排序方式: 共有6条查询结果,搜索用时 15 毫秒
1
1.
2.
桥梁结构在各种荷载作用下产生的内力和弯矩影响着桥梁的性能.桥梁弯曲、扭转和挠度等过大时会导致结构的破坏,这在结构设计阶段就应加以分析.本文提出一种有限条简化分析方法,可以较好地分析桥梁的挠度、弯曲和扭转变形.通过对一座简支板梁桥模型的分析,与现行有限元方法的分析结果进行了比较.结果表明,本方法能够较好地处理边界条件,只需要很少的输入工作就可以得到正确的分析结果,从而为结构工程师提供了一种用于分析板梁桥在交通荷载作用下行为的有效工具. 相似文献
3.
4.
An intense stratospheric jet on Jupiter 总被引:1,自引:0,他引:1
Flasar FM Kunde VG Achterberg RK Conrath BJ Simon-Miller AA Nixon CA Gierasch PJ Romani PN Bézard B Irwin P Bjoraker GL Brasunas JC Jennings DE Pearl JC Smith MD Orton GS Spilker LJ Carlson R Calcutt SB Read PL Taylor FW Parrish P Barucci A Courtin R Coustenis A Gautier D Lellouch E Marten A Prangé R Biraud Y Fouchet T Ferrari C Owen TC Abbas MM Samuelson RE Raulin F Ade P Césarsky CJ Grossman KU Coradini A 《Nature》2004,427(6970):132-135
The Earth's equatorial stratosphere shows oscillations in which the east-west winds reverse direction and the temperatures change cyclically with a period of about two years. This phenomenon, called the quasi-biennial oscillation, also affects the dynamics of the mid- and high-latitude stratosphere and weather in the lower atmosphere. Ground-based observations have suggested that similar temperature oscillations (with a 4-5-yr cycle) occur on Jupiter, but these data suffer from poor vertical resolution and Jupiter's stratospheric wind velocities have not yet been determined. Here we report maps of temperatures and winds with high spatial resolution, obtained from spacecraft measurements of infrared spectra of Jupiter's stratosphere. We find an intense, high-altitude equatorial jet with a speed of approximately 140 m s(-1), whose spatial structure resembles that of a quasi-quadrennial oscillation. Wave activity in the stratosphere also appears analogous to that occurring on Earth. A strong interaction between Jupiter and its plasma environment produces hot spots in its upper atmosphere and stratosphere near its poles, and the temperature maps define the penetration of the hot spots into the stratosphere. 相似文献
5.
Temperature-sensitive mutant of avian erythroblastosis virus suggests a block of differentiation as mechanism of leukaemogenesis. 总被引:26,自引:0,他引:26
A temperature sensitive mutant has been isolated for the first time from a replication defective acute leukaemia virus, AEV. In vivo, at 41 degrees C, the mutant shows a reduced leukaemogenic potential. In vitro, in erythroblasts transformed at 35 degrees C, haemoglobin synthesis can be induced by a shift to 41 degrees C. This indicates that the continuous expression of a viral gene product is necessary to maintain the undifferentiated state of the virus-transformed leukaemia cells. 相似文献
6.
de Bernardis P Ade PA Bock JJ Bond JR Borrill J Boscaleri A Coble K Crill BP De Gasperis G Farese PC Ferreira PG Ganga K Giacometti M Hivon E Hristov VV Iacoangeli A Jaffe AH Lange AE Martinis L Masi S Mason PV Mauskopf PD Melchiorri A Miglio L Montroy T Netterfield CB 《Nature》2000,404(6781):955-959
The blackbody radiation left over from the Big Bang has been transformed by the expansion of the Universe into the nearly isotropic 2.73 K cosmic microwave background. Tiny inhomogeneities in the early Universe left their imprint on the microwave background in the form of small anisotropies in its temperature. These anisotropies contain information about basic cosmological parameters, particularly the total energy density and curvature of the Universe. Here we report the first images of resolved structure in the microwave background anisotropies over a significant part of the sky. Maps at four frequencies clearly distinguish the microwave background from foreground emission. We compute the angular power spectrum of the microwave background, and find a peak at Legendre multipole Ipeak = (197 +/- 6), with an amplitude delta T200 = (69 +/- 8) microK. This is consistent with that expected for cold dark matter models in a flat (euclidean) Universe, as favoured by standard inflationary models. 相似文献
1