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961.
Summary Some errors of method occurring in A. C. measurements of the electrical conductivity of rocks are discussed. It is demonstrated that the difference between A.C. and D.C. conductivities, at given frequency, depends mostly on the magnitude of the D.C. conductivity and magnitude of the dielectric constant. 相似文献
962.
The evolution of the distortion of MgGeO3 enstatite and CaGeO3 wollastonite with increasing pressure, has been investigated using X-ray absorption spectroscopy (XAS) in a diamond anvil
cell. At room temperature and low pressure (P<7 GPa), the compressibility of the GeO4 tetrahedron is higher in MgGeO3 enstatite (K
[GeO4]∼135 GPa) than in CaGeO3 wollastonite (K
[GeO4]≥ 280 GPa). The compression mechanisms of the two compounds are different: the whole mineral compressibility of Ge-enstatite
appears to be very homogeneous, in contrast to that of Ge-wollastonite which exhibits an inhomogeneous tretrahedral compressibility.
This result is consistent with the variation of the Debye-Waller factors of the two compounds with increasing pressure. At
higher pressures, the coordination of germanium atoms in the two compounds gradually changes from fourfold to sixfold. For
CaGeO3 the coordination change starts at 7 GPa and is complete a 12 GPa, whereas it starts at about 8.5 GPa for MgGeO3 and is not complete at 31 GPa. The progressive evolution of the measured Ge-O distances as well as the modification in the
X-ray absorption near-edge structure indicate two coexisting different sites rather than a progressive site modification.
The transformation is found to be partially reversible in CaGeO3 wollastonite, whereas it is totally reversible in MgGeO3 enstatite. 相似文献
963.
964.
965.
Due to its physical and chemical properties, areas with a loess mantle of proper thickness favour arable farming. Loess as a parent material promotes the formation of soils of good structure, nutrient supply and water budget. The ongoing land evaluation project places particular emphasis on the consideration of parent material in its scoring system as soil and climatic parameters are assessed in conjunction with the grain size composition of subsurface material and soil texture.A test area most suitable for the presentation of the method seems to be a sandy alluvial fan with loess mantle and this circumstance allows the contrasting of the agroecological potentials of soils developed on the two parent materials of different nature.The favourable water storage properties of loess make this deposit particularly valuable under the conditions of climatic aridification. The geographical information system applied here is capable of simulating the agroecological potential changes caused by reduced precipitation, increased evaporation and dropping groundwater levels.The research for this paper was carried out as part of the MEDALUS II (Mediterranean Desertification and Land Use) collaborative research project. MEDALUS II was funded by the EC under its Environment Progamme, contract no. EV5V 0128/0166. A grant was also provided by the OTKA (Hungarian National Science Foundation), project no 1278. The support is gratefully acknowledged. 相似文献
966.
Márton Pécsi 《GeoJournal》1995,36(2-3):117-131
In the process of loessification, the development of loess fabric, the role of zonal, regional and partly of local environmental factors is regarded decisive. In the loess sequences various genetic types of loess pockets and paleosols occur and reflect different climatic and paleogeographical conditions.As a consequence, even within a single profile the colour, grain size and mineral composition, CaCO3 content, degree of weathering and fabric of loess may vary. Zonal, regional or even local variations in such loess properties may equally derive from syngenetic or postgenetic processes. For similar reasons, spatially and temporally different forms, types and subtypes of paleosol also developed.This way, loess and soil formation resulted in various spatial types in the same glacial, interstadial or interglacial phase in the various geographical zones and regions. Although there exist major loess regions where the interglacial soils (eg brown forest soils) are markedly distinct from interstadial steppe soils or from other types of humic soils, continental loess areas can also be observed where the paleosols developed under interglacial and interstadial conditions (eg steppe or forest steppe soils) cannot be referred into different genetic types. In such cases the changes in paleoenvironments are difficult and uncertain to reconstruct.The interregional correlation of paleosols is occasionally hindered by the various terminologies applied to denote them. In addition, there are uncertainties concerning the dating and identification of paleoenvironments of polygenetic soils and of soil complexes consisting of paleosol units: how many soil formation phases they represent and how long erosional gaps can be reckoned with between these phases. 相似文献
967.
研究了1992年福建省南日岛5.2级地震序列特征,认为这是一次孤立型地震,震前存在多学科的前兆异常,异常群体特征具有长、中、短临阶段性及形态复杂性.地震学异常持续时间长,前兆学科短临异常突出,可能是少震区地震前兆的特点。 相似文献
968.
Summary The classical barotropic model is used to indicate the possible connection between the intensification of atmospheric westerlies and the acceleration of the Earth's rotation. 相似文献
969.
Summary Four parameters defining the Earth's tri-axial ellipsoid (E) have been derived on the basis of the condition that the gravity potential on E be constant and equal to the actual geopotential value (W0) on the geoid. The geocentric gravitational constant, the angular velocity of the Earth's rotation, the actual 2nd degree geopotential Stokes parameters and W0 are taken to be the primary geodetic constants defining E and its (normal) gravity field. 相似文献
970.
Summary Annual average precipitation values obtained at 765 Italian raingauge stations south of the Rome parallel and in the Italian Isles, are analyzed. The analysis is extended over 18 years and marked variations in precipitation with the Zürich annual relative sunspot numbers are found. It is found furthermore that the magnitude of change appears to depend also on the average altitude of the 5 categories of stations considered.
Contribution of the Centro Nucleazione Aerosoli of the National Research Council of Italy; Via Vettore 4 (Monte Sacro) 相似文献
Riassunto In questo articolo viene fatta un'analisi sulle variazioni delle precipitazioni medie annue in base ai dati forniti da 765 stazioni pluviometriche dell'Italia meridionale, Sicilia e Sardegna, negli anni dal 1926 al 1943 incluso. Tali variazioni sembrano essere legate al numero medio annuo di macchie solari e dipendono anche dall'altezza delle stazioni.
Contribution of the Centro Nucleazione Aerosoli of the National Research Council of Italy; Via Vettore 4 (Monte Sacro) 相似文献