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  • 3101.
    Akhtar, Suleman
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Material Factors Influencing Crack Initiation and Propagation During Seamless Tube Rolling of Low Carbon Steel Grades2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Lower hot ductility can lead to cracks in steels. Hot ductility is affected by grain boundary sliding at temperatures higher than A3 and by the presence of thin films of ferrite at grain boundaries at temperatures lower than A3. Grain boundary sliding might occur because of the segregation of harmful elements like sulphur, etc. While thin films of ferrite at grain boundaries lead to easy interlinking of MnS precipitates at grain boundaries and ultimately may cause cracks in the material. Also, stress concentration is higher at thin ferrite films at grain boundaries which for being softer as compared to austenite matrix lead to cracks in the material. Elongated  (Fe, Mn)S sulphides are more detrimental for the hot ductility as compared to round ones. Higher aspect ratio of the precipitates is also dependent on sulphur content. The higher the sulphur content, the higher would be the hot ductility. Silicon, being a ferrite stabilizer, causes the volume fraction of ferrite to increase which improves the hot ductility of the steels. Hot ductility can be improved by adding Boron that segregates to grain boundaries instead of sulphur improving the strength of grain boundaries. Increasing silicon content can lead to higher volume fraction of ferrite thus improving ductility because stress would uniformly be distributed across the grain and not merely on the grain boundaries. Apart from that, decreasing the solution treatment temperature and increasing holding time on solution treatment temperature can lead to lower dissolved content of sulphur and coarser MnS precipitates hence improving hot ductility. 

  • 3102.
    Akhter, Shirin
    et al.
    Swedish Univ Agr Sci, Linnean Ctr Plant Biol, Uppsala Bioctr, Dept Plant Biol, Uppsala, Sweden..
    Kretzschmar, Warren W.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Nordal, Veronika
    Swedish Univ Agr Sci, Linnean Ctr Plant Biol, Uppsala Bioctr, Dept Plant Biol, Uppsala, Sweden..
    Delhomme, Nicolas
    Swedish Univ Agr Sci, Dept Forest Genet & Plant Physiol, Umea Plant Sci Ctr, Umea, Sweden..
    Street, Nathaniel R.
    Umea Sweden, Dept Plant Physiol, Umea Plant Sci Ctr, Umea, Sweden..
    Nilsson, Ove
    Swedish Univ Agr Sci, Dept Forest Genet & Plant Physiol, Umea Plant Sci Ctr, Umea, Sweden..
    Emanuelsson, Olof
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Sundström, Jens F.
    Swedish Univ Agr Sci, Linnean Ctr Plant Biol, Uppsala Bioctr, Dept Plant Biol, Uppsala, Sweden..
    Integrative Analysis of Three RNA Sequencing Methods Identifies Mutually Exclusive Exons of MADS-Box Isoforms During Early Bud Development in Picea abies2018In: Frontiers in Plant Science, ISSN 1664-462X, E-ISSN 1664-462X, Vol. 9, article id 1625Article in journal (Refereed)
    Abstract [en]

    Recent efforts to sequence the genomes and transcriptomes of several gymnosperm species have revealed an increased complexity in certain gene families in gymnosperms as compared to angiosperms. One example of this is the gymnosperm sister Glade to angiosperm TM3-like MADS-box genes, which at least in the conifer lineage has expanded in number of genes. We have previously identified a member of this subclade, the conifer gene DEFICIENS AGAMOUS LIKE 19 (DAL19), as being specifically upregulated in cone-setting shoots. Here, we show through Sanger sequencing of mRNA-derived cDNA and mapping to assembled conifer genomic sequences that DAL19 produces six mature mRNA splice variants in Picea abies. These splice variants use alternate first and last exons, while their four central exons constitute a core region present in all six transcripts. Thus, they are likely to be transcript isoforms. Quantitative Real-Time PCR revealed that two mutually exclusive first DAL19 exons are differentially expressed across meristems that will form either male or female cones, or vegetative shoots. Furthermore, mRNA in situ hybridization revealed that two mutually exclusive last DAL19 exons were expressed in a cell-specific pattern within bud meristems. Based on these findings in DAL19, we developed a sensitive approach to transcript isoform assembly from short-read sequencing of mRNA. We applied this method to 42 putative MADS-box core regions in P abies, from which we assembled 1084 putative transcripts. We manually curated these transcripts to arrive at 933 assembled transcript isoforms of 38 putative MADS-box genes. 152 of these isoforms, which we assign to 28 putative MADS-box genes, were differentially expressed across eight female, male, and vegetative buds. We further provide evidence of the expression of 16 out of the 38 putative MADS-box genes by mapping PacBio Iso-Seq circular consensus reads derived from pooled sample sequencing to assembled transcripts. In summary, our analyses reveal the use of mutually exclusive exons of MADS-box gene isoforms during early bud development in P. abies, and we find that the large number of identified MADS-box transcripts in P. abies results not only from expansion of the gene family through gene duplication events but also from the generation of numerous splice variants.

  • 3103.
    Akhter, Tahmina
    KTH, School of Computer Science and Communication (CSC).
    Implementation of Conduction Delay and Collective Communication in a Parallel Spiking Neural Network Simulator.2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Tahmina Akther

    Implementation of conduction delay and collective communication in a parallel spiking neural network simulator

    As we know neural networks have a parallel structure and it is well suited for implementations in a parallel environment. The Bayesian Confidence Propagation Neural Network (BCPNN) which has been developed past thirty years is the main subject this thesis. An important issue is the implementation of communications between the processors. The aim of this thesis is to investigate point to point and collective communication methods and check how it works in real time. A second goal is to introduce time delay in point-to-point communication. These schemes have been implemented on Blue Gene Supercomputer using Message Passing Interface (MPI). At the end of thesis, the comparison between the two communication methods and the results of the two different models are shown.

  • 3104.
    Akhter, Tasmiah
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Mohsin, Mael
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Lean produktion i två olika branscher: - En jämförelse mellan sjukvård och industri2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Abstract

    Lean production is a well-known concept in the industry that aims to become resource efficient and improved with a customer focus. In lean production there are several methods and philosophies to consider and this report deals with 5S method, seven wastes and commitment in an organization. The success of lean production in manufacturing has led to implementation across several different industries, especially health care. This implementation has been met with varying opinions.

    The purpose of this report is to examine if the implementation of lean production in health care can be just as effective as in industry. The implementation of Lean in health care has partially been proved successful, but often the set goals are not achieved. With the aid of three sub-questions, the main question can be answered: Can the implementation of lean production be as effective in the health care as in the industry?

    Through field trips and interviews from both health care and industry, empirical data will be gathered to gain an understanding of how the implementation is today. Karolinska University Hospital in Huddinge represents the health care and Scania represents the industry. After these interviews a comparison was created between health care and industry implementations and a score-table is formed to see how well the organizations meets lean production according to the theory.

    The comparison between the health care and the industry resulted in the conclusion that health care can be just as effective as the industry with its implementation of lean production. The efficiency potential was seen in the majority of the steps of the methods concerned. In seven of the ten steps there are scope for rationalization, where the health care can apply lean as well as the industry.

  • 3105.
    AKHTER, TASMIAH
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    ÅKERLIND, TOBIAS
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Agile IT Infrastructure Transformation: A Case Study of a Nordic Incumbent Telco2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In a growing digital economy, where demands for network services and competition from various communication-over-the-network service providers intensify, telecommunication companies need to keep up in an ever-changing environment. As there is a need to reduce time-to-market for new network services, agility becomes restrained by having to operate within large legacy IT infrastructure environments. While agile methodologies in modern time have attained recognition in the field of software development for the way they help to manage changing customer demands and deliver early value incontinuous increments, it is yet uncertain how agile methodologies can best be adopted for IT infrastructure deliveries to achieve the same purpose. Hence, this study explores how legacy IT infrastructure can be transformed in an agile way into modernized infrastructure landscapes supporting the business with fast enough development, release and deployment of new network services in demand. More precisely, the study investigates how larger IT infrastructure transformation projects can be executed by the help of agile practices. In order to investigate this, the study carries out a case study at Telia Company, a large Nordic incumbent telecommunications company possessing a big legacy of IT infrastructure. The study conducts internal interviews with Telia employees as well as external interviews with agile experts. Also, benchmarking is conducted with a well-established Swedish bank to better understand the challenges and how agile practices can best be applied.The study concludes that agile practices influenced by agile frameworks Scrum and Kanban can advantageously be applied at team level for more agile execution. However, the surrounding organizational business landscape greatly sets the limits for agile deliveries, due to dependencies on cooperation from the business side in the execution phase and the need to be aligned with business needs and stakeholder requirements. Further, the study also shows that the application of agile practices at team level in combination with a close dialogue with stakeholders and a scaled agile approach requiring investing in automation, is the key for more agile infrastructure deliveries. In this way, aligned end-to-end delivery processescan be better developed and infrastructure needs better understood and implemented at the right time. As a contribution, the study proposes a model with inspiration from agile frameworks Scrum, Kanban and SAFe, for how this may work in practice.

  • 3106.
    Akiki, Maroun
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Falk, Agneta
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Ett bostadshus i prefabricerad trästomme: Ett gestaltningsarbete anpassat efter volymelementsbyggande2014Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This report is a compilation of the planning of a 5-storey residential building. The building in question has been designed to be built entirely in a wooden frame mainly consisting of a modular building system. Modules also referred to as prefabricated volume elements are room units that have been constructed through industrial means. These room units can be developed enough to be delivered with complete facades or even fixtures. Since the planning of the residential building has been made based on a modular building system, adaptations to the project has had to been made as to accommodate necessary requirements. A practical example of this is how the apartment plan has been affected based on laws concerning the maximum amount of allowed width/height during transportation on public roads. These laws control the size of how big volume elements can become and as a result the apartment layout.

    The report consists of a study into the area of industrial wood construction, but foremost it treats the practical challenges and possibilities that have surfaced as a consequence of planning residential housing based on a modular basis.

  • 3107.
    Akillioglu, Hakan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Demand Responsive Planning: A dynamic and responsive planning framework based on workload control theory for cyber-physical production systems2015Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Recent developments in the area of Cyber-Physical Production Systems prove that high technology readiness level is already achieved and industrialization of such technologies is not far from today. Although these technologies seem to be convenient in providing solutions to environmental uncertainties, their application provides adaptability only at shop floor level. Needless to say, an enterprise cannot reach true adaptability without ensuring adaptation skills at every level in its hierarchy. Commonly used production planning and control approaches in industry today inherit from planning solutions which are developed in response to historical market characteristics. However, market tendency in recent years is towards making personalized products a norm. The emerging complexity out of this trend obliges planning systems to a transition from non-recurring, static planning into continuous re-planning and re-configuration of systems. Therefore, there is a need of responsive planning solutions which are integrated to highly adaptable production system characteristics.

    In this dissertation, Demand Responsive Planning, DRP, is presented which is a planning framework aiming to respond to planning needs of shifting trends in both production system technologies and market conditions. The DRP is based on three main constructs such as dynamicity, responsiveness and use of precise data. These features set up the foundation of accomplishing a high degree of adaptability in planning activities. By this means, problems from an extensive scope can be handled with a responsive behavior (i.e. frequent re-planning) by the use of precise data. The use of precise data implies to execute planning activities subject to actual demand information and real-time shop floor data. Within the context of the DRP, both a continuous workload control method and a dynamic capacity adjustment approach are developed. A test-bed is coded in order to simulate proposed method based on a system emulation reflecting the characteristics of cyber-physical production systems at shop floor level.

    Continuous Precise Workload Control, CPWLC, method is a novel approach aiming at precise control of workload levels with the use of direct load graphs. Supported by a multi-agent platform, it generates dynamic non-periodic release decisions exploiting real time shop floor information. As a result, improved shop floor performances are achieved through controlling workload levels precisely by the release of appropriate job types at the right time.

    Presented dynamic capacity adjustment approach utilizes rapid re-configuration capability of cyber-physical systems in achieving more frequent capacity adjustments. Its implementation architecture is integrated to the CPWLC structure. By this means, a holistic approach is realized whereby improved due date performance is accomplished with minimized shop floor congestion. Hence, sensitivity to changing demand patterns and urgent job completions is improved.

  • 3108.
    Akillioglu, Hakan
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Evolvable Production Systems: Demand Responsive Planning2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Dynamic and unforeseeable characteristic of the current market and production environment is not feasible to be met through pre-set parameters being dependent on the predictions. Handling this matter requires to keep focus on production system adaptability. Evolvable Production System has achieved fully system reconfigurability through process oriented modularity and multi agent based distributed control system architecture. One of the essential enhancements provided by EPS on the shop floor is achieving minimized/eliminated system setup time in response to changing product requirements.

    Manufacturing planning and control system, on the other hand, follows hierarchical principles which are quite much reliant on the predicted information so to structure production and planning environment on it. Production system limitations, such as lack of adaptability in response to changing conditions, are in fact influencing the planning system to be structured on the predictions. The enhancements which are ensured by the architecture of EPS enable to relax the constraints on planning system which are imposed by the limitations of production system. These enhancements have an effect at different levels in the planning hierarchy. On the light of these improvements, the planning framework as it is used so far in the industry becomes invalid and this arise a requirement for planning system structure to be designed according to a fully reconfigurable system to be able to benefit such a production system by all means.

    This thesis targets to enlighten the relation between the production system characteristics and planning system structure by emphasizing the planning problems and proposing a planning reference architecture solution to be able achieve a responsive planning framework.

  • 3109.
    Akillioglu, Hakan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Dias-Ferreira, Joao
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Maffei, Antonio
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Neves, Pedro
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Onori, Mauro
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Continuous precise workload control method2014In: IEEE International Conference on Industrial Engineering and Engineering Management, 2014, p. 511-515Conference paper (Refereed)
    Abstract [en]

    The diversity of requirements and the frequency of change in the market can only be competed with dynamicity and responsiveness in both production and planning systems. In this sense, working principles of a novel workload control method, called continuous precise workload control are presented in this paper. The implementation of the method is based on a multi-agent based architecture. The presented approach generates dynamic non periodic release decisions exploiting real time shop floor information. The performance of the system and correlation of norm value against the assessment range are investigated through an experimented test case.

  • 3110.
    Akillioglu, Hakan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Dias-Ferreira, Joao
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Onori, Mauro
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Characterization of Continuous Precise Workload Control and Analysis of Idleness Penalty2014In: CIE 44 and IMSS14 proceedings, 2014, p. 1998-2011Conference paper (Refereed)
    Abstract [en]

    The variability in the market conditions is growing in terms of its frequency of change and range of diversity. In response to this new industrial panorama, research on production systems is aiming to achieve truly reconfigurable shop floors. Frequent changes in such systems require also frequent re-planning with updated information. In this regard the Continuous Precise Workload Control method, is a recent approach aiming at precise control of workload in the shop floor with the use of direct load graphs. Supported by a multi-agent platform, it generates dynamic non-periodic release decisions exploiting real time shop floor information. The study in this paper is two folded; (1) in order to highlight its distinctive characteristics, the presented workload approach is defined in terms of eight dimensions of the workload control concept and (2) the penalty of idleness which affects the decision of release is analyzed by an experiment design in order to investigate its correlation with two critical parameters, norm value and assessment range. The results show that the idleness penalty factor decreases the idleness of the resources up to a point where the adverse effect is initiated. Besides there are strong indications towards the correlation of idleness penalty factor with the norm value.

  • 3111.
    Akillioglu, Hakan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Dias-Ferreira, João
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Onori, Mauro
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Characterization of continuous precise workload control and analysis of idleness penalty2016In: Computers & industrial engineering, ISSN 0360-8352, E-ISSN 1879-0550, Vol. 102, p. 351-358Article in journal (Refereed)
    Abstract [en]

    The variability in the market conditions is growing in terms of its frequency of change and range of diversity. In response to this new industrial panorama, research on production systems is aiming to achieve highly reconfigurable shop floors. Frequent changes in such systems require also frequent re-planning with updated information. In this regard the Continuous Precise Workload Control method, is a recent approach aiming at precise control of workload in shop floor with the use of direct load graphs. Supported by a multi-agent platform, it generates dynamic non-periodic release decisions exploiting real time shop floor information. The study in this paper is two folded; (1) the presented workload approach is defined in terms of eight dimensions of the workload control concept in order to highlight its distinctive characteristics and (2) the impact of idleness penalty factor is analyzed by an experiment design in order to investigate its effect on the job release decision. The results show that the idleness penalty factor decreases the idleness of the resources up to a point where the adverse effect is initiated.

  • 3112.
    Akillioglu, Hakan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Ferreira, Joao
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Onori, Mauro
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Demand responsive planning: workload control implementation2013In: Assembly Automation, ISSN 0144-5154, E-ISSN 1758-4078, Vol. 33, no 3, p. 247-259Article in journal (Refereed)
    Abstract [en]

    Purpose – Evolvable production systems enable fully reconfiguration capabilities on the shop floor through process-oriented modularity and multiagent-based distributed control. To be able to benefit architectural and operational characteristics of evolvable systems, there is a need of a newplanning approach which links shop floor characteristics and planning operations. This paper seeks to address these issues.

    Design/methodology/approach – Evolvable production system has a structured methodology in itself. Consistent to this, a reference planningarchitecture is developed aiming to achieve agility on planning activities. Besides a workload control method is proposed and implemented as a part ofthe planning architecture.

    Findings – First applications of evolvable systems have been implemented through European research projects. Shop floor working principles andarchitectural characteristics are consistent to facilitate more agility on planning activities which are framed at a planning reference architecture calleddemand responsive planning. As an implementation case, an agent-based workload control method is proposed and implemented. The characteristicsof EPS and proposed planning architecture enable continuous and dynamic workload control of the shop floor to be implemented.

    Originality/value – This paper presents a new planning model compatible with evolvable production systems targeting to agility to demand onplanning and control activities benefiting shop floor enhancements of a fully reconfigurable system which enables to relax constraints imposed fromproduction systems to planning. In addition, a continuous and dynamic workload control method is proposed and implemented.

  • 3113.
    Akillioglu, Hakan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Maffei, Antonio
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Neves, Pedro
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Ferreira, Joao
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Operational characterization of evolvable productionsystems2012In: 4th CIRP Conference on Assembly Technologies and Systems – CATS 2012, 2012, p. 85-90Conference paper (Refereed)
    Abstract [en]

    On the way to achieve mass customization production systems have to obtain the capability of rapid reconfiguration of not only physical components but also from control point of view. Evolvable Production System targets highly adaptable mechanical and control solutions that can enhance reusability and interoperability of modules, enabling lifetime extension of the modules. The focus of EPS paradigm is to achieve overall system adaptability by autonomous modules which are dedicated to specific processes with the capability of short deployment time at shop floor without reprogramming effort. From the operational point of view EPS brings significant enhancements considering shop floor dynamics and performances therefore positioning of EPS principles and approaches in production system typology from different perspectives is essential. This has been done by two means which are process flow structure and customer order decoupling point location.

  • 3114.
    Akillioglu, Hakan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Neves, Pedro
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Onori, Mauro
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Evolvable Assembly Systems: Mechatronic Architecture Implications and Future Research2010Conference paper (Refereed)
    Abstract [en]

    The balance between assembly process optimality and their system’s ability to adapt to new requirements is a key to success for assembly companies. To increase SME’s survivability, an effective methodology is needed to handle the requirements of both agility and mass customization. Evolvable Assembly Systems (EAS) paradigm is a next generation assembly systems focused on these issues. Three key issues are here in focus: process-oriented approach, fine modular granularity, and module intelligence through lighter multi-agent technology at the shop floor level. These issues

  • 3115.
    Akillioglu, Hakan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Onori, Mauro
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Production Systems.
    Evolvable production systems and impacts on production planning2011Conference paper (Other academic)
    Abstract [en]

    Production planning and control strategies have been changing in line with the constant change on product and customer requirements, under the light of technological and scientific advancements. Production systems which are based on mass production became obsolete in time hence companies, being profit oriented, are in need of new solutions towards mass customization to handle rapidly changing market conditions. To deal with this issue, production systems and production planning strategies have to be complementing each other. In this paper Evolvable Production Systems and its compatibility to Just in Time (JIT) Production compared to Material Requirement Planning (MRP) will be discussed.

  • 3116.
    Akin, Danny E.
    et al.
    Richard B. Russell Agricultural Research Center, Agricultural Research Service, US Department of Agriculture, Athens.
    Henriksson, Gunnar
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Evans, J. D.
    South Central Poultry Research Laboratory, Agricultural Research Service, US Department of Agriculture, USA.
    Adamsen, A. S. P.
    Agro Business Par, Denmark.
    Foulk, J. A.
    Cotton Quality Research Station, Agricultural Research Service, US Department of Agriculture, USA.
    Dodd, R. B.
    Department of Agricultural and Biological Engineering, Clemson University.
    Progress in enzyme-retting of flax2004In: Journal of Natural Fibers, ISSN 1544-0478, Vol. 1, no 1, p. 21-47Article in journal (Refereed)
    Abstract [en]

    New methods for retting flax are sought to overcome problems in the current method of dew-retting of flax. Published data are reviewed and new data presented on the development and testing of a method to ret flax using pectinase-rich enzyme mixtures plus chelators based on cost and fiber yield and properties. In spray enzyme retting (SER), flax stems are crimped to physically disrupt the plant's protective barrier and then sprayed until soaked with, or briefly immersed in, an enzyme/ chelator formulation. Flax is then incubated at temperatures optimal for enzyme activity, washed, and dried. Pilot scale tests, conducted with 10 kg samples of flax retted with a series of formulations, showed that this method effectively retted flax stems from a variety of sources, including fiber flax, mature fiber flax, and linseed straw. Fiber yield, strength, and fineness were significantly influenced by variations in enzyme-chelator amounts. Cellulases in pectinase mixtures appeared to preferentially attack dislocations in fibers and fiber bundles resulting in loss of fiber strength. Polygalacturonases alone effectively separated fiber from non-fiber components. The SER method proved to be an effective framework for further tests on enzyme-chelator formulations that now must be integrated with physical processing to optimize the extraction of flax fibers based on cost and fiber yield and properties.

  • 3117.
    Akisheva, Yulia
    et al.
    KTH, School of Electrical Engineering (EES).
    Farid, Ramin
    KTH, School of Electrical Engineering (EES).
    Radiation Dose Analysis of the MIST Satellite2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 3118.
    Akius, Kim
    KTH, School of Information and Communication Technology (ICT).
    Approaching micrometer size graphene flakes on an insulating substrate with STM2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this study, a method for landing with a Scanning Tunneling Microscope (STM) on a µm size ake of graphene was developed. Two approaches were explored, one using physical guides to navigate on the sample and another one using capacitive pickup in the system. We show that with no modication of the STM that was used, we could land on a micrometer size ake of graphene.

  • 3119.
    Akkaya, Deniz
    KTH, School of Information and Communication Technology (ICT).
    Wireless Inspirational Bits for Facilitating Early Design2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Proof of concept systems are the significant examples of technology designs to test and analyze technology ideas. Toolkits enable technology developers to decrease the complexity and time to create draft designs with many iterations. Toolkits with combinations of sensors and actuators may lead technology designers to new design spaces and opportunities by decreasing design difficulties. This thesis proposes a new wireless toolkit, called Earl, for beginner level technology designers. Without being experienced on engineering skills Earl allows technology designers to create proof of concept systems in shorter time than implementing the system from scratch. For experiencing with sensors and actuators, this toolkit has a vision to design plug and experience systems. By using Earl, designers can connect analog actuators and sensors by plugging them to toolkit. Additionally, Earl is designed to increase the experience time by lowering the power consumption as much as possible. Therefore, application developers can use Earl portably in long term experiments. Furthermore, Earl is designed in Internet of Things concept. By using Earl web services, technology designer can access the data sent from the sensors and can control the actuators connected to hardware toolkit from a web browser. Earl hardware toolkit aims to provide long experiment time as much as possible. This is why, Earl hardware toolkit is designed to lower the power consumption if hardware toolkit is not actively handling processes. In sensing only mode, technology developers can use Earl hardware toolkit more than 1 month without recharging the toolkit battery. Using actuators in application may change power consumption of the hardware toolkit. Therefore, applications with actuators may have lower experiment time.

  • 3120. Akkoyun, S.
    et al.
    Algora, A.
    Alikhani, B.
    Ameil, F.
    de Angelis, G.
    Arnold, L.
    Astier, A.
    Ataç, Ayşe
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Aubert, Y.
    Aufranc, C.
    Austin, A.
    Aydin, S.
    Azaiez, F.
    Badoer, S.
    Balabanski, D. L.
    Barrientos, D.
    Baulieu, G.
    Baumann, R.
    Bazzacco, D.
    Beck, F. A.
    Beck, T.
    Bednarczyk, P.
    Bellato, M.
    Bentley, M. A.
    Benzoni, G.
    Berthier, R.
    Berti, L.
    Beunard, R.
    Lo Bianco, G.
    Birkenbach, B.
    Bizzeti, P. G.
    Bizzeti-Sona, A. M.
    Le Blanc, F.
    Blasco, J. M.
    Blasi, N.
    Bloor, D.
    Boiano, C.
    Borsato, M.
    Bortolato, D.
    Boston, A. J.
    Boston, H. C.
    Bourgault, P.
    Boutachkov, P.
    Bouty, A.
    Bracco, A.
    Brambilla, S.
    Brawn, I. P.
    Brondi, A.
    Broussard, S.
    Bruyneel, B.
    Bucurescu, D.
    Burrows, I.
    Buerger, A.
    Cabaret, S.
    Cahan, B.
    Calore, E.
    Camera, F.
    Capsoni, A.
    Carrio, F.
    Casati, G.
    Castoldi, M.
    Cederwall, Bo
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Cercus, J. -L
    Chambert, V.
    El Chambit, M.
    Chapman, R.
    Charles, L.
    Chavas, J.
    Clement, E.
    Cocconi, P.
    Coelli, S.
    Coleman-Smith, P. J.
    Colombo, A.
    Colosimo, S.
    Commeaux, C.
    Conventi, D.
    Cooper, R. J.
    Corsi, A.
    Cortesi, A.
    Costa, L.
    Crespi, F. C. L.
    Cresswell, J. R.
    Cullen, D. M.
    Curien, D.
    Czermak, A.
    Delbourg, D.
    Depalo, R.
    Descombes, T.
    Desesquelles, P.
    Detistov, P.
    Diarra, C.
    Didierjean, F.
    Dimmock, M. R.
    Doan, Q. T.
    Domingo-Pardo, C.
    Doncel, M.
    Dorangeville, F.
    Dosme, N.
    Drouen, Y.
    Duchene, G.
    Dulny, B.
    Eberth, J.
    Edelbruck, P.
    Egea, J.
    Engert, T.
    Erduran, M. N.
    Erturk, S.
    Fanin, C.
    Fantinel, S.
    Farnea, E.
    Faul, T.
    Filliger, M.
    Filmer, F.
    Finck, Ch.
    de France, G.
    Gadea, A.
    Gast, W.
    Geraci, A.
    Gerl, J.
    Gernhaeuser, R.
    Giannatiempo, A.
    Giaz, A.
    Gibelin, L.
    Givechev, A.
    Goel, N.
    Gonzalez, V.
    Gottardo, A.
    Grave, X.
    Grebosz, J.
    Griffiths, R.
    Grint, A. N.
    Gros, P.
    Guevara, L.
    Gulmini, M.
    Goergen, A.
    Ha, H. T. M.
    Habermann, T.
    Harkness, L. J.
    Harroch, H.
    Hauschild, K.
    He, C.
    Hernandez-Prieto, A.
    Hervieu, B.
    Hess, H.
    Hueyuek, T.
    Ince, E.
    Isocrate, R.
    Jaworski, G.
    Johnson, Arne
    Jolie, J.
    Jones, P.
    Jonson, B.
    Joshi, P.
    Judson, D. S.
    Jungclaus, A.
    Kaci, M.
    Karkour, N.
    Karolak, M.
    Kaskas, A.
    Kebbiri, M.
    Kempley, R. S.
    Khaplanov, Anton
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Klupp, S.
    Kogimtzis, M.
    Kojouharov, I.
    Korichi, A.
    Korten, W.
    Kroell, Th.
    Kruecken, R.
    Kurz, N.
    Ky, B. Y.
    Labiche, M.
    Lafay, X.
    Lavergne, L.
    Lazarus, I. H.
    Leboutelier, S.
    Lefebvre, F.
    Legay, E.
    Legeard, L.
    Lelli, F.
    Lenzi, S. M.
    Leoni, S.
    Lermitage, A.
    Lersch, D.
    Leske, J.
    Letts, S. C.
    Lhenoret, S.
    Lieder, R. M.
    Linget, D.
    Ljungvall, J.
    Lopez-Martens, A.
    Lotode, A.
    Lunardi, S.
    Maj, A.
    van der Marel, J.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Mariette, Y.
    Marginean, N.
    Marginean, R.
    Maron, G.
    Mather, A. R.
    Meczynski, W.
    Mendez, V.
    Medina, P.
    Melon, B.
    Menegazzo, R.
    Mengoni, D.
    Merchan, E.
    Mihailescu, L.
    Michelagnoli, C.
    Mierzejewski, J.
    Milechina, Larissa
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Million, B.
    Mitev, K.
    Molini, P.
    Montanari, D.
    Moon, S.
    Morbiducci, F.
    Moro, R.
    Morrall, P. S.
    Moeller, O.
    Nannini, A.
    Napoli, D. R.
    Nelson, L.
    Nespolo, M.
    Ngo, V. L.
    Nicoletto, M.
    Nicolini, R.
    Le Noa, Y.
    Nolan, P. J.
    Norman, M.
    Nyberg, J.
    Obertelli, A.
    Olariu, A.
    Orlandi, R.
    Oxley, D. C.
    Ozben, C.
    Ozille, M.
    Oziol, C.
    Pachoud, E.
    Palacz, M.
    Palin, J.
    Pancin, J.
    Parisel, C.
    Pariset, P.
    Pascovici, G.
    Peghin, R.
    Pellegri, L.
    Perego, A.
    Perrier, S.
    Petcu, M.
    Petkov, P.
    Petrache, C.
    Pierre, E.
    Pietralla, N.
    Pietri, S.
    Pignanelli, M.
    Piqueras, I.
    Podolyak, Z.
    Le Pouhalec, P.
    Pouthas, J.
    Pugnere, D.
    Pucknell, V. F. E.
    Pullia, A.
    Quintana, B.
    Raine, R.
    Rainovski, G.
    Ramina, L.
    Rampazzo, G.
    La Rana, G.
    Rebeschini, M.
    Recchia, F.
    Redon, N.
    Reese, M.
    Reiter, P.
    Regan, P. H.
    Riboldi, S.
    Richer, M.
    Rigato, M.
    Rigby, S.
    Ripamonti, G.
    Robinson, A. P.
    Robin, J.
    Roccaz, J.
    Ropert, J. -A
    Rosse, B.
    Rossi Alvarez, C.
    Rosso, D.
    Rubio, B.
    Rudolph, D.
    Saillant, F.
    Sahin, E.
    Salomon, F.
    Salsac, M. -D
    Salt, J.
    Salvato, G.
    Sampson, J.
    Sanchis, E.
    Santos, C.
    Schaffner, H.
    Schlarb, M.
    Scraggs, D. P.
    Seddon, D.
    Senyigit, M.
    Sigward, M. -H
    Simpson, G.
    Simpson, J.
    Slee, M.
    Smith, J. F.
    Sona, P.
    Sowicki, B.
    Spolaore, P.
    Stahl, C.
    Stanios, T.
    Stefanova, E.
    Stezowski, O.
    Strachan, J.
    Suliman, G.
    Soderstrom, P. -A
    Tain, J. L.
    Tanguy, S.
    Tashenov, Stanislav
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Theisen, Ch.
    Thornhill, J.
    Tomasi, F.
    Toniolo, N.
    Touzery, R.
    Travers, B.
    Triossi, A.
    Tripon, M.
    Tun-Lanoe, K. M. M.
    Turcato, M.
    Unsworth, C.
    Ur, C. A.
    Valiente-Dobon, J. J.
    Vandone, V.
    Vardaci, E.
    Venturelli, R.
    Veronese, F.
    Veyssiere, Ch.
    Viscione, E.
    Wadsworth, R.
    Walker, P. M.
    Warr, N.
    Weber, C.
    Weisshaar, D.
    Wells, D.
    Wieland, O.
    Wiens, A.
    Wittwer, G.
    Wollersheim, H. J.
    Zocca, F.
    Zamfir, N. V.
    Zieblinski, M.
    Zucchiatti, A.
    AGATA-Advanced GAmma Tracking Array2012In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 668, p. 26-58Article in journal (Refereed)
    Abstract [en]

    The Advanced GAmma Tracking Array (AGATA) is a European project to develop and operate the next generation gamma-ray spectrometer. AGATA is based on the technique of gamma-ray energy tracking in electrically segmented high-purity germanium crystals. This technique requires the accurate determination of the energy, time and position of every interaction as a gamma ray deposits its energy within the detector volume. Reconstruction of the full interaction path results in a detector with very high efficiency and excellent spectral response. The realisation of gamma-ray tracking and AGATA is a result of many technical advances. These include the development of encapsulated highly segmented germanium detectors assembled in a triple cluster detector cryostat, an electronics system with fast digital sampling and a data acquisition system to process the data at a high rate. The full characterisation of the crystals was measured and compared with detector-response simulations. This enabled pulse-shape analysis algorithms, to extract energy, time and position, to be employed. In addition, tracking algorithms for event reconstruction were developed. The first phase of AGATA is now complete and operational in its first physics campaign. In the future AGATA will be moved between laboratories in Europe and operated in a series of campaigns to take advantage of the different beams and facilities available to maximise its science output. The paper reviews all the achievements made in the AGATA project including all the necessary infrastructure to operate and support the spectrometer.

  • 3121.
    Akkuratov, Evgeny E.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab. St Petersburg State Univ, Inst Translat Biomed, St Petersburg, Russia.
    Gelfand, Mikhail S.
    Skolkovo Inst Sci & Technol, Ctr Data Intens Biomed & Biotechnol, Moscow, Russia.;Russian Acad Sci, Inst Informat Transmiss Problems, Moscow, Russia.;Natl Res Univ, Higher Sch Econ, Fac Comp Sci, Moscow, Russia.;MM Lomonosov Moscow State Univ, Dept Bioengn & Bioinformat, Moscow, Russia..
    Khrameeva, Ekaterina E.
    Skolkovo Inst Sci & Technol, Ctr Data Intens Biomed & Biotechnol, Moscow, Russia.;Russian Acad Sci, Inst Informat Transmiss Problems, Moscow, Russia..
    Neanderthal and Denisovan ancestry in Papuans: A functional study2018In: Journal of Bioinformatics and Computational Biology, ISSN 0219-7200, E-ISSN 1757-6334, Vol. 16, no 2, article id 1840011Article in journal (Refereed)
    Abstract [en]

    Sequencing of complete nuclear genomes of Neanderthal and Denisovan stimulated studies about their relationship with modern humans demonstrating, in particular, that DNA alleles from both Neanderthal and Denisovan genomes are present in genomes of modern humans. The Papuan genome is a unique object because it contains both Neanderthal and Denisovan alleles. Here, we have shown that the Papuan genomes contain different gene functional groups inherited from each of the ancient people. The Papuan genomes demonstrate a relative prevalence of Neanderthal alleles in genes responsible for the regulation of transcription and neurogenesis. The enrichment of specific functional groups with Denisovan alleles is less pronounced; these groups are responsible for bone and tissue remodeling. This analysis shows that introgression of alleles from Neanderthals and Denisovans to Papuans occurred independently and retention of these alleles may carry specific adaptive advantages.

  • 3122.
    Akkus, Zeynettin
    et al.
    KTH. Department of Medical Physics, University Hospitals of Leicester, NHS Trust, Leicester, UK.
    Ramnarine, K. V.
    Dynamic assessment of carotid plaque motion2010In: Ultrasound, ISSN 1742-271X, Vol. 18, no 3, p. 140-147Article in journal (Refereed)
    Abstract [en]

    Assessment of dynamic plaque behaviour may help identify vulnerable carotid plaque before rupture and hence has potential clinical value for screening patients at risk of stroke. The aim of this study was to develop non-invasive ultrasound methods for quantifying dynamic plaque and vessel wall behaviour and assess their potential clinical utility. Ultrasound data from the carotid arteries of one normal subject and four patients with atherosclerotic disease were acquired using a 10 MHz linear array transducer recording raw RF/IQ data at a frame rate up to 80 Hz for 3-6 seconds. Image reconstruction and processing was performed using Matlab. Speckle tracking techniques were developed to characterize: (1) intraplaque deformation; and (2) plaque surface and vessel wall motion. Speckle tracking techniques were able to measure the range of intraplaque tissue deformation (-1.3 to 1.7 mm), plaque surface displacement (0.2-0.7 mm) and vessel wall radial strain (0.02-0.13) throughout the cardiac cycle. The feasibility of using an intraplaque deformation parameter, based on the deformation of a square template, is demonstrated. Speckle tracking techniques can be used to assess dynamic carotid plaque behaviour. Further work is required to evaluate how best to quantify biomechanical behaviour to help predict plaque rupture and hence improve risk stratification models for stroke.

  • 3123. Akman, O.
    et al.
    Kavas, H.
    Baykal, A.
    Toprak, Muhammet S.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
    Coruh, Ali
    Aktas, B.
    Magnetic metal nanoparticles coated polyacrylonitrile textiles as microwave absorber2013In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 327, p. 151-158Article in journal (Refereed)
    Abstract [en]

    Polyacrylonitrile (PAN) textiles with 2 mm thickness are coated with magnetic nanoparticles in coating baths with Ni, Co and their alloys via an electroless metal deposition method. The crystal structure, morphology and magnetic nature of composites are investigated by X-ray Powder diffraction, Scanning Electron Microscopy, and dc magnetization measurement techniques. The frequency dependent microwave absorption measurements have been carried out in the frequency range of 12.4-18 GHz (X and P bands). Diamagnetic and ferromagnetic properties are also investigated. Finally, the microwave absorption of composites is found strongly dependent on the coating time. One absorption peak is observed between 14.3 and 15.8 GHz with an efficient absorption bandwidth of 3.3-4.1 GHz (under -20 dB reflection loss limit). The Reflection loss (RL) can be achieved between -30 and -50 dB. It was found that the RL is decreasing and absorption bandwidth is decreasing with increasing coating time. While absorption peak moves to lower frequencies in Ni coated PAN textile, it goes higher frequencies in Co coated ones. The Ni-Co alloy coated composites have fluctuating curve of absorption frequency with respect to coating time. These results encourage further development of magnetic nanoparticle coated textile absorbers for broadband applications.

  • 3124.
    Ako, Thomas
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Design of invisibility cloaks with an open tunnel2010In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, no 26, p. 27060-27066Article in journal (Refereed)
    Abstract [en]

    In this paper we apply the methodology of transformation optics for design of a novel invisibility cloak which can possess an open tunnel. Such a cloak facilitates the insertion (retrieval) of matter into (from) the cloak's interior without significantly affecting the cloak's performance, overcoming the matter exchange bottleneck inherent to most previously proposed cloak designs. We achieve this by applying a transformation which expands a point at the origin in electromagnetic space to a finite area in physical space in a highly anisotropic manner. The invisibility performance of the proposed cloak is verified by using full-wave finite-element simulations. (C) 2010 Optical Society of America

  • 3125.
    Akpe, Victor
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Photophysical and Chemical Approaches to Cellular Biophysics2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The central theme in this thesis is reversibility. Two main attempts has been made to approach reversibility in cellular systems from both chemical and physical points of view. Reversibility of immunolabeling of proteins on the cell surface has been adressed by development of new fluorescent substances optimized for CALI (Chromophore-Assisted Laser Inactivation of protein). Aluminum phthalocyanine (AlPc) is here identified to be a good candidate for a new generation of fluorophores for efficient hydroxyl radical generation. It is shown that cells can be reversibly labeled with antibody-AlPc conjugates. In experiments on living cells the AlPcs were not only active as classic fluorophores but also as photocatalytic substances with destaining properties. Reversibility of cell immobilization is also reported, where cells cultured in microstructures were immobilized and 3D supported using hydrogels. Hydrogel formulation and application was optimized to achieve a system where both viability and ease of use was satisfied. Gel reversibility was actualized with pH and enzyme treatment. The developped method offers the possibility of stop flow culturing cells in controlled and reusable 3D environments.

  • 3126.
    Akpe, Victor
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Nyokong, Tebello
    Osadebe, P. O.
    Photophysical and photochemical parameters of octakis (benzylthio) phthalocyaninato zinc, aluminium and tin: Red shift index concept in solvent effect on the ground state absorption of zinc phthalocyanine derivatives2010In: Journal of Molecular Structure, ISSN 0022-2860, E-ISSN 1872-8014, Vol. 984, no 1-3, p. 1-14Article in journal (Refereed)
    Abstract [en]

    This paper addresses the synthesis of octa-substituted benzylthio metallophthalocyanines (OBTMPcs) that contain the central metal ions of Zn2+, Al3+ and Sn4+. The ground state absorption of ZnPc(SR)(8) (OBTZnPc) along with the ZnPc derivatives, well documented in literature were used to study a new concept called the red shift index (RsI). The concept is based on the empirical values of RsI of the different complexes in solvent media. Unequivocally, parameters used in this paper show strong correlations that are consistent with the results obtained. For instance, 12,1 of the complexes tend to increase as the refractive index, n(D), and solvent donor, DN, of solvent increases. Photodegradation (photobleaching) quantum yield, phi(d) measurements of these compounds show that they are highly photostable, phi(d) (0.03-0.33 x 10(-5)). The triplet quantum yield, phi(T) (0.40-0.53) and the triplet lifetime, tau(T) (610-810 mu s) are within the typical range for metallophthalocyanines in DMSO. The photosensitisation efficiency. S-Delta, is relatively high for all the molecules (0.74-0.90). (C) 2010 Elsevier B.V. All rights reserved.

  • 3127.
    Akpe, Victor
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Nyokong, Tebello
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Photophysics and photochemistry of zinc, aluminium and tin octakis (benzylthio) phthalocyanines2008Report (Other academic)
  • 3128.
    Akpe, Victor
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Ogunsipe, Abimbola
    Madu, Christian
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Red-Shift Index Concept in Solvent Effects of Chromophore-Substituted Metallophthalocyanines: A Look at the Empirical Relationship of the Macroscopic Properties of the Solute-Solvent Interactions2015In: Journal of Solution Chemistry, ISSN 0095-9782, E-ISSN 1572-8927, Vol. 44, no 2, p. 307-326Article in journal (Refereed)
    Abstract [en]

    Solvent effects on the UV/vis spectra of metallopthalocyanines (MPcs) have been interpreted using the red-shift index concept (R (s) I). The concept connects empirically, direct, experimental, easily accessible optical spectral data, which are explained by considering the differential behavior of the solute-solvent interactions at the ground state and excited state using the spectral values of MPcs along with the derived concept, called the associated solvation energy (ASE). R (s) I is formulated from three fundamental parameters, which are: ground state electronic absorption spectrum, polarization red-shift and a scaling factor of MPc (N (dye)) in the respective solvents. The R (s) I is a reflection of the index value of the chromophore substituent of MPc in the solvent; thus, the concept can be used as a solvatochromic parameter to study a wide range of supramolecular and heterocyclic compounds that can be modified at their periphery or 'handles'. Particularly, in this study, the concept has been used to rank MPc candidates by using the statistical mean performance of the solvatochromic parameters, which are red shift index, polarizability efficiency and ASE. We hereby review the solvent effects on the UV/vis spectra of substituted and unsubstituted MPcs.

  • 3129.
    Akpe, Victor
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Vernet, Erik
    KTH, School of Biotechnology (BIO), Molecular Biotechnology.
    Gräslund, Torbjörn
    KTH, School of Biotechnology (BIO), Molecular Biotechnology.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Characterization studies of aluminum phthalocyanine binding to antibodies from SKBR 3 cell line2008Report (Other academic)
  • 3130.
    Akpe, Victor
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Vernet, Erik
    KTH, School of Biotechnology (BIO), Protein Technology.
    Madu, Christian
    Obirai, Joseph C.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Understanding the Photochemical Pathway of In Vitro Target Delivery of Aluminium Phthalocyanine: A Mechanistic Approach Using Radical Reaction Chemistry2014In: ChemPlusChem, ISSN 2192-6506, Vol. 79, no 5, p. 671-679Article in journal (Refereed)
    Abstract [en]

    A classical dye, aluminium phthalocyanine (AlPc), is used to study the photochemical processes involved in the chromophore-assisted laser inactivation technique. Both cell-free and cell-based systems are investigated by novel methods and radical reaction chemistry. Findings on the photochemical pathways in two models representing cell-free and a cell-based systems are reported. In the cell-free system, the unsubstituted, free, fluorescence-active photosensitiser AlPc recovers its fluorescence signal by means of phosphorescence through a reversible photobleaching process. In the cell-based system, photoactivation of substituted AlPc conjugated to an antibody results in the loss of fluorescence signal at the area examined. Reinjection of the AlPc-conjugated antibodies restores the fluorescence signal.

  • 3131. Akram, M. N.
    et al.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Marcinkevicius, Saulius
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Berggren, J.
    Experimental evaluation of carrier transport, gain, T0 and chirp of 1.55 mm MQW structures with different barrier compositions2005In: 31st European Conference on Optical Communications (ECOC 2005), 2005, Institution of Engineering and Technology, 2005, Vol. 2005, no CP502, p. 297-298Conference paper (Refereed)
    Abstract [en]

    Direct carrier transport measurements were performed for different InGaAsP/InGaAlAs MQW test structures. Shallow InGaAlAs barrier QW showed faster carrier transport. Semi-insulating regrown FP lasers with InGaAlAs barrier QW showed improved high temperature operation, modal gain, differential modal gain and chirp.

  • 3132.
    Akram, Muhammad
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    A Freundlich-based model for prediction of pH-dependent sulfate adsorption in forest soil.2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The period of industrialization after the second World War in Europe released SO2 and NOx by combustion of fossil fuels and contributed the formation of S and N compounds in the forest ecosystem. The Swedish forest soil systems were influenced by emissions of SO2 followed by H2SO4 deposition, consequently the pool of SO42- had increased in the forest ecosystem. This thesis studied SO42- adsorption in a podzolic Bs horizon soils taken from a Swedish forest soil system. The soil samples from five different sampling sites were collected and the results revealed different amounts of adsorbed SO42- in response to changes in equilibrium concentration and pH. This study found that the amount of adsorbed SO42- (mmol/kg) increased with an added equilibrium concentration of SO42- (mmol/l) and with a decreasing pH. This was determined by equilibration experiments. Based on the results a Freundlich-based model was developed to predict the pool of adsorbed SO42- in the soil samples. The model predicted the pool of adsorbed SO42- (mmol/kg) as a function of pH and the equilibrium concentration of SO42- (mmol/l) in the soil solution system. The extended Freundlich model was optimized in three different ways: by use of unconstrained, constrained and simplified two-point calibration. The results showed that the adsorption of sulfate in the Kloten Bs1 and Risbergshöjden B soils was higher as compared to the Tärnsjo B, Österström B, and Risfallet B soils. The coefficient of determination (R2) determined from an unconstrained fit of the extended Freundlich model (with three adjustable parameters) for Risbergshöjden B and Kloten Bs1 were R2 =0.998 and R2=0.993. Nearly as good fits were found in a constrained fit with two adjustable parameters when it was assumed that nearly 2 protons (2 H+) are co-adsorbed with one SO42- ion (Risbergshöjden B; R2=0.997 and Kloten Bs; R2=0.992). The simplified two-point calibration with two adjustable parameters showed similar parameter values for all most soils and was considered the best optimization method of extended Freundlich model, especially as it requires only limited input data.

  • 3133. Akram, Muhammad Nadeem
    et al.
    Xiang, Yu
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yu, Xingang
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zabel, Thomas
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Influence of base-region thickness on the performance of Pnp transistor-VCSEL2014In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 22, no 22, p. 27398-27414Article in journal (Refereed)
    Abstract [en]

    We have recently reported a 980nm GaAs-based three terminal Pnp transistor-vertical-cavity surface-emitting laser (TVCSEL) operating at room temperature with optical power up to 1.8mW. However, the current gain beta = Delta I-c/Delta I-b was near zero just before lasing and became negative after the lasing threshold. The main cause of the negative current gain was found to be a gradual and position-dependent forward-biasing (saturation) of the base-collector junction with increasing bias even before lasing threshold. In this article, detailed multi-physics device simulations are performed to better understand the device physics, and find ways to avoid the premature saturation of the base-collector junction. We have optimized the thickness of the base region as well as its doping concentration and the location of the quantum wells to ensure that the T-VCSEL is in the active mode throughout its range of operation. That is, the emitter-base junction is forward biased and base-collector junction is reversed biased for sweeping the excess charges out of the base region.

  • 3134. Akram, N. M.
    et al.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Marcinkevicius, Saulius
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Experimental evaluation of carrier transport, gain, T0 and chirp of 1.55 mu;m MQW structures with different barrier compositions2005In: Optical Communication, 2005. ECOC 2005. 31st European Conference on, 2005, Vol. 2, p. 297-298Conference paper (Refereed)
    Abstract [en]

    Direct carrier transport measurements were performed for different InGaAsP/InGaAlAs MQW test structures. Shallow InGaAlAs barrier QW showed faster carrier transport. Semi-insulating regrown FP lasers with InGaAlAs barrier QW showed improved high temperature operation, modal gain, differential modal gain and chirp.

  • 3135.
    Akram, Nadeem
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Lateral current injection (LCI) multiple quantum-well 1.55 mu m laser with improved gain uniformity across the active region2004In: Optical and quantum electronics, ISSN 0306-8919, E-ISSN 1572-817X, Vol. 36, no 9, p. 827-846Article in journal (Refereed)
    Abstract [en]

    A simulation study of lateral current injection 1.55 mum laser with strain-compensated multiple quantum-well (MQW) active region (InGaAsP well, InGaAlAs barrier) is presented using self-consistent 2D numerical simulations. The effects of different mesa width and p-doping in the QWs on the carrier and gain uniformity across the active region are explored. A high p-doping in the quantum wells is found to increases the carrier and gain non-uniformity across the active region. The QW region close to the n-contact side does not provide much gain at high optical powers. An asymmetric optical waveguide design is proposed to help reduce the gain non-uniformity across the active region. By shifting the optical modal peak toward the p-side, the modal overlap between the gain region and the optical mode is improved and a more even carrier and gain distribution is obtained. However, due to reduced bandgap of the quaternary InGaAsP p-cladding, an enhanced electron leakage out of the QWs into the p-cladding degrades the laser efficiency and increases the threshold current. Transient time - domain simulations are also performed to determine the small-signal modulation response of the laser promising a simulated high modulation bandwidth suitable for direct-modulation applications.

  • 3136.
    Akram, Nadeem
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Photonic devices with MQW active material and waveguide gratings: modelling and characterisation2005Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The research work presented in this thesis deals with modelling, design and characterisation of passive and active optical waveguide devices. The rst part of the thesis is related to algorithm development and numerical modelling of planar optical waveguides and gratings using the Method of Lines (MoL). The basic three-point central-di erence approximation of the δ2=δx2 operator used in the Helmholtz equation is extended to a new ve-point and seven-point approximation with appropriate interface conditions for the TE and TM elds. Di erent structures such as a high-contrast waveguide and a TM surface plasmon mode waveguide are simulated, and improved numerical accuracy for calculating the optical mode and propagation constant is demonstrated. A new fast and stable non-paraxial bi-directional beam propagation method, called Cascading and Doubling algorithm, is derived to model deep gratings with many periods. This algorithm is applied to model a quasi-guided multi-layer anti-resonant reecting optical waveguide (ARROW) grating polarizing structure.

    In the second part of the thesis, our focus is on active optical devices such as vertical-cavity and edge-emitting lasers. With a view to improve the bandwidth of directly modulated laser, an InGaAsP quantum well with InGaAlAs barrier is studied due to its favorable band o set for hole injection as well as for electron con nement. Quantum wells with di erent barrier bandgap are grown and direct carrier transport measurements are done using time and wavelength resolved photoluminescence upconversion. Semi-insulating regrown Fabry-Perot lasers are manufactured and experimentally evaluated for light-current, optical gain, chirp and small-signal performance. It is shown that the lasers having MQW with shallow bandgap InGaAlAs barrier have improved carrier transport properties, better T0, higher di erential gain and lower chirp. For lateral current injection laser scheme, it is shown that a narrow mesa is important for gain uniformity across the active region. High speed directly modulated DBR lasers are evaluated for analog performance and a record high spurious free dynamic range of 103 dB Hz2=3 for frequencies in the range of 1-19 GHz is demonstrated. Large signal transmission experiment is performed at 40 Gb/s and error free transmission for back-to-back and through 1 km standard single mode ber is achieved.

  • 3137.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Chacinski, Marek
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Olsson, Fredrik
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Berrier, Audrey
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Experimental characterization of high-speed 1.55 mu m buried heterostructure InGaAsP/InGaAlAs quantum-well lasers2009In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 26, no 2, p. 318-327Article in journal (Refereed)
    Abstract [en]

    Detailed experimental characterization is performed for 1550 nm semi-insulating regrown buried heterostructure Fabry-Perot (FP) lasers having 20 InGaAsP/InGaAlAs strain-balanced quantum wells (QWs) in the active region. Light-current-voltage performance, electrical impedance, small-signal response below and above threshold, amplified spontaneous emission spectrum below threshold and relative intensity noise spectrum are measured. Different laser parameters such as external differential quantum efficiency eta(d), background optical loss alpha(i), K-factor, D-factor, characteristic temperature T-0, differential gain dg/dn, gain-compression factor epsilon, carrier density versus current, differential carrier lifetime tau(d), optical gain spectrum below threshold, and chirp parameter alpha are extracted from these measurements. The FP lasers exhibited a high T-0 (78-86.5 degrees C) and very high-resonance frequency (23.7 GHz). The results indicate that appropriately designed lasers having a large number of InGaAsP well/InGaAlAs barrier QWs with shallow valence-band discontinuity can be useful for un-cooled high-speed direct-modulated laser applications.

  • 3138.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Chacinski, Marek
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Olsson, Fredrik
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Berrier, Audrey
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    High-Speed Performance of 1.55 µm Buried Hetero-Structure Lasers with 20 InGaAsP/InGaAlAs Quantum-Wells2006In: 2006 European Conference on Optical Communications Proceedings, ECOC 2006, IEEE , 2006, p. 1-2Conference paper (Refereed)
    Abstract [en]

    1550 nm re-grown FP lasers having 20 InGaAsP/InGaAlAs strain-balanced QWs exhibit low threshold current density, high T0 (78.0 #x000B0;C) and high resonance frequency (24 GHz) indicating that a large number of shallow barrier QWs are attractive for un-cooled high-speed direct-modulation applications.

  • 3139.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Marcinkevičius, Saulius
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Olsson, Fredrik
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Lourdudoss, Sebastian
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    The effect of barrier composition on the vertical carrier transport and lasing properties of 1.55-mu m multiple quantum-well structures2006In: IEEE Journal of Quantum Electronics, ISSN 0018-9197, E-ISSN 1558-1713, Vol. 42, no 7, p. 713-714Article in journal (Refereed)
    Abstract [en]

    In this paper, the effect of barrier bandgap and composition on the optical performance of 1.55-mu m InGaAsP/In-GaAsP and InGaAsP/InGaAlAs multiple quantum-well structures and Fabry-Perot lasers is evaluated experimentally. Direct vertical carrier transport measurements were performed through strain-compensated multiple quantum-well (MQW) test structures using femto-second laser pulse excitation and time-resolved photoluminescence up-conversion method. MQW test structures were grown with different barrier composition (InGaAsP and InGaAlAs) and barrier bandgap (varied from lambda(g) = 1440 to 1260 nm) having different conduction band Delta E-c and valence band discontinuity Delta E-v, while keeping the same InGaAsP well composition for all the structures. The ambipolar carrier transport was found to be faster in the structures with lower valence band discontinuity Delta E-v. Regrown semi-insulating buried heterostructure Fabry-Perot (SIBH-FP) lasers were fabricated from similar QWs and their static light-current-voltage characteristics (including optical gain and chirp spectra below threshold) and thermal characteristics were measured. Lasers with InGaAlAs barrier showed improved high-temperature operation, higher optical gain, higher differential gain, and lower chirp, making them suitable candidates for high-bandwidth directly modulated uncooled laser applications.

  • 3140.
    Akram, Nadeem
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kjebon, Olle
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Influence of electrical parasitics and drive impedance on the laser modulation response2004In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 16, no 1, p. 21-23Article in journal (Refereed)
    Abstract [en]

    In this letter, we analyze the effects of electrical parasitics and drive impedance on the laser modulation response. It is found that for lasers with small active-region volume, e.g., vertical-cavity surface-emitting lasers, the finite drive impedance and/or the laser parasitic capacitance can significantly enhance the damping of the laser resonance peak at low bias. This is due to the voltage fluctuations across the laser diode active layer during modulation. It is also shown that the real pole of the small-signal response transfer function corresponding to the laser parasitic cutoff frequency is not fixed but decreases with the increased bias level.

  • 3141.
    Akram, Nadeem
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Silfvenius, Christofer
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Material Physics (Closed 20120101), Semiconductor Materials, HMA (Closed 20120101).
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Design optimization of InGaAsP-InGaAlAs 1.55 mu;m strain-compensated MQW lasers for direct modulation applications2004In: Indium Phosphide and Related Materials, 2004. 16th IPRM. 2004 International Conference on, IEEE , 2004, p. 418-421Conference paper (Refereed)
    Abstract [en]

    A comprehensive simulation study of InGaAsP (well)/InGaAlAs(barrier) 1.55 mu;m strain-compensated MQW lasers is presented. For MQWs, a uniform vertical distribution of holes is achieved due to a reduced effective hole confinement energy by optimizing the bandgap and strain of the barriers and p-doping in the active region. Some preliminary results are also presented for the manufactured lasers using these QWs indicating a good material platform.

  • 3142.
    Akram, Nadeem
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Silfvenius, Christofer
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Kjebon, Olle
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Design optimization of InGaAsP-InGaAlAs 1.55 mu m strain-compensated MQW lasers for direct modulation applications2004In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 19, no 5, p. 615-625Article in journal (Refereed)
    Abstract [en]

    In this paper, a simulation study of InGaAsP(well)/InGaAlAs(barrier) 1.55 mum strain-compensated multi-quantum well (MQW) lasers is presented. Due to a large conduction band discontinuity in this material system, a higher material gain and differential gain can be obtained from such a quantum well (QW) as compared to a traditional InGaAsP/InGaAsP quantum well. The deeper electron well should also improve elevated temperature operating characteristics and reduce the electron spillover from QWs. For MQWs, a uniform vertical distribution of holes is achieved due to a reduced effective hole confinement energy by optimizing the bandgap and the strain in the barriers. A large number of quantum wells can be uniformly pumped, reducing the carrier density in each individual well. A uniform and low carrier density in all the wells help reduce the total Auger recombination current. High p-doping in the active region is shown to enhance the carrier and gain non-uniformity in the MQWs. A simulated high modulation bandwidth has been demonstrated, promising directly modulated lasers as a low-cost source for short to medium distance (1-10 km) high speed optical links.

  • 3143.
    Akram, Saad Ullah
    KTH, School of Computer Science and Communication (CSC).
    Visual Recognition of Isolated Swedish Sign Language Signs.2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Visual Recognition of Isolated Swedish Sign Language Signs

    Saad Ullah Akram saadua@kth.se

    Abstract:

    Deaf people face serious challenges when communicating with people who have hearing capability, vast majority of whom do not have any sign language skills. Deaf people in these situations have to rely on written language which is usually not their primary language. Most of the deaf children are born to hearing parents who usually have very rudimentary sign language skills, these children do not get enough opportunity to practice and improve their signing skills outside the school environment. This puts these children at a disadvantage as they take more time to be able to communicate complex ideas with others.

    This project proposes a method for recognition of Isolated Swedish Sign Language signs in a natural environment using Kinect sensor with only one important restriction that signer must wear a full-sleeved non-skin colored clothing. An adaptive histogram based skin color model and motion information are used to segment hands. 3D position of the hands relative to the torso are used as a cue together with the hand shape, and HMMs (Hidden Markov Models) trained with this input are used for classification. This project also presents a method which is able to solve one (hand over face) of the two common (other being hand over hand) occlusions encountered in sign language.

    The results obtained show that Sign Language Recognition problem for very challenging medium sized (94 signs) vocabulary can be solved with very good performance (92% recognition accuracy) in signer dependent case and with reasonable performance (42% recognition accuracy) in signer independent case.

  • 3144. Akrami, Yashar
    et al.
    Hassan, S. F.
    Koennig, Frank
    Schmidt-May, Angnis
    Solomon, Adam R.
    Bimetric gravity is cosmologically viable2015In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 748, p. 37-44Article in journal (Refereed)
    Abstract [en]

    Bimetric theory describes gravitational interactions in the presence of an extra spin-2 field. Previous work has suggested that its cosmological solutions are generically plagued by instabilities. We show that by taking the Planck mass for the second metric, M-f, to be small, these instabilities can be pushed back to unobservably early times. In this limit, the theory approaches general relativity with an effective cosmological constant which is, remarkably, determined by the spin-2 interaction scale. This provides a late-time expansion history which is extremely close to Lambda CDM, but with a technically-natural value for the cosmological constant. We find M-f should be no larger than the electroweak scale in order for cosmological perturbations to be stable by big-bang nucleosynthesis. We further show that in this limit the helicity-0 mode is no longer strongly-coupled at low energy scales. (C) 2015 The Authors. Published by Elsevier B.V.

  • 3145. Akrami, Yashar
    et al.
    Koivisto, Tomi S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Solomon, Adam R.
    The nature of spacetime in bigravity: Two metrics or none?2015In: General Relativity and Gravitation, ISSN 0001-7701, E-ISSN 1572-9532, Vol. 47, no 1, p. 1838-Article in journal (Refereed)
    Abstract [en]

    The possibility of matter coupling to two metrics at once is considered. This appears natural in the most general ghost-free, bimetric theory of gravity, where it unlocks an additional symmetry with respect to the exchange of the metrics. This double coupling, however, raises the problem of identifying the observables of the theory. It is shown that if the two metrics couple minimally to matter, then there is no physical metric to which all matter would universally couple, and that moreover such an effective metric generically does not exist even for an individual matter species. By studying point particle dynamics, a resolution is suggested in the context of Finsler geometry.

  • 3146.
    Akrami, Yashar
    et al.
    Leiden Univ, Lorentz Inst Theoret Phys, POB 9506, NL-2300 RA Leiden, Netherlands..
    Kuhnel, Florian
    Stockholm Univ, AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, Dept Phys, SE-10691 Stockholm, Sweden..
    Sandstad, Marit
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Uncertainties in primordial black-hole constraints on the primordial power spectrum2018In: Physics of the Dark Universe, ISSN 0953-8585, E-ISSN 2212-6864, Vol. 19, p. 124-128Article in journal (Refereed)
    Abstract [en]

    The existence (and abundance) of primordial black holes (PBHs) is governed by the power spectrum of primordial perturbations generated during inflation. So far no PBHs have been observed, and instead, increasingly stringent bounds on their existence at different scales have been obtained. Up until recently, this has been exploited in attempts to constrain parts of the inflationary power spectrum that are unconstrained by cosmological observations. We first point out that the simple translation of the PBH non-observation bounds into constraints on the primordial power spectrum is inaccurate as it fails to include realistic aspects of PBH formation and evolution. We then demonstrate, by studying two examples of uncertainties from the effects of critical and non-spherical collapse, that even though they may seem small, they have important implications for the usefulness of the constraints. In particular, we point out that the uncertainty induced by non-spherical collapse may be much larger than the difference between particular bounds from PBH non-observations and the general maximum cap stemming from the condition Omega <= 1 on the dark-matter density in the form of PBHs. We therefore make the cautious suggestion of applying only the overall maximum dark-matter constraint to models of early Universe, as this requirement seems to currently provide a more reliable constraint, which better reflects our current lack of detailed knowledge of PBH formation. These, and other effects, such as merging, clustering and accretion, may also loosen constraints from non-observations of other primordial compact objects such as ultra-compact minihalos of dark matter. 

  • 3147.
    Akrawi, Kahi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Halim, Magdalena
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Ombyggnation av befintlig byggnad till hotell2018Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
  • 3148.
    Akrawi, Kahi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Sharif, Vina
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Tätningsmetoder av tunnlar för skydd av installationer: En studie baserad på litteratur, intervjuer och tidigare arbeten.2016Independent thesis Basic level (university diploma), 5 credits / 7,5 HE creditsStudent thesis
  • 3149. Akselsen, O. M.
    et al.
    Aune, Ragnhild E.
    Fostervoll, H.
    Harsvoer, A. S.
    Dry hyperbaric welding of subsea pipelines2006In: Welding Journal, ISSN 0043-2296, Vol. 85, no 6, p. 52-55Article in journal (Refereed)
  • 3150. Akselsen, O. M.
    et al.
    Harsvaer, A.
    Fostervoll, H.
    Aune, Ragnhild E.
    Root bead profiles in hyperbaric GTAW of X70 pipeline2006In: International Journal of Offshore and Polar Engineering, ISSN 1053-5381, Vol. 16, no 2, p. 123-127Article in journal (Refereed)
    Abstract [en]

    This investigation began with the goal of studying the root bead penetration profiles in hyperbaric GTAW welding of X70 pipelines. Such profiles may vary substantially depending on the wire and base metal chemical composition. Root beads were deposited with a pressure corresponding to 75-m seawater depth, and with a systematic increase of 10 A in the pulse current until burnthrough took place. The results obtained showed that the penetration profiles were different between the 2 wires included in the welding program. The largest penetration width was found for wire B with the highest sulphur content (0.013% S), with a maximum width of about 8-mm width on the pipe inside for 160 A. At pulse current levels of 120 to 170 A, the difference between the 2 wires was about 1 mm. With current beyond 180 A, the profiles approached similar values, followed by burnthroughs for both wires at 190 A. However, the welding parameters were already too hot at 180 A. These results are probably caused by a Marangoni convection in the weld pool. A high content of surface active elements (e.g., sulphur) is known to shift the How pattern, providing deeper penetration. In practice, small variations in the bead penetration profile may have large consequences during offshore tie-in welding. Cost-increasing repair operations may be required if nondestructive inspection later reveals poor root bead quality. Such actions require mobilisation of huge resources.

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