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1.
This paper deals with the solution of the problem of the dynamic response of the leg of a tension leg platform subjected to an axial, suddenly applied load at one end, considering a highly simplified model but taking into account several complicating factors. The problem is solved by means of a non-harmonic Fourier expansion in terms of eigenfunctions obtained from a non-regular Sturm-Liouville system. 相似文献
2.
3.
A clamped square-plate is subjected to a uniform state of stress in the x-direction. The present study deals with the basic question of determining the variation of the lower natural frequencies of transverse vibration of a plate as a small diameter, central hole is made in it, introducing a stress concentration field. 相似文献
4.
R.E. Rossi P.M. Belles P.A.A. Laura S. La Malfa L. Ercoli D. Pasqua 《Ocean Engineering》1996,23(3):271-276
A numerical solution is obtained for the title problem by means of the popular finite element method. An experimental investigation of the problem is also presented for plates of square planform. The agreement between theoretical and experimental values is very good in the case of the fundamental frequency, and reasonably good when the second and third normal modes of transverse vibration are considered. It is concluded that beneficial effects are obtained in the sense that one generates a lighter structural element with higher fundamental frequency of transverse vibration. Hence, dynamic stiffening is achieved. 相似文献
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6.
Production of a molybdophore during metal-targeted dissolution of silicates by soil bacteria 总被引:1,自引:0,他引:1
Laura J. Liermann Robin L. Guynn Ariel Anbar Susan L. Brantley 《Chemical Geology》2005,220(3-4):285-302
Although many bioessential metals are scarce in natural water and rock systems, microbial secretion of high-affinity ligands for metal extraction from solid phases has only been documented for Fe. However, we have discovered that Mo is extracted from a silicate by a high-affinity ligand (a possible “molybdophore”) secreted by an N2-fixing soil bacterium. The putative molybdophore, aminochelin, is secreted as a siderophore under Fe-depleted conditions, but is also secreted under Fe-sufficient, Mo-depleted conditions. Presumably, molybdophore production facilitates uptake of Mo for use in Mo enzymes. In contrast, an Fe-requiring soil bacterium without a special Mo requirement only enhances the release of Fe from the silicate. Fractionation of Mo stable isotopes during uptake to cells may provide a “fingerprint” for the importance of chelating ligands in such systems. Many such metal-specific ligands secreted by prokaryotes for extraction of bioessential metals, their effects on Earth materials, and their possible utility in the recovery of economic metals remain to be discovered. 相似文献
7.
Adsorption of Copper, Nickel, and Cadmium on Goethite in the Presence of Organic Ligands 总被引:2,自引:0,他引:2
Adsorption of copper, cadmium and nickel at low concentrations on goethite was studied in the presence of the simple organic
ligands oxalate, salicylate, and pyromellitate. The experimental metal adsorption behavior was compared to calculations with
a surface complexation model to evaluate the most important interactions. Oxalate mostly decreased Cu and Ni adsorption at
high pH-values by competition between solution and surface complexation but had no effect on Cd adsorption. Cu adsorption
in the presence of oxalate below pH 6 could best be described by defining a ternary complex of type A (surface-metal-ligand).
Salicylate had only minor effects on metal adsorption. The adsorption of Cu in the presence of salicylate above pH 5 could
be explained by a ternary complex of type A. Pyromellitate increased the adsorption of Cu and Cd in the acidic pH-range, likely
by formation of ternary surface complexes of type B (surface-ligand-metal). 相似文献
8.
9.
The occurrence of a severe storm in the Argentine littoral has been analyzed. Although general atmospheric conditions were not favorable to the development of deep convection, this storm produced strong winds and hail of considerable intensity. Its occurrence was associated with the entrance of a pulse of humid air at low levels and could be related to the development of two vorticity centers in the region. Atmospheric conditions existing above a low-level inversion are used to simulate two possible clouds, with base altitudes at 2200 and 3000 m and updraft speeds reaching maximum values of 27 and 29 m s−1 respectively. It is noted that the base temperature of about 13°C, found for the first cloud, can be correlated with the prevalence of frozen drop embryos, observed in an analyzed hailstone sample. Hailstone vertical trajectories are simulated in both modeled clouds, assuming spheroidal and spherical particles and assigning different values to the drag coefficient Cd. 相似文献
10.
Filippo Giorgi Erika Coppola Francesca Raffaele Gulilat Tefera Diro Ramon Fuentes-Franco Graziano Giuliani Ashu Mamgain Marta Pereira Llopart Laura Mariotti Csaba Torma 《Climatic change》2014,125(1):39-51
We analyze changes of four extreme hydroclimatic indices in the RCP8.5 projections of the Phase I CREMA experiment, which includes 21st century projections over 5 CORDEX domains (Africa, Central America, South America, South Asia, Mediterranean) with the ICTP regional model RegCM4 driven by three CMIP5 global models. The indices are: Heat Wave Day Index (HWD), Maximum Consecutive Dry Day index (CDD), fraction of precipitation above the 95th intensity percentile (R95) and Hydroclimatic Intensity index (HY-INT). Comparison with coarse (GPCP) and high (TRMM) resolution daily precipitation data for the present day conditions shows that the precipitation intensity distributions from the GCMs are close to the GPCP data, while the RegCM4 ones are closer to TRMM, illustrating the added value of the increased resolution of the regional model. All global and regional model simulations project predominant increases in HWD, CDD, R95 and HY-INT, implying a regime shift towards more intense, less frequent rain events and increasing risk of heat wave, drought and flood with global warming. However, the magnitudes of the changes are generally larger in the global than the regional models, likely because of the relatively low “climate sensitivity” of the RegCM4, especially when using the CLM land surface scheme. In addition, pronounced regional differences in the change signals are found. The data from these simulations are available for use in impact assessment studies. 相似文献