Transition-State Spectroscopy of Cyclooctatetraene

The 351-nanometer photoelectron spectrum of the planar cyclooctatetraene radical anion (COT·-) shows transitions to two electronic states of cyclooctatetraene (COT). These states correspond to the D4h 1A1g state, which is the transition state for COT ring inversion, and the D8h 3A2u state. The electron binding energy of the 1A1g transition state is 1.099 ± 0.010 electron volts, which is lower by 12.1 ± 0.3 kilocalories per mole than that of the 3A2u state. The photoelectron spectrum shows that the singlet lies well below the triplet in D8h COT and confirms ab initio predictions that the molecule violates Hund's rule. Vibrational structure is observed for both features and is readily assigned by use of a simple potential energy surface.     

Quantum-well states as fabry-Perot modes in a thin-film electron interferometer

Angle-resolved photoemission from atomically uniform silver films on iron (100) shows quantum-well states for absolutely determined film thicknesses ranging from 1 to approximately 100 monolayers. These states can be understood in terms of Fabry-Perot modes in an electron interferometer. A quantitative line shape analysis over the entire two orders of magnitude of thickness range yields an accurate measurement of the band structure, quasiparticle lifetime, electron reflectivity, and phase shift. Effects of confinement energy gap, reflection loss, and surface scattering caused by controlled roughness are demonstrated.     

Competition of superconducting phenomena and Kondo screening at the nanoscale

Magnetic and superconducting interactions couple electrons together to form complex states of matter. We show that, at the atomic scale, both types of interactions can coexist and compete to influence the ground state of a localized magnetic moment. Local spectroscopy at 4.5 kelvin shows that the spin-1 system formed by manganese-phthalocyanine (MnPc) adsorbed on Pb(111) can lie in two different magnetic ground states. These are determined by the balance between Kondo screening and superconducting pair-breaking interactions. Both ground states alternate at nanometer length scales to form a Moiré-like superstructure. The quantum phase transition connecting the two (singlet and doublet) ground states is thus tuned by small changes in the molecule-lead interaction.     

非谐振子Gazeau-Klauder与Klauder-Perelomov相干态

利用Kinani-Daoud方法构造了非谐振子势的Gazeau-Klauder(GK)相干态和Klauder-Perelomov(KP)相干态,表明两种相干态在非线性谐振子势下具有完全不同的形式,并对两种相干态的完备性以及各自构成的Hilbert空间进行了讨论. 对相干态的Mandel Q参数的研究表明：GK相干态服从亚Poisson统计分布,KP相干态服从超Poisson统计分布.     

Uranium power and horizontal proliferation of nuclear weapons

Only a few nonnuclear weapons states with uranium-fueled power plants have kept the weapons option open, and none has evidenced activities intended for diverting fissionable material from its civilian system. Analysis of alternative strategies shows that acquisition of nuclear weapons material would probably depend on military production facilities rather than diversion. Horizontal proliferation is primarily a political issue and is related only marginally to uranium power development. Restrictions of the Nuclear Non-Proliferation Act on the supply of equipment and fuel by the United States appear to have induced, in some nonnuclear weapons states, the building of small-scale facilities that can be modified for production of weapons material. More attention should be given to the international political, economic, and military factors that persuade such states to abjure nuclear weapons.     

Single-molecule fluorescence experiments determine protein folding transition path times

The transition path is the tiny fraction of an equilibrium molecular trajectory when a transition occurs as the free-energy barrier between two states is crossed. It is a single-molecule property that contains all the mechanistic information on how a process occurs. As a step toward observing transition paths in protein folding, we determined the average transition-path time for a fast- and a slow-folding protein from a photon-by-photon analysis of fluorescence trajectories in single-molecule F?rster resonance energy transfer experiments. Whereas the folding rate coefficients differ by a factor of 10,000, the transition-path times differ by a factor of less than 5, which shows that a fast- and a slow-folding protein take almost the same time to fold when folding actually happens. A very simple model based on energy landscape theory can explain this result.     

河南地方野生小鼠遗传多样性分析

利用56个微卫星标记对河南省地方野生小鼠与4个实验室小鼠品系进行了遗传多样性分析。结果共检测出230个等位基因,平均每个位点等位基因数为4.107个,其中D4Mit9位点最多,为8个,D8Mit154、D7Mit8、D6Mit77、D17Mit244、D18Mit119位点最少,均为2个;野生小鼠基因位点平均纯合率为68.98%,除KM小鼠以外,其余实验室小鼠品系所有检测位点均为纯合;野生小鼠与PWK小鼠的平均多态性为0.657 0,与BALB/c小鼠的平均多态性为0.855 8,与B6小鼠的平均多态性为0.919 7,与KM小鼠的平均多态性为0.837 6;聚类分析结果显示,野生小鼠与PWK小鼠遗传距离最近。野生小鼠与实验室常用品系小鼠相比多态性较好,具有较高的遗传多样性和育种价值,对丰富实验小鼠基因库有着重要意义。     

Resonating valence-bond ground state in a phenalenyl-based neutral radical conductor

An organic material composed of neutral free radicals based on the spirobiphenalenyl system exhibits a room temperature conductivity of 0.3 siemens per centimeter and a high-symmetry crystal structure. It displays the temperature-independent Pauli paramagnetism characteristic of a metal with a magnetic susceptibility that implies a density of states at the Fermi level of 15.5 states per electron volt per mole. Extended Hückel calculations indicate that the solid is a three-dimensional organic metal with a band width of approximately 0.5 electron volts. However, the compound shows activated conductivity (activation energy, 0.054 electron volts) and an optical energy gap of 0.34 electron volts. We argue that these apparently contradictory properties are best resolved in terms of the resonating valence-bond ground state originally suggested by Pauling, but with the modifications introduced by Anderson.     

Quantum point contact switches

Switching behavior between electron tunneling and ballistic transport states was induced by repeatedly bringing a sharpened nickel wire into contact with a gold surface. The high-conductivity ballistic state had a quantized conductance of 0.977 +/- 0.015 (2e(2)/h). Switching was accomplished by moving the electrodes with a piezoelectric actuator over a distance of 2 angstroms. The two electrodes and the actuator form a three-terminal device that is demonstrated to be a reliable digital and analog switch; it shows good discrimination between high and low states and possesses the important property of power gain. The conductance channel is most likely only one atom wide and possibly consists of a single atom.     

Crystal Structures at High Pressures of Metallic Modifications of Compounds of Indium, Gallium, and Aluminum

X-ray diffraction shows that the high-pressure modifications (at 22 to 130 kilobars) of the antimonides of indium, gallium, and aluminum are analogous to white tin. The arsenide and phosphide of indium transform to NaCl type. The transformation of these semiconductors to their metallic states is empirically related to their energy gap under normal conditions.     

无桩靴夯扩桩在复杂地基中的应用

论述了无桩靴夯扩桩的成桩工艺及其独特优点，提出了无桩靴夯扩桩适用条件和设计计算原则。工程实例表明，无桩靴夯扩桩是一种技术性能可靠，社会、经济效益显著，值得广泛推广运用的新颖桩型。     

End states in one-dimensional atom chains

End states--the zero-dimensional analogs of the two-dimensional states that occur at a crystal surface--were observed at the ends of one-dimensional atom chains that were self-assembled by depositing gold on the vicinal Si(553) surface. Scanning tunneling spectroscopy measurements of the differential conductance along the chains revealed quantized states in isolated segments with differentiated states forming over end atoms. A comparison to a tight-binding model demonstrated how the formation of electronic end states transforms the density of states and the energy levels within the chains.     

Localization and its absence: a new metallic state for conducting polymers

A widely held view in solid-state physics is that disorder precludes the presence of long-range transport in one dimension. A series of models has been recently proposed that do not conform to this view. The primary model is the random dimer model, in which the site energies for pairs of lattice sites along a linear chain are assigned one of two values at random. This model has a set of conducting states that ultimately allow an initially localized particle to move through the lattice almost ballistically. This model is applicable to the insulator-metal transition in a wide class of conducting polymers, such as polyaniline and heavily doped polyacetylene. Calculations performed on polyaniline demonstrate explicitly that the conducting states of the random dimer model for polyaniline are coincident with recent calculations of the location of the Fermi level in the metallic regime. A random dimer analysis on polyparaphenylene also indicates the presence of a set of conducting states in the vicinity of the band edge. The implications of this model for the metallic state in other polymers, including heavily doped polyacetylene, are discussed.     

Optical atomic coherence at the 1-second time scale

Highest-resolution laser spectroscopy has generally been limited to single trapped ion systems because of the rapid decoherence that plagues neutral atom ensembles. Precision spectroscopy of ultracold neutral atoms confined in a trapping potential now shows superior optical coherence without any deleterious effects from motional degrees of freedom, revealing optical resonance linewidths at the hertz level with a good signal-to-noise ratio. The resonance quality factor of 2.4 x 10(14) is the highest ever recovered in any form of coherent spectroscopy. The spectral resolution permits direct observation of the breaking of nuclear spin degeneracy for the 1S0 and 3P0 optical clock states of 87Sr under a small magnetic bias field. This optical approach for excitation of nuclear spin states allows an accurate measurement of the differential Landé g factor between 1S0 and 3P0. The optical atomic coherence demonstrated for collective excitation of a large number of atoms will have a strong impact on quantum measurement and precision frequency metrology.     

Pressure Dependence of Superconductivity in Single-Phase K3C60

The superconducting compound K(3)C(60) (with transition temperature T(c) = 19.3 kelvin at ambient pressure), formed as a single phase by reaction of alkali vapor with solids of the icosahedral C(60) molecule (buckminsterfullerene), shows a very large decrease of T(c) with increasing pressure. Susceptibility measurements on sintered pellets showing bulk superconductivity are reported up to 21 kilobars of pressure, where T(c) is already less than 8 kelvin. The results are consistent with a piling up of the density of states at the Fermi level.     

Experimental verification of decoherence-free subspaces

Using spontaneous parametric down-conversion, we produce polarization-entangled states of two photons and characterize them using two-photon tomography to measure the density matrix. A controllable decoherence is imposed on the states by passing the photons through thick, adjustable birefringent elements. When the system is subject to collective decoherence, one particular entangled state is seen to be decoherence-free, as predicted by theory. Such decoherence-free systems may have an important role for the future of quantum computation and information processing.     

青蛤人工育苗中附着基的选择

试验在黄砂、海泥和不投附着基三种状态下,观察了青蛤幼虫在变态时期的附着量和成活率的变化,以及附着后稚贝的生长与成活情况。结果表明:海泥是青蛤工厂化育苗最适宜的附着基,然后在此基础上进行了不同厚度海泥对不同大小稚贝生长的影响试验。试验结果显示:不同厚度的海泥对稚贝生长的影响不明显。我们认为在生产中应选用1mm厚度的海泥做为青蛤育苗的附着基是最适宜的。     

青蛤人工育苗中附着基的选择

试验在黄砂、海泥和不投附着基三种状态下,观察了青蛤幼虫在变态时期的附着量和成活率的变化,以及附着后稚贝的生长与成活情况。结果表明:海泥是青蛤工厂化育苗最适宜的附着基,然后在此基础上进行了不同厚度海泥对不同大小稚贝生长的影响试验。试验结果显示:不同厚度的海泥对稚贝生长的影响不明显。我们认为在生产中应选用1mm厚度的海泥做为青蛤育苗的附着基是最适宜的。     

吸附法油气回收装置油气吸附量的计量方式

活性炭吸附法是目前国内油库使用最广泛的油气回收技术,而油气吸附量计量是活性炭吸附法油气回收装置切换控制的核心和依据,是确保装置正常工作的前提.介绍了吸附法油气回收装置常见的几种油气吸附量计量方式,包括利用进气流量和浓度计量吸附量,利用进气和排气流量计算吸附量,以及根据鹤管发油信号估算吸附量等方式.阐述了不同计量方式的工作原理、吸附量计算方法以及各自的优缺点,给出了各方法在实际运行中出现的问题和应对的措施.对各种计量方式的综合比较结果表明,通过在油气回收装置进气和排气管道上分别安装超声涡街流量计,能够实现对装置的精确测量和控制,降低成本的同时确保装置的稳定运行.（图3,参10）