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1.
We present the astrophysical conditions necessary for the ejection of shielded microorganisms from a solar system and the biological conditions involving ultraviolet and ionizing radiations to which they are subjected in space. The radiation dose for both UV and ionizing radiation from the host star, the destination star and interstellar space is calculated for three different micro-organisms. The time of transport and the survival of the micro-organisms are strongly dependent on the composition and thickness of any mantle encasing the micro-organism and on the mass/luminosity ratio of the two stars. The maximum size of grains that can be ejected from the vicinity of one solar mass main sequence and red giant stars ranges from 0.65-0.35µm and 2.1-1.2µm respectively, for a reasonable range of densities. We conclude that unshielded known micro-organisms are immediately killed by ultraviolet radiation, and that an ice mantle does not provide sufficient shielding for either type of star. However, micro-organisms shielded by a carbonaceous thin-film mantle can be ejected from the vicinity of a one solar-mass red-giant star, and such micro-organisms have a high probability of surviving damage from the ultraviolet and ionizing radiations to which they are exposed. 相似文献
2.
Triggered earthquakes and deep well activities 总被引:1,自引:0,他引:1
Earthquakes can be triggered by any significant perturbation of the hydrologic regime. In areas where potentially active faults are already close to failure, the increased pore pressure resulting from fluid injection, or, alternatively, the massive extraction of fluid or gas, can induce sufficient stress and/or strain changes that, with time, can lead to sudden catastrophic failure in a major earthquake. Injection-induced earthquakes typically result from the reduction in frictional strength along preexisting, nearby faults caused by the increased formation fluid pressure. Earthquakes associated with production appear to respond to more complex mechanisms of subsidence, crustal unloading, and poroelastic changes in response to applied strains induced by the massive withdrawal of subsurface material. As each of these different types of triggered events can occur up to several years after well activities have begun (or even several years after all well activities have stopped), this suggests that the actual triggering process may be a very complex combination of effects, particularly if both fluid extraction and injection have taken place locally. To date, more than thirty cases of earthquakes triggered by well activities can be documented throughout the United States and Canada. Based on these case histories, it is evident that, owing to preexisting stress conditions in the upper crust, certain areas tend to have higher probabilities of exhibiting such induced seismicity. 相似文献
3.
Quantifying Organization of Atmospheric Turbulent Eddy Motion Using Nonlinear Time Series Analysis 总被引:3,自引:0,他引:3
Using three methods from nonlinear dynamics, we contrast the level of organization inthe vertical wind velocity (w) time series collected in the atmospheric surface layer(ASL) and the canopy sublayer (CSL) for a wide range of atmospheric stability ()conditions. The nonlinear methods applied include a modified Shannon entropy, waveletthresholding, and mutual information content. Time series measurements collected overa pine forest, a hardwood forest, a grass-covered forest clearing, and a bare soil, desertsurface were used for this purpose. The results from applying all three nonlinear timeseries measures suggest that w in the CSL is more organized than that in the ASL, and that as the flows in both layers evolve from near-neutral to near-convective conditions, the level of organization increases. Furthermore, we found that the degree of organization in w associated with changes in is more significant than the transition from CSL to ASL. 相似文献
4.
5.
An exact solution of the transport equation in radiative transfer for an axially symmetric Rayleigh scattering problem in semi-infinite planetary atmosphere both for emergent intensity and intensity at any optical depth has been derived with the help of the Laplace transform and the Wiener-Hopf technique, and by use of the constancy of net flux. Chandrasekhar's results for emergent intensity have been verified. New expressions for theH
l
andH
r
functions have been obtained. 相似文献
6.
The definition of the Richter Ml magnitude scale is in terms of seismic wave horizontal components recorded on Wood‐Anderson seismographs. However, at many seismograph sites only the vertical component is available, and at sedimentary sites horizontal components are usually significantly amplified, causing complications in the assignment of a magnitude to an earthquake. Because each earthquake can be recorded at a different subset of sites, each subset having a different combination of site amplifications, the assignment of a magnitude is dependent upon the seismograph site combination that records a particular earthquake. Although there is some amplification of the vertical component at sedimentary foundation sites, it is shown that a reduced spread of values of Ml magnitude, consistent with low amplification (bedrock) site magnitudes, can be achieved using the vertical component to compute the magnitude and adding 0.2 to adjust to the Ml magnitude scale (defined in terms of the horizontal components). This presupposes that the sites used by Richter were on bedrock; however, even if this is incorrect, it appears to be a necessary precondition for the world‐wide unification of the Richter scale along with defining the true gain of Wood‐Anderson seismographs rather than accepting the design gain of 2800. Site corrections would be smaller than those established using the horizontal components. Taking into account the use of only the vertical component in the calculation of Ml and including the 0.2 adjustment to the equivalent horizontal component derived magnitude, the expression for the calculation of magnitudes in the Victoria region becomes: Ml = logAz ‐ logSz + 0.9 + logR + 0.0056Re‐0.0013R where Az is the equivalent Wood‐Anderson seismograph displacement amplitude, Sz is the site amplification (vertical component) and R is the hypocentral distance. 相似文献
7.
Derek Burrage Joel Wesson Carlos Martinez Tabare Pérez Osmar Möller Jr. Alberto Piola 《Continental Shelf Research》2008
Major river systems discharging into continental shelf waters frequently form buoyant coastal currents that propagate along the continental shelf in the direction of coastal trapped wave propagation (with the coast on the right/left, in the northern/southern hemisphere). The combined flow of the Uruguay and Paraná Rivers, which discharges freshwater into the Río de la Plata estuary (Lat. ∼36°S), often gives rise to a buoyant coastal current (the ‘Plata plume’) that extends northward along the continental shelf off Uruguay and Southern Brazil. Depending upon the prevailing rainfall, wind and tidal conditions, the Patos/Mirim Lagoon complex (Lat. ∼32°S) may also produce a freshwater outflow plume that expands across the inner continental shelf. Under these circumstances the Patos outflow plume can be embedded in temperature, salinity and current fields that are strongly influenced by the larger Plata plume. The purpose of this paper is to present observations of such an embedded plume structure and to determine the dynamical characteristics of the ambient and embedded plumes. 相似文献
8.
Paul S. Wesson 《Astrophysics and Space Science》1975,36(2):363-382
Attention is given to the radiation of microwaves by charged dust in space. Presently-used particle distributions do not restrict the presence in space of large numbers of small (r<10–6 cm) silicate grains, but it is shown that such densities (10–25–10–26 g cm–3) of small grains would produce a microwave background with an energy density of the same order of magnitude as the energy density of the (presumed) cosmological 3 K background. Limits set by the isotropy of the latter are: (HI clouds)10–26, (Galactic plane)10–30, (Halo)10–32, (Local Group)10–34 g cm–3. These limits imply that either there is a cutoff in particle distributions atr10–6 cm, or that the density of silicate grains in space has been generally overestimated, or that cosmic rays have broken up a lot of grains so that they now form a population of grains of very small size (10–7 cm) which are difficult to detect by conventional methods. One way to look for the latter population is by studying expected distortions of the 3 K spectrum to the short wavelength side of the portion hitherto observed (grains may have a size distribution able to give an approximate black-body curve for radiation from larger grains of 10–6 cm size), and by testing the effective energy density of the 3 K field in other galaxies. 相似文献
9.
Paul S. Wesson 《Astrophysics and Space Science》1978,54(2):489-495
An exact solution of Einstein's equation is stated in which the density (), pressure (p), scale factorS and metric coefficients are functions of only one dimensionless self-similar variable,ct/R, wheret is cosmic time andR is a co-moving radial coordinate. The solution represents a cosmology that begins as a static sphere having R
–2 and evolves into an expanding model which is pressure-free and has a hierarchical type of density law ( R
–, approximately, with =a number, 02). It is suggested that this model should supersede the previous models of Wesson and other workers, since it appears to be the simplest cosmology for a hierarchy. 相似文献
10.
Paul S. Wesson 《Astrophysics and Space Science》1976,42(2):285-330
A semi-continuous hierarchy, (i.e., one in which there are galaxies outside clusters, clusters outside superclusters etc.), is examined using an expression of the field equations of general relativity in a form due to Podurets, Misner and Sharp. It is shown (a) that for a sufficiently populous hierarchy, the thinning factor(
i+1/
i
[r
i
/r
i+1]
is approximately equal to the exponentN in a continuous density law (=aR
–N) provided (r
i
/r
i+1)3-1; (b) that a hierarchical Universe will not look decidedly asymmetric to an observer like a human being because such salient observers live close to the densest elements of the hierarchy (viz stars), the probability of the Universe looking spherically symmetric (dipole anisotropy0.1 to such an observer being of order unity; (c) the existence of a semi-continuous or continuous hierarchy (Peebles) requires that 2 if galaxies, not presently bound to clusters were once members of such systems; (d) there are now in existence no less than ten arguments for believing 2, though recent number counts by Sandageet al. seem to be in contradiction to such a value; (e) Hubble's law, withH independent of distance, can be proved approximately in a relativistic hierarchy provided (i)N=2, (ii)2GM(R)/c
2
R1; (iii)Rc (iv)M0 in a system of massM, sizeR (f) Hubble's law holds also in a hierarchy with density jumps; (g)H100 km s–1 Mpc–1; (h) objects forming the stellar level of the hierarchy (in a cosmology of the Wilson type) must once have had 2GM/c
2
R1; (i) there is a finite pressurep=2Ga in all astrophysical systems (a=R
N
,N2); (j) for the Galaxy, theory predictsp
G7×10–12 dyn cm–2, observation givesp
G5×10–12 dyn cm–2; (k) if the mass-defect (or excess binding energy) hypothesis is taken as a postulate, all non-collapsed astrophysical systems must be non-static, and any non-static, p0 systems must in any case be losing mass; (1) the predicted mass-loss rate from the Sun is 1012 g s–1, compared to 1011 g s–1 in the observed solar wind; (m) the mass-loss rates known by observation imply timescales of 5×109 years for the Sun and 1010 years for other astrophysical systems; (n) degenerate superdense objects composed of fermions must haveN-2 if they were ever at their Schwarzschild radii and comprised a finite numberN
B of baryons; (o)N
B1057N
for degenerate fermion and boson systems; (p)285-4; (q) the metric coefficients for superdense bodies give equations of motion that imply equal maximum luminosities for all evolving superdense bodies (L
max1059 erg s–1); (r) larger bodies have longer time-scales of energy radiation atL
max (10–5 s for stars,1 h for QSO's) (s) expansion velocities are c soon after the initial loss of equilibrium in a superdense object; (t) if the density parametera(t) in aR
–N isa=a (non-atomic constants of physicsc, G, A), andA, thenN=2; (u) N2 is necessary to giveMM
at the stellar level of the hierarchy;(v) systems larger than, and including, galaxies must have formed by clumping of smaller systems and not (as advocated by Wertz and others) in a multiple big bang. 相似文献