共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
The first unambiguous full-disk radar mapping of Mercury at 3.5-centimeter wavelength, with the Goldstone 70-meter antenna transmitting and 26 antennas of the Very Large Array receiving, has provided evidence for the presence of polar ice. The radar experiments, conducted on 8 and 23 August 1991, were designed to image the half of Mercury not photographed by Mariner 10. The orbital geometry allowed viewing beyond the north pole of Mercury; a highly reflective region was clearly visible on the north pole during both experiments. This polar region has areas in which the circular polarization ratio (pt) was 1.0 to 1.4; values < approximately 0.1 are typical for terrestrial planets. Such high values of have hitherto been observed in radar observations only from icy regions of Mars and icy outer planet satellites. 相似文献
3.
Fluxes of protons with energies of approximately 550 kev and electrons with energies of approximately 300 kev which exceed approximately 10(4) and 10(5) cm(-2) sec(-1), respectively, have been discovered in the magnetosphere of Mercury. Electron fluxes > 10(3) cm(-2) sec(-1) also are observed in the outbound pass of the Mariner 10 spacecraft throuigh the magnetosheath. The intensity versus time profiles of the particle fluxes in the magnetosphere appear with sudden onsets of approximately 10(4) cm(-2) sec(-1) beginning at interplanetary background levels and persisting for times equivalent to their being distriblited spatially over regions having a scale size comparable to the planetary radius. For a spectral form dJ/dE alpha E-gamma, where J is the differential particle intensity and E is the kinetic energy, the typical values of gamma are gamma(p) = 5.5 for protons above 500 kev and gamma(e) >/= 9 for electrons above 170 kev. Large coherent electron intensity oscillations (variations of factors of 10 to 100) have been discovered with characteristic periods of approximately 6 seconds and with higher frequency components. In some cases proton bursts are found in phase with these oscillations. On the basis of the experimental evidence and a knowledge of the general magnetic field intensities and directions along the trajectory of Mariner 10 provided by the magnetic field observations, it is shown that the radiation events observed in the magnetosphere and magnetosheath are transient and are not interpretable in terms of stable trapped particle populations. Furthermtiore, experimental evidence strongly supports the view that the particles are impulsively accelerated and that the acceleration source is not more distant from the point of observation along lines of force than approximately 8 x 10(3) to 16 x 10(3) kilometers (3 to 6.5 units of Mercury's radius). Candidates for the regions most likely to be sources of particle acceleration are discussed, namely, the magnetotail and the magnetosheath. It is pointed out that the phenomena discovered at Mercury will place more stringent conditions on allowed mnodels for electron and proton acceleration than have heretofore been possible in studies within the earth's magnetosphere. 相似文献
4.
The University of Chicago instrumnents on board the Mariner 10 spacecraft bound for Mercury have measured energy spectra and fluxes of electrons from 0.18 to 30 million electron volts and protons from 0.5 to 68 million electron volts along the plasma wake and in the bow shock regions associated with Venus. Unusually quiet solar conditions and improved instrumentation made it possible to search for much lower fluxes of protons and electrons in similar energy regions as compared to earlier Mariner missions to Venus-that is, lower by a factor of 10(2) for protons and 10(3) for electrons. We found no evidence for electrons or protons either in the form of increases of intensity or energy spectral changes in the vicinity of the planet, nor any evidence of bursts of radiation in or near the observed bow shock where bursts of electrons might have been expected in analogy with the bow shock at the earth. The importance of these null results for determining the necessary and sufficient conditions for particle acceleration is discussed with respect to magnetometer evidence that Venus does not have a magnetosphere. 相似文献
5.
Ogilvie KW Scudder JD Hartle RE Siscoe GL Bridge HS Lazarus AJ Asbridge JR Bame SJ Yeates CM 《Science (New York, N.Y.)》1974,185(4146):145-151
A fully developed bow shock and magnetosheath were observed near Mercury, providing unambiguous evidence for a strong interaction between Mercury and the solar wind. Inside the sheath there is a distinct region analogous to the magnetosphere or magnetotail of Earth, populated by electrons with lower density and higher temperature than the electrons observed in the solar wind or magnetosheath. At the time of encounter, conditions were such that a perpendicular shock was observed on the inbound leg and a parallel shock was observed on the outbound leg of the trajectory, and energetic plasma electron events were detected upstream from the outbound shock crossing. The interaction is most likely not atmospheric, but the data clearly indicate that the obstacle to solar wind flow is magnetic, either intrinsic or induced. The particle fluxes and energy spectra showed large variations while the spacecraft was inside the magnetosphere, and these variations could be either spatial or temporal. 相似文献
6.
Choi M Scholl UI Yue P Björklund P Zhao B Nelson-Williams C Ji W Cho Y Patel A Men CJ Lolis E Wisgerhof MV Geller DS Mane S Hellman P Westin G Åkerström G Wang W Carling T Lifton RP 《Science (New York, N.Y.)》2011,331(6018):768-772
Endocrine tumors such as aldosterone-producing adrenal adenomas (APAs), a cause of severe hypertension, feature constitutive hormone production and unrestrained cell proliferation; the mechanisms linking these events are unknown. We identify two recurrent somatic mutations in and near the selectivity filter of the potassium (K(+)) channel KCNJ5 that are present in 8 of 22 human APAs studied. Both produce increased sodium (Na(+)) conductance and cell depolarization, which in adrenal glomerulosa cells produces calcium (Ca(2+)) entry, the signal for aldosterone production and cell proliferation. Similarly, we identify an inherited KCNJ5 mutation that produces increased Na(+) conductance in a Mendelian form of severe aldosteronism and massive bilateral adrenal hyperplasia. These findings explain pathogenesis in a subset of patients with severe hypertension and implicate loss of K(+) channel selectivity in constitutive cell proliferation and hormone production. 相似文献
7.
Monochromatic images of Mercury at the sodium D(2) emission line showed excess sodium emission in localized regions at high northern and southern latitudes and day-to-day global variations in the distribution of sodium emission. These phenomena support the suggestion that magnetospheric effects could be the cause. Sputtering of surface minerals could produce sodium vapor in polar regions during magnetic substorms, when magnetospheric ions directly impact the surface. Another important process may be the transport of sodium ions along magnetic field lines toward polar regions, where they impact directly on the surface of Mercury and are neutralized to regenerate neutral sodium atoms. Day-to-day variations in planetary sodium distributions could result from changing solar activity, which can change the magnetosphere in time scales of a few hours. Observations of the sodium exosphere may provide a tool for remote monitoring of the magnetosphere of Mercury. 相似文献
8.
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
9.
Stone EC Cummings AC Loooper MD Selesnick RS Lal N McDonald FB Trainor JH Chenette DL 《Science (New York, N.Y.)》1989,246(4936):1489-1494
The Voyager 2 cosmic ray system (CRS) measured significant fluxes of energetic [>/=1 megaelectron volt (MeV)] trapped electrons and protons in the magnetosphere of Neptune. The intensities are maximum near a magnetic L shell of 7, decreasing closer to the planet because of absorption by satellites and rings. In the region of the inner satellites of Neptune, the radiation belts have a complicated structure, which provides some constraints on the magnetic field geometry of the inner magnetosphere. Electron phase-space densities have a positive radial gradient, indicating that they diffuse inward from a source in the outer magnetosphere. Electron spectra from 1 to 5 MeV are generally well represented by power laws with indices near 6, which harden in the region of peak flux to power law indices of 4 to 5. Protons have significantly lower fluxes than electrons throughout the magnetosphere, with large anisotropies due to radial intensity gradients. The radiation belts resemble those of Uranus to the extent allowed by the different locations of the satellites, which limit the flux at each planet. 相似文献
10.
水稻品种对大米产地溯源判别正确性的影响 总被引：1，自引：0，他引：1
为提高大米产地溯源判别的正确性,试验研究了水稻品种对于大米产地溯源判别正确性的影响。利用原子吸收分光光度法(AAS)检测来自吉林省松原市、德惠市、梅河口市3个产地的3个水稻品种120个样品中11种矿物元素(Pb,Cd,K,Na,Ca,Mg,Zn,Cu,Fe,Mn,Cr)的含量,对大米中矿物元素数据进行差异分析、雷达分析和线性判别分析。结果显示:元素Cd、Cr、Fe、K、Mg、Zn、Pb在大米品种与产地间均存在相对较大的差异。德惠(同一产地)不同品种大米的判别正确率为100%,成功利用不同品种大米中矿物元素含量将大米品种进行正确分类。进行大米产地判别时,3个产地不同品种大米的判别分析正确率为90%,3个产地同一品种大米的产地判别分析正确率为100%,证明了水稻品种对于大米产地溯源判别正确性有影响。 相似文献
11.
Analysis of data obtained by the ultraviolet experiment on Mariner 10 indicates that Mercury is surrounded by a thin atmosphere consisting in part of helium. The partial pressure of helium at the terminator is about 5 x 10(-12) millibar. The total surface pressure of the atmosphere is less than about 2 x 10(-9) millibar. Upper limits are set for the abundance of various gases, including hydrogen, oxygen, carbon, argon, neon, and xenon. The wavelength dependence of Mercury's surface albedo is similar to that of the moon over a broad range of wavelengths from 500 to 1600 angstroms. Strong signals were recorded by the airglow instrument as Mariner 10 passed through the cavity behind Mercury. They are as yet unexplained but may provide information on the properties of the local plasma. 相似文献
12.
The drinking of seawater and absorption of water along with sodium across the intestinal epithelium are well-known osmoregulatory events in marine teleosts. The insecticide DDT impairs fluid absorption in intestinal sacs from eels adapted to seawater. Furthermore, this functional impairment has an enzymatic basis; DDT also inhibits the (Na(+) and K(+)) activated, Mg(2+)-dependent adenosine triphosphatase in homogenates of the intestinal mucosa. Thus, the extreme sensitivity of teleosts to organochlorine pollutants may involve the disruption of osmoregulatory transport mechanisms. 相似文献
13.
The construction of solar or stellar models is hindered by the difficulty of computing, with sufficient accuracy, the convective fluxes in unstable regions. Although the mixing-length theory of convection has been used for more than three decades, its validity has neither been tested by experiment nor verified by computation. This report presents the results of a three-dimensional numerical simulation of deep and efficient convection that support two conclusions: (i) the basic picture proposed by the mixing-length theory is physically valid-the vertical correlation of the motion of fluid elements is proportional to the pressure scale height; and (ii) some dynamical variables, including the convective flux, can be approximately computed from the structure of the stratification with mixing-length approximations. 相似文献
14.
Swain EB Engstrom DR Brigham ME Henning TA Brezonik PL 《Science (New York, N.Y.)》1992,257(5071):784-787
Mercury contamination of remote lakes has been attributed to increasing deposition of atmospheric mercury, yet historic deposition rates and inputs from terrestrial sources are essentially unknown. Sediments of seven headwater lakes in Minnesota and Wisconsin were used to reconstruct regional modern and preindustrial deposition rates of mercury. Whole-basin mercury fluxes, determined from lake-wide arrays of dated cores, indicate that the annual deposition of atmospheric mercury has increased from 3.7 to 12.5 micrograms per square meter since 1850 and that 25 percent of atmospheric mercury deposition to the terrestrial catchment is exported to the lake. The deposition increase is similar among sites, implying regional or global sources for the mercury entering these lakes. 相似文献
15.
Diazacholesterol myotonia: accumulation of desmosterol and increased adenosine triphosphatase activity of sarcolemma 总被引：1，自引：0，他引：1
Myotonia induced in rats by 20,25-diazacholesterol is accompanied by accumulation of desmosterol in serum, fragmented sarcoplasmic reticulum, and sarcolemma. Activities of (Na(+),K(+))- and Ca(2+)-stimulated adenosine triphosphatases of the sarcolemma are increased, but not the Mg(2+)-stimulated adenosine triphosphatase. The altered sterol composition of the sarcolemma may cause this type of myotonia by decreasing the chloride conductance of the membrane. 相似文献
16.
Head JW Chapman CR Strom RG Fassett CI Denevi BW Blewett DT Ernst CM Watters TR Solomon SC Murchie SL Prockter LM Chabot NL Gillis-Davis JJ Whitten JL Goudge TA Baker DM Hurwitz DM Ostrach LR Xiao Z Merline WJ Kerber L Dickson JL Oberst J Byrne PK Klimczak C Nittler LR 《Science (New York, N.Y.)》2011,333(6051):1853-1856
MESSENGER observations from Mercury orbit reveal that a large contiguous expanse of smooth plains covers much of Mercury's high northern latitudes and occupies more than 6% of the planet's surface area. These plains are smooth, embay other landforms, are distinct in color, show several flow features, and partially or completely bury impact craters, the sizes of which indicate plains thicknesses of more than 1 kilometer and multiple phases of emplacement. These characteristics, as well as associated features, interpreted to have formed by thermal erosion, indicate emplacement in a flood-basalt style, consistent with x-ray spectrometric data indicating surface compositions intermediate between those of basalts and komatiites. The plains formed after the Caloris impact basin, confirming that volcanism was a globally extensive process in Mercury's post-heavy bombardment era. 相似文献
17.
18.
Tritiated digoxin binding to (Na+ + K+)-activated adenosine triphosphatase: possible allosteric site 总被引：9，自引：0，他引：9
Tritiated H(3)-digoxin specifically binds to a cardiac (Na(+) + K(+))-activated adenosine triphosphatase. In the presence of adenosine triphosphate and other nucleoside di- and triphosphates, binding is stimulated by sodium ion, the apparent rate constant being similar to that reported for phosphorus-32 incorporation from adenosine triphosphate and for the adenosine triphosphatase activity. In the presence of magnesium, manganese, inorganic phosphate, or other ions, sodium ion inhibits binding. The data support an allosteric type of sodium-potassium ion pump. 相似文献
19.
The relationship between the (Na(+) and K(+))-activated adenosine triphosphatase enzyme system implicated in sodium-transport by cell membranes and the calcium-activated adenosine triphosphatase, which is generally associated with calcium uptake, was examined in microsomes from skeletal muscle. Whereas sodium and potassium did not modify the relatively low adenosine triphosphatase activity seen in the absence of calcium, a pattern similar to that of the sodium-transport enzyme system was seen afer the addition of CaCl(2). The calcium-activated adenosine triphosphatase was stimulated equally by sodium or potassium alone, but both the rate and extent of calcium uptake were enhanced more by potassium than by sodium at concentrations below 0.12 mole per liter. In the absence of either of these ions addition of calcium failed to activate adenosine triphosphatase although significant amounts of calcium were taken up by the microsomes. 相似文献
20.
Zuber MT Smith DE Solomon SC Phillips RJ Peale SJ Head JW Hauck SA McNutt RL Oberst J Neumann GA Lemoine FG Sun X Barnouin-Jha O Harmon JK 《Science (New York, N.Y.)》2008,321(5885):77-79
A 3200-kilometers-long profile of Mercury by the Mercury Laser Altimeter on the MESSENGER spacecraft spans approximately 20% of the near-equatorial region of the planet. Topography along the profile is characterized by a 5.2-kilometer dynamic range and 930-meter root-mean-square roughness. At long wavelengths, topography slopes eastward by 0.02 degrees , implying a variation of equatorial shape that is at least partially compensated. Sampled craters on Mercury are shallower than their counterparts on the Moon, at least in part the result of Mercury's higher gravity. Crater floors vary in roughness and slope, implying complex modification over a range of length scales. 相似文献