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1.
A numerical analysis of cyclotron instabilities is carried out by computing the dispersion relation for a three component cold plasma-beam system. Rates of growth and damping for various values of the stream density are calculated from the dispersion relation. The rates of growth and damping increase monotonically as the number density of the proton stream increases. It is found that the frequencies at the rates of maximum growth and the damping decrease slightly to lower frequencies and a sharp peak at these frequencies becomes blunt. The minimum e-folding times of an ion cyclotron wave for (a) σs = 10−4, σi = 10−2 and (b) σs = 10−1, σi = 10−2 are about 3·84 and 0·16 sec respectively in the vicinity of the equatorial plane at 6 Re, where σs and σi are the ratios of the beam density Ns and the helium ion (H6+) density Ni to the total positive ions in the plasma-beam system.  相似文献   

2.
Small-scale spatially periodic distortions of auroral forms have been studied utilizing low-light level television observations made at various locations in the Northern and Southern Hemispheres. The most commonly observed features were folds and vortex-like curl formations. The curls, identified here with the Kelvin-Helmholtz instability due to fluid shear, invariably had a counterclockwise rotational shape and motion when viewed in a direction anti-parallel to the Earth's magnetic field. The typical measured wavelength (5 km) and measured growth rate (4.2 sec−1) were used to evaluate the Kelvin-Helmholtz dispersion relation for the apparent shear ωs = ∂ νx/ ∂y (28 sec−1). The apparent horizontal velocities of both folds (0–5 km/sec) and curls (0–22 km/sec) were invariably observed to be counterclockwise with respect to the multiple arc centre when viewed antiparallel to B. Consistent agreement between rotational shape and rotational motion suggests that the apparent growth rate and the apparent horizontal velocities closely approximate the actual values. If the shear results from E×B drifts in a space charge field, the calculated value for ωs, implies an unneutralized electron density 0–1 cm−3 and a ΔE across the arc element 500mV/m. The velocity measurements indicate that the ΔE values for individual elements can combine to produce transient electric fields at the edges of multiple arcs as high as 1000 mV/m.  相似文献   

3.
A method of joint estimation of the parameters and the variance σ2 in the linear model is presented in this paper. The M-estimators with finite rejection points are adopted for estimating the parameters. In order to estimate the variance σ2, the Grubbs statistics and the Kurtosis test statistics are adopted to test the residual sequence {;ri};. And the sample variance of {;ri}; after discarding the outliers is taken as the estimation of σ2. This method of estimating σ2 is less computational demanding and more accurate, compared with the well-known method which takes 1.483 medi |ri| as the estimation of σ. The breakdown point of the above estimation of σ2 is more than 20%, while the brekdown point is less than 10%, if only the Grubbs statistics is used.  相似文献   

4.
Inspection of recent spectra presented by Sivjee (1983) show evidence of the 0–4 and 0–5 bands of the N2(c′41Σu+ → a1Πg) Gaydon-Herman system. In conjunction with earlier spectra, it is now possible that this band system is a significant auroral component, with an intensity approx. 7% that of the N2 2P system. The absence in aurorae of the potentially far stronger N2(c′41Σu+ → X1Πg) system is discussed. It is that the O2(A3Σu+ → X3Σg−) band system is indiscernible in Sivjee's auroral spectra, under conditio the foreground nightglow is expected to be clearly visible. On the other hand, at least one relatively strong O2(A′3Δu → a1Δg) band appears to be present in these spectra.  相似文献   

5.
Co-ordinated rocket measurements of the O2(a1Δg−X3Σg−) Infrared Atmospheric (0-0) band emission profile and the atomic oxygen densities in an undisturbed night-time atmosphere are used to investigate the processes responsible for the excitation of O2(a1Δg) in the terrestrial nightglow. It is shown that three-body recombination of atomic oxygen, and subsequent energy transfer processes, can explain only part of the observed emission profile and that at least two other sources of O2(a1Δg) emission must exist. One of these additional sources, responsible for most of the emission observed below 90km, is identified as arising from the night-time residual of the very large dayglow 1Δg population. The other additional source is required to explain most of the emission observed above 95km. The processes responsible for this high altitude component cannot be identified but the vertical distribution of the required source function strongly resembles the profile of the atomic oxygen density squared and suggests that a two-body radiative recombination process may be involved. However, the measured zenith emission rates can also be explained without the high altitude source of O2(a1Δg) if optical emission at 1.27 μm was induced by the rocket as it penetrated the nightglow layer.  相似文献   

6.
We analysed the emission spectra of solar prominences using the complete linearization method [5] and found simultaneously the optical depth at the line centre τ0, the doppler width of the line ΔλD and the damping width a. The results show 1) that the complete linearization method has a larger radius of convergence, 2) that we must consider the variation of the source function with depth, when determining τ0, and 3) that the calculated values of the damping constant for the H, Hβ of hydrogen and H and K lines of Calcium are all much greater than the theoretical values from doppler broadening and radiation damping, showing that other mechanisms besides these two also contribute to the broadening of prominence lines.  相似文献   

7.
An analytical theory of whistler wave propagation in axially symmetric field-aligned density ducts is developed. Both enhancements and rarefactions of the density (crests and troughs) are considered. Simple equations giving the dependence of the number of modes n upon the angular frequency ω are derived. From these results it follows that in density crests n decreases when ω approaches ωc/2 for ω < ωc/2. The limiting frequency of the wave trapping is calculated. An analytical investigation of wave attenuation in a density crest due to wave leakage is presented. An analysis of the whistler modes in density troughs for ω < ωc/2, ω > ωc/2, and ω → ωc/2 shows that the number of modes is of the same order of magnitude in these three cases.  相似文献   

8.
We compute the big bang nucleosynthesis limit on the number of light neutrino degrees of freedom in a model-independent likelihood analysis based on the abundances of 4He and 7Li. We use the two-dimensional likelihood functions to simultaneously constrain the baryon-to-photon ratio and the number of light neutrinos for a range of 4He abundances Yp = 0.225–0.250, as well as a range in primordial 7Li abundances from (1.6 to 4.1) ×10−10. For (7Li/H)p = 1.6 × 10−10, as can be inferred from the 7Li data from Population II halo stars, the upper limit to Nν based on the current best estimate of the primordial 4He abundance of Yp = 0.238 is Nν < 4.3 and varies from Nν < 3.3 (at 95% C.L.) when Yp = 0.225 to Nν < 5.3 when Yp = 0.250. If 7Li is depleted in these stars the upper limit to Nν is relaxed. Taking (7Li/H)p = 4.1 × 10−10, the limit varies from Nν < 3.9 when Yp = 0.225 to Nν 6 when Yp = 0.250. We also consider the consequences on the upper limit to Nν if recent observations of deuterium in high-redshift quasar absorption-line systems are confirmed.  相似文献   

9.
In this paper we analyse the observational data obtained by the Chinese-made PZT in the two periods 1979 Feb – 1980 May and 1981 Dec – 1983 March. The internal accuracy of single star is found to be mu = ±13.0 ms, mφ = ±0. “144 for the first period, and mu = ±14.6 ms, mφ = ±0.” 152 for the second. Correction of star position is found by the chain method. The systematic error caused by the sealed window of the evacuated chamber and the temperature effect of the plate scale are investigated. Monthly means of time and latitude are given.  相似文献   

10.
The dependence of geomagnetic activity during a recurrent magnetic storm on the solar-wind magnetic field and plasma parameters has been studied. According to variations of solar-wind magnetic field strength B, a recurrent magnetic storm is divided into two stages: the first proceeding during the peak of B, and the second proceeding after the return of B to quiet level. The Kp index vs solar-wind parameters scattering diagrams for stages I and II differ significantly. In particular, the random scattering for stage I is much larger than for stage II. It was found that for stage I the Kp index correlates with B, with the sign and value of northsouth field component Bz and with the magnitude ΔB of field fluctuations, the situation being similar to that during sporadic magnetic storms, though the scale of the event is smaller. For stage II, the Kp index does not correlate with B, but strongly correlates with ΔB and weaker—with Bz. So geomagnetic activity at stage II is supported mainly by solar-wind magnetic field fluctuations. The dependence of the Kp index on plasma parameters (concentration of protons n, bulk velocity v and temperature T) is weak for both stages.  相似文献   

11.
Charged boson stars and vacuum instabilities   总被引：1，自引：0，他引：1  
We consider charged boson stars and study their effect on the structure of the vacuum. For very compact particle like “stars”, with constituent mass m* close to the Planck mass mPl, i.e. m2* = O(m2Pl), we argue that there is electric charge Zc, which, primarily, is due to the formation of a pion condensate (Zc 0.5−1e, where is the fine structure constant and e is the electric charge of the positron). If the charge of the “star” is larger than Zc we find numerical evidence for a complete screening indicating a limiting charge for a very compact object. There is also a less efficient competing charge screening mechanism due to spontaneous electron-positron pair creation in which case Zc −1e. Astrophysical and cosmological abundances of charged compact boson stars are briefly discussed in terms of dark matter.  相似文献   

12.
Muon and tau neutrinos (νx) interact with protoneutron star matter only via neutral currents and exchange energy with the stellar gas predominantly by neutrino-electron scattering and neutrino-pair processes. In contrast, electron neutrinos and antineutrinos (νe and ) are frequently absorbed and produced in charged-current mediated reactions with nucleons. Therefore the emergent νe and originate from layers with lower temperatures further out in the star and are emitted with much lower characteristic spectral temperatures. In addition, a major contribution to the νe and opacities is due to absorptions, while the opacity of νx is strongly dominated by scattering reactions with nucleons and nuclei in which the νx energy is (essentially) conserved. Therefore the νx distribution is nearly isotropic when νx decouple energetically and their outward diffusion is slowed down. In a generalized form to include this effect, the Stefan-Boltzmann Radiation Law can account for both the facts that νe ( ) and νx emerge from the star with similar luminosities but with very different characteristic spectral temperatures. Simple analytical expressions to estimate the effect are given. If, as recently argued, even at densities significantly below nuclear matter density neutral-current scatterings were associated with considerable energy transfer between neutrino and target particle, one might expect spectral temperatures of νx much closer to those of νe and . This is of relevance for the detection of neutrino signals from supernovae.  相似文献   

13.
Unusually great fluctuations in the ΔB module of the geomagnetic field have been observed in the polar cap from the satellite Cosmos-321. They are explained by small-scale two-sheet field-aligned current systems which exist during the periods when magnetic fields having a considerable northward Bz(Bz 10 nT) component are observed in interplanetary space.  相似文献   

14.
We calculate the event rates induced by a 51Cr νe source and by a 90Sr---90Y source in BOREXINO through elastic scattering on electrons, assuming a nonzero neutrino magnetic moment μν. We consider a source activity of about 2 MCi and estimate the solar ν (“source-off”) background for various oscillation scenarios. It is shown that values of μν as low as 0.5 × 10−10μB ( 0.2 × 10−10μB) can be proved with the 51Cr source (90Sr source) in about 100 days of data taking.  相似文献   

15.
The Solar Maximum Mission satellite did not record any γ-ray counts in excess of the background for a time interval of 223 s after the arrival of the first e's from the supernova 1987A. On the basis of the original data we derive a new 3σ upper limit on the γ fluence for this period and derive improved bounds on the νi → νjγ and νT → νee−e+γ radiative decay channels for neutrino masses up to the experimentally allowed value of around 30 MeV.  相似文献   

16.
We discuss the data of trignometric parallaxes determined along and δ published by the US Naval Observatory and Van Vleck Observatory. We found that the absolute difference δπ = πx−πy shows a very similar periodic variation with for both observations. This variation is shown to be due to errors in πy and to be related to the current practice of maximising the parallax factor for parallax determination in right ascension. Therefore, if possible, we should increase observations where the parallax factor in declination is maximised.  相似文献   

17.
In this paper we give, for the case where the proper motions of stars are unknown, a method of calculating the correct relative proper motion, the linear model being assumed always. We also show that the proper motion usually found on assuming Σxμx = Σyμx = 0, Σxμy = Σyy = 0, Σμx = 0, Σμy = 0, is not the relative proper motion, and that the difference between the two depends on the positions of the reference stars on the plate.  相似文献   

18.
The hydromagnetic Kelvin-Helmholtz (K-H) instability problem is studied for a three-layered system analytically by arriving at the marginal instability condition. As the magnetic field directions are taken to vary in the three regions, both the angle and finite thickness effects are seen on the instability criterion. When the relative flow speed of the plasmas on the two sides of the interfaces separating the inner and the surrounding layers is U < Uc, where Uc is the critical speed, the system is stable both for symmetric and asymmetric perturbations. However, unlike the case of the interface bounded by two semiinfinite media, Uc is no longer the minimum critical speed above which the system will be unstable for all wavenumbers; another critical speed U* > Uc is introduced due to the finiteness of the system. When Uc < U < U*, the instability can set in either through the symmetric or asymmetric mode, depending on the ratio of the plasma parameters and angle between the magnetic field directions across the boundaries. The instability arises for a finite range of wavenumbers, thus giving rise to the upper and lower cut-off frequencies for the spectra of hydromagnetic surface waves generated by the K-H instability mechanism. When U > U*, both the modes are unstable for short wavelengths. The results are finally used to explain some observational features of the dependence of hydromagnetic energy spectra in the magnetosphere on the interplanetary parameters.  相似文献   

19.
The existence of sidereal semidiurnal variation of cosmic-ray intensity in a rigidity region 102-103 GV has been reported by many researchers, but there is no consensus of opinion on its origin. In this paper, using the observed semidiurnal variations in a rigidity range (300–600 GV) with 10 directional muon telescopes at Sakashita underground station (geog. lat. = 36°, long. = 138°E, DEPTH = 80 m.w.e.), the authors determine the magnitudes (η1, η2) and directions (a1, a2) of the first- and second-order anisotropies in the following galactic cosmic-ray intensity distribution (j)
jdp = j0{1 + η1P1(cos χ1) + η2P2(cos χ2)}dp
, where Pnis the nth order spherical function and χn is the pitch angle of cosmic rays with respect to an. For the determination, the influence of cosmic-ray's heliomagnetospheric modulation, geomagnetic deflection and nuclear interaction with the terrestrial material and also of the geometric configuration of the telescopes are taken into account. Usually, the semidiurnal variation is produced by the second-order anisotropy. The present observation, however, requires also the first-order anisotropy which usually produces only the diurnal variation, but can produce also the semidiurnal variation as a result of the heliospheric modulation. The first- and second-order anisotropies are characterized with η1) > 0 and η2 < 0 have almost the same direction (a1 a2) specified by the right ascension ( 0.75 h) and declination (δ 50°S) and, therefore, they can be expressed, as a whole, by an axis-symmetric anisotropy of loss-cone type (i.e. deficit intensities in a cone). It is noteworthy that this anisotropy approximately coincides with that inferred from the air shower observation at Mt Norikura in the rigidity region 104 GV.  相似文献   

20.
A simultaneous, maximum-likelihood determination of the distance and kinematic parameters of the Pleiades is made. The results are: distance of the cluster d = 135.56 ± 0.72 pc, dispersion σd = 7.66 ± 0.80 pc; space velocity V = 25.94 ± 0.13 km/s, dispersion σv = 0.58 ± 0.09 km/s coordinates of the convergent point A = 101.95° ± 0.47°, D = −41.36° ± 0.29°.  相似文献   

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