共查询到20条相似文献，搜索用时 31 毫秒
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C. Wolf 《Astronomische Nachrichten》1990,311(1):1-4
It is shown that the primordial entropy of the universe can be generated in the residual phase prior to Calabi-Yau splitting and following the passing to the field theory limit of the heterotic super-string in ten space-time dimensions, wherein matter is represented by either a radiative equation of state or the equation of state for stiff matter. 相似文献
3.
The effects of both density stratification and magnetic field expansion on torsional Alfvén waves in solar spicules are studied. Also, their eigenfrequencies, eigenfunctions, and the period ratio P 1/P 2 are obtained with a novel mathematical method. We showed that under some circumstances this ratio can approach its observational value even though it departs from its canonical value of 2. Moreover, Eigenfunction height variations show that the oscillations amplitude are increasing towards higher heights which is in agreement with the observations. This means that with a little increase in height, amplitude of oscillations expands due to the significant decrease in the density. 相似文献
4.
Rabindra Nath Das 《Astrophysics and Space Science》1978,57(2):409-417
Neutrinos couple through a weak neutral current to the density of matter, in particular to the neutron density. Density fluctuations, or phonons, in the neutron fluid may be emitted or absorbed by neutrinos passing through the matter. At high densities, temperatures and neutrino energies the neutrino mean free paths for phonon emission and absorption can be 106 cm. Significant changes in the neutrino momentum and energy accompany these processes. We present a model calculation for neutrino scattering by phonons, and representative numerical results for the neutrino mean free path and mean energy and momentum changes fork
B
T andE
v both ranging from 1 to 27 MeV.Research supported by the National Research Council of Canada. 相似文献
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6.
《天文和天体物理学研究(英文版)》2014,(8)
We present large scale observations of C18O(1–0) towards four massive star forming regions: MON R2,S156,DR17/L906 and M17/M18. The transitions of H2CO(110–111),C18O(1–0) and the 6 cm continuum are compared in these four regions. Our analysis of the observations and the results of the Non–LTE model shows that the brightness temperature of the formaldehyde absorption line is strongest in a background continuum temperature range of about 3 – 8 K. The excitation of the H2 CO absorption line is affected by strong background continuum emission. From a comparison of H2 CO and C18 O maps,we found that the extent of H2 CO absorption is broader than that of C18 O emission in the four regions. Except for the DR17 region,the maximum in H2 CO absorption is located at the same position as the C18 O peak. A good correlation between intensities and widths of H2 CO absorption and C18 O emission lines indicates that the H2 CO absorption line can trace the dense,warm regions of a molecular cloud. We find that N(H2CO) is well correlated with N(C18O) in the four regions and that the average ratio of column densities is N(H2CO)/N(C18O) ～ 0.03. 相似文献
7.
《Planetary and Space Science》1999,47(8-9):1029-1050
We predict the amount of cometary, interplanetary, and interstellar cosmic dust that is to be measured by the Cometary and Interstellar Dust Analyzer (CIDA) and the aerogel collector on board the Stardust spacecraft during its fly-by of comet P⧸Wild 2 and during the interplanetary cruise phase. We give the dust flux on the spacecraft during the encounter with the comet using both, a radially symmetric and an axially symmetric coma model. At closest approach, we predict a total dust flux of 1060 m−2 s−1 for the radially symmetric case and 1065 m−2 s−1 for the axially symmetric case. This prediction is based on an observation of the comet at a heliocentric distance of 1.7 AU. We reproduce the measurements of the Giotto and VEGA missions to comet P⧸Halley using the same model as for the Stardust predictions. The planned measurements of interstellar dust by Stardust have been triggered by the discovery of interstellar dust impacts in the data collected by the Ulysses and Galileo dust detector. Using the Ulysses and Galileo measurements we predict that 25 interstellar particles, mainly with masses of about 10−12 g, will hit the target of the CIDA experiment. The interstellar side of the aerogel collector will contain 120 interstellar particles, 40 of which with sizes greater than 1 μm. Furthermore, we investigate the contamination of the CIDA and collector measurements by interplanetary particles during the cruise phase. 相似文献
8.
《Planetary and Space Science》1986,34(9):789-800
Volume emission profiles of the O2(b1Σg+−X3Σgt-)(O-O) Atmospheric Band and the O(1S-1D) green line are used together with coordinated measurements of the atomic oxygen concentrations to test the hypothesis that both emissions are excited by Barth type mechanisms. By considering O2(b1Σg+) to be produced from an excited O2 precursor, with O2 as transfer agent, and O(1S) to be formed from a similar precursor with atomic oxygen as the transfer agent, precursor quenching rates are obtained as a function of altitude. These quenching profiles can be well resolved into components corresponding to collisional deactivation by O(3P) and O2 (or N2), and support the suggestion that Barth type mechanisms are involved. Minimum efficiencies for the production of the two precursors in oxygen atom recombination and ratios for the quenching of each by O(3P) and O2 (or N2) are deduced. Differences in the quenching coefficients for the two precursors are discussed. 相似文献
9.
Power-law spectra of 1–2 GHz narrowband dm-spikes 总被引：3，自引：0，他引：3
Twelve examples of clouds of narrowband dm-spikes, observed by the Ondejov radiospectrograph in the 1–2 GHz frequency range, are analyzed. After transforming of the frequency scales to heights in the solar atmosphere, the indices of the power-law power spectra are determined. The derived power-law indices are scattered in a broad range of values (–0.80––2.85). In some cases they considerably deviate from the previously found value of –5/3. A change of the power-law index above logk2.5 was also found in some cases. In the two longest events the time evolution of their power spectra as well as their indices were studied. While in most parts of the radio spectra the spectral index remains constant, in one part its absolute value increases with the spike intensity increase. Finally, the results, especially the broad range of power-law indices, are briefly discussed. 相似文献
10.
Nadjinangar Gotoum Kamel Hammami L. C. Owono?Owono Nejm-Eddine Jaidane 《Astrophysics and Space Science》2012,337(2):553-561
Rotational excitation cross sections and rate coefficients of AlF collisions with para-H2 are computed at low temperature, i.e., for T≤70 K. Prior to collisional calculations, a four-dimensional (4D) potential energy surface (PES) for the AlF-H2 system is calculated at the ab initio Coupled-Cluster level of the theory with an aug-cc-pVQZ Gaussian basis set. This 4D-PES is further reduced to a two-dimensional
(2D) PES based on the considerations related to collisional studies with para-H2. The [Al-F] and [H-H] bond lengths are frozen at their experimental equilibrium value r
e
=1.654369 bohr and r
e
=1.4011 bohr respectively. The interaction energy presents a global minimum located ∼63 cm−1 below the AlF-H2 dissociation limit. With this PES, cross sections are determined in the Close-Coupling (CC) approach and rate coefficients
are inferred by averaging the cross sections over a Maxwell-Boltzman distribution of kinetic energies. These quantities are
significantly magnified in comparison with their AlF-He counterparts. The already observed propensity towards ΔJ=1 transitions for AlF-He remains. 相似文献
11.
The superfluid core (“npe” phase) of a neutron star, consisting of superfluid neutrons, superconducting protons, and normal
electrons, is considered. The Gibbs thermodynamic potential of a superconducting proton vortex in a proton superconductor
of the second kind, interacting with the normal core of a neutron vortex of radius r ≪ λ parallel to it (λ is the depth of
penetration), is calculated. It is shown that under this assumption, the capture by the core of only one vortex turns out
to be energetically favored. The force exerted on the proton vortex by the entrainment current, always directed toward the
core, is found. The corresponding force for a proton antivortex is directed outward toward the outer boundary of the neutron
vortex. It is shown that the fluctuational formation of a vortex-antivortex pair is possible at a large distance from the
core under the action of the entrainment current. Under the action of the entrainment current, the antivortex travels outward,
while the vortex remains inside the neutron vortex. It is shown that the formation of new proton vortices is possible only
in the region in which the entrainment magnetic field strength is H(ρ) > Hcl (Hcl is the first critical field).
Translated from Astrofizika, Vol. 42, No. 2, pp. 225–234, April–June, 1999 相似文献
12.
本文给出在北京天文台兴隆观测站获得的盾牌座δ型变星金牛座θ~2的新光电测光资料,它们是新近开展的一次多台站国际联合观测的一部分。以前得到的四频率解(文[1])与新资料符合得极好。单次测量的残差约±0.003星等。 相似文献
13.
J.P. Delaboudinière 《Planetary and Space Science》1977,25(2):193-195
Intensity of dayglow emmisions in the lines of 0 II at 537 and 581 Å is evaluated from presently accepted atomic parameters, EUV solar fluxes and atmospheric models. An improvement of the experimental techniques used up to now is suggested to identify these emissions and provide new data on ionospheric processes. 相似文献
14.
Hard X-ray and radio observations lead to the conclusion that production of non-thermal electrons is a common phenomenon of the active Sun. A preliminary analysis of three hard X-ray bursts observed with the OGO-5 satellite and the radio observations reported in the literature indicates that non-thermal particles are present in the flare region prior to the impulsive (flash) phase and also during the gradual rise and fall (GRF) bursts which are usually explained in terms of purely thermal radiation. The principal difference between the non-thermal electrons observed before the flash phase and during the flash phase appears to be in their total number rather than in the hardness of their energy spectrum. This indicates that the basic characteristics of the two acceleration processes are probably similar although the total energy converted into non-thermal electrons is considerably larger in the flash phase than in the build-up phase. Transient absorbing H features and filament activations are discussed in terms of their ability to produce energetic particle events and magnetic energy release.Presently at the Space Sciences Laboratory, University of California, Berkeley and Institute of Plasma Research, Stanford University, Stanford, California. 相似文献
15.
In this paper it is suggested that inclusion of mutual gravitational interactions among the particles in the early dense universe
can lead to a ‘pre-big bang’ scenario, with particle masses greater than the Planck mass implying an accelerating phase of
the universe, which then goes into the radiation phase when the masses fall below the Planck mass. The existence of towers
of states of such massive particles (i.e. multiples of Planck mass) as implied in various unified theories, provides rapid
acceleration in the early universe, similar to the usual inflation scenario, but here the expansion rate goes over ‘smoothly’
to the radiation dominated universe when temperature becomes lower than the Planck temperature. 相似文献
16.
Computations of the equivalent widths of absorption lines as a function of planetary phase angle are made for a homogeneous cloud with particles having the properties (shape, refractive index, and size distribution) deduced from polarimetry of Venus. The computed equivalent widths show an “inverse phase effect” comparable to that which is observed for CO2 lines on Venus. This result verifies a recent suggestion of Regas et al. that the existence of an inverse phase effect does not by itself imply the presence of multiple layers of scattering particles in the atmosphere of Venus. 相似文献
17.
N2 2P fluorescent intensity was monitored as a function of incident photon energy from 40 to 70 eV. A structure was seen near 52.2 eV. This feature is attributed to the scattering of photoelectrons originating from the N2 2σg molecular orbital with a binding energy of about 37.7 eV. The kinetic energy of these photoelectrons corresponds to the peak of the 2P excitation cross section at 14.5 eV. 相似文献
18.
Studying the evolution of magnetic clouds entrained in coronal mass ejections using in-situ data is a difficult task, since only a limited number of observational points is available at large heliocentric distances. Remote sensing observations can, however, provide important information for events close to the Sun. In this work we estimate the flux rope orientation first in the close vicinity of the Sun (2?–?20 R ⊙) using forward modeling of STEREO/SECCHI and SOHO/LASCO coronagraph images of coronal mass ejections and then in situ using Grad–Shafranov reconstruction of the magnetic cloud. Thus, we are able to measure changes in the orientation of the erupted flux ropes as they propagate from the Sun to 1 AU. We present both techniques and use them to study 15 magnetic clouds observed during the minimum following Solar Cycle 23 and the rise of Solar Cycle 24. This is the first multievent study to compare the three-dimensional parameters of CMEs from imaging and in-situ reconstructions. The results of our analysis confirm earlier studies showing that the flux ropes tend to deflect towards the solar equatorial plane. We also find evidence of rotation on their travel from the Sun to 1 AU. In contrast to past studies, our method allows one to deduce the evolution of the three-dimensional orientation of individual flux ropes rather than on a statistical basis. 相似文献
19.
One hundred eighty-seven reflectance spectra (0.33–1.10 μm) of the Galilean satellites have been obtained. Solar phase angle color correction coefficients were derived and the spectra corrected to a solar phase of 6°. Solar phase angle coefficients beyond 0.55 μm are presented for the first time. The spectra as a function of orbital phase angle are presented in the form of images to display hemispheric spectral variations. Io and Europa are redder on their trailing hemispheres while Callisto is redder on its leading hemisphere. Ganymede shows small longitudinal color variations despite the complex albedo structure visible in Voyager images. Comparisons of these data with previous measurements reveal that most differences can be attributed to the solar calibration. Reflectance measurements of Io at 0.73 μm observed 8.5 years apart show a 6% global reflectance decrease. However, it is difficult to unambigously attribute this particular decrease in reflectance to a change in Io's surface composition. 相似文献
20.
The long awaited event of the detection of a gravitational wave from a binary neutron star merger and its electromagnetic counterparts marked the beginning of a new era in observational astrophysics. The brand-new field of gravitational wave astronomy combined with multi-messenger observations will uncover violent, highly energetic astrophysical events that could not be explored before by humankind. This article focuses on the presumable appearance of a hadron–quark phase transition and the formation of regions of deconfined quark matter in the interior of a neutron star merger product. The evolution of density and temperature profiles inside the inner region of the produced hypermassive/supramassive neutron star advises an incorporation of a hadron–quark phase transition in the equation of state of neutron star matter. The highly densed and hot neutron star matter of the remnant populate regions in the QCD phase diagram where a non neglectable amount of deconfined quark matter is expected to be present. If a strong hadron–quark phase transition would happen during the post-merger phase, it will be imprinted in the spectral properties of the emitted gravitational wave signal and might give an additional contribution to the dynamically emitted outflow of mass. 相似文献