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31.
Martin M. Roth Thomas Fechner Dieter Wolter Andreas Kelz Thomas Becker 《Experimental Astronomy》2002,14(2):99-105
PMAS, the Potsdam Multi-Aperture Spectrophotometer, is a new integral field spectrograph in the optical, which is optimized
for good transmission and high image quality from 350 nm to 1 μm. We present our plan to implement a CCD charge-shuffle mode
to allow for beam switching with a very high degree of sky subtraction accuracy for faint object 3-D spectroscopy.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
32.
Miniature gravity corer for recovering short sediment cores 总被引:12,自引:0,他引:12
John R. Glew 《Journal of Paleolimnology》1991,5(3):285-287
33.
In this paper the second order characteristic (discontinuous bifurcation) condition is derived for the granular flow (fully plastic) equations. This second order bifurcation equation is shown to be formally identical to the first order localization requirement during steady elastoplastic deformation provided the elastic compliance tensor is substituted for the product of the plastic multiplier with the flow Hessian. For isotropic yield and flow functions the invariant form of the characteristic condition is given in detail, as well as an alternative expression in adapted co‐ordinates. The characteristic condition can be regarded as defining a hardening function which is maximized to identify the critical angles. When the method is applied to 3D Coulomb flow, Mohr's 3D fracture plane conditions are obtained uniquely. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
34.
In this paper, we present 50 surface water samples collected during the IMAGES III cruise (June–July 1997) along a transect from New Zealand to the China Sea (42°S–178°E, 21°N–120°E) covering a temperature range from 13.3 to 30.4 °C. A very worthwhile aspect of this study is a coupling of both biomarker (alkenone) and coccolithophorid counting. We show that the U37k′–temperature relationship is very similar to the Prahl et al. [Geochim. Cosmochim. Acta 52 (1988) 2203] culture calibration and to the global core top calibration of Müller et al. [Geochim. Cosmochim. Acta 62 (1998) 1757]. However, in the warmest surface waters of the Western Pacific ocean (>26.4 °C) where Gephyrocapsa oceanica is likely the most widespread species, the associated U37k′ has a constant value of 1.0. The consequence is that above this temperature threshold, U37k′ cannot be used as an accurate paleothermometer. 相似文献
35.
We derive the classical Delaunay variables by finding a suitable symmetry action of the three torus T3 on the phase space of the Kepler problem, computing its associated momentum map and using the geometry associated with this structure. A central feature in this derivation is the identification of the mean anomaly as the angle variable for a symplectic S
1 action on the union of the non-degenerate elliptic Kepler orbits. This approach is geometrically more natural than traditional ones such as directly solving Hamilton–Jacobi equations, or employing the Lagrange bracket. As an application of the new derivation, we give a singularity free treatment of the averaged J
2-dynamics (the effect of the bulge of the Earth) in the Cartesian coordinates by making use of the fact that the averaged J
2-Hamiltonian is a collective Hamiltonian of the T3 momentum map. We also use this geometric structure to identify the drifts in satellite orbits due to the J
2 effect as geometric phases. 相似文献
36.
Belinda Kalomeni E. Rennan PekÜnlÜ Kadri Yakut 《Astrophysics and Space Science》2005,296(1-4):477-480
In this study, we present a photometric study of AM Her, a prototype of a class of magnetic CVs. Optical photometry of AM
Her was obtained using the Russian–Turkish 1.5 m telescope at TüBİTAK National Observatory (TUG) in August 2003. The R band light curve of the system shows two maxima and two minima during one orbital cycle. In both observing nights the star
showed flickering at a significant level. The measured flickering time scale is about 5 min. 相似文献
37.
Hari Om Vats 《Journal of Astrophysics and Astronomy》2006,27(2-3):227-235
Examples of extreme events of solar wind and their effect on geomagnetic conditions are discussed here. It is found that there
are two regimes of high speed solar wind streams with a threshold of ∼ 850 km s-1. Geomagnetic activity enhancement rate (GAER) is defined as an average increase in Ap value per unit average increase in
the peak solar wind velocity (Vp) during the stream. GAER was found to be different in the two regimes of high speed streams
with +ve and-ve IMF. GAER is 0.73 and 0.53 for solar wind streams with +ve and -ve IMF respectively for the extremely high
speed streams (< 850 km s-1). This indicates that streams above the threshold speed with +ve IMF are 1.4 times more effective in enhancing geomagnetic
activity than those with -ve IMF. However, the high speed streams below the threshold with -ve IMF are 1.1 times more effective
in enhancing geomagnetic activity than those with +ve IMF. The violent solar activity period (October–November 2003) of cycle
23 presents a very special case during which many severe and strong effects were seen in the environment of the Earth and
other planets; however, the z-component of IMF (Bz) is mostly positive during this period. The most severe geomagnetic storm
of this cycle occurred when Bz was positive. 相似文献
38.
Burkhard Fuchs 《Astrophysics and Space Science》2003,284(2):719-722
An update of the set of low surface brightness galaxies is presented which can be used to set constraints on the otherwise
ambiguous decompositions of their rotation curves into contributions due to the various components of the galaxies. The selected
galaxies show all clear spiral structure and arguments of density wave theory of galactic spiral arms are used to estimate
the masses of the galactic disks. Again these estimates seem to indicate that the disks of low surface brightness galaxies
might be much more massive than currently thought. This puzzling result contradicts stellar population synthesis models. This
would mean also that low surface brightness galaxies are not dominated by dark matter in their inner parts.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
39.
M.L. Litvak I.G. Mitrofanov A.B. Sanin W.V. Boynton D. Hamara R.S. Saunders 《Icarus》2006,180(1):23-37
In this paper, we have analyzed neutron spectroscopy data gathered by the High Energy Neutron Detector (HEND) instrument onboard Mars Odyssey for comparison of polar regions. It is known that observation of the neutron albedo of Mars provides important information about the distribution of water-ice in subsurface layers and about peculiarities of the CO2 seasonal cycle. It was found that there are large water-rich permafrost areas with contents of up to ∼50% water by mass fraction at both the north and south Mars polar regions. The water-ice layers at high northern latitudes are placed close to the surface, but in the south they are covered by a dry and relatively thick (10-20 cm) layer of soil. Analysis of temporal variations of neutron flux between summer and winter seasons allowed the estimation of the masses of the CO2 deposits which seasonally condense at the polar regions. The total mass of the southern seasonal deposition was estimated as 6.3×1015 kg, which is larger than the total mass of the seasonal deposition at the north by 40-50%. These results are in good agreement with predictions from the NASA Ames Research Center General Circulation Model (GCM). But, the dynamics of the condensation and sublimation processes are not quite as consistent with these models: the peak accumulation of the condensed mass of CO2 occurred 10-15 degrees of Ls later than is predicted by the GCM. 相似文献
40.
A new model of albedo and emissivity of planetary surfaces covered by volatile ices in the form of porous slab-like deposits is described. In the model, a radiative transfer model is coupled with a microphysical model in order to link changes in albedo and emissivity to changes in porosity caused by ice metamorphism. Preliminary results for Triton, Pluto, and Io are presented (the martian CO2 caps will be the subject of a separate publication). The coupled model will aid in the interpretation of ground-based and spacecraft observations and should lead to advances in surface and atmospheric modeling. 相似文献