Long-range order in electronic transport through disordered metal films

Ultracold atom magnetic field microscopy enables the probing of current flow patterns in planar structures with unprecedented sensitivity. In polycrystalline metal (gold) films, we observed long-range correlations forming organized patterns oriented at +/-45 degrees relative to the mean current flow, even at room temperature and at length scales larger than the diffusion length or the grain size by several orders of magnitude. The preference to form patterns at these angles is a direct consequence of universal scattering properties at defects. The observed amplitude of the current direction fluctuations scales inversely to that expected from the relative thickness variations, the grain size, and the defect concentration, all determined independently by standard methods. Ultracold atom magnetometry thus enables new insight into the interplay between disorder and transport.     

Long-range electron transfer in heme proteins

Kinetic experiments have conclusively shown that electron transfer can take place over large distances (greater than 10 angstroms) through protein interiors. Current research focuses on the elucidation of the factors that determine the rates of long-range electron-transfer reactions in modified proteins and protein complexes. Factors receiving experimental and theoretical attention include the donor-acceptor distance, changes in geometry of the donor and acceptor upon electron transfer, and the thermodynamic driving force. Recent experimental work on heme proteins indicates that the electron-transfer rate falls off exponentially with donor-acceptor distance at long range. The rate is greatly enhanced in proteins in which the structural changes accompanying electron transfer are very small.     

Long-range correlations in the diffuse seismic coda

The late seismic coda may contain coherent information about the elastic response of Earth. We computed the correlations of the seismic codas of 101 distant earthquakes recorded at stations that were tens of kilometers apart. By stacking cross-correlation functions of codas, we found a low-frequency coherent part in the diffuse field. The extracted pulses have the polarization characteristics and group velocities expected for Rayleigh and Love waves. The set of cross-correlations has the symmetries of the surface-wave part of the Green tensor. This seismological example shows that diffuse waves produced by distant sources are sufficient to retrieve direct waves between two perfectly located points of observation. Because it relies on general properties of diffuse waves, this result has potential applications in other fields.     

Long-range interactions within a nonnative protein

Protein folding and unfolding are coupled to a range of biological phenomena, from the regulation of cellular activity to the onset of neurodegenerative diseases. Defining the nature of the conformations sampled in nonnative proteins is crucial for understanding the origins of such phenomena. We have used a combination of nuclear magnetic resonance (NMR) spectroscopy and site-directed mutagenesis to study unfolded states of the protein lysozyme. Extensive clusters of hydrophobic structure exist within the wild-type protein even under strongly denaturing conditions. These clusters involve distinct regions of the sequence but are all disrupted by a single point mutation that replaced residue Trp62 with Gly located at the interface of the two major structural domains in the native state. Thus, nativelike structure in the denatured protein is stabilized by the involvement of Trp62 in nonnative and long-range interactions.     

Electron localization in metallic quasicrystals

Bulk icosahedral-quasicrystalline aluminum-palladium-rhenium alloys of high structural quality and thermal stability are found to exhibit low-temperature electrical resistivities that are four orders of magnitude larger than those found in disordered metals and metallic glasses. Experiments suggest that these quasiperiodic alloys, which have a semimetallic electron density, are insulators at low temperature. The findings are discussed in light of theories on electron localization and band-gap formation in ordered metallic systems.     

未确知拓扑空间的连通性

在２个未确知拓扑空间之间的未确知连续函数的基础上,通过未确知同胚函数的定义,未确知子集的分离的定义,确定未确知拓扑空间的连通性。给出连通未确知子集的定义和相关的定理;未确知拓扑空间连通性的定义和定理,以及连通分支的定义、定理。     

Submicrometer metallic barcodes

We synthesized multimetal microrods intrinsically encoded with submicrometer stripes. Complex striping patterns are readily prepared by sequential electrochemical deposition of metal ions into templates with uniformly sized pores. The differential reflectivity of adjacent stripes enables identification of the striping patterns by conventional light microscopy. This readout mechanism does not interfere with the use of fluorescence for detection of analytes bound to particles by affinity capture, as demonstrated by DNA and protein bioassays.     

Ultralight metallic microlattices

Ultralight (<10 milligrams per cubic centimeter) cellular materials are desirable for thermal insulation; battery electrodes; catalyst supports; and acoustic, vibration, or shock energy damping. We present ultralight materials based on periodic hollow-tube microlattices. These materials are fabricated by starting with a template formed by self-propagating photopolymer waveguide prototyping, coating the template by electroless nickel plating, and subsequently etching away the template. The resulting metallic microlattices exhibit densities ρ ≥ 0.9 milligram per cubic centimeter, complete recovery after compression exceeding 50% strain, and energy absorption similar to elastomers. Young's modulus E scales with density as E ~ ρ(2), in contrast to the E ~ ρ(3) scaling observed for ultralight aerogels and carbon nanotube foams with stochastic architecture. We attribute these properties to structural hierarchy at the nanometer, micrometer, and millimeter scales.     

Long-range electronic perturbations caused by defects using scanning tunneling microscopy

Real-space observations of long-range electronic perturbations caused by defects have been made with scanning tunneling microscopy. The defects are isolated adsorbed molecules on the surface of graphite. These defects perturb the charge density, giving periodic oscillations similar to Friedel oscillations. The oscillations have a wavelength radical3 times that of the graphite lattice, and the symmetry of the oscillations reflects the nature of the defect.     

A novel topological compression mechanism in a covalent liquid

Monte Carlo simulations of tetrahedrally bonded SiO(2) liquid show that pressure induces large changes in the topology of its four-coordinated framework structure but leaves the average properties of local coordination environments virtually unchanged. Ring statistics are used to describe the liquid's topology; the observed changes paradoxically indicate that the liquid compresses primarily by increasing the size of its rings. A theory for the effects of ring formation on density, which also explains the density of crystalline tectosilicates, accounts for the compression of the liquid.     

Normal metallic point contacts

The measured voltage derivative of the nonlinear resistance of tiny point contacts can be separated into a phonon-emission effect (alpha(2)F) and an analytic functional form (background effect). The alpha(2)F's show structure coincident with bulk phonon densities of states. Values of the integral of 2 alpha(2)F/omega are closely related to literature values. The background effect is related to the impurity concentration of the materials.     

锦鲤长途运输后的人工繁殖技术研究

2014年3月底从广州采购4组锦鲤亲鱼运至昆明,在未对亲鱼进行暂养调整的情况下,立即对亲鱼进行人工催产。催产药物选用LRH-A2与DOM的组合,采用二次注射法,成功催产3组亲鱼。采用干法人工授精方式,并用滑石粉脱粘,获得受精卵73万粒。亲鱼产后进行人工护理,状态恢复良好。     

Phase separation in pyrex glass

The contrast between phases in pyrex glass was heightened for viewing in the electron microscope by exchanging silver ions for sodium ions in the glass. The scale of phase separation in pyrex was foud to be about 30 angstroms; sample of commercial soda-lime glass, prepared in the same way, showed no phase separtion.     

Actinide topological insulator materials with strong interaction

Topological band insulators have recently been discovered in spin-orbit coupled two-and three-dimensional systems. We theoretically predict a class of topological insulators where interaction effects play a dominant role. In actinide elements, simple rocksalt compounds formed by Pu and Am lie on the boundary between metals and insulators. We show that interaction drives a quantum phase transition to a topological insulator phase with a single Dirac cone on the surface. These putative topological insulators may provide a setting for both applied and fundamental investigation.     

Superconductivity of metallic aluminum antimonide

The high-pressure metallic phase of aluminunm antimnonide is super conducting [critical temperature T(c) (P approximately 125 kilobars) = 2.8 degrees +/-0.2 degrees K]. This transition temperature is significantly lower than the transition temperature of metallic germanium under an equivalent high pressure. A similar result had been previously found for superconducting indiumantimonide in comparison to tin.     

Modulated magnetic phases in rare Earth metallic systems

Neutron scattering has played a key role in the microscopic understanding of the static and dynamic properties of magnetic materials. Modulated magnetic structures first discovered in the late fifties can no longer be referred to as exotic; more than a hundred such phases have already been found in a variety of magnetic systems. Neutron and x-ray magnetic scattering have played a complementary role in the recent discovery and understanding of the modulated magnetic phases in rare earth metallic systems.