37 research outputs found
Topological semimetal to insulator quantum phase transition in the Zintl compounds Ba2X(X = Si,Ge)
No full textBy first-principles calculations, we find that Ba[subscript 2]X(X=Si,Ge) hosts a topological semimetal phase with one nodal ring in the k[subscript x]=0 plane, which is protected by the glide mirror symmetry when spin-orbit coupling (SOC) is ignored. The corresponding drumheadlike surface flat band appears on the (100) surface in surface Green's function calculation. Furthermore, a topological-semimetal-to-insulator transition is found. The nodal line semimetal would evolve into a topological insulator as SOC is turned on. The topologically protected metallic surface states emerge around the [bar over]Γ point, which could be tuned into the topologically trivial insulator state by more than 3% hydrostatic strain. These results reveal a category of materials showing quantum phase transition between topological semimetal and insulator, and tunability through elastic strain engineering.National Basic Research Program of China (973 Program) (Contract 2012CB619402)Xi’an Jiaotong University. 985 ProjectNational Science Foundation (U.S.) (Grant DMR-1410636)Solid-State Solar-Thermal Energy Conversion CenterUnited States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-SC0001299/DE-FG02- 09ER46577
Investigation of magnetic interactions in topological insulators
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015.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 95-111).Topological insulators are a category of phases in condensed matter with inverted conduction and valence bands, which is protected by time reversal symmetry. As a result, the bulk keeps insulating while the surface supports an exotic high-mobility spin-polarized electronic states. Introducing magnetism into topological insulators will break the surface time reversal symmetry and alter the spin texture at the surface, and is an essential step to bring topological insulators towards the observation of new quantum states and for device applications. This thesis is a comprehensive study of magnetic interactions in topological insulators, from both experimental and theoretical perspective. Generically, there are two approaches to bring TI magnetic, the proximity effect and the conventional transitional metal ion doping. In the proximity effect, a layer of magnetic insulator is in proximally contact with a topological insulator, which forms a heterostructure and introduces magnetic exchange with the topological insulator states; while in the transitional metal ion doping, the magnetic dopants will induce magnetic order inside topological insulators. The main content and contribution of this thesis are five-fold. First and foremost, this thesis provides conclusive experimental evidence to demonstrate a long-predicted new type of magnetism, the "Van Vleck ferromagnetism" in magnetic topological insulator Vanadium doped Sb2Te3. Compared with the traditional RKKY magnetism in diluted magnetic semiconductors which needs undesired free carriers to mediate the magnetism, such magnetism has an carrier-free origin and solves the dark current issue for spintronics applications, such as quantum anomalous Hall effect. Secondly, this thesis provides conclusive experimental evidence to demonstrate the magnetic proximity effect at topological insulator / ferromagnetic insulator interface, where magnetism is penetrated into the side of topological insulator. The main obstacle for this study is the inter-diffusion of magnetic ions to topological insulator, causing false positive signal. This is conquered through experimental means which is capable to resolve the layer-dependent compositional contrast as well as magnetization simultaneously. Thirdly, this thesis discusses a theoretical proposal to show that how to resolve the particular electronic state of topological insulator participating in the proximity effect. The determination of the magnetized electronic state of topological insulator turns out to be highly difficult for conventional experiments. We utilize the indirect interlayer exchange coupling, i.e. the magnetic coupling between two magnetic layers when a topological insulator is sandwiched in between, to demonstrate the possibility to resolve electronic state in a direct manner. The fourth point, this thesis also discusses a theoretical model to describe a plasmonic device based on topological insulator / superconductor hybrid structure, which has much low energy dissipation compared with metallic plasmon device and might be used to detect Majorana Fermions, an yet-to-be-confirmed particle as building block for quantum computation. Last but not least, combining the merits of high-Curie temperature of magnetic doping and the uniformity of magnetic proximity effect, we also report an enhanced proximity effect based on proximity induced coupling in magnetically doped topological insulator hybrid heterostructure.by Mingda Li.Ph. D
Torque Production Limit of Surface Permanent Magnet Synchronous Machines and their Electromagnetic Scalability
No full textIn view of the increasing demand in torque density, this article propounds the idea of looking for an upper bound of the torque production and average shear stress for surface permanent magnet (SPM) synchronous machines. The derivation is based on the assumption of an infinite permeability of the iron core and employs the transfer relation between the normal magnetic flux density and the tangential magnetic strength. The result is written as functions of the machine's major geometries and excitation conditions. The ratio of the actual value and this upper bound may be used as a metric of measuring the usage of materials’ electromagnetic capability, or reversely as an indicator of the marginal gain of the iron core of higher relative permeability. The result is further investigated to discuss the electromagnetic scalability and the sizing law of SPM machines. Specifically, the reason for increasing volumetric torque density as the machine size goes up is revealed. The optimal remanence flux density of permanent magnets is also predicted at 1.91T , providing that the lamination saturates at 2T .Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag
Extending Winding Function Theory to Incorporate Secondary Effects in the Design of Induction Machines and Drives
No full textHigh-performance electric drive applications necessitate a high fidelity model to predict the terminal characteristics of machines in the design stage to fulfill a system-level evaluation together with the converters. This article interprets winding function theory (WFT) from the field perspective and incorporates secondary effects, such as slotting and iron nonlinearity into it to accurately predict the main flux linkage in induction machines. The method is centered on resolving the magnetic scalar potential on the two sides of the air gap and computes the flux linkage via a winding function. Its performance is benchmarked against 2-D finite-element analysis (FEA) and the state-of-the-art magnetic equivalent circuit (MEC) method. Flux linkage and torque results indicate that the relative error is within 3.1% even in a highly saturated region when comparing to FEA, while MEC using the same circuit network may present a 20% error.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag
Visualized analysis of research hotspots and evolution trends in the field of motivation in physical activity
No full textThe open access publication is available at https://doi.org/10.1016/j.ajsep.2025.01.002Physical activity (PA) is a green and effective way to maintain health. Research in the field of motivation in PA is always an important research topic for researchers and policymakers in maintaining public health, but few studies focus on the development of motivation in PA research. Summarize the research strengths, hotspots, and stages of scientific evolution in the field of motivation in PA by performing visualization analysis which used CiteSpace software on 2375 publications including from January 1st, 1980, to January 31st, 2024, in the Web of Science Core Collection (WOSCC). The findings are as follows: (1) Over the past thirty years, the field has developed rapidly, with current characteristics aligning with the third stage of the four-stage model of scientific evolution. (2) Core countries and core institutions have been formed, with the most influential country being the United Kingdom, and the most influential institution being Brown University. (3) The research hotspot focuses on intervention research in the field of motivation in PA under self-determination theory (SDT). This study provides researchers with an overview of the development in the field of motivation in PA research. It offers valuable information to researchers for identifying potential collaborators (institutions) and better positioning their research directions
Investigating the effect of non-stationary transports in UTB MOSFETs with elevated and recessed source/drain by using full band Monte Carlo simulation method
No full textThis paper presents on-state characteristics of two types of UTB FD MOSFETs simulated by Monte Carlo method. The two devices under investigation have elevated and recessed source/drain respectively. The comparison of non-stationary transports effect is made between the two devices. Different non-stationary transports effect in the two devices is the cause of different on state characteristics. Transit time and intrinsic capacitance of these devices, which can also affected by non-stationary transports effect, are further presented. ?2010 IEEE.EI
Grinding Force and Surface Formation Mechanisms of 17CrNi2MoVNb Alloy When Grinding with CBN and Alumina Wheels
No full textThe 17CrNi2MoVNb alloy is widely used for manufacturing heavy-duty gears in vehicles’ transmission systems, where grinding is a significant process affecting gears’ working performance and service life. This work comprehensively analyzed the grinding force, surface morphology, and surface roughness when grinding 17CrNi2MoVNb alloy using alumina and CBN grinding wheels. Results showed that the maximum normal grinding force from the CBN wheel was only ~67% of the one from the alumina wheel. Due to the small size and limited cutting depth of CBN grains, the grinding force increased by about 20% when the grinding depth increased from 0.02 to 0.03 mm for CBN grinding wheels. Surface defects, including cavities and material tearing, were mainly found on the ground surface when using an alumina grinding wheel. The surface roughness Ra recorded from the CBN grinding wheel mainly ranged from 0.263 to 0.410 μm, accounting for less than 40% of the one from the alumina grinding wheel. The information from this work could provide benchmark data and references for optimizing grinding tools and parameters when manufacturing gears in the vehicle industry
Predicting college students’ exercise dependence: a machine learning approach
No full textExercise dependence behavior among college students is a critical issue in sports psychology that deserve closer examination, and artificial intelligence offer a useful ways to explore its mechanisms and predicting associated risks. In this study, data were collected from 2,745 college students using three standardized questionnaires, covering (i) exercise dependence behavior, (ii) psychological characteristics (e.g., exercise identity, weight biases), and (iii) basic demographic information. We used four widely used machine learning algorithms: logistic regression, random forest, extreme gradient boosting (XGBoost), and multilayer perceptron, and their outputs were further integrated through an ensemble learning techniques to further enhance the robustness and predictive power of the models. The stacking ensemble model achieved a mean AUC of 0.96 in identifying exercise dependence risk among college students, demonstrating that integrating multiple machine learning approaches can yield robust and highly accurate risk prediction in this setting. Among the variables, the most influential predictors of exercise dependence behavior included prolonging exercise to obtain the desired effect, allocating most leisure time on exercise, experiencing difficulty in reducing exercise frequency, and actual exercise time longer than originally planned. These findings uncovers the key psychological and behavioral mechanisms underlying in exercise dependence among college students and show that artificial intelligence methods can be effectively applied to support risk monitoring in sport and psychological health contexts
Degradation Effects of Gate Oxide and STI Charge in SOI LDMOS
No full textIn this paper, the effects of oxide charges at different locations on on-state and off-state performance of SOI LDMOS devices are investigated through simulation. According to the results, the channel end region and channel side of STI have great effect on device on-state performance while the drain side of STI greatly affect off-state performance.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000304037500137&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Engineering, Electrical & ElectronicPhysics, AppliedEICPCI-S(ISTP)
