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  • 124251. Xu, Peng
    et al.
    Liu, Peng
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Li, Yuanyuan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology. KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center.
    Xu, B.
    Kloo, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Sun, Licheng
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Organic chemistry.
    Hua, Y.
    D-A-D-Typed Hole Transport Materials for Efficient Perovskite Solar Cells: Tuning Photovoltaic Properties via the Acceptor Group2018In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 23, p. 19697-19703Article in journal (Refereed)
    Abstract [en]

    Two D-A-D-structured hole-transport materials (YN1 and YN2) have been synthesized and used in perovskite solar cells. The two HTMs have low-lying HOMO levels and impressive mobility. Perovskite-based solar cells (PSCs) fabricated with YN2 showed a power conversion efficiency (PCE) value of 19.27% in ambient air, which is significantly higher than that of Spiro-OMeTAD (17.80%). PSCs based on YN1 showed an inferior PCE of 16.03%. We found that the incorporation of the stronger electron-withdrawing group in the HTM YN2 improves the PCE of PSCs. Furthermore, the YN2-based PSCs exhibit good long-term stability retaining 91.3% of its initial efficiency, whereas PSCs based on Spiro-OMeTAD retained only 42.2% after 1000 h lifetime (dark conditions). These promising results can provide a new strategy for the design of D-A-D HTMs for PSC applications in future.

  • 124252.
    Xu, Q.
    et al.
    TaiYuan Univ Technol, Coll Phys & Optoelect, Taiyuan 030024, Shanxi, Peoples R China..
    Xiao, Z. G.
    Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China..
    Zhu, S. J.
    Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China..
    Qi, C.
    KTH, School of Engineering Sciences (SCI), Physics.
    Jia, H.
    Qi, B.
    Shandong Univ, Inst Space Sci, Shandong Prov Key Lab Opt Astron & Solar Terr Env, Weihai 264209, Peoples R China..
    Wang, R. S.
    Soochow Univ, Coll Med, Sch Radiat Med & Protect, Renai Rd 199, Suzhou 215123, Peoples R China.;Jiangsu Higher Educ Inst, Collaborat Innovat Ctr Radiol Med, Renai Rd 199, Suzhou 215123, Peoples R China..
    Cheng, W. J.
    Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China..
    Zhang, Y.
    Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China..
    Yi, H.
    Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China..
    Lu, L. M.
    Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China..
    Wang, Y. J.
    Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China..
    Li, H. J.
    Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China..
    Huang, Y.
    Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China..
    Zhang, Z.
    Tsinghua Univ, Dept Phys, Beijing 100084, Peoples R China..
    Wu, X. G.
    China Inst Atom Energy, Beijing 102413, Peoples R China..
    Li, C. B.
    China Inst Atom Energy, Beijing 102413, Peoples R China..
    Zheng, Y.
    China Inst Atom Energy, Beijing 102413, Peoples R China..
    Chen, Q. M.
    China Inst Atom Energy, Beijing 102413, Peoples R China..
    Zhou, W. K.
    China Inst Atom Energy, Beijing 102413, Peoples R China..
    Li, G. S.
    China Inst Atom Energy, Beijing 102413, Peoples R China..
    Investigation of high spin states in Cs-1332018In: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 54, no 5, article id 83Article in journal (Refereed)
    Abstract [en]

    High spin states in Cs-133 nucleus have been studied with the reaction Te-130 (Li-7, 4n) at a beam energy of 38 MeV. The level scheme has been expanded with spin up to 31/2 (h) over bar. Compared with a recent paper, ground state band and other two collective band structures at lower spin states have been confirmed. Another collective band structure at higher spin states as well as some levels and transitions are updated. Compared with the experimental data, large-scale shell model and tilted axis cranking model calculations have been carried out. The results show that the band-head configuration of yrast band based on 7/2(+) ground state and the side band built on the 5/2(+) state are a pair of pseudospin partner states with pi (f) over tilde 7/2,5/2. The negative parity band based on 1071.5 keV level originates from pi h(11/2) orbital. Another band built on 2642.9 keV level at high spin states has been proposed with oblate deformation. Other characteristics for these bands were also discussed.

  • 124253. Xu, Rong
    et al.
    Wu, Yan
    Wang, Xunying
    Zhang, Jing
    Yang, Xiang
    Zhu, Bin
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. Hubei University, China.
    Enhanced ionic conductivity of yttria-stabilized ZrO2 with natural CuFe-oxide mineral heterogeneous composite for low temperature solid oxide fuel cells2017In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 42, no 27, p. 17495-17503Article in journal (Refereed)
    Abstract [en]

    We report for the first time that the commercial yttrium stabilized zirconia (YSZ) nano composite with a natural CuFe-oxide mineral (CF) exhibits a greatly enhanced ionic conductivity in the low temperature range (500-600 degrees C), e.g. 0.48 S/cm at 550 degrees C. The CF YSZ composite was prepared via a nanocomposite approach. Fuel cells were fabricated by using a CF YSZ electrolyte layer between the symmetric electrodes of the Ni0.8Co0.2Al0.5Li (NCAL) coated Ni foam. The maximum power output of 562 mW/cm(2) has been achieved at 550 degrees C. Even the CF alone to replace the electrolyte the device reached the maximum power of 281 mW/cm(2) at the same temperature. Different ion-conduction mechanisms for YSZ and CF YSZ are proposed. This work provides a new approach to develop natural mineral composites for advanced low temperature solid oxide fuel cells with a great marketability.

  • 124254. Xu, S.
    et al.
    Dverstorp, B.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Klos, R.
    Marklund, L.
    Developing a Regulatory Performance Assessment Approach for Final Disposal of Spent Nuclear Fuel2005In: Proceedings of the 2nd International Conference on Radioactivity in the Environment, 2005, p. 380-384Conference paper (Refereed)
  • 124255. Xu, S. L.
    et al.
    Wörman, Anders
    Dverstorp, B.
    Heterogeneous matrix diffusion in crystalline rock - implications for geosphere retardation of migrating radionuclides2001In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 47, no 04-feb, p. 365-378Article in journal (Refereed)
    Abstract [en]

    As a basis for an analysis of the effect of rock heterogeneity on radionuclide migration in a single fracture, the geostatistics of the main properties governing solute transport in crystalline rock have been determined experimentally for two granitic rock types. The rock samples were collected at the Aspo Hard Rock Laboratory, Sweden and used to deduce the auto-covariance functions for the porosity, effective diffusivity and partition coefficient, k(d). and adsorption kinetics. One-dimensional analytical solutions for the mean values of the temporal moments of the residence time probability density function (PDF) show that the heterogeneity of the rock properties can have a substantial impact on the transport, A case study of the effect of heterogeneity in matrix diffusion for a single fracture could be performed by decomposing the transport problem into a one-dimensional mass transfer problem and a two-dimensional flow problem using a Lagrangian method of description. Monte Carlo simulations of the flow field indicate that the correlation length of the aperture is much longer along the trajectory paths than along an arbitrary direction. Increasing the correlation lengths and variances of the aperture and matrix diffusion increases significantly the variance of the travel time PDF.

  • 124256. Xu, S.
    et al.
    Zhang, Q.
    Feng, Zhaoxuan
    KTH, School of Chemical Science and Engineering (CHE).
    Meng, X.
    Zhao, T.
    Li, C.
    Yang, C.
    Shan, H.
    A high-surface-area silicoaluminophosphate material rich in Brönsted acid sites as a matrix in catalytic cracking2012In: Journal of Natural Gas Chemistry, ISSN 1003-9953, Vol. 21, no 6, p. 685-693Article in journal (Refereed)
    Abstract [en]

    A transparent gel-like mesoporous silicoaluminophosphate material (SAP) with a Si/Al molar ratio of 20 was synthesized by hydrothermal method. The physicochemical features of SAP were characterized by XRD, XRF, BET, SEM and FT-IR spectroscopy of pyridine adsorption techniques. The results indicated that incorporation of phosphorus (P) into aluminasilica system altered the basic textural characteristics of aluminasilica. Especially after hydrothermal treatment, the material with large special surface area (up to 492 m 2/g) exhibited a good performance on hydrothermal stability. Moreover, the phosphorus modifier can not only increase the amount of Brönsted acidic sites (up to 48.44 μmol/g) and the percentage of weak acidic sites in total acidic sites, but also regulate the acid type, such as the ratio of B/L (Brönsted acid/Lewis acid) increases to 1.15. The performances of samples as matrices for the catalytic cracking of heavy vacuum gas oil (VGO) were investigated. At 520°C, the catalysts showed much higher gasoline and diesel oil yields achieving to 45.59 wt and 19.20 wt, respectively, and lower coke selectivity (2.86) than conventional FCC matrices, such as kaolin and amorphous silica-alumina.

  • 124257. Xu, Shaohui
    et al.
    Chen, Qiang
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Zhu, Yiping
    Wang, Lianwei
    Zheng, Lirong
    KTH, School of Information and Communication Technology (ICT), Electronic Systems.
    Chu, Paul K.
    Modeling and Optimization of Thermoelements by a Combined Analytical and Numerical Method2014In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 43, no 2, p. 404-413Article in journal (Refereed)
    Abstract [en]

    A combined analytical and numerical process has been developed to model and optimize thermoelements. In this way, the performance of commercial n- and p-type thermoelectric materials can be optimized to deliver the maximum output power and conversion efficiency. The validity of the method is demonstrated using a silicon germanium unicouple.

  • 124258.
    Xu, Shulan
    et al.
    Swedish Radiation Protection Authority, Stockholm, Sweden.
    Dverstorp, Björn
    Klos, Ryk
    Wörman, Anders
    Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Marklund, Lars
    Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Application of a Regulatory Performance Assessment Approach for Comparison with the Proponent’s Calculations2006In: Proceedings of the 11th International High Level Radioactive Waste Management Conference, IHLRWM, 2006, p. 980-985Conference paper (Refereed)
    Abstract [en]

    To be able to carry out review functions regulatory authorities must be able to make critical evaluations of proponents PA cases. In Sweden the Swedish Radiation Protection Authority (SSI) aims to have in place its own suite of performance assessment (PA) tools. These will be used to address the forthcoming PAs submitted by the Swedish Nuclear Waste Management Company (SKB)for an encapsulation plant (2006) and a geological repository for spent fuel (2008). This paper looks at the role and application of the regulator's models to important features of current modelling in SKB's latest PAs. The SSI modelling tools are applied to a mire system in which radionuclides are assumed to be released from a geological repository. Results are presented which illustrate the importance of a deeper understanding of the geosphere-biosphere interface zone than has been the case in assessments to date.

  • 124259. Xu, Shulan
    et al.
    Dverstorp, Björn
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Predication of Concentration and Model Validation: Key issues in assessment of long term safety for radioactive waste disposal2008In: Proceedings of the int. Conference on Radioecology and Environmental Radioactivit / [ed] Per Strand, Justin Brown and Torun Jolle, 2008Conference paper (Refereed)
  • 124260. Xu, Shulan
    et al.
    Dverstorp, Björn
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Prediction of concentration and model validation: Key issues in assessment of long term safety for radioactive waste disposal2008In: Proceedings of the International Conference on Radioecology and Environmental Radioactivity / [ed] Per Strand, Justin Brown, Torun Jolle, 2008Conference paper (Refereed)
  • 124261. Xu, Shulan
    et al.
    Marklund, Lars
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Dverstorp, Anders
    A regulatory modelling strategy for review of dose calculations2008In: Proceedings of The 12th International High-Level Radioactive Waste managemenent Conference, American Nuclear Society , 2008, p. 466-472Conference paper (Refereed)
    Abstract [en]

    To be able to carry out review functions regulatory authorities must be able to make critical evaluations of proponent's performance assessment (PA) cases. In Sweden the Swedish Radiation Protection Authority (SSI) aims to have in place its own suite of PA tools. These will be used to address the forthcoming PAs submitted by the Swedish Nuclear Waste Management Company (SKB) for a geological repository for spent fuel (2010). This paper looks at the role and application of the regulator's models to important features of current modelling in SKB 's latest PAs. The SSI modelling tools are applied to demonstrate a possible size of the contaminant area due to leakage of radionuclides from a damaged canister. An improved representation of these processes will enhance our understanding of biosphere functions and provide a better basis for evaluating radiological consequences in the safety assessment.

  • 124262. Xu, Shulan
    et al.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Dverstorp, Bjorn
    Criteria for resolution-scales and parameterisation of compartmental models of hydrological and ecological mass flows2007In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 335, no 04-mar, p. 364-373Article in journal (Refereed)
    Abstract [en]

    The effect of compartment resolution-scale, i.e. number of compartments and compartment size, on prediction of transport of water and solute mass in watersheds is analysed by using numerical discretisation and temporal moments methods. The one-dimensional advection-diffusion model is used as a theoretical frame of reference for representing transport along a single series of compartments along a pathway in the surface water or ecosystem. Criteria for parameterisation of compartment models and error estimates are derived for two cases: (1) requiring an exact match with the advection-diffusion model; and (2) requiring as good match as possible with a simplified compartment model using a small number of compartments. The matching criteria are based on a comparison of numerical discretisation and temporal moments of the compartmental backflow model with those of the one-dimensional advection-diffusion equation. We derived solutions in terms of temporal moments of both the advection-diffusion equation and compartmental backflow model. with arbitrary input concentration vs. time boundary condition. This approach can be used to translate parameters between the models and analyse the error caused by any arbitrary structure of the compartmental model as a function of boundary conditions and the physical parameters of the advective-diffusive equation. Data from tracer experiments were compared with model predictions to provide a practical frame of reference.

  • 124263. Xu, Shulan
    et al.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Dverstorp, Björn
    Effects of compartmental model structure and long-term inflow on model predictions2005In: Radioprotection - Revue de la Societé Francaise de Radioprotection, ISSN 0033-8451, E-ISSN 1769-700X, Vol. 40, no 1, p. 477-483Article in journal (Refereed)
    Abstract [en]

    Model predictions of solute transport in a wetland were compared with tracer experimental data to illustrate that the number of compartments in a compartmental model should be selected according to certain rules to accurately describe the transport process. If the input pulse is short, the model structure affects the output significantly. The temporal moments of the residence time distribution was obtained from a general solution of the compartmental model in the Laplace domain derived with an arbitrary inflow pollutograph. The variance of the residence time can be used as a useful tool to analyse the effect of model structure and long-term inflow pollutograph on the response of the model predictions.

  • 124264. Xu, Shulan
    et al.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Dverstorp, Björn
    Prediction of concentration and model validation2008In: Radioprotection - Revue de la Societé Francaise de Radioprotection, ISSN 0033-8451, E-ISSN 1769-700X, Vol. 43, no 1, p. 701-706Article in journal (Refereed)
    Abstract [en]

    In this paper we examine some critical aspects concerning the justification of simplified radioecological models used in safety assessments for geological repositories. We propose a modelling approach for regulatory review of dose and risk calculations for a nuclear waste repository. The SSI modelling tools are applied to explore uncertainties in the size of the contaminant area due to leakage of radionuclides from a damaged nuclear waste canister. We demonstrate that an improved representation of geosphere transport processes will also enhance our understanding of radionuclide migration in the biosphere and provide a better basis for evaluating radiological consequences in the safety assessment.

  • 124265.
    Xu, Shuqi
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Learning Model Predictive Control for Autonomous Racing: Improvements and Model Variation in Model Based Controller2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this work, an improved Learning Model Predictive Control (LMPC)architecture for autonomous racing is presented. The controller is referencefree and is able to improve lap time by learning from history data of previouslaps. A terminal cost and a sampled safe set are learned from history data toguarantee recursive feasibility and non-decreasing performance at each lap.Improvements have been proposed to implement LMPC on autonomousracing in a more efficient and reliable way. Improvements have been doneon three aspects. Firstly, system identification has been improved to be runin a more efficient way by collecting feature data in subspace, so that thesize of feature data set is reduced and time needed to run sorting algorithmcan be reduced. Secondly, different strategies have been proposed toimprove model accuracy, such as least mean square with/without lifting andGaussian process regression. Thirdly, for reducing algorithm complexity,methods combining different model construction strategies were proposed.Also, running controller in a multi-rate way has also been proposed toreduced algorithm complexity when increment of controller frequency isnecessary. Besides, the performance of different system identificationstrategies have been compared, which include strategy from newton’s law,strategy from classical system identification and strategy from machinelearning. Factors that can possibly influence converged result of LMPCwere also investigated, such as prediction horizon, controller frequency.Experiment results on a 1:10 scaled RC car illustrates the effectiveness ofproposed improvements and the difference of different system identificationstrategies.

  • 124266. Xu, Sihong
    et al.
    Niu, Xiaomeng
    Chen, Mingming
    Wang, Chengyang
    Zhu, Bin
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Carbon doped MO-SDC material as an SOFC anode2007In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 165, no 1, p. 82-86Article in journal (Refereed)
    Abstract [en]

    Oxide mixtures MO-SDC, M=Cu, Ni, Co, SDC=Ce0.9Sm0.1O1.95 were synthesized by employing a citrate/nitrate combustion technique. Two kinds of Carbon materials, activated carbon (AC) and vapor grown carbon fiber (VGCF) were homogeneously dispersed into the MO-SDC. The materials can be used as anodes to fabricate single cells using a uniaxial die-press method. The sintering temperature was studied to optimize cell performance. Experimental results showed that cells sintered at 700 degrees C had better performance. When the temperature was above 750 degrees C, the cells were severely distorted, and cannot be tested. Compared with the basic MO-SDC anode, AC and VGCF improve the solid oxide fuel cell (SOFC) anode properties, due to a change of the microstructures of the anode materials which enhance their electron conductivity. Single cell performances were evaluated by I-V measurements, and when 1.25 wt.%VGCF was introduced into the MO-SDC by ball-milling, termed: 1.25 wt.%VGCF-MO-SDC, the 1.25 wt.%VGCF-MO-SDC anode material could achieve the highest power density of up to 0.326 W cm(-2) with H-2 as fuel. The calcination temperature of the MO-SDC dry gel also strongly influenced the electrochemical performance of the 1.25 wt.%VGCF-MO-SDC material. XRD spectra for each calcined temperature and the I-V measurement both suggest that calcinations at 550 degrees C for 1 h are suitable. 1.0 wt.%AC-MO-SDC and 1.25 wt.%VGCF-MO-SDC have similar performance when the cell was fed in methanol/3%H2O, and the corresponding power density was up to 0.253 W cm(-2). Traces of carbon were found in the off-gases.

  • 124267. Xu, T.
    et al.
    Bayvel, P.
    Liu, T.
    Zhang, Y.
    Jacobsen, G.
    Li, J.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Carrier phase estimation in dispersion-unmanaged optical transmission systems2017In: Proceedings of 2017 IEEE 2nd Advanced Information Technology, Electronic and Automation Control Conference, IAEAC 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 1860-1864, article id 8054335Conference paper (Refereed)
    Abstract [en]

    The study on carrier phase estimation (CPE) approaches, involving a one-tap normalized least-mean-square (NLMS) algorithm, a block-wise average algorithm, and a Viterbi-Viterbi algorithm has been carried out in the long-haul high-capacity dispersion-unmanaged coherent optical systems. The close-form expressions and analytical predictions for bit-error-rate behaviors in these CPE methods have been analyzed by considering both the laser phase noise and the equalization enhanced phase noise. It is found that the Viterbi-Viterbi algorithm outperforms the one-tap NLMS and the block-wise average algorithms for a small phase noise variance (or effective phase noise variance), while the three CPE methods converge to a similar performance for a large phase noise variance (or effective phase noise variance). In addition, the differences between the three CPE approaches become smaller for higher-level modulation formats.

  • 124268. Xu, T. C.
    et al.
    Guang, L.
    Yin, A. W.
    Yang, B.
    Liljeberg, P.
    Tenhunen, Hannu
    Department of Information Technology, University of Turku.
    An analysis of designing 2D/3D chip multiprocessor with different cache architecture2010In: NORCHIP, 2010, 2010Conference paper (Refereed)
    Abstract [en]

    Network-on-Chip (NoC) has become a widely acceptedon-chip communication architecture which provides apromising solution to integrate a large number of components ona single chip. However, with the increasingly higher performancedemands for on-chip systems, NoCs are facing several criticalchallenges such as wire delay and power consumption. Therefore,in this paper, we explore different cache architecture designsin 2D/3D NoC architectures. Integrated core/cache and splitcore/cache architectures have been analyzed in terms of areaand wire delay. We present benchmark results using a cycleaccurate full system simulator. Experiments show that, by usingthe proposed 3D NoC architecture, compared with the integratedcore/cache design, the average network latency and average linkutilization are reduced by 5.01% and 26.07% respectively.

  • 124269.
    Xu, T. C.
    et al.
    Turku Centre for Computer Science (TUCS).
    Liljeberg, P.
    Turku Centre for Computer Science (TUCS).
    Plosila, J.
    Turku Centre for Computer Science (TUCS).
    Tenhunen, Hannu
    Exploration of heuristic scheduling algorithms for 3D multicore processors2012In: Proceedings of the 15th International Workshop on Software and Compilers for Embedded Systems, 2012, p. 22-31Conference paper (Refereed)
    Abstract [en]

    In this paper, we explore heuristic scheduling algorithms for future multicore processors. It is expected that hundreds or even thousands of cores will be integrated on a single chip, known as a Chip Multiprocessor (CMP). To reduce on-chip communication delay and improve efficiency, three-dimensional (3D) integration with Through Silicon Vias (TSVs) is introduced to replace the traditional two-dimensional (2D) implementation. Multiple functional layers can be stacked in 3D CMPs. However, operating system process scheduling has not been well addressed for such systems. We define a model for 3D CMPs, and propose a heuristic scheduling algorithm which aims to reduce cache access latencies and the delay of inter process communication. We explore different scheduling methods and discuss the advantages and disadvantages of our algorithm. Experimental results show that under three different workloads, the execution times of our scheduling method in two configurations are reduced by 14.5% and 5.86% respectively, compared with the other scheduling methods. Two scheduling methods from different heuristics for 8-thread tasks are also compared. This research provides a guideline for designing scheduling algorithms for future 3D CMPs.

  • 124270. Xu, T. C.
    et al.
    Liljeberg, P.
    Tenhunen, Hannu
    Department of Information Technology, University of Turku.
    A Greedy Heuristic Approximation Scheduling Algorithm for 3D Multicore Processors2011In: HPPC 2011: (Hand-out) Proceedings of the 5th Workshop onHighly Parallel Processingon a Chip, 2011, p. 38-47Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose a greedy heuristic approximationscheduling algorithm for future multicore processors. It is expected thathundreds of cores will be integrated on a single chip, known as a ChipMultiprocessor (CMP). To reduce on-chip communication delay, 3D integrationwith Through Silicon Vias (TSVs) is introduced to replace the2D counterpart. Multiple functional layers can be stacked in a 3D CMP.However, operating system process scheduling, one of the most importantdesign issues for CMP systems, has not been well addressed forsuch a system. We define a model for future 3D CMPs, based on whicha scheduling algorithm is proposed to reduce cache access latencies andthe delay of inter process communications (IPC). We explore differentscheduling possibilities and discuss the advantages and disadvantages ofour algorithm. We present benchmark results using a cycle accurate fullsystem simulator based on realistic workloads. Experiments show thatunder two workloads, the execution times of our scheduling in two configurations(2 and 4 threads) are reduced by 15.58% and 8.13% respectively,compared with the other schedulings. Our study provides a guideline fordesigning scheduling algorithms for 3D multicore processors.

  • 124271. Xu, T. C.
    et al.
    Liljeberg, P.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Electronic Systems. KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK.
    A study of Through Silicon Via impact to 3D Network-on-Chip design2010In: 2010 International Conference on Electronics and Information Engineering, ICEIE 2010, 2010, Vol. 1, p. V1333-V1337Conference paper (Refereed)
    Abstract [en]

    The adoption of a 3D Network-on-Chip (NoC) design depends on the performance and manufacturing cost of the chip. Therefore, a study of Through Silicon Via (TSV), that connects different layers of a 3D chip, is crucial. In this paper, we analysis the impact of TSV design in 3D NoCs. A 3D NoC with five layers is modeled based on modern 2D chips. We discuss the TSV number required for a 3D NoC. Different placements of half and quarter layer-layer connections are explored. We present benchmark results using a cycle accurate full system simulator based on realistic workloads. Experiments show that under different workloads, the average network latencies in full and half layer-layer connection are reduced by 5.24% and 2.18% respectively, compared with quarter design. Our analysis and experiment results provide a guideline for designing TSVs in 3D NoCs to leverage the trade-off between performance and manufacturing cost.

  • 124272.
    Xu, T. C.
    et al.
    Turku Centre for Computer Science (TUCS).
    Liljeberg, P.
    Turku Centre for Computer Science (TUCS).
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Electronic Systems. KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK.
    An Optimized Network-on-Chip Design for Data Parallel FFT2012In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 30, p. 311-318Article in journal (Refereed)
    Abstract [en]

    In this paper, we propose an optimized Network-on-Chip (NoC) design for data parallel FFT applications. NoC based architecture is proposed for future multicore processors due to its scalability. FFT is widely used in digital systems. The implementation of FFT on conventional architectures have been studied. However, the evaluation of data parallel FFT in a NoC platform has not been well addressed. We analyse data parallel FFT in terms of traffic patterns and propose an optimized NoC design. Experiments show that, the execution time of our optimized design is 12.13% faster than the original

  • 124273. Xu, T. C.
    et al.
    Liljeberg, P.
    Tenhunen, Hannu
    Department of Information Technology, University of Turku.
    Explorations of optimal core and cache placements for Chip Multiprocessor2011In: NORCHIP, 2011, 2011, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this paper, we study and analyse optimal core and cache placements for modern Chip Multiprocessors (CMPs). As the number of cores increases, traditional on-chip interconnects such as bus and crossbar suffer from poor scalability and low efficiency. Ring based design has been proposed and implemented to mitigate these problems. However, the continuation growth of number of cores will render the ring interconnect infeasible. Network based designs are therefore proposed for future CMPs for better scalability. In this paper, we explore the interconnect of a state-of-the-art CMP. We analyse and compare the implementation of the ring-based and the network-based interconnect. The placement of cores and caches in a network is proved crucial for system performance. We investigate optimal core/cache placement for CMPs. The benchmark results are presented by using a cycle accurate full system simulator. Results show that, by using the optimal network interconnect, compared with the ring interconnect, the average network latency and execution time are reduced by 11.93% and 19.53% respectively, for four configurations and two applications.

  • 124274. Xu, T. C.
    et al.
    Liljeberg, P.
    Tenhunen, Hannu
    Department of Information, Technology,University of Turku.
    Exploring DRAM Last Level Cache for 3D Network-on-Chip Architecture2010In: Proceedings of the IEEE International Conference on Embedded System and Microprocessors, 2010, p. 39-44Conference paper (Refereed)
  • 124275. Xu, T. C.
    et al.
    Liljeberg, P.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Electronic Systems. KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK.
    Optimal number and placement of Through Silicon Vias in 3D Network-on-Chip2011In: 14th IEEE International Symposium on Design and Diagnostics of Electronic Circuits and Systems, DDECS 2011, 2011, p. 105-110Conference paper (Refereed)
    Abstract [en]

    In this paper, we analyze the performance impact of different number of Through Silicon Vias (TSVs) in 3D Network-on-Chip (NoC). The adoption of a 3D NoC design depends on the performance and manufacturing cost of the chip. Therefore, a study of the placement of the TSV, that connects different layers of a 3D chip, is crucial. A 64-core 3D NoC is modeled based on state-of-the-art 2D chips. We discuss the number of TSVs required for a 3D NoC. Different placements of layer-layer connections are explored. We present benchmark results using a cycle accurate full system simulator based on realistic workloads. Experiments show that under different workloads, the average network latencies in two configurations (full and quarter connection) are reduced by 14.78% and 7.38% respectively, compared with the one-eighth connection design. The improvement of performance is a trade-off of manufacturing cost. Our analysis and experiment results provide a guideline for selecting optimal number of TSVs in 3D NoCs.

  • 124276. Xu, T. C.
    et al.
    Yin, A. W.
    Liljeberg, P.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Electronic Systems. KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK.
    A study of 3d network-on-chip design for data parallel h. 264 coding2011In: Microprocessors and microsystems, ISSN 0141-9331, E-ISSN 1872-9436, Vol. 35, no 7, p. 603-612Article in journal (Refereed)
    Abstract [en]

    In this paper, we implement, analyze and compare different Network-on-Chip (NoC) architectures aiming at higher efficiencies for MPEG-4/H.264 coding. Two-dimensional (2D) and three-dimensional (3D) NoCs based on Non-Uniform Cache Access (NUCA) are analyzed. We present results using a full system simulator with realistic workloads. Experiments show the average network latencies in two 3D NoCs are reduced by 28% and 34% respectively, comparing with 20 design. It is also shown that heat dissipation is a trade-off in improving performance of 3D chips. Our analysis and experiment results provide a guideline to design efficient 3D NoCs for data parallel H.264 coding applications.

  • 124277. Xu, T. C.
    et al.
    Yin, A. W.
    Liljeberg, P.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    A study of 3D Network-on-Chip design for data parallel H.264 coding2009In: 2009 NORCHIP, 2009Conference paper (Refereed)
    Abstract [en]

    In this paper, we study and analyze different Network-on-Chip (NoC) designs for MPEG-4/H.264 coding. The encoding and decoding processes of H.264 have been analyzed. We discuss the parallelism of H.264, and an open-source encoding program is used as a case study. The contribution of this paper lies in the NoC design method and performance evaluation of data parallel H.264 coder. It is shown in our study that the inter-thread data dependency of shared reads and writes are performance bottlenecks. Different non-uniform cache access NoC designs have been explored. Two-dimensional (2D) and three-dimensional (3D) NoCs have been analyzed in terms of hop count and heat dissipation. We present benchmark results using a cycle accurate full system simulator based on realistic workloads. Experiments show that under different workloads, the average network latencies in two 3D NoC designs are reduced up to 34% compared with the 2D NoC. It is also shown that the heat dissipation is a trade-off consideration in improving the performance of 3D IC. Our analysis and experiment results provide a guideline to design efficient 3D NoCs for data parallel H.264 coding applications.

  • 124278. Xu, T. C.
    et al.
    Yin, A. W.
    Liljeberg, P.
    Tenhunen, Hannu
    University of Turku, Department of Information Technology.
    Operating system processor scheduler design for future chip multiprocessor2010In: 2010 23rd International Conference on Architecture of Computing Systems (ARCS), 2010Conference paper (Refereed)
    Abstract [en]

    Today’s Chip Multiprocessor (CMP) designs are mainly based on the shared-bus communication architecture. However,as the scale of CMPs increase, this architecture suffers from high communication delay and power inefficiency. Therefore,network-on-chip (NoC) based architecture is proposed as a promising technique for future very large scale CMPs. Theoperating system (OS) scheduling is one of the most important design issues for CMP systems. In this paper, limitationsof state-of-the-art OS scheduler are discussed, with Sun Solaris used as a case study. The contribution of this paper lies inthe on-chip data traffic calculation of runtime applications. By evaluating FFT and SPECjbb as benchmarks, it is shownthat the Solaris scheduler does not provide the optimal communication scheme and thus suffers from the network latencyand overall performance degradation. We define a model for NoC-based CMP, based on which a scheduling algorithmis proposed to minimize communication latencies. The weights of memory access and inter process communication inscheduling are analyzed. A protocol for OS implementation of the algorithm has been proposed in this paper. Our analysisand experiment results provide a guideline for the designs of future multicore schedulers.

  • 124279. Xu, T.
    et al.
    Jacobsen, Gunnar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Acreo Swedish ICT AB, Sweden.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Liu, T.
    Zhang, Y.
    Bayvel, P.
    Analytical estimation in differential optical transmission systems influenced by equalization enhanced phase noise2016In: 2016 Progress In Electromagnetics Research Symposium, PIERS 2016 - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 4844-4848Conference paper (Refereed)
    Abstract [en]

    An analytical model is presented for assessing the performance of the bit-error-rate (BER) in the differential m-level phase shift keying (m-PSK) transmission systems, where the influence of equalization enhanced phase noise (EEPN) has been considered. Theoretical analysis has been carried out in differential quadrature phase shift keying (DQPSK), differential 8-PSK (D8PSK), and differential 16-PSK (D16PSK) optical transmission systems. The influence of EEPN on the BER performance, in term of signal-to-noise ratio (SNR), are investigated for different fiber dispersion, LO laser linewidths, symbol rates, and modulation formats. Our analytical model achieves a good agreement with previously reported EEPN induced BER floors, and can give an accurate prediction for the DQPSK system, and a leading-order approximation for the D8PSK and the D16PSK systems.

  • 124280.
    Xu, T.
    et al.
    Turku Centre for Computer Science (TUCS).
    Liljeberg, P.
    Turku Centre for Computer Science (TUCS).
    Tenhunen, Hannu
    A greedy heuristic approximation scheduling algorithm for 3d multicore processors2012In: Euro-Par 2011: Parallel Processing Workshops, 2012, p. 281-291Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose a greedy heuristic approximation scheduling algorithm for future multicore processors. It is expected that hundreds of cores will be integrated on a single chip, known as a Chip Multiprocessor (CMP). To reduce on-chip communication delay, 3D integration with Through Silicon Vias (TSVs) is introduced to replace the 2D counterpart. Multiple functional layers can be stacked in a 3D CMP. However, operating system process scheduling, one of the most important design issues for CMP systems, has not been well addressed for such a system. We define a model for future 3D CMPs, based on which a scheduling algorithm is proposed to reduce cache access latencies and the delay of inter process communications (IPC). We explore different scheduling possibilities and discuss the advantages and disadvantages of our algorithm. We present benchmark results using a cycle accurate full system simulator based on realistic workloads. Experiments show that under two workloads, the execution times of our scheduling in two configurations (2 and 4 threads) are reduced by 15.58% and 8.13% respectively, compared with the other schedulings. Our study provides a guideline for designing scheduling algorithms for 3D multicore processors.

  • 124281. Xu, T.
    et al.
    Liljeberg, P.
    Tenhunen, Hannu
    Study of hierarchical n-body methods for network-on-chip architectures2012In: Euro-Par 2011: Parallel Processing Workshops, 2012, p. 365-374Conference paper (Refereed)
    Abstract [en]

    In this paper, we study two hierarchical N-Body methods for Network-on-Chip (NoC) architectures. The modern Chip Multiprocessor (CMP) designs are mainly based on the shared-bus communication architecture. As the number of cores increases, it suffers from high communication delays. Therefore, NoC based architecture is proposed. The N-Body problem is a classical problem of approximating the motion of bodies. Two methods, namely Barnes-Hut (Barnes) and Fast Multipole (FMM), have been developed for fast simulation. The two algorithms have been implemented and studied in conventional computer systems and Graphics Processing Units (GPUs). However, as a promising unconventional multicore architecture, the evaluation of N-Body methods in a NoC platform has not been well addressed. We define a NoC model based on state-of-the-art systems. Evaluation results are presented using a cycle accurate full system simulator. Experiments show that, Barnes scales better (53.7x/Barnes and 36.6x/FMM for 64 processing elements) and requires less cache than FMM. However, we observe hot-spot traffic in Barnes. Our analysis and experiment results provide a guideline for studying N-Body methods in a NoC platform

  • 124282. Xu, Tao
    et al.
    Xu, Michelle
    Kumari, Priyadarshini
    Aitchison, Stewart
    Ruda, Harry
    Zhu, Ning
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT).
    Silicon-on-insulator nanopillar-array optical sensor2011In: Progress in Biomedical Optics and Imaging - Proceedings of SPIE / [ed] Alexander N. Cartwright, Dan V. Nicolau, SPIE - International Society for Optical Engineering, 2011Conference paper (Refereed)
    Abstract [en]

    Pillar-array based optical cavities have unique properties, e.g., having a large and connected low dielectric index space (normally air space), having a large percent of electric field energy in air and standing on a substrate. These properties make them well suitable to make ultra compact and highly sensitive label-free optical sensors to detect bio-/chemical reactions. We designed, fabricated, and measured a silicon-on-insulator pillar array microcavity that possesses a quality factor as high as 27,600. We studied its sensitivity for both bulk index change and surface index modification. As a bulk index sensor, for environmental refractive index change of 0.01, a resonance peak wavelength shift of 3.5 nm was measured. As a surface index sensor, the simulations show, for a coating with thickness of 1 nm, the resonance wavelength shifts as large as 2.86 nm. Combining with a sharp 0.06 nm wide resonance peak, our pillar-array sensor is able to resolve ultra small bulk and surface refractive index changes caused by target molecules.

  • 124283. Xu, Tao
    et al.
    Zhu, Ning
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Xu, Michelle Y. C.
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Aitchison, J. Stewart
    Ruda, H. E.
    Pillar-array based optical sensor2010In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, no 6, p. 5420-5425Article in journal (Refereed)
    Abstract [en]

    An optical microcavity based on pillar arrays has been fabricated in Si/SiO2 material system. Transmission measurement was taken and a quality factor as high as 27,600 was observed. This cavity was tested for sensing applications by immersing into optical fluids with accurate refractive indices. For refractive index change of 0.01, a resonance peak wavelength shift of 3.5 nm was measured. We also compare cavities consisting of pillars with different aspect ratios.

  • 124284.
    Xu, Tao
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Zhu, Ning
    Xu, Michelle Y.-C.
    Wosinski, Lech
    KTH, School of Information and Communication Technology (ICT).
    Aithison, J. Stewart
    Ruda, Harry E.
    A pillar-array based 2-dimensional photonic crystal microcavity2009In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, p. 241110-Article in journal (Refereed)
    Abstract [en]

    Experimental results are presented for a high quality factor cavity based on pillar arrays. The cavityis formed from a square lattice of silicon pillars of finite height. The quality factor of the fundamental mode is about 7300 when the cavity is in air and 7800 when it is immersed in water.Since a pillar array has a large percent of connected void space and confines TM modes effectively,it has great promise for use in numerous areas including biochemical sensing and quantum cascade lasers.

  • 124285.
    Xu, Tian
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Enabling Database-based Unified Diagnostic Service over Local Interconnect Network2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Unified Diagnostic Service (UDS), which is an international and not a company-specific standard, is used in almost all new electronic control units (ECUs) by now. Modern vehicles have a diagnostic interface for off-board diagnostics, which makes it possible to connect a diagnostic tool to the vehicle’s bus system like Controller Area Network (CAN) and Local Interconnect Network (LIN). However, as the most commonly used method, sequential method on the UDS data transmission over LIN does not only result in low reliability and flexibility but also fails to meet the standard for LIN development defined in the latest LIN specification published by the consortium. With standard workflow and application interfaces, this Master Thesis will develop and evaluate a database-based method to build a UDS system over LIN, where all the information for the network is defined in the LIN database, and the protocol properties are realized in a reusable model so that it can be easily reconfigured for the future development of other services. As a result, a new method including a layered-structure LIN protocol model and a LIN database has been successfully designed and implemented. The prototype is built on the device PIC32MX795, and the database can be deployed by the configuration tool to specify the UDS communication schedule. Further, several performance evaluations have been performed. The tests indicate that the system is qualified on the limited hardware platform and the configuration flexibility is proved by different databases.

  • 124286.
    Xu, Tianhao
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Experimental evaluation of air-to-water propane heat pumps with 40kW heating capacity2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis presents the experimental work on testing the seasonal performance of a 40 kW air-to-water propane heat pump, as a part of the research project Next Heat Pump Generation working with Natural fluids (NxtHPG) that has been carried out in ‘Applied thermodynamics and refrigeration Division’ in the department of Energy Technology, KTH. The thesis work involves three parts: preparation of the HP unit test rigs, experimental campaign and the evaluation of test results. In the first part, the set-up of the measurement device and necessary modifications to the heat pump unit as well as the test rigs have been completed to create an accurate measuring environmental for the experimental campaign. During the second stage, two series of experimental campaign have been done in the heating mode of the heat pump unit, and satisfactory results have been obtained in parts of the test conditions. Finally, the evaluation on the system performance as well as the behaviors of the components is discussed. The variation between experimental results and the simulation conducted by IMST-ART model is within reasonable range, proving that the heat pump unit has been working in good conditions. The compressor is proved to have been performing as manufacturer expected. However, some further investigations on the behaviors of the heat exchangers and expansion valve, such as superheat oscillation, are recommended be carried out in the future work. The completion of the rest of tests in which minus air temperature should be maintained and the ones with the desuperheater working should be done as well.

  • 124287.
    Xu, Tianhao
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. KTH.
    Chiu, Justin NingWei
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Sawalha, Samer
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Experimental investigation on cylindrically macro-encapsulated latent heat storage for space heating applications2019In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 182, p. 166-177Article in journal (Refereed)
    Abstract [en]

    The integration of latent heat thermal energy storage (LHTES) units with heating systems in buildings is regarded as a promising technology for heating load management; however, so far a limited number of experimental studies have been reported that focus on space heating applications on a representative scale. In this study, we develop and test a 0.38 m3 LHTES unit containing cylindrically macro-encapsulated phase change materials (PCMs) with a melting temperature range of 44–53 °C and with gross mass of 154 kg. The unit has been tested with two tank orientations, horizontal and vertical. In the horizontal orientation tests, parametric studies show that increasing the difference between heat transfer fluid (HTF) supply temperatures and phase-change temperatures of PCMs, as well as increasing HTF flowrates, can both reduce the complete melting/solidification and complete charging/discharging time. Non-linear charging/discharging rates in PCMs are observed. The vertical orientation enables the forming of either a stratified or mixed flow regime in the tank. For charging, the stratified flow provides higher charging rates in PCMs compared to the mixed flow. When discharging the unit with a stratified HTF flow at 35 °C, lower HTF flowrates prolong the discharging time during which the released heat sustains an outlet temperature above 45 °C. Finally, comparisons between horizontal and vertical orientation tests reveal that although the vertical orientation can shorten the charging/discharging time by up to 20% for the entire unit to reach an energy density of 30 kWh/m3, it leads to decrease in PCM thermal capacity by at most 8.2%. The speculated cause of this loss is phase segregation suggested by observed fluid motions in PCM cylinders. This study comprehensively characterizes an LHTES unit providing insights to optimizing its operating strategies considering its coupling with space heating systems.

  • 124288.
    Xu, Tianhao
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Gunasekara, Samman Nimali
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Chiu, Justin NingWei
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Sawalha, Samer
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Thermal behavior of a sodium acetate trihydrate-based PCM: T-history and full-scale tests2020In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 261, article id 114432Article in journal (Refereed)
    Abstract [en]

    Latent heat thermal energy storage (LHTES) has been receiving increasing attention from researchers and engineers. A practical LHTES installation requires a deep understanding of phase change material’s (PCM’s) thermal behavior under thermal property testing and realistic operating conditions. To enrich this understanding, an experimental study on a commercial sodium acetate trihydrate-based PCM (Climsel C58) is presented in this article. C58 was characterized with two test methods: T-history tests and full-scale LHTES tests. The results are presented and discussed to exhibit the thermal behavior of C58 with these two test methods and the variations between them. With T-history tests, the thermal properties of C58 such as melting/solidification temperature range (57–61 °C/55–50 °C) and latent heat of fusion (216 kJ/kg) were determined. In full-scale LHTES tests, a parametric study was conducted to investigate the effects of heat transfer fluid flowrate and operating temperature range on the thermal performance of a 0.38 m3 storage prototype containing cylindrically macro-encapsulated C58. Moreover, longitudinal and radial PCM temperature distributions in full-scale tests were analyzed, suggesting the presence of phase separation. In general, C58 behaved differently between the two test methods regarding phase separation (negligible in T-history tests), supercooling effects (within 3 K in full-scale but up to 10 K in T-history tests), and thermal energy storage capacity (10% lower in full-scale tests). When using C58 or other salt hydrate-based PCMs for large-scale heat storage, these thermal behavior differences between the property-measurement and the application-oriented environments should be properly addressed in the design stage to ensure performance.

  • 124289.
    Xu, Tianhao
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Navarro-Peris, Emilio
    Piscopiello, Salvatore
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Sawalha, Samer
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Corberán, José M.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Large-Capacity Propane Heat Pumps for DHW Production in Residential Buildings2018In: Refrigeration Science and Technology, Valencia, Spain, 2018, p. 1222-1230Conference paper (Refereed)
    Abstract [en]

    Using heat pump technology to provide Space Heating (SH) and to produce Domestic Hot Water (DHW) for residential buildings has been widely applied during past decades. In this study, two scenarios adopting large-capacity propane heat pumps are defined and evaluated. These two scenarios, which are named after Scenario A and Scenario B respectively, provide SH and DHW either separately by two units or integrally by one unit. The COP1s of two scenarios are compared based on the simulation results from experimentally validated models. The results show that two scenarios have almost equal efficiency; the relative difference is within 6%. In the optimization analysis of Scenario B, varying DHW heating capacity produced by the desuperheater in the heat pump is modelled. The DHW demand ratio varies from approximately 9% to 20% with no detectable influences on the COP1. The corresponding COP1s and temperature profiles in the heat exchangers are demonstrated. The simulation results indicate that increasing DHW capacity in Scenario B can narrow down the temperature approach in the condenser and insignificantly improves the overall COP1s.

  • 124290.
    Xu, Tianhao
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Sawalha, Samer
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Mazzotti, Willem
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Björn, Palm
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Performance Evaluation of a Large Capacity Air-Water Heat Pump Using Propane as Refrigerant2016Conference paper (Refereed)
    Abstract [en]

    Heat pump applications working with hydrocarbons as refrigerant have been under significant development along with the gradual phasing-out of conventional HFC systems. In this study, a large capacity air-water heat pump prototype using propane as refrigerant is tested to evaluate its heating performance under different operating conditions. The experimental set-up is briefly explained. The results of the experimental investigations of the heat pump prototype are presented in terms of the COP1, heating capacity and the compressor efficiency. At the design point, the experimental COP1 and heating capacity are 3.43 and 36.59 kW respectively. Experimental results for all test conditions are compared to simulation results generated from the model, which is created by the software IMST-ART. The model is validated through comparisons of those parameters since a good agreement between simulated and experimental data have been found. The maximum discrepancies of COP1 and heating capacity are around 5% and 10% respectively.

  • 124291.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Digital Dispersion Equalization and Carrier Phase Estimation in 112-Gbit/s Coherent Optical Fiber Transmission System2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Coherent detection employing multilevel modulation format has become one of the most promising technologies for next generation high speed transmission system due to the high power and spectral efficiencies. With the powerful digital signal processing (DSP), coherent optical receivers allow the significant equalization of chromatic dispersion (CD), polarization mode dispersion (PMD), phase noise (PN) and nonlinear effects in the electrical domain. Recently, the realizations of these DSP algorithms for mitigating the channel distortions in the transmission system are the most attractive investigations. 

    The CD equalization can be performed by the digital filters developed in the time and the frequency domain, which can suppress the fiber dispersion effectively. The PMD compensation is usually performed in the time domain with the adaptive least mean square (LMS) and constant modulus algorithms (CMA) equalization. Feed-forward and feed-back carrier phase estimation algorithms are employed to mitigate the phase noise from the transmitter and local oscillator lasers. The fiber nonlinearities are compensated by using the digital backward propagation methods based on solving the nolinear Schrodinger (NLS) equation and the Manakov equation. 

    In this dissertation, we present a comparative analysis of three digital filters for chromatic dispersion compensation, an analytical evaluation of carrier phase estimation with digital equalization enhanced phase noise and a brief discussion for PMD adaptive equalization. To implement these investigations, a 112-Gbit/s non-return-to-zero polarization division multiplexed quadrature phase shift keying (NRZ-PDM-QPSK) coherent transmission system is realized in the VPI simulation platform. With the coherent transmission system, these CD equalizers have been compared by evaluating their applicability for different fiber lengths, their usability for dispersion perturbations and their computational complexity. Meanwhile, the bit-error-rate (BER) floor in carrier phase estimation using a one-tap normalized LMS filter is evaluated analytically, and the numerical results are compared to a differential QPSK detection system.

  • 124292.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    DSP based Chromatic Dispersion Equalization and Carrier Phase Estimation in High Speed Coherent Optical Transmission Systems2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Coherent detection employing multilevel modulation formats has become one of the most promising technologies for next generation high speed transmission systems due to the high power and spectral efficiencies. Using the powerful digital signal processing (DSP), coherent optical receivers allow the significant equalization of chromatic dispersion (CD), polarization mode dispersion (PMD), phase noise (PN) and nonlinear effects in the electrical domain. Recently, the realizations of these DSP algorithms for mitigating the channel distortions in the coherent transmission systems are the most attractive investigations.

    The CD equalization can be performed by the digital filters developed in the time and the frequency domain, which can suppress the fiber dispersion effectively. The PMD compensation is usually performed in the time domain with the adaptive least mean square (LMS) and constant modulus algorithms (CMA) equalization. Feed-forward and feed-back carrier phase estimation (CPE) algorithms are employed to mitigate the phase noise (PN) from the transmitter (TX) and the local oscillator (LO) lasers. The fiber nonlinearities are compensated by using the digital backward propagation methods based on solving the nonlinear Schrödinger (NLS) equation and the Manakov equation.

    In this dissertation, we present a comparative analysis of three digital filters for chromatic dispersion compensation, a comparative evaluation of different carrier phase estimation methods considering digital equalization enhanced phase noise (EEPN) and a brief discussion for PMD adaptive equalization. To implement these investigations, a 112-Gbit/s non-return-to-zero polarization division multiplexed quadrature phase shift keying (NRZ-PDM-QPSK) coherent transmission system with post-compensation of dispersion is realized in the VPI simulation platform. In the coherent transmission system, these CD equalizers have been compared by evaluating their applicability for different fiber lengths, their usability for dispersion perturbations and their computational complexity. The carrier phase estimation using the one-tap normalized LMS (NLMS) filter, the differential detection, the block-average (BA) algorithm and the Viterbi-Viterbi (VV) algorithm is evaluated, and the analytical predictions are compared to the numerical simulations. Meanwhile, the phase noise mitigation using the radio frequency (RF) pilot tone is also investigated in a 56-Gbit/s NRZ single polarization QPSK (NRZ-SP-QPSK) coherent transmission system with post-compensation of chromatic dispersion. Besides, a 56-Gbit/s NRZ-SP-QPSK coherent transmission system with CD pre-distortion is also implemented to analyze the influence of equalization enhanced phase noise in more detail.

  • 124293.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Jacobsen, G.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, J.
    Sergeyev, S.
    Mitigation of EEPN in long-haul n-PSK coherent transmission system using modified optical pilot carrier2013In: Asia Communications and Photonics Conference, ACP 2013, Optical Society of America, 2013Conference paper (Refereed)
    Abstract [en]

    We present the compensation of the equalization enhanced phase noise (EEPN) in the long-haul n-level phase shift keying (n-PSK) coherent optical transmission system, by employing a scheme of phase modulated optical pilot carrier.

  • 124294.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Jacobsen, G.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, J.
    Sergeyev, S.
    Zhang, Y.
    Analysis of carrier phase extraction methods in 112-Gbit/s NRZ-PDM-QPSK coherent transmission system2012In: 2012 Asia Communications And Photonics Conference (ACP), IEEE , 2012, p. AS1C.2-Conference paper (Refereed)
    Abstract [en]

    We present a comparative analysis on three carrier phase extraction approaches, including a one-tap normalized least mean square method, a block-average method, and a Viterbi-Viterbi method, in coherent transmission system considering equalization enhanced phase noise.

  • 124295.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Jacobsen, G.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Li, J.
    Wang, Ke
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Variable-step-size LMS adaptive filter for digital chromatic dispersion compensation in PDM-QPSK coherent transmission system2009In: 2009 International Conference on Optical Instruments and Technology: Optical Systems and Modern Optoelectronic Instruments, SPIE - International Society for Optical Engineering, 2009, p. 75062I-Conference paper (Refereed)
    Abstract [en]

    High bit rates optical communication systems pose the challenge of their tolerance to linear and nonlinear fiber impairments. Digital filters in coherent optical receivers can be used to mitigate the chromatic dispersion entirely in the optical transmission system. In this paper, the least mean square adaptive filter has been developed for chromatic equalization in a 112-Gbit/s polarization division multiplexed quadrature phase shift keying coherent optical transmission system established on the VPIphotonics simulation platform. It is found that the chromatic dispersion equalization shows a better performance when a smaller step size is used. However, the smaller step size in least mean square filter will lead to a slower iterative operation to achieve the guaranteed convergence. In order to solve this contradiction, an adaptive filter employing variable-step-size least mean square algorithm is proposed to compensate the chromatic dispersion in the 112-Gbit/s coherent communication system. The variable-step-size least mean square filter could make a compromise and optimization between the chromatic dispersion equalization performance and the algorithm converging speed. Meanwhile, the required tap number and the converged tap weights distribution of the variable-step-size least mean square filter for a certain fiber chromatic dispersion are analyzed and discussed in the investigation of the filter feature.

  • 124296.
    Xu, Tianhua
    et al.
    Univ Warwick, Coventry CV4 7AL, W Midlands, England..
    Jacobsen, Gunnar
    RISE Acreo AB, SE-16440 Stockholm, Sweden..
    Li, Jie
    RISE Acreo AB, SE-16440 Stockholm, Sweden..
    Leeson, Mark
    Univ Warwick, Coventry CV4 7AL, W Midlands, England..
    Popov, Sergei
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Dynamic physical layer equalization in optical communication networks2018In: Optoelectronics and Advanced Materials Rapid Communications, ISSN 1842-6573, E-ISSN 2065-3824, Vol. 12, no 5-6, p. 292-298Article in journal (Refereed)
    Abstract [en]

    In optical transport networks, signal lightpaths between two terminal nodes can be different due to current network conditions. Thus the transmission distance and accumulated dispersion in the lightpath cannot be predicted. Therefore, the adaptive compensation of dynamic dispersion is necessary in such networks to enable flexible routing and switching. In this paper, we present a detailed analysis on the adaptive dispersion compensation using the least-mean-square (LMS) algorithm in coherent optical communication networks. It is found that the variable-step-size LMS equalizer can achieve the same performance with a lower complexity, compared to the traditional LMS algorithm.

  • 124297.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Jacobsen, Gunnar
    Acreo AB, Electrum 236, Kista, Sweden.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Forzati, M.
    Acreo AB, Electrum 236, Kista, Sweden.
    Mårtensson, J.
    Acreo AB, Electrum 236, Kista, Sweden.
    Mussolin, M.
    University of Padova, Italy.
    Li, J.
    Acreo AB, Electrum 236, Kista, Sweden.
    Wang, Ke
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Zhang, Y.
    Tianjin University, Tianjin, China.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Frequency-domain chromatic dispersion equalization using overlap-add methods in coherent optical system2011In: Journal of optical communications, ISSN 0173-4911, E-ISSN 2191-6322, Vol. 27, no 2Article in journal (Refereed)
    Abstract [en]

    The frequency domain equalizers (FDEs) employing two types of overlap-add zero-padding (OLA-ZP) methods are applied to compensate the chromatic dispersion in a 112-Gbit/s non-return-to-zero polarization division multiplexed quadrature phase shift keying (NRZ-PDM-QPSK) coherent optical transmission system. Simulation results demonstrate that the OLA-ZP methods can achieve the same acceptable performance as the overlap-save method. The required minimum overlap (or zero-padding) in the FDE is derived, and the optimum fast Fourier transform length to minimize the computational complexity is also analyzed.

     

  • 124298.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Jacobsen, Gunnar
    Acreo AB.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Friberg, Ari
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Li, Jie
    Acreo AB.
    Zhang, Yimo
    Phase noise mitigation in coherent transmission system using a pilot carrier2011In: Optical Transmission Systems, Subsystems, and Technologies IX / [ed] Xiang Liu, SPIE - International Society for Optical Engineering, 2011Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate the phase noise elimination employing an optical pilot carrier in the high speed coherent transmission system considering the equalization enhanced phase noise (EEPN). The numerical simulations are performed in a 28-Gsymbol/s quadrature phase shift keying (QPSK) coherent system with a polarization multiplexed pilot carrier. The carrier phase estimation is implemented by the one-tap normalized least mean square (NLMS) filter and the differential phase detection, respectively. Simulation results demonstrate that the application of the optical pilot carrier is very effective for the intrinsic laser phase noise cancellation, while is less efficient for the EEPN mitigation.

  • 124299. Xu, Tianhua
    et al.
    Jacobsen, Gunnar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, J.
    Sergeyev, S.
    Friberg, Ari T.
    Liu, T.
    Zhang, Y.
    Analysis of chromatic dispersion compensation and carrier phase recovery in long-haul optical transmission system influenced by equalization enhanced phase noise2017In: Optik (Stuttgart), ISSN 0030-4026, E-ISSN 1618-1336, Vol. 138, p. 494-508Article in journal (Refereed)
    Abstract [en]

    The performance of long-haul coherent optical fiber transmission system is significantly affected by the equalization enhanced phase noise (EEPN), due to the interaction between the electronic dispersion compensation (EDC) and the laser phase noise. In this paper, we present a comprehensive study on different chromatic dispersion (CD) compensation and carrier phase recovery (CPR) approaches, in the n-level phase shift keying (n-PSK) and the n-level quadrature amplitude modulation (n-QAM) coherent optical transmission systems, considering the impacts of EEPN. Four CD compensation methods are considered: the time-domain equalization (TDE), the frequency-domain equalization (FDE), the least mean square (LMS) adaptive equalization are applied for EDC, and the dispersion compensating fiber (DCF) is employed for optical dispersion compensation (ODC). Meanwhile, three carrier phase recovery methods are also involved: a one-tap normalized least mean square (NLMS) algorithm, a block-wise average (BWA) algorithm, and a Viterbi-Viterbi (VV) algorithm. Numerical simulations have been carried out in a 28-Gbaud dual-polarization quadrature phase shift keying (DP-QPSK) coherent transmission system, and the results indicate that the origin of EEPN depends on the choice of chromatic dispersion compensation methods, and the effects of EEPN also behave moderately different in accordance to different carrier phase recovery scenarios.

  • 124300.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101). Acreo AB, Sweden.
    Jacobsen, Gunnar
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Li, J.
    Wang, Ke
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101). Acreo AB, Sweden.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Digital compensation of chromatic dispersion in 112-Gbit/s PDM-QPSK system2009In: Optical Transmission Systems, Switching, and Subsystems VII, SPIE - International Society for Optical Engineering, 2009, p. 763202-Conference paper (Refereed)
    Abstract [en]

    High bit rates optical communication systems pose the challenge of their tolerance to linear and nonlinear fiber impairments. Coherent optical receivers using digital signal processing techniques can mitigate the fiber impairments in the optical transmission system, including the chromatic dispersion equalization with digital filters. In this paper, an adaptive finite impulse response filter employing normalized least mean square algorithm is developed for compensating the chromatic dispersion in a 112-Gbit/s polarization division multiplexed quadrature phase shift keying coherent communication system, which is established in the VPI simulation platform. The principle of the adaptive normalized least mean square algorithm for signal equalization is analyzed theoretically, and at the meanwhile, the taps number and the tap weights in the adaptive finite impulse response filter for compensating a certain fiber chromatic dispersion are also investigated by numerical simulation. The chromatic dispersion compensation performance of the adaptive filter is analyzed by evaluating the behavior of the bitor-rate versus the optical signal-to-noise ratio, and the compensation results are also compared with other present digital filters.

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