检索结果-南通市图书馆

Novel high torque bearingless two-sided rotary ultrasonic motor

在线全文

学校读者我要写书评

暂无评论

Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2007年第5期8卷 786-792页

作者： LI Xia CHEN Wei-shan XIE Tao LIU Jun-kao Department of Mechatronics Engineering Harbin Institute of Technology Harbin 150001 China

Applications are limited at present because the currently available ultrasonic motors (USMs) do not provide suffi-ciently high torque and power. The conventional travelling-wave USM needs the bearing to support, which required lubricant. To solve the above problem, a bearingless travelling-wave USM is designed. First, a novel structure of the two-sided USM consisting of a two-sided teeth stator and two disk-type rotors is designed. And the excitation principle of the two-sided travelling-wave USM is analyzed. Then, using ANSYS software, we set up the model of the stator to predict the excitation frequency and modal response of the stator. The shape of the vibration mode was obtained. Last, the load characteristics of the USM are measured using ex-perimental method. The maximum stall torque and the no-load speed were obtained. The results showed that the characteristics of the two-sided USM are better than those of the conventional one-sided USM.

关键词： Two-sided Ultrasonic motor (USM) Piezoelectric motor Travelling-wave Bearingless

New cross section measurements on tungsten isotopes around 14 MeV neutrons and their excitation functions

在线全文

学校读者我要写书评

暂无评论

Chinese Physics C 2022年第5期46卷 95-107页

作者： Yong Li Fengqun Zhou Yajuan Hao Xiaoqiang Ma Pengfei Ji Xiaopeng Zhang Shuqing Yuan School of Electrical and Mechanical Engineering Pingdingshan UniversityPingdingshan 467000China School of Information Engineering Pingdingshan UniversityPingdingshan 467000China

New cross sections of the^(183)W(n,α)^(180m)Hf,^(186)W(n,d*)^(185)Ta,^(182)W(n,p)^(182)Ta,^(184)W(n,p)^(184)Ta,^(182)W(n,2n)^(181)W,^(184)W(n,α)^(181)Hf,and^(186)W(n,α)^(183)Hf reactions were measured in the neutron energy range of 13.5-14.8 MeV via the activation technique to improve the database and resolve *** neutrons in this energy range were produced via the T(d,n)^(4)He reaction on a solid Ti-T *** activities of the irradiated monitor foils and samples were measured using a well-calibrated high-resolution HPGe *** calculations of the excitation functions of the seven nuclear reactions mentioned above in the neutron energies from the threshold to 20 MeV were performed using the nuclear theoretical model program TALYS-1.9 to aid new evaluations of cross sections on tungsten *** experimental data obtained were analyzed and compared with that of previous experiments conducted by other researchers,and with the evaluated data available in the five major evaluated nuclear data libraries of IAEA(namely ENDF/B-VIII.0 or ENDF/B-VII.0,JEFF-3.3,JENDL-4.0u+,CENDL-3.2,and BROND-3.1 or ROSFOND-2010),and the theoretical values acquired using TALYS-1.9 nuclear-reaction modeling *** new cross section measurements agree with those of some recent experiments and theoretical excitation curves at the corresponding *** consistency of the theoretical excitation curves based on TALYS-1.9 with these experimental data is better than that of the evaluated curves available in the five major nuclear data libraries of IAEA.

关键词： cross sections tungsten activation technique off-line gamma-ray spectrometry theoretical calculations TALYS-1.9

Performance analysis of IEEE 802.11e EDCA in wireless LANs

在线全文

学校读者我要写书评

暂无评论

Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2007年第1期8卷 18-23页

作者： ZHANG Wei SUN Jun LIU Jing ZHANG Hai-bin Department of Electronic Engineering Shanghai Jiao Tong University Shanghai 200240 China State Key Laboratory of Integrated Service Networks Xidian University Xi＇an 710071 China

In this paper, we propose an analytical model for the performance evaluation of IEEE 802.1 le enhanced distributed channel access （EDCA）. Different from most previous analytical studies based on the saturation assumption, we extend the analytical model to non-saturation conditions. An empty state is introduced into the Markov chain to represent the status of transmission queue being empty. This model can be used to calculate the traffic priority, throughput, and MAC layer delay with various configurations of contention parameters. A detailed simulation is provided to validate the proposed model. With the help of this model, the contention parameters can be configured appropriately to achieve specific quality-of-service （QoS） requirements.

关键词： IEEE 802.11 e Saturation assumption Non-saturation assumption Enhanced distributed channel access (EDCA)

THE HAUSDORFF DIMENSION OF THE SPECTRUM OF A CLASS OF GENERALIZED THUE-MORSE HAMILTONIANS

在线全文

学校读者我要写书评

暂无评论

数学物理学报:B辑英文版 2023年第5期43卷 1997-2004页

作者：刘庆晖唐志毅 School of Computer Science and Technology Beijing Institute of TechnologyBeijing 100081China School of Mathematics and Physics Hubei Polytechnic UniversityHuangshi 435003China

Letτbe a generalized Thue-Morse substitution on a two-letter alphabet{a,b}:τ(a)=ambm,τ(b)=bmam for the integer m≥***ξbe a sequence in{a,b}Z that is generated byτ.We study the one-dimensional Schr?dinger operator Hm,λon l2(Z)with a potential given by v(n)=λVξ(n),whereλ>0 is the coupling and Vξ(n)=1(Vξ(n)=-1)ifξ(n)=a(ξ(n)=b).LetΛ2=2,and for m>2,letΛm=m if m≡0 mod 4;letΛm=m-3 if m≡1 mod 4;letΛm=m-2if m≡2 mod 4;letΛm=m-1 if m≡3 mod *** show that the Hausdorff dimension of the spectrumσ(Hm,λ)satisfies that dimHσ(Hm,λ)>logΛm/(log 64m+4).It is interesting to see that dimHσσ(Hm,λ)tends to 1 as m tends to infinity.

关键词： one-dimensional Schrodinger operator generalized Thue-Morse sequence Hausdorff dimension

Creep Damage Characteristics of Soft Rock under Disturbance Loads

在线全文

学校读者我要写书评

暂无评论

Journal of china University of Geosciences 2008年第3期19卷 292-297页

作者：付志亮郭华高延法 College of Energy and Safety Anhui University of Science & TechnologyHuainan 232001 China Exploration & Mining Center Commonwealth Scientific and Industrial Research Organisation Queensland 883 Australia School of Mechanics & Civil Engineering China University of Mining & TechnologyBeijing 100083 China

This article focuses on the process of rock creep damage and micro-damage evolution properties of gray green mudstone under impacting disturbance load conditions for the first time using the real time computerized tomography （CT） testing technique. The results indicate that axial load comes into limit strength neighborhood, rock micro-crack links into larger crack, creep rate increases in a short time, larger plastic deformation happens; this is called disturbance accelerating creep stage. When rock is within limit strength neighborhood, there occurs creep micro-damage under smaller disturbance load. When disturbance load is larger, rock directly enters into disturbance accelerating creep stage, failure occurs instantaneously. On the basis of experimental research, the CT scanning method was used to describe the creep micro-damage of soft rock, also helpful in the prediction of roadways＇ service life and evaluation of geotechnical engineering stability.

关键词： CT scanning micro-damage impacting disturbance micro-crack creep.

New finding on out-of-step separation configuration of large-scale power systems

在线全文

学校读者我要写书评

暂无评论

Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2007年第8期8卷 1340-1345页

作者： WANG Chao GAO Peng ZHANG Xue-song SHAO Wei Department of Electrical Engineering Zhejiang University Hangzhou 310027 China NARI Relays Electric Co. Ltd. Nanjing 211100 China Zhejiang Electrical Power Research and Test Institute Hangzhou 310014 China California Independent System Operator Folsom CA 95630 USA

In this paper,two new concepts—“main out-of-step mode” and “minor out-of-step mode”—are proposed for power system reliability analysis. Large-scale power system studies found that out-of-step generator groups may have characteristics of the main out-of-step mode and the minor out-of-step mode. The generator groups with main out-of-step modes can determine the out-of-step interface of the large-scale power system,while generators with the minor out-of-step modes cannot play such a role. Therefore,the method of capturing the out-of-step interface by seeking the lowest voltage point(the out-of-step center) can only group the generators with the main out-of-step modes,and may fail to combine the generators with the minor out-of-step modes into proper coherent generator groups. Thus,it is necessary in engineering applications to equip the generators that are likely to have the characteristics of the minor out-of-step modes with separation devices based on off-line simulation studies in order to reduce the risk of further accidents caused by these generators after system separation.

关键词： Out-of-step center Out-of-step interface Separation device Main out-of-step mode Minor out-of-step mode

Hole transport and phonon scattering in epitaxial PbSe films

在线全文

学校读者我要写书评

暂无评论

Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2008年第1期9卷 137-142页

作者： Jian-xiao SI Hui-zhen WU Tian-ning XU Chun-fang CAO Department of Physics Zhejiang University Hangzhou 310027 China College of Physics and Mathematics Zhejiang Normal University Jinhua 321004 China

The combined characterizations of mobility and phonon scattering spectra allow us to probe hole transport process in epitaxial PbSe crystalline films grown by molecular beam epitaxy (MBE). The measurements of Hall effect show p-type con- ductivity of PbSe epitaxial films. At 295 K, the PbSe samples display hole concentrations of (5～8)×1017 cm–3 with mobilities of about 300 cm2/(V·s), and at 77 K the hole mobility is as high as 3×103 cm2/(V·s). Five scattering mechanisms limiting hole mobilities are theoretically analyzed. The calculations and Raman scattering measurements show that, in the temperatures between 200 and 295 K, the scattering of polar optical phonon modes dominates the impact on the observed hole mobility in the epitaxial PbSe films. Raman spectra characterization observed strong optical phonon scatterings at high temperature in the PbSe epitaxial films, which is consistent with the result of the measured hole mobility.

关键词： Electrical properties of PbSe Mobility Scattering mechanism

Wind-induced internal pressure response for structure with single windward opening and background leakage

在线全文

学校读者我要写书评

暂无评论

Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2008年第3期9卷 313-321页

作者： Shi-ce YU Wen-juan LOU Bing-nan SUN College of Civil Engineering and Architecture Zhejiang University Hangzhou 310027 China Department of Architecture Engineering Ningbo College of Technology Zhejiang University Ningbo 315100 China

Theoretical analysis and wind tunnel tests were carried out to study wind-induced intemal pressure response for the structure with single windward opening and background leakage. Its goveming differential equation was derived by the Bemoulli equation in an unsteady-isentropic form. Numerical examples were provided to study the additive damping caused by background leakage in laminar and turbulent flow, and the influence of background leakage on fluctuating internal pressure response was quantized. A series of models for low-rise building with various opening ratios and background leakage were designed and wind tunnel tests were conducted. It is shown that the fluctuating intemal pressure reduces when the background leakage are considered and that the effect of background leakage can be predicted accurately by the governing differential equation deduced in this paper.

关键词： Single windward opening Internal pressure Background leakage Governing equation Time-history analysis

AN EXPERIMENTAL INVESTIGATION OF PRESSURE AND CAVITATION CHARACTERISTICS OF HIGH VELOCITY FLOW OVER A CYLINDRICAL PROTRUSION IN THE PRESENCE AND ABSENCE OF AERATION

在线全文

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2008年第1期20卷 60-66页

作者： DONG Zhi-yong LIU Zhi-ping WU Yi-hong ZHANG Dong china Hydraulic and Municipal Engineering Research Institute Zhejiang University of Technology Hangzhou 310014 China Institute of Water Resources and Hydroelectric Power Research Beijing 100038 China

This article experimentally investigated the pressure and cavitation characteristics of high velocity flow over a surface irregularity with and without aeration in a non-circulating water tunnel system. The surface irregularity is a cylindrical protrusion made of stainless steel of 6 mm diameter and 2 mm height. Pressures with and without aeration were measured with MPX400D pressure transducers and real-timely acquired by a SINOCERA YE6263 data acquisition system. Variations in flow regimes with and without aeration were observed. Pressure profiles and their variations with air concentration upper and lower cylindrical protrusion on the invert and obvert walls were determined. Variations of cavitation number with air concentration lower cylindrical protrusion were analyzed. Also, cavitation numbers in the presence and absence of aeration were compared.

关键词： cylindrical protrusion aeration pressure cavitation number high velocity flow