共查询到20条相似文献，搜索用时 62 毫秒
1.
The trillionfold concentration of sound energy by a trapped gas bubble, so as to emit picosecond flashes of ultraviolet light, is found to be extremely sensitive to doping with a noble gas. Increasing the noble gas content of a nitrogen bubble to about 1% dramatically stabilizes the bubble motion and increases the light emission by over an order of magnitude to a value that exceeds the sonoluminescence of either gas alone. The spectrum also strongly depends on the nature of the gas inside the bubble: Xenon yields a spectral peak at about 300 nanometers, whereas the helium spectrum is so strongly ultraviolet that its peak is obscured by the cutoff of water. 相似文献
2.
Hydrophobic collapse in multidomain protein folding 总被引：1，自引：0，他引：1
We performed molecular dynamics simulations of the collapse of a two-domain protein, the BphC enzyme, into a globular structure to examine how water molecules mediate hydrophobic collapse of proteins. In the interdomain region, liquid water persists with a density 10 to 15% lower than in the bulk, even at small domain separations. Water depletion and hydrophobic collapse occur on a nanosecond time scale, which is two orders of magnitude slower than that found in the collapse of idealized paraffin-like plates. When the electrostatic protein-water forces are turned off, a dewetting transition occurs in the interdomain region and the collapse speeds up by more than an order of magnitude. When attractive van der Waals forces are turned off as well, the dewetting in the interdomain region is more profound, and the collapse is even faster. 相似文献
3.
Simpson HJ Trier RM Olsen CR Hammond DE Ege A Miller L Melack JM 《Science (New York, N.Y.)》1980,207(4435):1071-1073
Plutonium isotopes, derived from global fallout following atmospheric testing of nuclear weapons, have been measured in the water and sediments of a natural alkaline, saline lake. The activities of fallout plutonium in the water column are about two orders of magnitude greater than in most freshwater lakes, where these nuclides are found predominantly in the sediments. 相似文献
4.
为了更好的处理液化气罐再生过程中烟气的循环废水利用,以桂林市某液化气灌装公司烟气厂处理废水为实验对象,通过絮凝法、砂滤法处理试验。结果显示,絮凝剂聚合硫酸铝和聚合硫酸铁均对废水中悬浮物絮凝有良好效果,但聚合硫酸铁处理后的清液色度超过要求,聚合硫酸铝絮凝后的废水清液在后继处理中加入氧化剂后溶液变黄,色度超标;砂滤法在以32cm砂滤厚度,14mL·min-1流量下,出水浊度为2.0,后继处理以NaClO为氧化剂,当加入2mLNaClO,溶液COD降低15.4%,重金属Zn、Mg、Mn、Cu、Fe时指标值分别降低66.5%、38.1%、72.8%、76.0%、95.7%,处理后出水浊度为1.3,色度为浅黄色。结果表明:采用絮凝法处理效果欠佳;采用以砂滤法-氧化法系统处理废水,具有高的悬浮物去除效果和色度去除效果。 相似文献
5.
Tont SA 《Science (New York, N.Y.)》1976,194(4268):942-944
An analysis of the weekly averages of diatom biomass measured near the coast of Southern California (32 degrees 50'N, 117 degrees 10'W) during the period from 1928 through 1939 indicates that three major blooms account for 85 percent of each year's diatom biomass. The average duration of a single bloom is 5.5 weeks. The diatom blooms coincide with upwelling, but their individual characteristics depend on the detailed features of the circulation patterns of the water masses. That is, if upwelling takes place after a large influx of subtropical or even tropical water because of the slackening California Current, the resulting diatom blooms are smaller by several orders of magnitude than those observed when the flow of the current is strong. This influx of subtropical water into the region is reflected in positive anomalies of temperature, salinity, and sea level. 相似文献
6.
Gans et al. (Reports, 26 August 2005, p. 1387) provided an estimate of soil bacterial species richness two orders of magnitude greater than previously reported values. Using a re-derived mathematical model, we reanalyzed the data and found that the statistical error exceeds the estimate by a factor of 26. We also note two potential sources of error in the experimental data collection and measurement procedures. 相似文献
7.
SPAC中油松栓皮栎混交林水分特征与气体交换 总被引：9，自引：3，他引：6
20 0 1年 4— 10月 ,通过林内标准地观测的方式 ,对北京西山地区一块 3 1年生的油松栓皮栎混交林的水势 (用压力室测定 )日变化、净光合速率和蒸腾速率 (用Licor 640 0测定 )日变化过程进行测定 .结果表明 ,在土壤 植物 大气连续体 (SPAC)系统中 ,生长季内水势的波动幅度按从大到小的顺序是大气 >植物 >土壤 ,其中大气水势的绝对值要比植物和土壤水势高 1～ 3个数量级 .土壤、植物和大气水势的日变化规律类似 ,并表现出明显的季节差异 .在生长季不同标准日内 ,油松和栓皮栎的净光合速率和蒸腾变化规律差异较大 .通常 ,栓皮栎的净光合速率和蒸腾速率明显高于油松 ,但在水分胁迫时 ,二者的差异会减小 .在生长季中的绝大部分时段 ,树木由于环境因子特别是土壤水分的限制作用不能达到其潜在的光合和蒸腾能力 相似文献
8.
A simple hydrologic model of seawater circulation at ocean ridge axes implies that the transient occurrence of large volumes of buoyant, heated water in the oceanic water column (megaplumes) can be attributed to the emplacement of dikes in oceanic crust. For dikes to generate megaplume flow, the permeability of both the recharge areas and the upflow zone must be greater than that required for ordinary black smokers. An increase in permeability in the upflow zone by several orders of magnitude results from dike emplacement, and megaplume discharge ceases as the dike cools. Vigorous black smoker venting may not persist very long at a megaplume site after the event occurs. 相似文献
9.
Scanometric DNA array detection with nanoparticle probes 总被引：1，自引：0，他引：1
A method for analyzing combinatorial DNA arrays using oligonucleotide-modified gold nanoparticle probes and a conventional flatbed scanner is described here. Labeling oligonucleotide targets with nanoparticle rather than fluorophore probes substantially alters the melting profiles of the targets from an array substrate. This difference permits the discrimination of an oligonucleotide sequence from targets with single nucleotide mismatches with a selectivity that is over three times that observed for fluorophore-labeled targets. In addition, when coupled with a signal amplification method based on nanoparticle-promoted reduction of silver(I), the sensitivity of this scanometric array detection system exceeds that of the analogous fluorophore system by two orders of magnitude. 相似文献
10.
Modern sea-floor phosphorite nodules sampled from off the coast of Peru are shown to grow at rates of millimeters per thousand years in spite of the fact that the measured accumulation rates of the underlying sediment are two to four orders of magnitude faster. Phosphate nodules grow downward into soft sediment, and the rates of phosphorus accumulation into nodules are approximately equal to the upward diffusive flux of dissolved phosphate inferred from pore water profiles. These results demonstrate that phosphorus in nodules originates from regeneration in sediments rather than as a result of direct precipitation from bottom waters. 相似文献
11.
Polychlorinated biphenyls (PCB), DDT, and chlordane concentrations were measured in air sampled from a tower on the south shore of Bermuda and in Sargasso Sea surface water approximately 80 to 320 kilometers south of Bermuda. The atmospheric chlorinated hydrocarbons appeared to be gaseous, and the DDT concentration was two orders of magnitude higher than previously reported particulate values. The PCB and DDT were enriched in the surface microlayer (150 micrometers) relative to their concentrations in water at a depth of 30 centimeters. Atmospheric residence times for PCB and DDT of 40 to 50 days, calculated from the concentrations in the air and water, are 20 times shorter than values previously estimated for DDT from rainfall and DDT production data. 相似文献
12.
The feasibility of electrochemically synthesizing methane by a Fischer-Tropsch type reaction by use of a solid oxide electrolyte has been demonstrated. This solid-state ionic approach provides in situ control of the oxygen activity at the gascatalyst interface by imposing a suitable voltage drop across an oxygen-conducting solid electrolyte from an external source. Methanation rates for hydrogen-carbon monoxide and hydrogen-carbon dioxide synthesis gas mixtures upon nickel electrodes showed substantial enhancement with the use of this technique, reaching values nearly two orders of magnitude higher than their intrinsic rates. 相似文献
13.
RJ Schoelkopf P Wahlgren AA Kozhevnikov P Delsing DE Prober 《Science (New York, N.Y.)》1998,280(5367):1238-1242
A new type of electrometer is described that uses a single-electron transistor (SET) and that allows large operating speeds and extremely high charge sensitivity. The SET readout was accomplished by measuring the damping of a 1.7-gigahertz resonant circuit in which the device is embedded, and in some ways is the electrostatic "dual" of the well-known radio-frequency superconducting quantum interference device. The device is more than two orders of magnitude faster than previous single-electron devices, with a constant gain from dc to greater than 100 megahertz. For a still-unoptimized device, a charge sensitivity of 1.2 x 10(-5) e/hertz was obtained at a frequency of 1.1 megahertz, which is about an order of magnitude better than a typical, 1/f-noise-limited SET, and corresponds to an energy sensitivity (in joules per hertz) of about 41 Planck's over 2pi. 相似文献
14.
气液混输管道中常常出现由气相流量变化引起的瞬态过程，在接近现场管道的多相流环道上进行了气量变化的瞬态试验，讨论了瞬态压力特性。当气量突变后，压力波向下游传播，各点依次发生变化，变化趋势相同，而压力最大变化值沿线衰减，压力变化速率也递减。当突然增加气相流量时，管道压力突增，其峰值超过最终稳态压力值，在峰值附近有一段时间压力基本不变，随后压力降低，向终稳态发展，而突然减小气量，变化方向则相反。气量减小的瞬态过程时间长于气量增加的瞬态过程时间。小液量和大液量工况下的瞬态压力变化有所不同，两种情况下的过冲量沿线变化趋势相反。 相似文献
15.
Highly turbid bottom water at the margin of the Sohm Abyssal Plain was identified by its temperature, salinity, and oxygen content as originating upslope on the continental rise. The fact that the particulate concentrations were one to two orders of magnitude higher than are normally found in deep ocean waters suggests a turbidity current as the agent bringing this water downslope. 相似文献
16.
Locally resonant sonic materials 总被引：2，自引：0，他引：2
Liu Z Zhang X Mao Y Zhu YY Yang Z Chan CT Sheng P 《Science (New York, N.Y.)》2000,289(5485):1734-1736
We have fabricated sonic crystals, based on the idea of localized resonant structures, that exhibit spectral gaps with a lattice constant two orders of magnitude smaller than the relevant wavelength. Disordered composites made from such localized resonant structures behave as a material with effective negative elastic constants and a total wave reflector within certain tunable sonic frequency ranges. A 2-centimeter slab of this composite material is shown to break the conventional mass-density law of sound transmission by one or more orders of magnitude at 400 hertz. 相似文献
17.
A study of the equilibrium and disequilibrium thermochemistry of the recently discovered carbon monoxide on Jupiter suggests that the presence of this gas in the visible atmosphere is a direct result of very rapid upward mixing from levels in the deep atmosphere where the temperature is about 1100 degrees K and where carbon monoxide is thermodynamically much more stable. As a consequence the observed carbon monoxide mixing ratio is a sensitive function of the vertical eddy mixing coefficient. We infer a value for this latter coefficient which is about three to four orders of magnitude greater than that in the earth's troposphere. This result directly supports existing structural and dynamical theories implying very rapid convection in the deep Jovian atmosphere, driven by an internal heat source. 相似文献
18.
Diffusion of atoms in a crystalline lattice is a thermally activated process that can be strongly accelerated by defects such as grain boundaries or dislocations. When carried by dislocations, this elemental mechanism is known as "pipe diffusion." Pipe diffusion has been used to explain abnormal diffusion, Cottrell atmospheres, and dislocation-precipitate interactions during creep, although this rests more on conjecture than on direct demonstration. The motion of dislocations between silicon nanoprecipitates in an aluminum thin film was recently observed and controlled via in situ transmission electron microscopy. We observed the pipe diffusion phenomenon and measured the diffusivity along a single dislocation line. It is found that dislocations accelerate the diffusion of impurities by almost three orders of magnitude as compared with bulk diffusion. 相似文献
19.
Singer SF 《Science (New York, N.Y.)》1967,156(3778):1080-1083
The recent detection of radioactive Al(26) in marine sediments has led to the conclusion that it is brought into the earth's atmosphere by micrometeorites which have been exposed, in interplanetary space, to solar high-energy protons. The Al(26) method is not precise enough to yield directly a reliable value for the mass accretion rate to the earth to better than about 3 orders of magnitude, but is sufficiently accurate to allow a crucial decision between two widely differing of interplanetary dust which have been proposed to explain observations of the zodiacal light. The two models lead to Al(26) concentrations which would differ by about 5 orders of magnitude. Thus, the presence of Al(26) is consistent with the zodiacal dust model with particles of some tens of microns rather then with submicron particles. From this model a mass accretion to the earth then be calculated which is set at 1250 (upper limit, 2500; lower limit, 250) tons per day, or 2.8 x 10(-15) g/cm(2) sec, or 4.5 x 10(11) g over the earth per This value does not depend on the flux of the solar high-energy particles, which may be uncertain by an order of magnitude or more. The presence of Al(26) supports the idea that an important fraction of the dust is stony in composition material density, and thus eliminates some more exotic dust models, as such one consisting entirely of carbon grains. We may also conclude that the accreted dust particles have been in the solar system and exposed to protons from solar high-energy particles for a time interval which is greater than a significant of the Al(26) half-life (0.74 x 10(6) years). 相似文献
20.
A hydrogen-rich early Earth atmosphere 总被引：1，自引：0，他引：1
We show that the escape of hydrogen from early Earth's atmosphere likely occurred at rates slower by two orders of magnitude than previously thought. The balance between slow hydrogen escape and volcanic outgassing could have maintained a hydrogen mixing ratio of more than 30%. The production of prebiotic organic compounds in such an atmosphere would have been more efficient than either exogenous delivery or synthesis in hydrothermal systems. The organic soup in the oceans and ponds on early Earth would have been a more favorable place for the origin of life than previously thought. 相似文献