49 research outputs found
In situ power-loss estimation of IGBT modules
No full textA fault detection and prediction method for insulated-gate bipolar transistors (IGBTs) has been improved over the past decades to reduce system downtime. In situ lifetime estimation of IGBT modules has been challenging due to a number of requirements: the necessity to operate at high voltage in the switching environment and the measurement precision of the gate-threshold voltage or collector-to-emitter voltage. This thesis presents a wear-fatigue estimation framework that consists of collector-to-emitter measurement, power loss calculation, and thermal lifetime prediction model. The measurement circuit enables the estimation of power loss across a variety of IGBT modules with minimum impact on system reliability.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2023-05-01The student, Qichen Jin, accepted the attached license on 2021-04-29 at 10:53.The student, Qichen Jin, submitted this Thesis for approval on 2021-04-29 at 10:58.This Thesis was approved for publication on 2021-04-29 at 15:19.DSpace SAF Submission Ingestion Package generated from Vireo submission #16596 on 2021-09-16 at 20:14:39Made available in DSpace on 2021-09-17T04:06:56Z (GMT). No. of bitstreams: 2
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Previous issue date: 2021-04-29Embargo set by: Seth Robbins for item 118716
Lift date: 2023-09-17T04:07:01Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemAuthor requested closed access (OA after 2yrs) in Vireo ETD systemLimite
Ab initio study of electron transport in lead telluride
No full textThesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 91-97).Last few years have witnessed significant enhancement of thermoelectric figure of merit of lead telluride (PbTe) via nanostructures. Despite the experimental progress, current understanding of the electron transport in PbTe is based on either band structure simulated using first-principles in combination with constant relaxation time approximation or empirical models, both requiring adjustable parameters obtained by fitting experimental data. This thesis aims to compute thermoelectric properties of PbTe all from first-principles. We start by discussing the formalism based on Boltzmann transport equation to calculate the electron transport properties in PbTe using first principles and identify the importance to calculate electron-phonon interaction accurately. We then discuss the challenges in studying electron-phonon interaction in semiconductors using first-principles and introduce electron-phonon Wannier interpolation which allows us to calculate the strength of electron-phonon coupling on a very fine mesh. In polar materials like PbTe, the Fröhlich interaction due to long-range dipole field of longitudinal optical phonons contributes to the electron-phonon coupling as well. As the long-range nature of the dipole field makes the standard Wannier interpolation fail, we have discussed the detailed procedures for correction. Next, we study the screening effect of free carriers on electron transport by modulating the polar scattering. These considerations enabled us to report parameter-free first-principles calculation of electron and phonon transport in PbTe, including mode-by-mode electron-phonon scattering, leading to detailed information on electron mean free paths and the cumulative contributions by electrons and phonons with different mean free paths to thermoelectric transport properties in PbTe. Such information will help to rationalize the use and optimization of nanostructures to achieve high thermoelectric figure of merit.by Qichen Song.S.M
Emerg Infect Dis
No full textWe identified a novel ceftazidime/avibactam resistance mechanism in sequence type 11 Klebsiella pneumoniae carbapenemase 2-producing K. pneumoniae. Plasmid recombination and chromosomal integration formed a novel virulence plasmid and provided an additional promoter for bla|, leading to bla| overexpression and ceftazidime/avibactam resistance. Genetic rearrangement contributed to convergence of hypervirulence and ceftazidime/avibactam resistance
Lightweight Dual-Stream Human Behavior Inference Network Based on Multi-Layer Perceptron
No full textThe recognition of human behaviors in videos is a critical domain within human activity analysis. However, the current architectures and mechanisms of human behavior recognition methods dominated by CNN, GCNs, and LSTM are unduly complex resulting in high computational complexity of the models. Furthermore, these methods often exhibit poor robustness when it comes to recognizing behaviors across different environmental conditions and video angles. To address these challenges, this paper introduces a lightweight human skeleton interaction behavior inference network based on a multi-layer perceptron. This network leverages human skeleton information and utilizes minimal prior knowledge to infer limb behavior encoding. To reduce computational complexity, videos are divided into smaller segments, serving as the minimum computation units. This approach integrates three essential types of information: independent global information about individual postures, local interaction information regarding different limb parts, and temporal distance information. These three types of information are coupled through LSTM, incorporating temporal changes into network for recognition and classification. In comparison to previous similar methods, our proposed method is more lightweight, exhibits stronger robustness against interference and enables behavior recognition across different environments and perspectives
Enhanced photocatalytic activity of Fe-doped TiO2 coated on N-doped activated carbon composites for photocatalytic degradation of dyeing wastewater
No full text
Study on the high precision frequency measurement algorithm in the mine intelligent power supply system
No full textTo solve the problem of the error of frequency measurement algorithm with time-varying frequency in mine power supply system, an improved software zero-crossing algorithm is proposed.The relationship among the phase angle, the time and the frequency of the voltage of the system is established.The relation formula between the real-time frequency and the period of zero-crossing point is derived when rate of frequency variation is not zero according to the relationship between two adjacent with the direction of the zero-crossing phase difference of 2π.The exact calculation formula of the period is obtained by using the Newton three interpolation polynomial, the Newton iteration method and the Qin Jiushao algorithm.Hence, the frequency and rate of frequency variation can be obtained.A variety of situations , including signals without harmonics, signals with harmonics and random noise, as well as the frequency rapid decline process in system failure, are simulated using MATLAB, The simulation results show that the algorithm of this paper can accurately measure the real-time frequency of the system and rate of frequency variation in above situations, and this method is superior to conventional zero-crossing algorithm in measurement accuracy, instantaneity and computation.This algorithm is suitable for application of protection, control and monitoring devices and automation equipment in mine intelligent power supply system
Design and analysis on trusted network equipment access authentication protocol
No full textabstract: Cloud security is a system engineering problem. A common approach to address the problem is to adapt existing Trusted Network Connection (TNC) framework in the cloud environment, which can be used to assess and verify end clients’ system state. However, TNC cannot be applied to network equipment attached to the cloud computing environment directly. To allow the network devices to access the trusted network devices safely and reliably, we first developed a Trusted Network Equipment Access Authentication Protocol (TNEAAP). We use the BAN logic system to prove that TNEAAP is secure and credible. We then configure the protocol in an attack detection mode to experimentally show that the protocol can withstand attacks in the real network. Experiment results show that all the nine goals that decide the protocol’s security have been achieved.NOTICE: this is the author's version of a work that was accepted for publication in SIMULATION MODELLING PRACTICE AND THEORY. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in SIMULATION MODELLING PRACTICE AND THEORY, 51, 157-169. DOI: 10.1016/j.simpat.2014.10.01
Fabrication of Collagen Gel Hollow Fibers by Covalent Cross-Linking for Construction of Bioengineering Renal Tubules
No full textComprehensive Evaluation of Functional Diversity of Urban Commercial Complexes Based on Dissipative Structure Theory and Synergy Theory: A Case of SM City Plaza in Xiamen, China
No full textUrban commercial complex is an architectural form formed in the high-density urban building environment based on the diversified concentration of human consumption behavior and the composite utilization of space. It can effectively cope with the problem of tight land resources and insufficient development capacity in urban centers and promote sustainable urban development. Additionally, the diversity of functions is the key to ensure its healthy operation. Based on the homogenization phenomenon of commercial complex development in some big cities in China in recent years, this study applies dissipative structure theory and synergistic effect theory to the study of functional diversity system of urban commercial complexes, and proposes a Shannon–Weiner biodiversity index model and calculation indexes based on the functional diversity measurement model. At the same time, correlation analysis and comparative analysis were conducted between the measurement results of spatial vitality and the calculation results of the diversity model to verify the scientificity and rationality of the proposed model. Finally, the SM City Plaza commercial complex in Xiamen was selected as a representative research object to measure the functional diversity of its weekdays and holidays and the coupling relationship between functional diversity and changes in spatial vitality. The calculation results show that although the comprehensive index of functional diversity of SM commercial complex is in a dynamic state of change, the overall level is high. The reasonable proportion of the six functional formats shows a high level of diversity, which effectively promotes the generation of commercial vitality and enhances the comprehensive benefits of the commercial complex; the change trends of functional diversity in time and space dimensions are in line with the actual situation, indicating that the proposed model has certain scientific and application values. On the basis of the completed empirical work, the scope of application and limitations of the calculation model and evaluation method, as well as the optimization of the index system are further pointed out
