Isotope separation by carrier diffusion

Nitrogen isotope fractionation in the Hoering-Moore experiment, injection of N2 into CO2 carrier and flow through sandstone, is due to diffusion in the gas phase rather than to surface interaction. This process, called "carrier diffusion," produces a characteristic fractionation pattern relative to a fraction coordinate, with points of zero fractionation at 16 and 84 percent and heavy isotope enrichment between these points. Carrier diffusion is an efficient enrichment process for low-abundance isotopes lighter than the abundant species and for helium and hydrogen in gas mixtures.     

Separation of calcium isotopes by liquid phase thermal diffusion

Significant separation of the isotopes of calcium was obtained by thermogravitational thermal diffusion of an aqueous calcium nitrate solution. A flow of solvent was used to partially offset the large solute-solvent separation effect in the experimental column. Further development of this technique may lead to separation of the isotopes of calcium and of other elements on a practical scale.     

Isotope separation in a "seeded beam%"

A new method of separating isotopes in a gaseous mixture is described. The method takes advantage of the differences in velocities of isotopic species in a molecular beam formed by expansion of the mixture with a light gas from a nozzle source. For the separation of the hexafluorides of uranium-235 and uranium-238 the technique has an estimated separative work factor about 500 times higher than the gaseous diffusion process and 100 times higher than the curved-jet method.     

乳状液膜在金属离子测定中的分离富集作用

简要介绍乳状液膜技术在金属离子分析测定中的分离富集作用以及新的研究和应用进展状况。     

高效液相色谱(HPLC)分离和检测蛋白质

对近年来利用高效液相色谱(HPLC)分离检测蛋白质的研究作了综述.比较详细地介绍了用于蛋白质分析的各种HPLC模式、检测器、以及联用技术的发展情况,肯定了高效液相色谱在蛋白质分离检测中的重要作用.     

乳状液膜分离氨基酸的研究进展

综述了乳状液膜技术的基本原理及其在分离提取氨基酸方面的研究进展状况。     

Elastic torque and the levitation of metal wires by a nematic liquid crystal

Anisotropic particles suspended in a nematic liquid crystal disturb the alignment of the liquid crystal molecules and experience small forces that depend on the particles' orientation. We have measured these forces using magnetic nanowires. The torque on a wire and its orientation-dependent repulsion from a flat surface are quantitatively consistent with theoretical predictions based on the elastic properties of the liquid crystal. These forces can also be used to manipulate submicrometer-scale particles. We show that controlled spatial variations in the liquid crystal's alignment convert the torque on a wire to a translational force that levitates the wire to a specified height.     

Benzo(a)pyrene metabolites: efficient and rapid separation by high-pressure liquid chromatography

High-pressure liquid chromatography can separate eight metabolites of benzo[a] pyrene formed by rat liver microsomes. This method offers major advantages over previous techniques used for the separation of oxygenated polycyclic aromatic hydrocarbons.     

Venus ionosphere: photochemical and thermal diffusion control of ion composition

The major photochemical sources and sinks for ten of the ions measured by the ion mass spectrometer on the Pioneer Venus bus and orbiter spacecraft that are consistent with the neutral gas composition measured on the same spacecraft have been identified. The neutral gas temperature (Tn) as a function of solar zenith angle (chi) derived from measured ion distributions in photochemical equilibrium is given by Tn (K) = 323 cos(1/5)chi. Above 200 kilometers, the altitude behavior of ions is generally controlled by plasma diffusion, with important modifications for minor ions due to thermal diffusion resulting from the observed gradients of plasma temperatures. The dayside equilibrium distributions of ions are sometimes perturbed by plasma convection, while lateral transport of ions from the dayside seems to be a major source of the nightside ionosphere.     

Structure of a Langmuir film on a liquid metal surface

The structure of organic monolayers on liquid surfaces depends sensitively on the details of the molecular interactions. The structure of a stearic acid film on a mercury surface was measured as a function of coverage with angstrom resolution. Unlike monolayers on water, the molecules were found here to undergo a transition from surface-parallel to surface-normal orientation with increasing coverage. At high coverage, two condensed hexatic phases of standing-up molecules were found. At low coverage, a two-dimensional (2D) gas phase and condensed single- and double-layered phases of flat-lying molecular dimers were revealed, exhibiting a 1D longitudinal positional order. This system should provide a broader tunability range for nanostructure construction than solid-supported self-assembled monolayers.     

The role of a bilayer interfacial phase on liquid metal embrittlement

Intrinsically ductile metals are prone to catastrophic failure when exposed to certain liquid metals, but the atomic-level mechanism for this effect is not fully understood. We characterized a model system, a nickel sample infused with bismuth atoms, by using aberration-corrected scanning transmission electron microscopy and observed a bilayer interfacial phase that is the underlying cause of embrittlement. This finding provides a new perspective for understanding the atomic-scale embrittlement mechanism and for developing strategies to control the practically important liquid metal embrittlement and the more general grain boundary embrittlement phenomena in alloys. This study further demonstrates that adsorption can induce a coupled grain boundary structural and chemical phase transition that causes drastic changes in properties.     

Carbon Isotope Abundance in Meteoritic Carbonates

The C(13)/C(12) ratio in the carbonate minerals of Orgueil, a carbonaceous chondrite, is 6 percent greater than the ratio in any known terrestrial carbon. The effect may be produced by a chemical isotope fractionation involving processes not common on earth, or it may be the result of incomplete homogenization of substances with different histories of nucleosynthesis.     

From a single-band metal to a high-temperature superconductor via two thermal phase transitions

The nature of the pseudogap phase of cuprate high-temperature superconductors is a major unsolved problem in condensed matter physics. We studied the commencement of the pseudogap state at temperature T* using three different techniques (angle-resolved photoemission spectroscopy, polar Kerr effect, and time-resolved reflectivity) on the same optimally doped Bi2201 crystals. We observed the coincident, abrupt onset at T* of a particle-hole asymmetric antinodal gap in the electronic spectrum, a Kerr rotation in the reflected light polarization, and a change in the ultrafast relaxational dynamics, consistent with a phase transition. Upon further cooling, spectroscopic signatures of superconductivity begin to grow close to the superconducting transition temperature (T(c)), entangled in an energy-momentum-dependent manner with the preexisting pseudogap features, ushering in a ground state with coexisting orders.     

Catalysis by small metal clusters

Experimental and theoretical studies of small clusters of metal atoms are aimed at revealing how properties change in the ultrafinely divided state. Thermodynamic, electronic, and structural features can be size-dependent and may be involved in determining the activity of small-particle catalysts. Correlations between these properties give indications of the features important in catalysis.     

基于信息扩散理论的广东大宝山地区土壤重金属污染评价

为探讨信息扩散理论在土壤重金属污染评价中的可行性,通过广东大宝山地区24个土壤样品重金属数据,采用信息扩散理论结合地累积指数,评价了该地区土壤Pb、Zn、Cu和Cd的污染现状及发生概率。结果表明:大宝山地区土壤受Cd污染最为严重,其次为Cu污染,Pb和Zn污染较轻。通过信息扩散理论计算的地累积指数发生概率表明:大宝山地区土壤受Cd污染发生轻度-中等污染以上的概率为71.65%,中等污染以上的概率为56.76%,中等-强污染以上的概率为39.76%,强污染以上的概率为25.38%,强-极严重污染以上的概率为15.05%,极严重污染以上的概率为0.02%;Cu污染发生轻度-中等污染以上的概率为55.61%,中等污染以上的概率为38.65%,中等-强污染以上的概率为25.09%,强污染以上的概率为15.88%,强-极严重污染以上的概率为9.27%。综上,信息扩散理论可用于土壤重金属污染评价,评价结果可为土壤重金属污染的管理和治理提供参考。     

Large-scale thermal events in the solar nebula: evidence from Fe,Ni metal grains in primitive meteorites

Chemical zoning patterns in some iron, nickel metal grains from CH carbonaceous chondrites imply formation at temperatures from 1370 to 1270 kelvin by condensation from a solar nebular gas cooling at a rate of approximately 0.2 kelvin per hour. This cooling rate requires a large-scale thermal event in the nebula, in contrast to the localized, transient heating events inferred for chondrule formation. In our model, mass accretion through the protoplanetary disk caused large-scale evaporation of precursor dust near its midplane inside of a few astronomical units. Gas convectively moved from the midplane to cooler regions above it, and the metal grains condensed in these parcels of rising gas.     

Electronic separation of biological cells by volume

A device capable of separating biological cells (suspended in a conducting medium) according to volume has been developed. Cell volume is measured in a Coulter aperture, and the cells are subsequently isolated in droplets of the medium which are charged according to the sensed volume. The charged droplets then enter an electrostatic field and are deflected into a collection vessel. Mixtures of mouse and human erythrocytes and a large volume component of mouse lymphoma cells were separated successfully. In tests with Chinese hamster ovary cells essentially all cells survived separation and grew at their normal rate.     

环境同位素在地表水中的应用

自然界的各种水体（降水、地表水、地下水、土壤水）中都广泛存在着环境同位素,同位素技术在地下水中的应用趋于成熟,但在地表水中的应用不是十分广泛。从基流分割、径流平均传播时间、水环境三个方面重点论述环境同位素在地表水应用,并结合研究现状分析存在的问题和探讨应用前景。     

Reticulated nanoporous polymers by controlled polymerization-induced microphase separation

Materials with percolating mesopores are attractive for applications such as catalysis, nanotemplating, and separations. Polymeric frameworks are particularly appealing because the chemical composition and the surface chemistry are readily tunable. We report on the preparation of robust nanoporous polymers with percolating pores in the 4- to 8-nanometer range from a microphase-separated bicontinuous precursor. We combined polymerization-induced phase separation with in situ block polymer formation from a mixture of multifunctional monomers and a chemically etchable polymer containing a terminal chain transfer agent. This marriage results in microphase separation of the mixture into continuous domains of the etchable polymer and the emergent cross-linked polymer. Precise control over pore size distribution and mechanical integrity renders these materials particularly suited for various advanced applications.