共查询到20条相似文献，搜索用时 31 毫秒
1.
It is shown that phosphorus availability is in close balance with the phosphorus requirement of the bacterial grain model. This correspondence, which would be fortuitous if the interstellar grains were of inorganic origin, points to the correctness of the biological model. 相似文献
2.
The reaction of elemental phosphorus and H atoms to form PH3 was observed and should be a major factor in the recycling of PH3 in the stratosphere of Jupiter. The formation of PH3 in this manner should predominate at high altitudes where, due to the very low temperatures, reactions that require higher activation energies than these atom reactions cannot occur. At lower altitudes, in the troposphere, the rapid formation of H atoms from the strong absorption of light by NH3 will contribute to phosphine production also in this same manner. Recent experiments have also shown that elemental phosphorus reacts readily with aqueous ammonia to form PH3. This reaction may also be important in the recycling of PH3 in the upper troposphere of Jupiter if water-ammonia clouds, as had been previously thought, exist. Considerations of the coloration of the Great Red Spot have been made based upon the nature of the phosphorus obtained by decomposition of phosphine. 相似文献
3.
E. Margaret Burbidge 《Astrophysics and Space Science》1999,265(1-4):99-101
Absorption features in the UV spectra in about 10–15% of quasars show very broad profiles, indicating outflow velocities from
the quasars of one or even two tenths the speed of light. Determinations of the abundances of some elements, particularly
phosphorus, have yielded apparent large overabundances relative to solar. However, it has recently been shown that the absorbing
gas which does not completely cover the continuum source of the emission-line clouds may have large optical depth so that
the absorption lines are heavily saturated, leading to spurious overabundances of some elements, including phosphorus.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
P. D. Dobbie M. A. Barstow I. Hubeny J. B. Holberg M. R. Burleigh A. E. Forbes 《Monthly notices of the Royal Astronomical Society》2005,363(3):763-768
We report the detection, from the Far Ultraviolet Spectroscopic Explorer (FUSE) data, of phosphorus in the atmospheres of GD71 and two similar DA white dwarfs. This is the first detection of a trace metal in the photosphere of the spectrophotometric standard star GD71. Collectively, these objects represent the coolest DA white dwarfs in which photospheric phosphorus has been observed. We use a grid of homogeneous non-local thermodynamic equilibrium synthetic spectra to measure abundances of [P/H]=−8.57+0.09 −0.13 , −8.70+0.23 −0.37 and −8.36+0.14 −0.19 in GD71, RE J1918+595 and RE J0605−482 respectively. At the observed level we find that phosphorus has no significant impact on the overall energy distribution of GD71. We explore possible mechanisms responsible for the presence of this element in these stars, concluding that the most likely is an interplay between radiative levitation and gravitational settling, possibly modified by weak mass loss. 相似文献
5.
J. Zussman 《Earth, Moon, and Planets》1972,5(3-4):422-435
Crystallization from the molten state has been an important process for the formation of rocks on the Moon; the phenomenon of fractional crystallization is therefore discussed. The principal chemical and mineralogical features of the Apollo 11, 12 and 14 basaltic crystalline rocks are described, and an account is given of other rock types and minerals which are represented among the coarser particles in the lunar soils. A comparison is made between the chemical compositions (major, minor and trace element concentrations) of rocks and soils.Based upon the above data, one possible model for the outer shell of the Moon is presented, which consists of an outer layer of Al-rich rocks underlain by a layer which is more ferromagnesian in character. Partial melting of the latter was probably responsible for the extrusion of lavas at the surface which spread to form the basalts (Apollo 11 and 12) of the non-circular maria. The Apollo 14 (Fra Mauro) basalts are relatively enriched in potassium, rare earth elements, zirconium, phosphorus and certain other elements and may derive from partial melting of the more aluminous upper layer.The separation of the outer Moon into two layers could have occurred through gravity-aided fractional crystallization at an early stage (first few hundred m yr) in lunar history.Paper presented to the NATO Advanced Study Institute on Lunar Studies, Patras, Greece, September 1971. 相似文献
6.
Ilian T. Iliev Paul R. Shapiro 《Monthly notices of the Royal Astronomical Society》2001,325(2):468-482
An analytical model is presented for the post-collapse equilibrium structure of virialized objects that condense out of a low-density cosmological background universe, either matter-dominated or flat with a cosmological constant. This generalizes the model we derived previously for an Einstein–de Sitter (EdS) universe. The model is based upon the assumption that cosmological haloes form from the collapse and virialization of 'top-hat' density perturbations, and are spherical, isotropic and isothermal. This leads to the prediction of a unique, non-singular, truncated isothermal sphere (TIS), a particular solution of the Lane–Emden equation (suitably modified when Λ≠0) . The size and virial temperature are unique functions of the mass and redshift of formation of the object for a given background universe. The central density is roughly proportional to the critical density of the universe at the epoch of collapse. This TIS model is in good agreement with observations of the internal structure of dark-matter-dominated haloes on scales ranging from dwarf galaxies to X-ray clusters. It also reproduces many of the average properties of haloes in simulations of the cold dark matter (CDM) model to good accuracy, suggesting that it is a useful analytical approximation for haloes that form from realistic initial conditions. Our TIS model matches the density profiles of haloes in CDM N -body simulations outside the innermost region, while avoiding the steep central cusp of the latter which is in apparent conflict with observations. The TIS model may also be relevant to non-standard CDM models, such as that for self-interacting dark matter, recently proposed to resolve this conflict. 相似文献
7.
M.A. Dopita 《Astrophysics and Space Science》2000,272(1-3):79-89
This paper examines the relationship between the accretion flows into the accretion disk around the black holes of active
galactic nuclei (AGN), and the jets which they produce. A large-scale accretion flow around the nucleus is proposed as the
thick dusty toroid structure of the unified model. Physically, this is similar to the Kahn ‘cocoon star’ model. High (super-Eddington)
accretion rates into the accretion disk are needed. It is assumed that all black holes produce relativistic jets. However,
entrainment of thermal (wind) material into the jet determines the AGN class, radio-loud or radio quiet. The jet interacts
with the ambient medium as it expands, generating a cocoon of fast radiative or partially-radiative shocks around it. Such
a model can explain both the radio properties and the emission line properties over a wide variety of AGN classes.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
A model of two compact components (one contributes at radio and submillimeter wavelength and the other is very small and emits at the infrared region) is proposed to interpret the spectrum of quasi-stellar objects at radio and infrared wavelengths. The physical parameters are estimated from the observed data of 3C 273 for our model and for the model which is derived by assuming the infrared emission as an extrapolation of the synchrotron radio-source. It was proved that our model can explain the observational spectra, while the other model has some difficulties to interpret them completely.This work was partially supported by the Brasilian research agency CNPq 相似文献
9.
Samuel R. Kaplan 《Celestial Mechanics and Dynamical Astronomy》2001,79(1):1-14
We present a special model which is a caricature of the collinear three-body problem. Near triple-collision behavior for the model is governed by the collision manifold. We study the bifurcations of the dynamics on this manifold as we vary the ratio of masses. Both analytic and numerical results are presented.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献
10.
The shape of pulsar radio beams 总被引：1，自引：0，他引：1
Using all available multicomponent radio pulse profiles for pulsars with medium to long periods and good polarization data, we have constructed a two-dimensional image of the mean radio beam shape. This shows a peak near the centre of the beam but is otherwise relatively uniform with only mild enhancements in a few regions. This result supports the patchy beam model for emission beams, in which the mean beam shape represents the properties of the emission mechanism and observed pulse components result from emission sources distributed randomly across the beam. 相似文献
11.
Photolysis of NH3PH3 mixtures (11 Torr) at 175°K resulted in the same initial rate of P2H4 formation as when the 11 Torr of pure PH3 was photolyzed. A higher yield of P2H4 is obtained at 175°K than at 298°K because some of the P2H4 condenses on the cell wall at 175°K and is not subject to further reaction. Some reaction of P2H4 is taking place as observed by the decrease in its yield and on the formation of red phosphorus on extended photolysis of PH3 at 175°K. No NH2PH2 or (PN)x were detected as photoproducts as indicated by the absence of change in the UV spectral properties of the P2H4 and red phosphorus fraction, respectively, when NH3 is present. Although the pathway for PH3 decomposition is changed, the outcome of the photochemical process is essentially the same in the absence or presence of NH3. The formation of P2H4 and red phosphorus was not inhibited by small amounts of C2H4 and C2H2, so the low levels of hydrocarbons on Jupiter and Saturn will not have a significant effect on the course of PH3 photolysis. The ratio of products of PH3 photolysis are only slightly affected by the wavelength of light used. Use of xenon lamp, with a continuous emission in the ultraviolet where P2H4 absorbs, results in only a modest decrease in the yield of P2H4 and a modest increase in the rate of formation of red phosphorus as compared to the rates observed with a 206.2-nm light source. The quantum yield for P2H4 formation is pressure independent in the 0.5–11 Torr range. This quantum yield is not affected by lowering the temperature to 157°K or by the addition of 100 Torr of H2. It is concluded that photolysis of PH3 to P2H4 and the subsequent conversion of P2H4 to red phosphorus are likely procses on Jupiter and Saturn and that particles of P2H4 condense in the atmospheres of these planets. The conversion of some of the P2H4 to red phosphorus may take place on Jupiter. 相似文献
12.
Using eigenmode expansion of the Mark III and SFI surveys of cosmological radial velocities, a goodness-of-fit analysis is applied on a mode-by-mode basis. This differential analysis complements the Bayesian maximum likelihood analysis that finds the most probable model given the data. Analyzing the surveys with their corresponding most likely models from the CMB-like family of models, as well as with the currently popular LambdaCDM model, reveals a systematic inconsistency of the data with these "best" models. There is a systematic trend of the cumulative chi(2) to increase with the mode number (where the modes are sorted by decreasing order of the eigenvalues). This corresponds to a decrease of the chi(2) with the variance associated with a mode and hence with its effective scale. It follows that the differential analysis finds that on small (large) scales the global analysis of all the modes "puts" less (more) power than actually required by the data. This observed trend might indicate one of the following: (1) the theoretical model (i.e., power spectrum) or the error model (or both) have an excess of power on large scales, (2) velocity bias, or (3) the velocity data suffers from systematic errors that have not yet been corrected. 相似文献
13.
Bernd Vollmer Chantal Balkowski Veronique Cayatte 《Astrophysics and Space Science》2002,281(1-2):359-362
We investigate the effects of ram pressure stripping of spiral galaxies using a numerical model that is directly confronted
with interferometric observations. The current status of our research is presented.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
14.
D. L. Khokhlov 《Astrophysics and Space Science》2011,333(1):209-212
The Einstein static model of the universe as a whole is considered in Euclidean space and absolute time of a privileged reference
frame. The universe as a whole is stable that specifies observers at rest relative to the global space of the universe. An
observer in the centre of the universe is assumed to experience downward inertial acceleration along a certain radius due
to the kinetic energy of the universe, with the total acceleration over all radii being equal zero. This yields the Doppler
effect for the photon coming from the distant source that may explain the Hubble law in the static universe. The predictions
of the model are qualitatively in agreement with the observations in the cosmological tests of a standard candle and a standard
rod. Explanation of stretching of the light curve of SN Ia is proposed within the model considered. 相似文献
15.
This paper describes General Circulation Model (GCM) simulations of the martian water cycle focusing on the effects of an adsorbing regolith. We describe the 10-layer regolith model used in this study which has been adapted from the 1-D model developed by Zent, A.P., Haberle, R.M., Houben, H.C., Jakosky, B.M. [1993. A coupled subsurface-boundary layer model of water on Mars. J. Geophys. Res. 98 (E2), 3319-3337, February]. Even with a 30-min timestep and taking into account the effect of surface water ice, our fully implicit scheme compares well with the results obtained by Zent, A.P., Haberle, R.M., Houben, H.C., Jakosky, B.M. [1993. A coupled subsurface-boundary layer model of water on Mars. J. Geophys. Res. 98 (E2), 3319-3337, February]. This means, however, that the regolith is not able to reproduce the diurnal variations in column water vapour abundance of up to a factor of 2-3 as seen in some observations, with only about 10% of the atmospheric water vapour column exchanging with the subsurface on a daily basis. In 3-D simulations we find that the regolith adsorbs water preferentially in high latitudes. This is especially true in the northern hemisphere, where perennial subsurface water ice builds up poleward of 60° N at depths which are comparable to the Odyssey observations. Much less ice forms in the southern high latitudes, which suggests that the water ice currently present in the martian subsurface is not stable under present conditions and is slowly subliming and being deposited in the northern hemisphere. When initialising the model with an Odyssey-like subsurface water ice distribution the model is capable of forcing the simulated water cycle from an arbitrary state close to the Mars Global Surveyor Thermal Emission Spectrometer observations. Without the actions of the adsorbing regolith the equilibrated water cycle is found to be a factor of 2-4 too wet. The process by which this occurs is by adsorption of water during northern hemisphere summer in northern mid and high latitudes where it remains locked in until northern spring when the seasonal CO2 ice cap retreats. At this time the water diffuses out of the regolith in response to increased temperature and is returned to the residual water ice cap by eddie transport. 相似文献
16.
Rachel S. Somerville Joel R. Primack S. M. Faber 《Monthly notices of the Royal Astronomical Society》2001,320(4):504-528
Using semi-analytic models of galaxy formation set within the cold dark matter (CDM) merging hierarchy, we investigate several scenarios for the nature of the high-redshift ) Lyman-break galaxies (LBGs). We consider a 'collisional starburst' model in which bursts of star formation are triggered by galaxy–galaxy mergers, and find that a significant fraction of LBGs are predicted to be starbursts. This model reproduces the observed comoving number density of bright LBGs as a function of redshift and the observed luminosity function at and with a reasonable amount of dust extinction. Model galaxies at have star formation rates, half-light radii, colours and internal velocity dispersions that are in good agreement with the data. Global quantities such as the star formation rate density and cold gas and metal content of the Universe as a function of redshift also agree well. Two 'quiescent' models without starbursts are also investigated. In one, the star formation efficiency in galaxies remains constant with redshift, while in the other, it scales inversely with disc dynamical time, and thus increases rapidly with redshift. The first quiescent model is strongly ruled out, as it does not produce enough high-redshift galaxies once realistic dust extinction is accounted for. The second quiescent model fits marginally, but underproduces cold gas and very bright galaxies at high redshift. A general conclusion is that star formation at high redshift must be more efficient than locally. The collisional starburst model appears to accomplish this naturally without violating other observational constraints. 相似文献
17.
John C. Brown 《Solar physics》1972,26(2):441-459
The directivity and polarisation of solar hard X-ray bursts is discussed in terms of two bremsstrahlung source models. These involve continuous and impulsive injection of electrons respectively, as described widely in the literature.A detailed analysis is made of the continuous injection model in which electrons are accelerated downward into the dense chromosphere where their velocity distribution is greatly modified by collisions. This thick target scattering is described by a simple analytical model. Directivity and polarisation of the bremsstrahlung emission are calculated in detail for a thick target model in which the guiding magnetic field is vertical.It is predicted for this model that X-ray sources should brighten from the centre to the limb of the solar disk, while the degree of polarisation should rise from zero to around 30 % near the limb. The plane of maximum intensity for any source is that containing the source and the disk centre. Both the directivity and polarisation should increase with increasing photon energy.Very recent observations agree with these predictions though they suggest that the field is significantly non-vertical. If scattering is not included in the model, or if an impulsive injection model is taken, agreement with observations is not obtained.Temporarily at the Lehrstuhl für Theoretische Astrophysik der Universität Tübingen, West Germany. 相似文献
18.
本文在考虑磁光效应条件下,根据对斯托克斯参数转移方程组求得的数值解,计算了单极太阳黑子的线偏振讯号的单色像,并与美国马歇尔空间飞行中心的观测资料进行了对比,结果表明,径向黑子磁场模型给出与观测相似的单色像,而旋涡形模型导致与观测有显著差异的图像。因此可以认为径向模型更接近于实际情况。 相似文献
19.
The strength of regolith and rubble pile asteroids 总被引：1，自引：0，他引：1
We explore the hypothesis that, due to small van der Waals forces between constituent grains, small rubble pile asteroids have a small but nonzero cohesive strength. The nature of this model predicts that the cohesive strength should be constant independent of asteroid size, which creates a scale dependence with relative strength increasing as size decreases. This model counters classical theory that rubble pile asteroids should behave as scale‐independent cohesionless collections of rocks. We explore a simple model for asteroid strength that is based on these weak forces, validate it through granular mechanics simulations and comparisons with properties of lunar regolith, and then explore its implications and ability to explain and predict observed properties of small asteroids in the NEA and Main Belt populations, and in particular of asteroid 2008 TC3. One conclusion is that the population of rapidly rotating asteroids could consist of both distributions of smaller grains (i.e., rubble piles) and of monolithic boulders. 相似文献
20.
Based on the observations of the EUV spectroheliograms, the effective chromosphere-corona transition region is assumed to be restricted in a small volume element in the boundaries of the supergranular network. The center-to-limb variation of the quiet Sun at cm and dm wavelengths is analyzed to determine where the transition region is located in the network boundaries. Expressions are derived for the theoretical center-to-limb variation of the hypothetical brightness temperature only from the transition region, taking into account the orientation of the spicules. Comparison with the observations shows that the spicule-sheath model (Brueckner and Nicolas, 1973) and the hot plagette model (Foukal, 1974) are not compatible with the observations, because the limb brightening predicted by these models is too great. A new picture is therefore proposed that thin platelet transition regions are placed on top of the chromosphere and scattered between the network boundaries (the platelet transition-region model). This model is in accord with the observed center-to-limb variation of the radio emission. 相似文献