instability in the 9q22.3 region is a late event in the development of squamous cell carcinoma.1998In: Oncogene, ISSN 0950-9232, E-ISSN 1476-5594, Vol. 17, no 14Article in journal (Refereed)
    Abstract [en]

    Squamous cell carcinoma (SCC) of the skin represents a group of neoplasms which is associated with exposure to UV light. Recently, we obtained data suggesting that invasive skin cancer and its precursors derive from one original neoplastic clone. Here, the analysis were extended by loss of heterozygosity (LOH) analysis in the chromosome 9q22.3 region. A total of 85 samples, taken from twenty-two sections of sun-exposed sites, corresponding to normal epidermis, morphological normal cells with positive immuno-staining for the p53 protein (p53 patches), dysplasias, cancer in situ (CIS) and squamous cell carcinomas (SCC) of the skin were analysed. Overall, about 70% of p53 patches had mutations in the p53 gene but not LOH in the p53 gene or 9q22.3 region. Approximately 70% of the dysplasias showed p53 mutations of which about 40% had LOH in the p53 region but not in the 9q22.3 region. In contrast, about 65% of SCC and CIS displayed LOH in the 9q22.3 region, as well as frequent (80%) mutations and/or LOH in the p53 gene. These findings strongly suggest that alterations in the p53 gene is an early event in the progression towards SCC, whereas malignant development involves LOH and alterations in at least one (or several) tumor suppressor genes located in chromosome 9q22.3.

  • 2702.
    Ahmadian, Afshin
    et al.
    KTH, Superseded Departments, Biotechnology.
    Russom, Aman
    KTH, Superseded Departments, Biotechnology.
    Andersson, Helene
    KTH, Superseded Departments, Biotechnology.
    Uhlén, Mathias
    KTH, Superseded Departments, Biotechnology.
    Stemme, Göran
    KTH, Superseded Departments, Biotechnology.
    Nilsson, Peter
    KTH, Superseded Departments, Biotechnology.
    SNP analysis by allele-specific extension in a micromachined filter chamber2002In: BioTechniques, ISSN 0736-6205, E-ISSN 1940-9818, Vol. 32, no 4, p. 748-754Article in journal (Refereed)
  • 2703.
    Ahmadian Saieni, Hooman
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Non-linear vibrations of tensegrity structures2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A study has been done on different methods to solve the linear and non-linear problems with single or multi degrees of freedom structures. To do that direct time integration methods are used to solve the dynamic equilibrium equations. It has been tried to perform general methods to apply in most structures. In this thesis structures are made of cables and bars but the solution methods which is presented can be applied for any structure, and to utilize those implicit and explicit methods for all structures it is needed to know the tangent stiffness matrix and mass matrix for the structure. Then, it would be possible to analyze the dynamic response of structures under general loads and by general it can be understood that by application of arbitrary forces on different nodes of structure, the method generates result based on applied forces. It is crucial to get the right tangent stiffness matrix and mass matrix to know the dynamic equation in each node. Hence, the method will then work correctly to solve the dynamic problems. More, a parametric study has been done to see the effects of times step, stiffness of elements, length of elements, and other mechanical properties of elements, and this parametric study enables one to produce new results by changing every parameter. Also, continuation of the study on x-frame tensegrity has been done by solving them to check out dynamic response of structure with proposed methods of this thesis. Moreover, a method is presented to use the codes of solver methods of current thesis to apply them for other structures. Hence, as a future work, one can combine the codes of structures and solver codes of this thesis for dynamic response of structure. In fact the main effort of this thesis is on presenting different methods to solve various structures.

  • 2704. Ahmadian, Zahra
    et al.
    Salimi, Somayeh
    Salahi, Ahmad
    New Attacks on UMTS Network Access2009Conference paper (Refereed)
    Abstract [en]

    In this paper we propose two new attacks on UMTS network. Both attacks exploit the UMTS-GSM interworking and are possible in the GSM access area of UMTS network. The first attack allows the attacker to eavesdrop on the entire traffic of the victim UMTS subscriber in the GERAN coverage of the UMTS network. The second attack is an impersonation attack i.e. the attacker impersonates a genuine UMTS subscriber to a UMTS network and fools the network to provide services at the expense of the victim subscriber in its GERAN coverage.

  • 2705. Ahmadian, Zahra
    et al.
    Salimi, Somayeh
    Salahi, Ahmad
    Security Enhancement of UMTS-GSM Interworking Attacks2010In: Elsevier Journal of Computer Networks, ISSN 1389-1286, Vol. 54, no 18, p. 2256-2270Article in journal (Refereed)
    Abstract [en]

    In this paper we first present three new attacks on Universal Mobile Telecommunication System (UMTS) in access domain. We exploit the interoperation of UMTS network with its predecessor, Global System for Mobile communications (GSMs). Two attacks result in the interception of the entire traffic of the victim UMTS subscriber in the GSM access area of UMTS network. These attacks are applicable, regardless of the strength of the selected GSM encryption algorithm. The third attack is an impersonation attack and allows the attacker to impersonate a genuine UMTS subscriber to a UMTS network and fool the network to provide services at the expense of the victim subscriber. Then, we propose some countermeasures to strengthen the UMTS network against the mentioned attacks with emphasis on the practicality in present networks. The proposed solutions require limited change of the network elements or protocols, insignificant additional computational load on the network elements and negligible additional bandwidth consumption on the network links.

  • 2706.
    Ahmadi-Djam, Adrian
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematical Statistics.
    Belfrage Nordström, Sean
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematical Statistics.
    Forecasting Non-Maturing Liabilities2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With ever increasing regulatory pressure financial institutions are required to carefully monitor their liquidity risk. This Master thesis focuses on asserting the appropriateness of time series models for forecasting deposit volumes by using data from one undisclosed financial institution. Holt-Winters, Stochastic Factor, ARIMA and ARIMAX models are considered with the latter being the one with best out-of-sample performance. The ARIMAX model is appropriate for forecasting deposit volumes on a 3 to 6 month horizon with seasonality accounted for through monthly dummy variables. Explanatory variables such as market volatility and interest rates do improve model accuracy but vastly increases complexity due to the simulations needed for forecasting.

  • 2707. Ahmadinejad, F.
    et al.
    Møller, S. G.
    Hashemzadeh-Chaleshtori, M.
    Bidkhori, Gholamreza
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Jami, M. -S
    Molecular mechanisms behind free radical scavengers function against oxidative stress2017In: Antioxidants, ISSN 2076-3921, Vol. 6, no 3, article id 51Article in journal (Refereed)
    Abstract [en]

    Accumulating evidence shows that oxidative stress is involved in a wide variety of human diseases: rheumatoid arthritis, Alzheimers disease, Parkinsons disease, cancers, etc. Here, we discuss the significance of oxidative conditions in different disease, with the focus on neurodegenerative disease including Parkinsons disease, which is mainly caused by oxidative stress. Reactive oxygen and nitrogen species (ROS and RNS, respectively), collectively known as RONS, are produced by cellular enzymes such as myeloperoxidase, NADPH-oxidase (nicotinamide adenine dinucleotide phosphate-oxidase) and nitric oxide synthase (NOS). Natural antioxidant systems are categorized into enzymatic and non-enzymatic antioxidant groups. The former includes a number of enzymes such as catalase and glutathione peroxidase, while the latter contains a number of antioxidants acquired from dietary sources including vitamin C, carotenoids, flavonoids and polyphenols. There are also scavengers used for therapeutic purposes, such as 3,4-dihydroxyphenylalanine (L-DOPA) used routinely in the treatment of Parkinsons disease (not as a free radical scavenger), and 3-methyl-1-phenyl-2-pyrazolin-5-one (Edaravone) that acts as a free radical detoxifier frequently used in acute ischemic stroke. The cell surviving properties of L-DOPA and Edaravone against oxidative stress conditions rely on the alteration of a number of stress proteins such as Annexin A1, Peroxiredoxin-6 and PARK7/DJ-1 (Parkinson disease protein 7, also known as Protein deglycase DJ-1). Although they share the targets in reversing the cytotoxic effects of H2O2, they seem to have distinct mechanism of function. Exposure to L-DOPA may result in hypoxia condition and further induction of ORP150 (150-kDa oxygen-regulated protein) with its concomitant cytoprotective effects but Edaravone seems to protect cells via direct induction of Peroxiredoxin-2 and inhibition of apoptosis.

  • 2708.
    Ahmady, Tobias
    et al.
    KTH, School of Technology and Health (STH), Medical Engineering, Computer and Electronic Engineering.
    Klein Rosmar, Sander
    KTH, School of Technology and Health (STH), Medical Engineering, Computer and Electronic Engineering.
    Translation of keywords between English and Swedish2014Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this project, we have investigated how to perform rule-based machine translation of sets of keywords between two languages. The goal was to translate an input set, which contains one or more keywords in a source language, to a corresponding set of keywords, with the same number of elements, in the target language. However, some words in the source language may have several senses and may be translated to several, or no, words in the target language. If ambiguous translations occur, the best translation of the keyword should be chosen with respect to the context. In traditional machine translation, a word's context is determined by a phrase or sentences where the word occurs. In this project, the set of keywords represents the context.

    By investigating traditional approaches to machine translation (MT), we designed and described models for the specific purpose of keyword- translation. We have proposed a solution, based on direct translation for translating keywords between English and Swedish. In the proposed solu- tion, we also introduced a simple graph-based model for solving ambigu- ous translations. 

  • 2709.
    AHMADZADEH, KARAN
    KTH, School of Chemical Science and Engineering (CHE).
    Interaktions potentialla energin mellan ändliga rektangulära disperserade celullosa nanofibriller2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Thermodynamically, native cellulose nano fibrils are more stable in an aggregated state. The aggregated state is however not useful from a material development perspective. Therefore much research has been done to stabilize the dispersal of the fibrils. One method to overcome this instability is by surface substitution of the O6 hydroxyl group with carboxylate groups, to make highly charged fibrils in aqueous solutions. It is therefore of much interest to understand the interaction of highly charged fibrils in aqueous solutions. In this study, we aim to model the interaction potential energy between native and surface modified cellulose nanofibrils in order to understand under what conditions the contribution from the dipole interactions can be neglected. To achieve this we propose to use a continuum electrostatic approach, modeling the electrostatic interactions as a function of the fibrils relative dipole orientation, separation, surface charge as well as ionic strength of the solution, by means of using the Poisson-Boltzmann equation.

  • 2710.
    Ahmarinejad, Pegah
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    Fastighetsobligationer – Prissättningen av säkerställda kontra icke-säkerställda obligationer på en växande2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 2711. Ahmed, A. A.
    et al.
    Almeida, Teresa
    KTH, School of Electrical Engineering and Computer Science (EECS), Media Technology and Interaction Design, MID.
    Choi, J. O.
    Pincus, J.
    Ireland, K.
    What’s at issue: Sex, stigma, and politics in ACM publishing2018In: Proceeding CHI EA '18 Extended Abstracts of the 2018 CHI Conference on Human Factors in Computing Systems, Association for Computing Machinery (ACM), 2018, article id alt07Conference paper (Refereed)
    Abstract [en]

    Because publishing with the ACM is essentially required to advance our careers, we must examine its practices critically and constructively. To this end, we reflect on our experience working with the ACM student publication Crossroads. We encountered rigid content limitations related to sex and sexuality, preventing some contributors from foregrounding their connection to political activism, and others from publishing altogether. We explore the underlying institutional and sociopolitical problems and propose starting points for future action, including developing a transparent content approval policy and new organizations for politically-engaged computing researchers, all of which should center the leadership of marginalized individuals.

  • 2712. Ahmed, A.
    et al.
    Raza, Rizwan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. COMSATS Institute of Information Technology, Pakistan.
    Khalid, M. S.
    Saleem, M.
    Alvi, F.
    Javed, M. S.
    Sherazi, T. A.
    Akhtar, M. N.
    Akram, N.
    Ahmad, M. A.
    Rafique, A.
    Iqbal, J.
    Ali, A.
    Ullah, M. K.
    Imran, S. K.
    Shakir, I.
    Khan, M. A.
    Zhu, B.
    Highly efficient composite electrolyte for natural gas fed fuel cell2016In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 41, no 16, p. 6972-6979Article in journal (Refereed)
    Abstract [en]

    Solid oxide fuel cells (SOFCs) have the ability to operate with different variants of hydro carbon fuel such as biogas, natural gas, methane, ethane, syngas, methanol, ethanol, hydrogen and any other hydrogen rich gas. Utilization of these fuels in SOFC, especially the natural gas, would significantly reduce operating cost and would enhance the viability for commercialization of FC technology. In this paper, the performance of two indigenously manufactured nanocomposite electrolytes; barium and samarium doped ceria (BSDC-carbonate); and lanthanum and samarium doped ceria (co-precipitation method LSDC-carbonate) using natural gas as fuel is discussed. The nanocomposite electrolytes were synthesized using co-precipitation and wet chemical methods (here after referred to as nano electrolytes). The structure and morphology of the nano electrolytes were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The fuel cell performance (OCV) was tested at temperature (300-600 °C). The ionic conductivity of the nano electrolytes were measured by two probe DC method. The detailed composition analysis of nano electrolytes was performed with the help of Raman Spectroscopy. Electrochemical study has shown an ionic conductivity of 0.16 Scm-1 at 600 °C for BSDC-carbonate in hydrogen atmosphere, which is higher than conventional electrolytes SDC and GDC under same conditions. In this article reasonably good ionic conductivity of BSDC-carbonate, at 600 °C, has also been achieved in air atmosphere which is comparatively greater than the conventional SDC and GDC electrolytes.

  • 2713.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swedish National Road and Transport Research Institute (VTI).
    Biligiri, Krishna Prapoorna
    Department of Civil Engineering Indian Institute of Technology Kharagpur .
    Hakim, Hassan
    Swedish National Road and Transport Research Institute (VTI).
    An Algorithm to Estimate Rational Values of Phase Angles and Moduli of Asphalt Mixtures2013In: International Journal of Pavement Research and Technology, ISSN 1996-6814, Vol. 6, no 6, p. 745-754Article in journal (Refereed)
    Abstract [en]

    The objective of this study was to develop and evaluate an algorithm based on Fast Fourier Transform (FFT) that can calculate rational values of phase angle (f) and moduli of the variants of asphalt mixtures for the data obtained from the different frequency sweep tests. f and moduli for ten different asphalt mixtures resulting in over 690 data points collected from both USA and Sweden were computed using FFT. Theoretical observations revealed that there were significant differences for f between FFT and other methods to the order of 10-50%; however, there was no difference in moduli estimates for any mix and was independent of the test. Precisely, the FFT method produced rational f for mixtures that deviate from conventional mixture properties. Furthermore, statistical comparisons corroborated the predicted f estimates indicative of significant differences between the analysis techniques; but, the moduli were unaffected by the analysis methods. The study successfully illustrated the FFT technique, a user-friendly analytical procedure that can obviate the errors in the rational estimation of the acutely sensitive viscoelastic parameters.

  • 2714.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. Swedish National Road and Transport Research Institute, Sweden.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. Swedish National Road and Transport Research Institute, Sweden; University of Iceland.
    Characterisation of heavy traffic axle load spectra for mechanistic-empirical pavement design applications2015In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 16, no 6, p. 488-501Article in journal (Refereed)
    Abstract [en]

    Heavy traffic axle load spectrum (ALS) is one of the key inputs for mechanistic-empirical analysis and design of pavement structures. Frequently, the entire ALS is aggregated into number of equivalent single axle loads or assumed to have constant contact area (CCA) or constant contact pressure. These characterisations affect the accuracy and computational performance of the pavement analysis. The objective of this study was to evaluate these characterisations based on predicted performances to rutting and fatigue cracking of several pavement structures subjected to ALS data collected from 12 bridge weigh in motion stations. The results indicated that for layers below the top 25cm, all characterisations produced similar values of predicted rutting. However, for the top 25cm, the methods differed in the predicted performances to rutting and fatigue cracking. Furthermore, an improvement to the CCA approach was proposed that enhanced the accuracy while maintaining the same level of computational performance.

  • 2715.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. VTI.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. VTI.
    Characterization of heavy traffic axle load spectra for mechanistic-empirical pavement design applicationsIn: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268XArticle in journal (Refereed)
  • 2716.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. Swedish National Road and Transport Research Institute, Sweden.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Transport Science. Swedish National Road and Transport Research Institute, Sweden.
    Evaluation of a permanent deformation model for asphalt concrete mixtures using extra-large wheel tracking and heavy vehicle simulator tests2015In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 16, no 1, p. 154-171Article in journal (Refereed)
    Abstract [en]

    This paper evaluates a mechanistic–empirical permanent strain model for asphalt concrete mixtures. The evaluation was carried out based on two different types of tests: an extra-large wheel-tracking (ELWT) test and a full-scale accelerated pavement test using a heavy vehicle simulator (HVS). Asphalt slabs from three different types of asphalt mixtures were prepared for the ELWT test and tested at several pavement temperatures and tyre inflation pressures. Lateral wandering was also incorporated. The measured permanent deformations in the asphalt slabs were thereafter modelled using the permanent strain model from the US Mechanistic-Empirical Pavement Design Guide and model parameters were estimated for the three types of mixes. For validation, data from an HVS tested pavement structure consisting of the same asphalt mixtures as those tested using the ELWT were used. A set of calibration factors for the three mixtures were therefore obtained between the two tests. In all cases, the calibration factors were within ±20% from unity. Differences in geometry, scale, wheel loading configuration as well as the speed of loading between the two test devices could be the possible reasons for the differences in observed calibration factors.

  • 2717.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Erlingsson, Sigurdur
    Evaluation of permanent deformation models for unbound granular materials using accelerated pavement tests2013In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 14, no 1, p. 178-195Article in journal (Refereed)
    Abstract [en]

    Mechanistic-empirical (M-E) pavement design methods have become the focus of modern pavement design procedure. One of the main distresses that M-E design methods attempt to control is permanent deformation (rutting). The objective of this paper is to evaluate three M-E permanent deformation models for unbound granular materials, one from the US M-E pavement design guide and two other relatively new models. Two series of heavy vehicle simulator (HVS) tests with three different types of base material were used for this purpose. The permanent deformation, wheel loading, pavement temperature, and other material properties were continuously controlled during the HVS tests. Asphalt concrete layers were considered as linear elastic where stress-dependent behaviour of unbound materials was considered when computing responses for the M-E permanent deformation models with a nonlinear elastic response model. Traffic wandering was also accounted for in modelling the traffic by assuming it was normally distributed and a time-hardening approach was applied to add together the permanent deformation contributions from different stress levels. The measured and predicted permanent deformations are in general in good agreement with only small discrepancies between the models. Model parameters were also estimated for three different types of material.

  • 2718.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. Swedish National Road and Transport Research Institute, Pavement Technology, VTI, Linköping, Sweden .
    Erlingsson, Sigurdur
    Swedish National Road and Transport Research Institute, Pavement Technology, VTI, Linköping, Sweden .
    Modeling of flexible pavement structure behavior - Comparisons with Heavy Vehicle Simulator measurements2012In: Advances in Pavement Design Through Full-Scale Accelerated Pavement Testing - Proceedings of the 4th International Conference on Accelerated Pavement Testing, 2012, p. 493-503Conference paper (Refereed)
    Abstract [en]

    A response model to be employed in a mechanistic-empirical pavement performance prediction model based on multilayer elastic theory has been developed.An iterative approach using a method of successive over-relaxation of a stress dependency model is used to account for the nonlinear behavior of unbound materials. Asphalt and subgrade materials are assumed to be linear elastic. The response model was verified against two series of Heavy Vehicle Simulator (HVS) response measurements made under a variety of wheel load configurations and at different pavement temperatures.A comparison with FallingWeight Deflectometer (FWD) data was also carried out. The model was subsequently used to predict permanent deformation from the HVS testing using simplework hardening models.Atime hardening approach has been adopted to combine permanent deformation contributions from stress levels of different magnitude.The response model outputs and the predicted permanent deformations were generally in good agreement with the measurements.

  • 2719.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory. Swedish National Road and Transport Research Institute, Sweden.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Highway Engineering Laboratory. Swedish National Road and Transport Research Institute, Sweden.
    Numerical validation of viscoelastic responses of a pavement structure in a full-scale accelerated pavement test2017In: The international journal of pavement engineering, ISSN 1029-8436, E-ISSN 1477-268X, Vol. 18, no 1, p. 47-59Article in journal (Refereed)
    Abstract [en]

    This paper demonstrates the application of a generalised layered linear viscoelastic (LVE) analysis for estimating the structural response of flexible pavements. A comparison of the direct layered viscoelastic responses with approximate solutions based on the linear elastic (LE) and LVE collocation methods was also carried out. The different approaches were implemented by extending a layered elastic program with an improved computational performance. The LE and LVE collocation methods were further extended for analysis of pavements under moving loads. The methods were illustrated by analysing a pavement structure subjected to moving wheel loads of 30, 50, 60 and 80kN using a Heavy Vehicle Simulator (HVS). The various responses (stresses and strains) in the pavement, at pavement temperatures of 0, 10 and 20 degrees C, were measured using various types of sensors installed in the structure. It was shown that the approximated LVE solution based on the LE collocation method agreed very well with the measurements and is computationally the least expensive.

  • 2720.
    Ahmed, Abubeker W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. VTI.
    Erlingsson, Sigurdur
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering. VTI.
    Viscoelastic modelling of pavement structure behaviour in a full scale accelerated pavement testManuscript (preprint) (Other academic)
  • 2721.
    Ahmed, Abubeker Worake
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Mechanistic-Empirical Modelling of Flexible Pavement Performance: Verifications Using APT Measurements2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Mechanistic-Empirical  (M-E)  pavement  design  procedures  are  composed  of  a  reliable  response model to estimate the state of stress in the pavement and distress models in order to predict the different types of pavement distresses due to the prevailing traffic and environmental conditions. One of the main objectives of this study was to develop a response model based on multilayer elastic  theory   (MLET)  with  improved  computational  performance  by   optimizing  the   time consuming parts of the MLET processes. A comprehensive comparison of the developed program with  two  widely  used  programs  demonstrated  excellent  agreement  and  improved  computational performance.  Moreover,  the  program  was  extended  to  incorporate  the  viscoelastic  behaviour  of bituminous materials through elastic-viscoelastic correspondence principle. A procedure based on collocation of linear viscoelastic (LVE) solutions at selected key time durations was also proposed that improved the computational performance for LVE analysis of stationary and moving loads. A comparison  of  the  LVE  responses  with  measurements  from  accelerated  pavement  testing  (APT) revealed a good agreement. Furthermore the developed response model was employed to evaluate permanent deformation models  for  bound  and  unbound  granular  materials  (UGMs)  using  full  scale  APTs.  The  M-E Pavement  Design  Guide  (MEPDG)  model  for  UGMs  and  two  relatively  new  models  were evaluated  to  model  the  permanent  deformation  in  UGMs.  Moreover,  for  bound  materials,  the simplified  form  of  the  MEPDG  model  for  bituminous  bound  layers  was  also  evaluated.  The measured  and  predicted  permanent  deformations  were  in  general  in  good  agreement,  with  only small discrepancies between the models. Finally, as heavy traffic loading is one of the main factors affecting the performance of flexible pavement, three types of characterizations for heavy traffic axle load spectrum for M-E analysis and design of pavement structures were evaluated. The study recommended an improved approach that enhanced the accuracy and computational performance. 

  • 2722.
    Ahmed, Amber
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Industrial Ecology.
    Gong, Jindan
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Industrial Ecology.
    Assessment of the Electricity Generation Mix in Ghana: the Potential of Renewable Energy2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Electricity is a fundamental part a functioning society. Ghana’s electricity system is strained by an ever-growing climate instability and increase of population. Therefore, it is crucial for the country's development that it's electricity supply is done in a sustainable way.

    This report aims to analyze Ghana’s ability to reach SDG 7.1 and the Marrakech Vision, an outcome from the COP 22 meeting in Morocco. This was done by creating a model over Ghana’s electricity system and how it develops over time, called BAU, using the analytical tools: OSeMOSYS and OnSSET. A practical implementation of BAU was then discussed. After that, three development scenarios with different renewable energy targets for the electricity system, were implemented in the model. The results show that CSP and natural gas power plants were the most prominent electricity producers. The growing share of renewable energy in the target scenarios was mostly due to wind power, replacing the natural gas power plants.

    Ghana has local natural gas resources as well as high solar potential. The rising share of renewable energy limits the fossil fuel emission. At the same time, this increased share also endangers the reliability of the electricity supply, as the capacity of renewable energy resources fluctuate and could lead to high investment costs. BAU can be a possible solution which minimizes the fossil fuel consumption and limits the CO2 emissions, but at the risk of possibly having an unreliable electricity supply. To be able to meet SDG 7.1, increasing the share of renewable energy in electricity generation can be a solution, but at the same time, not all requirements of the goal will be fulfilled.

  • 2723. Ahmed, Aseel Bala
    et al.
    Jibril, B.
    Danwittayakul, S.
    Dutta, Joydeep
    Sultan Qaboos Univ, Water Res Ctr, Chair Nanotechnol, Muscat, Oman.
    Microwave-enhanced degradation of phenol over Ni-loaded ZnO nanorods catalyst2014In: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 156-157, p. 456-465Article in journal (Refereed)
    Abstract [en]

    Nickel was loaded onto hydrothermally-grown ZnO nanorods on cordierite substrates and tested as catalysts in microwave-enhanced degradation of phenol from its aqueous solution (100 ppm) at 70 degrees C. Effects of metal loadings (1, 10 and 20 mM impregnation solutions) on the degradation of phenol in aqueous solution was investigated. The catalyst performances were monitored based on phenol degradation, product distributions and carbon dioxide (CO2) evolutions. Based on the type of the catalysts, two different mechanistic pathways for the decomposition were observed-through catechol and/or hydroquinone as intermediates. It was found that the 10mM nickel loaded sample catalyzed the degradation through one pathway with hydroquinone as the benzenediol intermediate formed, while the 20 mM nickel impregnated sample catalyzed the reaction through two pathways, producing catechol as well as hydroquinone by products. These differences in reaction pathways were attributed to the variation in the composition of the nickel compounds and surface structures between the two catalysts. Furthermore, the effect of hydrogen peroxide (H2O2) as an oxidant was explored. It was found that although addition of H2O2 led to an increase in the degree of phenol degradation, it also led to enhanced catalyst leaching. There was also an increase in CO2 evolution due to the addition of H2O2. It was observed that 20 mM nickel-loaded sample without the addition of H2O2 exhibited optimum performance in terms of phenol degradation and CO2 evolution with no drawback of catalyst leaching. Catalytic microwave enhanced degradation is an effective means for the removal of dissolved organic compounds from wastewater.

  • 2724.
    Ahmed, Ashraf Awadelkarim Widaa
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Towards Affordable Provisioning Strategies for Local Mobile Services in Dense Urban Areas: A Techno-economic Study2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The future mobile communication networks are expected to cope with growing local usage patterns especially in dense urban areas at more affordable deployment and operation expenses. Beyond leveraging small cell architectures and advanced radio access technologies; more radio spectrum are expected to be required to achieve the desired techno-economic targets. Therefore, the research activity has been directed towards discussing the benefits and needs for more flexible and local spectrum authorization schemes. This thesis work is meant to be a contribution to this ongoing discussion from a techno-economic perspective.

     

    In chapter three, the engineering value of the different flexible authorization options are evaluated from the perspective of established mobile network operators using the opportunity cost approach. The main results in chapter three indicate the economic incentives to deploy more small cells based on flexible spectrum authorization options are subject to the potential saving in the deployment and operation costs. Nonetheless; high engineering value can be anticipated when the density of small cells is equal or larger than the active mobile subscribers’ density.

     

    While in chapter four, the possible local business models around different flexible authorization options are investigated from the perspective of emerging actors with limited or ’no’ licensed spectrum resources. In this context, dependent or independent local business can be identified according to surrounding spectrum regulations. On possible independent local business models for those emerging actors is to exploit the different flexible spectrum authorization options to provision tailored local mobile services. Other viable dependent local business models rest with the possibility to enter into different cooperation agreements to deploy and operate dedicated local mobile infrastructure on behalf established mobile network operators.

  • 2725.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Chatzimichail, Konstantinos
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Techno-economics of Green Mobile Networks Considering Backhauling2014In: European Wireless 2014; 20th European Wireless Conference; Proceedings of, Barcelona: VDE Verlag GmbH, 2014, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this paper we consider a comparative analysis of different deployment solutions in terms of total cost of ownership (TCO) and impact of energy efficiency as a cost parameter, i.e. mobile operator's electric bill. Different deployment options for the wireless segment of the network are considered: macro only versus heterogeneous networks with femto cells to support indoor traffic demand. In addition to the wireless segment different technologies for the backhauling segment are also considered: microwave versus fiber (10G-PON). Considering different user traffic intensities in an urban area and different environments such as business and residential areas, the impact of energy consumption on the TCO has been analyzed. The scope of the paper is extended to compare different backhaul technologies considering the annual increase in the traffic demand up to year 2020. The obtained results indicate that the impact of electric bill becomes more significant over the TCO especially after year 2018. Moreover, the heterogeneous deployment strategy utilizing indoor femto-cells achieves significant savings in terms of electric bill and TCO compared to the macro only solution. However, the saving ratio varies according to the adopted backhauling technology.

  • 2726.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Impact of the flexible spectrum aggregation schemes on the cost of future mobile network2015In: 2015 22nd International Conference on Telecommunications, ICT 2015, IEEE conference proceedings, 2015, p. 96-101Conference paper (Refereed)
    Abstract [en]

    Nowadays the spectrum regulations landscape is changing towards more flexible spectrum management schemes, such trends are expected to make additional spectrum resources available and lowers the spectrum access hurdles. In this paper, different spectrum aggregation scenarios have been compared focusing on the tradeoff between the total cost of ownership and the targeted QoS under different market conditions. The main finding in this study thereof indicates that the addition of more spectrum resources will lead to an overall reduction in the total cost of ownership (TCO) as long as the spectrum price remains small compared to the cost of the network infrastructure. Moreover, schemes such as LSA and secondary access will enable operators who have insufficient licensed spectrum resource to expand their mobile network infrastructure especially in hotspots with high subscribers demand in a cost-effective way. In this regard, the harmonization of spectrum use for LSA and TVWS across multiple countries stands as a key requirement for the reduction of the production cost of equipment and hence, the creation of an economy of scale considering both of the network equipment (i.e. radio base station) and end-subscriber devices. © 2015 IEEE.

  • 2727.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Interplay Between Cost,Capacity and Power Consumption in Heterogeneous Mobile Networks2014In: 2014 21st International Conference on Telecommunications, ICT 2014, Lisbon: IEEE Press, 2014, , p. 5p. 98-102Conference paper (Refereed)
    Abstract [en]

    Mobile operators nowadays tend to deploy dense heterogeneous layers of 3G and 4G networks in outdoor and indoor environments by adding more macrocells and small cells (e.g. microcells, picocells and femtocells) in response to the increasing demand for coverage and capacity. Another main driver and enabler behind this tendency is the phenomenon that around 80% of power consumption in mobile communication networks stems from the radio base stations. This situation makes mobile operators opt for the use of lowpower radio base stations to provide better coverage, capacity and an environmentally-friendly operation. In this paper the interplay between the deployment costs, targeted QoS and power consumptions have been studied considering two deployment options for the provisioning of the required mobile broadband coverage and capacity; namely the heterogeneous network (HetNet) option versus the homogenous macrocell deployment option. The main findings indicate that, the perceived saving in the total cost of ownership (TCO) resulting from offloading percentage of network traffic to indoor smallcell, in the case of HetNet, is bounded by the mobile subscriber density per area, their usage patterns, the adopted backhaul solution and the used spectrum resources. In general, a quite paying cost and power saving can be achieved by the heterogonous deployment solution for scenarios with high demand levels especially when there is a need to use the spectrum resources more efficiently.

  • 2728.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Cavdar, Cicek
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Ghanbari, Amirhossein
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Study on the effects of backhual solutions on indoor mobile deployment "macrocell vs. femtocell"2013In: 2013 IEEE 24th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC), IEEE conference proceedings, 2013, p. 2444-2448Conference paper (Refereed)
    Abstract [en]

    The deployment of low cost and low power base stations has been recognized in recent years as a promising cost-efficient solution and energy-efficient strategy. In this paper the femtocell and macrocell deployment options have been compared in the context of indoor mobile broadband deployment, with focus on the effect of different backhauling solutions in power consumption and the total deployment cost. This study has been based on the deployment of mobile broadband services within an area of one square kilometers in a new densely populated business district where the different user demands, spectrum bandwidths, backhaul technologies and radio access technologies are taken into account. Moreover, various deployment scenarios reflecting the business perspectives of mobile operators have been looked into as well. The main findings reached indicate that backhaul solutions contribute differently to cost and power consumption depending on the employed deployment strategy. However, contributions to the total power consumption and to the CapEx and OpEx elements of the total deployment cost elements turned to be more significant in the case of femtocell deployment scenarios than in the case of macrocell ones. It is worthy of notice that the femtocell deployment is more cost-efficient, especially in high demand situation when new macro sites are needed to be deployed.

  • 2729.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Ghanbari, Amirhossein
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Evaluation of Spectrum Access Options for Indoor Mobile Network Deployment2013In: 2013 IEEE 24th International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC Workshops), IEEE , 2013, p. 138-142Conference paper (Refereed)
    Abstract [en]

    The investments in indoor mobile networks are highly related to the spectrum availability and its associated authorization options. The aim of this paper is to discuss the differences in the spectrum demand taking into consideration both wide and local area network deployment requirements and the kind of actor that provides the indoor wireless access. The analysis covers different authorizations options namely licensed, unlicensed, licensed shared access (LSA) and secondary access. A quantitative approach is used to analyze the differences between macrocell and femtocell deployments focusing on deployment cost and spectrum demand. This is complemented by a qualitative study to explore and discuss the strategic business decisions of different actors in view of the available spectrum bands and spectrum authorization options. The main conclusions from this study are; spectrum has more value in macrocell deployment scenarios than in femtocell ones. More spectrum in macrocell deployment scenarios means that operators can deploy less number of new sites and exploit previous infrastructure investments. Femtocell networks are often coverage limited which allows for frequency re-use. As a consequence, the value of spectrum is not the same for mobile network operators (MNOs) and for local network operator (LNOs). MNOs are traditionally confined to macrocell deployment strategies which entail the exclusive usage of licensed bands. While, the use of licensed spectrum by LNOs may incur more cost than the cost of infrastructure deployment. This explains why the use of unlicensed bands is lucrative and viable for LNOs. Furthermore, the LSA scheme may or could soon become an enabler for LNO's business due to the prevailing technical, regulation and policies developments.

  • 2730.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Ghanbari, Amirhossein
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Investment strategies for different actors in indoor mobile market: "in view of the emerging spectrum authorization schemes"2013In: 24th European Regional Conference of the International Telecommunication Society, Florence, Italy, 20-23 October 2013, 2013Conference paper (Refereed)
    Abstract [en]

    The regulatory landscape is changing towards more flexible spectrum management schemes. Such schemes are expected to make additional spectrum resources available and lower the spectrum access barriers. Emerging spectrum authorization schemes such as secondary access (TV White Space) and Licensed Shared Access (LSA) are expected to open doors for new actors rather than traditional MNOs to access licensed spectrum resources at reasonable costs. These schemes will allow actors such as Facility Owners (FO), Mobile Virtual Network Operators (MVNO) and Internet Service Providers (ISPs) to invest in indoor mobile network infrastructure. These actors can act as Local Network Operators (LNO) and build their business models around provisioning of mobile services in locations where there seems to be a hole or lack of service coverage in a particular area within the mobile network operators (MNOs) service footprint. This paper highlights the differences between indoor deployment and outdoor deployment in the light of the available spectrum bands to be used and the possible business models for MNOs and LNOs. In short, the possible investment strategies for provisioning indoor mobile services vary between MNOs and LNOs cases due to economic and regulatory aspects surrounding them. The main finding in this study indicates that the willingness of MNOs to invest in dedicated indoor solutions is driven by the balance between the potential revenues and the deployment cost. Moreover MNOs have more spectrum and investment options compared to LNOs who must bond their investment strategies to the available spectrum resources (i.e. the regulations of spectrum access).

  • 2731.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth. KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Ghanbari, Amirhossein
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    The Incentives and Challenges of Delivering Linear Broadcasting Services over Cellular Network in Developing Countries: Sudan as Case study2014In: The 25th European Regional Conference of the International Telecommunications Society,Brussels, Belgium, 22nd - 25th June 2014, Brussels: nternational Telecommunications Society , 2014Conference paper (Other academic)
    Abstract [en]

    The Broadcasting sector has been evolved in terms of service production, transmission platform and reception devices in the last few decades. In contrast to cable and satellite platform, which are suitable for fixed reception only, the terrestrial digital platform can support portable, mobile and fixed reception scenarios. In general, there are two options of mobile multimedia service; one is based on a mobile communication network with IP cast known as MBMS (Multimedia Broadcast Multicast Services), while the other is based on broadcast technology. In the context of convergence, the players in the mobile sector argues that unlike traditional mobile  network systems, where the use was restricted to a given application, emerging  mobile networks will be able to carry a variety of services and accordingly separate broadcasting networks will no longer be required. In line with argument, it is not economically viable to roll out dedicated wireless broadband networks by the broadcasters to meet the increasing demand for interactive broadcasting services. That is why the broadcasters may look for innovative mechanism to deliver the broadcast services over mobile broadband network owned by the telecommunication operators.

    The focus on this paper is to investigate the incentives and challenges for such trend in developing countries; taking Sudan as case study. The main conclusion in this paper indicate that a potential economic incentive for delivering the broadcasting service over cellular network in Sudan subject to the deployment of high efficient mobile network. Moreover, the mobile operators may consider support such approach considering the increase demand for additional frequency resource.  However, the key challenges remain in how to develop a suitable regulations landscape to assure fair and competitive business practices on hand while guaranteeing the continuation of the public broadcasting service. In this regard, a new regulation framework needs to be developed to separate the three key functions in digital terrestrial broadcasting value chain (namely the content production and distribution). Further on, the necessary interconnection regulations need to put on place in order to pave the way for rollout of common platform that are necessary for interactive and nonlinear services. 

  • 2732.
    Ahmed, Ashraf Awadelkarim Widaa
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Ghanbari, Amirhossein
    KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.
    Toward capacity-efficient, cost-efficient and power-efficient deployment strategy for indoor mobile broadband2013In: 24th European Regional ITS Conference, Florence 2013, 2013Conference paper (Refereed)
    Abstract [en]

    Mobile operators nowadays tend to deploy dense heterogeneous layers of 3G and 4G networks in outdoor and indoor environments by adding more macrocells and smallcells (e.g. microcells, picocells and femtocells) in response to the increasing subscriber demand for coverage and capacity. The main driver and enabler behind this tendency is the phenomenon that around 80% of power consumption in mobile communication networks stems from the radio base stations. This situation makes mobile operators opt for the use low-power radio base stations to provide better coverage, capacity and a more environment-friendly operation. The use of low-power radio base stations leads to reduction of energy consumption in mobile communication networks power. The aim of this study is to conduct a comparative study between homogenous macrocell deployment and indoor smallcell deployments as alternative solutions for provision of the required indoor coverage and capacity. Moreover, the study highlights the importance of backhaul solutions being critical components in the smallcell network deployment. Furthermore, the scope of the study is extended to cover the investigation of the value of the heterogeneous (i.e. hybrid marcocell-femtocell) deployment scenario as a cost and power-efficient solution versus the homogenous marcocell deployment scenario in view of the variations in the mobile network traffic during the day. The main findings indicate that the CapEx and OpEx of the backhaul solution represent the major part of the total deployment cost in the indoor smallcell deployment scenario (i.e. femtocell case) compared to those of the macrocell deployment scenario. Nonetheless, the perceived saving in the total cost of ownership (TCO) resulting from the use of indoor smallcell (i.e. femtocell) remains a satisfactory and convenient motivation considering the traffic variation across the day, traffic distribution between indoor and outdoor locations and the keenness to use the spectrum resources more efficiently.

  • 2733.
    Ahmed, Ashraf
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Yang, Yanpeng
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Won Sung, Ki
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Markendahl, Jan
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    On the Engineering Value of Spectrum in Dense Mobile Network Deployment Scenarios2015Conference paper (Refereed)
    Abstract [en]

    the continuing growth in the mobile data traffic magnifies the challenges for the design and deployment of scalable high-capacity mobile networks that can meet the future demand at reasonable cost levels. In order to meet the future traffic demand, an operator should invest on both infrastructure, i.e. densification of base stations, and more radio spectrum. Knowing the effectiveness of each element is thus of utmost importance for minimizing the investment cost. In this paper, we study the economic substitutability between spectrum and densification. For this, we measure the engineering value of spectrum, which refers to the potential saving in the total cost of ownership (TCO) as result of acquiring additional spectrum resources. Two countries are considered to represent different market situations: India with dense population and high spectrum price and Sweden with moderate population density and low spectrum fee. Numerical results indicate that additional amount of spectrum substantially relieves the need for densifying radio base stations, particularly for providing high user data rate in dense India. Nonetheless, the engineering value of spectrum is low in India (i.e. spectrum acquisition has less cost benefit) under the high spectrum price of today, whereas spectrum is instrumental in lowering the total cost of ownership in Sweden. Our finding highlights the importance of affordable and sufficient spectrum resources for future mobile broadband provisioning.

  • 2734. Ahmed, Engy
    et al.
    Hugerth, Luisa W.
    KTH, School of Biotechnology (BIO), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Logue, Jürg Brendan
    KTH, School of Biotechnology (BIO), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Bruchert, Volker
    Andersson, Anders F.
    KTH, School of Biotechnology (BIO), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Holmström, Sara J. M.
    Mineral Type Structures Soil Microbial Communities2017In: Geomicrobiology Journal, ISSN 0149-0451, E-ISSN 1521-0529, Vol. 34, no 6, p. 538-545Article in journal (Refereed)
    Abstract [en]

    Soil microorganisms living in close contact with minerals play key roles in the biogeochemical cycling of elements, soil formation, and plant nutrition. Yet, the composition of microbial communities inhabiting the mineralosphere (i.e., the soil surrounding minerals) is poorly understood. Here, we explored the composition of soil microbial communities associated with different types of minerals in various soil horizons. To this effect, a field experiment was set up in which mineral specimens of apatite, biotite, and oligoclase were buried in the organic, eluvial, and upper illuvial horizons of a podzol soil. After an incubation period of two years, the soil attached to the mineral surfaces was collected, and microbial communities were analyzed by means of Illumina MiSeq sequencing of the 16S (prokaryotic) and 18S (eukaryotic) ribosomal RNA genes. We found that both composition and diversity of bacterial, archaeal, and fungal communities varied across the different mineral surfaces, and that mineral type had a greater influence on structuring microbial assemblages than soil horizon. Thus, our findings emphasize the importance of mineral surfaces as ecological niches in soils.

  • 2735.
    Ahmed, Fuad
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Porous Asphalt Clogging Performance Under Swedish Conditions2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Porous asphalt has gradually gained a lot of popularity in the past ten years for its ability to reduce traffic noise, especially noise generated between tire and road surface. The acoustical absorption properties are mainly due to the pore structure and the texture of the mixture. However, the percentage of these pores decrease during the lifetime. The main reason is that dirt and organic material get stuck in the air void structure and eventually cause clogging. In Nordic countries, particles from the road which get released due to the use of spiked tires accelerate clogging. To minimize wear and tear of these roads, larger aggregates are used. But, larger stone size diminishes the noise absorption ability of the mixture. Another reason that is attributed to void reduction is post-compaction. The fact that these mixtures damage prematurely and need more maintenance than conventional pavements is the main reason for its limited use.

    Given these problem, it is therefore important to understand how clogging can be minimized and/or reverted via operational maintenance actions. Different types of cleaning vehicles have been used previously to restore porosity. Unfortunately, these cleaning attempts have led to ambiguities and the effect of cleaning is widely debated. A method to look inside and to measure this effect is needed.

    This thesis has compared nine field core samples of porous asphalt from E4 Huskvarna, with the aim to conduct an in depth analysis of the air voids distribution before and after cleaning with a particular cleaning method. For this, the Skanska maintenance vehicle was selected, named VägRen  which is claimed to be optimized for porous asphalt under Nordic conditions has been used to clean a 100 m section. Cores were drilled before and after cleaning. The samples were scanned with high resolution X-ray computed tomography (CT) scanner in order to capture the entire morphology.  The digital image analysis program, AvizoFire® was used to characterize the 3D internal structure of air voids. Porosity evaluation as a function of depth of the asphalt layers has been studied to analyze the void distribution and cleaning effectiveness of the dirt with the investigated method.

    The results show that: (i) No visible damage induced by VägRen could be detected. (ii) Skanska's maintenance vehicles increased the air voids in the entire cleaned core and connected air voids increased by 83 %. The knowledge generated from this study can assist in the broader understanding of effectively utilizing porous asphalt under Nordic Conditions, though more research will be needed for conclusive results on the general effectiveness of the cleaning method and the effect of the life time of the pavement. 

  • 2736.
    Ahmed, Fuad
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Tabatabaei Araghi, Pedram
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Radonfritt boende: Stegen till att eliminera radongas med rätt Grundläggningsmetod2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    People who live in northern part of the world spend much more time indoors than those who live in warmer countries. In addition that home should be safe, it should also protect one against heat, cold, sunlight and pollution. The indoor environment is affected by installations, material and how the building is formed. Those anomalies that are visible, felt or smelled can be noticed and be rectified. But it’s much more difficult if these abilities are missing. Building houses in Sweden means that you have restrictions to follow. One has to adapt its house so that Swedish standards are maintained. Planning’s Building Regulation must be followed. Planning and Building Act and regulations must be met. Account has been takes for these provisions during the planning and design stage of the house. The following thesis will describe how various parameters have interacted for the design of the house. In depth the essay will illustrate how to build a radon resistant house and address how the air we inhale in our homes may eventually be harmful and finally how this problem is seen globally. International studies show that radon gas in indoor air increases the risk of getting lung cancer. By 2020, all single-family homes and public facilities must be remediated to a statutory value annual average level. It is one of sixteen environmental requirements that the parliament has set as a target for indoor environment. The National Board of health and Welfare has a guideline as a recommendation for indoor radon for existing homes while Planning´s Building Regulation has a limit for new constructions, which is binding. The quality of accommodation differs worldly. According to the Radiation Authority radon gas is attributed to 15 % of all peace lung cancer cases per year in Sweden. The percentage increases with population. Radon gas enters through foundation, through well water used in household and through building materials. Planning

    and Building Regulations survey 2010 showed that people are exposed to the highest radon levels at home. Consumers are becoming more aware of the risk of exposure to high radon levels over long period. New dwellings of radon resistant homes would benefit both producers and consumers. Before this goal will be achieved one has to know the significance choice of foundation. Result show that crawlspace is the most effective foundation method to radon build radon resistant homes.

  • 2737.
    Ahmed, Furqan
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Alfredo Dowhuszko, Alexis
    Tirkkonen, Olav
    Self-Organizing Algorithms for Interference Coordination in Small Cell Networks2017In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 66, no 9, p. 8333-8346Article in journal (Refereed)
    Abstract [en]

    This paper discusses novel joint (intracell and intercell) resource allocation algorithms for self-organized interference coordination in multicarrier multiple-input multiple-output (MIMO) small cell networks. The proposed algorithms enable interference coordination autonomously, over multiple degrees of freedom, such as base station transmit powers, transmit precoders, and user scheduling weights. A generic a-fair utility maximization framework is considered to analyze performance-fairness tradeoff and to quantify the gains achievable in interference-limited networks. The proposed scheme involves limited inter-base station signaling in the form of two step (power and precoder) pricing. Based on this decentralized coordination, autonomous power and precoder update decision rules are considered, leading to algorithms with different characteristics in terms of user data rates, signaling load, and convergence speed. Simulation results in a practical setting show that the proposed pricing-based self-organization can achieve up to 100% improvement in cell-edge data rates when compared to baseline optimization strategies. Furthermore, the convergence of the proposed algorithms is also proved theoretically.

  • 2738. Ahmed, H. M.
    et al.
    Viswanathan, N. N.
    Seetharaman, Seshadri
    KTH.
    Gas-Condensed Phase Reactions - A Novel Route to Synthesize Alloys and Intermetallics Involving Refractory Metals2016Conference paper (Refereed)
    Abstract [en]

    Reduction and simultaneous reduction-carburization of oxide mixtures to get intermetallics and composite materials may open up shorter process routes towards the end-user needs. The use of natural gas or hydrogen would be environment-friendly. With these aims, the corresponding kinetics were studied by thermogravimetry, gas chromatography as well as laser-flash method. It was found that, under identical conditions, the Arrhenius activation energy for the reduction is proportional to the thermodynamic stability of the compound reduced. Intermetallics could be synthesized successfully and the product was found to have nanograins. Also, Metallic coating on copper surfaces was successfully developed.

  • 2739.
    Ahmed, Haroon
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Sund, Gabriel
    KTH, School of Information and Communication Technology (ICT).
    Security challenges within Software Defined Networks2014Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    A large amount of today's communication occurs within data centers where a large number of virtual servers (running one or more virtual machines) provide service providers with the infrastructure needed for their applications and services. In this thesis, we will look at the next step in the virtualization revolution, the virtualized network. Software-defined networking (SDN) is a relatively new concept that is moving the field towards a more software-based solution to networking. Today when a packet is forwarded through a network of routers, decisions are made at each router as to which router is the next hop destination for the packet. With SDN these decisions are made by a centralized SDN controller that decides upon the best path and instructs the devices along this path as to what action each should perform. Taking SDN to its extreme minimizes the physical network components and increases the number of virtualized components. The reasons behind this trend are several, although the most prominent are simplified processing and network administration, a greater degree of automation, increased flexibility, and shorter provisioning times. This in turn leads to a reduction in operating expenditures and capital expenditures for data center owners, which both drive the further development of this technology.

    Virtualization has been gaining ground in the last decade. However, the initial introduction of virtualization began in the 1970s with server virtualization offering the ability to create several virtual server instances on one physical server. Today we already have taken small steps towards a virtualized network by virtualization of network equipment such as switches, routers, and firewalls. Common to virtualization is that it is in early stages all of the technologies have encountered trust issues and general concerns related to whether software-based solutions are as rugged and reliable as hardwarebased solutions. SDN has also encountered these issues, and discussion of these issues continues among both believers and skeptics. Concerns about trust remain a problem for the growing number of cloud-based services where multitenant deployments may lead to loss of personal integrity and other security risks. As a relatively new technology, SDN is still immature and has a number of vulnerabilities. As with most software-based solutions, the potential for security risks increases. This thesis investigates how denial-of-service (DoS) attacks affect an SDN environment and a singlethreaded controller, described by text and via simulations.

    The results of our investigations concerning trust in a multi-tenancy environment in SDN suggest that standardization and clear service level agreements are necessary to consolidate customers’ confidence. Attracting small groups of customers to participate in user cases in the initial stages of implementation can generate valuable support for a broader implementation of SDN in the underlying infrastructure. With regard to denial-of-service attacks, our conclusion is that hackers can by target the centralized SDN controller, thus negatively affect most of the network infrastructure (because the entire infrastructure directly depends upon a functioning SDN controller). SDN introduces new vulnerabilities, which is natural as SDN is a relatively new technology. Therefore, SDN needs to be thoroughly tested and examined before making a widespread deployment.

  • 2740.
    Ahmed, Hassan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Energy and Climate Studies, ECS.
    Energy need assessment and preferential choice survey of rural people in Bangladesh2013Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This study is a part of a poly generation project which will use animal waste or agricultural waste to produce biogas and will provide cooking gas, electricity and arsenic free clean water for drinking in rural areas of Bangladesh.  The study mainly analyzes the cooking and lighting energy demand of households across different income groups in a village named “Pani Para” in the Faridpur district in Bangladesh and also looks at the potential of biogas in the village. It has been done by adopting case study method and conducting a survey in the village using a questionnaire.

    Fuel mix across different income groups for meeting their cooking and lighting energy needs have also been studied along with socio-economic situation of the villagers and their preferences to change their current cooking fuel utilization patterns. Various scenarios like variation in fuel consumption patterns, priority of income expenditure and access to fuel with income level have been examined. The study also focuses to analyze the awareness of the villagers about biogas technology and their willingness to contribute for the poly generation project along with the willingness of households to pay for embracing change in current cooking and lighting fuels. Biomass potential i.e. cow dung and agricultural waste is also calculated in the surveyed village along with the production of biogas from the available biomass resources. The scenarios to provide the cooking gas, electricity and clean water through biogas poly generation project from the available resources are also investigated.

    Analysis reveals that the total energy consumption (cooking and lighting) increases with the increase in the income level among the households. Average household cooking and lighting energy demand by low, medium and high income groups is 8492 kWh/yr, 9789 kWh/yr and 14806 kWh/yr respectively. Cooking energy demand and agricultural waste consumption also show an increasing trend with the increase in land holding size. Among the income expenditure priorities food is one of the most important priorities and energy being less important due to availability of biomass at little or no cost. Awareness of biogas technology among the households and willingness to contribute for the poly generation plant shows an increasing trend with the increase in education level. The study shows that there is a positive response of the villagers for being willing to embrace the change in the current cooking patterns as well as welcoming new technologies that could support such a change.

    It was found that the cow dung resource in the village is not enough to produce sufficient biogas for the poly generation project. With the incorporation of the agricultural waste with the cow dung, biogas production comes quite close to requirement of the poly generation plant but however could not suffice it completely due to the lack of raw material in the studied village. In that case the scenario of providing electricity and clean water to all the villagers and providing all the three facilities to the 2/3rd of households is investigated. 1/3rd of the low income households then could meet their cooking demands by provision of improved cooking stoves as cooking gas could not be provided to them due to limited feedstock. The study shows that despite of the fact that cooking and lighting energy needs increase with income but there is not much variation in the fuel mix and almost everyone in the village rely on biomass to meet their energy demand. It is because there is very limited access to the modern fuel for cooking and no electricity access in the village, so the households have to rely on the traditional fuels. 

  • 2741.
    Ahmed, Hesham M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Investigations of the Kinetics of Reduction and Reduction/Carburization of NiO-WO3 Precursors.2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Kinetic studies of reduction of the mixtures of NiO and WO3 having different Ni/(Ni+W) molar ratios in flowing hydrogen gas were investigated by means of Thermo Gravimetric Analysis (TGA), Fluidized Bed (FB) technique as well as Thermal diffusivity measurements under isothermal conditions. In the case of TGA, the reaction progress was monitored by mass loss, while evolved gas analysis by a gas chromatograph was the indicator of the reaction progress in the case of FB. The results indicate that the reduction reaction proceeds through three consecutive steps, viz.

    NiO-WO3 Ni-WO3 Ni-WO2 Ni-W

    The present results show that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.

    During the investigations, it was found that there was a delay in the reaction during the hydrogen reduction of NiO-WO3 mixed oxides in a fluidized bed reactor. In order to understand the same, a theoretical model was developed to estimate the apparent reaction rate constant for the reduction reaction from the intrinsic chemical reaction rate constant. Appropriate differential mass balance equations based on intrinsic chemical reaction rate constants and thermodynamic equilibria were developed. The proposed model was successfully applied in predicting the overall reaction kinetics of a fluidized bed reactor. This model is also suitable for scale-up calculations.

    SEM images showed that the particle size of the final product was dependent on the Ni/(Ni+W) molar ratio; smaller particles were formed at higher nickel contents. X-ray diffractions of the reduced precursors exhibited slight shift of Ni peaks from the standard one indicating the dissolution of W into Ni.

    A new method for studying kinetics of the hydrogen reduction of NiO-WO3 precursors was developed in which the reaction progress was monitored by following the change of thermal diffusivity of the precursors. Activation energies of reduction as well as sintering were calculated. This method is considered unique as it provides information regarding the physical changes like sintering, change of porosity and agglomeration along with the chemical changes occurring during the gas/solid reaction.

    As a continuation of the kinetic studies, Ni-W-C ternary carbides were synthesized by simultaneous reduction–carburization of Ni-W-O system using H2-CH4 gas mixtures by TGA. The results showed that the reduction of the oxide mixture was complete before the carburization took place. The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. The above-mentioned experiments were conducted in such a way to ensure that the reaction was controlled by the chemical reaction. The activation energies of the reduction as well as carburization processes at different stages were calculated accordingly.

    The present dissertation demonstrates the potential of the investigations of gas/solid reactions towards tailoring the process towards materials with optimized properties as for example introduction of interstitials. The present process design is extremely environment-friendly with reduced number of unit processes and the product being H2O.

  • 2742.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    El-Geassy, A. H. A.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Kinetics of Reduction of NiO-WO3 Mixtures by Hydrogen2010In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 41, no 1, p. 161-172Article in journal (Refereed)
    Abstract [en]

    The kinetics of reduction of the oxide mixtures of Ni-W with different Ni/(Ni-W) molar ratios within the range of 923 K to 1173 K in flowing hydrogen gas was investigated by means of thermogravimetric analysis under isothermal conditions. The products were examined by X-ray diffraction, scanning electron microscope (SEM), and electron dispersion spectroscopy (EDS) analyses. Five different oxide mixtures apart from the pure oxides were studied in the present work. The results indicate that the reduction reaction proceeds through three consecutive steps that are as follows: NiO-WO3 -> Ni-WO3 -> Ni-WO2 -> Ni-W From the experimental results, the Arrhenius activation energies of the three steps were evaluated for all of the studied compositions. The activation energy for the first step was calculated to be approximately 18 kJ/mol. For the second and third stages, the activation energy values varied from 62 to 38 kJ/mol for the second stage and 51 to 34 kJ/mol for the third stage depending on the Ni/(Ni + W) molar ratio in the precursors; the activation energy increased with increasing ratios. SEM images showed that the grain size of the final product was dependent on the Ni/(Ni + W) molar ratio; smaller grains were formed at higher nickel contents.

  • 2743.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    El-Geassy, Abdel-Hady A.
    Viswanathan, Nurni Neelakantan
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Kinetics and Mathematical Modeling of Hydrogen Reduction of NiO-WO(3) Precursors in Fluidized Bed Reactor2011In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 51, no 9, p. 1383-1391Article in journal (Refereed)
    Abstract [en]

    In the present work, Fluidized bed reduction of NiO-WO(3) precursors was investigated isothermally at temperatures 973-1 273 K. The reaction progress was monitored by analysis of H(2)O evolved during the reaction process using a gas chromatograph instrument. A theoretical model based on intrinsic chemical reaction rate constants and thermodynamic equilibria was developed to estimate the apparent reaction rate constant for the reduction reaction. In developing the model, the particles are considered to be in a completely mixed condition and gas flow is described as plug flow. The proposed model is also suitable for scale-up calculations. The interfacial chemical reaction model was found to fit the experimental results. The apparent activation energy values of the reduction process at different stages were calculated accordingly. The present investigation proved that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.

  • 2744.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    El-Geassy, Abdel-Hady
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Kinetic Studies of the Hydrogen Reduction of NiO-WO3 precursors in a Fluidized-bed reactorIn: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916Article in journal (Other academic)
  • 2745.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Isothermal dynamic thermal diffusivity studies of the reduction of NiO and NiWO(4) precursors by hydrogen2011In: International Journal of Materials Research - Zeitschrift für Metallkunde, ISSN 1862-5282, E-ISSN 2195-8556, Vol. 102, no 11, p. 1336-1344Article in journal (Refereed)
    Abstract [en]

    Thermal diffusivity measurements of uniaxially cold pressed NiO and NiWO(4) were carried out in a dynamic mode in order to monitor the kinetics of hydrogen reduction of the above-mentioned materials using a laser flash unit. The calculated activation energy was found to be higher than that for chemically-controlled reaction obtained earlier by thermogravimetry. The difference has been attributed to physical changes occurring along with the chemical reaction. The activation energy of sintering of the products was evaluated to be 33 and 36 kJ.mol(-1) for NiO and NiWO(4), respectively. Thermal conductivities were calculated taking into consideration the change in heat capacity considering the compositional and the structural changes with the progress of the reaction. The potentiality of the laser-flash method as a complementary technique to thermogravimetry in understanding the mechanism of gas solid reactions is discussed.

  • 2746.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Reduction-Carburization of NiO-WO3 Under Isothermal Conditions Using H2-CH4 Gas Mixture2010In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 41, no 1, p. 173-181Article in journal (Refereed)
    Abstract [en]

    Ni-W-C ternary carbides were synthesized by simultaneous reduction–carburization of NiO-WO3 oxide precursors using H2-CH4 gas mixtures in the temperature range of 973 to 1273 K. The kinetics of the gas–solid reaction were followed closely by monitoring the mass changes using the thermogravimetric method (TGA). As a thin bed of the precursors were used, each particle was in direct contact with the gas mixture. The results showed that the hydrogen reduction of the oxide mixture was complete before the carburization took place. The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. Consequently, the reaction rate could be conceived as being controlled by the chemical reaction. From the reaction rate, Arrhenius activation energies for reduction and carburization were evaluated. Characterization of the carbides produced was carried out using X-ray diffraction and a scanning electron microscope (SEM) combined with electron dispersion spectroscopy (SEM-EDS) analyses. The grain sizes also were determined. The process parameters, such as the temperature of the reduction–carburization reaction and the composition of the gas mixture, had a strong impact on the carbide composition as well as on the grain size. The results are discussed in light of the reduction kinetics of the oxides and the thermodynamic constraints.

  • 2747.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Viswanathan, N. N.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    On The Kinetics of Hydrogen Reduction of NiO-WO3 Precursors in Fluidized Bed- A Modeling Approach2011In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 51, no 9, p. 1383-1391Article in journal (Refereed)
    Abstract [en]

    In the present work, Fluidized bed reduction of NiO-WO3 precursors was investigated isothermally at temperatures 973-1 273 K. The reaction progress was monitored by analysis of H2O evolved during the reaction process using a gas chromatograph instrument. A theoretical model based on intrinsic chemical reaction rate constants and thermodynamic equilibria was developed to estimate the apparent reaction rate constant for the reduction reaction. In developing the model, the particles are considered to be in a completely mixed condition and gas flow is described as plug flow. The proposed model is also suitable for scale-up calculations. The interfacial chemical reaction model was found to fit the experimental results. The apparent activation energy values of the reduction process at different stages were calculated accordingly. The present investigation proved that the fluidized bed technique can be successfully utilized in bulk production of intermetallics containing W and a transition metal (or a composite material) wherein the process conditions would have a strong impact on the particle size of the end product.

  • 2748.
    Ahmed, Hesham M.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Viswanathan, Nurini N.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Dynamic Thermal Diffusivity Measurements - A Tool for Studying Gas-Solid Reactions2011In: DIFFUSION IN SOLIDS AND LIQUIDS VI, PTS 1 AND 2, 2011, p. 217-222Conference paper (Refereed)
    Abstract [en]

    In the present work, the thermal diffusivity measurements of uniaxially cold pressed NiWO(4) has been carried out. The measurements were performed isothermally at temperatures between 973 and 1273 K under H(2) gas using the laser flash technique. The experimental thermal diffusivity values were found to increase with the reduction progress as well as with increasing temperature. The calculated activation energy was found to be higher than that for chemically controlled reaction. The difference has been attributed to factors like agglomeration of the product as well as sintering of the precursor along with the chemical reaction. In order to sort out the sintering effect on the thermal diffusivity values, complementary experiments have been done on pressed NiWO(4) and Ni-W, produced by the reduction of NiWO(4) at 1123K, under Argon gas. The porosity change and its effect on thermal diffusivity values have been studied.

  • 2749.
    Ahmed, Hesham
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Mis, Michal
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    El-Geassy, Abdel-Hady
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Seethararnan, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Reduction-Carburization of the Oxides of Ni and W Towards the Synthesis of Ni-W-C Carbides2010In: ADVANCED MATERIALS FORUM V, PT 1 AND 2  / [ed] Rosa LG; Margarido F, 2010, Vol. 636-637, p. 952-962Conference paper (Refereed)
    Abstract [en]

    Ternary Ni-W-C cemented carbides were synthesized directly from mixture powder of NiO-WO3 by simultaneous reduction-carburization in mixed H-2-CH4 gas environment in a thin bed reactor in the temperature range 973-1273K. The kinetics of the reaction was closely followed by monitoring the mass change using thermogravimetric method (TGA). The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. The gas mixture ratio was adjusted in such a way that the Ni-W-C formed was close to the two phase tie line. In view of the fact that each particle was in direct contact with the gas mixture, the reaction rate could be conceived as being controlled by the combined reduction-carburization reaction. From the reaction rate, the Arrhenius activation energies were evaluated. Characterization of the carbides produced was carried out by using X-ray diffraction, SEM-EDS as well as high resolution electron microscope (HREM). The grain sizes were also determined. Correlations were found between the carbide composition as well as grain size and the process parameters such as temperature of the reduction-carburization reaction as well as the composition of the gas mixture. The results are discussed in the light of the kinetics of the reduction of oxides and the thermodynamic constraints.

  • 2750. Ahmed, Hesham
    et al.
    Morales-Estrella, R.
    Viswanathan, Nurin
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Gas-Solid Reaction Route toward the Production of Intermetallics from Their Corresponding Oxide Mixtures2016In: METALS, ISSN 2075-4701, Vol. 6, no 8, article id 190Article in journal (Refereed)
    Abstract [en]

    Near-net shape forming of metallic components from metallic powders produced in situ from reduction of corresponding pure metal oxides has not been explored to a large extent. Such a process can be probably termed in short as the "Reduction-Sintering" process. This methodology can be especially effective in producing components containing refractory metals. Additionally, in situ production of metallic powder from complex oxides containing more than one metallic element may result in in situ alloying during reduction, possibly at lower temperatures. With this motivation, in situ reduction of complex oxides mixtures containing more than one metallic element has been investigated intensively over a period of years in the department of materials science, KTH, Sweden. This review highlights the most important features of that investigation. The investigation includes not only synthesis of intermetallics and refractory metals using the gas solid reaction route but also study the reaction kinetics and mechanism. Environmentally friendly gases like H-2, CH4 and N-2 were used for simultaneous reduction, carburization and nitridation, respectively. Different techniques have been utilized. A thermogravimetric analyzer was used to accurately control the process conditions and obtain reaction kinetics. The fluidized bed technique has been utilized to study the possibility of bulk production of intermetallics compared to milligrams in TGA. Carburization and nitridation of nascent formed intermetallics were successfully carried out. A novel method based on material thermal property was explored to track the reaction progress and estimate the reaction kinetics. This method implies the dynamic measure of thermal diffusivity using laser flash method. These efforts end up with a successful preparation of nanograined intermetallics like Fe-Mo and Ni-W. In addition, it ends up with simultaneous reduction and synthesis of Ni-WN and Ni-WC from their oxide mixtures in single step.

52535455565758 2701 - 2750 of 124287
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