1,009 research outputs found
The DV-Xα molecular-orbital calculation method
No full textThis multi-author contributed volume contains chapters featuring the development of the DV-Xα method and its application to a variety of problems in Materials Science and Spectroscopy written by leaders of the respective fields. The volume contains a Foreword written by the Chairs of Japanese and Korea DV-X alpha Societies. This book is aimed at individuals working in Quantum Chemistry
Relationship of cognitive function in patients with schizophrenia in remission to disability: a cross-sectional study in an Indian sample
No full textBackground: Cognitive deficits in various domains have been consistently replicated in patients with schizophrenia. Most studies looking at the relationship between cognitive dysfunction and functional disability are from developed countries. Studies from developing countries are few. The purpose of the present study was to compare the neurocognitive function in patients with schizophrenia who were in remission with that of normal controls and to determine if there is a relationship between measures of cognition and functional disability.
<p/>Methods: This study was conducted in the Psychiatric Unit of a General Hospital in Mumbai, India. Cognitive function in 25 patients with schizophrenia in remission was compared to 25 normal controls. Remission was confirmed using the brief psychiatric rating scale (BPRS) and scale for the assessment of negative symptoms (SANS). Subjects were administered a battery of cognitive tests covering aspects of memory, executive function and attention. The results obtained were compared between the groups. Correlation analysis was used to look for relationship between illness factors, cognitive function and disability measured using the Indian disability evaluation and assessment scale.
<p/>Results: Patients with schizophrenia showed significant deficits on tests of attention, concentration, verbal and visual memory and tests of frontal lobe/executive function. They fared worse on almost all the tests administered compared to normal controls. No relationship was found between age, duration of illness, number of years of education and cognitive function. In addition, we did not find a statistically significant relationship between cognitive function and scores on the disability scale.
<p/>Conclusion: The data suggests that persistent cognitive deficits are seen in patients with schizophrenia under remission. The cognitive deficits were not associated with symptomatology and functional disability. It is possible that various factors such as employment and family support reduce disability due to schizophrenia in developing countries like India. Further studies from developing countries are required to explore the relationship between cognitive deficits, functional outcome and the role of socio-cultural variables as protective factors
The Impact of a Brief Intervention on Medical Students\u27 Readiness to Screen for DV - Changes in Decisional Balance and Self-Efficacy
No full textIntroduction: Domestic violence (DV) affects millions of Americans each year. Yet, there is a dearth of theory-based DV curricula, resulting in physicians unprepared to screen for DV. This study utilized a survey based on constructs from the Transtheoretical Model to assess the readiness of first- and second-year medical students to screen for DV. Information from this survey will be used to help institutionalize DV education into the medical curriculum. [See PDF for complete abstract
The Improvement Based on the DV-Hop Localization Algorithm for Wireless Sensor Networks
No full textAs the problems of lower localization accuracy appeared in the traditional DV-Hop algorithm，the
author analyzed three main factors that influence the localization accuracy of original DV-Hop algorithm which
started from the calculation of the average jump distance in algorithm and the calculation of node coordinates. The
author then proposed the calculation method of average jump distance based on the weighted correction of the ＲSSI
( Ｒeceive Signal Strength Indicator ) and the calculation method of unknown node coordinates based on the
correction of the total least squares ( TLS) . The simulation result shows that compared to the traditional DV-Hop
algorithm，the accuracy of the improved algorithm increased by about 30% in distance measurement as well as rose
approximately by 35% in relative localization precision
DV kagaishiya rinsho: Risk assessment [Domestic violence offenders intervention approach: Risk assessment] [In press]
No full textQuantitative IC-DV diagnostics
No full textThis MATLAB app is for quantitative diagnostics of degradation in lithium batteries. From the initial discharge curve and post-aged discharge curve, it calculates 1) loss of lithium inventory (LLI), 2) loss of active materials (LAM) in anode during lithiation, 3) LAM in anode during delithiation, 4) LAM in cathode during lithiation and 5) LAM in cathode during delithiation. To use the app, first run the peak locator app to identify peak positions and then input the peak positions in the IC-DV app. Our journal article manuscript can be downloaded here: http://hdl.handle.net/10044/1/92598Contact UsFor code inquiry: [email protected]; [email protected] author for the journal article and Principle Investigator of the project: [email protected] DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV
Evaluation of turn-off dV/dt controllability and switching characteristics of 1.2 kV GaN polarisation superjunction heterostructure field-effect transistors
No full textJapanese Journal of Applied Physics
The Japan Society of Applied Physics, find out more
REGULAR PAPER • THE FOLLOWING ARTICLE ISOPEN ACCESS
Evaluation of turn-off dV/dt controllability and switching characteristics of 1.2 kV GaN polarisation superjunction heterostructure field-effect transistors
Alireza Sheikhan1, Sankara Narayanan Ekkanath Madathil1, Hiroji Kawai2, Shuichi Yagi2 and Hironobu Narui2
Published 5 July 2023 • © 2023 The Author(s). Published on behalf of The Japan Society of Applied Physics by IOP Publishing Ltd
Japanese Journal of Applied Physics, Volume 62, Number 6
Citation Alireza Sheikhan et al 2023 Jpn. J. Appl. Phys. 62 064502
DOI 10.35848/1347-4065/acd975
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1 Department of Electronic and Electrical Engineering, The University of Sheffield, Sheffield, United Kingdom
2 Powdec K.K. Oyama, Tochigi, Japan
ORCID iDs
Alireza Sheikhan https://orcid.org/0000-0002-2207-1593
Dates
Received 16 April 2023
Revised 18 May 2023
Accepted 26 May 2023
Published 5 July 2023
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Abstract
Gallium nitride (GaN) devices inherently offer many advantages over silicon power devices, including a higher operating frequency, lower on-state resistance and higher operating temperature capabilities, which can enable higher power density and more efficient power electronics. Turn-off dV/dt controllability plays a key role in determining common-mode voltage in electrical drives and traction inverter applications. The fast-switching edges of GaN can introduce challenges such as electromagnetic interference, premature insulation failure and high overshoot voltages. In this paper, the device working principle, characteristics and dV/dt controllability of 1.2 kV GaN polarisation superjunction (PSJ) heterostructure FETs (HFETs) are presented. The effect of gate driving parameters and load conditions on turn-off dV/dt are investigated. It is shown that in PSJ HFETs the dV/dt can be effectively controlled to as low as 1 kV μs−1 by controlling the gate, with a minimum increase in switching losses. These results are highly encouraging for the application of the devices in motor drives
Modeling and Detection of Stator Winding Insulation Degradation in VSI-fed Electric Machines Under High dv/dt
No full textNowadays, in many advanced applications, for example electric vehicles and aircrafts, electric motors are being fed by voltage source inverters (VSIs). These inverters generally utilize fast-switching power electronics devices to provide the modulated pulse voltages for motor operation. Motor’s winding insulation undergoes additional electrical stress due to high voltage slew rate (dv/dt) resulted from the use of VSI, which may cause accelerated insulation degradation. To investigate and quantify this electrical stress, various modeling techniques have been proposed over the years with a goal to optimize the motor stator design for safer and more reliable operation. In this thesis, various winding insulation modeling techniques are investigated, in which a simple case study along with comparative analysis is performed to analyze the electrical stress for different dv/dt levels. Based on this investigation, finite element (FE) based approach is selected for detailed stator winding insulation modeling, parameter determination and analysis.
Degradation of winding insulation is inevitable due to various internal and external factors. Therefore, monitoring of the insulation condition becomes necessary to ensure a safe and reliable operation of the VSI-fed electric machines. Detecting degradation in insulation in an early stage can prevent major failure in the machine and the drive system. To this end, an online insulation monitoring technique is required. Based on the existing literature, the high frequency transient current could be a good indicator for online insulation monitoring. In this thesis, how winding insulation degradation affects the machine transient current is investigated. To do so, complex random wound stator winding is modeled at first using the FE based approach, in which detailed arrangement of each wire inside the stator slot and different insulation layers are considered. Thereafter, insulation degradations of various types and severity are emulated within the FE based model, including the turn to ground (TG) degradations and turn to turn (TT) degradations. With the emulated winding insulation degradations, the effectiveness of the detection techniques is investigated. In this work, a new insulation condition detection technique based on current response and wavelet packet decomposition (WPD) is proposed, which has the capability to determine the overall state of health (SOH) of insulation and classify types of insulation degradation. Therefore, the stator winding insulation is modeled and the SOH indicator for insulation degradation detection is also developed through this thesis research
Study and Development of Multilevel Inverter Drive for e-Transportation
No full textDue to increasing demand for high power and efficiency, low operating cost, and most importantly reduced air pollution, mobility is changing drastically, and great attention is focused on the electrification of transportation. Hence, power electronics and electric machines are needed to be much more reliable, efficient, compact, quieter, and have high power density. To accomplish increasing high power demand, the electric vehicles (EV) consisting of an electric powertrain will need very high power and medium voltage drives. It can be realized either by implementing traditional converter topologies with conventional semiconductor technology or by developing new multilevel topologies with lower voltage semiconductor devices. The conventional semiconductor devices have limitations on the rating of the devices when employed in the conventional power converters for high power applications, except when they are operated in the parallel mode to meet the high power requirement, which increases complexity. While new multilevel topologies allow the use of easily available lower voltage semiconductor devices to reach high power demand. Traditionally a 2-level inverter (TLI) is used in medium voltage drives but suffers from many disadvantages such as large dv/dt in the phase voltages and causes electromagnetic interference (EMI) and increased stress on the motor winding insulation, higher blocking voltage across the switches, lower switching frequency needs to be used to reduce the switching losses, poor harmonic performance. Thus, multilevel inverters (MLI) have become preferred alternatives in high and medium power applications since it offers quasi-sinusoidal phase voltage, low total harmonic distortion (THD), reduced torque ripple, reduced dv/dt in the phase voltage, reduced EMI. Among multilevel topologies, Cascaded H-Bridge provides an attractive solution with numerous advantages in terms of high efficiency and modularity. It appears to be the most appropriate for an electric vehicle (EV) application as on-vehicle low voltage battery modules can be arranged in such a way that each H-bridge has its own dc source. In this thesis, a comparative study of electric powertrain between TLI and MLI (different levels like 5, 7, and 9) considering the factors like torque ripple, THD and switching losses is presented. The research study presents a two-fold solution for developing a prototype of an electric powertrain. Firstly, it discusses the trade-offs to decide the best suitable number of level and then validates the same with the simulation and experimental studies by using field-oriented control method with PI controller for the speed control of permanent magnet synchronous motor (PMSM). PMSM is a widely accepted machine due to its cardinal features like high power density, low inertia, high efficiency, less maintenance and reliability. But, it is also vulnerable to variations in the motor parameters and external disturbance. Thus, higher order controller called super twisting sliding mode (STSM) controller design is proposed to track the desired rotor velocity for PMSM fed with the nine-level inverter for critical applications like full electric aircraft. The selected controller maintains the advantages of first-order sliding mode control and removes the chattering phenomenon; MLI further improves the drive performance. Simulation and experimental studies show the efficacy of the proposed PMSM drive. The proposed controller is compared with the conventional PI controller which proves the superiority of the STSM controller. The bidirectional DC-DC converter between the battery module and the inverter is also simulated in order to keep the dc link voltage constant. In the boost mode, the motor is fed by the battery, while in the buck mode, the power flows in reverse and the braking energy is exploited for charging the battery. All the works are experimentally implemented in real-time using DSP TMS320F28379D and FPGA cyclone V controllers
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