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Dynamics of Below—Band—Gap Carrier in Highly Excited GaN

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Chinese Physics Letters 2003年第5期20卷 749-752页

作者： GUOBing WONGKam-Sing YEZhi-Zhen JIANGHong-Xing LINJing-Yu DepartmentofPhysics TheHongKongUniveristyofScienceandTechnologyClearWaterBaykowloonHongKong StateKeyLaboratoryofsiliconMaterials ZhejiangUniversityHangzhou310027 DepartmentofPhysics KansasStateUniversityManhattanKansas66506-2601USA

Femtosecond time-resolved reflectivity was used to investigate below-band-gap (3.1 eV) carrier dynamics in a nominally undoped GaN epilayer under high excitation. A 2.5-ps rising process can be observed in the transient trace. This shot rising time results from the hot phonon effects which can cause a delayed energy relaxation of the initial photocarriers toward the band edge. From the density dependence of the carrier dynamics, the Mott density was estimated to be 1.51-1.56×1019 cm-3. Below the Mott density, the initial probed carrier dynamics was explained to the effect of acoustic phonon-assisted tunnelling for localized states, where a significant excitation density dependence of the tunnelling probability was observed due to the optically induced bandtail extension to lower energies. Above the Mott density, the measured carrier dynamics reflected the relaxation of an electron-hole plasma, in which a distinct fast decay component of 2.3 ps was observed due to the onset of nonlinear relaxation processes such Auger recombination.

关键词： GaN 氮化镓半导体反射率动力学光谱分析性质热声效应隧道效应

Magnetic Bingham fluid-assisted deterministic polishing for super-smooth surfaces

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Chinese Science Bulletin 2005年第2期50卷 172-178页

作者： CHENGHaobo FENGZhijing WANGYingwei LEIShuting DepartmentofPrecisionInstrumentsandMechanology TsinghuaUniversityBeijing100084China DepartmentofScience ChangchunUniversityofScienceandTechnologyChangchun130021China DepartmentofIndustrialandManufacturingSystemsEngineering KansasStateUniversityUSA

The characteristics of magnetorheological fin- ishing (MRF) technique such as the behavior of magnetic particles and the magnetic field distribution have been inves- tigated. Based on the established theoretical model, material removal function and removal rate experiments involving a K9 glass mirror are designed and carried out. Further experiments are carried out to improve the surface roughness of the workpiece. The final surface roughness with an initial value of 17.58 nm reached 0.4351 nm rms after 35 min of deterministic MRF, and the AFM measurements on microstructures of the polished surface are also improved by 0.445 nm rms without obvious defects.

关键词：超平滑磁性流变学流体 MRF 磨光面拆换率宾汉流体

Behavioral and olfactory responses of grasshopper hatchlings, Melanoplus sanguinipes, to plant odours and volatile compounds

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Chinese Science Bulletin 2004年第2期49卷 136-141页

作者： KANGLe T.L.Hopkins StateKeyLaboratoryofIntegratedManagementofPestInsects&Rodents.InstituteofZoology ChineseAcademyofSciencesBeijing100080China DepartmentofEntomology KansasStateUniversityManhattanKS66506USA

Behavior and olfactory responses of grasshopper hatchlings, Melanoplus sanguinipes (F.), to odours from plant foliage and volatile compounds were tested using a glass Y-tube olfactometer and electroantennogram (EAG)techniques respectively. In single choice trials, newly hatched hoppers were much more sensitive to the odour from intact leaves and chopped foliage of ryegrass and wheat than other plants. Chopped sorghum leaves, but not stem-cut sorghum,were also significantly attractive. The orientation responses of grasshopper hatchlings to these plants were highly consistent with those of last instar hoppers and adults. When ryegrass was employed as the control, the odour from stem-cut alfalfa was more attractive. There was no significant difference in hopper orientation responses to the odours from chopped seedlings of sorghum, alfalfa, wheat or ***, significantly more hoppers preferred the chopped ryegrass control to chopped Louisanna sage. Measurement of the EAG response of first instar hoppers to these plant odours showed that the odour of Louisanna sage elicited the greatest response amplitudes. In olfactory tests using different volatile components, Z-3-hexenol, E-3-hexenol,Z-hex-3-enyl acetate, E-2-hexenal and hexenal gave greater EAG responses than geraniol and 1-octen-3-ol. These results are also consistent with comparable data from adults. Newly hatched grasshoppers had similar EAG response profiles to plant materials and chemicals to those of adults, although the absolute EAG values of young hoppers were much lower than those of adults. Therefore, newly hatched hoppers were able to distinguish plants from an air control, and even host plants from non-host plants, and the feeding experience of hoppers probably has little influence on their subsequent ability as adults to identify and locate food plants.

关键词：嗅觉蝗虫挥发性化合物植物保护

Time-Resolved Photoluminescence Studies of Indium-Rich InGaN Alloys

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Chinese Physics Letters 2005年第2期22卷 472-474页

作者：陈光德竹有章颜国君苑进社 K.H.Kim J.Y.Lin H.X.Jiang DepartmentofAppliedPhysics Xi'anJiaotongUniversityXi'an710049 DepartmentofPhysics KansasStateUniversityManhattanKansas66506-2601USA DepartmentofAppliedPhysics Xi'anJiaotongUniversityXi'an710049

Time-resolved photoluminescence (PL) spectroscopy has be used to investigateindium-rich InGaN alloys grown on sapphire substrates by metal organic chemical vapor *** measurement indicates two dominant emission lines originating from phase-separatedhigh- and low-indium-content regions. Temperature and excitation intensity dependence of the twomain emission lines in these InGaN alloys have been measured. Temperature and energy dependence ofPL decay lifetime show clearly different decay behaviour for the two main lines. Our results showthat photo-excited carriers are deeply localized in the high indium regions while photo-excitedcarriers can be transferred within the low-indium-content regions as well as to high-contentregions.

关键词： OPTICAL-PROPERTIES EMITTING-DIODES QUANTUM-WELL FILMS

FEEDFORWARD CONTROL STRATEGIES FOR TRACKING PERFORMANCE IN MACHINE AXES

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Chinese Journal of Mechanical Engineering 2005年第1期18卷 5-9页

作者： WeiZhouhong SchinstockDaleE Input／OutputCompany 12300ParcCrestDnveStaffordTexas77477USA Mechanical＆NuclearEngineering KansasStateUniversityManhattanKansas66506USA

Three feedforward (FFD) control techniques for position-servo machine axesare compared. All three FFD controllers are used with two different PID feedback (FBK) *** two different FBK controllers have two different closed-loop bandwidths. They are demonstratedusing experimental data from a linear motor test system and from simulations. Laboratory resultsusing the linear motor hardware demonstrate that the velocity & acceleration (V&A) FFD controllerimproves tracking in all case considered, while the other two FFD controllers actually degradeperformance in many cases. Through simulation this degradation is attributed to extreme sensitivityto round off errors. This sensitivity is the result of a complex controller that is implementedoutside of the feedback loop.

关键词： Three feedforward (FFD) control Linear motor system Tracking

Upper Bounds on Character Sums with Rational Function Entries

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Acta Mathematica Sinica,English Series 2003年第2期19卷 327-338页

作者： ToddCOCHRANE ChunLeiLIU ZhiYongZHENG DepartmentofMathematics KansasStateUniversityManhattanKS66506USA DepartmentofMathematics ZhengzhouUniversityZhengzhou450002P.R.China DepartmentofMathematics TsinghuaUniversityBeijing100084P.R.China

We obtain formulae and estimates for character sums of the type $S\left( {\chi ,f,p^m } \right) = \sum\nolimits_{x = 1}^{p^m } {\chi \left( {f\left( x \right)} \right),} $ where pm is a prime power with m S 2, L is a multiplicative character (mod p^m), and f=f1/f2 is a rational function over ê. In particular, if p is odd, d=deg(f1)+deg(f2) and d* = max(deg(f1), deg(f2)) then we obtain $\left| {S\left( {\chi ,f,p^m } \right)} \right| \le \left( {d - 1} \right)p^{m\left( {1 - {1 \over {d*}}} \right)}$ for any non-constant f (mod p) and primitive character L. For p = 2 an extra factor of $2\sqrt 2$ is needed.

关键词： Exponential sums Character sums

Late Pleistocene/Holocene wetland events recorded in southeast Tengger Desert lake sediments,NW China

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Chinese Science Bulletin 2003年第14期48卷 1423-1429页

作者： D.B.Madsen CHENFahu Ch.G.Oviatt ZHUYan P.J.Brantinaham R.GoElston R.L.Bettinger TexasArcheologicalResearchLaboratory UniversityofTexasAustinTX78712USA CAEENationalLaboratoryofWesternChina'sEnvironmentalSystem LanzhouUniversityLanzhou730000China DepartmentofGeoi0gy KansasStateUniversityKansasUSA DepartmentofAnthropology UniversityofCaliforniaLosAngelsUSA SilverCity Nevada.USA DepartmentofAnthropology UniversityofCaliforniaDavisCA95616USA

The area along the eastern and southeastern margins of the Tengger Desert, NW China, which is sensitive to the summer monsoon variations, was selectedfor studying the environmental conditions surrounding the transition between Paleolithic foragers and Neolithic farmer/pastoral- ists. Short cores were obtained from four lake basins in the southwestern Tengger using a hand-driven piston coring device. Proxies from these cores were supplemented by ra- diocarbon ages obtained from lake sediment cores, shoreline features and spring mound deposits. Together these records provide evidence of millennial-scale climate change events from the Pleistocene-Holocene transition to the present. Lake/wetland events, representing periods of more intensive summer monsoon, occur in the records at ～12.7-11.6, ～10.1, ～9.3, ～8.0, ～5.4, ～1.5, and ～0.8 ka BP. They do suggest that century- to millennial-scale climatic cycles are characteristic of the Holocene in the southeastern Tengger Desert although the chronology must be considered extremely tentative.

关键词：中国西北地区腾葛尔沙漠晚更新世全新世湖泊沉积物古气候

他们必须坐在那里吗？——帮助学生学习物理的思考

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国际物理教育通讯 1998年第21期 8-12页

作者： D．Zollman 荣玮美国kansasstateuniversity 山东工程学院

眼前的情景，使我想起了许多往事，想起了那些使我的理想成为现实的人们。我真正对物理学产生兴趣，始于一个暑期实验班。当时，苏联的人造地球卫星刚上天。不久，国家科学基金为参加暑期培训的、即将由高中升人大学的学生提供助学金。... 详细信息

眼前的情景，使我想起了许多往事，想起了那些使我的理想成为现实的人们。我真正对物理学产生兴趣，始于一个暑期实验班。当时，苏联的人造地球卫星刚上天。不久，国家科学基金为参加暑期培训的、即将由高中升人大学的学生提供助学金。我恰是第一期学员。后来在我读研究生的学校里又获得了鼓励在大学任教的福德基金会提供的奖金。因此，我21岁时，已和各种奖金结下了不解之缘。

关键词：学生学习助学金物理学大学暑期学校研究生理想实验班人造地球卫星

TRANSGENIC PLANTS EXPRESSING BACILLUS THURINGIENSIS DELTA-ENDOTOXINS

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Entomologia Sinica 2003年第3期10卷 155-166页

作者： Hua-rong,Li BrendaOppert KunYanZhu RandallA.Higgins Fang-nengHuang LawrentL.Buschman Departments of Entomology Manhattan KS66506USA Grain Marketing and Production Research Center USDA-ARS1515 College AvenueManhattanKS66502USA 2415E.Highway83WeslacoTX78596-8399USA DepartmentofGrainScienceandIndustry KansasStateUniversityManhattanKS66506USA

Commercial varieties of transgenic Bacillus thuringiensis (Bt) plants have been developed in many countries to control target pests. Initially, the expression of native Bt genes in plants was low due to mRNA instability, improper splicing, and post translation modifications. Subsequently, modifications of the native Bt genes greatly enhanced expression levels. This is a review of the developments that made modern high expression transgenic Bt plants possible, with an emphasis on the reasons for the low level expression of native Bt genes in plant systems, and the techniques that have been used to improve plant expression of Bt toxin genes.

关键词： Bacillus thuringiensis Cry protein genetic modification insecticidal protein transgenic plants