Ice nucleation by solid solutions of silver-copper iodide

The lattice misfit between ice and silver iodide can be reduced by partial substitution of copper atoms for silver atoms in the silver iodide lattice. The best crystal match is obtained with a composition of CuI-3AgI, which corresponds to the most active silver-copper iodide nucleation catalyst.     

Ice nucleation by coprecipitated silver iodide and silver bromide

The ability of silver iodide to cause freezing of supercooled water is improved if up to 30 percent of the iodine atoms in the crystal are replaced with bromine atoms.     

Liquids at large negative pressures: water at the homogeneous nucleation limit

An isochoric cooling method for obtaining unprecedented tensions on liquids was used to determine the homogeneous nucleation limit for stretching of water at a variety of water densities. At densities in the range 0.55 to 0.68 gram per milliliter (g/ml), the data agree with the homogeneous nucleation temperatures measured by Skripov for superheated water at positive pressures. At densities between 0.68 and 0.93 g/ml, cavitation occurred only at negative pressures (that is, under tension). The cavitation tensions measured were in excellent agreement with those predicted by Fisher's 1948 vapor nucleation theory. A maximum tension of 140 megapascals (=1400 bars) was reached at 42 degrees C, which lies on an extrapolation of the line of isobaric density maxima. At higher densities, cavitation of droplets that survived heterogeneous nucleation failed to occur at all unless provoked, at much lower temperatures, by freezing. This observation confirms the existence of a density maximum at 42 degrees C and -140 megapascals and hence greatly strengthens the basis for Speedy's conjecture of a reentrant spinodal for water.     

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.     

Photoinduced nucleation of water vapor

Strong photoinduced nucleation of pure water vapor was found to occur in a wavelength range where no ultraviolet absorption of water vapor has been reported. Systematic studies were made of the dependence of the nucleation rate and the delay time for the initiation of nucleation on light intensity. The results obtained were accurately fitted by a phenomenological mechanism whereby the nucleation is initiated by clusters accumulating an appropriate number of photoexcited water molecules.     

Abrupt decrease in tropical Pacific sea surface salinity at end of Little Ice Age

A 420-year history of strontium/calcium, uranium/calcium, and oxygen isotope ratios in eight coral cores from the Great Barrier Reef, Australia, indicates that sea surface temperature and salinity were higher in the 18th century than in the 20th century. An abrupt freshening after 1870 occurred simultaneously throughout the southwestern Pacific, coinciding with cooling tropical temperatures. Higher salinities between 1565 and 1870 are best explained by a combination of advection and wind-induced evaporation resulting from a strong latitudinal temperature gradient and intensified circulation. The global Little Ice Age glacial expansion may have been driven, in part, by greater poleward transport of water vapor from the tropical Pacific.     

Green, catalytic oxidation of alcohols in water

Alcohol oxidations are typically performed with stoichiometric reagents that generate heavy-metal waste and are usually run in chlorinated solvents. A water-soluble palladium(II) bathophenanthroline complex is a stable recyclable catalyst for the selective aerobic oxidation of a wide range of alcohols to aldehydes, ketones, and carboxylic acids in a biphasic water-alcohol system. The use of water as a solvent and air as the oxidant makes the reaction interesting from both an economic and environmental point of view.     

Crystallinity of the double layer of cadmium arachidate films at the water surface

A crystalline counterionic layer at the interface between an electrolyte solution and a charged layer of insoluble amphiphilic molecules was observed with grazing incidence synchrotron x-ray diffraction. Uncompressed arachidic films spread over 10(-3) molar cadmium chloride solution (pH 8.8) spontaneously form crystalline clusters with coherence lengths of approximately 1000 angstroms at 9 degrees C. Ten distinct diffraction peaks were observed, seven of which were attributed to scattering only from a crystalline Cd(2+) layer and the other three to scattering primarily from the arachidate layer. The reflections from the Cd(2+) layer were indexed according to a 2 x 3 supercell of the arachidate lattice with three Cd(2+) ions per cadmium unit cell.     

武夷山国家级重点风景名胜区流域地表水质时空变化

通过对2008~2009年武夷山国家风景名胜区流域8个监测点不同水期水质污染物指标的跟踪监测分析,研究流域地表水质的时空变化特征。结果表明,在空间上,流域干流自上游至下游污染物含量总体上表现为:上游下游中游的趋势;在季节上,枯水期NH3-N、TP、NO-3-N浓度大于丰、平水期,主要与水量大小有关;TN、CODMn浓度表现为丰水期高于枯、平水期,与丰水季节降雨形成的非点源污染有关。该流域内水文特征环境因素、人类、农业活动及流域空间分布是造成溪流水质污染物特征的重要原因。     

Band structure and Fermi surface of electron-doped C60 monolayers

C60 fullerides are challenging systems because both the electron-phonon and electron-electron interactions are large on the energy scale of the expected narrow band width. We report angle-resolved photoemission data on the band dispersion for an alkali-doped C60 monolayer and a detailed comparison with theory. Compared to the maximum bare theoretical band width of 170 meV, the observed 100-meV dispersion is within the range of renormalization by electron-phonon coupling. This dispersion is only a fraction of the integrated peak width, revealing the importance of many-body effects. Additionally, measurements on the Fermi surface indicate the robustness of the Luttinger theorem even for materials with strong interactions.     

防止输气管道站场设备冰堵的表面改性处理防止输气管道站场设备冰堵的表面改性处理

天然气管道低温输送时容易发生冰堵,影响正常的输气生产。以站场设备的冰堵防治为目的,通过冰冻实验,使用接触角测试仪、扫描电镜进行测试并结合理论分析,探索了通过表面改性方法调节站场运行设备表面的化学性质,进而防治冰堵的可行性。研究表明:适当的表面处理和硅烷改性,可以在钢表面形成一层疏水或超疏水纳米膜,增加水在其表面的接触角,使水难以在钢表面停留,同时冰冻实验也证明表面改性可以延长结冰时间;经疏水和超疏水改性后,由于接触角增大,引起水结晶成冰的形核功大幅增加,并且接触角越大,形核功越大,越难结晶成冰。实验和理论研究结果证明,钢表面疏水改性,可以解决站场设备的冰堵问题,具有应用潜力。     

内陆地表水体水质遥感监测研究进展

【目的】 水质监测是水生态管理的一个重要环节。近年来内陆地表水体污染问题严重,及时、准确地获取内陆地表水质信息,可为水污染防治政策的制定提供科学依据,对合理调节城市生产生活污水排放以及保障内陆水域生态安全具有重要意义。【方法】 文章系统总结了国内外近年来内陆地表水体水质遥感监测的研究现状,介绍了内陆地表水体水质遥感监测常用的指标及其选择依据,归纳了内陆地表水体遥感监测中各种模型或方法的使用情况,指出了现有内陆地表水体水质遥感监测研究存在的问题。【结果】 当前内陆地表水体水质遥感监测存在以下问题：①实测数据获取成本高,亟需建立大规模共享平台,提高数据利用率;②绝大多数研究中的多种遥感数据源各自独立处理,需要进一步研究多元数据融合;③主要模型在实际研究中对实测数据依赖性较高,需要进一步优化算法模型,提高普适性;④已有研究中研究区多数为大面积湖泊或河流,需要增强对高分辨率卫星遥感和无人机遥感数据的利用,对细微水体水质进行监测研究。【结论】 该文分析了现有内陆地表水体水质遥感监测研究存在的问题,并提出了未来的发展趋势,旨在为实现内陆地表水体水质高效准确监测提供借鉴和参考。     

Mass Balance of the Greenland Ice Sheet at High Elevations

Comparison of ice discharge from higher elevation areas of the entire Greenland Ice Sheet with total snow accumulation gives estimates of ice thickening rates over the past few decades. On average, the region has been in balance, but with thickening of 21 centimeters per year in the southwest and thinning of 30 centimeters per year in the southeast. The north of the ice sheet shows less variability, with average thickening of 2 centimeters per year in the northeast and thinning of about 5 centimeters per year in the northwest. These results agree well with those from repeated altimeter surveys, except in the extreme south, where we find substantially higher rates of both thickening and thinning.     

Formation of cyclic water hexamer in liquid helium: the smallest piece of Ice

The cyclic water hexamer, a higher energy isomer than the cage structure previously characterized in the gas phase, was formed in liquid helium droplets and studied with infrared spectroscopy. This isomer is formed selectively as a result of unique cluster growth processes in liquid helium. The experimental results indicate that the cyclic hexamer is formed by insertion of water molecules into smaller preformed cyclic complexes and that the rapid quenching provided by the liquid helium inhibits its rearrangement to the more stable cage structure.     

2001-2002年间南极埃默里冰架水的空间分布与季节变化

南极冰架水是由海洋—冰架相互作用形成的位温低于局地冰点的水团,较周围水体相对低温、低盐,是衡量冰架物质平衡的良好指示剂。基于澳大利亚埃默里冰架海洋研究计划（AMISOR）2001至2002年的现场观测资料,本文开展了埃默里冰架水空间分布的季节变化与输运特性研究。CTD结果显示,冰架水夏季普遍分布在冰架前缘的西部、中部和东部海域,但中、西部海域的冰架水核心温度更低、分布范围更广。锚碇潜标结果显示,冰架水的分布存在显著的季节变化：冬季,冰架水盘踞在冰架前缘71.0°E以西海域和71.5-72.5°E的中部海域,以流出为主要特征;夏季,除了冰架前缘71.5-72.5°E的中部海域仍被冰架水控制,冰架水还出现在冰架前缘73.5°E以东海域,并以流入为主要特征。而冰架水在冰架前缘西部海域的出流强度明显大于东部海域的入流强度,全年冰架水主要从冰架底部输出进入普里兹湾占主导。     

Discovery of till deposition at the grounding line of Whillans Ice Stream

We report on the discovery of a grounding-line sedimentary wedge ("till delta") deposited by Whillans Ice Stream, West Antarctica. Our observation is that grounding-line deposition serves to thicken the ice and stabilize the position of the grounding line. The ice thickness at the grounding line is greater than that of floating ice in hydrostatic equilibrium. Thus, the grounding line will tend to remain in the same location despite changes in sea level (until sea level rises enough to overcome the excess thickness that is due to the wedge). Further, our observation demonstrates the occurrence of rapid subglacial erosion, sediment transport by distributed subglacial till deformation, and grounding-line sedimentation, which have important implications for ice dynamics, numerical modeling of ice flow, and interpretation of the sedimentation record.     

Optical levitation of liquid drops by radiation pressure

Charged and neutral liquid drops in the diameter range from 1 to 40 microns can be stably levitated and manipulated with laser beams. The levitation technique has been extended toward smaller particles (about 1 micron), lower laser power (less than 1 milliwatt), and deeper traps (greater than ten times the particle's weight). The techniques developed here have particular importance in cloud physics, aerosol science, fluid dynamics, and optics. The interactions of the drops with light, the electric field, the surrounding gas, and one another can be observed with high precision.     

Particle formation by ion nucleation in the upper troposphere and lower stratosphere

Unexpectedly high concentrations of ultrafine particles were observed over a wide range of latitudes in the upper troposphere and lower stratosphere. Particle number concentrations and size distributions simulated by a numerical model of ion-induced nucleation, constrained by measured thermodynamic data and observed atmospheric key species, were consistent with the observations. These findings indicate that, at typical upper troposphere and lower stratosphere conditions, particles are formed by this nucleation process and grow to measurable sizes with sufficient sun exposure and low preexisting aerosol surface area. Ion-induced nucleation is thus a globally important source of aerosol particles, potentially affecting cloud formation and radiative transfer.