共查询到20条相似文献，搜索用时 15 毫秒
1.
G. Eichhorn 《Planetary and Space Science》1976,24(8):771-781
Hypervelocity microparticle impact experiments were performed with a 2 MV Van De Graaff dust accelerator. From measurements of the light intensity I and the total light energy E, the relations I=c1mv4.1 and E=c2mv3.2 were obtained, where m is the projectile mass, ν the projectile velocity and c1,c2 are constants, depending on projectile and target material. Using the measured values of the spectral distribution of the light emitted during impact, the temperature of the radiating material was estimated to be between 2500 and 5000 K depending on the projectile velocity. From an analysis of these measurements the angular distribution of secondary particle velocities as well as the relative mass distribution of these particles was determined. Approximately 90% of the detected ejecta mass (ν?1 km/sec) is found between 50° and 70° ejection angle. For ejection angles smaller than 20°, ejecta velocities of up to 30 km/sec were detected when the primary particle velocity was 4.8 km/sec. Using the dependence of the light intensity on pressure in the target chamber, an estimate of the total amount of material vaporized during impact could be derived. It was concluded that at 7.4 km/sec particle impact velocity at least 1.6% of the displaced projectile and crater material was vaporized. 相似文献
2.
CLAY P. BUTLER 《Meteoritics & planetary science》1966,3(2):59-70
Abstract On the basis of reported optical measurements of iron and stony meteorites, upper and lower limits for solar absorptance and hemispherical emittance of the surfaces of meteoroids have been established. Temperatures of three classes of meteoroids, none larger than approximately 10 meters in radius, have been calculated for various orbits and a/e ratios. These classes are light chondrites, dark chondrites and the irons. Temperatures for a meteoroid in a Mercury orbit range from 100° C for a light chondrite to 400° C for an iron. 相似文献
3.
Abstract— The x‐ray powder diffraction patterns of 50–100 μm C‐rich grains from five ureilitic meteorites—Kenna, Allan Hills (ALH) 78019, Yamato (Y)‐82100, Y‐791538, and ALH 77257—were obtained by using a Gandolfi camera. The results reveal that the basal spacing of part of the graphite coexisting with diamond is slightly smaller compared to the normal spacing. Compressed graphite is experimentally known to occur at the initial stage of the direct transformation from graphite to diamond structures at high pressures and temperatures. The presence of the compressed graphite in ureilites, therefore, gives clear evidence that the diamond formed by high‐pressure conversion of graphite. The modes of occurrence of C minerals observed with reflected light through an optical microscope reveal that graphite coexisted with olivine and pyroxene during igneous or metamorphic processes and, furthermore, that part of the graphite was converted to diamond by impact. The relative x‐ray intensity of diamond to graphite increases in the following order: ALH 78019 and Y‐82100 < Y‐791538 < Kenna < ALH 77257. This correlates with the shock level that is estimated mainly on the basis of the shock features of silicates. Therefore, the relative amounts of diamond to graphite suggested by x‐ray intensities may be useful as a measure of the degree of shock. 相似文献
4.
Shinsuke Abe Noboru Ebizuka Hideyuki Murayama Katsuhito Ohtsuka Satoru Sugimoto Masa-yuki Yamamoto Hajime Yano Jun-ichi Watanabe Jiří Borovička 《Earth, Moon, and Planets》2004,95(1-4):265-277
Spectra of persistent meteor trains were observed at wavelength between 300 and 930 nm. Two obtained train spectra during
the 1998 and 2001 Leonid meteor showers are reported here. During the 1998 Leonids, one train was detected by a photographic
camera with a spectrograph covering 370–640 nm region. On the other hand, during the 2001 Leonids, video observations were
carried out using image intensified cameras in ultraviolet (UV), visible and near infrared (near-IR) wavelengths. Temperatures
in persistent trains have been measured by atmospheric O2 A(0,1) band at the wavelength near 864.5 nm. From a video spectrum obtained just 7 s after parent fireball’s flare, a rotational
temperature of 250 K at altitude of 88.0±0.5 km was estimated. We can say that the cooling time scale of train strongly depends
on the initial mass of its fireball at least for Leonids. Based on cooling constant calculated from our results, we estimated
a temperature of ∼
∼130 K as a final exothermic temperature at early stage of persistent trains. 相似文献
5.
Abstract— Using a dust flux model and experimental data on the efficiency of light emission upon impact, the number of impact flashes visible on the Moon by a camera on a lunar orbiter is estimated. 相似文献
6.
About a year's observations of the N2+ band (3914 Å) at Kitt Peak (latitude 32°) are reported. Morning intensities are the same throughout the year, but there is a strong winter maximum in the evening. It is suggested that the additional ionization is produced by photoelectrons from the magnetic conjugate point. Heights are estimated by the zenith-horizon method, which gives 235 km for the constant component and 350 km during the evening enhancement. The intensity variation through twilight is therefore entirely due to changes of the N2+ concentration; each ion scatters light at a constant rate. The rotational distribution resembles that for a temperature of 1600°K, much higher than the temperature of the atmosphere. It is suggested that part of the ions may be produced by charge transfer from metastable O+(2D). N2+ concentrations resulting from photoionization are calculated; they give a fair account of the observed horizon intensities, but not the zenith. Non-local electrons from higher in the atmosphere are suggested as a possible extra source; alternatively, the zenith measurements may be perturbed by scattered horizon light. The band intensity in the nightglow cannot be measured; the upper limit is 1 R. 相似文献
7.
Temperatures measured by the OGO-6 satellite using the 6300 Å airglow spectrum are compared with temperatures derived from total densities and N2 densities. It is shown that while the variation of the total densities with latitude and magnetic activity agree well with values used for CIRA (1972), the temperature behavior is very different. While the temperatures derived from the N2 density were in much better agreement there were several important differences which radically affect the pressure gradients. The variation of temperature with magnetic activity showed seasonal and local time variations. Neutral temperature, density, pressure and boundary oxygen variations for the storm of 8 March 1970 are presented. 相似文献
8.
Peter M. Woiceshyn 《Icarus》1974,22(3):325-344
The Mariner 9 S-band radio occultation measurements, which were taken over half a Martian year, were examined for seasonal variations in atmospheric pressures and temperatures. Seasonally related atmospheric pressure oscillations on a global scale were discovered when the pressures were compared on equi-potential levels. There was a global increase in pressure of about 13% between northern winter and spring seasons, and a global decrease in pressure of nearly 14% between northern spring and summer seasons. The maximum global pressure occurred during the northern spring season approximately one Martian month prior to aphelion. These pressure oscillations were correlated with the seasonal growth and decay, and the total area of the polar caps.Temperatures in the mid-latitude regions near the subsolar points were highest during the northern winter season when Mars was closest to the sun. In addition, high latitudinal temperature gradients (up to 2°K per degree latitude) were found. This has important atmospheric dynamical implications, especially for the growth of baroclinic waves.Occultation observations also indicated that the average elevation of the southern hemisphere was nearly 4km higher than the northern hemisphere when referenced to an equipotential level. The occultation measurements showed that the atmospheric pressures near the surface in the southern hemisphere were 33 to 43% lower than the atmospheric pressures near the surface in the northern hemisphere. In addition to other parameters, the asymmetry in the density of the Martian atmosphere and the hemispheric altitude differences are important in understanding the seasonal dynamic processes that exist in the polar cap regions and in the Martian atmosphere generally. 相似文献
9.
M. Nafi Toksőz Sean C. Solomon John W. Minear David H. Johnston 《Earth, Moon, and Planets》1972,4(1-2):190-213
The thermal history and current state of the lunar interior are investigated using constraints imposed by recent geological and physical data. Theoretical temperature models are computed taking into account different initial conditions, heat sources, differentiation and simulated convection. To account for the early formation of the lunar highlands, the time duration of magmatism and presentday temperatures estimated from lunar electrical conductivity profiles, it is necessary to restrict initial temperatures and abundances of radioactivie elements. Successful models require that the outer half of the Moon initially heated to melting temperatures, probably due to rapid accretion. Differentiation of radioactive heat sources toward the lunar surface occurred during the first 1.6 billion years. Temperatures in the outer 500 km are currently low, while the deep interior (radius less than 700 to 1000 km) is warmer than 1000°C, and is of primordial material. In some models there is a partially melted core. The calculated surface heat flux is between 25 and 30 erg/cm2 s.Presently at the Research Triangle Institute, Research Triangle, North Carolina 27709, U.S.A. 相似文献
10.
We report on the survivability in hypervelocity impacts of yeast in spore form, and as mature cultures, at impact velocities from 1 to 7.4 km s?1, corresponding to an estimated peak shock pressure of ～43 GPa. Spores from a yeast strain (BY4743), deficient in an enzyme required for uracil production, were fired into water (to simulate oceanic impact from space) using a light gas gun. The water was then retrieved and filtered and the resulting retentate and filtrate cultured to determine viability and survival rates of remnant spores. Yeast growth (confirmed as coming from the original sample as it had the same enzyme deficiency) was found in recovered samples at all impact speeds, albeit in smaller quantities at the higher speeds. The survival probabilities were measured as ～50% at 1 km s?1, falling to ～10?3% at 7.4 km s?1. This follows the pattern observed in previous work on survival of microbial life and spores exposed to extreme shock loading, where there is reasonable survival at low peak shock pressures with more severe lethality above a critical shock pressure at the GPa scale (here between 2 and 10 GPa). These results are explained in the context of a general model for survival against extreme shock and are relevant to the hypotheses of panspermia and litho-panspermia, showing that extreme shocks during transfer across space are not necessarily sterilising. 相似文献
11.
Observations of coronal Fe XIV emission lines from the NE quadrant during the 1973 solar eclipse are reported. Temperatures are deduced from a pure thermal broadening model, and, in the region near an observed white-light enhancement, an alternative interpretation of halfwidth as being in part due to turbulent velocities is suggested.On leave from the Los Alamos National Laboratory 1981 - present. 相似文献
12.
Michaël Friedjung 《Astrophysics and Space Science》1974,29(1):L5-L6
FeII and [FeII] intensity measures enable the size of the region containing singly ionized iron to be estimated, calculations for a phase near maximum light support a continued ejection model. 相似文献
13.
Yu. G. Kuznetsova 《Kinematics and Physics of Celestial Bodies》2008,24(6):331-333
The monochromatic brightness factors for morphologically nonuniform cloudy surface fields of Jupiter and Saturn in the visible wavelength range were calculated. In the spectra of both giant planets, the combination (Raman) light scattering feature (a pseudoemission peak) was detected in the range of a strong Fraunhofer line H Ca II; and its intensity was estimated. 相似文献
14.
The intensity of a sunspot was measured in eight wavelength regions during the Mercury transit of 9 May 1970. The observations have been corrected for scattered light in the Earth's atmosphere as well as in the instrument using two different methods plus a combination of these. One method consists of using Mercury as a calibration spot. In the second method the corrections for scattered light are determined from solar limb observations. 相似文献
15.
Frank Wlotzka 《Meteoritics & planetary science》2005,40(11):1673-1702
Abstract— Many Equilibrated Ordinary Chondrites Contain (Besides Chromites Of Constant Composition) Cr Spinel With A Large Spread In Cr/(Cr + Al) Ratios. They Occur Mainly As Large Grains In Chondrules Rich In Mesostasis, Preventing Complete Equilibration In Cr/Al But Not In Fe/Mg. This Partially Equilibrated Cr Spinel Turned Out To Be Particularly Useful For The Selection Of An Appropriate Olivine/Spinel Thermometer And For The Determination Of Equilibration Temperatures. The Main Results Are:
- 1) The H3.7 To 3.8 And The L3.7 To 3.8 Chondrites Analyzed Show Temperatures Of 625 To 680 °C;
- 2) Equilibrated Chondrites Show A Range Of Olivine/Cr‐Spinel Temperatures Between 700 And 820 °C, And The Same Average Temperatures For Type 4 To 6 (Number Of Analyzed Meteorites In Brackets): H4 (9) 766 °C, H5 (7) 774 °C, H6 (3) 775 °C, L4 (5) 752 °C, L5 (4) 754 °C, L6 (1) 754 °C. These Temperatures Are Interpreted As Equilibration Temperatures. One Indication Is That The Measured Isotherms Are Straight Lines Down To Low Cr/(Cr + Al) Ratios, Which Have A Higher Fe/Mg Interdiffusion Coefficient Than Grains With High Ratios. And There Is No Correlation Of Measured Temperature With Grain Size Of Cr Spinel.
- 3) Chromites Sensu Stricto Show Temperatures About 50 To 100 °C Lower Than Cr Spinel, And A Correlation With Grain Size. This Is A Closure Temperature Established During Cooling And In Situ Crystallization.
16.
17.
Gareth S. COLLINS H. Jay MELOSH Robert A. MARCUS 《Meteoritics & planetary science》2005,40(6):817-840
Abstract— We have developed a Web‐based program for quickly estimating the regional environmental consequences of a comet or asteroid impact on Earth ( http:www.lpl.arizona.eduimpacteffects ). This paper details the observations, assumptions and equations upon which the program is based. It describes our approach to quantifying the principal impact processes that might affect the people, buildings, and landscape in the vicinity of an impact event and discusses the uncertainty in our predictions. The program requires six inputs: impactor diameter, impactor density, impact velocity before atmospheric entry, impact angle, the distance from the impact at which the environmental effects are to be calculated, and the target type (sedimentary rock, crystalline rock, or a water layer above rock). The program includes novel algorithms for estimating the fate of the impactor during atmospheric traverse, the thermal radiation emitted by the impact‐generated vapor plume (fireball), and the intensity of seismic shaking. The program also approximates various dimensions of the impact crater and ejecta deposit, as well as estimating the severity of the air blast in both crater‐forming and airburst impacts. We illustrate the utility of our program by examining the predicted environmental consequences across the United States of hypothetical impact scenarios occurring in Los Angeles. We find that the most wide‐reaching environmental consequence is seismic shaking: both ejecta deposit thickness and air‐blast pressure decay much more rapidly with distance than with seismic ground motion. Close to the impact site the most devastating effect is from thermal radiation; however, the curvature of the Earth implies that distant localities are shielded from direct thermal radiation because the fireball is below the horizon. 相似文献
18.
The abundances of light elements (deuterium, helium and lithium) are calculated in unconventional cosmologies in which these elements are produced by interaction of fast -particles ejected by massive pregalactic stars with a purely hydrogenous cosmological substrate. The number density and energetics of such stars needed for suitable production of light elements are estimated. It is shown that the models always lead to overproduction of lithium. The intensity of ultraviolet, X-ray, and -ray emission caused by explosions of pregalactic massive stars is calculated. The distortions of cosmic background radiation by Compton losses of electrons heated by explosive stars are also calculated. 相似文献
19.
Various areas of the sky, including the Galactic-center region and the region with the X-ray binaries 4U 1700-37 and GRO J1655-40, were observed in the hard (10–300 keV) energy range during the Grif experiment onboard the Mir orbiting station. An epoch-folding analysis of the data has revealed periodicities with periods of 82 and 62 h, which are equal to the orbital periods of 4U 1700-37 and GRO J1655-40. Previously, these periodicities were observed during the Prognoz-9 X-ray experiment. Periodicities with periods in the range of days, 98 and 152 h, which were also observed during the Prognoz-9 experiment, were not revealed by the Grif data. We obtained upper limits on the intensities of these periodicities in various energy ranges. For the 62-h periodicity, we constructed an average 25–50-keV light curve and estimated the spectral flux density, which characterizes the intensity of the periodic component at different energies in different observing intervals during 1995–1997. The Prognoz-9 and Grif observations of GRO J1655-40 are compared with its CGRO, RXTE, and BeppoSax observations. The orbital periodicity is shown to manifest itself in the hard emission from the extremely bright X-ray transient GRO J1655-40, a likely black-hole candidate, even at the epochs between its X-ray outbursts. 相似文献
20.
S. Evren 《Astrophysics and Space Science》1988,140(1):125-130
The double-lined spectroscopic and eclipsing binary ER Vul was observed in blue and yellow light during the 1984 and 1985 observing seasons. In 1984 four and in 1985 three different light curves in each colour were obtained. The system sometimes is too active and sometimes too quite. The wave-like distortion has been obtained for each light curve and a period of migration has been estimated to be about 8–9 months. The light fluctuations, which are the main characteristics of ER Vul, seems to be related with the wave minimum, (e.g., spotted regions) of the component(s). 相似文献