共查询到20条相似文献，搜索用时 566 毫秒
1.
Waite JH Niemann H Yelle RV Kasprzak WT Cravens TE Luhmann JG McNutt RL Ip WH Gell D De La Haye V Müller-Wordag I Magee B Borggren N Ledvina S Fletcher G Walter E Miller R Scherer S Thorpe R Xu J Block B Arnett K 《Science (New York, N.Y.)》2005,308(5724):982-986
The Cassini Ion Neutral Mass Spectrometer (INMS) has obtained the first in situ composition measurements of the neutral densities of molecular nitrogen, methane, molecular hydrogen, argon, and a host of stable carbon-nitrile compounds in Titan's upper atmosphere. INMS in situ mass spectrometry has also provided evidence for atmospheric waves in the upper atmosphere and the first direct measurements of isotopes of nitrogen, carbon, and argon, which reveal interesting clues about the evolution of the atmosphere. The bulk composition and thermal structure of the moon's upper atmosphere do not appear to have changed considerably since the Voyager 1 flyby. 相似文献
2.
Burch JL Mende SB Mitchell DG Moore TE Pollock CJ Reinisch BW Sandel BR Fuselier SA Gallagher DL Green JL Perez JD Reiff PH 《Science (New York, N.Y.)》2001,291(5504):619-624
The IMAGE spacecraft uses photon and neutral atom imaging and radio sounding techniques to provide global images of Earth's inner magnetosphere and upper atmosphere. Auroral imaging at ultraviolet wavelengths shows that the proton aurora is displaced equatorward with respect to the electron aurora and that discrete auroral forms at higher latitudes are caused almost completely by electrons. Energetic neutral atom imaging of ions injected into the inner magnetosphere during magnetospheric disturbances shows a strong energy-dependent drift that leads to the formation of the ring current by ions in the several tens of kiloelectron volts energy range. Ultraviolet imaging of the plasmasphere has revealed two unexpected features-a premidnight trough region and a dayside shoulder region-and has confirmed the 30-year-old theory of the formation of a plasma tail extending from the duskside plasmasphere toward the magnetopause. 相似文献
3.
Waite JH Combi MR Ip WH Cravens TE McNutt RL Kasprzak W Yelle R Luhmann J Niemann H Gell D Magee B Fletcher G Lunine J Tseng WL 《Science (New York, N.Y.)》2006,311(5766):1419-1422
The Cassini spacecraft passed within 168.2 kilometers of the surface above the southern hemisphere at 19:55:22 universal time coordinated on 14 July 2005 during its closest approach to Enceladus. Before and after this time, a substantial atmospheric plume and coma were observed, detectable in the Ion and Neutral Mass Spectrometer (INMS) data set out to a distance of over 4000 kilometers from Enceladus. INMS data indicate that the atmospheric plume and coma are dominated by water, with significant amounts of carbon dioxide, an unidentified species with a mass-to-charge ratio of 28 daltons (either carbon monoxide or molecular nitrogen), and methane. Trace quantities (<1%) of acetylene and propane also appear to be present. Ammonia is present at a level that does not exceed 0.5%. The radial and angular distributions of the gas density near the closest approach, as well as other independent evidence, suggest a significant contribution to the plume from a source centered near the south polar cap, as distinct from a separately measured more uniform and possibly global source observed on the outbound leg of the flyby. 相似文献
4.
Metal ions including 23(+) (Na(+)), 24(+) (Mg(+)) 28(+) (Si(+)), 39(+) (K(+)), 40(+) (Ca(+)), 45(+) (Sc(+)), 52(+) Cr(+)). 56(+) (Fe(+)), and 58(+) (Ni(+)) have been detected in the upper atmosphere during the period of the Beta Taurids meteor shower. The abundances of these ions relative to Si(+) show, agreement in most instances with abundances in chondrites. A notable exception is 45(+), which, if it is Sc(+), is 100 times more abundant than neutral scandium found in chondrites. 相似文献
5.
Laser vaporization of graphite generates C(60)(+) cluster ions that are fullerenes and a mixture of roughly planar polycyclic polyyne ring isomers. Experimental studies of the annealing of the non-fullerene C(60)(+) ions indicate that they can be converted (in the gas phase) into the fullerene and an isomer that appears to be a large monocyclic ring. Some fragmentation is associated with conversion to the fullerene geometry, but the majority of the non-fullerene C(60)(+) isomers are cleanly converted into an intact fullerene. The emergence of the monocyclic ring (as the clusters are annealed) suggests that this is a relatively stable non-spheroidal form of these all carbon molecules. The estimated activation energies for the observed structural interconversions are relatively low, suggesting that these processes may play an important role in the synthesis of spheroidal fullerenes. 相似文献
6.
柿单宁在重金属吸附中的应用研究进展 总被引：3，自引：0，他引：3
柿单宁是一种来源丰富的天然高分子,由于其分子结构中的B环含有丰富的邻位酚羟基,对金属离子具有很强的降价吸附能力。以柿单宁为有效成分的金属吸附剂具有成本低、环保和高效等优势,近年来发展迅速。本文主要介绍柿单宁的结构特点及其吸附重金属(放射性元素、贵金属、有毒重金属等)离子的研究进展,初步探讨其吸附重金属离子的机理,并对该金属吸附剂的发展趋势进行展望。 相似文献
7.
The major photochemical sources and sinks for ten of the ions measured by the ion mass spectrometer on the Pioneer Venus bus and orbiter spacecraft that are consistent with the neutral gas composition measured on the same spacecraft have been identified. The neutral gas temperature (Tn) as a function of solar zenith angle (chi) derived from measured ion distributions in photochemical equilibrium is given by Tn (K) = 323 cos(1/5)chi. Above 200 kilometers, the altitude behavior of ions is generally controlled by plasma diffusion, with important modifications for minor ions due to thermal diffusion resulting from the observed gradients of plasma temperatures. The dayside equilibrium distributions of ions are sometimes perturbed by plasma convection, while lateral transport of ions from the dayside seems to be a major source of the nightside ionosphere. 相似文献
8.
Several recent developments have implications for the neutral particle environment of Jupiter. Very hot sulfur ions have been detected in the Io torus with gyrospeeds comparable to the corotation speed, a phenomenon that would result from a neutral sulfur cloud. Current evidence supports the hypothesis that extensive neutral clouds of oxygen and sulfur exist in the Jupiter magnetosphere and that they are important sources of ions and energy for the Io torus. 相似文献
9.
A neutral templating route for preparing mesoporous molecular sieves is demonstrated based on hydrogen-bonding interactions and self-assembly between neutral primary amine micelles (S degrees ) and neutral inorganic precursors (l degrees ). The S degrees l degrees templating pathway produces ordered mesoporous materials with thicker framework walls, smaller x-ray scattering domain sizes, and substantially improved textural mesoporosities in comparison with M41S materials templated by quaternary ammonium cations of equivalent chain length. This synthetic strategy also allows for the facile, environmentally benign recovery of the cost-intensive template by simple solvent extraction methods. The S degrees 1 degrees templating route provides for the synthesis of other oxide mesostructures (such as aluminas) that may be less readily accessible by electrostatic templating pathways. 相似文献
10.
Krimigis SM Mitchell DG Hamilton DC Krupp N Livi S Roelof EC Dandouras J Armstrong TP Mauk BH Paranicas C Brandt PC Bolton S Cheng AF Choo T Gloeckler G Hayes J Hsieh KC Ip WH Jaskulek S Keath EP Kirsch E Kusterer M Lagg A Lanzerotti LJ Lavallee D Manweiler J McEntire RW Rasmuss W Saur J Turner FS Williams DJ Woch J 《Science (New York, N.Y.)》2005,307(5713):1270-1273
The Magnetospheric Imaging Instrument (MIMI) onboard the Cassini spacecraft observed the saturnian magnetosphere from January 2004 until Saturn orbit insertion (SOI) on 1 July 2004. The MIMI sensors observed frequent energetic particle activity in interplanetary space for several months before SOI. When the imaging sensor was switched to its energetic neutral atom (ENA) operating mode on 20 February 2004, at approximately 10(3) times Saturn's radius RS (0.43 astronomical units), a weak but persistent signal was observed from the magnetosphere. About 10 days before SOI, the magnetosphere exhibited a day-night asymmetry that varied with an approximately 11-hour periodicity. Once Cassini entered the magnetosphere, in situ measurements showed high concentrations of H+, H2+, O+, OH+, and H2O+ and low concentrations of N+. The radial dependence of ion intensity profiles implies neutral gas densities sufficient to produce high loss rates of trapped ions from the middle and inner magnetosphere. ENA imaging has revealed a radiation belt that resides inward of the D ring and is probably the result of double charge exchange between the main radiation belt and the upper layers of Saturn's exosphere. 相似文献
11.
Zurbuchen TH Raines JM Gloeckler G Krimigis SM Slavin JA Koehn PL Killen RM Sprague AL McNutt RL Solomon SC 《Science (New York, N.Y.)》2008,321(5885):90-92
The region around Mercury is filled with ions that originate from interactions of the solar wind with Mercury's space environment and through ionization of its exosphere. The MESSENGER spacecraft's observations of Mercury's ionized exosphere during its first flyby yielded Na+, O+, and K+ abundances, consistent with expectations from observations of neutral species. There are increases in ions at a mass per charge (m/q) = 32 to 35, which we interpret to be S+ and H2S+, with (S+ + H2S+)/(Na+ + Mg+) = 0.67 +/- 0.06, and from water-group ions around m/q = 18, at an abundance of 0.20 +/- 0.03 relative to Na+ plus Mg+. The fluxes of Na+, O+, and heavier ions are largest near the planet, but these Mercury-derived ions fill the magnetosphere. Doubly ionized ions originating from Mercury imply that electrons with energies less than 1 kiloelectron volt are substantially energized in Mercury's magnetosphere. 相似文献
12.
Weisenhorn AL Mac Dougall JE Gould SA Cox SD Wise WS Massie J Maivald P Elings VB Stucky GD Hansma PK 《Science (New York, N.Y.)》1990,247(4948):1330-1333
The adsorption of neutral molecules and ions on the surfaces of zeolites was observed in real time with an atomic force microscope (AFM). Direct imaging of the surface of the zeolite clinoptilolite was possible by using a diluted tert-butyl ammonium chloride solution as a medium. Images of the crystal in different liquids revealed that molecules could be bound to the surface in different ways; neutral molecules of tert-butanol formed an ordered array, whereas tert-butyl ammonium ions formed clusters. These absorbed molecules were not rearranged by the AFM tip when used in an imaging mode. However, when a sufficiently large force was applied, the tip of the AFM could rearrange the tert-butyl ammonium ions on the zeolite surface. This demonstration of molecular manipulation suggests new applications, including biosensors and lithography. 相似文献
13.
Frank LA Paterson WR Ackerson KL Coroniti FV Vasyliunas VM 《Science (New York, N.Y.)》1991,253(5027):1528-1531
Plasma measurements were obtained with the Galileo spacecraft during an approximately 3.5-hour interval in the vicinity of Venus on 10 February 1990. Several crossings of the bow shock in the local dawn sector were recorded before the spacecraft passed into the solar wind upstream from this planet. Although observations of ions of the solar wind and the postshock magnetosheath plasmas were not possible owing to the presence of a sunshade for thermal protection of the instrument, solar wind densities and bulk speeds were determined from the electron velocity distributions. A magnetic field-aligned distribution of hotter electrons or ;;strahl' was also found in the solar wind. Ions streaming into the solar wind from the bow shock were detected. Electron heating at the bow shock, 相似文献
14.
J D Baldeschwieler 《Science (New York, N.Y.)》1968,159(812):263-273
Ion cyclotron resonance spectroscopy yields information on many aspects of ion-molecule chemistry. The method is ideally suited for experiments involving ion energies below several electron volts, and hence provides a valuable complement to other techniques (27). eyclotron double resonance is uniquely suitable for establishing relationships between reactant ions and their product ions in complex ion-molecule reaction sequences. The double-resonance experiments with isotopic species yield information on reaction mechanisms and the nature of intermediate species. Ion-molecule reactions which occur at low energies are quite sensitive to the nature of functional groups and the details of molecular structure (28). Reactions of ions or neutral molecules with specific reagents in the cyclotron spectrometer can thus be used to characterize unknown species. Once the systematic ion-molecule chemistry of useful reagents has been worked out, it should be possible to proceed in a manner directly analogous to classical chemical methods. Suppose, for example, that reagents A(+), B(+), C(+), and D(+) each have characteristic reactions with different functional groups. Then these reagents can all be mixed with an unknown neutral species, X, and each of the reactions, X + A(+) --> ?, X + B(+) --> ?, . . . . can be examined. In contrast to solution chemistry, all the reagents can be added simultaneously to the unknown, since each of the specific reactions can be examined by cyclotron double resonance. The reactions which occur, the species synthesized , and the products of degradation then characterize X. The same methodology can be applied to characterize an unknown ionic epecies X(+), through use of neutral reagents A, B, C, and D. For example, proton transfer reactions to neuteal species have been applied in studying ions of mass 45 produced from various sources (29). The order of the proton affinities of the neutral reagent molecules are as follows: NH(3) isobutylene propene. Ions of mass 45 can be produced by the protonation of ethylene oxide (see structure III), the protonation of acetaldehyde (see structure IV), and the fragmentation of dimethyl ether (see structure V). Those ions might be expected to have, respectively, the three structures: Proton transfer from the mass-45 ions from sources III and IV to NH(3) and to isobutylene occurs readily, but not proton transfer to propene. For the ion from source V, proton transfer to NH3 occurs, but not proton transfer to isobutylene or propene. Thus the proton transfer reactions to various neutral reagents demonstrate that the mass-45 ions from the various sources are different. This example is only a rudimentary version of an approach to the characterization of unusual ionic species; niore sophisticated applications can follow when the systematic chemistry of more reagents is available. This approach should be ideal for comparing nonclassical carbonium ions produced by different routes. Some very interesting ionic species are produced by rearrangements in the fragmentation of molecules, following electron impact. Such molecular rearrangements frequently result in the fragmentation of an ion radical to another ion radical with the elimination of a small neutral species (30). It should be possible to run these reactions in reverse to check the postulated mechanisms. An interesting result of the systematic study of proton transfer to various functional groups is the finding that the proton affinity of various amines and pyridine is extremely high (31). Species such as VI and VII: might be expected to be very stable; they are in fact so stable that they are unreactive with respect to subsequent chemistry at the charge center. Thus, if there are other functional groups on the ion, the important reactions should occur at these functional groups. It should be possible to design species for which the presence of the charge has little influence on the reactivity of a neutral functional group. In this case the charge functions simply as an inert label which makes the study of neutral-neutral reactions accessible by cyclotron resonance: Various routes for development of the basic technique also appear to be very promising. Echo phenomena following sequences of pulsed excitation have been observed in electron cyclotron resonance (32). Analogous transient phenomena should also occur in ion cvclotron resonances (33). Pulsed-cyclotron-resonance techniques of course have intriguing analogies to nuclear-magnetic-resonance spin-echo experiments (34) and may be the technique of choice for making accurate measurements of ion-molecule-reaction cross sections as a function of energy for low ion energies. Finally, many ion-molecule reactions yield products in excited electronic states (35). For example, the reaction N(2)- + CO --> N(2) + CO- (46) has been studied by beam techniques (36). A straightforward procedure is to observe optical emission from the cyclotron spectrometer by placing a window at the end of the cyclotron cell (37). The emission can be analyzed with a crude set of optical filters, or with a high-speed spectrograph. Optical emission from the cyclotron cell can of course originate from many sources. The radiation from a specific excited product ion can be selected by a radio-frequency-optical double-resonance experiment. If, in the generai reaction A+ + B --> *C+ + D, (47) ion A+ is irradiated at its cyclotron resonance frequency, the number density of optical emitters *C+ is changed. If the irradiating frequency is modulated, then the number of optical emitters will be modulated, so that the intensity of emission from *C+ will also be modulated. When the optical emission from *C+ is analyzed in a spectrograph with a photoelectric cell, the output of the photoelectric cell can be detected with a phase sensitive detector referenced to the modulation frequency. This highly specific modulation-detection scheme should discriminate against other sources of light in the cyclotron cell. 相似文献
15.
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
16.
E L Sharp 《Science (New York, N.Y.)》1967,156(780):1359-1360
Atmospheric ions, identified by mobility characteristics, were associated with germination of lyophilized uredospores of Puccinia striiformis West. at Bozeman Montana. Ions of intermediate size were highest in concentration, and percentage germination of spores was lowest during periods conducive to air pollution. In duplicate experiments at an isolated site near Barrow. Alaska, essentially all atmospheric ions were small ions and the fungus spores were consistently germinated near maximum. 相似文献
17.
Trauger JT 《Science (New York, N.Y.)》1984,226(4672):337-341
18.
研究了基于氮杂冠醚为中性载体的阳离子选择性电极,该电极在pH为3．0的硝酸缓冲介质中对铝离子有近能斯特响应,其线性范围为8．0×10^-5～1．0×10^-1mol／L,检测限为4．0×10^-5mol／L,斜率为20．0mV／dec．响应时间为20．0S．该电极用于EDTA的电位滴定,结果令人满意． 相似文献
19.
纳豆芽孢杆菌配伍发酵产中性蛋白酶的性质研究 总被引：1，自引：0，他引：1
为研究纳豆芽孢杆菌SH和B1配伍发酵产物中中性蛋白酶的性质,通过Folin-酚法测定中性蛋白酶的最适作用温度、最适作用pH值、pH稳定性、热稳定性和金属离子、表面活性剂、抑制剂、模拟胃肠道环境对酶活力的影响,绘制相对酶活力变化图。结果表明:该酶的最适作用温度为70℃,最适作用pH为11.0,其次是pH为7.0,40℃时热稳定性较好,在pH6～7时比较稳定,属中性蛋白酶。金属离子、抑制剂和模拟胃环境对酶有抑制作用,而10g/LTween-80和模拟肠道环境对酶有激活作用。 相似文献
20.
Mitchell DG Brandt PC Roelof EC Dandouras J Krimigis SM Mauk BH 《Science (New York, N.Y.)》2005,308(5724):989-992
The Cassini Magnetospheric Imaging Instrument (MIMI) observed the interaction of Saturn's largest moon, Titan, with Saturn's magnetosphere during two close flybys of Titan on 26 October and 13 December 2004. The MIMI Ion and Neutral Camera (INCA) continuously imaged the energetic neutral atoms (ENAs) generated by charge exchange reactions between the energetic, singly ionized trapped magnetospheric ions and the outer atmosphere, or exosphere, of Titan. The images reveal a halo of variable ENA emission about Titan's nearly collisionless outer atmosphere that fades at larger distances as the exospheric density decays exponentially. The altitude of the emissions varies, and they are not symmetrical about the moon, reflecting the complexity of the interactions between Titan's upper atmosphere and Saturn's space environment. 相似文献