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1.
Results of impact fragmentation experiments for basalts and pyrophyllites are reported. Aluminum cylindrical projectiles were impacted on cubic basalt and pyrophyllite targets at velocities of 70 to 990 m/sec. The targets and projectiles were 20 g to 3.3 kg and 2 to 20 g in weight respectively. Weights of the fragments produced by impacts were measured and the size distributions of fragments were examined. Data of the largest fragment mass (mL) normalized to the original target mass (Mt), mL/Mt, correlate better with the nondimensional impact stress, PI, a new scaling parameter introduced by H. Mizutani, Y. Takagi, and S. Kawakami (1984, in preparation) than the conventional projectile's kinetic energy per unit target mass, E/Mt, used in the previous studies. All the mL/Mt data for basalts obtained in the present study are summarized by mL/Mt = 2.95 × 10?2PI?1 where PI = P0L3/YR3, P0 = peak shock pressure, L = projectile size, R = target size and Y = material strength of target. For aluminum targets, however, the mL/Mt is 2.5 orders of magnitude larger than that for brittle targets at impacts with the same PI. Size distributions of fragments expressed in a log N - log (m/Mt) diagram divided into three regimes bounded by two inflection points. In each regime the curve is expressed by . The slopes, a, of the log curves in the regimes of a large and a medium size range are positively correlated with the nondimensional impact stress, PI, and expressed as a = C3 + a3log PI. The slopes, a, in the smallest size range are, on the other hand, nearly constant and have values of . Present results indicate that the impact fragmentation is scaled well by the new scaling parameter, PI, of Mizutani, Takagi, and Kawakami and that the present experimental data may shed new light on planetary impact processes. 相似文献
2.
A.T.Y. Lui C.-I. Meng L.A. Frank K.L. Ackerson S.-I. Akasofu 《Planetary and Space Science》1981,29(8):837-842
The temperature and density of the plasma in the Earth's distant plasma sheet at the downstream distances of about 20–25 Re are examined during a high geomagnetic disturbance period. It is shown that the plasma sheet cools when magnetospheric substorm expansion is indicated by the AE index. During cooling, the plasma sheet temperature, T, and the number density, N, are related by (adiabatic process) in some instances, while by T ∝ N?1 (isobaric process) in other cases. The total plasma and magnetic pressure decreases when and increases when T ∝ N?1. Observation also indicates that the dawn-dusk component of plasma flow is frequently large and comparable to the sunward-tailward flow component near the central plasma sheet during substorms. 相似文献
3.
There are a few methods of measuring pulse widths. Among the most often used pulse widths there are Wpp (the distance between two peak value points), W50 (the width at the place of 50% of the highest peak intensity) and W10 (the width at the place of 10% of the highest peak intensity). In addition, there are also the width Wc50 at the place of 50% of their respective intensities and the width Wc10 at the place of 10% of the respective intensities of the two outermost components. The data of the pulse profiles of the sample of 16 double-cone peak pulsars and 7 core-cone triple peak pulsars at 1.4 GHz are utilized to measure 5 kinds of pulse widths. The pulsars with the data of the magnetic inclination α and impact angle β are employed to derive the corresponding radiation beam radius ρ, and the relation between ρ and the pulsar period P, ρ ∝ P?0.5, is verified. Via a comparison between the qualities of the relation between ρ and P derived from the 5 kinds of pulse widths it is found that the width between the outermost components is better than any one of the first 3 kinds of widths, of which the correlative relation obtained from the Wc50 width is the best. From this it is considered that Wc50 is the measured value that can fully reflect the emission beam width. The symmetry of the pulse profile is also discussed and it is found that from the comparison with the preceding cone emission component the following cone emission component is much closer to the core emission component, and the widths of the two cone emission components are basically the same according to statistics. 相似文献
4.
We make a statistical analysis of the periodsP and period-derivativesP of pulsars using a model independent theory of pulsar flow in theP-P diagram. Using the available sample ofP andP values, we estimate the current of pulsars flowing unidirectionally along theP-axis, which is related to the pulsar birthrate. Because of radio luminosity selection effects, the observed pulsar sample
is biased towards lowP and highP. We allow for this by weighting each pulsar by a suitable scale factor. We obtain the number of pulsars in our galaxy to
be 6.05−2.80
+3.32 × 105 and the birthrate to be 0.048−0.011
+0.014 pulsars yr−1 galaxy−1. The quoted errors refer to 95 per cent confidence limits corresponding to fluctuations arising from sampling, but make no
allowance for other systematic and random errors which could be substantial. The birthrate estimated here is consistent with
the supernova rate. We further conclude that a large majority of pulsars make their first appearance at periods greater than
0.5 s. This ‘injection’, which runs counter to present thinking, is probably connected with the physics of pulsar radio emission.
Using a variant of our theory, where we compute the current as a function of pulsar ‘age’ (1/2P/P), we find support for the
dipole braking model of pulsar evolution upto 6 × 106 yr of age. We estimate the mean pulsar braking index to be 3.7−0.8
+0.8. 相似文献
5.
A significant sink of geomagnetic pulsation energy is due to Joule dissipation in the ionosphere. To investigate this we have computed the damping experienced by standing Alfvén waves in a dipole magnetic field. Both the uncoupled poloidal and toroidal modes are considered with Joule dissipation being introduced through a boundary condition which relates the electric and magnetic field strengths at the ionosphere, viz: is the height integrated Pederson conductivity. The damping rates are strongly dependent on the ionospheric conductivity and we find that typically the normalized damping rate, for nightside values of conductivity and ～0.01 for the dayside. This would account for the observed scale of bandwidths in pulsation signals. Away from regions of extreme damping we find γ ∝ L?1Σp?1. 相似文献
6.
Models of the collapse of a protostellar cloud and the formation of the solar nebula reveal that the size of the nebula produced will be the larger of (where J, M, and cs are the total angular momentum, total mass, and sound speed of the protosetellar material; G is the gravitational constant; k is a number of order unity; and v is the effective viscosity in the nebula). From this result it can be deduced that low-mass nebulas are produced if P ≡ (RV/RCF)2 ? 1; “massive” nebulas result if P ? 1. Gravitational instabilities are expected to be important for the evolution of P ? 1 nebulas. The value of J distinguishes most current models of the solar nebula, since P ∝ J?4. Analytic expressions for the surface density, nebular mass flux, and photospheric temperature distributions during the formation stage are presented for some simple models that illustrate the general properties of growing protostellar disks. It does not yet seem possible to rule out either P ? 1 or P < 1 for the solar nebula, but observed or possible heterogeneities in composition and angular-momentum orientation favor P < 1 models. 相似文献
7.
《Chinese Astronomy and Astrophysics》1981,5(2):212-216
We made a statistical analysis using the Cambridge 5km, 5 GHz data on double radio sources and found highly significant correlations between the following pairs of parameters; the energies in the hot spots and the extended regions, Eh and Ee; their luminosities, Lh and Le; energy density in the hot spots K and the total luminosity Lt and the ratio of energy densities and Lt. These correlations exemplify the role of the hot spots in the radio sources. 相似文献
8.
New characteristics of VLF chorus in the outer magnetosphere are reported. The study is based on more than 400 hours of broadband (0.3–12.5 kHz) data collected by the Stanford University/Stanford Research Institute VLF experiment on OGO 3 during 1966–1967. Bandlimited emissions constitute the dominant form of whistler-mode radiation in the region . Magnetospheric chorus occurs mainly from 0300 to 1500 LT, at higher L at noon than at dawn, and moves to lower L during geomagnetic disturbance, in accord with ground observations of VLF chorus. Occurrence is moderate near the equator, lower near 15°, and maximum at high latitudes (far down the field lines). The centre frequency ? of the chorus band varies as L?3> and at low latitudes is closely related to the electron gyrofrequency on the dipole field line through the satellite. Based on the measured local gyrofrequency , the normalized frequency distribution of chorus observed within 10° of the dipole equator shows two peaks, at and . This bimodal distribution is a persistent statistical feature of near equatorial chorus, independent of L, LT and Kp. However there is considerable variability in individual events, with chorus often observed above, below, and between these statistical peaks; in particular, it is not unusual for single emissions to cross . When two bands are simultaneously present individual emission elements only rarely show one-to-one correlation between bands. For low Kp the median bandwidth of the upper band, gap and lower band are all ～16% of their centre frequencies, independent of L; for higher Kp the bandwidth of the lower band increases. Bandwidth also increases with latitude beyond ~10°. Starting frequencies of narrowband emissions range throughout the band. The majority of the emissions rise in frequency at a rate between 0.2 and 2.0 kHz/sec; this rate increases with Kp and decreases with L. Falling tones are rarely observed at dipole latitudes <2.5°. The observations are interpreted in terms of whistler-mode propagation theory and a gyroresonant feedback interaction model. An exact expression is derived for the critical frequency, , at which the curvature of the refractive index surface vanishes at zero wave normal angle. Near this frequency rays with initial wave normal angles between 0° and ?20° are focused along the initial field line for thousands of km, enhancing the phase-bunching of incoming gyroresonant electrons. The upper peak in the bimodal normalized frequency distribution is attributed to this enhancement near the critical frequency, at latitudes of ~5°. Slightly below the critical frequency interference between modes with different ray velocities may contribute to the dip in the bimodal distribution. The lower peak may reflect a corresponding peak in the resonant electron distribution, or guiding in field-aligned density irregularities. The observations are consistent with gyroresonant generation of emissions near the equator, followed by spreading of the radiation over a range of L shells farther down the field lines. 相似文献
9.
Paul G. Steffes 《Icarus》1985,64(3):576-585
Microwave absorption observed in the 35- to 48-km-altitude region of the Venus atmosphere has been attributed to the presence of gaseous sulfuric acid (H2SO4) in that region. This has motivated the laboratory measurement of the microwave absorption at 13.4- and 3.6-cm wavelengths from gaseous H2SO4 in a CO2 atmosphere under simulated conditions for that region. As part of the same experiments, upper limits on the saturation vapor pressure of gaseous H2SO4 have also been determined. The measurements for microwave absorption have been made in the 1- to 6-atm pressure range, with temperatures in the 500 to 575°K range. Using a theoretically derived temperature dependence, the best-fit expression for absorption from gaseous H2SO4 in a CO2 atmosphere at the 13.4-cm wavelength is is the H2SO4 number mixing ratio, P is the pressure in atmospheres, and T is the temperature in degrees Kelvins. The best-fit expression for absorption at the 3.6-cm wavelength is 4.52 × 1010q(P)0.85T?3 (dB km?1). The inferred H2SO4 vapor pressure above liquid H2SO4 corresponds to ln p = 8.84 ? 7220/t where p is the H2SO4 vapor pressure (in atm) and T is the temperature in degrees Kelvins. These results suggest that abundances of gaseous H2SO4 on the order of 15 to 30 ppm could account for the microwave absorption observed by radio occultation experiments at 13.3- and 3.6-cm wavelengths. They also suggest that such abundances would correspond to saturation vapor pressure existing at or above the 46- to 48-km range, which correlates with the observed cloud base. It is suggested that future measurements of absorption in the 1- to 3-cm wavelength range will provide additional tools for monitoring variations in H2SO4 abundance via radio occultation and radio astronomical observations. 相似文献
10.
I. P. Lopin 《Astronomy Letters》2007,33(6):411-418
The response of an isothermal atmosphere of a thin vertical magnetic flux tube to the presence of an acoustic-gravity wave field in the external medium is considered. The Laplace transform method is used to solve a problem with initial conditions. The structure of the solution for disturbances in the tube is a superposition of forced oscillations at the source frequency and oscillations decaying as ～ t ?3/2 (the so-called wave wake). Both components are analogues of the corresponding disturbances in an external medium with a modified amplitude. The excitation under consideration is shown to be effective in the ranges of external oscillation frequencies 0 mHz ≤ v ≤ 3.3 mHz and v ≥ 6.5 mHz. The time-averaged energy flux density for high-frequency magnetoacoustic-gravity waves in the tube is estimated to be ∝ 3.0 × 107 erg cm?2 s?1, a value of the same order of magnitude as that required for heating local regions in the solar chromosphere, ∝ 107 erg cm?2 s?1. 相似文献
11.
A ring current model has been obtained which permits calculations ofDst variations on the Earth's surface during magnetic storms. The changes in Dst are described by the equation where ; p = mnv2 is solar wind pressure; F(EM) is the function, controlled by the electromagnetic parameters of interplanetary medium, of injection into ring current ; τ is the constant of ring current decay. , where C is the level of the Dst-variation field measurements; ? is the injection function characterizing the quasisteady-state injection of energy into the ring-current region. The constant Ç is determined from the condition that the change of the ring current energy from magnetic storm commencement to end should equal the difference between the injected and dissipated energy throughout the storm. The values of the factors b and τ were found by the method of minimizing the sum of the quadratic deviations of the calculated Dst from the values observed throughout the storm : b = 0.23 nT/(eV cm?3), τ = 8.2 h at Dst? ? 55 nT and τ = 5.8 h at -120 ? Dst ? — 55 nT. The injection function F(EM) is of the form F(EM) = d(Ey? A) at the values of the azimuthal component of the solar wind electric field Ey ? A, and F(EM) =0 at A?Ey.d = ? 1.2 × 10?3 Ts?1 (mV/m)?1 and A = ? 0.9 mV m?1 . Thus, the injection to ring current is possible at the northward Bz component of the IMF. 相似文献
12.
《Chinese Astronomy and Astrophysics》1982,6(3):199-204
The 1978 photoeletric observations of the late type close binary RZ Dra were reanalyzed with the Wilson and Devinney approach. Photometric parameters were determined (in Tab. 1.). The system is found to be semi-detached where the less massive component fills its Roche surface, whereas the other component almost does so. The configuration of the system is shown in Fig. 1. The absolute dimensions of the system are found to be M1 = 0.61M⊙, . Both components appear to be overluminous and oversized for their masses and spectral types. Its evolutionary stage is also discussed. The variability in the brightness of the primary mlnimum(Fig. 4) indicates mass loss from the vicinity of L2, which would be mainly responsible for the long-term decrease in its period. 相似文献
13.
The Stokes parameters of resonance radiation scattered by a Na atom with the angular momentum F aligned by directed unpolarized radiation in a magnetic field H ～ 10?5?10?1 Oe are presented. An influence of the orientation of the magnetic field on these parameters are studied; the intensity ratio changes within ±5%, and the polarization degree P(D2) within ±25%. Measurements of and P(D2), if the geometry of scattering is known, may give information on the direction of the magnetic field in the sodium atmospheres of comets, as well as Io's sodium cloud or man-made cosmic clouds. 相似文献
14.
A method is proposed for constructing a map of the electron density distribution in the galactic plane. Data on the dispersion
measures DM of more than 1500 pulsars and their distances, found by an independent method, are used. The independent distances
of the pulsars are estimated using an empirical relation of the form L=γP
α
Ṗ
β
W
δ between the radio luminosity L of the pulsars and their periods P, the rate of change Ṗ. of their periods, and the half width W of their pulses. A map of the electron density distribution in the galactic plane
within a ±400 pc layer is provided.
__________
Translated from Astrofizika, Vol. 49, No. 2, pp. 277–287 (May 2006). 相似文献
15.
Both hypervelocity impact and dynamic spall experiments were carried out on a series of well-indurated samples of gabbro to examine the relation between spall strength and maximum spall ejecta thickness. The impact experiments carried out with 0.04- to 0.2-g, 5- to 6-km/sec projectiles produced decimeter- to centimeter-sized craters and demonstrated crater efficiencies of 6 × 10?9 g/erg, an order of magnitude greater than in metal and some two to three times that of previous experiments on less strong igneous rocks. Most of the crater volume (some 60 to 80%) is due to spall failure. Distribution of cumulative fragment number, as a function of mass of fragments with masses greater than 0.1 g yield values of b = d(log Nf)/d log(m) ?0.5 ?0.6, where N is the cumulative number of fragments and m is the mass of fragments. These values are in agreement or slightly higher than those obtained for less strong rocks and indicate that a large fraction of the ejecta resides in a few large fragments. The large fragments are plate-like with mean values of B/A and C/A 0.8 0.2, respectively (A = long, B = termediate, and C = short fragment axes). The small equant-dimensioned fragments (with mass < 0.1 g and B ～ 0.1 mm) represent material which has been subjected to shear failure. The dynamic tensile strenght of San Marcos gabbro was determined at strain rates of 104 to 105 sec?1 to be 147 ± 9 MPa. This is 3 to 10 times greater than inferred from quasi-static (strain rate 100 sec?1) loading experiments. Utilizing these parameters in a continuum fracture model predicts a tensile strenght of , where ε is strain rate. It is suggested that the high spall strenght of basic igneous rocks gives rise to enhanced cratering efficiencies due to spall in the <102-m crater diamter strength-dominated regime. Although the impact spall mechanism can enhance cratering efficiencies it is unclear that resulting spall fragments achieve sufficient velocities such that fragments of basic rocks can escape from the surfaces of planets such as the Moon or Mars. 相似文献
16.
The paper gives the results of detailed studies of the frequency spectra of the chain of the wave packets Fs(t) of geomagnetic pulsations PC-1 recorded at the Novolazarevskaya station. The bulk of the energy of Fs(t) is concentrated in the vicinity of the central frequencies of spectra—the carrier frequencies of the signals. The velocity of the flux of protons generating these signals correspond to them. The spectra of the signals have oscillations—“satellites” irregularly distributed in frequency. These satellites, as the authors believe, testify to the presence of the individual groups of protons of low concentration whose velocities vary within 103–104 km s?1.Their energy is only of the order of 10?2–10?3 of the energy of the main proton flux. Clearly pronounced maxima on double and triple frequencies are detected. They show that the generation of pulsations PC-1 is accompanied by the generation on the overtones of wave packets called in this paper “two-fold” and “three-fold” pulsations PC-1. Intensive symmetrical satellites of a modulation character have been discovered on frequencies . Frequency differences correspond to them. The authors believe that the values of Δ?±sK are resonance frequencies of the magnetospheric cavity in which geomagnetic pulsations PC-1 are generated. It is established that the values of Δ?±sK coincide closely with the carrier frequencies of geomagnetic pulsations PC-3 and PC-4 generated in the magnetosphere. This leads to the conclusion that the resonance oscillations of the magnetospheric cavity are their source. Thus, the generation of geomagnetic pulsations of different types and resonance oscillations in the magnetosphere are integrated into a unified process. The importance of the results obtained and the necessity to check further their trustworthiness and universality, using experimental data gathered in different conditions, is stressed. 相似文献
17.
We have measured the decorrelation frequency (f
v
) and decorrelation time (t
v
) for 15 pulsars. We show by combining our data with those of others thatfv∫ DM-1.79±0.14 andt
v
∫ DM-0.80±0.15 up to a dispersion measure (DM) of about 60 cm3 pc. The combined data set does not form a complete sample, but the relations obtained from our measurements on 14 pulsars,
which form almost a complete sample up to 41 cm3 pc, are consistent with the above relations, suggesting that these relations are not seriously affected by selection effects.
The relations are broadly in agreement with those expected from a homogeneous interstellar medium and are in disagreement
with earlier conclusions by others that these relations steepen even for low-DM pulsars. The agreement suggests that the local
interstellar medium is homogeneous at least up to a distance of about 2 kpc. 相似文献
18.
Kenneth Fox 《Icarus》1975,24(4):454-459
The basis for “quasipolar” absorption (QPA) by CH4 is the existence of a small electric dipole moment in its ground state. The integrated intensity αQPA at a temperature of 90K is calculated to be between 4.8 × 10?5 and 1.9 × 10?2 cm?2 atm?1. With an assumed mean pressure of 0.1 atm and a relative abundance of , it is estimated that the ratio of quasipolar to pressure-induced absorption (PIA) is 0.05 ? αQPA/αPIA ? 18 for the spectral range from 0 to 300 cm?1. This result suggests that quasipolar absorption may contribute to a weak, CH4-induced greenhouse in the atmosphere of Titan. 相似文献
19.
We present the results of a statistical study of the star formation rates (SFR) derived from the Galaxy Evolution Explorer (GALEX) observations in the ultraviolet continuum and in the Hα emission line for a sample of about 800 luminous compact galaxies (LCGs). Galaxies in this sample have a compact structure and include one or several regions of active star formation. Global galaxy characteristics (metallicity, luminosity, stellar mass) are intermediate between ones of the nearby blue compact dwarf (BCD) galaxies and Lyman-break galaxies (LBGs) at high redshifts z>2–3. SFRs were corrected for interstellar extinction which was derived from the optical Sloan Digital Sky Survey (SDSS) spectra. We find that SFRs derived from the galaxy luminosities in the far ultraviolet (FUV) and near ultraviolet (NUV) ranges vary in a wide range from 0.18 M ⊙?yr?1 to 113 M ⊙?yr?1 with median values of 3.8 M ⊙?yr?1 and 5.2 M ⊙?yr?1, respectively. Simple regression relations are found for luminosities L(Hα) and L(UV) as functions of the mass of the young stellar population, the starburst age, and the galaxy metallicity. We consider the evolution of L(Hα), L(FUV) and L(NUV) with a starburst age and introduce new characteristics of star formation, namely the initial Hα, FUV and NUV luminosities at zero starburst age. 相似文献
20.
Quasars, pulsars and other cosmic sources of intense radiation are known to have large brightness temperature (kT b?mc 2) and relativistic electron density values. In this case the induced Compton scattering by relativistic electrons should be considered. The probability of scattering with decreasing radiation frequency is derived for isotropic radiation scattering. When induced scattering takes place, the relativistic electron obtains its energy by transforming high-frequency quanta into the low-frequency ones. In the most intensive sources electrons would receive energiesE?mc 2 ××(kT b/mc 2)1/7 due to the heating rate proportional toE ?5 with the cooling rate proportional toE 2. Considerable distortion of the quasar spectrum is possible for reasonably large values of relativistic electron density (N?106cm?3) notwithstanding that the heating is negligible. In pulsars relativistic electron heating and spectrum distortion appear to depend more on the induced Compton scattering. 相似文献