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941.
Some experimental data on the process of impulsive ultrasonic machining are presented. Also given are the data on variations in the impulsive vibration frequency of a workpiece and a tool. 相似文献
942.
T Takakura E Goto M Tanaka 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(4-5):255-258
An axis clinostat was constructed to create micro and negative gravity also a rotated flat disk was constructed with different rotation rates to give increased gravity, by centrifugal force up to 48 g. Rice seeds were grown on agar in tubes at the constant air temperature of 20 degrees C under an average light condition of 110 micromol/m2/sec(PPF). Humidity was not controlled but was maintained above 90%. Since the tube containers were not large enough for long cultivation, shoot and root growth were observed every 12 hours until the sixth day from seeding. The lengths of shoots and roots for each individual plant were measured on the last day. The stem lengths were increased by microgravity but the root lengths were not. Under the negative gravity, negative orthogeotropism and under microgravity, diageotropism was observed. No significant effect of increased gravity was observed on shoot and root growth. 相似文献
943.
944.
G. A. Gusev B. N. Lomonosov K. M. Pichkhadze N. G. Polukhina V. A. Ryabov T. Saito V. K. Sysoev E. L. Feinberg V. A. Tsarev V. A. Chechin 《Cosmic Research》2006,44(1):19-38
An estimate of the feasibility of the ultrahigh-energy cosmic ray and neutrino detection using a lunar satellite-borne radio receiver is presented. The data obtained in the proposed experiment will make resolving the current contradictions in the ultrahigh-energy cosmic ray spectra measured with the major ground-based instruments possible. Moreover, they will enable us to considerably extend the accessible energy range and to check predictions of various models of the origin of the highest-energy particles in the Universe. At the same time the lunar radio detector provides a means of searching for ultrahigh-energy neutrinos with a high sensitivity combined with a very large target effective mass. 相似文献
945.
F. Montmessin 《Space Science Reviews》2006,125(1-4):457-472
Solar variability influences the climate of a planet by radiatively forcing changes over a certain timescale; orbital variations
of a planet, which yield similar solar forcing modulations, can be studied within the same scientific context. It is known
for Earth that obliquity changes have played a critical role in pacing glacial and interglacial eras. For Mars, such orbital
changes have been far greater and have generated extreme variations in insolation. Signatures associated with the presence
of water ice reservoirs at various positions across the surface of Mars during periods of different orbital configurations
have been identified. For this reason, it has been proposed that Mars is currently evolving between ice ages. The advent of
climate tools has given a theoretical frame to the study of orbitally-induced climate changes on Mars. These models have provided
an explanation to many puzzling observations, which when put together have permitted reconstruction of almost the entire history
of Mars in the last 10 million years. This paper proposes to give an overview of the scientific work dedicated to this topic. 相似文献
946.
Understanding properties of solar energetic particle (SEP) events associated with coronal mass ejections has been identified
as a key problem in solar-terrestrial physics. Although recent CME shock acceleration models are highly promising, detailed
agreement between theoretical predictions and observations has remained elusive. Recent observations from ACE have shown substantial
enrichments in the abundances of 3He and He+ ions which are extremely rare in the thermal solar wind plasma. Consequently, these ions act as tracers of their source material,
i.e.,
3He ions are flare suprathermals and He+ ions are interstellar pickup ions. The average heavy ion composition also exhibits unsystematic differences when compared
with the solar wind values, but correlates significantly with the ambient suprathermal material abundances. Taken together
these results provide compelling evidence that CME-driven shocks draw their source material from the ubiquitous but largely
unexplored suprathermal tail rather than from the more abundant solar wind peak. However, the suprathermal energy regime has
many more contributors and exhibits much larger variability than the solar wind, and as such needs to be investigated more
thoroughly. Answers to fundamental new questions regarding the preferred injection of the suprathermal ions, the spatial and
temporal dependence of the various sources, and the causes of their variability and their effects on the SEP properties are
needed to improve agreement between the simulations and observations. 相似文献
947.
M. van der Klis 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2675-2679
Some aspects of the rapid X-ray variability of low magnetic-field neutron stars in low-mass X-ray binaries are briefly summarized. 相似文献
948.
Effects of variable thermal properties (specific heat and thermal conductivity) of the solid phase on the combustion of composite solid propellants are studied analytically. Both steady and unsteady burning are considered. It is shown that the effects of variable thermal properties are small and can be accounted for by choosing proper average values of specific heat and thermal conductivity. 相似文献
949.
A. Galli P. Wurz S. Barabash A. Grigoriev H. Gunell R. Lundin M. Holmström A. Fedorov 《Space Science Reviews》2006,126(1-4):267-297
We present measurements of energetic hydrogen and oxygen atoms (ENAs) on the nightside of Mars detected by the neutral particle
detector (NPD) of ASPERA-3 on Mars Express. We focus on the observations for which the field-of-view of NPD was directed at
the nightside of Mars or at the region around the limb, thus monitoring the flow of ENAs towards the nightside of the planet.
We derive energy spectra and total fluxes, and have compiled maps of hydrogen ENA outflow. The hydrogen ENA intensities reach
105 cm−2 sr−1 s−1, but no oxygen ENA signals above the detection threshold of 104 cm−2 sr−1 s−1 are observed. These intensities are considerably lower than most theoretical predictions. We explain the discrepancy as due
to an overestimation of the charge-exchange processes in the models for which too high an exospheric density was assumed.
Recent UV limb emission measurements (Galli et al., this issue) point to a hydrogen exobase density of 1010 m−3 and a very hot hydrogen component, whereas the models were based on a hydrogen exobase density of 1012 m−3 and a temperature of 200 K predicted by Krasnopolsky and Gladstone (1996). Finally, we estimate the global atmospheric loss
rate of hydrogen and oxygen due to the production of ENAs. 相似文献
950.
A highly reliable and economical system design is presented for a multiport amplifier (MPA) system, which has attracted considerable attention for its potential use in multibeam mobile satellite communications. An MPA is composed of multiple input/output ports and an array of multiple high-power amplifier (HPAs). Since the HPAs are shared among multiple beams, this design solves the problems of traffic imbalance among beams, traffic changes due to terminal movement, and changes in propagation conditions, and can efficiently utilize the total transmitting power with maximum flexibility and minimum hardware. The problem is that HPA failures degrade the MPA beam isolation, causing multipath interference in the surrounding area due to leakage through adjacent beams. To address this problem, we investigated the MPA performance and survival probability when HPAs fail, by taking the specific properties of the MPA configuration into account. Based on our analysis, we found that there is an optimum operational HPA on/off mode in the event of HPA failure, and we were able to obtain optimal performance and reliability by reconfiguring the HPA on/off states in orbit upon the occurrence of HPA failures. Our proposed self-redundant, reconfigurable MPA can achieve high reliability without any need for additional redundant units or switches. 相似文献