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171.
Lutz Hasse 《Boundary-Layer Meteorology》1976,10(4):393-407
The theoretical developments yielding the resistance law for the planetary boundary layer are summarized, including the refinements of the ageostrophic method. This leads to the hypothesis that the resistance law for the simple non-stationary, advective boundary layer is obtained from the one for a stationary, horizontally homogeneous boundary layer, if the modulous of the geostrophic wind in the latter is replaced with a generalized frictionless wind in the former. The generalized frictionless wind includes the inertial terms.Contribution from the Sonderforschungsbereich Meeresforschung Hamburg of the Deutsche Forschungsgemeinschaft. 相似文献
172.
A fold structure within a pyrite ore specimen has been analysed with respect to the amount and distribution of pyrrhotite modifications present. The relative distribution of the two types of pyrrhotite, hexagonal 5C and monoclinic 4C, was found to be strongly dependent upon the stress distribution. Within very short distances the hexagonal fraction of the total amount of pyrrhotite varied from nearly zero up to 0.65 giving steep and structurally well defined gradients. The monoclinic phase was preferably located to regions deformed by intense shearing. It is suggested that the influence of anisotropic stresses accelerated the conversion of hexagonal to monoclinic pyrrhotite. Variations in the distribution of the total amount of pyrrhotite were also observed and partly ascribed to migration of pyrrhotite. 相似文献
173.
Lutz Kübler 《Physics and Chemistry of Minerals》1985,12(6):353-362
Single crystals of hexagonal and monoclinic pyrrhotite, Fe1?xS, have been experimentally deformed by uniaxial compression at 300 MPa confining pressure, and at a strain rate of 1 × 10?5 s?1 in the temperature range from 200° C to 400° C. Very high anisotropy characterizes the mechanical behaviour of the crystal structure. During compression parallel to thec-axis, when no slip system may be activated, the maximum strength is observed. One or two degrees of non-parallelism between [c] and σ1 results in slip on the basal plane, illustrating the very low resistance of the lattice against shear in this plane. At σ1 Λ(0001)=45°, i.e. when maximum resolved shear stress is attained on the basal plane, the strength reaches a minimum. Thecritical resolved shear stress (CRSS) increases from less than 4.7 MPa at 400° C to 52 MPa at 200° C. A new slip system, \((10\overline 1 0)\parallel \left\langle {1\overline 2 10} \right\rangle \) prism slip, is described. It is activated only at high angles (>70°) between σ1 and [c]. The CRSS of the prism slip ranges from 7 MPa (400° C) to 115 MPa (200° C). Twinning on \((10\overline 1 2)[(10\overline 1 2):(1\overline 2 10)]\) , earlier reported by several authors, has been produced only at the highest temperature either as secondary feature during pressure release (compression ‖[c]) or in heterogeneously strained areas (compression ⊥[c]). As twinning and prism slip attain their maximum values of the Schmidt factor under nearly equal stress conditions it is postulated that the former of the two deformation modes has the higher shear resistance. 相似文献
174.
Geostrophic drag coefficients are obtained from direct measurements of the momentum flux and from an objective analysis of the synoptic pressure field by the method of least squares. At a site in the Kiel Bight, a mean geostrophic drag coefficient c
g
= 0.0223 was obtained with near neutral/ slightly unstable conditions and a surface Rossby Number of 1.2 × 109.Contribution of the sonderforschungsbereich Meeresforschung Hamburg der Deutschen Forschungsgemeinschaft, Hamburg, F.R.G. 相似文献
175.
176.
Volker Stähle Rainer Altherr Mario Koch Lutz Nasdala 《Contributions to Mineralogy and Petrology》2008,155(4):457-472
The microtextures of stishovite and coesite in shocked non-porous lithic clasts from suevite of the Ries impact structure
were studied in transmitted light and under the scanning electron microscope. Both high-pressure silica phases were identified
in situ by laser-Raman spectroscopy. They formed from silica melt as well as by solid-state transformation. In weakly shocked
rocks (stage I), fine-grained stishovite (≤1.8 μm) occurs in thin pseudotachylite veins of quartz-rich rocks, where it obviously
nucleated from high-pressure frictional melts. Generally no stishovite was found in planar deformation features (PDFs) within
grains of rock-forming quartz. The single exception is a highly shocked quartz grain, trapped between a pseudotachylite vein
and a large ilmenite grain, in which stishovite occurs within two sets of lamellae. It is assumed that in this case the small
stishovite grains formed by the interplay of conductive heating and shock reverberation. In strongly shocked rocks (stages
Ib–III, above ∼30 GPa), grains of former quartz typically contain abundant and variably sized stishovite (<6 μm) embedded
within a dense amorphous silica phase in the interstices between PDFs. The formation of transparent diaplectic glass in adjacent
domains results from the breakdown of stishovite and the transformation of the dense amorphous phase and PDFs to diaplectic
glass in the solid state. Coesite formed during unloading occurs in two textural varieties. Granular micrometre-sized coesite
occurs embedded in silica melt glass along former fractures and grain boundaries. These former high-pressure melt pockets
are surrounded by diaplectic glass or by domains consisting of microcrystalline coesite and earlier formed stishovite. The
latter is mostly replaced by amorphous silica. 相似文献
177.
Lutz Nasdala Ronald Miletich Katja Ruschel Tamás Váczi 《Physics and Chemistry of Minerals》2008,35(10):597-602
Pressure-induced changes of Raman band parameters of four natural, gem-quality zircon samples with different degrees of self-irradiation
damage, and synthetic ZrSiO4 without radiation damage, have been studied under hydrostatic compression in a diamond anvil cell up to ~10 GPa. Radiation-damaged
zircon shows similar up-shifts of internal SiO4 stretching modes at elevated pressures as non-damaged ZrSiO4. Only minor changes of band-widths were observed in all cases. This makes it possible to estimate the degree of radiation
damage from the width of the ν3(SiO4) band of zircon inclusions in situ, almost independent from potential “fossilized pressures” or compressive strain acting
on the inclusions. An application is the non-destructive analysis of gemstones such as corundum or spinel: broadened Raman
bands are a reliable indicator of self-irradiation damage in zircon inclusions, whose presence allows one to exclude artificial
color enhancement by high-temperature treatment of the specimen. 相似文献
178.
179.
180.
Mars is the fourth planet out from the sun. It is a terrestrial planet with a density suggesting a composition roughly similar
to that of the Earth. Its orbital period is 687 days, its orbital eccentricity is 0.093 and its rotational period is about
24 hours. Mars has two small moons of asteroidal shapes and sizes (about 11 and 6 km mean radius), the bigger of which, Phobos,
orbits with decreasing semimajor orbit axis. The decrease of the orbit is caused by the dissipation of tidal energy in the
Martian mantle. The other satellite, Deimos, orbits close to the synchronous position where the rotation period of a planet
equals the orbital period of its satellite and has hardly evolved with time. Mars has a tenous atmosphere composed mostly
of CO with strong winds and with large scale aeolian transport of surface material during dust storms and in sublimation-condensation
cycles between the polar caps. The planet has a small magnetic field, probably not generated by dynamo action in the core
but possibly due to remnant magnetization of crustal rock acquired earlier from a stronger magnetic field generated by a now
dead core dynamo. A dynamo powered by thermal power alone would have ceased a few billions of years ago as the core cooled
to an extent that it became stably stratified. Mars' topography and its gravity field are dominated by the Tharsis bulge,
a huge dome of volcanic origin. Tharsis was the major center of volcanic activity, a second center is Elysium about 100° in
longitude away. The Tharsis bulge is a major contributor to the non-hydrostaticity of the planet's figure. The moment of inertia
factor together with the mass and the radius presently is the most useful constraint for geophysical models of the Martian
interior. It has recently been determined by Doppler range measurements to the Mars Pathfinder Lander to be (Folkner et al. 1997). In addition, models of the interior structure use the chemistry of the SNC meteorites which are widely
believed to have originated on Mars. According to the models, Mars is a differentiated planet with a 100 to 200 km thick basaltic
crust, a metallic core with a radius of approximately half the planetary radius, and a silicate mantle. Mantle dynamics is
essential in forming the elements of the surface tectonics. Models of mantle convection find that the pressure-induced phase
transformations of -olivine to -spinel, -spinel to -spinel, and -spinel to perovskite play major roles in the evolution of mantle flow fields and mantle temperature. It is not very likely
that the -spinel to perovskite transition is present in Mars today, but a few 100 km thick layer of perovskite may have been present
in the lower mantle immediately above the core-mantle boundary early in the Martian history when mantle temperatures were
hotter than today. The phase transitions act to reduce the number of upwellings to a few major plumes which is consistent
with the bipolar distribution of volcanic centers of Mars. The phase transitions also cause a partial layering of the lower
mantle which keeps the lower mantle and the core from extensive cooling over the past aeons. A relatively hot, fluid core
is the most widely accepted explanation for the present lack of a self-generated magnetic field. Growth of an inner core which
requires sub-liquidus temperatures in the core would have provided an efficient mechanism to power a dynamo up to the present
day.
Received 10 May 1997 相似文献