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1.
We review recent progress in the use of analyses of fluctuations in the cosmic X-ray background (XRB) to determine the source counts below the detection thresholds. Three flux domains are discussed: the range around 10−12erg cm−2 s−1 where the Ginga and Einstein Observatory results remain inconsistent unless the sources at these fluxes (mainly Seyfert galaxies) are highly absorbed at low energies, the 10−14erg cm−2 s−1 zone where the flattening of the source counts predicted by fluctuation analyses of Einstein Observatory images is now confirmed by Rosat, and the 10−15erg cm−2 s−1 flux domain, where fluctuation analyses of Rosat images show that source counts remain subeuclidean with very little contribution to the XRB coming from these sources.  相似文献   

2.
The spectra of neutrons >10 MeV and gamma-rays 1.5–100 MeV under the Earth Radiation Belts, restored from the data, obtained onboard orbital complex “SALUTE-7”-“KOSMOS-1686”, are presented. The spectra shapes are similar to those for albedo neutrons and gamma-rays, but absolute values of their fluxes (0.2 cm−2 s−1 for neutrons, 0.8 cm−2 s−1 for gamma-rays at the equator and 1.2 cm−2 s−1, 1.9 cm−2 s−1, accordingly, at L=1.9) are several times as large. It is possibly explained by the fact that most of the detected particles were produced by the cosmic ray interactions with the orbital complex matter. Neutron and gamma-ray fluxes obtained from “CORONAS-I” data are near those for albedo particles.  相似文献   

3.
The experimental results on high-velocity impacts reported in the literature are analyzed in detail, with the purpose: (a) to check the possibility of applying to asteroidal collisions, without a size-dependent scaling, the critical energy densities associated with various degrees of fragmentation; (b) to ascertain which fraction of the projectile's energy is converted into kinetic energy of fragments after a catastrophic breakup.

The results of our analysis on these two problems indicate that: (a) the critical energy density is independent on size only for super-catastrophic events, when no massive core survives, while it slowly decreases for larger targets when the fragmentation is only partial (barely-catastrophic collisions). Therefore the “energy gap” between cratering and complete distruction is probably wider for the asteroids than for the small experimental targets. (b) the inelasticity coefficient (i.e., the resulting fraction of kinetic energy) depends both on the impact velocity and on the projectile-to-target mass ratio; for asteroidal catastrophic collisions, it probably ranges from 10−2 to 10−1.  相似文献   


4.
S3 absorption cross section equals 6×10−17 cm2 at 400 nm, 6 × 10−19 cm2 at 500 nm (less by a factor of 4 than that given by Sanko), 4×10−20 cm2 at 600 nm. That of S4 equals 1.5 × 10−17 cm2 at 450 nm, 8 × 10−17 cm2 at 500 nm, and 4.7 × 10−17 cm2 at 600 nm. Preliminary evaluation of the S3 mixing ratio in the lower atmosphere of Venus is (8±3)×10−11 at 5 to 25km according to the Venera 14 measurements and several times lower at the locations of the Veneras-11 and -13.  相似文献   

5.
The Geminga light curve obtained with the “Gamma-1” telescope features two peaks separated by 0.5 ± 0.03 period. The light curve is pronounced for γ-quanta energies higher than 400 MeV. The pulsed flux upper limit (1σ) in the energy interval 50 – 300 MeV is 6·10−7 cm−2sec−1. For energies >300 MeV the pulsed component power law spectrum has an exponent 1.1 −0.3+1.1 and an integral flux (1.1±0.3)·10−6 cm−2sec−1.  相似文献   

6.
Spatial distribution of the continuum radiation in the range of 0.95–1.9 μm presumes total dust production rate of the comet of 10ρ tonne s−1 (ρ is the dust material density) and its angular distribution proportional cos . Observations of the water vapor band at 1.38 μ m reveal strong jets, their time shift from the dust jet measured in situ is consistent with gas velocity of 0.82±0.1 km s−1 and dust velocity of 0.55±0.08 km s−1. The OH vibrational-rotational bands observed are excided directly via photolysis of water vapor. Water vapor production rate deduced from the H2O band and OH band intensities is 8×1029 s−1. Intensity of the CN(0,0) band result in the CN column density of 9×1012 cm−2, i.e. larger by a factor of 3 than given by the violet band.  相似文献   

7.
The speed distribution of meteoroids encountering the Earth is shown to be similar for all meteoroid masses in the range 1 g to 10−12 g. The speed distribution of interplanetary meteoroids encountering the Earth has usually been inferred from meteor observations. This paper reviews commonly quoted distributions and introduces more recent estimates. The influence quoted measurement uncertainties have on the distribution of Earth encounter velocities presented by Sekanina and Southworth (1975) and Erickson (1968) is presented. The Divine (1993) model of interplanetary meteoroids fits a set of orbital distributions to a wide range of spacecraft and ground based dust detector observations. By ‘flying’ the Earth through this model the distribution of geocentric encounter velocities has been obtained for typical particle masses, 10−9 and 10−12 g while those at 10−4 and 10−5 g are shown to be in error.  相似文献   

8.
Calibration of the DIDSY experiment momentum sensors for the GIOTTO Mission to Comet Halley requires laboratory simulation of impacts at 68 km s−1 for particle mass values in the range 10−6 g to 10−10 g. Existing techniques for particle acceleration cannot simultaneously attain these extreme values of velocity and particle mass, making it necessary to adopt some less direct method of impact simulation. This paper considers the application of high power pulsed lasers for laboratory simulation of the momentum impulse produced by a cometary dust particle impact on the GIOTTO spacecraft.  相似文献   

9.
It is still debated whether or not gravity can stimulate unicellular organisms. This question may be settled by revealing changes in the membrane potential in a manner depending on the gravitational forces imposed on the cell. We estimated the gravity-dependent membrane potential shift to be about 1 mV G−1 for Paramecium showing gravikinesis at 1–5 G, on the basis of measurements of gravity-induced changes in active propulsion and those of propulsive velocity in solutions, in which the membrane potential has been measured electrophysiologically. The shift in membrane potential to this extent may occur from mechanoreceptive changes in K+ or Ca2+ conductance by about 1% and might be at the limit of electrophysiological measurement using membrane potential-sensitive dyes. Our measurements of propulsive velocity vs membrane potential also suggested that the reported propulsive force of Paramecium measured in a solution of graded densities with the aid of a video centrifuge microscope at 350 G was 11 times as large as that for −29 mV, i.e., the resting membrane potential at [K+]o = 1 mM and [Ca2+]o = 1 mM, and, by extrapolation, that Paramecium was hyperpolarized to −60 mV by gravity stimulation of 100- G equivalent, the value corrected by considering the reduction of density difference between the interior and exterior of the cell in the graded density solution. The estimated shift of the membrane potential from −29 mV to −60 mV by 100- G equivalent stimulation, i.e., 0.3 mV G−1, could reach the magnitude entirely feasible to be measured more directly.  相似文献   

10.
A 40.6 cm Newtonian telescope has been interfaced to the Fabry-Perot interferometer at the Arecibo Observatory to make high spectral resolution measurements of Comet Halley emissions at 6562.72 Å (H-alpha) and 6300.3 Å (OI). In March 1986 the H-alpha surface brightness for a 5′.9 field of view centered on the comet nucleus decreased from 39±7.8 rayleighs on 12 March to 16±3.8 rayleighs on 23 March. The atomic hydrogen production rate on 12 March 1986 was 1.62±0.5 × 1030 s−1, and on 23 March 1986 it was 6.76±2.3 × 1029 s−1. Using spectral resolution of 0.196 Å, we found the atomic hydrogen outflow velocity to be approximately 7.9±1.0 km s−1. In general, the H-alpha spectra are highly structured, and indicative of a multiple component atomic hydrogen velocity distribution. An isotropic outflow of atomic hydrogen at various velocities is not adequate to explain the spectra measured at H-alpha. The 6300.3 Å emission of O(1D) had a surface brightness of 81±16 rayleighs on 15 March 1986, and 95±11 rayleighs on 17 March 1986. After adjustment for atmospheric extinction, the implied O(1D) production rate on 15 March is 6.44±3.0 × 1028 s−1, and the production rate on 17 March is 5.66±2.7 × 1028 s−1. These spectra included a feature at 6300.8 Å that we attribute to NH2. The brightness of this emission feature was 37±11 rayleighs on 15 March.  相似文献   

11.
Experimental drop tube of the metallurgy department of Grenoble   总被引:1,自引:0,他引:1  
The drop tube which will be available in the “Centre d'Etudes Nucléaires de Grenoble” is described. Its main features are the following: - Dimensions : Drop height : 47.1 m Drop time : 3.1 s Tube inside diameter : 0.2 m - Experimental atmosphere : 1 Ultra-vacuum : 10−6 to 10−7 Pa - Residual gravity level : 10−8 to 10−9 g according to the vacuum level and drop diameter.

This facility is unique insofar as it enables experiments to be performed under ultra-vacuum conditions which, by delaying the formation of surface oxides, should contribute to improving maximum undercooling values.

The techniques used for obtaining small metallic drops (0.5 to 3 mm) are described. The availability of this instrument for the scientific community is also foreseen by the french sponsoring organizations (CEA, CNES, CNRS) ; some practicle informations will be given to potential experimenters.  相似文献   


12.
We report the statistical properties of narrow coronal mass ejections (CMEs, angular width < 20°) withparticular emphasis on comparison with normal CMEs. We investigated 806 narrow CMEs from an online LASCO/CME catalog and found that (1) the fraction of narrow CMEs increases from 12% to 22% towards solar maximum, (2) during the solar maximum, the narrow CMEs are generally faster than normal ones, (3) the maximum speed of narrow CMEs (1141 km s−1) is much smaller than that of the normal CMEs (2604 km s−1). These results imply that narrow CMEs do not form a subset of normal CMEs and have a different acceleration mechanism from normal CMEs.  相似文献   

13.
Strong interplanetary scintillations (IPS) of the quasar 2314+03 were recorded at 103 MHz at Thaltej-Ahmedabad, India with a transit type correlation interferometer on 18, 19 and 20 December 1985, as the radio source was predicted to be occulted by the ion tail of the comet Halley.

On 18th through 20th very strong scintillations, with periodicities of 1 sec average were observed, their amplitude progressively decreasing as the source approached the tail-end. The rms variations of scintillating flux of the source on 18, 19 & 20 were about 18, 11 & 4.7 Jy, as against 3.3 Jy on control days 17 and 21 December for solar elongation of 87°.

Assuming Gaussian irregularities with weak scattering, the rms density variations, ΔN, of 10, 6, 3 and 1 elec./cm3 on 18 through 21 December, from the comet nucleus towards its tail-end, varied as (ΔN) ∝ r−3.3 as against (ΔN) ∝ r−2 in the solar plasma.

Quasi-periodic modulations of the enhanced scintillating flux possibly imply 104 km scale-size ion condensations and mean electron density of 103 to 104 electrons/cm3 in the Halley's plasma tail.  相似文献   


14.
Nonlinear calculations of the anomalous electrical conductivity in the plasma of the earth's plasma mantle, the tail plasma sheet boundary layer and the ionospheric F-region density-trough are presented provided that lower-hybrid-drift turbulence exists. It is shown that in these regions the stabilization of the wave growth is mainly caused by current relaxation. Further, the fluctuations of the electrical currents are estimated via Ampère's and Ohm's laws. It is found that the lower-hybrid-drift turbulence causes maximum anomalous collision frequencies of the order of 10−2 Hz in the magnetosphere. The maximum current fluctuations are about 3 10−9 A/m2. The theoretical results are in agreement with ISEE and Prognoz-8 measurements.  相似文献   

15.
The data from the synchronous-orbit satellites of the Gorizont series are used to study the dependences of the ion flux variation amplitudes in the synchronous altitude region (the diurnal behaviour) on particle energies and on the form and rigidity of the particle energy spectrum. The proton fluxes were measured in the energy range E 60–120 keV, and the [N,0]2+ and [C,N,0]4+ ion fluxes in the energy range E 60–70 keV/e.

The ratio of the diurnal variation amplitudes of the studied ions is shown to correspond to the similarity of their energy spectra in the E/Q representation. The magnetically-quiet time gradient of the distribution function F(μ,J,L) in the synchronous-orbit region is shown to be (∂F/∂L)=0 for the H+ and [N,0]2+ ions and (∂F/∂L) > 0 for the [C,N,0]4+ ions (at the values of μ corresponding to the examined energy ranges). During magnetically-disturbed periods the inner boundary of the (∂F/∂L)=0 region shifts to lower L and (∂ F/∂L) = O in the synchronous altitude region must be also for the [C,N,O]4+ ions.  相似文献   


16.
The Dust Impact Detection System (DIDSY) for the Giotto Halley Mission consists of two types of sensors for the detection of cometary dust particles: two impact plasma sensors and five piezo-electric momentum sensors. One sensor of each type is covered by a penetration film. A 1 μm thick aluminum film covers an impact plasma sensor. One momentum sensor is mounted onto the rear shield behind the 1 mm front shield made from aluminum. The parameters measured are the total charge released upon impact and the amplitude of the acoustic signal generated by the impact. Both quantities depend on the mass and speed of the impacting particles. At the impact speed of 68 km/sec the mass of cometary dust particles can be determined in the mass range from 10−17 g to 10−3 g. From the difference in the countrates measured by the sensors with and without penetration film the average bulk density of dust particles of masses 10−14 g and 10−6 g can be determined. With appropriate calibration an accuracy of a factor of 2 for both the mass and density determination can be obtained.  相似文献   

17.
Results of the 2.5–5 micron spectroscopic channel of the IKS instrument on Vega are reported and the data reduction process is described. H2O and CO2 molecules have been detected with production rates of 1030 s−1 and 1.5 1028 s−1 respectively. Emission features between 3.3 and 3.7 microns are tentatively attributed to CH - bearing compounds - CO is marginally detected with a mixing ratio CO/H2O 0.2. OH emission and H2O - ice absorption might also be present in the spectra.  相似文献   

18.
We report on the luminosity dependent change of the cyclotron resonance energy obtained from a transient X-ray pulsar, 4U 0115+63. Using RXTE data observed on 1999 March, we found that the fundamental resonance energy stayed constant (11 keV) when the source luminosity was above 5 × 1037 erg s−1. As the luminosity decreased below 5 × 1037 erg s−1, the fundamental resonance energy gradually increased up to 16 keV at 0.16 × 1037 erg s−1. The luminosity dependence of the resonance energy can be understood by the change of the accretion column height.  相似文献   

19.
Information about the amount and spatial structure of atmospheric water vapor is essential in understanding meteorology and the Earth environment. Space-borne remote sensing offers a relatively inexpensive method to estimate atmospheric water vapor in the form of integrated water vapor (IWV). The research activity reported in the present paper is based on the data acquired by the HRPT/MODIS (High Resolution Picture Transmission, MODerate resolution Imaging Spectroradiometer) receiving station established in Budapest (Hungary) by the Space Research Group of the Eötvös Loránd University. Integrated water vapor is estimated by the remotely sensed data of the MODIS instrument with different methods and also by the operational numerical weather prediction model of the European Centre for Medium-Range Weather Forecasts (ECMWF). Radiosonde data are used to evaluate the accuracy of the different IWV fields though it has been pointed out that the in situ data also suffers from uncertainties. It was found that both the MODIS and the ECMWF based fields are of good accuracy. The satellite data represent finer scale spatial structures while the ECMWF data have a relatively poor spatial resolution. The high quality IWV fields have proved to be useful for radiative transfer studies such as the atmospheric correction of other satellite data from times different than the overpass times of satellites Terra/Aqua and the forecast times of the model data. For this purpose the temporal variability of IWV is scrutinized both using ECMWF and MODIS data. Taking advantage of Terra and Aqua overpasses, the mean rate of change of IWV estimated by the near infrared method was found to be 0.47 ± 0.45 kg m−2 h−1, while it was 0.13 ± 0.65 kg m−2 h−1 based on the infrared method. The numerical weather prediction model’s analysis data estimated −0.01 ± 0.13 kg m−2 h−1 for the mean growth rate, while using forecast data it was 0.24 ± 0.18 kg m−2 h−1. MODIS data should be used when available for the estimation of the IWV in other studies. If no satellite data are available, or available data are only from one overpass, ECMWF based IWV can be used. In this case the analysis fields (or the satellite field) should be used for temporal extrapolation but the rate of change should be calculated from the forecast data due to its higher temporal resolution.  相似文献   

20.
We investigate the nature of the faint X-ray source population through X-ray spectroscopy and variability analyses of 136 active galactic nuclei (AGN) detected in the 2 Ms Chandra Deep Field-North Survey with >200 background-subtracted 0.5–8.0 keV counts [F0.5–8.0 keV = (1.4−200) × 10−15 erg cm−2 s−1]. Our preliminary spectral analyses yield median spectral parameters of Γ = 1.61 and intrinsic NH = 6.2 × 1021 cm−2 (z = 1 assumed when no redshift available) when the AGN spectra are fitted with a simple absorbed power-law model. However, considerable spectral complexity is apparent (e.g., reflection, partial covering) and must be taken into account to model the data accurately. Moreover, the choice of spectral model (i.e., free vs. fixed photon index) has a pronounced effect on the derived JVH distribution and, to a lesser extent, the X-ray luminosity distribution. We also find that among the 136 AGN, 10 (≈7%) show significant Fe K emission-line features with equivalent widths in the range 0.1–1.3 keV. Two of these emission-line AGN could potentially be Compton thick (i.e., Γ < 1.0 and large Fe K equivalent width). Finally, we find that 81 (≈60%) of the 136 AGN show signs of variability, and that this fraction increases significantly (≈80–90%) when better photon statistics are available.  相似文献   

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