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1.
The structure, energetics, and dynamics of shock conditions generated in a nano-cluster upon impact on a crystalline surface are investigated with molecular-dynamics simulations for a 561-atom argon cluster incident with a velocity of 3 kilometers per second onto a sodium chloride surface. The "piling-up" shock phenomenon occurring upon impact, coupled with cascades of energy and momentum transfer processes and inertial confinement of material in the interior of the cluster, creates a transient medium lasting for about a picosecond and characterized by extreme local density, pressure, and kinetic temperature. The nano-shock conditions and impulsive nature of interactions in the newly formed compressed nonequilibrium environment open avenues for studying chemical reactivity and dynamics catalysed via cluster impact. 相似文献
2.
K Bromann C Felix H Brune W Harbich R Monot J Buttet K Kern 《Science (New York, N.Y.)》1996,274(5289):956-958
Variable-temperature scanning tunneling microscopy was used to study the effect of kinetic cluster energy and rare-gas buffer layers on the deposition process of size-selected silver nanoclusters on a platinum(111) surface. Clusters with impact energies of 相似文献
3.
Killian TC 《Science (New York, N.Y.)》2007,316(5825):705-708
Ultracold neutral plasmas occupy an exotic regime of plasma physics in which electrons form a swarming, neutralizing background for ions that sluggishly move in a correlated manner. Strong interactions between the charged particles give rise to surprising dynamics such as oscillations of the average kinetic energy during equilibration and extremely fast recombination. Such phenomena offer stimulating and challenging problems for computational scientists, and the physics can be applied to other environments, such as the interior of gas giant planets and plasmas created by short-pulse laser irradiation of solid, liquid, and cluster targets. 相似文献
4.
We used angle-resolved photoemission spectroscopy to measure the electronic dispersion and single-particle spectral function in a liquid metal. A lead monolayer supported on a copper (111) surface was investigated as the temperature was raised through the melting transition of the film. Electron spectra and momentum distribution maps of the liquid film revealed three key features of the electronic structure of liquids: the persistence of a Fermi surface, the filling of band gaps, and the localization of the wave functions upon melting. Distinct coherence lengths for different sheets of the Fermi surface were found, indicating a strong dependence of the localization lengths on the character of the constituent atomic wave functions. 相似文献
5.
为研究腐植酸可降解地膜的生物降解性,采用微生物降解试验和受控埋土试验观察微生物生长情况,并测定了可降解地膜在降解过程中的重量损失;以埋有地膜的土壤为材料测定了微生物数量和土壤酶活性,探讨了残膜对土壤微生物代谢活动的影响。结果表明:微生物对地膜的降解起促进作用,真菌对地膜降解的影响最为明显,且淀粉含量最高的地膜降解速度最快;地膜降解的中间产物能促进土壤微生物的数量和生化活性,与无地膜填埋土壤相比,埋有地膜a土壤的细菌数量提高了205.1%,真菌数量提高了110.4%,埋有地膜b土壤的放线菌数量提高了46.9%;埋有地膜b土壤的过氧化氢酶活性提高了156.2%,埋有地膜a土壤的蔗糖酶活性提高了198.6%,埋有地膜b土壤的呼吸强度提高了24%,其影响不仅与腐植酸含量有关,还与地膜的降解程度有关。 相似文献
6.
The competitive binding of a molecule forming a liquid crystal and a targeted analyte to a common molecular receptor presented at a solid surface possessing nanometer-scale topography is used to trigger an easily visualized surface-driven change in the orientation of a micrometer-thick film of liquid crystal. Diffusion of the targeted analyte from atmosphere to surface-immobilized receptor across the micrometer-thick film of liquid crystal is fast (on the order of seconds), and the competitive interaction of the targeted analyte and liquid crystal with the receptor provides a high level of tolerance to nontargeted species (water, ethanol, acetone, and hexanes). Systems that provide parts-per-billion (by volume) sensitivity to either organoamine or organophosphorus compounds are demonstrated, and their use for imaging of spatial gradients in concentration is reported. This approach does not require complex instrumentation and could provide the basis of wearable personalized sensors for measurement of real-time and cumulative exposure to environmental agents. 相似文献
7.
The kinetics of the Fe(2+)-Mg, order-disorder phenomenon in a highly ordered natural anthophyllite have been determined over the temperature range from 400 degrees to 720 degrees C at a pressure of 2 kilobars. At temperatures of 600 degrees C and above, equilibrium is attained by disordering as well as ordering reactions. The intracrystalline exchange is defined by a standard Gibbs free energy of 4247 +/- 54 calories per formula unit. Rate studies at 550 degrees and 500 degrees C show that equilibrium is attained by ordering but not by disordering within the same time scale and that the exchange reaction is characterized by an activation energy of approximately 55 kilocalories per formula unit. An equilibration temperature for the natural anthophyllite of 270 degrees C is determined from the termination of the ordering process owing to excessively slow reaction kinetics after approximately 10(7) years. From the rate constants of the exchange process, for different crystallization temperatures, the apparent equilibration temperature of 270 degrees C defines a maximum linear cooling rate for the rock of 1 x 10(4) degrees C per year. 相似文献
8.
9.
在我们过去研究成功的锦橙硅窗袋藏法的基础上,改用FC-8型布基硅橡胶膜作硅窗,加用“增效剂”和乙烯吸收剂,效果显著提高。锦橙在产地常温下贮藏4个月,不检查,好果率98％左右,腐果率0-1.68％,失重1.50-1.67％,果汁丰富、味浓,果肉化渣,果实新鲜、色泽红艳。方法的性质为低乙烯、简易动态气调辅助下的化学贮藏。 相似文献
10.
液体地膜覆盖对滴灌棉花生长及土壤水温盐环境的影响 总被引：1，自引：0，他引：1
干旱区棉田残膜污染日益严重,液体地膜覆盖能从根本上杜绝农田残膜增加。为探索液体地膜代替塑料薄膜与滴灌结合的可行性,采用测坑试验研究3种覆盖方式[液体地膜覆盖(LFD)、塑料地膜覆盖(PFD)和裸地对照(NFD)]对滴灌棉花生长及土壤水温盐环境的影响。结果表明,LFD棉花可提高土壤含水率和地温,加快滴灌棉花前期生长速度及适度抑制后期旺长。平均籽棉产量较NFD增长7.2%,相对PFD降低2.1%。LFD棉花对土壤环境无不良影响,在干旱区滴灌棉田具有应用前景。 相似文献
11.
We directly observed the hydration dynamics of an excess electron in the finite-sized water clusters of (H2O)n- with n = 15, 20, 25, 30, and 35. We initiated the solvent motion by exciting the hydrated electron in the cluster. By resolving the binding energy of the excess electron in real time with femtosecond resolution, we captured the ultrafast dynamics of the electron in the presolvated ("wet") and hydrated states and obtained, as a function of cluster size, the subsequent relaxation times. The solvation time (300 femtoseconds) after the internal conversion [140 femtoseconds for (H2O)35-] was similar to that of bulk water, indicating the dominant role of the local water structure in the dynamics of hydration. In contrast, the relaxation in other nuclear coordinates was on a much longer time scale (2 to 10 picoseconds) and depended critically on cluster size. 相似文献
12.
The CUO molecule, formed from the reaction of laser-ablated U atoms with CO in a noble gas, exhibits very different stretching frequencies in a solid argon matrix [804.3 and 852.5 wave numbers (cm(-1))] than in a solid neon matrix (872.2 and 1047.3 cm(-1)). Related experiments in a matrix consisting of 1% argon in neon suggest that the argon atoms are interacting directly with the CUO molecule. Relativistic density functional calculations predict that CUO can bind directly to one argon atom (U-Ar = 3.16 angstroms; binding energy = 3.2 kilocalories per mole), accompanied by a change in the ground state from a singlet to a triplet. Our experimental and theoretical results also suggest that multiple argon atoms can bind to a single CUO molecule. 相似文献
13.
Melting of diamond at high pressure and the properties of liquid carbon at pressures greater than 1 megabar were investigated with a first-principles molecular dynamics technique. The results indicate an increase of the diamond melting temperature with pressure, which is opposite to the behavior of silicon and germanium. This is contrary to long-held assumptions, but agrees with recent experiments, and has important implications for geology and astrophysics. As is the case for the solid phase of carbon at low temperature, which changes greatly with pressure from graphite to diamond, the structural and bonding properties of liquid carbon vary strongly with pressure. 相似文献
14.
Turner G 《Science (New York, N.Y.)》1970,167(3918):466-468
Seven crystalline rock samples returned by Apollo 11 have been analyzed in detail by means of the (40)Ar-(-39)Ar dating technique. The extent of radiogenic argon loss in these samples ranges from 7 percent to >/= 48 percent. Potassium-argon ages, corrected for the effects of this loss, cluster relatively closely around the value of 3.7 x 10(9) years. Most of the vulcanism associated with the formation of the Mare Tranquillitatis presumably occurred around 3.7 x 10(9) years ago. A major cause of the escape of gas from lunar rock is probably the impact event which ejected the rock from its place of origin to its place of discovery. Upper limits for the times at which these impact events occurred have been estimated. 相似文献
15.
我国是农业大国,但不是农业强国。在国内外众多学者的努力下,设施农业因其直接经济效益得到广泛的发展。随着我国设施农业的发展,对农膜的需求量也随之增多。截止到2020年我国农膜的数量达到238.86万吨,与20年前相比,增加了78.87%,其中地膜覆盖面积达到1738.68万公顷。农膜给设施农业生产带来增产、增收效益的同时,也给土壤、作物、大气带来了影响,尤其是残留在土壤中的农膜治理是事关耕地土壤质量、农产品健康安全的重要工作。本文介绍了农膜种类和使用情况,简要分析了农膜对土壤、作物、大气带来的影响,并对残膜造成的环境污染提出治理措施。 相似文献
16.
Cossaro A Mazzarello R Rousseau R Casalis L Verdini A Kohlmeyer A Floreano L Scandolo S Morgante A Klein ML Scoles G 《Science (New York, N.Y.)》2008,321(5891):943-946
The structure of self-assembled monolayers (SAMs) of long-chain alkyl sulfides on gold(111) has been resolved by density functional theory-based molecular dynamics simulations and grazing incidence x-ray diffraction for hexanethiol and methylthiol. The analysis of molecular dynamics trajectories and the relative energies of possible SAM structures suggest a competition between SAM ordering, driven by the lateral van der Waals interaction between alkyl chains, and disordering of interfacial Au atoms, driven by the sulfur-gold interaction. We found that the sulfur atoms of the molecules bind at two distinct surface sites, and that the first gold surface layer contains gold atom vacancies (which are partially redistributed over different sites) as well as gold adatoms that are laterally bound to two sulfur atoms. 相似文献
17.
Saecker ME Govoni ST Kowalski DV King ME Nathanson GM 《Science (New York, N.Y.)》1991,252(5011):1421-1424
By means of controlled collisions of atoms and molecules with liquid surfaces, molecular beam experiments can be used to probe how gases stick to, rebound from, and exchange energy with molecules in the liquid phase. This report describes measurements of energy exchange in collisions between gases (neon, xenon, and sulfur hexafluoride) and polyatomic liquids (squalane and perfluoropolyether). Energy transfer depends critically on liquid composition and is more efficient for the hydrocarbon than for the perfluorinated ether. 相似文献
18.
菲在不同性质黑炭上的吸附动力学和等温线研究 总被引：8，自引：3，他引：8
在300、500和700℃3种条件下加热木屑制备得到3种黑炭,并对其结构和组成进行了表征。通过吸附动力学实验和平衡吸附实验,研究了菲在这些黑炭样品上的吸附动力学和平衡吸附,分别应用拟一阶、拟二阶和叶洛维奇3种动力学模型及Freundlich吸附等温方程对实验数据进行了拟合。结果表明,菲在黑炭样品上的吸附可以分为极快吸附、快吸附和慢吸附3个阶段,拟一阶动力学和叶洛维奇动力学方程仅能对菲在黑炭上吸附动力学的某个阶段拟合较好,而拟二阶动力学模型可较好地拟合菲的整体吸附动力学过程。说明菲在黑炭上的吸附由多个过程控制,水膜扩散、吸附剂颗粒表面扩散和吸附剂内部微孔扩散等多个过程导致了其吸附动力学的复杂性。在快吸附阶段,菲在各个黑炭上吸附动力学的差异,主要受黑炭疏水性影响。Freundlich模型对吸附等温数据的拟合结果进一步证实,多环芳烃菲在黑炭样品上的吸附受多种机制影响。 相似文献
19.
不同覆膜方式对甘薯生长发育的影响 总被引：3，自引：0，他引：3
通过比较3种不同覆膜方式即黑膜、透明膜及不覆膜对甘薯生长发育过程中土壤温湿度、孔隙度、甘薯地上部及地下部生长发育动态的影响,确定最佳的覆膜方式。结果表明,土壤孔隙度在覆膜与不覆膜之间存在明显差异,覆膜可以使土壤保持疏松透气,同时还可以起到增温保墒的作用,为甘薯膨大提供一个好的环境;相对于透明膜而言,覆黑膜可以将地温控制在更能适宜甘薯膨大的范围之内,抑制膜下的杂草生长。不同栽培方式对甘薯产量的影响依次为黑膜>透明膜>无膜。可见,在甘薯生长发育过程中,覆膜可以提高产量,并且覆黑膜比覆透明膜的效果更好,应当在甘薯栽培中推广黑膜覆盖技术。 相似文献
20.
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. 相似文献