Mechanism for multiplication of atmospheric ice crystals: apparent charge distribution on laboratory crystals

Replication of ice crystals with vapor of methyl 2-cyanoacrylate has produced evidence of whiskers on them; an additional mechanism for the necessary multiplication of ice crystals in the atmosphere is suggested. This replication technique also confirms crystal clustering in the atmosphere and appears to confirm the distribution of electrical charge on ice crystals.     

Observation of charge transport by negatively charged excitons

We report transport of electron-hole complexes in semiconductor quantum wells under applied electric fields. Negatively charged excitons (X-), created by laser excitation of a high electron mobility transistor, are observed to drift upon applying a voltage between the source and drain. In contrast, neutral excitons do not drift under similar conditions. The X- mobility is found to be as high as 6.5 x 10(4) cm2 V-1 s-1. The results demonstrate that X- exists as a free particle in the best-quality samples and suggest that light emission from opto-electronic devices can be manipulated through exciton drift under applied electric fields.     

Global transport of organic pollutants: ambient concentrations in the remote marine atmosphere

Concentrations of organic pollutants in the air and in precipitation have been measured at Enewetak Atoll in the North Pacific Ocean. These data from a site removed from industrial and human activity indicate the present concentrations of synthetic organic pollutants in the atmosphere and establish the long-range atmospheric transport of organic pollutants to remote marine areas. Hexachlorobenzene and hexachlorocyclohexane isomers are present in the remote marine atmosphere. Polychlorobiphenyls, total DDT, dieldrin, chlordane, and two phthalate ester plasticizers were also found in the samples. The concentrations of pollutants in the atmosphere remote from continental sources are good measures of the minimum concentrations of air pollutants on Earth.     

Cyclic polyether-protonated organic amine binding: significance in enzymatic and ion transport processes

The cyclic polyether, 18-crown-6, reacts with protonated amines in methanol to form complexes whose formation constants (log K) decrease in the order NH4+, RNH3+ greater than R2NH2+ greater than R3NH+. In the case of the organic amines, this stability order is identical to the earlier observed permeability sequence for protonated organic amines in glyceryl dioleate bilayers treated with valinomycin, nonactin, or gramicidin, and in bullfrog and rabbit gallbladder membranes. The decrease in log K values in the above series is primarily a result of decreased enthalpy change (deltaH) values, the entropy change (TdeltaS) term being essentially constant for the systems studied.     

Constraints on transport and kinetics in hydrothermal systems from zoned garnet crystals

Zonation of oxygen isotope ratios, fluorine, and rare earth element abundances across garnet crystals from the Permian Oslo Rift reflect temporal variation of the hydrothermal system in which the garnets grew. A sharp rimward decrease in the (18)O/(16)O ratio (of 5 per mil) across the interface between aluminum-rich garnet cores and iron-rich rims indicates influx of meteoric fluids to a system initially dominated by magmatic fluids. This influx may record the transition from ductile to brittle deformation of the hydrothermally altered rocks. In contrast, fluorine and light rare earth element concentrations increase at the core-rim interface. These data may reflect enhanced advective transport and notable kinetic control on trace element uptake by the garnets during brittle deformation.     

The role of driving energy and delocalized States for charge separation in organic semiconductors

The electron-hole pair created via photon absorption in organic photoconversion systems must overcome the Coulomb attraction to achieve long-range charge separation. We show that this process is facilitated through the formation of excited, delocalized band states. In our experiments on organic photovoltaic cells, these states were accessed for a short time (<1 picosecond) via infrared (IR) optical excitation of electron-hole pairs bound at the heterojunction. Atomistic modeling showed that the IR photons promote bound charge pairs to delocalized band states, similar to those formed just after singlet exciton dissociation, which indicates that such states act as the gateway for charge separation. Our results suggest that charge separation in efficient organic photoconversion systems occurs through hot-state charge delocalization rather than energy-gradient-driven intermolecular hopping.     

羊奶果的共生固氮及氮素的运转形式

对羊奶果根瘤的固氮、吸氧、防氧保护及固氮产物的运转进行研究。羊奶果是热带植物，离体根瘤固氮活性在25－30℃时最高，且在离体3h以内无显著变化；35－40℃的高温对根瘤吸氢活性有促进作用，离体根瘤的吸氢活性可保持6h 以上，低温对固氮活性有明显的抑制作用。羊奶果为酰脲型植物，根、根瘤和木质部中都含有大量的尿囊酸，酰脲含量均占氮化合物总量的50％以上，说明它的根瘤和根都能将氮素转化成酰脲并经过木质部 向上转运，还有部分氮素通过丝氨酸、蛋氨酸为主的氨基酸形式运输。根瘤中未检测到血红蛋白，但有较高含量的SOD、ASA和GSH.     

Atmospheric temperature: successful test of remote probing

The Nimbus III satellite carries the satellite infrared spectrometer (SIRS). It measures the radiance of the earth and the atmosphere in seven narrow spectral intervals in the 15-micrometer carbon dioxide band and in one interval of minimum absorption at 11.1 micrometers. Seven simultaneous equations are solved to obtain the vertical temperature profile; the eighth measurement is used to determine the boundary condition (cloud or surface temperature). Results agree with those obtained from conventional radiosondes.     

Guest transport in a nonporous organic solid via dynamic van der Waals cooperativity

A well-known organic host compound undergoes single-crystal-to-single-crystal phase transitions upon guest uptake and release. Despite a lack of porosity of the material, guest transport through the solid occurs readily until a thermodynamically stable structure is achieved. In order to actively facilitate this dynamic process, the host molecules undergo significant positional and/or orientational rearrangement. This transformation of the host lattice is triggered by weak van der Waals interactions between the molecular components. In order for the material to maintain its macroscopic integrity, extensive cooperativity must exist between the molecules throughout the crystal, such that rearrangement can occur in a well-orchestrated fashion. We demonstrate here that even weak dispersive forces can exert a profound influence over solid-state dynamics.     

Pulsars in binary systems: probing binary stellar evolution and general relativity

Radio pulsars in binary orbits often have short millisecond spin periods as a result of mass transfer from their companion stars. They therefore act as very precise, stable, moving clocks that allow us to investigate a large set of otherwise inaccessible astrophysical problems. The orbital parameters derived from high-precision binary pulsar timing provide constraints on binary evolution, characteristics of the binary pulsar population, and the masses of neutron stars with different mass-transfer histories. These binary systems also test gravitational theories, setting strong limits on deviations from general relativity. Surveys for new pulsars yield new binary systems that increase our understanding of all these fields and may open up whole new areas of physics, as most spectacularly evidenced by the recent discovery of an extremely relativistic double-pulsar system.     

小分子有机酸对纳米颗粒CNTs和SBA-15在多孔介质中迁移的影响

【目的】了解有机酸对硅酸盐纳米颗粒(SBA-15)和碳纳米管(CNTs)在多孔介质中迁移行为的影响差异。【方法】采用恒定流速柱迁移试验,探讨不同浓度(0,1,2.5和5 mmol/L)乙酸、酒石酸、柠檬酸对CNTs和SBA-15纳米颗粒在多孔介质(石英砂)中穿透曲线的影响。【结果】平衡对流-弥散方程能描述多孔介质中CNTs和SBA-15迁移过程的穿透曲线。在石英砂多孔介质中,CNTs的迁移能力强于SBA-15。体系不含有机酸时,CNTs、SBA-15流出液中的纳米颗粒浓度(C)与纳米悬液进入砂柱前的初始浓度(C_0)比值(C/C_0)的峰值分别为0.74和0.25,最远迁移距离L_(max)分别为221.2和45.1cm。3种有机酸对CNTs和SBA-15在多孔介质中的迁移具有类似的抑制作用,随着介质中3种有机酸浓度的增加,CNTs和SBA-15纳米颗粒的C/C_0减小,C/C_0平台峰值对应空隙体积(PV)倍数增大,迁移阻滞因子R和不可逆吸附系数μ增大,最远迁移距离L_(max)减小。柠檬酸对CNTs和SBA-15迁移的抑制作用强于乙酸和酒石酸。Zeta电位分析表明,当体系中引入有机酸后,随着有机酸浓度的增加,石英砂、CNTs和SBA-15纳米颗粒悬液的Zeta电位均逐渐增大。【结论】有机酸会改变多孔介质和CNTs、SBA-15这2种纳米颗粒的表面电荷特征,从而使得纳米颗粒悬液在多孔介质中的迁移行为更容易受团聚、滞留和沉积作用的影响。不管在何种有机酸中,CNTs的迁移能力均强于SBA-15。     

长期施用有机肥对潮土土壤肥力及硝态氮运移规律的影响

以连续不同年限定位施用有机肥的小麦-玉米轮作农田为研究对象,设置4个处理:连续施用化肥(长期施用化肥,未施用有机肥);3年连续施用有机肥(不施化肥);5年连续施用有机肥(不施化肥);20年连续施用有机肥(不施化肥),探索不同年限连续有机施肥下土壤肥力、小麦产量和土体硝态氮累积量分布的变化。结果表明,连续施用有机肥可显著降低土壤容重、增加土壤中速效养分含量,且年限越长,效果越明显。化肥处理的小麦产量显著高于有机肥处理,有机肥处理中小麦产量随施肥年限的增加而降低,但无显著性差异。不同土壤深度硝态氮累积量表现为有机肥处理大于无机肥处理,小麦季大于玉米季;随着土壤深度增加土壤硝态氮累积量呈现先降低后增加的趋势,且各土层硝态氮累积量随施用有机肥年限增加而增加;通过分析80~100 cm土层硝态氮累积量发现,20年连续施用有机肥处理在此层的累积量最大达240 kg·hm~(-2)。由此可见,连续施用有机肥可降低小麦产量,连续20年施用有机肥土壤硝态氮总累积量和土体下层累积量均达到最大,具有一定的硝态氮淋失风险。因此,需采取一定的措施来增加作物产量,减少硝态氮累积,防止地下水硝态氮污染。     

Chick interferon: heterogeneity of electric charge

Chick interferon from allantoic fluid, virus-induced and partly purified, consists of several active components of different charge. The components are separable by elution at different pH values from a carboxymethyl-Sephadex column; they also occupy different pH zones in electrofocusing gradients. Most of the interferon is, however, isoelectric near neutrality.     

Ultrafast probing of core hole localization in N2

Although valence electrons are clearly delocalized in molecular bonding frameworks, chemists and physicists have long debated the question of whether the core vacancy created in a homonuclear diatomic molecule by absorption of a single x-ray photon is localized on one atom or delocalized over both. We have been able to clarify this question with an experiment that uses Auger electron angular emission patterns from molecular nitrogen after inner-shell ionization as an ultrafast probe of hole localization. The experiment, along with the accompanying theory, shows that observation of symmetry breaking (localization) or preservation (delocalization) depends on how the quantum entangled Bell state created by Auger decay is detected by the measurement.     

Multiple sclerosis: serum factor producing reversible alterations in bioelectric responses

Serums obtained from patients during acute exacerbations of multiple sclerosis produce a reversible depression of polysynaptic reflex responses when applied to the isolated spinal cord of the frog. Motoneuron discharges initiated by monosynaptic activation through an axosomatic spinal pathway are much less affected than reflex discharges. The active factor in serum appears to depend on the presence of complement.     

Early receptor potential: photoreversible charge displacement in rhodopsin

When the eye is illuminated by an intense flash, the visual pigment rhodopsin begins to pass rapidly through a series of intermediate states, eventually becoming bleached. If a second flash is delivered during the lifetimes of these intermediates the rhodopsin can be photoregenerated. A fast electrical response of the visual receptors, the early receptor potential, is elicited by the first flash. A similar response is elicited by the second flash, but the polarity of this response is reversed. Moreover, this response can be separated into three components, each arising from the action of light on a different intermediate. It is likely that all these fast responses, including the early receptor potential, arise from charge displacements in the visual-pigment molecule.     

Ice nucleation: elemental identification of particles in snow crystals

A scanning field-emission electron microscope combined with an x-ray analyzer is used to locate the ice nucleus within a three-dimensional image of a snow crystal and determine the chemical composition of the nucleus. This makes it possible to better understand the effect of nuclei in cloud seeding.     

Cosmology in the laboratory: defect dynamics in liquid crystals

Liquid crystals are remarkably useful for laboratory exploration of the dynamics of cosmologically relevant defects. They are convenient to work with, they allow the direct study of the "scaling solution" for a network of strings, and they provide a model for the evolution of monopoles and texture. Experiments described here support the simple "one-scale" model for cosmic string evolution, as well as some qualitative predictions of string statistical mechanics. The structure of monopoles and their apparent cylindrical but not spherical symmetry is discussed. A particular kind of defect known as texture is described and is shown to have a dynamical instability-it can decay into a monopole-antimonopole pair. This decay process has been observed occurring in the liquid crystal, and studied with numerical simulations.