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Sample records for a-ga010 studiedby spa-leed

  1. Au-chains grown on Ge(100): A detailed SPA-LEED study

    Lichtenstein, T.; Teiken, H.; Pfnür, H.; Wollschläger, J.; Tegenkamp, C.

    2015-02-01

    Au-induced wire structures grown on Ge(100) were shown to exhibit spectroscopic signatures of strong electronic correlation. However, the atomistic structure of these wires is still controversially discussed. In this study the morphology has been investigated by means of low energy electron diffraction (SPA-LEED). The detailed analysis of diffraction profiles favors strongly to the model of an Au-induced giant missing row (GMR) structure rather than the heterodimer model. Systematic variation of the initial Au-coverage has revealed further that approximately 0.25 ML of the deposited Au coverage penetrates into subsurface positions stabilizing the adsorbate-induced surface structure.

  2. A combined STM and SPA-LEED study of the "explosive" nucleation and collective diffusion in Pb/Si(111)

    Hattab, H.; Hupalo, M.; Hershberger, M. T.; Horn von Hoegen, M.; Tringides, M. C.

    2016-04-01

    A novel type of very fast nucleation was recently found in Pb/Si(111) with 4- to 7-layer high islands becoming crystalline in an "explosive" way, when the Pb deposited amount in the wetting layer is compressed to θc ~ 1.22 ML, well above the metallic Pb(111) density. This "explosive" nucleation is very different from classical nucleation when island growth is more gradual and islands grow in size by single adatom aggregation [8]. In order to identify the key parameters that control the nucleation we used scanning tunneling microscopy (STM) and spot profile analysis low energy electron diffraction (SPA-LEED). It was found that the number and duration of steps in iterative deposition used to approach θc and the flux rate have dramatic effects on the crystallization process. Larger depositions over shorter times induce greater spatial coverage fluctuations, so local areas can reach the critical coverage θc easier. This can trigger the collective motion of the wetting layer from far away to build the Pb islands "explosively". The SPA-LEED experiments show that even low flux experiments in iterative deposition experiments can trigger transfer of material to the superstable 7-layer islands, as seen from the stronger satellite rings close to the (00) spot.

  3. Growth of NaCl on thin epitaxial KCl films on Ag(100) studied by SPA-LEED

    Marquardt, Christian; Paulheim, Alexander; Sokolowski, Moritz

    2015-11-01

    We investigated the growth of NaCl on thin (100)-oriented films of KCl by spot profile analysis of low energy electron diffraction (SPA-LEED). The underlying question of this investigation was how the system accommodates to the misfit of - 10% between the NaCl and KCl lattices. The KCl films (3 atomic layers thick) were epitaxially grown on a Ag(100) single crystal. We studied the heteroepitaxial growth of NaCl on KCl at 300 K and at 500 K, respectively. At 300 K, the first NaCl monolayer (ML) grows pseudomorphically on the KCl film. From the second layer onward, the NaCl lattice relaxes. The NaCl multilayers roughen, and a small rotational disorder (± 4°) of the NaCl domains is observed. The roughening results from the formation of multilayer islands of limited lateral size due to the misfit to the pseudomorphic first NaCl layer. At a growth temperature of 500 K, no pseudomorphic NaCl layer forms, instead relaxed multilayer island growth of NaCl is observed from the first layer onward. Similarly to the growth at 300 K, we find NaCl multilayer islands of limited lateral size. For both temperatures, we explain this growth behavior by the misfit that makes the adsorption sites at the island edges of the first relaxed NaCl layer less favorable for larger islands, promoting nucleation of multilayer islands.

  4. SPA-LEED Study of the Morphology and Nucleation of a Novel Growth Mode and the ''devil's staircase'' on Pb/Si(111)

    This thesis was developed to address the following questions for the Pb/Si(111) system: (1) Is it possible to control the nano-structure growth by changing the initial substrate; (2) is the nucleation theory applicable to the case of the 7-step growth mode; and (3) what phase or phases could be formed between coverage 6/5 ML and 4/3 ML? The first question was answered in chapter 2, different growth results were observed for different initial substrate, suggesting the possibility of controlling nano-structure growth by selecting the initial substrate. The applicability of nucleation theory was determined to be unclear in chapter 3, from the results that the saturation island density does not depend on deposition rate, in contrary to the prediction of nucleation theory. Chapter 4 revealed a novel ''devil's staircase'' in Pb/Si(111) within the coverage range 6/5 ML and 4/3 ML. Low temperature deposition experiments showed high order of self-organization in such a system. Theoretical studies are needed to understand such a low temperature behavior. In general, this thesis provides possibilities of controlling nano-structure growth, which can be possibly an indication for future application. It also raises interesting questions in fundamental researches: a modified theory of nucleation is needed, and a detailed study of low temperature behavior is required. Details of the conclusions in each of the chapters are collected in the following sections

  5. Reactivity of Au nanoparticles supported over SiO2 and TiO2 studiedby ambient pressure photoelectron spectroscopy

    Herranz, Tirma; Deng, Xingyi; Cabot, Andreu; Alivisatos, Paul; Liu, Zhi; Soler-Illia, Galo; Salmeron, Miquel

    2009-04-15

    The influence of the metal cluster size and the identity of the support on the reactivity of gold based catalysts have been studied in the CO oxidation reaction. To overcome the structural complexity of the supported catalysts, gold nanoparticles synthesized from colloidal chemistry with precisely controlled size have been used. Those particles were supported over SiO{sub 2} and TiO{sub 2} and their catalytic activity was measured in a flow reactor. The reaction rate was dependent on the particle size and the support, suggesting two reaction pathways in the CO oxidation reaction. In parallel, ambient pressure photoelectron spectroscopy (APPS) has been performed under reaction conditions using bidimensional model catalysts prepared upon supporting the Au nanoparticles over planar polycrystalline SiO{sub 2} and TiO{sub 2} thin films by means of the Langmuir-Blodgett (LB) technique to mimic the characteristic of the powder samples. In this way, the catalytically active surface was characterized under true reaction conditions, revealing that during CO oxidation gold remains in the metallic state.

  6. Adsorption of PTCDA on GaN(0001) surfaces

    Schulz, Christian; Tessarek, Christian; Figge, Stephan; Flege, Jan Ingo; Schmidt, Thomas; Hommel, Detlef; Falta, Jens [Institute of Solid State Physics, University of Bremen, 28359 Bremen (Germany); Jaye, Cherno; Fischer, Daniel A. [Ceramics Division, National Institute of Standards and Technology, Gaithersburg, MD (United States)

    2010-07-01

    Ordered growth of thin PTCDA layers is mainly observed on metals but recent reports have shown that some molecules also show ordered layers on unpassivated III-V semiconductor surfaces. In this work we investigate the adsorption of PTCDA on gallium-polar GaN(0001) with different methods. X-ray photoelectron spectroscopy (XPS) shows that the molecules are not dissociating after deposition, because the peak area ratios (including the shake-up's) for the perylene to carboxylic C1s feature is near the expected ratio for the intact molecule. Scanning tunneling microscopy (STM) and spot profile analyzing low energy electron diffraction (SPA-LEED) measurements reveal an island growth mode. For monolayer equivalent deposits, the near edge X-ray absorption fine structure (NEAFS) data of the C K-edge exhibit no polarization dependence indicating a disordered mixture of molecules in upstanding and down-lying geometry. However, for multilayer equivalent deposits a polarization dependence is observed which suggests a flat-lying geometry of the molecules. These findings are in good agreement with high-resolution STM and SPA-LEED data which reveal lateral ordering, compatible with a bulk-like configuration, within the islands.

  7. Adsorption of phthalocyanines on noble metal surfaces; Adsorption von Phthalocyaninen auf Edelmetalloberflaechen

    Kroeger, Ingo

    2011-05-20

    In this thesis the adsorbate systems CuPc/Ag(111), CuPc/Au(111), CuPc/Cu(111), H2Pc and TiOPc/Ag(111) were investigated and characterized in great detail using complementary methods. The focus of the experiments was the determination of lateral geometric structures with spot-profile-analysis low energy electron diffraction (SPA-LEED) and scanning tunneling microscopy (STM), as well as the measurement of adsorption heights using the method of normal incidence X-ray standing waves (NIXSW). High resolution electron energy loss spectroscopy (HREELS) was used to characterize the vibronic properties of the molecule and the interface dynamical charge transfer (IDCT). The electronic structure and the charge transfer into the molecule were investigated with ultraviolet photoelectron spectroscopy (UPS). The most important results of this work are related with the interplay between adsorbate-substrate and adsorbate-adsorbate interaction of Phthalocyanines in the submonolayer regime. (orig.)

  8. Controlling atomistic processes on Pb films via quantum size effects and lattice rotation

    Binz, Steven [Iowa State Univ., Ames, IA (United States)

    2012-01-01

    The two main techniques used to record the data in this dissertation were Spot Profile Analysis - Low Energy Electron Diffraction (SPA-LEED) and Scanning Tunneling Microscopy (STM). A specific data analysis technique for LEED data called G(S) curves is described in depth. G(S) curves can provide a great deal of structural information about the surface; including step heights, island size, and island separation. The effects of quantum size effects (QSE) on the diffusion and critical island sizes of Pb and In on Pb films are reported. Pb depositions on the 2D In phases {radical}3 and {radical}31 to see how the phases affect the Pb growth and its strong QSE are reported.

  9. PROCESS STUDY ON DEPHENOLIZATION OF BPA-PHENOL ADDUCT BY SOLID DECOMPOSITION REACTION%双酚A-苯酚加合物固相分解反应脱酚的工艺研究

    刘宗章; 张敏华; 李传兆; 钱胜华; 谈遒

    1999-01-01

    The process condition of dephenolization of bisphenol A-phenol adduct is studied,by using the solid decomposition reaction on the basis of thermodynamic property of bisphenol A-phenol and the kinetics of solid decomposition reaction.The process condition is proposed with high quality bisphenol A product.A new method of dephenolization in the production of bisphenol A is developed.

  10. OSCILLATION OF A SECOND-ORDER HALF-LINEAR NEUTRAL DAMPED DIFFERENTIAL EQUATION WITH TIME-DELAY

    2012-01-01

    In this paper,the oscillation for a class of second-order half-linear neutral damped differential equation with time-delay is studied.By means of Yang-inequality,the generalized Riccati transformation and a certain function,some new sufficient conditions for the oscillation are given for all solutions to the equation.

  11. Surface stress and large-scale self-organization at organic-metal interfaces

    Pollinger, Florian

    2009-01-22

    The role of elastic interactions, particularly for the self-organized formation of periodically faceted interfaces, was investigated in this thesis for archetype organic-metal interfaces. The cantilever bending technique was applied to study the change of surface stress upon formation of the interface between 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) and Ag(111). The main focus of this work was on the investigation of the formation of the long-range ordered, self-organized faceted PTCDA/Ag(10 8 7) interface. Reciprocal space maps of this interface were recorded both by spot profile analysis low energy electron diffraction (SPA-LEED) and low energy electron microscopy (LEEM) in selected area LEED mode. Complementary to the reciprocal data, also microscopic real-space LEEM data were used to characterize the morphology of this interface. Six different facet faces ((111), (532), (743), (954), (13 9 5), and (542)) were observed for the preparation path of molecular adsorption on the substrate kept at 550 K. Facet-sensitive dark-field LEEM localized these facets to grow in homogeneous areas of microscopic extensions. The temperature-dependence of the interface formation was studied in a range between 418 K and 612 K in order to learn more about the kinetics of the process. Additional steeper facets of 27 inclination with respect to the (111) surface were observed in the low temperature regime. Furthermore, using facet-sensitive dark-field LEEM, spatial and size distributions of specific facets were studied for the different temperatures. Moreover, the facet dimensions were statistically analyzed. The total island size of the facets follows an exponential distribution, indicating a random growth mode in absence of any mutual facet interactions. While the length distribution of the facets also follows an exponential distribution, the width distribution is peaked, reflecting the high degree of lateral order. This anisotropy is temperature-dependent and occurs

  12. Switching orientation of adsorbed molecules: Reverse domino on a metal surface

    Braatz, C. R.; Esat, T.; Wagner, C.; Temirov, R.; Tautz, F. S.; Jakob, P.

    2016-01-01

    A thus far unknown phase of 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) on Ag(111), characterized by an all perpendicular orientation of the planar molecules and bound to the Ag substrate through the carboxyl oxygen atoms has been identified using infrared absorption spectroscopy and scanning tunneling microscopy. Its formation process requires second layer NTCDA to squeeze into empty spaces between relaxed monolayer NTCDA molecules. Remarkably, this process causes initially parallel oriented NTCDA to likewise adopt the new, highly inclined adsorption geometry. According to our SPA-LEED and STM findings, the new phase displays a distinct long range order and shows a pronounced tendency to form 1D rows or narrow islands. We suggest that extra NTCDA preferentially transforms into the upright configuration close to existing islands and attaches to them, i.e. the transformation process proceeds in a directed and recurrent manner (reverse domino scenario). Identical processing starting with a compressed NTCDA/Ag(111) monolayer leads to a purely parallel oriented bilayer, that is, the NTCDA monolayer phase is retained and merely acts as a passive template for bilayer NTCDA. The new vertical NTCDA phase represents an unusual molecular system with π-orbitals oriented parallel to a metal surface. A substantially reduced coupling of these orbitals to Ag(111) electronic levels is conjectured, which will have a major impact on intermolecular couplings and electronically excited state lifetimes.

  13. Morphological transformation of the silicon(112) surface through metal adsorption. Faceting vs. stabilization; Morphologische Transformation der Silizium(112) Oberflaeche durch Metalladsorption. Facettierung vs. Stabilisierung

    Wiethoff, Christian

    2010-06-21

    Semiconductor nanowires lately attracted immense attention in worldwide research. Lots of possible applications were discussed and partially realized. Gold is the most commonly used metal in catalyzed nanowire growth, but exhibits poor electronic properties for building integrated circuits. Recently, aluminium was achieved to work as a catalyst and the nanowires grown this way showed extremely smooth surfaces. This is in contrast to surfaces grown with other metals. In this work the modification of the silicon (112) surface by metal adsorption is studied. Since nanowires with [111] growth direction have [112]-like sidewalls, this way a virtually endless nanowire surface is used to study the interaction of gold, silver and aluminium with the silicon surface. Spot Profile Analysis Low Energy Electron Diffraction (SPA-LEED) is used to analyze the surfaces. This high resolution diffraction method allows for detailed characterization of the surface structures and facets. Gold adsorption leads to eight different surface phases, the most stable one exhibits 111- and 113-facets and is shown to occur on nanowire surfaces if they were grown with gold as a catalyst. Silver adsorption pushes the surface to form 111- and 115-facets. The facet size distribution is quite narrow, so the finite size effect creates intensity minima in the vicinity of the bragg points in diffraction patterns. Aluminium adsorption finally leads to a stabilization of the silicon (112) surface, no facets are formed. This atomic flat surface was seen on nanowire sidewalls, grown with aluminium as catalyst. (orig.)

  14. The growth of ultra thin Praseodymia oxide films on boron-passivated Si(111) surfaces

    Silicon on insulator (SOI) CMOS technology already have an enormous commercial impact with Si dioxide as insulating material. Alternative insulating materials are in the focus of investigation to integrate semiconductors for system on chip (SOC) solutions that cannot be built on Si alone. Due to its good insulations characteristics and a high dielectric constant, praseodymium oxide is an interesting candidate for such applications. To prevent the formation of silicate at the substrate-oxide interface it is essential to use passivated silicon substrates. In this work the influence of boron-passivation is investigated. Prior to praseodymium oxide evaporation by molecular beam epitaxy the Si substrate surface was passivated by boron via evaporation of boric acid and subsequent annealing of the substrate to 900 C. In situ Spot Profile Analysis Low Energy Electron Diffraction (SPA-LEED) and Auger Electron Spectroscopy (AES) were used to characterize the surface structure and morphology. Additional Ex-situ X-Ray Reflectivity (XRR) and X-Ray Diffraction (XRD) analyses were performed. The results show that at a substrate temperature of 500 C a single crystalline oxide film is formed.

  15. Surface stress and its consequences: In-situ study of PTCDA induced faceting of vicinal Ag(111)

    Pollinger, Florian; Vrdoljak, Pavo; Schmitt, Stefan; Kumpf, Christian; Schoell, Achim [Universitaet Wuerzburg, Experimentelle Physik II, Wuerzburg (Germany); Tian, Zhen; Sander, Dirk; Kirschner, Juergen [Max-Planck-Institut fuer Mikrostrukturphysik, Halle (Germany); Umbach, Eberhard [Universitaet Wuerzburg, Experimentelle Physik II, Wuerzburg (Germany); Forschungszentrum Karlsruhe (Germany)

    2008-07-01

    Adsorption of organic molecules on vicinal metal surfaces is known to promote faceting and self-organized ordering on mesoscopic scales. The adsorption of PTCDA on vicinal Ag(111) surfaces leads to grating-like structures after annealing. The system PTCDA/Ag(10 8 7) was investigated using two complementary techniques: An optical cantilever bending technique sensitive to changes in surface stress and spot-profile analysis low energy electron diffraction (SPA-LEED) to monitor the development of the interface structure during faceting. The data was compared to the related, non-faceting system PTCDA on Ag(111). Overall, we find a surface stress change of 0.7 N/m due to the PTCDA-induced faceting, whereas the adsorption of PTCDA without faceting induces a change of 0.4 N/m. Moreover, the data allows an explicit and unambiguous correlation of the surface stress change to the structural and morphological evolution of the interface during the adsorption of the PTCDA adlayer. In conclusion, the results provide experimental evidence for significant surface stress induced by an organic adsorbate and for its importance for faceting and long-range ordering at metal-organic interfaces.

  16. Uenbinding'' an adsorbed organic molecule: K plus PTCDA on Ag(110)

    Bauer, Oliver; Schmitz, Christoph H.; Fiedler, Benjamin; Sokolowski, Moritz [Institut fuer Physikalische und Theoretische Chemie, Universitaet Bonn (Germany); Mercurio, Giuseppe; Subach, Sergey; Tautz, Frank Stefan [Institut fuer Bio- und Nanosysteme 3, Forschungszentrum Juelich (Germany)

    2010-07-01

    We have doped the well-known brick-wall structure of pristine PTCDA which is present in the monolayer on the Ag(110) surface with potassium (K) and investigated the induced structural and electronic changes at the interface. SPA-LEED measurements reveal that the structural order of the PTCDA molecules is strongly altered upon K dosing: A variety of co-existing binary phases is observed within the monolayer. In addition we have conducted XPS and NIXSW measurements on K+PTCDA/Ag(110). The photoemission experiments indicate that the K atoms preferentially interact with the carboxylic groups of the co-adsorbed PTCDA molecules. This interpretation is further supported by the NIXSW results: The adsorption geometries of the carboxylic and the anhydride oxygen (O) atoms are highly influenced by the presence of K on the surface, the bonding distances are extended. The adsorption height of the perylene core is also increased by K doping. Hence we conclude that the local Ag-O bonds at the interface are partially lifted by the co-adsorbed K and that K and Ag atoms compete for the interaction with the carboxylic groups of PTCDA while the bonding across the interface is weakened.

  17. Coordination Structure of Aluminum in Magnesium Aluminum Hydroxide Studied by 27Al NMR

    2003-01-01

    The coordination structure of aluminum in magnesium aluminum hydroxide was studiedby 27Al NMR. The result showed that tetrahedral aluminum (AlⅣ) existed in magnesiumaluminum hydroxide, and the contents of AlⅣ increased with the increase of the ratio of Al/Mg andwith the peptizing temperature. AlⅣ originated from the so-called Al13 polymer with the structureof one Al tetrahedron surrounded by twelve Al octahedrons.

  18. Verification of the spin-weighted spheroidal equation in the case of s =1

    Zhang Qing; Tian Gui-Hua; Sun Yue; Dong Kun

    2012-01-01

    The spin-weighted spheroidal equation in the case of s =1 is studied.By transforming the independent variables,we make it take the Schr(o)dinger-like form.This Schr(o)dinger-like equation is very interesting in itself.We investigate it by using super-symmetric quantum mechanics and obtain the ground eigenvalue and eigenfunction,which are consistent with the results previously obtained.

  19. To tilt or not to tilt: Correction of the distortion caused by inclined sample surfaces in low-energy electron diffraction

    Sojka, Falko, E-mail: falko.sojka@uni-jena.de [Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 5, 07743 Jena (Germany); Meissner, Matthias; Zwick, Christian; Forker, Roman [Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 5, 07743 Jena (Germany); Vyshnepolsky, Michael; Klein, Claudius; Horn-von Hoegen, Michael [University of Duisburg-Essen, Department of Physics, Lotharstr. 1, 47057 Duisburg (Germany); Fritz, Torsten, E-mail: torsten.fritz@uni-jena.de [Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 5, 07743 Jena (Germany)

    2013-10-15

    Low-energy electron diffraction (LEED) is a widely employed technique for the structural characterization of crystalline surfaces and epitaxial adsorbates. For technical reasons the accessible reciprocal space is limited at a given primary electron energy E. This limitation may be overcome by sweeping E to observe higher diffraction orders decisively enhancing the quantitative examination. Yet, in many cases, such as molecular films with rather large unit cells, the adsorbate reflexes become less pronounced at energies high enough to observe substrate reflexes. One possibility to overcome this problem is an intentional inclination of the sample surface during the measurement at the expense of the quantitative interpretability of then severely distorted diffraction patterns. Here, we introduce a correction method for the axially symmetric distortion in LEED images of tilted samples. We provide experimental confirmation for micro-channel plate LEED and spot-profile analysis LEED instruments using the (7×7) reconstructed surface of a Si(111) single crystal as a reference sample. Finally, we demonstrate that the correction of this distortion considerably improves the quantitative analysis of diffraction patterns of adsorbates since substrate and adsorbate reflexes can be evaluated simultaneously. As an illustrative example we have chosen an epitaxial monolayer of 3,4,9,10-perylenetetracarboxylic dianhydride on Ag(111) that is known to form a commensurate superstructure. - Highlights: • We introduce a method to correct distortions in LEED patterns of tilted surfaces. • Higher diffraction orders unobservable at higher beam energies can be evaluated. • Our procedure makes LEED patterns of tilted samples quantitatively analyzable. • Experimental confirmation with SPA-LEED and MCP-LEED is presented. • The method is applied to PTCDA on Ag(111) confirming earlier literature values.

  20. Nonlinear transport of Bose-Einstein condensates in a double barrier potential

    Fang Jian-Shu

    2008-01-01

    The stable nonlinear transport of the Bose-Einstein condensates through a double barrier potential in a waveguide is studied.By using the direct perturbation method we have obtained a perturbed solution of Gross-Pitaevskii equation.Theoretical analysis reveals that this perturbed solution is a stable periodic solution,which shows that the transport of Bose-Einstein condensed atoms in this system is a stable nonlinear transport.The corresponding numerical results are in good agreement with the theoretical analytical results.

  1. Rabi Oscillations in Two-Component Bose-Einstein Condensates with a Coupling Drive

    LI Wei-Dong; FAN Wen-Bing; ZHOU Xiao-Ji; WANG Yi-Qiu; LIANG Jiu-Qing

    2002-01-01

    The Rabi oscillations in two-component Bose-Einstein condensates with a coupling drive are studiedby means of a pair of bosonic operators. The coupling drive and initial phase difference will affect the amplitudeand the period of the Rabi oscillations. The Rabi oscillations will vanish in the evolution of the condensate densityfor some special initial phase differences (ψ = 0 or π). Our theory provides not only an analytical framework forquantitative predictions for two-component condensates, but also gives an intuitive understanding of some mysteriousfeatures observed in experiments and numerical. simulations.

  2. Investigation on characteristics of self-organization in Mach-Zehnder erbium-doped fiber laser cavity

    Fengnian Liu; Bo Liu; Bangcai Huang; Guiyun Kai; Shuzhong Yuan; Xiaoyi Dong

    2008-01-01

    The characteristics of coherent coupling in Mach-Zehnder erbium-doped fiber laser cavity are experimentally studied.By virtue of a seemly controlling of length difference between two interferometric arms,the obtained comb-like spectrum of interferometer resonator with a period of 0.06 nm commendably agrees with the theory of self-organization coherence The coherent output exits from the output mirror of a fiber Bragg grating with 4.5% reflectivity.A high coherent combining efficiency of 94% is obtained.Investigation on characteristics of the leak power opens out self-organization mechanism in Mach-Zehnder composite cavity.

  3. CYCLOSTATIONARITY-BASED OFDM SIGNAL SENSING OVER DOUBLY-SELECTIVE FADING CHANNELS

    Tian Jinfeng; Jiang Yonglei; Chen Huaxia; Hu Honglin

    2011-01-01

    In this paper,using cyclostationarity-based sensing method to detect the presence of Orthogonal Frequency Division Multiplexing (OFDM) signal over doubly-selective fading channels is studied.By approximating the channel with Basis Expansion Model (BEM),we derive the second-order cyclostationary statistics of the received OFDM signal over doubly-selective fading channels.Theoretical analysis indicates that new cyclostationary signatures produced by Doppler spread and multipath delay can be further exploited in the detecting process.Simulation examples demonstrate that the sensing methods using channel-induced cyclostationary features provide substantial improvements on detection performance.

  4. Coexistance of C40 and C54 TiSi2 during the solid state reaction of Ti/Mo/Si system

    2002-01-01

    The effect of a 0.9 nm Mo interlayer at the interface of Ti film depositedon a Si substrate on phase formation of TiSi2 during annealing has been studiedby using transmission electron micro-diffraction technique. When Ti/Mo/Si was an-nealed at low temperature as 550℃ for 30 min in Ar ambient, a metastable phase, i.e.,hexagonal C40 TiSi2, and the equilibrium phase, i.e., orthorhombic C54 TiSi2, wereboth detected. The experimental patterns of the C40 and C54 compare well with thesimulated ones.

  5. On the mean value problem of the Smarandache Ceil function%关于Smarandache Ceil函数的一类均值问题

    吕二兵

    2013-01-01

    The mean value distribution problem of Smarandache Ceil function and product of prime divisor function U(n) is studied.By using the analytic methods,an asymptotic formula of (Sk (n)-U(n))2 is given,with k≥2,n is any natural number.%研究了Smarandache Ceil函数与素因子积函数U(n)的均方值的分布问题.利用解析方法给出了(Sk (n)-U(n))2的一个有趣的渐近公式,其中k≥2,n为自然数.

  6. Stabilization and trajectory tracking of autonomous airship's planar motion

    Zhang Yan; Qu Weidong; Xi Yugeng; Cai Zili

    2008-01-01

    The stabilization and trajectory tracking problems of autonomous airship's planar motion are studied.By denning novel configuration error and velocity error,the dynamics of error systems are derived.By applying Lyapunov stability method,the state feedback control laws are designed and the close-loop error systems are proved to be uniformly asymptotically stable by Matrosov theorem.In particular,the controller does not need knowledge on system parameters in the case of set-point stabilization,which makes the controller robust with respect to parameter uncertainty.Numerical simulations illustrate the effectiveness of the controller designed.

  7. Courses Studied by New York Librarianship Students Affect Their Perceived Readiness for Employment. A Review of: Creel, S. L., & Pollicino, E. B. (2012. Practitioners’ & LIS students’ perceptions on preparedness in the New York metropolitan area. Education for Information, 29, 53-69. doi: 10.3233/EFI-2010-0911

    Kirsty Thomson

    2012-12-01

    Full Text Available Objective – To investigate whetherlibrarianship students felt ready to enter theworkforce, and whether practitioners feltrecent graduates were suitably prepared.Design – Survey.Setting – A university in New York City, andschool and public librarians working in theNew York metropolitan area.Subjects – 55 MLS students, 167 school librarypractitioners, and 181 public librarypractitioners.Methods – Students surveyed practitionersabout new graduates’ readiness to work aslibrarians. The students also assessed theirown readiness.Main Results – Detailed analysis of differencesbetween the responses of the four subjectgroups – public librarians, school librarians,public library students, and school librarystudents – for each of six survey statements isprovided. Practitioners and students felt thatschool librarianship graduates were moreprepared for work than public librarianshipgraduates. This may have been due todifferences in the practical components of theircourses.Conclusion – Preparedness for libraryemployment is related to the courses studiedby librarianship students.

  8. Properties of radicals created by γ-ray irradiation of silk fabrics

    2002-01-01

    The properties of radicals from γ-ray irradiated silk fabrics were studiedby electron spin resonance method (ESR). The ESR spectra of silk fabrics irradiated inN2 showed a doublet at room temperature. The doublet became a singlet at g=2.0057after placing the sample in air for 24 hours. This can be explained by formation ofperoxide radicals. The radical concentration of the irradiated silk fabric and the decayrate of radicals are significantly affected by irradiation conditions, which include theabsorbed dose, atmosphere, and water content of the silk fabric samples. However, nodose rate effect on the radical concentration was observed. The results are of help in ourpractice of property modification of silk products by radiation graft copolymerization.``

  9. THE STUDY ON MECHANISM OF BINDER MIGRATION DURING COATING PROCESS

    YunLiang; KefuChen

    2004-01-01

    Binder migration during coating process and themechanism of binder migration were studied in thispaper. After the latex was tagged by osmium, thedegree of binder migration was measured byenergy-dispersive X-ray spectrometer. For the wetsample just after coating application, the realinformation of binder distribution was kept byquenching the sample in liquid nitrogen followed byfreeze-drying. The results showed: under thecondition of this research, binder migration occurredboth in the process of coating application and drying.But the amount of binder migration occurred duringcoating application was much little than that occurredduring drying. The mechanism of binder migrationduring the process of coating application was studiedby force analyses. And one viewpoint was proposedthat was binder migration was caused by Magnusforce and Saffman force.

  10. Crystalline and lattice matched Ba0.7Si0.3O layers on plane and vicinal Si(001) surfaces

    In this work the low temperature growth conditions of epitaxial and lattice-matched Ba0.7Sr0.3O layers on Si(100) were investigated using the combination of low energy electron diffraction (LEED), x-ray photoemission (XPS) and electron energy loss spectroscopy (EELS). With these methods crystallinity, stoichiometry and electronic structure of both occupied and unoccupied levels were studied as a function of layer thickness. Oxide layers were generated by evaporating the metals in oxygen ambient pressure with the sample at room temperature. Perfect crystallinity and lattice matching was only obtained starting with a preadsorbed monolayer (ML) of Sr or Ba at a concentration close to one monolayer. The XPS analysis shows that Ba0.7Sr0.3O as a high-K gate dielectric offers an adequate band gap, an appropriate band alignment and a atomically sharp interface to the Si(001) substrate. No silicide and silicate species, or SiO2 formation at the interface after oxidation were found. To show that Ba0.7Sr0.3O is really appropriate to replace SiO2 as a gate dielectric, first C-V and I-V curves of MOS-diodes with SrO, BaO and Ba0.7Sr0.3O as gateoxide were measured under ambient conditions. Besides other results, it turns out that the measured dielectric constant of Ba0.7Sr0.3O conforms with the expected value of ε ∼ 25 - 30. Exploring ways for self-organized structuring of insulating films, the possibility to produce replicas of step trains, given by a vicinal Si(001)-4 [110] surface, in layers of crystalline and perfectly lattice matched Ba0.7Sr0.3O were investigated. For this purpose high-resolution spot profile analyses in low-energy electron diffraction (SPA-LEED) both on flat Si(001) and on vicinal Si(001)-4 [110] were carried out. The G(S) analysis of these mixed oxide layers reveals a strong influence of local compositional fluctuations of Sr and Ba ions and their respective scattering phases, which appears as an unphysically large variation of layer distances

  11. RESEARCH ON RELATION OF TIME-EFFECT WITH PARTS’CURL DISTORTION IN STEREOLITHOGRAPHY%激光快速成形中时间效应与零件翘曲性关系研究

    段玉岗; 王素琴; 李涤尘; 吴懋亮; 卢秉恒

    2001-01-01

    Solidification process and phenomenon of solidyfication shrinkage lagging polymerization are studied in SL,time-effect conception is put forward and the effect of shrinkage time-effect on parts'curl distortion and several embodiment are studied.By manufacturing parts,the theory put forward is validated.Improving manufacture process based on time-effect is used to minish the curl distortion of parts,the result shows the curl distortion is improved greatly.%研究了激光快速成形中树脂固化过程以及固化收缩滞后于聚合速度的现象,提出了收缩完成的时间效应概念,通过实物原形制作研究了时间效应对零件翘曲的影响及几种表现,并利用时间效应对成形工艺进行了改进,使零件翘曲性得到很大的改善。

  12. A novel weighted evolving network model based on clique overlapping growth

    YANG Xu-hua; WANG Bo; SUN Bao

    2010-01-01

    A novel weighted evolving network model based on the clique overlapping growth was proposed.The model shows different network characteristics under two different selection mechanisms that are preferential selection and random selection.On the basis of mean-field theory,this model under the two different selection mechanisms was analyzed.The analytic equations of distributions of the number of cliques that a vertex joins and the vertex strength of the model were given.It is proved that both distributions follow the scale-free power-law distribution in preferential selection mechanism and the exponential distribution in random selection mechanism,respectively.The analytic expressions of exponents of corresponding distributions were obtained.The agreement between the simulations and analytical results indicates the validity of the theoretical analysis.Finally,three real transport bus networks(BTNs)of Beijing,Shanghai and Hangzhou in China were studied.By analyzing their network properties,it is discovered that these real BTNs belong to a kind of weighted evolving network model with clique overlapping growth and random selection mechanism that was proposed in this context.

  13. Analysis of streamwise conduction in forced convection of microchannels using fin approach

    Suhandran MUNIANDY; Yew Mun HUNG

    2011-01-01

    The effects induced by streamwise conduction on the thermal characteristics of forced convection for single-phase liquid flow in rectangular microchannel heat sinks under imposed constant wall temperature have been studied.By employing the fin approach in the first law of analysis,models with and without streamwise conduction term in the energy equation were developed for hydrodynamically and thermally fully-developed flow under local thermal non-equilibrium for the solid and fluid phases.These two models were solved to obtain closed form analytical solutions for the fluid and solid temperature distributions and the analysis emphasized details of the variations induced by the streamwise conduction on the fluid temperature distributions.The effects of the Peclet number,aspect ratio,and thermal conductivity ratio on the thermal characteristics of forced convection in microchannel heat sinks were analyzed and discussed.This study reveals the conditions under which the effect of streamwise conduction is significant and should not be neglected in the forced convective heat transfer analysis ofmicrochannel heat sinks.

  14. On Crystallization in Polypropylene-Polyethylene Blends

    2001-01-01

    Blends of polypropylene(PP) and low-density polyethylene (LDPE) have beencrystallized to form open structures(“cluster spherulites”) where the droplets of the minorityPP are bridged by PP lamellae which have grown in the LDPE-rich matrix. These are studiedby permanganic etching followed by electron and optical microscopies. Two similar PP typesare compared, one synthesized with Ziegler-Natta catalyst and one with metallocenecatalyst. The metallocene-catalysed material crystallized much more slowly due to thepresence of regio defects in the chains, even though the overall concentration of tacticitydefects in the Ziegler-Natta material is much higher. A mechanism involving reversal ofhelical direction at the regio defect interfering with the regular chain packing in the crystal issuggested. Growth of “cluster spherulites” is faster in regions where low molecular weightmaterial is concentrated. It is slower where droplets are larger, and this is attributed tocompetition between PP lamellar growth in the matrix and diffusion of PP to alreadycrystallized droplets.

  15. Technology development and application of asepsis cool-filling desserts%无菌冷罐装含乳甜点的技术开发和应用

    胡姝敏; 朱雅玲

    2013-01-01

    Abstracts:The technology development and application of asepsis cool-filling desserts that fit for China were studied.By studying technical characters of asepsis cool-filling desserts and relative hydrocolloids application character,the technology (parameter),technology flow and hydrocolloids were confirmed,and the hydrocolloids were composed for functional system applied for asepsis cool-filling desserts to produce desserts that have very good texture and sensory organ property,including neutrosphere chocolate dessert and acidic pudding dessert.%研究了适合我国现有生产条件和市场发展状况的无菌冷灌装甜点的技术与应用.通过研究无菌冷灌装甜点的工艺特征及相关胶体应用特征,选择适合的亲水胶体,通过科学实验设计和生产验证,完成了利用超高温灭菌和无菌罐装技术生产不同质构的含乳甜点的工艺流程和稳定体系的设计.

  16. Estimation of snow cover distribution in Beas basin, Indian Himalaya using satellite data and ground measurements

    H S Negi; A V Kulkarni; B S Semwal

    2009-10-01

    In the present paper,a methodology has been developed for the mapping of snow cover in Beas basin,Indian Himalaya using AWiFS (IRS-P6)satellite data.The complexities in the mapping of snow cover in the study area are snow under vegetation,contaminated snow and patchy snow. To overcome these problems,field measurements using spectroradiometer were carried out and reflectance/snow indices trend were studied.By evaluation and validation of different topographic correction models,it was observed that,the normalized difference snow index (NDSI)values remain constant with the variations in slope and aspect and thus NDSI can take care of topography effects.Different snow cover mapping methods using snow indices are compared to find the suitable mapping technique.The proposed methodology for snow cover mapping uses the NDSI (estimated using planetary re flectance),NIR band reflectance and forest/vegetation cover information.The satellite estimated snow or non-snow pixel information using proposed methodology was validated with the snow cover information collected at three observatory locations and it was found that the algorithm classify all the sample points correctly,once that pixel is cloud free.The snow cover distribution was estimated using one year (2004 –05)cloud free satellite data and good correlation was observed between increase/decrease areal extent of seasonal snow cover and ground observed fresh snowfall and standing snow data.

  17. Study and Realization of Fault Diagnosis for CRDM in PWR Nuclear Power Station%压水堆核电站CRDM故障诊断研究与实践

    昌正科; 董治国; 常乐莉

    2013-01-01

    The fault diagnosis method for control rod drive mechanism (CRDM) in pressurized water reactor nuclear power station is studied.By using virtual instrument technology,the coil current waveform of CRDM is monitored on line,then the characteristics of the waveform and movement point are analyzed and recognized,thus the operating status of the drive mechanism and its current regulating output loop are judged.The analysis results are saved in real time database for long term performance trending analysis.The system is significant to enhance the operation reliability of CRDM,and has been applied in Qinshan Phase Ⅱ Nuclear Power Plant,it possesses better promotion value.%对压水堆核电站控制棒驱动机构故障诊断方法进行了研究.通过采用虚拟仪器技术,在线监测控制棒驱动机构线圈电流波形、分析波形特征、辨识驱动机构动作特征点,从而判断驱动机构及其电流调节输出回路的运行情况.分析结果实时保存到数据库,可用于驱动机构性能变化趋势的长期分析.系统对提高控制棒驱动机构运行可靠性具有重要意义,已成功应用于秦山第二核电厂,具有一定的推广价值.

  18. The Technology of Extending the Existing Tunnels to Construct Harbin Metro%哈尔滨地铁利用既有隧道扩挖区间技术

    刘效永

    2012-01-01

    哈尔滨地铁西大桥—教化广场区间和教化广场—铁路局区间建设为利用既有人防工程进行扩挖改建,属国内首例。针对既有隧道破除的结构安全性问题,通过对其首破及破除后结构内力变化的研究,选择适宜的首破点和破除方向,采用临时竖撑预支加固、先侧墙后仰拱、径向注浆和跳槽扩挖等施工方法和措施,使既有结构内力变化在可控范围内,有效地控制了拱顶沉降、仰拱上浮和地层位移,保障了结构安全和施工安全,确保了工程的顺利进展。%Harbin Metro from West Bridge to Jiaohua Square and Jiaohua Square to the railway bureau is constructed by extending the existing civil air defense engineering.Aiming at its structural-broken security problems,the structure internal force variations for first breaking and after breaking are studied.By means of appropriately selecting the first-breaking point and breaking direction,interim vertical pre-support enforcing from sidewall to arch invert as well as vertical grouting and interval digging expanding,the structure internal force variations are within controllable range,and the vault settlement,arch invert floating and ground movement are effectively controlled.The structure and constructing security and the smooth project process are ensured.

  19. Study of photosynthesis process in the presence of low concentrations of clomazone herbicide in tobacco (Nicotiana tabacum

    Darwish, Majd

    2013-02-01

    Full Text Available The effect of chemical residues of clomazone on photosynthetic processes has been studiedby using several low concentrations of the herbicide (0, 1, 0.1, 0.01, 0.001, 0.0001 and 0.00001 µM and seedlings of two varieties of tobacco (Nicotiana tabacum L. cv. Virginie vk51, Nicotiana tabacum, L. cv. Xanthi. The content of photosynthetic pigments, the parameters of the chlorophyll-a fluorescence and the JIP-test were performed on an adult leaf (AL and a young leaf (YL, that gave a complementary designto know the action's mode of clomazone on the plant physiological processes. Clomazone reducedthe total chlorophyll (a+b, carotenoids pigments (reduction in size antenna pigments judged by an increase in the chlorophyll a/b ratio in young leaves more than adults leaves. The maximal photochemical efficiency (Fv/Fm of photosystem II (PSII decreased significantly in youngleavescompared to adult leaves and in (Virginie variety than (Xanthi variety. Among the parameters calculated of the JIP-test most affected by the treatment, PIabs, 1-VJ, ABS/RC, DI0/RC, TR0/RC, ET0/RC, ET0/ABS, which indicated acomparable effects of clomazone(1μM, 0.1µM, 0.01µM between the two types of leaves and the varieties used. More, the results showed that the concentration ( 1μM was the most effective amongthe other low concentrations used and the (Virginie variety ismore sensitive than the (Xanthivariety. We conclude that clomazone has probably two combined functions (physiological, toxic judged by the different behavior of both types of leaves in the presence of the herbicide.

  20. 专利保护对考虑市场细分闭环供应链的影响%Effect of Patent Protection on Closed-Loop Supply Chain with Market Segmentation Considered

    熊中楷; 黎雪

    2013-01-01

    在细分绿色消费者和普通消费者的基础上,研究了原始设备制造商(OEM)生产新产品和再制造商生产再制造品时,OEM征收再制造专利许可费对OEM与再制造商相互竞争的供应链的影响.分别构建了征收专利许可费和不征收专利许可费两种情形下的供应链定价模型,求得了OEM和再制造商的最优定价策略以及OEM的最优专利许可费征收策略,并对征收专利许可费和不征收专利许可费两种情形下的最优决策进行了比较分析.通过数值仿真,分别分析了绿色市场份额大小和普通消费者对再制造品的接受度对最优专利许可费、产品销售价格、供应链成员利润的影响.%By segmenting green consumer and primary consumer,the effect of patent protection on closedloop supply chain where OEM competes with an independent remanufacturer is studied.By establishing supply chain pricing models with and without patent protection fee,optimal pricing strategy and optimal protection fee decision strategy are derived.Comparison is made between the two different models.By using numerical simulation,the impacts of the degree of primary consumer acceptance to remanufactured products,the impacts of the green consumer share on the optimal price,profit,and patent protection fee are analyzed,respectively.

  1. 基于语音控制的人机交互智能系统研究∗%Intelligent System Research based on Voice Control Human-computer Interaction

    梁汉泉; 陈锦彪

    2015-01-01

    The voice control is one of the most promising emerging technologies,and it currently has been widely used in auto-motive terminals,intelligent robot,etc.The application of speech recognition in the toy car is studied.By DSP chips for voice con-trol system based on a highly integrated design,use the double silicon wheat noise reduction to achieve the audio data clearly.Based on DTW algorithm and dynamic template matching,the input speech in signal endpoint is detected,and someone's isolated word is recognized.When multiple semantic approximation vocabulary is failed to be correctly identified,provide selection processing,make the speech engine timbre and tone color different for the flexible processing,improve the recognition rate and the user experience. The speech recognition is tested in the normal life environment,and it can adapt to application in daily life or work environment. The results show that the scheme and algorithm has accurate recognition effect.%语音控制是当前最具发展前景的新兴技术之一,目前已广泛应用于车载终端、智能机器人等场合。对语音识别在玩具车上的应用进行了深入研究。基于高度集成的 DSP 芯片进行语音控制系统的设计,使用了双硅麦减噪,能够获取到清晰的音频数据。根据 DTW 算法和动态模板匹配,对输入语音信号进行了端点检测,对特定人的孤立词进行了识别。当多个语意近似词汇无法准确识别时,提供选择处理,使语音引擎对音质、音色的区别进行了灵活的处理,提高了识别率和用户体验感受。该语音识别在正常生活环境中进行了测试,能适应日常生活或工作环境。研究结果表明,此方案和算法具有准确的识别效果。

  2. Analysis on ultrasonic phased array inspection imaging quality for train wheel rim%列车轮辋超声相控阵成像质量分析

    胡宏伟; 王哲; 刘希玲; 王向红

    2015-01-01

    To solve the problem of low image quality and defect identification difficulty when using ultrasonic phased array to inspect train wheel rim,the sound pressure characteristics of phased array transducer were ana-lyzed.Besides,the suitable detection depth was obtained as well.The effects of the rim contact surface and cou-pling status for the image quality were analyzed.An ultrasonic phased array inspection experiment was carried out on a wheel rim test block.Taking a horizontal hole and a slot as defect examples,the echo amplitude chan-ging characteristic and image quality were studied.By comparing with flat block analysis,the main factors and influencing rule for ultrasonic phased array imaging quality were obtained.The study provides a reference to im-prove the ultrasonic phased array inspection process and the accuracy of defect detection for rim.%为解决超声相控阵检测列车轮辋易出现的成像质量低和缺陷识别困难等问题,分析相控阵换能器声压特性,获取合适的缺陷检测深度,讨论轮辋界面及耦合情况对成像质量的影响,开展轮辋试块相控阵检测实验。以水平孔和管穿槽缺陷为例,研究不同深度缺陷的回波幅值变化特点及成像质量,并通过与平面试块对比分析,获得轮辋相控阵成像质量的主要影响因素和影响规律,为改进轮辋超声相控阵检测工艺和提高缺陷检测精度提供参考。

  3. 辊式磁选机典型磁系结构磁场特性分析%Analysis on the Magnetic Field Characteristic of Roll Magnetic Separators with Different Magnetic System Structure

    张义顺; 史长亮; 马娇; 王飞跃

    2013-01-01

    辊式磁选机对中强磁性矿物分选多为经验式分选,不同磁系磁场特性与对应磁选矿物基本物性(密度、比磁化率)间的相互关系并无探讨.基于MagNet软件模拟辊式磁选机单环磁系、四级拼接磁系(无轭铁)、八级拼接磁系(有/无轭铁)的磁力线及磁感应强度分布情况,得出各磁系磁场沿辊表周向变化趋势及磁感应强度随分选行程变化函数关系;考察了单元磁性颗粒在力平衡条件下其密度同比磁化率的比值与各磁系磁感应强度函数关系,综合分析得出不同磁系类型下矿物的分选标准.对辊式磁选机常用磁系磁场特性分析,为选择合适的辊式磁选机进行中强磁性矿物的高效分选提供基础理论指导.%Roll magnetic separators are blandly used to separate moderate and strong susceptibility minerals,but the correlation between the magnetic field characteristic of different magnetic system and the characteristics (density and per magnetic susceptibility) of minerals is rarely discussed.The paper simulated the magnetic field lines distribution and magnetic induction intensity of different magnetic system,including:single ring prototype,four-magnetic splicing poles prototype without yoke,eight-magnetic splicing poles prototype with and without yoke.The function between the magnetic induction intensity and separation distance was given.The function between ratios of the density and magnetic susceptibility of single magnetic particle,and the magnetic field strength of different magnetic system was studied.By comprehensive analysis,the minerals separation standard corresponding to magnetic system prototype was obtained.The magnetic field characteristics of roll magnetic separators with different magnetic system were analyzed,the results could provide basic theoretical guidance for the selection of a suitable roll magnetic separator to efficiently separate moderate and strong magnetic minerals.

  4. Computation of Vibration and Sound Radiation from Cylindrical Shells with Frame Coated by Damping Layer%含阻尼层基座的加筋柱壳振动及声辐射计算

    谢天宇; 王永生; 付建; 魏应三; 王旅

    2013-01-01

    The influence on the vibration and sound radiation of submarine with frame coated by damping layer is systematically studied.By finite element analysis of constrained damping plate is presented and the nature frequencies match with theoretical ones well,which verifies the rationality of damping model.After that,the numerical of analysis of sound radiation from a submerged cylindrical stiffened shell have been carried out by using FEM and BEM,which approximately equals to the testing results.Taking constrained damping plates and cylindrical stiffened shells with frame as research objects,analysis of the influence on vibration character of frame and the underwater sound radiation noise of stiffened cylindrical shells whether the constrained damping layer covers on frame in it.The result shows with constrained damping layer the radiation noise of cylindrical shell and its frame will be reduced effectively.%为研究敷设阻尼材料基座对艇体振动辐射噪声的影响,采用有限元法计算得到约束阻尼板的固有频率同理论值吻合较好,验证了阻尼材料建模的合理性;并利用有限元/边界元法分析了加肋柱壳受激后的水下声辐射,结果同试验值基本一致;最后以加筋板(裸基座)和含基座的加肋圆柱壳作为对象,计算分析了约束阻尼对裸基座振动特性的影响以及基座敷设阻尼材料前后壳体辐射声场的变化.结果表明:敷设约束阻尼能有效降低加肋圆柱壳体及其内部基座的辐射噪声.

  5. Research of upper surface roughness of metal parts fabricated by selective laser melting%选区激光熔化成型金属零件上表面粗糙度的研究

    刘睿诚; 杨永强; 王迪

    2013-01-01

    In order to provide the theory basis to improve the surface quality , the main factors affecting the upper surface roughness of metal parts fabricated by selective laser melting (SLM) were studied.By studying the single track melting, the upper surface roughness of SLM parts was analyzed from the view of melting track lapping .The metal parts were fabricated by using the self-developed fabrication equipment Dimetal-280 and the measure roughness parameters were compared with the theoretical value.The theoretical value of arithmetical mean deviation of the profile Ra was 3.21μm and the theoretical value of ten-point height of irregulartlies Rz was 12.79μm.The actual value was Ra =7.36μm and Rz =40.01μm.After electrochemical polishing, the surface roughness was reduced to Ra =2.34μm and Rz =10.86μm.The results prove that upper surface roughness of the metal part was influenced by melting track width , scanning space and layer thickness altogether.The reason of the discrepancy between theoretical value and actual value was some defects such as instability in melting track, spheroidization on the surface and dust adhesiveness .The quality of surface roughness was greatly improved after electrochemical polishing .The metal parts processed by selective laser melting could obtain satisfied surface roughness in this experiment .The results provide guidance to surface research and industrial application in the future.%  为了改善成型件表面质量,从微观上研究了决定选区激光熔化成型金属零件的上表面粗糙度的主要因素,通过研究单熔道成型,从熔道搭接的角度理论分析了成型件的上表面粗糙度,基于自主研发的成型设备Dimet-al-280加工实体零件进行了实际测量对比,获得表面粗糙度的轮廓算术平均偏差Ra 的理论值为3.21μm,微观不平度十点高度Rz 的理论值为12.79μm,其实测值Ra =7.36μm,Rz =40.01μm;进行喷砂和电解抛光处理后,

  6. Investigações sobre doenças de Psittacideos

    Genesio Pacheco

    1932-08-01

    to be different from that of the virus of psittacosis studiedby him. We are very much obliged to him for the attention he paid to this verification. Virus of psittacosis - Infectiousness: man, monkey, rabbit, mouse, hen, canary. Neurotropic affinity. Inclusions: small, protoplasmic. Exsiccation: the virus has good power of preservation. Symptoms: inactivity, drowsiness, frequent diarrhoea, oculo-nasal discharge and cough, coma. Duration: 4 to 5 days. Bodily lesions: congestion of intestines, splenomegaly. Virus of S. Paulo - Infects only psittacidae, particularly those of the genus Amazona. No localization in the nervous system. Large, nuclear. Is rapidly destroyed. Inactivity, inappetency, adynamia (drooping of the wings, indifference, leaning its beak against the bars of the cage in order not to fall down; profuse diarrhoea, of whitish stools, at times enterorrhagia; prolonged coma. 2 to 8 days. Foci of yellowish necrosis in liver, spleen and lung. At times, congestion of intestines. Characteristic features common to the two viruses.-They act in great dilutions, filter through tight candles though being partly retained, are preserved under glycerine or Bedson's solution, are stable at 55°C. heat and are destroyed by physical and chemical agents. Both virus diseases are very seldom met with in psittacidae: only once, amongst numberless sick parrots, the author met with a disease of the virus differring from that of psittacosis. This disease, greatly transmissible to man, ought to be more frequent, if it were common in parrots. On the contrary, bacteria cause diseases in these animals with great frequency, presenting variable characters, from a severe epizootic form, rapidly mortal, to ambulatory or silent forms, for the most part developing towards a cure or assuming a chronic character. Amongst the bacteria which cause the infection of this group the salmonellae predominate and amongst them the bacterium discovered by Nocard, as well as a species which in the

  7. 苹果酸/盐对暗棕壤磷有效性及林木吸收磷的影响%Effects of Malic Acid/Malate on Phosphorus Availability of Dark Brown Forest Soils and Absorption of Forest Seedlings

    宋金凤; 宋俊杰; 褚永磊; 王勇; 崔晓阳; 彭红梅

    2011-01-01

    By simulating malic acid/malate contents in forest litter leachates,the effects and mechanism of different concentrations of malic acid/malate solutions on phosphorus(P) availability of air-dry dark brown forest soils were studied.By pot experiments,the role of malic acid/malate solutions on solublizing P were validated in natural dark brown forest soils,and the effects of malic acid/malate on P absorption of Larix olgensis and Fraxinus mandshurica seedlings were also discussed.The results showed that,malic acid and malate substantially encouraged soil P release of air-dry A1 and B horizons soils,and dissolved P contents increased with the extractant concentrations,but the effects on B horizon were relatively weak.Malate solutions had much higher soil-P-release efficiency than that of malic acid at the same concentration,therefore,the mechanisms for malic acid and malate to solublize P should be dominated by reactions of malate anion.The effects of malate anion on P release was found to be cumulative,and the amount of P released was primarily controlled by cumulative malate loading rate.When malate anion was loaded as sodium malate solutions,the regression equation between A1 horizon P release and cumulative malic loading rate was:Y=-0.0005X2+0.1929X+1.8192,R2=0.959 3.Merely on a quantitative basis of malate anion leached from forest litter,the increased P release from A1 horizon was estimated to be 3.04 kg/(hm2·a),accounting for 1/4~1/3 of the annual P absorption in middle-aged forests.The results of natural dark brown forest soils' experiments also showed that,malic acid/malate solutions of appropriate concentrations could stimulate soil P release,and were also helpful for P absorption of Fraxinus mandshurica and Larix olgensis seedings.In the processes of P mobilization and absorption,the concentration of 1.0 mmol/L or 5.0 mmol/L had the best function,and malate was better than malic acid.%模拟森林凋落物淋洗液中苹果酸/盐浓度范