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71.
On hyperelasticity for clays 总被引:1,自引:0,他引:1
Under purely elastic conditions a constitutive model for clays should be conservative. This can be achieved by using a hyperelastic stress–strain relation derived from an elastic potential. To circumvent problems connected with formulation of a suitable potential a simple concept of back-stress elasticity is proposed. Several elastic models are critically reviewed, two of which had been originally incorrectly classified as hyperelastic. A novel elastic potential which can be used to generate various hyperelastic models is proposed. Its salient feature is that the resulting stiffness is a homogeneous function of order 1 with respect to stress. An example of Mathematica calculation with tensorial differentiation is enclosed (Wolfram S. Mathematica. A system for doing mathematics by computer. Addison-Wesley Publishing, 1988). © 相似文献
72.
Tourist farms in Lower Silesia, Poland 总被引:1,自引:0,他引:1
Stanisław Grykień 《GeoJournal》1998,46(3):279-281
In view of the small size of most Polish farms, attempts have been made to encourage diversification into rural tourism. The
paper examines the progress made in Lower Silesia which has good resources for domestic and international tourism. Thanks
to the promotional work of the Agricultural Consultative Centres over a hundred farms are now providing services. They do
not generate a large share of the farm income but business is expanding and some areas are becoming very popular. Thus a base
has been established for future expansion. Further development depends on easier access to credit and government support for
ecological agriculture. Better promotion is also needed to increase interest in rural tourism in Poland and attract more visitors
from abroad.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
73.
74.
Jan Kryński 《Journal of Geodesy》1979,53(1):19-36
Summary The concept of satellite-to-satellite tracking measuring the relative velocity of two orbiting satellites spaced some hundreds
kilometers on a close orbit, provides now possibilities for the investigation of the Earth’s gravity field. In the paper only
medium and short wave length effects affecting the measured relative velocity have been considered. Collocation is used in
such an analysis of local geoid improvement, because this method allows to combine heterogeneous data in a consistent way.
Covariance functions relevant for the particular case of a circular equatorial orbit are given. Two kinds of observation equations
have been formulated. The choice of observation equation with regard to satellites configuration is discussed.
It is found that it is sufficient to have a limited number of satellite-to-satellite observations in a 7o×7o area around the estimation point with distances between profiles of about 1o.5 and between the two satellites forming the pair of 200+350 km; the altitude of satellite-to-satellite observations should
be as low as possible. The accuracy of the geoid determination strongly depends on the degree and order of the reference field
used. An accuracy of about ±1 m can be achieved with an assumed reference field of (40,40).
The influence of measuring errors is discussed and it is shown that only satellite-to-satellite observations with accuracy
better then 0.1 mm/sec will give an improvement of the geoid. Finally, some results on the combination of low-low satellite-to-satellite
tracking and terrestrial gravity data are given.
The proposed method seems to be especially interesting for unsurveyed areas. Furthermore, it has the practical advantage that
only a local coverage data is needed. 相似文献
75.
Andrzej Kijko 《Pure and Applied Geophysics》1977,115(4):1011-1021
Summary Seven optimal networks consisting of 4 to 10 stations are compared for a given region, where velocity-depth profiles and the distribution of seismic intensity are known. Assuming that the standard error of arrival time is
t
=0.05 s and the standard errors of the parameters of velocity-depth profiles are equal to 5% of their values, the average standard errors of the origin time
and focus coordinates
are estimated. The application of optimum methods to the planning of seismic networks in the Lublin Coal Basin is presented, and maps of standard errors of origin time
, depth
and epicenter (
xy
) for the case of an optimum network of 6 seismic stations are given. 相似文献
76.
Summary Satellite gradiometry is studied as a means to improve the geoid in local areas from a limited data coverage. Least-squares
collocation is used for this purpose because it allows to combine heterogeneous data in a consistent way and to estimate the
integrated effect of the attenuated spectrum. In this way accuracy studies can be performed in a general and reliable manner.
It is shown that only three second-order gradients contribute significantly to the estimation of the geoidal undulations and
that it is sufficient to have gradiometer data in a 5°×5° area around the estimation point. The accuracy of the geoid determination
is strongly dependent on the degree and order of the reference field used. An accuracy of about ±1 m can be achieved with
a reference field of (12, 12). There is an optimal satellite altitude for each reference field and this altitude may be higher
than 300 km for a field of low degree and order. The influence of measuring errors is discussed and it is shown that only
gradiometer data with accuracies better than ±0.05 E will give a significant improvement of the geoid. Finally, some results
on the combination of satellite gradiometry and terrestrial gravity measurements are given.
The proposed method seems to be well suited for local geoid determinations down to the meter range. It is especially interesting
for unsurveyed and difficult areas because no terrestrial measurements are necessary. Furthermore, it has the practical advantage
that only a local data coverage is needed. 相似文献
77.
On the basis of thermodynamic calculations, diagrams of metastable electrochemical equilibria of the system copper-potassium ethylxanthate-water, at 25°C were constructed. The equilibria equations and diagrams for the total activity of [EtX?] + [HEtX] + 2 [(EtX)2] (equalling 10?1, 10?4 and 10?7 mol/dm3), are presented. The practical conclusions resulting from these diagrams for the flotation of native copper are discussed. 相似文献
78.
79.
80.
Andrzej J. Maciejewski Maria Przybylska 《Celestial Mechanics and Dynamical Astronomy》2011,110(1):17-30
We consider the planar problem of three bodies which attract mutually with the force proportional to a certain negative integer
power of the distance between the bodies. We show that such generalisation of the gravitational three-body problem is not
integrable in the Liouville sense. 相似文献