Reactions at interfaces as a source of sulfate formation in sea-salt particles

Understanding the formation of sulfate particles in the troposphere is critical because of their health effects and their direct and indirect effects on radiative forcing, and hence on climate. Laboratory studies of the chemical and physical changes in sodium chloride, the major component of sea-salt particles, show that sodium hydroxide is generated upon reaction of deliquesced sodium chloride particles with gas-phase hydroxide. The increase in alkalinity will lead to an increase in the uptake and oxidation of sulfur dioxide to sulfate in sea-salt particles. This chemistry is missing from current models but is consistent with a number of previously unexplained field study observations.     

Diurnal variation of stratospheric chlorine monoxide: a critical test of chlorine chemistry in the ozone layer

This article reports measurements of the column density of stratospheric chlorine monoxide and presents a complete diurnal record of its variation (with 2-hour resolution) obtained from ground-based observations of a millimeter-wave spectral line at 278 gigahertz. Observations were carried out during October and December 1982 from Mauna Kea, Hawaii. The results reported here indicate that the mixing ratio and column density of chlorine monoxide above 30 kilometers during the daytime are approximately 20 percent lower than model predictions based on 2.1 parts per billion of total stratospheric chlorine. The observed day-to-night variation of chlorine monoxide is, however, in good agreement with recent model predictions, confirms the existence of a nighttime reservoir for chlorine, and verifies the predicted general rate of its storage and retrieval. From this evidence, it appears that the chlorine chemistry above 30 kilometers is close to being understood in current stratospheric models. Models based on this chemistry and measured reaction rates predict a reduction in the total stratospheric ozone content in the range of 3 to 5 percent in the final steady state for an otherwise unperturbed atmosphere, although the percentage decrease in the upper stratosphere is much higher.     

海盐胁迫对海滨雀稗植株形态与生长的影响

分别以0、6.8、13.6、20.4、27.2、34.0g/L海盐同1/2 Hoagland营养液混配,用作不同含盐量灌溉处理,研究海盐胁迫对海滨雀稗植株形态与生长的影响.结果表明,随着海盐处理浓度提高,海滨雀稗叶宽变窄,直立茎和匍匐茎变细,海盐质量浓度高于6.8g/L,海滨雀稗生长明显受到抑制,根、茎和叶干物重显著降低;海盐质量浓度为27.2g/L和34 g/L时,无匍匐茎生出,海盐质量浓度在0～20.4g/L范围内匍匐茎节间长度无显著变化;叶宽、直立茎茎粗、匍匐茎茎粗和根、茎、叶干重均与海盐处理液电导率值呈极显著负相关.     

An ab initio molecular dynamics study of the aqueous liquid-vapor interface

We present an ab initio molecular dynamics simulation of the aqueous liquid-vapor interface. Having successfully stabilized a region of bulk water in the center of a water slab, we were able to reproduce and further quantify the experimentally observed abundance of surface "acceptor-only"(19%) and "single-donor"(66%) moieties as well as substantial surface relaxation approaching the liquid-vapor interface. Examination of the orientational dynamics points to a faster relaxation in the interfacial region. Furthermore, the average value of the dipole decreases and the average value of the highest occupied molecular orbital for each water molecule increases approaching the liquid-vapor interface. Our results support the idea that the surface contains, on average, far more reactive states than the bulk.     

水相凝胶色谱法测定草炭土溶解态有机质的分子质量及分子质量分布

以水为流动相,宽分布葡聚糖为标准,用水相凝胶色谱法测定土壤溶解态有机质的分子质量及分子质量分布.样品的进样量、流动相流速对测定结果无明显影响,测定结果的相对标准偏差小于10%.     

Diels-alder in aqueous molecular hosts: unusual regioselectivity and efficient catalysis

Self-assembled, hollow molecular structures are appealing as synthetic hosts for mediating chemical reactions. However, product binding has inhibited catalytic turnover in such systems, and selectivity has rarely approached the levels observed in more structurally elaborate natural enzymes. We found that an aqueous organopalladium cage induces highly unusual regioselectivity in the Diels-Alder coupling of anthracene and phthalimide guests, promoting reaction at a terminal rather than central anthracene ring. Moreover, a similar bowl-shaped host attains efficient catalytic turnover in coupling the same substrates (although with the conventional regiochemistry), most likely because the product geometry inhibits the aromatic stacking interactions that attract the planar reagents to the host.     

臭氧对鲢鱼鱼丸品质的影响

研究了在漂洗和擂溃工序中添加臭氧对鲢鱼鱼丸色泽和凝胶强度的影响,并对臭氧处理鱼丸的条件进行优化.结果表明:在擂溃工序中添加0.8 mg.L-1臭氧,在40℃下水浴35 min,鱼丸的持水性、色泽和质构特性最佳.     

Formation of a carbon-carbon triple bond by coupling reactions in aqueous solution

Formation of a carbon-carbon triple bond by coupling reactions usually takes place at high temperatures, in anhydrous media and anaerobic conditions. We describe the formation of a carbon-carbon triple bond at room temperature in an aqueous solution exposed to the atmosphere. Two ethylidyne ligands of a trimolybdenum cluster coupled spontaneously to form 2-butyne. This unexpected result demonstrates the plausibility of alkylidyne chain lengthening and metathesis processes under ambient, environmentally friendly conditions.     

Formation of glasses from liquids and biopolymers

Glasses can be formed by many routes. In some cases, distinct polyamorphic forms are found. The normal mode of glass formation is cooling of a viscous liquid. Liquid behavior during cooling is classified between "strong" and "fragile," and the three canonical characteristics of relaxing liquids are correlated through the fragility. Strong liquids become fragile liquids on compression. In some cases, such conversions occur during cooling by a weak first-order transition. This behavior can be related to the polymorphism in a glass state through a recent simple modification of the van der Waals model for tetrahedrally bonded liquids. The sudden loss of some liquid degrees of freedom through such first-order transitions is suggestive of the polyamorphic transition between native and denatured hydrated proteins, which can be interpreted as single-chain glass-forming polymers plasticized by water and cross-linked by hydrogen bonds. The onset of a sharp change in ddT( is the Debye-Waller factor and T is temperature) in proteins, which is controversially indentified with the glass transition in liquids, is shown to be general for glass formers and observable in computer simulations of strong and fragile ionic liquids, where it proves to be close to the experimental glass transition temperature. The latter may originate in strong anharmonicity in modes ("bosons"), which permits the system to access multiple minima of its configuration space. These modes, the Kauzmann temperature T(K), and the fragility of the liquid, may thus be connected.     

Release of particles containing metals from vegetation into the atmosphere

Studies with radioisotopes indicate that in the laboratory pea plants and pine tree seedlings release zinc and lead into the atmosphere. Field studies carried out on radiolabeled plots vegetated with a variety of grasses and small herbaceous plants also show that these elements are released into the atmosphere. The metals, associated with particles of various sizes, are released from the plant surfaces, and the loss mechanism is influenced by growth conditions, the concentrations of the elements in the leaves, and meteorological factors. For plants whose leaves have about equal concentrations of zinc and lead, the amount of zinc released is usually two orders of magnitude greater than the amount of lead. The significance of the process is discussed in terms of the overall trace metal composition of atmospheric particulates.     

Observations of ozone formation in power plant plumes and implications for ozone control strategies

Data taken in aircraft transects of emissions plumes from rural U.S. coal-fired power plants were used to confirm and quantify the nonlinear dependence of tropospheric ozone formation on plume NO(x) (NO plus NO(2)) concentration, which is determined by plant NO(x) emission rate and atmospheric dispersion. The ambient availability of reactive volatile organic compounds, principally biogenic isoprene, was also found to modulate ozone production rate and yield in these rural plumes. Differences of a factor of 2 or greater in plume ozone formation rates and yields as a function of NO(x) and volatile organic compound concentrations were consistently observed. These large differences suggest that consideration of power plant NO(x) emission rates and geographic locations in current and future U.S. ozone control strategies could substantially enhance the efficacy of NO(x) reductions from these sources.     

Volatilization of high molecular weight DNA by pulsed laser ablation of frozen aqueous solutions

DNA has been volatilized by pulsed laser ablation of a thin film of a frozen aqueous DNA solution. The target film was irradiated in vacuum by a pulsed laser at power densities sufficient to ablate the ice matrix. The expanding ablated water vapor entrained embedded DNA molecules and expelled them into the gas phase. Ejection of DNA molecules as large as 410 kilodaltons was verified by collection of the ablation products and subsequent mass analysis by polyacrylamide gel electrophoresis with autoradiographic detection.     

烤烟对氯的吸收积累特性

采用大田试验。在基肥中用部分氯化钾替代硫酸钾,追肥仍然使用原专用追肥。研究在不同氯浓度处理下烤烟三个重要的生理时期(团棵期、现蕾期、成熟期)对氯的吸收积累特性,以及对氮、磷、钾吸收的影响。结果表明:对烤烟烟叶各部位氯含量的测定分析得出:烟叶氯的积累量为下部叶>中部叶>上部叶。团棵期烤烟氯的积累量随氯肥替代的增加出现曲折下降趋势,20%氯替代时达到最大积累量0.36%,现蕾期和成熟期各部烟叶在50%氯替代下,烟叶氯含量分别超过0.2%和0.5%。上部叶的烟叶含氮量随氯替代的增加而降低,中、下部叶含氮量无明显变化;各处理下,下部烟叶的钾含量均较上、中部烟叶高,无氯替代、20%氯替代和30%氯替代处理下差异较为明显,而上部烟叶与中部烟叶的含钾量无明显差异。施氯处理与不施氯处理对烟株磷含量的积累,无太大影响。