• Title/Summary/Keyword: low-loss

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Effect of Outdated Channel Estimates on Multiple Antennas Multiple Relaying Networks

  • Wang, Lei;Cai, Yueming;Yang, Weiwei;Yan, Wei;Song, Jialei
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.9 no.5
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    • pp.1682-1701
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    • 2015
  • In this paper, we propose an intergraded unified imperfect CSI model and investigate the joined effects of feedback delay and channel estimation errors (CEE) for two-hop relaying systems with transmit beamforming and relay selection. We derived closed-form expressions for important performance measures including the exact analysis and lower bounds of outage probability as well as error performance. The ergodic capacity is also included with closed-form results. Furthermore, diversity and coding gains based on the asymptotic analysis at high SNRs are also presented, which are simple and concise and provide new analytical insights into the corresponding power allocation scheme. The analysis indicates that delay effect results in the coding gain loss and the diversity order loss, while CEE will merely cause the coding gain loss. Numerical results verify the theoretical analysis and illustrate the system is more sensitive to transmit beamforming delay compared with relay selection delay and also verify the superiority of optimum power allocation. We further investigate the outage loss due to the CEE and feedback delays, which indicates that the effect of the CEE is more influential at low-to-medium SNR, and then it will hand over the dominate role to the feedback delay.

Electron Microburst Generation by Wave Particle Interaction

  • Lee, Jae-Jin;Hwang, Jung-A;Parks, George K.;Min, Kyoung-Wook;Lee, En-Sang
    • Bulletin of the Korean Space Science Society
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    • 2009.10a
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    • pp.43.2-43.2
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    • 2009
  • Electron microbursts are the intense electron precipitation which durations are less than one second. We measured the energy spectra of the microbursts from 170 keV to 340 keV with solid state detectors aboard the low-altitude (680km), polar-orbiting Korean STSAT-1 (Science and Technology SATellite). The data showed that the loss cone at these energies is empty except when microbursts abruptly appear and fill the loss cone in less than 50 msec. This fast loss cone filling requires pitch angle diffusion coefficients larger than ~ 10-2rad2/sec, while ~10-5 rad2/sec was proposed by a wave particle interaction theory. We recalculated the diffusion coefficient, and reviewed of electron microburst generation mechanism with test particle simulations. This simulation successfully explained how chorus waves make pitch angle diffusion within such short period. From considering the resonance condition between wave and electrons, we also showed ~ 100 keV electrons could be easily aligned to the magnetic field, while ~ 1MeV electrons filled loss cone partially. This consideration explained why precipitating microbursts have lower e-folding energy than that of quasi-trapped electrons, and supports the theory that relativistic electron microbursts that have been observed by satellite in-situ measurement have same origin with ~100 keV electron microbursts that have been usually observed by balloon experiments.

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Abrasion of abutment screw coated with TiN

  • Jung, Seok-Won;Son, Mee-Kyoung;Chung, Chae-Heon;Kim, Hee-Jung
    • The Journal of Advanced Prosthodontics
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    • v.1 no.2
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    • pp.102-106
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    • 2009
  • STATEMENT OF PROBLEM. Screw loosening has been a common complication and still reported frequently. PURPOSE. The purpose of this study was to evaluate abrasion of the implant fixture and TiN coated abutment screw after repeated delivery and removal with universal measuring microscope. MATERIAL AND METHODS. Implant systems used for this study were Osstem and 3i. Seven pairs of implant fixtures, abutments and abutment screws for each system were selected and all the fixtures were perpendicularly mounted in liquid unsaturated poly-esther with dental surveyor. After 20 times of repeated closing and opening test, the evaluation for the change of inner surface of implant and TiN-coated abutment screw, and weight loss were measured. Mann-Whitney test with SPSS statistical software for Window was applied to analyze the measurement of weight loss. RESULTS. TiN-coated abutment screws of Osstem and 3i showed lesser loss of weight than non-coated those of Osstem and 3i (P < .05, Mann-Whitney test). CONCLUSION. Conclusively, TiN coating of abutment screw showed better resistance to abrasion than titanium abutment screw. It was concluded that TiN coating of abutment screw would reduce the loss of preload with good abrasion resistance and low coefficient of friction, and help to maintain screw joint stability.

Evaluation of Hydraulic Conductivity of Bentonite Filter Cake Using Modified Fluid Loss Test

  • Nguyen, The Bao;Lee, Chul-Ho;Yang, Jung-Hun;Choi, Hang-Seok
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.10a
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    • pp.498-507
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    • 2008
  • The mixture of bentonite powder and water is generally used to maintain the stability of excavation surface during the construction of vertical cutoff walls. The filter cake on the sidewall surface is the result of filtration of slurry into the adjacent soil formation. The filter cake is believed to have a very low hydraulic conductivity compared to that of the cutoff wall. This paper evaluates hydraulic conductivities of bentonite filter cakes set up with three types of bentonites under various pressure levels. A modified fluid loss test was employed in this experiment. Theory of filtration process was reviewed to explain the procedure in the present experiment. Hydraulic conductivity of the filter cakes with consideration of the filter medium resistance was evaluated. The results of the experiment with two calculation methods and discussion are presented to show the efficiency of the modified fluid loss test.

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Evaluation of Hydraulic Conductivity of Bentonite Filter Cake Using Modified Fluid Loss Test

  • Nguyen, The Bao;Lee, Chul-Ho;Yang, Jung-Hun;Choi, Hang-Seok
    • Proceedings of the Korean Geotechical Society Conference
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    • 2008.10a
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    • pp.1502-1511
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    • 2008
  • The mixture of bentonite powder and water is generally used to maintain the stability of excavation surface during the construction of vertical cutoff walls. The filter cake on the sidewall surface is the result of filtration of slurry into the adjacent soil formation. The filter cake is believed to have a very low hydraulic conductivity compared to that of the cutoff wall. This paper evaluates hydraulic conductivities of bentonite filter cakes set up with three types of bentonites under various pressure levels. A modified fluid loss test was employed in this experiment. Theory of filtration process was reviewed to explain the procedure in the present experiment. Hydraulic conductivity of the filter cakes with consideration of the filter medium resistance was evaluated. The results of the experiment with two calculation methods and discussion are presented to show the efficiency of the modified fluid loss test.

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Fabrication and Magnetic Properties of A New Fe-based Amorphous Compound Powder Cores

  • Xiangyue, Wang;Feng, Guo;Caowei, Lu;Zhichao, Lu;Deren, Li;Shaoxiong, Zhou
    • Journal of Magnetics
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    • v.16 no.3
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    • pp.318-321
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    • 2011
  • A new Fe-based amorphous compound powder was prepared from Fe-Si-B amorphous powder by crushing amorphous ribbons as the first magnetic component and Fe-Cr-Mo metallic glassy powder by water atomization as the second magnetic component. Subsequently by adding organic and inorganic binders to the compound powder and cold pressing, the new Fe-based amorphous compound powder cores were fabricated. This new Fe-based amorphous compound powder cores combine the superior DC-Bias properties and the excellent core loss. The core loss of 500 kW/$m^3$ at $B_m$ = 0.1T and f = 100 kHz was obtained When the mass ratio of FeSiB/FeCrMo equals 3:2, and meanwhile the DC-bias properties of the new Fe-based amorphous compound powder cores just decreased by 10% compared with that of the FeSiB powder cores. In addition, with the increasing of the content of the FeCrMo metallic glassy powder, the core loss tends to decrease.

Influence of Different Frequency Harmonic Generated by Rectifier on High-speed Permanent Magnet Generator

  • Qiu, Hongbo;Wei, Yanqi;Yang, Cunxiang;Fan, Xiaobin
    • Journal of Electrical Engineering and Technology
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    • v.13 no.5
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    • pp.1956-1964
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    • 2018
  • Since the stator winding of High-Speed Permanent Magnet Generator (HSPMG) has few winding turns and low inductance value, it is more prone to be influenced by harmonic current. Moreover, the operation efficiency and the torque stability of HSPMG will be greatly influenced by harmonic current. Taking a 117 kW, 60 000 rpm HSPMG as an example, in order to analyze the effects of harmonic current on HSPMG in this paper, the 2-D finite element electromagnetic field model of the generator was established and the correctness of the model was verified by testing the generator prototype. Based on the model, the losses and torque of the generator under different frequency harmonic current were studied. The change rules of the losses and torque were found out. Based on the analysis of the influence of the harmonic phase angle on torque ripple, it is found that the torque ripple could be weakened through changing the harmonic phase angle. Through the analysis of eddy current density in rotor, the change mechanism of the rotor eddy current loss was revealed. These conclusions can contribute to reduce harmonic loss, prevent demagnetization fault and optimize torque ripple of HSPMG used in distributed power supply system.

Device Suitability Analysis by Comparing Performance of SiC MOSFET and GaN Transistor in Induction Heating System (유도 가열 시스템에서 SiC MOSFET과 GaN Transistor의 성능 비교를 통한 소자 적합성 분석)

  • Cha, Kwang-Hyung;Ju, Chang-Tae;Min, Sung-Soo;Kim, Rae-Young
    • The Transactions of the Korean Institute of Power Electronics
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    • v.25 no.3
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    • pp.204-212
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    • 2020
  • In this study, device suitability analysis is performed by comparing the performance of SiC MOSFET and GaN Transistor, which are WBG power semiconductor devices in the induction heating (IH) system. WBG devices have the advantages of low conduction resistance, switching losses, and fast switching due to their excellent physical properties, which can achieve high output power and efficiency in IH systems. In this study, SiC and GaN are applied to a general half-bridge series resonant converter topology to compare the conduction loss, switching loss, reverse conduction loss, and thermal performance of the device in consideration of device characteristics and circuit conditions. On this basis, device suitability in the IH system is analyzed. A half-bridge series resonant converter prototype using the SiC and GaN of a 650-V rating is constructed to verify device suitability through performance comparison and verified through an experimental comparison of power loss and thermal performance.

Depression in family caregivers of elderly people with dementia

  • LVAREZ, Yanelys Taset A;TORNES, Alisa Natividad Delgado;LEON, Diurkis Yarenis Madrigal
    • The Korean Journal of Food & Health Convergence
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    • v.6 no.3
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    • pp.31-41
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    • 2020
  • The caregivers of elderly people with dementia suffer an affectation in the psychological and social order due to the low probability of total rehabilitation of the elderly and the progressive course of this pathology. In the municipality of Guisa, Granma Province there is a health problem regarding this problem since family caregivers of the elderly with dementia constantly go to the Psychology and Psychiatry consultations, in search of specialized help because they report feeling depressed. For this reason, this research was carried out with the objective of determining the main manifestations of depression in these caregivers. The results emanating from the triangulation of methods (scientific observation) and techniques (questionnaire, interviews and inventory Beck), employees at three stages of work where it was found that the main manifestations of depression of these caregivers are: poss of interest or the ability to enjoy activities that were previously pleasurable, loss of emotional reactivity to pleasant environmental events and circumstances, sleep disturbances, marked loss of appetite, weight loss, irritability, muscular tension, feelings of sadness unmotivated that produces discomfort and sufferings, ansiety, entities of handicap, blame, loss of self-confidence and feelings of inferiority, gloomy perspective of the future.

A Control Method to Improve Power Conversion Efficiency of Three-level NPC-Based Dual Active Bridge Converter (Three-Level NPC-Based Dual Active Bridge Converter의 도통손실 절감을 위한 새로운 스위칭 방법)

  • Lee, Jun-Young;Choi, Hyun-Jun;Kim, Ju-Yong;Jun, Jee-Hoon
    • The Transactions of the Korean Institute of Power Electronics
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    • v.22 no.2
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    • pp.150-158
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    • 2017
  • This study proposes a new pulse-width modulation switching pattern for the low conduction loss of a three-level neutral point clamped (NPC)-based dual-active bridge (DAB) converter. The operational principle for a bidirectional power conversion is a phase-shift modulation. The conventional switching method of the three-level NPC-based DAB converter shows a symmetric switching pattern. This method has a disadvantage of high root-mean-square (RMS) value of the coupling inductor current, which leads to high conduction loss. The proposed switching method shows an asymmetrical pattern, which can reduce the RMS value of the inductor current with lower conduction loss than that of the conventional method. The performance of the proposed asymmetrical switching method is theoretically analyzed and practically verified using simulation and experiment.