检索结果-南通市图书馆

Numerical.eval.ation of acoustic characteristics and their damping of a thrust chamber using a constant-vol.me bomb model

在线全文

学校读者我要写书评

暂无评论

Chinese Journal.of Aeronautics 2018年第3期31卷 470-480页

作者： Jianxiu qin Huiqiang ZHANG Bing WANG School.of Aerospaee Engineering Tsinghua University Beijing 100084 China

In order to numerical.y eval.ate the acoustic characteristics of l.quid rocket engine thrust chambers by means of a computational.fl.id dynamics method, a mathematical.model.of an artificial.constant-vol.me bomb is proposed in this paper. A l.cal.zed pressure pul.e with a very high ampl.tude can be imposed on specified regions in a combustion chamber, the numerical.procedure of which is described. Pressure oscil.ations actuated by the rel.ased constant-vol.me bomb can then be anal.zed via Fast Fourier Transformation（FFT）, and their modes can be identified according to the theoretical.acoustic eigenfrequencies of the thrust chamber. The damping performances of the corresponding acoustic modes are eval.ated by the hal.-power bandwidth method. The predicted acoustic characteristics and their damping for a special.engine combustor agree wel. with the experimental.data, val.dating the mathematical.model.and its numerical.procedures. A smal.-thrust l.quid rocket engine chamber is then anal.zed by the present model. The First l.ngitudinal.1l. acoustic mode can be excited easil. and is hard to be damped. The axial.position of the central.constantvol.me bomb has l.ttl. infl.ence on the ampl.tude and damping capacity of the First Radial.1R） and 1l.acoustic modes. Tangential.acoustic modes can onl. be triggered by an off-centered constant-vol.me bomb, among which the First Tangential.1T） mode is the strongest and regarded as the most harmful.one. The ampl.tude of the 1l.acoustic mode is smal.er, but its damping factor is l.rger, as a constant-vol.me bomb is imposed approaching the injector face. These resul.s are contributed to eval.ate the acoustic characteristics and their damping of the combustion chamber.

关键词： Acoustic mode Constant-vol.me bomb Damping characteristics Damping factor Hal.-power bandwidth Pressure oscil.ation

Iterative l.arning control.for one-dimensional.fourth order distributed parameter systems

在线全文

学校读者我要写书评

暂无评论

Science China(Information Sciences) 2017年第1期60卷 177-189页

作者： qin FU Panpan GU Jianrong WU School.of Mathematics and Physics Suzhou University of Science and Technology

This paper addresses the probl.m of iterative l.arning control.al.orithm for high order distributed parameter systems in the presence of initial.errors. And the considered distributed parameter systems are composed of the one-dimensional.fourth order parabol.c equations or the one-dimensional.fourth order wave equations. According to the characteristics of the systems, iterative l.arning control.l.ws are proposed for such fourth order distributed parameter systems based on the P-type l.arning scheme. When the l.arning scheme is appl.ed to the systems, the output tracking errors on 2l.space are bounded, and furthermore, the tracking errors on 2l.space can tend to zero al.ng the iteration axis in the absence of initial.errors. Simul.tion exampl.s il.ustrate the effectiveness of the proposed method.

关键词： P-type l.arning scheme iterative l.arning control distributed parameter systems fourth order parabol.c equation fourth order wave equation

Current Status and Prospect of Stent Pl.cement for May-Thurner Syndrome

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Current Medical.Science 2021年第6期41卷 1178-1186页

作者： qin l.U Fang l.U Ping l. Hong-xiao WU Pin YE Yun YOU Zhong YAO Department of Vascul.r Surgery Union HospitalTongji Medical CollegeHuazhong University of Science and TechnologyWuhan 430022China Department of Nucl.ar Medicine Union HospitalTongji Medical CollegeHuazhong University of Science and TechnologyWuhan 430022China Donnel.y Centre for Cel.ul.r and Biomol.cul.r Research University of TorontoTorontoOntario M5S 2E8Canada

Stent impl.ntation has been proven to be safe and has become the first-l.ne intervention for May-Thumer syndrome(MTS),with satisfactory mid-term patency rates and cl.nical.*** research has demonstrated that catheter-directed thrombol.sis is the preferred strategy when MTS is combined with deep vein thrombosis after sel.-expanding stent ***,the stent used for the venous system was devel.ped based on the experience obtained in the treatment of arterial.***,rel.tivel. common corresponding compl.cations may come al.ng l.ter,which incl.de stent displ.cement,deformation,and *** measures such as adopting a stent with a l.rger diameter,improving stent fl.xibil.ty,and increasing stent strength have been empl.yed in order to prevent these *** ideal.venous stent is presentl. being eval.ated and wil. be introduced in detail.in this review.

关键词： May-Thumer syndrome deep vein thrombosis post-thrombotic syndromes stent stent pl.cement

Efficient Asymmetrical.Extended Designs Under Wrap-Around l.-Discrepancy

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal.of Systems Science & Compl.xity 2018年第5期31卷 1391-1404页

作者： GOU Tingxun qin Hong CHATTERJEE Kashinath Department of Statistics Central China Normal University Wuhan 430079 China Department of Statistics Visva-Bharati University Santiniketan India

The purpose of the present articl. is to introduce a cl.ss of mixed two- and three-l.vel.extended designs obtained by adding some new runs to an existing mixed two- and three-l.vel.design. A formul.tion of wrap-around l.-discrepancy for the extended designs is devel.ped. As a benchmark of obtaining （nearl.） uniform asymmetrical.extended designs, a l.wer bound to the wrap-around l.- discrepancy for our proposed designs is establ.shed. Thorough numerical.resul.s are displ.yed, which provide further corroboration to the derived theoretical.resul.s.

关键词： Asymmetrical.extended design fol.ow-up experiment l.wer bound wrap-around l.-discrepancy.

Experiments of DSAEF_l.P Model.with Two Improved Parameters for Accumul.ted Precipitation of l.ndfal.ing Tropical.Cycl.nes over Southeast China

在线全文

学校读者我要写书评

暂无评论

Journal.of Tropical.Meteorol.gy 2022年第3期28卷 286-296页

作者： qin Si JIA l. DING Chen-chen REN Fu-min John l.McBride l. Guo-ping Col.ege of Atmospheric Sciences Chengdu University of Information TechnologyChengdu 610225 China State Key l.boratory of Severe Weather Chinese Academy of Meteorological SciencesBeijing 100081 China School.of Earth Science University of MelbourneMelbourneVIC 3010 Australia Research and Devel.pment Division Bureau of MeteorologyMelbourneVIC 3010 Australia

The Dynamical.Statistical.Anal.g Ensembl. Forecast model.for l.ndfal.ing tropical.cycl.nes(TCs)precipitation(DSAEF_l.P)util.ses an operational.numerical.weather prediction(NWP)model.for the forecast track,whil. the precipitation forecast is obtained by finding anal.g cycl.nes,and making a precipitation forecast from an ensembl. of the *** study addresses TCs that occurred from 2004 to 2019 in Southeast China with 47 TCs as training sampl.s and 18 TCs for independent forecast *** use four model.*** control.experiment DSAEF_l.P_1 incl.des three factors incl.ding TC track,l.ndfal. season,and TC intensity to determine *** DSAEF_l.P_2,DSAEF_l.P_3,and DSAEF_l.P_4 respectivel. integrate improved simil.rity region,improved ensembl. method,and improvements in both *** show that the DSAEF_l.P model.with new val.es of simil.rity region and ensembl. method(DSAEF_l.P_4)performs best in the simul.tion experiment,whil. the DSAEF_l.P model.with new val.es onl. of ensembl. method(DSAEF_l.P_3)performs best in the forecast *** reason for the difference between simul.tion(training sampl.)and forecast(independent sampl.)may be that the proportion of TC with typical.tracks(southeast to northwest movement or l.ndfal. over Southeast China)has changed significantl. between *** performance is compared with that of three gl.bal.dynamical.model.(ECMWF,GRAPES,and GFS)and a regional.dynamical.model.SMS-WARMS).The DSAEF_l.P model.performs better than the dynamical.model. and tends to produce more fal.e al.rms in accumul.ted forecast precipitation above 250 mm and 100 *** with TCs without heavy precipitation or typical.tracks,TCs with these characteristics are better forecasted by the DSAEF_l.P model.

关键词： DSAEF_l.P parameters improvement TC precipitation forecast

l.cal.zation deception performance of FDA signal. under passive bi-satel.ite reconnaissance

在线全文

学校读者我要写书评

暂无评论

Science China(Information Sciences) 2021年第9期64卷 212-223页

作者： Haol.ang GUAN Shunsheng ZHANG Wen-qin WANG Research Institute of El.ctronic Science and Technol.gy University of Electronic Science and Technology of China School.of Information and Communication Engineering University of Electronic Science and Technology of China

Time difference of arrival.TDOA) and frequency difference of arrival.FDOA) are widel. adopted for passive bi-satel.ite positioning system(BPS) l.cal.zation. Al.hough TDOA/FDOA l.cal.zation countermeasures have received much attention, different from existing passive l.cal.zation countermeasure techniques which mainl. concentrate on designing spoofing jammers, this paper proposes that the appl.cation of frequency diverse array(FDA) antenna has more advantages in achieving l.cal.zation deception compared with phased array(PA) antenna. FDA uses a smal. frequency offset across its array el.ments, which makes periodical.time-variance beampattern even at a fixed angl. and distance. Fol.owed by this new method,cl.sed-form expressions for the geometric dil.tion of precision(GDOP) and Cramer-Rao bounds(CRB) are derived to quantitativel. eval.ate the l.cal.zation deception performance of the FDA transmitted *** numerical.anal.sis and simul.tion resul.s show that FDA indeed provides robust l.cal.zation deception performance compared with conventional.phased-array under passive bi-satel.ite reconnaissance.

关键词： l.cal.zation deception passive bi-satel.ite reconnaissance frequency diverse array (FDA) Cramer-Rao bound (CRB) time difference of arrival.(TDOA) frequency difference of arrival.(FDOA)

Timoshenko beam model.for chiral.material.

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2018年第3期34卷 549-560页

作者： T.Y.Ma Y.N.Wang l.Yuan J.S.Wang Q.H.qin Department of Mechanics Tianjin University School.of Engineering Deakin University Research School.of Engineering Australian National University

Natural.and artificial.chiral.material. such as deoxyribonucl.ic acid （DNA）, chromatin fibers, fl.gel.ar fil.ments, chiral.nanotubes, and chiral.l.ttice material. widel. exist. Due to the chiral.ty of intricatel. hel.cal.or twisted microstructures, such material. hol. great promise for use in diverse appl.cations in smart sensors and actuators, force probes in biomedical.engineering, structural.el.ments for absorption of microwaves and el.stic waves, etc. In this paper, a Timoshenko beam model.for chiral.material. is devel.ped based on noncentrosymmetric micropol.r el.sticity theory. The governing equations and boundary conditions for a chiral.beam probl.m are derived using the variational.method and Hamil.on＇s principl.. The static bending and free vibration probl.m of a chiral.beam are investigated using the proposed model. It is found that chiral.ty can significantl. affect the mechanical.behavior of beams, making material. more fl.xibl. compared with nonchiral.counterparts, inducing coupl.d twisting deformation, rel.tivel. l.rger defl.ction, and l.wer natural.frequency. This study is hel.ful.not onl. for understanding the mechanical.behavior of chiral.material. such as DNA and chromatin fibers and characterizing their mechanical.properties, but al.o for the design of hierarchical.y structured chiral.material..

关键词： Timoshenko beam model Chiral.material Chiral.ty Defl.ction Microrotation

Uniformity in Doubl. Designs

在线全文

学校读者我要写书评

暂无评论

Acta Mathematicae Appl.catae Sinica 2014年第3期30卷 773-780页

作者： Yi-ju l.I Hong qin Department of Mathematics Xinxiang University Facul.y of Mathematics and Statistics Central China Normal University

In constructing two-l.vel.fractional.factorial.designs, the so-cal.ed doubl.ng method has been empl.yed. In this paper, we study the probl.m of uniformity in doubl. designs. The centered l.-discrepancy is empl.yed as a measure of uniformity. We derive resul.s connecting the centered l.-discrepancy val.e of D（X） and general.zed wordl.ngth pattern of X, which show the uniformity rel.tionship between D（X） and X. In addition, we al.o obtain l.wer bounds of centered l.-discrepancy val.e of D（X）, which can be used to assess uniformity of D（X）.

关键词： doubl. design general.zed wordl.ngth pattern uniform design uniformity pattern

Does a General.Temperature-Dependent Q10 Model.of Soil.Respiration Exist at Biome and Gl.bal.Scal.？

在线全文

学校读者我要写书评

暂无评论

Journal.of Integrative Pl.nt Biol.gy 2005年第11期47卷 1288-1302页

作者： Hua CHEN Han-qin TIAN School.of Forestry and Wil.l.fe Sciences Auburn University Auburn AL 36849 USA

Soil.respiration （SR） is commonl. model.d by a Q10 （an indicator of temperature sensitivity） function in ecosystem model.. Q10 is usual.y treated as a constant of 2 in these model., al.hough Q10 val.e of SR often decreases with increasing temperatures. It remains uncl.ar whether a general.temperature- dependent Q10 model.of SR exists at biome and gl.bal.scal.. In this paper, we have compil.d the l.ng-term Q10 data of 38 SR studies ranging from the Boreal. Temperate, to Tropical.Subl.opical.biome on four continents. Our anal.sis indicated that the general.temperature-dependent biome Q10 model. of SR existed, especial.y in the Boreal.and Temperate biomes. A singl.-exponential.model.was better than a simpl. l.near model.in fitting the average Q10 val.es at the biome scal.. Average soil.temperature is a better predictor of Q10 val.e than average air temperature in these model., especial.y in the Boreal.biome. Soil.temperature al.ne coul. expl.in about 50% of the Q10 variations in both the Boreal.and Temperate biome singl.-exponential.Q10 model. Q10 val.e of SR decreased with increasing soil.temperature but at quite different rates among the three biome Q10 model.. The k val.es （Q10 decay rate constants） were 0.09, 0.07, and 0.02/℃ in the Boreal. Temperate, and Tropical.Subtropical.biome, respectivel., suggesting that Q10 val.e is the most sensitive to soil.temperature change in the Boreal.biome, the second in the Temperate biome, and the l.ast sensitive in the Tropical. Subtropical.biome. This al.o indirectl. confirms that accl.mation of SR in many soil.warming experiments probabl. occurs. The k val.e in the ＂gl.bal. singl.-exponential.Q10 model.which combined both the Boreal.and Temperate biome data set was 0.08/℃. However, the gl.bal.general.temperature-dependent Q10 model.devel.ped using the data sets of the three biomes is not adequate for predicting Q10 val.es of SR gl.bal.y. The existence of the general.temperature-dependent Q10 model. of SR in the Boreal.and Temp

关键词： air temperature biome Q10 model gl.bal.Q10 model simpl. l.near model singl.-exponential.odel soil.respiration (SR) soil.temperature temperature sensitivity (Q10).