排序方式: 共有26条查询结果,搜索用时 15 毫秒
1.
Summary Global average temperatures from 1860 to 1989 were analysed with a simple fitting procedure. The temperature records can be
fitted with a rising exponential up to 1946 and with the same exponential minus an increasing cooling action from 1946 to
1989. It is shown that the results are compatible with the hypothesis of an albedo increase caused by SO2 emissions. This hypothesis gives satisfactory explanations of the temperature drop in the years 1940–1970, of the different
warming of the northern and southern hemispheres and of the slower warming observed over North America. The results give an
indication that the greenhouse warming in the next years could be faster than predicted until now.
Due to the relevance of its scientific content, this paper has been given priority by the Journal Direction. 相似文献
2.
R. S. Brusa M. Duarte Naia D. Margoni A. Zecca 《Applied Physics A: Materials Science & Processing》1995,60(5):447-453
We have determined the positron mobility (+) in polyethylene samples (67.2% crystalline, glass transition temperatureT
g=151 K) in the 64–400 K temperature range by Doppler shift measurements. A method based on the simulataneous observation of two lines from133Ba and137Cs radioactive sources together with the positron annihilation line, was employed to measure the Doppler shift of the 511 keV line as a function of the electric field applied to the samples. With this method we were able to measure at the same time the drift velocity of positrons and theS parameter. This parameter is very important in the interpretation of the mobility trend in samples where the positron states change with temperature. The positron mobility was corrected for positronium formation. + at 64 K is 31.7±0.8 cm2 V–1 s–1 then decreases up to 123 K, increases at 148 K and decreases again up to 170 K (+=26.9±0.8 cm2 V–s–). This sharp change in mobility is centred around the glass transition temperature of our samples. Then the mobility remains almost constant up to 230 K. From 250 K to 377 K, + increases and reaches the value of 38.4±1.0 cm2 V–1s–1. The corrected experimental data were well fitted by a simple model taking into account scattering and a thermally activated process (hopping mechanism). 相似文献
3.
4.
5.
R. W. Brusa und C. Fröhlich 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1972,23(6):1009
Ohne Zusammenfassung 相似文献
6.
Some small scientific satellites can be regarded as free, multi-body, supercritical and statorless rotors. Classical rotordynamics does not cover the dynamic behaviour and the stability analysis of such rotating systems, being focused on fixed rotors. Attitude dynamics usually deals with single rigid spacecrafts, sometimes equipped with flexible appendices like solar arrays or antennas. The case of the Galileo Galilei Ground (GGG) test facility is herewith analyzed through a numerical and experimental investigation on the dynamic behaviour of a fixed multi-body fast-spinning rotor in order to validate the design approach proposed for Galileo Galilei (GG) spacecraft. 相似文献
7.
G. P. Karwasz R. S. Brusa Z. Idziaszek A. Karbowski 《The European physical journal. Special topics》2007,144(1):197-201
Total cross sections for positron scattering on benzene
and cyclohexane measured with high angular resolution in the 0.5–20 eV
range are compared with previous experimental data. Present data showing
a rise in the zero energy range agree much better with the theory than
previous experiments. The rise can be reproduced by the modified effective
range theory, using three partial waves. 相似文献
8.
The reaction between formic acid and bromine in strongly acid aqueous media at 298 K was studied by absorption spectrophotometry (λ = 447 nm). Reaction rates, expressed as R = -d[Br2]/dt, depend on the concentrations of HCOOH (0.3–2.4M), Br2[(2.7–13.6) × 10?3M], H+ (0.03–2.0M), and Br? (up to 0.6M). The mechanism with k1 = 20.2 ± 1.2 M?1 sec?1, pK2 = 3.76, pK3 = ?1.20, accounts for all experimental observations. Br3? and HCOOH can be considered unreactive within experimental error. Apparent deviations from the basic mechanism at higher acidities can be quantitatively ascribed to the nonideality of ionic species. 相似文献
9.
Rates of oxidation of XCOO? (X = H, D) by Br2 in acid aqueous media were measured between 274 and 332 K. The derived Arrhenius parameters for both reactions where θ = 4.575T × 10?3 kcal/mol, with (kH/kD)298K = 2.85, reveal a primary isotope effect, but the difference (ED - EH) = 3.29 kcal/mol and the ratio AD/AH = 91 fall beyond the limits imposed by semiclassical transition-state theory, suggesting tunneling or a multiple-stage mechanism. However, it can be shown that either tunneling in a single step or a three-step, internal return mechanism can be ruled out as alternative models, since both require unreasonable kinetic parameters to fit the data. The simplest scheme accounting for the present observations involves tunneling in the decomposition of a charge transfer complex in equilibrium with the reactants. 相似文献
10.
P. Możejko G. Kasperski Cz. Szmytkowski A. Zecca G.P. Karwasz L. Del Longo R.S. Brusa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(4):481-485
The absolute total cross-sections for electron scattering on SiCl4 molecules have been measured in two distinct electron-transmission experiments, in Gdansk and in Trento laboratory, for impact energy ranging from 0.3 to 250 eV and from 75 to 4000 eV, respectively. The e--SiCl4 total cross-section function shows two very distinct resonant-like features: the strong peak at 1.9 eV and much broader main maximum centered near 10 eV with some additional substructure close to 5 eV. The present results are compared with low-energy total experimental data and elastic theoretical calculations for electron collisions with silicon tetrachloride molecules. 相似文献