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  • 126551.
    Zhu, Xiaoqian
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Coordinated MIMO Precoder EvaluationBased on Measurement in IndoorEnvironment2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis, we investigate the performance of the coordinated MIMO precoders, using measured channels in indoorvenvironment. Instead of simulated radio propagationvconditions, measured channels are used to evaluate the precoder performance for real-world channels. Our measurement campaign includes several scenarios such as femtocell and “heterogeneous” networks. The study results illustrate that the precoders could reduce the interference significantly and support a high system throughput especially over high SNR where interference is dominant.

    Degree of freedom (DoF) is defined as the maximum number of data stream that could independently coordinate to be transmitted interference-free. Theoretically, the precoders could support 1 DoF per user, while DoF of uncoordinated transmission is 0 per user. Interference Alignment(IA) study arises from information theory of DoF in the interference channel (IC). Three precoding algorithms are investigated to align the interference: maximum sum rate, maxSINR and minWLI. Considering the distributed precoder methods, “maxSINR” always performs better than “minWLI”. Since it tries to maximize the user’s SINR instead of only repressing the interference as “minWLI” does. While “maximum sum rate” is not good at finding an IA like solution that scales well at high SNR. However “maximum sum rate” converges faster than “maxSINR” and “minWLI”.

    Our study about IA feasibility shows that precoding jointly over two subcarriers, using so called frequency extensions, allows 4 users to communicate interference-freeover a 2 × 2 MIMO IC. Without frequency extensions, only 3 users can communicate interference-free.

  • 126552. Zhu, Xuncheng
    et al.
    Ding, Zhizhong
    Punyal, Oscar
    Gross, James
    Design and Implementation of Baseband Algorithms for OFDM-based Wireless Communication Systems2011In: 7th International Conference on Wireless Communications, Networking and Mobile Computing (WiCOM), 2011, IEEE conference proceedings, 2011, p. 1-5Conference paper (Refereed)
    Abstract [en]

    Orthogonal frequency-division multiplexing (OFDM) is an appropriate solution to combat inter-symbol interference (ISI) caused by multi-path propagation in wireless communications. OFDM-based wireless communication systems become more and more popular and the base-band algorithm is one of the significant parts of the systems. In this paper, we present the design and implementation of base-band algorithms for OFDM-based wireless communication systems. The results show that the designed algorithms are effective for implementation of the system.

  • 126553. Zhu, Y.
    et al.
    Cheng, D.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Synchronization of a class of networked passive systems with switching topology2007In: Proceedings of the 46th IEEE Conference on Decision and Control, 2007, p. 2271-2276Conference paper (Refereed)
    Abstract [en]

    This paper considers the output synchronization of a class of networked agents. Each agent is a passive system. Local information, used by each agent to adjust its movement, forms a network with switching adjacent topology. First, we consider the asymptotic stability of nonlinear time-varying switched systems by using multiple Lyapunov function. An extended Lyapunov-like Lemma for switched systems is obtained. Then the result is applied to the output synchronization of a class of networked passive systems with switching topology. A pretty fair sufficient condition is presented.

  • 126554. Zhu, Y.
    et al.
    Engström, P. G.
    Tellgren-Roth, C.
    Baudo, C. D.
    Kennell, J. C.
    Sun, S.
    Billmyre, R. B.
    Schröder, M. S.
    Andersson, A.
    Holm, T.
    Sigurgeirsson, Benjamin
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Wu, G.
    Sankaranarayanan, S. R.
    Siddharthan, R.
    Sanyal, K.
    Lundeberg, Joakim
    KTH, School of Biotechnology (BIO), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Nystedt, B.
    Boekhout, T.
    Dawson, T.L., Jr.
    Heitman, J.
    Scheynius, A.
    Lehtiö, J.
    Proteogenomics produces comprehensive and highly accurate protein-coding gene annotation in a complete genome assembly of Malassezia sympodialis2017In: Nucleic Acids Research, ISSN 0305-1048, E-ISSN 1362-4962, Vol. 45, no 5, p. 2629-2643Article in journal (Refereed)
    Abstract [en]

    Complete and accurate genome assembly and annotation is a crucial foundation for comparative and functional genomics. Despite this, few complete eukaryotic genomes are available, and genome annotation remains a major challenge. Here, we present a complete genome assembly of the skin commensal yeast Malassezia sympodialis and demonstrate how proteogenomics can substantially improve gene annotation. Through long-read DNA sequencing, we obtained a gap-free genome assembly for M. sympodialis (ATCC 42132), comprising eight nuclear and one mitochondrial chromosome. We also sequenced and assembled four M. sympodialis clinical isolates, and showed their value for understanding Malassezia reproduction by confirming four alternative allele combinations at the two mating-type loci. Importantly, we demonstrated how proteomics data could be readily integrated with transcriptomics data in standard annotation tools. This increased the number of annotated protein-coding genes by 14% (from 3612 to 4113), compared to using transcriptomics evidence alone. Manual curation further increased the number of protein-coding genes by 9% (to 4493). All of these genes have RNA-seq evidence and 87% were confirmed by proteomics. The M. sympodialis genome assembly and annotation presented here is at a quality yet achieved only for a few eukaryotic organisms, and constitutes an important reference for future host-microbe interaction studies.

  • 126555. Zhu, Y.
    et al.
    Hjalmarsson, Håkan
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    The Box-Jenkins Steiglitz-McBride algorithm2016In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 65, p. 170-182Article in journal (Refereed)
    Abstract [en]

    An algorithm for identification of single-input single-output Box-Jenkins models is presented. It consists of four steps: firstly a high order ARX model is estimated; secondly, the input-output data is filtered with the inverse of the estimated disturbance model; thirdly, the filtered data is used in the Steiglitz-McBride method to recover the system dynamics; in the final step, the noise model is recovered by estimating an ARMA model from the residuals of the third step. The relationship to other identification methods, in particular the refined instrumental-variable method, are elaborated upon. A Monte Carlo simulation study with an oscillatory system is presented and these results are complemented with an industrial case study. The algorithm can easily be generalized to multi-input single-output models with common denominator.

  • 126556. Zhu, Y.
    et al.
    Hu, Y.
    Schmeink, A.
    Gross, James
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Energy Minimization of Mobile Edge Computing Networks with Finite Retransmissions in the Finite Blocklength Regime2019In: IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC, Institute of Electrical and Electronics Engineers (IEEE), 2019, article id 8815391Conference paper (Refereed)
    Abstract [en]

    We consider a mobile edge computing network supporting low-latency and ultra reliable services. Task off-loading from the user to the edge server is operated under a truncated retransmission process, i.e., the allowed retransmission times are finite. For such network, we first characterize the end-to-end error probability and the total energy consumption. We subsequently provide a framework design allowing to determine the optimal number of allowed retransmissions and the blocklength for a single transmission/retransmission, where the objective is to minimize the expected total energy consumption while guaranteeing the end-to-end reliability. Via simulation, we confirm our analytical model and evaluated the system performance.

  • 126557. Zhu, Y.
    et al.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Wang, W.
    Chen, X.
    On the iron oxides between railway wheels and rails using laboratory tests2015In: CM 2015 - 10th International Conference on Contact Mechanics of Wheel / Rail Systems, International Conference on Contact Mechanics of Wheel , 2015Conference paper (Refereed)
    Abstract [en]

    The contact between railway wheels and rails is influenced by various contaminants. Iron oxides present on both wheel and rail surfaces which constantly affects the wheel?rail adhesion and wear. The paper summarizes some laboratory work investigating the iron oxides between the wheel and rai contact which were previous performed in the authors’ group. A comparison of the contact conditions and application regarding the test rig (pin-on-disc and twin-disc) is also given. The influence of iron oxides on the coefficient of friction, adhesion coefficient and wear rate is presented and discussed. Results indicate iron oxides greatly influence the tribological behavior particularly under the wet condition. The author aims to highlight the importance of the iron oxides which may provide some hints to explain the difference between laboratory tests and field measurements. However, a quantitative study is needed based on controlled environmental conditions due to the complexity and fast transition of iron oxides.

  • 126558. Zhu, Y.
    et al.
    Wu, F.
    Xiong, Q.
    Lu, Zhonghai
    KTH, School of Information and Communication Technology (ICT), Electronics.
    Xie, C.
    ALARM: A Location-Aware Redistribution Method to Improve 3D FG NAND Flash Reliability2017In: 2017 IEEE International Conference on Networking, Architecture, and Storage, NAS 2017 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 8026841Conference paper (Refereed)
    Abstract [en]

    3D NAND flash memory is enjoying an increasing popularity as it dramatically increases the bit density, presenting a grand opportunity to satisfy the growing demand on the storage capacity. However, this vertically stacked structure also introduces more serious read disturb problems compared with planar flash devices. Characterization results show that the read disturb errors on 3D floating gate (FG) MLC NAND flash chips exhibit a large discrepancy on the locations and types of pages, implying that pages should not be treated equally when designing migration schemes. This paper makes a thorough observation on read access characteristics by analyzing contemporary workloads collected from a wide range of applications with various read ratios. Based on the characterization results, we build a read disturb error model and propose a location-aware redistribution method (ALARM) that utilizes the intrinsic characteristics of the 3D floating gate NAND flash and redistributes read-hot pages to locations inducing less read disturb errors to improve its reliability. We implement the read disturb error model and our proposed design on an event-driven simulator, and the experimental results show that ALARM can reduce the maximum and average raw bit error rates (RBERs) by up to 99.49% and 91.80% with an operation overhead of 0.70%.

  • 126559.
    Zhu, Yafeng
    KTH, School of Biotechnology (BIO).
    Identification and visualization of splice variants in shotgun proteomics data by Alternative Splicing Database2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    It has been shown in many studies that alternative splicing plays an important role in functional regulation and is associated with many neurological disorders and cancers. Current methods to detect splice variants are computational prediction by ESTs clustering and experimental approaches such as RNA probe microarray. These methods are only focusing on the the RNA level. But due to post transcriptional modification on pre-mRNA molecules, there is a weak correlation between mRNA abundance and protein expressin. Therefore, it is important to find evidence of these functioinally important splice variants at the protein level. Shotgun proteomics has become a favorable tool to do large scale identification of proteins. Recently, a tool called Protein Quantification and Peptide Quality Control (PQPQ) was develope to enhance information output from shotgun proteomics data and to detect protein variants. Here, we present a downstream program, SpliceView, a tool for analyzing and visualizing the output from PQPQ for finding splice variants. Proteomics data of A431 cell line was used to exemplify available functions of SpliceView.

  • 126560.
    Zhu, Yaoxuan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Huang, Xiaoting
    IMPROVEMENT OF COMPACTED GRAPHITE IRON DRILLING OPERATIONS WITH CUSTOMIZED CUTTING FLUID2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With its higher strength, Compacted Graphite Iron (CGI) is widely used in automotive industry. However, the machinability of CGI is challenging, mostly due to the high temperature in the cutting zone and the higher cutting force. This paper studies the influence of the different cutting fluids on the machinability of CGI material in drilling operations. The investigation compared a few customized cutting fluids having alkaline phase and oil phase, to a conventional cutting fluid. The oil phase of customized cutting fluid can help reduce the friction force in the machining process. The flank wear measurements showed there is no significant difference among the fluids. The thrust force measurements, however, showed that the customized cutting fluids could effectively reduce the cutting force by nearly 20%. By using the customized cutting fluid, the machining of CGI materials could either use higher feed rate to reduce cycle time when keeping the cutting force same, or use the same process data while reducing energy consumption.

  • 126561.
    Zhu, Yi
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Adhesion in the wheel-rail contact2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    To attract more customers and compete with other modes of transportation, railway transport needs to ensure safety, punctuality, high comfort, and low cost; wheel–rail adhesion, i.e., the transmitted tangential force in the longitudinal direction during driving and braking, plays an important role in all these aspects. Adhesion needs to be kept at a certain level for railway operation and maintenance. However, wheel−rail contact is an open system contact. Different contaminants can present between the wheel and rail surfaces, forming a third-body layer that affects the adhesion. Prediction of wheel–rail adhesion is important for railway operations and research into vehicle dynamics; however, this prediction is difficult because of the presence of contaminants.

    This thesis deals with wheel–rail adhesion from a tribological perspective. The five appended papers discuss wheel–rail adhesion in terms of dry conditions, lubricated conditions, leaf contamination, iron oxides, and environmental conditions. The research methodologies used are numerical modelling, scaled laboratory experiments, and field tests. The research objective is to understand the mechanisms of the adhesion loss phenomenon. 

    A numerical model was developed to predict wheel–rail adhesion based on real measured 3D surfaces. Computer simulation indicates that surface topography has a larger impact on lubricated than on dry contacts. Plastic deformation in asperities is found to be very important in the model. Ball-on-disc tests indicate that water can give an extremely low adhesion coefficient on smooth surfaces, possibly due to surface oxidation. Investigation of lubricated contacts at low speed indicates that oil reduces the adhesion coefficient by carrying a normal load, while adhesion loss due to water depends on the surface topography, water temperature, and surface oxidation. A field investigation indicates that leaves reduce the friction coefficient because of the chemical reaction between leaves and bulk materials. The thickness of the surface oxide layer was found to be an essential factor determining adhesion reduction. Pin-on-disc experiments found a transition in the friction coefficient with regard to the relative humidity, due to a trade-off between the water molecule film and the hematite on the surface. 

  • 126562.
    Zhu, Yi
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Adhesion in the wheel-rail contact under contaminated conditions2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Railway vehicles require a certain level of adhesion between wheel and rail to operate efficiently, reliably, and economically. Different levels of adhesion are needed depending on the vehicle running conditions. In the wheel tread–railhead contact, the dominant problem is low adhesion, as low adhesion on the railhead negatively affects railway operation: on one hand, the vehicle will lose traction resulting in delay when driving on low-adhesion tracks; on the other hand, low adhesion during deceleration will extend the braking distance, which is a safety issue.

    This thesis examines the influence of several contaminants, i.e., water, oil, and leaves, on the adhesion in the wheel tread–railhead contact. This study will improve our knowledge of the low-adhesion mechanism and of how various contaminants influence adhesion. The thesis consists of a summary overview of the topic and three appended papers (AC).

    Papers A and B focus mainly on water and oil contamination examined using two methods, numerical simulation and lab testing. In paper A, real measured wheel and rail surfaces, low- and high-roughness surfaces, along with generated smooth surfaces are used as input to the numerical model for predicting the adhesion coefficient. Water-lubricated, oil-lubricated, and dry contacts are simulated in the model. In the research reported in paper B, scaled testing using a mini traction machine (MTM) was carried out to simulate the wheel–rail contact under lubricated conditions. Two types of disc surfaces of different roughnesses were run at different contact pressures and temperatures. A stylus machine and atomic force microscopy (AFM) were used to measure the surface topography. A study of leaf contamination on the railhead surface, based on field testing, is presented in paper C. Railhead surface samples were cut and the friction coefficient was measured on five occasions over the course of a year. Electron spectroscopy for chemical analysis (ESCA) and glow discharge optical emission spectrometry (GD-OES) were used to detect the chemical composition of the leaf-contamination layer on the railhead surface.

    The main conclusion of the thesis is that different contaminants reduce the adhesion coefficient in different ways. Oil reduces the adhesion coefficient by carrying the normal force due to its high viscosity. Water can reduce the adhesion coefficient to different degrees depending on the surface topography and water temperature. The mixture of an oxide layer and water contamination may have an essential impact. A leaf-formed blackish layer causes low adhesion by means of a chemical reaction between the leaves and bulk material. The thickness of the friction-reducing oxide layer predicts the friction coefficient and the extent of leaf contamination.

  • 126563.
    Zhu, Yi
    KTH, School of Architecture and the Built Environment (ABE).
    Extracting masts of overhead supply and street lights from point cloud2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Regular inspection and documentation for railway assets are necessary to monitor the status of the traffic environment. Mobile Laser Scanning (MLS) makes it possible to collect highly accurate spatial information of railway environments in the form of point cloud, and an automatic method to extract interested objects from the point cloud is needed to avoid too much manual work.

    In this project, point cloud along a railway in Saltsjöbanan was collected by MLS and processed to extract interested objects from it. The main purpose of the project is to develop a workflow for automatic extraction of masts of overhead supply and street lights from the study area.

    Researchers have proposed various methods for object extraction, such as model-based method, shape-based method, semantic method, and machine learning method recently. Different methods were reviewed and Support Vector Machine was chosen for the classification. Several softwares were reviewed as well. TerraScan and CloudCompare were chosen for pre-processing, and the major part was done in MATLAB.

    The proposed method consists of 4 steps: pre-processing, voxelization and segmentation, feature computation, classification and validation. The method calculates features to describe every object segmented from the point cloud and learns from the manually classified objects to train a classifier.

    The study area was divided into training data and validating data. The SVM classifier was trained using training data and evaluated using validating data.

    In the classification, 90.84% of the masts and 67.65% of the lights were correctly classified. There was some object loss during the step of pre-processing and segmentation. When including the loss from the pre-processing and segmentation step, 87.5% of the masts and 53.49% of the lights were successfully detected. The street lights have more various outlook and more complicated surrounding environment, which caused a relatively low accuracy.

  • 126564.
    Zhu, Yi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi. Zhejiang University, The State Key Lab of Fluid Power Transmission and Control, China .
    Lyu, Yezhe
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Mapping the friction between railway wheels and rails focusing on environmental conditions2015In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 324, p. 122-128Article in journal (Refereed)
    Abstract [en]

    The coefficient of friction between railway wheels and rails is crucial to the railway adhesion, further greatly affecting railway operation and maintenance. Since the wheel-rail system is an open system, the coefficient of It is significantly influenced not only by various types of contaminants but also by environmental conditions. This paper conducted a set of pin-on-disc tests measuring the coefficient of friction focusing on the influence of environmental conditions (relative humidity and temperature). In addition, influences of iron oxides, leaves and glycol/water mixtures on the coefficient of friction were also studied. The friction results are shown in the form of friction maps. Results indicate that it oxides on the surfaces can prevent the samples from large friction reduction particularly at the low temperature. The friction mechanism is also discussed with the help of scanning electron microscopy photos. On the other hand, effects of leaves in reducing the coefficient of friction become limited with the presence of the glycol/water mixture.

  • 126565.
    Zhu, Yi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    An adhesion model for wheel-rail contact at the micro level using measured 3d surfaces2012In: 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, CM 2012, Southwest Jiaotong University , 2012, p. 550-562Conference paper (Refereed)
    Abstract [en]

    Railway vehicles require a certain level of wheel-rail adhesion for efficient, reliable, and economical operation. A comprehensive wheel-rail contact model is useful for optimizing the adhesion, to simulatevehicle running conditions and to predict wear and rolling contact fatigue. A new contact model using measured 3D surfaces has been developed, comprising normal contact, rolling-sliding contact, flash temperature, and local friction coefficient models. This model can predict the local contact pressure, including the plasticity, local flash temperature, local tangential stress, local friction coefficient, and global adhesion coefficient. The influence of surface topography, creep, and speed on the adhesion coefficient, real contact area, and contact temperature is discussed. Results indicate that, due to increased contact area, the adhesion coefficient decreases with increased surface roughness, although the change is small. Furthermore, increasing speed reduces the adhesion coefficient due to the increasing contact temperature.

  • 126566.
    Zhu, Yi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    An adhesion model for wheel-rail contact at the micro level using measured 3d surfaces2014In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 314, no 1-2, p. 162-170Article in journal (Refereed)
    Abstract [en]

    Railway vehicles require a certain level of wheel-rail adhesion for efficient, reliable, and economical operation. A comprehensive wheel-rail contact model is useful for optimizing the adhesion, to simulate vehicle running conditions and to predict wear and rolling contact fatigue. A new contact model using measured 3D surfaces has been developed, comprising normal contact, rolling-sliding contact, flash temperature, and local friction coefficient models. This model can predict the local contact pressure, including the plasticity, local flash temperature, local tangential stress, local friction coefficient, and global adhesion coefficient. The influence of surface topography, creep, and speed on the adhesion coefficient, real contact area, and contact temperature is discussed. Results indicate that, due to increased contact area, the adhesion coefficient decreases with increased surface roughness, although the change is small. Furthermore, increasing speed reduces the adhesion coefficient due to the increasing contact temperature.

  • 126567.
    Zhu, Yi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Chen, Hur
    Friction Between Wheel and Rail: A Pin-On-Disc Study of Environmental Conditions and Iron Oxides2013In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 52, no 2, p. 327-339Article in journal (Refereed)
    Abstract [en]

    The coefficient of friction between railway wheels and rails is crucial to railway operation and maintenance. Since the wheel-rail system is an open system, environmental conditions, such as humidity and temperature, affect the friction coefficient. Pin-on-disc testing was conducted to study the influence of environmental conditions and iron oxides on the coefficient of friction between the wheel and rail. The iron oxides were pre-created in a climate chamber. The surfaces of the tested samples were analysed using X-ray diffraction, scanning electron/focused ion beam microscopy, and Raman spectroscopy. Results indicate that the coefficient of friction decreases with increasing relative humidity (RH) up to a saturation level. Above this level, the coefficient of friction remains low and stable even when the RH increases. In particular, when the temperature is low, a small increase in the amount of water (i.e., absolute humidity) in the air can significantly reduce the coefficient of friction. At high humidity levels, a water molecule film can keep the generated haematite on the surfaces, counterbalancing the effect of rising humidity.

  • 126568.
    Zhu, Yi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Nilsson, R.
    Stockholm public transport AB, Stockholm, Sweden.
    A field test study of leaf contamination on railhead surfaces2014In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 228, no 1, p. 71-84Article in journal (Refereed)
    Abstract [en]

    Leaves on railway tracks affect the level of adhesion between the wheel and rail, especially in autumn. When crushed by wheels, leaves form a tarnished, low level of adhesion layer that sticks to the railhead and often requires mechanical removal. A Stockholm local traffic track with a long history of adhesion problems was subjected to field tests on railhead contamination. On five occasions under different conditions, spaced over a year, the friction coefficient was measured using a tribometer and samples of the rail were taken. The techniques of electron spectroscopy for chemical analysis and glow discharge optical emission spectrometry were conducted to determine the composition of the top layer of rail contaminants and hardness was measured using the nano-indentation technique. The tarnished layer contains much higher contents of calcium, carbon and nitrogen than do leaf residue layers and uncontaminated samples. These high element contents are generated from the leaf material, which chemically reacts with the bulk material. The hardness of the tarnished layer is one-fifth that of the non-tarnished layer of the same running band. A chemical reaction occurs from the surface to a depth of several microns. The thickness of the friction-reducing oxide layer can be used to predict the friction coefficient and extent of leaf contamination.

  • 126569.
    Zhu, Yi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Olofsson, Ulf
    KTH, Superseded Departments (pre-2005), Machine Design.
    Nilsson, R.
    Stockholm Public Transport AB, Stockholm, Sweden.
    A field test study of leaf contamination on railhead surfaces2012In: Civil-Comp Proceedings, ISSN 1759-3433, Vol. 98Article in journal (Refereed)
    Abstract [en]

    Leaves on train tracks cause low adhesion between wheels and rails, especially in the autumn. A Stockholm local traffic track with a long history of adhesion problems was subject to field tests of railhead contamination. Over a year, on five occasions under different conditions, the friction coefficient was measured using a hand-push tribometer and rail samples were taken. ESCA and GD-OES analyses were conducted to determine the composition of the top layer of rail contaminants. The blackish layer contains much higher contents of calcium, carbon, and nitrogen than other samples indicating a chemical reaction occurring from the surface to a depth of several microns. The thickness of the friction-reducing oxide layer predicts the friction coefficient and leaf contamination extent. 

  • 126570.
    Zhu, Yi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Persson, Karin
    Institute for Surface Chemistry, Life Science and Chemical Industries Section, Stockholm, Sweden.
    Investigation of factors influencing wheel-rail adhesion using a mini-traction machine2012In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 292/293, p. 218-231Article in journal (Refereed)
    Abstract [en]

    Adhesion in the wheel-rail contact is a key factor determining stable running conditions and safety during train driving and braking. This paper presents an experiment performed in a mini-traction machine to simulate the problems of low adhesion in the wheel-rail contact. Tests were conducted under dry conditions and using water or oil as lubricants to study the influence of surface roughness on the adhesion coefficient. The results indicate that the adhesion coefficient can be reduced to as low as 0.02 for smooth surfaces lubricated with water. For rougher contact surfaces, the water-lubricated tests indicate a higher adhesion coefficient than do oil-lubricated ones, but also a clear dependence on water temperature. The oil-lubricated tests indicate a very slight dependence of the adhesion coefficient on variation in rolling speed, temperature, and surface roughness.

  • 126571.
    Zhu, Yi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Söderberg, Anders
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    Adhesion modeling in the wheel-rail contact under dry and lubricated conditions using measured 3D surfaces2013In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 61, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Adhesion between wheels and rails plays an essential role in the safe, efficient, and reliable operation of a railway network. Particularly under lubricated conditions, which can be a natural lubricant as water and an applied lubricant as rail oil, trains can experience adhesion loss. This paper presents an adhesion model constructed using the measured 3D wheel-rail surfaces. The numerical model comprises of three parts: a normally loaded contact model; an interfacial fluid model; and a rolling-sliding contact model. Simulation examples use the numerical model to investigate how water or oil contamination might affect wheel-rail adhesion in contacts with different surface roughness levels. Simulation indicates that adhesion peaks are almost at the same creep on different surfaces. The fluid load capacity is inversely proportional to the adhesion coefficient, both of which are clearly dependent on vehicle speed. Oil reduces adhesion coefficient more than water does. The adhesion coefficient on the low roughness surfaces is higher than that on the generated smooth surfaces under oil-lubricated conditions while it is the opposite for water-lubricated contact.

  • 126572.
    Zhu, Yi
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Sundh, Jon
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Tribologi.
    A tribological view of wheel-rail wear maps2013In: The international Journal of railway technology, ISSN 2049-5358, E-ISSN 2053-602X, Vol. 2, no 3, p. 79-91Article in journal (Refereed)
  • 126573.
    Zhu, Yingming
    et al.
    Sichuan Univ, Inst New Energy & Low Carbon Technol, Chengdu 610065, Sichuan, Peoples R China..
    Wang, Fu
    Ningbo Univ, Fac Maritime & Transportat, Ningbo 315211, Zhejiang, Peoples R China.;Ningbo RX New Mat Tech Co Ltd, Ningbo 315200, Zhejiang, Peoples R China..
    Yan, Jinyue
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Energy Processes. Sichuan Univ, Inst New Energy & Low Carbon Technol, Chengdu 610065, Sichuan, Peoples R China..
    The Potential of Distributed Energy Resources in Building Sustainable Campus: The Case of Sichuan University2018In: RENEWABLE ENERGY INTEGRATION WITH MINI/MICROGRID / [ed] Yan, J Wang, C Yu, J Jia, H Wu, J Xu, T Zhang, Y, ELSEVIER SCIENCE BV , 2018, p. 582-585Conference paper (Refereed)
    Abstract [en]

    Distributed energy resources systems are decentralized, modular and more flexible technologies. These systems can comprise multiple generation and storage components. Sichuan University (SCU) has joined Global Urban Development program, and takes part in Sustainability Tracking, Assessment & Rating System, aims at a sustainable campus. So we investigated the potential of distributed energy resources, e.g. solar power, that can be used in SCU. Firstly, we build 4 micro-grids with a total 156 Kw PV capacities to collect the power generation data. The total roof area of SCU Jiangan campus is 165701 m(2), and the estimated installed capacity is 8.3MW-11.6MW. Based on this data, 33% similar to 46% power cost can be covered by PV power generation.

  • 126574. Zhu, Yinian
    et al.
    Shum, Ping
    Nanyang Techbological University, Singapore.
    Bay, Hui-Wen
    Yan, Min
    Nanyang Techbological University, Singapore.
    Yu, Xia
    Hu, Juanjuan
    Hao, Jianzhong
    Lu, Chao
    Strain-insensitive and high-temperature long-period gratings inscribed in photonic crystal fiber2005In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 4, p. 367-369Article in journal (Refereed)
  • 126575.
    zhu, yue
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Applying lean philosophy to the redesign of service delivery process: A case study in the telecommunication industry2012Independent thesis Advanced level (degree of Master (Two Years)), 80 credits / 120 HE creditsStudent thesis
    Abstract [en]

    Lean is an umbrella term for a powerful combination of techniques to maximize customer value by minimizing waste and achieving continuous flow through a sustainable culture of continuous improvement. The term ―lean is used in the U.S. for what was originally created as the "Toyota Production System" by the Japanese carmaker. It is so fashionable since it was born that it’s been widely used in the manufacturing industry during the past decades all over the world. No matter in the opinion of insiders or outsiders, this is a magical word stands for discovering and eliminating discreet wastes, reducing resources requirement and time demand for production, making the manufacturing process efficient and cost effective and eventually building the sustainable competitive advantage of the organization.

    There’s already a world of books discussing the implementations. But as for the service delivery process, especially within the telecom industry, there’s no qualitative research carried out to check the validation of lean tool yet. Most researchers still remain on the theoretical level, arguing and debating on the applicability. The objective of this research is to fill in this research niche, check the possibility of using lean tool, naming VSM, to study and redesign the service delivery process in a qualitative way. The research question comes to how to apply the tool in a qualitative way and exam the both sides of the coin.

    The author investigated on the service delivery process performance in the Business-As-Usual projects and the key performance indicators of the case company business unit to find out any inconsistencies. One of the powerful lean tools - VSM is used step by step, node by node to identify existing discreet wastes. Based on the lean philosophy and literature reviews, potential possible improvements are proposed to eliminate the wastes, afterwards an ideal new VSM is created, with which it is able to dramatically reduce the resources required to seize customer value, satisfy the same amount of customer demand, increase customer satisfaction, make the company focusing on continuous improvement, and in the end move the company to a higher position in the field with stronger competence to win more market share.

    This research work is conducted as a single case study under the lean philosophy by collecting and studying qualitative data using various semi-structured interviews and archival data analysis. Six applicable solutions to lead the organization lean is proposed, and based on which, a brand new Optimization Focus Matrix is introduced to have a broader applicability. Possible benefit, difficulties in implementation and potential risks are also presented. The thesis ends with conclusion, answer to the research questions and discussion on the thesis limitation & future research direction.

  • 126576.
    Zhu, Yunyi
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Numerical Analysis, NA.
    Epitope Mapping using Local Alignment Features2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Our immune system uses antibodies to neutralize pathogens such as bacteria and viruses. Antibodies bind to parts of foreign proteins with high efficiency and specificity. We call such parts epitopes. The identification of epitopes, namely epitope mapping, may contribute to various immunological applications such as vaccine design, antibody production and immunological diagnosis.

    Therefore, a fast and reliable method that can predict epitopes from the whole proteome is highly desirable.

     

    In this work we have developed a computational method that predicts epitopes based on sequence information. We focus on using local alignment to extract features from peptides and classifying them using Support Vector Machine. We also propose two approaches to optimize the features. Results show that our method can reliably predict epitopes and significantly outperforms some most commonly used tools.

     

  • 126577. Zhu, Z.
    et al.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Larsson, H.
    Reed, R. C.
    Isolation of optimal compositions of single crystal superalloys by mapping of a material's genome2015In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 90, p. 330-343Article in journal (Refereed)
    Abstract [en]

    The multicomponent composition space pertinent to the single crystal nickel-based superalloys is mapped and searched, using computational modelling. A resolution of 0.1 wt.% for the alloying elements is assumed, consistent with manufacturing practice. Databases are constructed of alloy compositions which are predicted to be of promising microstructural architecture: e.g. equal fractions of the γ and γ′ phases. These may be regarded as maps - one might term them genomes - of this class of structural alloy. By combining the databases with additional composition-dependent property models, it is demonstrated that compositions can be identified which - subject to the accuracy and limitations of the sub-models - are likely to prove optimal, e.g. on the basis of their creep resistance, density and cost. The methods circumvent the need for the traditional empirically-driven approaches to alloy design.

  • 126578. Zhu, Z.
    et al.
    Zhou, Y. J.
    Kang, M. -K
    Krivoruchko, A.
    Buijs, N. A.
    Nielsen, Jens
    KTH, Centres, Science for Life Laboratory, SciLifeLab. Chalmers University of Technology, Technical University of Denmark.
    Enabling the synthesis of medium chain alkanes and 1-alkenes in yeast2017In: Metabolic engineering, ISSN 1096-7176, E-ISSN 1096-7184, Vol. 44, p. 81-88Article in journal (Refereed)
    Abstract [en]

    Microbial synthesis of medium chain aliphatic hydrocarbons, attractive drop-in molecules to gasoline and jet fuels, is a promising way to reduce our reliance on petroleum-based fuels. In this study, we enabled the synthesis of straight chain hydrocarbons (C7–C13) by yeast Saccharomyces cerevisiae through engineering fatty acid synthases to control the chain length of fatty acids and introducing heterologous pathways for alkane or 1-alkene synthesis. We carried out enzyme engineering/screening of the fatty aldehyde deformylating oxygenase (ADO), and compartmentalization of the alkane biosynthesis pathway into peroxisomes to improve alkane production. The two-step synthesis of alkanes was found to be inefficient due to the formation of alcohols derived from aldehyde intermediates. Alternatively, the drain of aldehyde intermediates could be circumvented by introducing a one-step decarboxylation of fatty acids to 1-alkenes, which could be synthesized at a level of 3 mg/L, 25-fold higher than that of alkanes produced via aldehydes.

  • 126579. Zhu, Zhi-Shuang
    et al.
    Liao, Hua
    Cao, Huai-Shu
    Wang, Lu
    Wei, Yi-Ming
    Yan, Jinyue
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
    The differences of carbon intensity reduction rate across 89 countries in recent three decades2014In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 113, no SI, p. 808-815Article in journal (Refereed)
    Abstract [en]

    In the recent decades, most countries' CO2 intensity has decreased, but their decline rates are significantly different. Based on the data set of 89 countries from 1980 to 2008, this paper tries to quantitatively investigate the potential reasons for their differences, and discusses the possibility for developing countries to maintain a high carbon intensity reduction rate in the future as before. The econometric analysis implicate that (1) the decline rate of CO2 intensity in countries with high initial carbon intensity will be higher, which means CO2 intensity across the world has a significant convergence trend; and (2) keeping fast and steady economic growth can significantly help CO2 intensity decline, yet total carbon dioxide emissions will grow dramatically. Therefore, with the two objectives of intensity reduction and total amount control, carbon abatement policies need to weigh one against another. The results are robust to the initial year selection and country classification.

  • 126580. Zhu, Zhiwei
    et al.
    Zhou, Yongjin J.
    Krivoruchko, Anastasia
    Grininger, Martin
    Zhao, Zongbao K.
    Nielsen, Jens
    Expanding the product portfolio of fungal type I fatty acid synthases2017In: Nature Chemical Biology, ISSN 1552-4450, E-ISSN 1552-4469, Vol. 13, no 4, p. 360-362Article in journal (Refereed)
    Abstract [en]

    Fungal type I fatty acid synthases (FASs) are mega-enzymes with two separated, identical compartments, in which the acyl carrier protein (ACP) domains shuttle substrates to catalytically active sites embedded in the chamber wall. We devised synthetic FASs by integrating heterologous enzymes into the reaction chambers and demonstrated their capability to convert acyl-ACP or acyl-CoA from canonical fatty acid biosynthesis to short/ medium-chain fatty acids and methyl ketones.

  • 126581. Zhuang, C.
    et al.
    Marquez, Juan C.
    KTH, School of Technology and Health (STH), Medical Engineering, Medical sensors, signals and systems. Shanghai Jiao Tong University, China.
    Qu, H. E.
    He, X.
    Lan, N.
    A neuromuscular electrical stimulation strategy based on muscle synergy for stroke rehabilitation2015In: International IEEE/EMBS Conference on Neural Engineering, NER, IEEE Computer Society, 2015, p. 816-819Conference paper (Refereed)
    Abstract [en]

    Recent experiments have suggested that the central nervous system (CNS) makes use of muscle synergies as a neural strategy to simplify the control of a variety of movements by using a single pattern of neural command signal. This nature of muscle coordination could have great significance in the treatment and rehabilitation of upper limb impairments for hemiparetic patients post stroke. The use of neuromuscular electrical stimulation (NMES) for neural prosthetics or therapeutic applications has been demonstrated as a promising clinical intervention for stroke patients to recover motor function of the upper extremity. However, the existing NMES systems do not provide control methods for the patient to achieve an individualized and functional rehabilitation training. In this research work, muscle synergies from the flexionextension elbow antagonistic muscles were studied. Using motion information and EMG signals, muscle synergies were extracted using non-negative matrix factorization (NMF) method. Reconstructed signals obtained from the muscle synergies were then applied to the virtual arm (VA) model to test a synergy based NMES strategy. Results show close resemblance to the original elbow trajectory of normal movements and thus the feasibility to control movements in stroke patients for rehabilitation.

  • 126582. Zhuang, F.
    et al.
    Shen, Jianqi
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Ye, J.
    Controlling the photonic bandgap structures via manipulation of refractive index of electromagnetically induced transparency vapor2007In: Wuli xuebao, ISSN 1000-3290, Vol. 56, no 1, p. 541-545Article in journal (Refereed)
    Abstract [en]

    A new application of coherent manipulation of EIT (electromagnetically induced transparency) medium is suggested. A two-dimensional photonic crystal with a triangle lattice of elliptic air cylinders, which are filled with the EIT atomic vapor, in the KAs background material is designed. By manipulating the refractive index of the EIT vapor via the external control field, one can obtain the controllable bandgap structure that is sensitive to the variations of external conditions (e.g. the intensity of the control field) . It is shown that a large complete bandgap of about 0.0503ωe in the region of high normalized frequency could be achieved by choosing the specific parameters such as the spontaneous decay rate, dephasing rate, Rabi frequency of control light, atomic number density as well as elliptic geometric parameters.

  • 126583. Zhuang, F.
    et al.
    Wu, L.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    A two-dimensional photonic crystal with six large bandgaps formed by a hexagonal lattice of anisotropic cylinders2002In: Chinese Physics (Beijing), ISSN 1009-1963, E-ISSN 1741-4199, Vol. 11, no 8, p. 834-838Article in journal (Refereed)
  • 126584. Zhuang, F.
    et al.
    Wu, L.
    He, Sailing
    Band structures of two-dimensional photonic crystals with regular polygon cylinders calculated by linear operations2002In: Wuli xuebao, ISSN 1000-3290, Vol. 51, no 12, p. 2865-2870Article in journal (Refereed)
  • 126585. Zhuang, F.
    et al.
    Wu, L.
    Xiao, S. S.
    He, Sailing
    KTH, Superseded Departments, Electromagnetic Theory.
    Band structure of a two-dimensional photonic crystal with a triangular lattice of anisotropic elliptic cylinders2002In: Chinese Physics Letters, ISSN 0256-307X, E-ISSN 1741-3540, Vol. 19, no 1, p. 73-75Article in journal (Refereed)
  • 126586.
    Zhuang, Hao
    KTH, School of Information and Communication Technology (ICT).
    Performance Evaluation of Virtualization in Cloud Data Center2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Amazon Elastic Compute Cloud (EC2) has been adopted by a large number of small and medium enterprises (SMEs), e.g. foursquare, Monster World, and Netflix, to provide various kinds of services. There has been some existing work in the current literature investigating the variation and unpredictability of cloud services. These work demonstrated interesting observations regarding cloud offerings. However, they failed to reveal the underlying essence of the various appearances for the cloud services.

    In this thesis, we looked into the underlying scheduling mechanisms, and hardware configurations, of Amazon EC2, and investigated their impact on the performance of virtual machine instances running atop. Specifically, several instances with the standard and high-CPU instance families are covered to shed light on the hardware upgrade and replacement of Amazon EC2. Then large instance from the standard family is selected to conduct focus analysis. To better understand the various behaviors of the instances, a local cluster environment is set up, which consists of two Intel Xeon servers, using different scheduling algorithms.

    Through a series of benchmark measurements, we observed the following findings: (1) Amazon utilizes highly diversified hardware to provision different instances. It results in significant performance variation, which can reach up to 30%. (2) Two different scheduling mechanisms were observed, one is similar to Simple Earliest Deadline Fist (SEDF) scheduler, whilst the other one analogies Credit scheduler in Xen hypervisor. These two scheduling mechanisms also arouse variations in performance. (3) By applying a simple "trial-and-failure" instance selection strategy, the cost saving is surprisingly significant. Given certain distribution of fast-instances and slow-instances, the achievable cost saving can reach 30%, which is attractive to SMEs which use Amazon EC2 platform.

  • 126587.
    Zhuang, Qingyuan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Parametric Study on the Aeroelastic Stability of Rotor Seals2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Labyrinth seals are widely used in rotating machinery and have been shown to experience aeroelastic instabilities. The rapid development of computational fluid dynamics now provides a high fidelity approach for predicting the aeroelastic behavior of labyrinth seals in three dimension and exhibits great potential within industrial application, especially during the detailed design stages. In the current publication a time-marching unsteady Reynolds- averaged Navier-Stokes solver was employed to study the various historically identified parameters that have essential influence on the stability of labyrinth seals. Advances in understanding of the related aeroelastic (flutter) phenomenon were achieved based on extensive yet economical numerical analysis of a simplified seal model. Further, application of the same methodology to several realistic gas turbine labyrinth seal designs confirmed the perceived knowledge and received agreements from experimental indications. Abbott’s criteria in describing the labyrinth seal aeroelastic behaviors were reaffirmed and further developed. 

  • 126588. Zhuang, Xiahai
    et al.
    Li, Lei
    Payer, Christian
    Štern, Darko
    Urschler, Martin
    Heinrich, Mattias P
    Oster, Julien
    Wang, Chunliang
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Medical Imaging.
    Smedby, Örjan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Medical Imaging.
    Bian, Cheng
    Yang, Xin
    Heng, Pheng-Ann
    Mortazi, Aliasghar
    Bagci, Ulas
    Yang, Guanyu
    Sun, Chenchen
    Galisot, Gaetan
    Ramel, Jean-Yves
    Brouard, Thierry
    Tong, Qianqian
    Si, Weixin
    Liao, Xiangyun
    Zeng, Guodong
    Shi, Zenglin
    Zheng, Guoyan
    Wang, Chengjia
    MacGillivray, Tom
    Newby, David
    Rhode, Kawal
    Ourselin, Sebastien
    Mohiaddin, Raad
    Keegan, Jennifer
    Firmin, David
    Yang, Guang
    Evaluation of algorithms for Multi-Modality Whole Heart Segmentation: An open-access grand challenge.2019In: Medical Image Analysis, ISSN 1361-8415, E-ISSN 1361-8423, Vol. 58, article id 101537Article in journal (Refereed)
    Abstract [en]

    Knowledge of whole heart anatomy is a prerequisite for many clinical applications. Whole heart segmentation (WHS), which delineates substructures of the heart, can be very valuable for modeling and analysis of the anatomy and functions of the heart. However, automating this segmentation can be challenging due to the large variation of the heart shape, and different image qualities of the clinical data. To achieve this goal, an initial set of training data is generally needed for constructing priors or for training. Furthermore, it is difficult to perform comparisons between different methods, largely due to differences in the datasets and evaluation metrics used. This manuscript presents the methodologies and evaluation results for the WHS algorithms selected from the submissions to the Multi-Modality Whole Heart Segmentation (MM-WHS) challenge, in conjunction with MICCAI 2017. The challenge provided 120 three-dimensional cardiac images covering the whole heart, including 60 CT and 60 MRI volumes, all acquired in clinical environments with manual delineation. Ten algorithms for CT data and eleven algorithms for MRI data, submitted from twelve groups, have been evaluated. The results showed that the performance of CT WHS was generally better than that of MRI WHS. The segmentation of the substructures for different categories of patients could present different levels of challenge due to the difference in imaging and variations of heart shapes. The deep learning (DL)-based methods demonstrated great potential, though several of them reported poor results in the blinded evaluation. Their performance could vary greatly across different network structures and training strategies. The conventional algorithms, mainly based on multi-atlas segmentation, demonstrated good performance, though the accuracy and computational efficiency could be limited. The challenge, including provision of the annotated training data and the blinded evaluation for submitted algorithms on the test data, continues as an ongoing benchmarking resource via its homepage (www.sdspeople.fudan.edu.cn/zhuangxiahai/0/mmwhs/).

  • 126589. Zhuang, Zanyong
    et al.
    Chen, Hong
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Lin, Zhang
    Dang, Zhi
    Mn2O3 hollow spheres synthesized based on an ion-exchange strategy from amorphous calcium carbonate for highly efficient trace-level uranyl extraction2016In: ENVIRONMENTAL SCIENCE-NANO, ISSN 2051-8153, Vol. 3, no 6, p. 1254-1258Article in journal (Refereed)
    Abstract [en]

    Well-defined hierarchical hollow spheres constructed from Mn2O3 quantum dots were prepared via an ion-exchange strategy starting from small-sized amorphous calcium carbonate. They show outstanding capability to extract trace-level uranyl from field water.

  • 126590. Zhukavin, R. Kh
    et al.
    Kovalevsky, K. A.
    Orlov, M. L.
    Tsyplenkov, V. V.
    Bekin, N. A.
    Yablonskiy, A. N.
    Yunin, P. A.
    Pavlov, S. G.
    Abrosimov, N. V.
    Huebers, H. -W
    Radamson, Henry H.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Shastin, V. N.
    Terahertz-range spontaneous emission under the optical excitation of donors in uniaxially stressed bulk silicon and SiGe/Si heterostructures2015In: Semiconductors (Woodbury, N.Y.), ISSN 1063-7826, E-ISSN 1090-6479, Vol. 49, no 1, p. 13-18Article in journal (Refereed)
    Abstract [en]

    The results of measurements of the total terahertz-range photoluminescence of Group-V donors (phosphorus, antimony, bismuth, arsenic) in bulk silicon and SiGe/Si heterostructures depending on the excitation intensity are presented. The signal of bulk silicon was also measured as a function of uniaxial stress. The results of measurement of the dependence of the spontaneous emission intensity on the uniaxial stress is in rather good agreement with theoretical calculations of the relaxation times of excited states of donors in bulk silicon. Comparative measurements of the spontaneous emission from various strained heterostructures showed that the photoluminescence signal is caused by donor-doped silicon regions.

  • 126591. Zhukovskii, Y. F.
    et al.
    Kotomin, E. A.
    Herschend, B.
    Hermansson, Kersti
    KTH, Superseded Departments, Biotechnology.
    Jacobs, P. W. M.
    The adhesion properties of the Ag/alpha-Al2O3(0001) interface: an ab initio study2002In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 513, no 2, p. 343-358Article in journal (Refereed)
    Abstract [en]

    Ab initio computer simulations of the atomic and electronic structure of the Ag/alpha-Al2O3(0 0 0 1) (corundum) interface have been performed for a periodic two-dimensional slab model using the Hartree-Fock method and a posteriori electron correlation corrections. We have considered both Al- and O-terminated corundum substrate surfaces. The dependence of the adhesion energy on the interfacial distance has been analyzed for the two most favorable Ag adsorption positions over corundum and for two different metal coverages (a 1/3 monolayer (NIL) of the Ag(l 1 1) crystallographic plane and a full Ag(I 1 1) monolayer). The two different terminations (Al- and O-) give rise to qualitatively different results. The former case corresponds to the most stable termination of the pure corundum (0 0 0 1) substrate where small adhesion energies per Ag atom (0.15-0.25 eV for I ML and 0.40-0.55 eV for 1/3 NIL) are accompanied by minor interfacial charge transfer, indicating physisorption, which may be explained by a weak atomic polarization. In contrast, for O-terminated corundum, substantial adhesion energies (3-5 eV per Ag atom at I ML coverage and 6-11 eV for 1/3 ML) combined with noticeable charge transfer from silver atoms towards the substrate (0.5e to 0.9e) are clear indications of a strong interfacial ion bonding. For both terminations, the observed difference in Ag adhesion energies for 1/3 NIL and I NIL coverages arises from a transition from directed Ag-O bonding towards a more delocalized electron density distribution in the complete monolayer. The results of our calculations are compared with available experimental studies and theoretical simulations for various Me/Al2O3 interfaces.

  • 126592. Zhuo, S.
    et al.
    Shokri-Ghadikolaei, Hossein
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Fischione, Carlo
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wang, Z.
    Adaptive congestion control in cognitive industrial wireless sensor networks2015In: Proceeding - 2015 IEEE International Conference on Industrial Informatics, INDIN 2015, IEEE conference proceedings, 2015, p. 900-907Conference paper (Refereed)
    Abstract [en]

    Strict quality of service requirements of industrial applications, challenged by harsh environments and huge interference especially in multi-vendor sites, demand incorporation of cognition in industrial wireless sensor networks (IWSNs). In this paper, a distributed protocol of light complexity for congestion regulation in cognitive IWSNs is proposed to improve the channel utilization while ensuring predetermined performance for specific devices, called primary devices. By sensing the congestion level of a channel with local measurements, a novel congestion control protocol is proposed by which every device decides whether it should continue operating on the channel, or vacate it in case of saturation. Such a protocol dynamically changes the congestion level based on variations of non-stationary wireless environment as well as traffic demands of the devices. The proposed protocol is implemented on STM32W108 chips that offer IEEE 802.15.4 standard communications. Experimental results confirm substantial performance enhancement compared to the original standard, while imposing almost no signaling/computational overhead. In particular, channel utilization is increased by 56% with fairness and delay guarantees. The presented results provide useful insights on low-complexity adaptive congestion control mechanism in IWSNs.

  • 126593.
    Ziadi, Ahmed
    KTH, School of Computer Science and Communication (CSC).
    Facebook som komplement till modersmålsundervisning2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Facebook is the most widely used social media in Sweden. It allows the user to easily share the latest from their everyday life, their opinions, as well as communicate with their acquaintances. According to the latest poll from the Foundation for Internet Infrastructure, 33% of teenagers in the ages 12-15 spend their Internet time being active on social media. 63% of these teenagers visit Facebook on daily basis.

    Herein, we examined how Facebook can be exploited as a complement to the education of the mother tongue. The investigation was performed with a questionnaire as well as a test group that has been supplemented with semi-structured interviews. 

    In conclusion, the study showed promising results in the usage of Facebook with the education. By taking parts in discussions on Facebook, the students did not only improve their discussion abilities but also the writing. It was also observed that the communication between student and teacher was greatly improved. A remarkable observation was that students grown up in Sweden were more in favour for the use of Facebook as an educational tool than students grown up outside of Sweden.

  • 126594.
    Ziakouli, Marina
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
    Fagerberg, Erika
    KTH, School of Architecture and the Built Environment (ABE), Architecture, Urban Design.
    RIN♀EBY - Exploring feminist design tools2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This project aims on exploring ways to redefine the relationship of gender and space through urban design. Gender inequalities expressed in spatial manners have been theorized by feminist geography, an approach to human geography. Having a good understanding of this theoretical context will provide the tools to tackle distantiation, spatial separation, constraint and the limited spatial opportunities women experience in public places. Using Rinkeby square as the canvas for this exploration, the effort will be put on mapping the uses of the square through observation, quantitative research, as well as interviews with local organisations, shops and authorities close to the square. An inventory of the architectural features of the square will be made along with a site analysis focusing on the questions of effects on equality. Furthermore existing female networks and societies in the area will be contacted seeking possible collaborations for a later project work, workshops or events. Finally, as a result of the initial investigations, this project intends to explore how a physical intervention would affect these questions at Rinkeby square. It is the working hypothesis of this project that any project in order to be successful would need to be based on a deeper understanding of the challenges surrounding female presence on the square, and be tied into the already existing networks for women. This project therefore hopes to establish contact with existing female networks such as (D)Järva Kvinnor, Café Respekt and Tensta-Hjulsta Kvinnocenter, amongst others.

  • 126595. Zibar, Darko
    et al.
    Caballero, Antonio
    Yu, Xianbin
    Pang, Xiaodan
    RISE ACREO AB; Technical University of Denmark.
    Dogadaev, Anton K
    Monroy, I Tafur
    Hybrid optical fibre-wireless links at the 75–110 GHz band supporting 100 Gbps transmission capacities2011In: 2011 IEEE International Topical Meeting on Microwave Photonics - Jointly Held with the 2011 Asia-Pacific Microwave Photonics Conference, MWP/APMP 2011, 2011, p. 445-449, article id 6088767Conference paper (Refereed)
    Abstract [en]

    We present a photonic generation and down-conversion method for realizing a 40Gbps wireless link at the 75-110 GHz band exploiting the recent advances in photonic coherent detection technologies and digital signal processing. Furthermore, we analyze the capacities of hybrid optical fiber-wireless links at the 75-110GHz band, and propose several approaches to overcome the challenges towards 100Gbps wireless capacity.

  • 126596. Zibar, Darko
    et al.
    Sambaraju, Rakesh
    Caballero, Antonio
    Herrera, Javier
    Westergren, Urban
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Photonics.
    Walber, Achim
    Jensen, Jesper Beevense
    Marti, Javier
    Monroy, Idelfonso Tafur
    High-Capacity Wireless Signal Generation and Demodulation in 75-to 110-GHz Band Employing All-Optical OFDM2011In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 23, no 12, p. 810-812Article in journal (Refereed)
    Abstract [en]

    We present a radio-frequency (RF) and bit-rate scalable technique for multigigabit wireless signal generation based on all-optical orthogonal frequency-division multiplexing (OFDM) and photonic up-conversion. Coherent detection supported by digital signal processing is used for signal demodulation and data recovery. In order to demonstrate the RF frequency scalability and bit-rate transparency, the system is tested at 60 GHz and in the 75- to 110-GHz band at the baud rates of 5 and 10 Gbaud. In terms of the bit rate, the proposed system is experimentally tested up to 40 Gb/s for wireless signal generation and demodulation. The wireless transmission is not considered in this letter. Additionally, a novel digital carrier phase/frequency recovery structure is employed to enable robust phase and frequency tracking between the beating lasers.

  • 126597.
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    NbTiN for improved superconducting detectors2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The physics of single photons is fascinating, by manipulating them we can observe and probe quantum effects. Doing so requires the fabrication and utilization of single photon sources, of which many types have been developed including quantum dots, trapped atoms and ions, and color centers. On the other end of the experiments, single photon detectors play a role of utmost importance, and while several types of detectors exist, superconducting nanowire single photon detectors are now the state-of-the-art technology. By offering near unity detection efficiency from the ultra-violet to the mid-infrared light spectrum, with negligible noise and excellent time resolution, they made possible many experiments that were previously technologically unfeasible. The same appealing characteristics have found a use in applications outside of the quantum optics framework, with notably light detection and ranging, biomedical imaging or CMOS circuits testing.In this thesis a controlled growth method for tailoring the characteristics of niobium titanium nitride in the framework of superconducting nanowire single photon detectors was developed. Reactive co-sputter deposition of niobium titanium nitride was shown to be a versatile method, both in terms of the degree of control over the material composition, and in the choice of substrates that it allows. Unity internal detection efficiency of detectors at telecom wavelengths was achieved by optimizing the niobium content in the material. The influence of lattice matching on the critical temperatures of films deposited at room temperature was investigated. The fabrication of superconducting nanowire single photon detectors on aluminum nitride-on-sapphire, on lithium niobate nano-waveguides, on gallium arsenide, and the integration on SiN waveguides was achieved. The material was used to fabricate detectors with optimized response for any linear polarization of the incoming photons by using a fractal architecture. Another method was proposed to achieve the same results by encapsulating meandering detectors in a high index dielectric material, resulting in a decrease of the permittivity mismatch between the nanowire material and its surrounding and therefore optimizing the efficiency for both orthogonal linear polarizations.Finally, detectors were fabricated from films developed in this work, and were operated to enable the implementation of polarization-based entanglement distribution in optical fibers in a real-conditions scenario, over a record distance of 96 km. This paves the way for the development of quantum communication networks using existing optical fiber links.

  • 126598.
    Zichi, Julien
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Chang, Chang
    Steinhauer, Stephan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    von Fieandt, Kristina
    Los, Johannes W. N.
    Visser, Gijs
    Kalhor, Nima
    Lettner, Thomas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Elshaari, Ali W.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Esmaeil Zadeh, Iman
    Zwiller, Val
    NbxTi1-xN low timing jitter single-photon detectors with unity internal detection efficiency at 1550 nmManuscript (preprint) (Other academic)
    Abstract [en]

    The requirements in quantum optics experiments for high single photon detectionefficiency, low timing jitter, low dark count rate and short dead time have been fulfilled withthe development of superconducting nanowire single photon detectors. Although they offer adetection efficiency above 90%, achieving a high time resolution in devices made ofamorphous materials is a challenge, particularly at temperatures above 0.8 K. Devices madefrom niobium nitride and niobium titanium nitride allow to reach the best timing jitter, but inturn have stronger requirements in terms of film quality to achieve a high efficiency. Here wetake advantage of the flexibility of reactive co-sputter deposition to tailor the composition ofNbxTi1-xN superconducting films, and show that a Nb fraction of x = 0.62 allows for thefabrication of detectors from films as thick as 9 nm and covering an active area of 20 μm,with a wide detection saturation plateau at telecom wavelengths and in particular at 1550 nm.This is a signature of an internal detection efficiency saturation, achieved while maintainingthe high time resolution associated with NbTiN and operation at 2.5K. With our optimizedrecipe, we reliably fabricated detectors with high critical current densities reaching asaturation plateau at 1550 nm with 80% system detection efficiency, and with a FWHMtiming jitter as low as 19.47 ps.

  • 126599.
    Zichi, Julien
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Chang, Jin
    Delft Univ Technol, Fac Appl Sci, ImPhys Dept, Opt Res Grp, Lorentzweg 1, NL-2628 CJ Delft, Netherlands..
    Steinhauer, Stephan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Von Fieandt, Kristina
    Uppsala Univ, Angstrom Lab, Dept Chem, Inorgan Chem Res Programme, Box 538, SE-75121 Uppsala, Sweden..
    Los, Johannes W. N.
    Single Quantum BV, NL-2628 CH Delft, Netherlands..
    Visser, Gus
    Single Quantum BV, NL-2628 CH Delft, Netherlands..
    Kalhor, Nima
    Single Quantum BV, NL-2628 CH Delft, Netherlands..
    Lettner, Thomas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Elshaari, Ali W.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Zadeh, Iman Esmaeil
    Delft Univ Technol, Fac Appl Sci, ImPhys Dept, Opt Res Grp, Lorentzweg 1, NL-2628 CJ Delft, Netherlands..
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics. Single Quantum BV, NL-2628 CH Delft, Netherlands..
    Optimizing the stoichiometry of ultrathin NbTiN films for high-performance superconducting nanowire single-photon detectors2019In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 27, no 19, p. 26579-26587Article in journal (Refereed)
    Abstract [en]

    The requirements in quantum optics experiments for high single-photon detection efficiency. low timing jitter, low dark count rate and short dead time have been fulfilled with the development of superconducting nanowire single-photon detectors. Although they offer a detection efficiency above 90%, achieving a high time resolution in devices made of amorphous materials is a challenge, particularly at temperatures above 0.8 K. Devices made from niobium nitride and niobium titanium nitride allow us to reach the best timing jitter but. in turn, have stronger requirements in terms of film quality to achieve a high efficiency. Here we take advantage of the flexibility of reactive co-sputter deposition to tailor the composition of NbxTi1-xN superconducting films and show that a Nb fraction of x = 0.62 allows for the fabrication of detectors from films as thick as 9 nm and covering an active area of 20 mu m. with a wide detection saturation plateau at telecom wavelengths and in particular at 1550 nm. This is a signature of an internal detection efficiency saturation, achieved while maintaining the high time resolution associated with NbTiN and operation at 2.5K. With our optimized recipe, we reliably fabricated detectors with high critical current densities reaching a saturation plateau at 1550 nm with 80% system detection efficiency and with a FWHM timing jitter as low as 19.5 ps. Open Access Publishing Agreement

  • 126600.
    Zichi, Julien
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Gyger, Samuel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Baghban, Mohammad Amin
    Elshaari, Ali W.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Gallo, Katia
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    An NbTiN superconducting single photon detector implemented on a LiNbO3 nano-waveguide at telecom wavelength2019In: Poster session T.Po2, 2019Conference paper (Refereed)
    Abstract [en]

    Fiber-coupled superconducting nanowire single photon detectors are a ubiquitous tool for quantum optics experiments as they offer near unity detection efficiency over a broad wavelength range, low dark count rate, excellent time resolution and high saturation rate. Nevertheless, advancing quantum optics experiments and applications beyond the few-photon limit requires large scale integrated systems of quantum sources and detectors. In recent years there has been a tremendous progress with integrating single photon detectors with a variety of photonic platforms. This includes attempts on ion-diffused waveguides in LiNbO3, a non-linear and electro-optic material with widespread use for signal processing, frequency conversion, and quantum optics devices. However the realization of superconducting detectors on single mode waveguides remains elusive. Here we present an NbTiN superconducting single photon detector integrated directly on a LiNbO3 single mode nanophotonic waveguide at telecom wavelength, with a high critical current density and a dark count rate of 3 mHz at 99% of its critical current.

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