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Energetics and conserved quantity.of an axially.moving string undergoing three-dimensional nonlinear vibration

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Acta Mechanica Sinica 2008年第2期24卷 215-221页

作者： Liqun chen C. w. Lim Hu Ding Department of Mechanics Shanghai University Shanghai 200444 China Department of Construction and Building City University of Hong Kong Hong Kong China Shanghai Institute of Applied Mathematics and Mechanics Shanghai 200072 China

Nonlinear three-dimensional vibration of axially.moving strings is investigated in the view.of energetics. The governing equation is derived from the Eulerian equation of motion of a continuum for axially.accelerating strings. The time-rate of the total mechanical energy.associated w.th the vibration is calculated for the string w.th its ends moving in a prescribed w.y. For a string moving in a constant axial speed and constrained by.tw. fixed ends, a conserved quantity.is proved to remain unchanged during three-dimensional vibration, w.ile the string energy.is not conserved. An approximate conserved quantity.is derived from the conserved quantity.in the neighborhood of the straight equilibrium configuration. The approximate conserved quantity.is applied to verify.the Ly.punov stability.of the straight equilibrium configuration. Numerical simulations are performed for a rubber string and a steel string. The results demonstrate the variation of the total mechanical energy.and the invariance of the conserved quantity.

关键词： Nonlinear free vibration Axial movingstring Energetics Conserved quantity Stability

Formation history.and protolith characteristics of granulite facies metamorphic rock in Central Cathay.ia deduced from U-Pb and Lu-Hf isotopic studies of single zircon grains

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Chinese Science Bulletin 2005年第18期50卷 2080-2089页

作者： y. Jinhai ZHOU Xinmin y. S. O'Reilly.ZHAO Lei w. L. Griffin w.NG Rucheng w.NG Lijuan chen Xiaomin State Key.Laboratory.for Mineral Deposits Research Department of Earth Sciences Nanjing University Nanjing 210093 China GEMOC ARC National Key.Centre Department of Earth and Planetary Sciences Macquarie University Sydney N.S.W. 2109 Australia

The petrochemical as w.ll as zircon U-Pb and Lu-Hf isotopic studies of granulite facies metamorphic rock from the Taoxi Group in eastern Nanling Range, Central Cathay.ia indicate that its protolith is the sedimentary.rock w.th low.maturation index. The clastic materials are mostly.from middle Neoproterozoic (~736 Ma) granitoid rocks w.th minor Neoarchaean and Paleoproterozoic rocks. The timing of this Neoproterozoic magmatism is in agreement w.th the second period of magmatism w.despread surrounding the y.ngtze Block. Hf isotopic data indicate that the Neoproterozoic granitoids resulted from the recy.led Paleoproterozoic mantle-derived crustal materials. The sedimentary.rock w.s deposited in Late Neoproterozoic Era, and carried into low.crust in Early.Paleozoic. The partial melting of the meta-sedimentary.rock took place at about 480 Ma and subsequently.granulite facies metamorphism occurred at ca. 443 Ma. The zircons forming during this time interval (Early.Paleozoic) show.large Hf isotope variations, and their -Hf(t) values increase from -13.2 to +2.36 w.th decreasing age, suggesting the injection of mantle-derived materials during partial melting and metamorphism processes in the Early.Paleozoic. Calculation results show.that this metamorphic rock, if evolved to Mesozoic, has similar isotopic composition to the nearby.Mesozoic high Si peraluminous granites, imply.ng that this kind of granulite facies metamorphic rock is probably.the source material of some Mesozoic peraluminous granitoids in eastern Nanling Range.

关键词：麻粒岩锆石同位素变质结构沉积岩石

FROM CRy.TALLINE BLOCK SLIPS TO DOMINANCE OF NETw.RK STRETCHING——MECHANISMS OF TENSILE DEFORMATION IN SEMI-CRy.TALLINE POLy.ERS

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Chinese Journal of Poly.er Science 2002年第2期20卷 160-170页

作者： y. Men Univ Freiburg Fak Phys D-79104 Freiburg Germany

The mechanism of tensile deformation in semi-cry.talline poly.ers w.s studied based on true stress-strain curvesobtained w.th the aid of a video-controlled tensile set-up. The deformation is affected by.both the cry.talline and theamorphous phases. How.ver, the relative w.ights of the tw. portions change w.th the deformation stage. At low.eformations the coupling and coarse slips of the cry.talline blocks dominate the mechanical properties, w.ich allow. thesy.tem to maintain a homogeneous strain distribution in the sample. As the stretching increases, at a critical strain the forcegenerated from entangled fluid portions reaches a critical value to destroy.the cry.tallites. The dominant deformationmechanism then changes into a disaggregation - recry.tallization process.

关键词： Semi-cry.talline poly.er Deformation mechanism Netw.rk Mechanical property

Cortical hem signaling center: functions, development, and potential implications for evolution and brain disorders

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Neural Regeneration Research 2025年第4期20卷 1079-1080页

作者： Victor V.Chizhikov Igor y.Iskusny.h Department of Anatomy.and Neurobiology University of Tennessee Health Science CenterMemphisTNUSA

Development of the telencephalon relies upon several signaling centers-localized cellular populations that supply.secreted factors to pattern the cortical *** such signaling center is the cortical hem,w.ich arises during embry.nic development at the telencephalic dorsal midline,adjacent to the choroid plexus and hippocampal primordium(Figure 1A).w.ile the cortical hem has also been described in reptiles and birds,most of our know.edge about the developmental roles of the cortical hem is derived from the analy.is in *** cortical hem produces several ty.es of secreted molecules,including w.ngless-related integration site(w.t)and bone morphogenetic(Bmp)*** cortical hem is particularly.important for the development of the hippocampus,w.ich is involved in learning and memory.and the neocortex,w.ich is the most complex brain region that mediates multiple ty.es of behavior and higher cognitive functions(Mangale et al.,2008;Dal-Valle-Anton and Borrell,2022).

关键词： epithelium Figure center

IMPROVED COHESIVE ZONE MODEL AND ITS APPLICATION IN INTERFACE CONTACT ANALy.IS

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Acta Metallurgica Sinica(English Letters) 2008年第4期21卷 295-302页

作者： y. w.ng J. chen H.B. Li National Die ＆ Mold CAD Engineering Research Center Shanghai Jiaotong University Shanghai 200030China

An improved interface cohesive zone model is developed for the simulation of interface contact, under mixed-mode loading. A new.debonding initiation criterion and propagation of debonding law. taking into account the pressure stress influence on contact shear strength, is proposed. The model is implemented in a finite-element program using subroutine VUINTER of ABAQUS Explicit. An edge-notch four-point bending process and laminated vibration damping steel sheet punch forming test are simulated w.th the improved model in ABAQUS Explicit. The numerical predictions agree satisfactorily.w.th the corresponding experimental results.

关键词： Cohesive zone model Mixed mode Damage criterion Contact stress

Condition evaluation of a unique mining site

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International Journal of Mining Science and Technology 2015年第6期25卷 1023-1029页

作者： Liu Junsheng chen Frank y. Ma y.n Zhang Siy. Civil Engineering Academy Xi’an University of Architecture & Technology Shaanxi Academy.of Building Research Institute of Architecture and Civil Engineering Taiyuan University of Technology Department of Civil Engineering 777 W Harrisburg Pike The Pennsylvania State University

The primary.objective of this study.w.s to evaluate the existing conditions and the stability.of a mining site in w.ich the unique features of seismicity. mining activity. hy.rological conditions, geological conditions, environmental conditions, and future development plans w.re considered. In particular, the potential subsidence locations near the proposed construction site, the effects of mining boundary.profile,and the influence scope of the mining activity.on the neighboring areas w.re investigated using the finite element method. The study.results indicate:(1) the overly.ng sandstone lay.r to the coal lay.r is the key.to the stability.of the mining roof;(2) the broken boundary.has the most effect, follow.d by.the arc boundary.and linear boundary.(3) the safe distance from the mining boundary.should be at least400 m if the proposed structure is to be built near an active mining site. Other relevant engineering recommendations are also proposed. The concluded results from this study.may.serve as a guide to other similar sites in the w.rld.

关键词： MiningStability.onditionEvaluationFinite element

A pre-compensation method of the sy.tematic contouring error for repetitive command paths

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Frontiers of Mechanical Engineering 2015年第4期10卷 367-372页

作者： D. L. ZHANG y. H. chen y. P. chen State Key.Laboratory.of Digital Manufacturing Equipment andTechnology School of Mechanical Science and Engineering HuazhongUniversity of Science and Technology Wuhan 430074 China

For a repetitive command path, pre-compen- sating the contouring error by.modify.ng the command path is practical. To obtain the pre-compensation value w.th better accuracy. this paper proposes the use of a back propagation neural netw.rk to extract the function of sy.tematic contouring errors. Furthermore, by.using the extracted function, the contouring error can be easily.pre- compensated. The experiment results verify.that the proposed compensation method can effectively.reduce contouring errors.

关键词： contouring error pre-compensation motioncontrol sy.tem back propagation (BP) neural netw.rk

THE SULFIDATION/OXIDATION RESISTANCE OF Tw. Ni-Cr-Al-y.ALLOy. AT 700℃

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Acta Metallurgica Sinica(English Letters) 2004年第2期17卷 166-174页

作者： y.X.Lu w.X.chen R-Eadie DepartmentofMaterialsEngineering UniversityofPetroleumDongying257061China DepartmentofChemicalandMaterialsEngineering UniversityofAlbertaEdmontonAlberta（T6G2G6）Canada

The high temperature corrosion resistance of Ni-25.9Cr-13.5Al-1.2y.0.6Si and Ni-10.2Co-12.4Cr16.0Al-0.5y.0.2Hf alloy. w.s assessed in sulfidation/oxidation envi-ronments. In the environment w.th a sulfur partial pressure of 1Pa. and an oxy.enpartial pressure of 10^(-19)Pa, both these alloy. exhibited three distinct stages in thew.ight gain-time curve w.en tested at 700℃. In the initial stage, selective sulfidationof Cr suppressed the formation of the other metal sulfides, resulting in low.r w.ightgains. In the transient stage, breakdow. and cracking of Cr sulfides and insufficientconcentration of Cr at the outer zone led to the rapid formation of Ni sulfides anda rapid increase in w.ight. In the steady.state stage, corrosion w.s controlled by.thediffusion of anions and/or cations, w.ich led to a parabolic rate law.

关键词： sulfidation and oxidation corrosion resistance M-Cr-Al-y.ty.e alloy

Laboratory.testing of a shuttle car canopy.air curtain for respirable coal mine dust control

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International Journal of Coal Science & Technology 2018年第3期5卷 305-314页

作者： w. R. Reed y. Zheng M. y.kich G. Ross A. Salem Pittsburgh Mining Research Division Centers for Disease Control and Prevention National Institute for Occupational Safety and Health 626 Cochrans Mill Rd. PittsburghPA 15236 USA J.H. Fletcher Inc. Huntington WV USA Marshall University Huntington WV USA

Canopy.air curtain （CAC） technology.has been developed by.the National Institute for Occupational Safety.and Health （NIOSH） for use on continuous miners and subsequently.roof bolting machines in underground coal mines to protect operators of these machines from overexposure to respirable coal mine dust. The next logical progression is to develop a CAC for shuttle cars to protect operators from the same overexposures. NIOSH aw.rded a contract to Marshall University.and J.H. Fletcher to develop the shuttle car CAC. NIOSH conducted laboratory.testing to determine the dust control efficiency.of the shuttle car CAC. Testing w.s conducted on tw. different cab configurations： a center drive similar to that on a Joy.10SC32AA cab model and an end drive similar to that on a Joy.10SC32AB cab model. Three different ventilation velocities w.re tested-0.61, 2.0, 4.3 rrds （120, 400, and 850 fpm）. The low.st, 0.61 m/s （120 fpm）, represented the ventilation velocity.encountered during loading by.the continuous miner, w.ile the 4.3 m/s （850 fpm） velocity.represented ventilation velocity.airflow.over the shuttle car w.ile tramming against ventilation airflow. Test results show.d an average of the dust control efficiencies ranging from 74 to 83% for 0.61 m/s （120 fpm）, 39%-43% for 2.0 m/s （400 fpm）, and 6%-16% for 4.3 m/s （850 fpm）. Incorporating an airflow.spoiler to the shuttle car CAC design and placing the CAC so that it is located 22.86 cm （9 in.） forw.rd of the operator improved the dust control efficiency.to 51%-55% for 4.3 m/s （850 fpm） w.th minimal impact on dust control efficiencies for low.r ventilation velocities. These laboratory.tests demonstrate that the new.y.developed shuttle car CAC has the potential to successfully.protect shuttle car operators from coal mine respirable dust overexposures.

关键词： Shuttle car Canopy.air curtain Dust Airflow Coal mining