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排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Ya. O. Shablovskii 《Inorganic Materials》2007,43(12):1345-1349
The pyroelectric properties of lithium sulfate have been studied theoretically on the hypothesis of a pseudosymmetry of the structure of its polar phase. Analytical expressions are proposed for the temperature dependences of its pyroelectric polarization and pyroelectric coefficient at low temperatures and near the polymorphic transformation. The pyroelectric and piezoelectric coefficients of a polar crystal are shown to be in direct proportion. 相似文献
992.
M. V. Zagidullin V. D. Nikolaev M. I. Svistun N. A. Khvatov 《Journal of Engineering Physics and Thermophysics》2007,80(3):555-562
The results of parametric tests of a centrifugal bubble singlet-oxygen generator based on the reaction of chlorine with an
alkaline hydrogen peroxide solution have been given. The utilization of chlorine grows with bubble-layer height, whereas the
relative content of O2(1Δ) remains constant. Growth in centrifugal acceleration leads to a more efficient utilization of chlorine. A specific oxygen
output of more than 1 mmole·cm−2·sec−1 from the bubble layer for a degree of chlorine utilization of ∼95% and a singlet-oxygen yield of more than 50% has been attained.
It has been shown that a centrifugal bubble singlet-oxygen generator is an efficient energy source for an oxygen-iodine laser.
__________
Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 3, pp. 121–128, May–June, 2007. 相似文献
993.
Data from 2-dimensional video disdrometers (2DVD) taken in different locations are used to derive the specific attenuation for horizontal and vertical polarisations at 20 GHz. The data include both drop-size distribution and their axis ratio distributions. T-matrix calculations using data over 1 min integration time show a power-law dependence on rain rate. The best-fit coefficients are compared with those given in the ITU-R Recommendation P. 838, both versions 2 and 3. Closest agreement is seen for vertical polarisation for version 2 and the largest discrepancies are seen for horizontal polarisation for version 3. The discrepancies are attributed to the different assumptions in the drop-size distributions, as well as the upper limit of integration for deriving the specific attenuation. The variation of the crosspolar discrimination (XPD) against copolar attenuation (CPA) is also examined. The 2DVD data are used to simulate a beacon experimental scenario at 20 GHz, the actual locations of the two instruments being different but climatically similar. Good agreement is seen with one year of beacon measurements, but the latter shows more spread in the variation, partly attributed to drop oscillations. Calculations also show that XPD-CPA variation is sensitive to the assumed drop shapes 相似文献
994.
A new technique for the preparation of CuI nanoparticles from CuSO4 and KI ethanol solutions has been developed. Preparation conditions were optimized through a series of experiments. Under
these conditions, the yield of CuI reached 95.39%. The product was characterized and the reaction kinetics was studied. The
results show that the product takes a roughly spherical shape with an average particle size of less then 50 nm. The activation
energy of the formation of CuI is found to be E
a = 0.58 × 102 kJ/mol, and the preexponential factor in the Arrhenius equation is k
0 = 7.43 × 1016 mol/(l s).
The text was submitted by the authors in English. 相似文献
995.
996.
D. Boucher W. Geiselmann F. Ulmer 《Applicable Algebra in Engineering, Communication and Computing》2007,18(4):379-389
We generalize the notion of cyclic codes by using generator polynomials in (non commutative) skew polynomial rings. Since
skew polynomial rings are left and right euclidean, the obtained codes share most properties of cyclic codes. Since there
are much more skew-cyclic codes, this new class of codes allows to systematically search for codes with good properties. We
give many examples of codes which improve the previously best known linear codes. 相似文献
997.
Holly Rushmeier Jason Dykes John Dill Peter Yoon 《Computer Graphics and Applications, IEEE》2007,27(6):12-16
Defining visualization education is still a work in progress. Visualization education is not just a subject within computer science. Computer scientists are not always the appropriate choice to teach visualization courses on their own. Visualization is not just mastering a set of concepts but acquiring skills. Student should learn by doing, either using one tool or a variety of tools, depending on the course's focus. 相似文献
998.
This paper deals with the time-optimal control problem for a class of control systems which includes controlled mechanical systems with possible dissipation terms. The Lie algebras associated with such mechanical systems have certain special properties. These properties are explored and used in conjunction with the Pontryagin maximum principle to determine the structure of singular extremals and, in particular, time-optimal trajectories. The theory is illustrated by an application to a time-optimal problem for a class of underwater vehicles. 相似文献
999.
John Watrous 《Computational Complexity》2003,12(1-2):48-84
This paper studies the space-complexity of predicting the
long-term behavior of a class of stochastic processes based on evolutions
and measurements of quantum mechanical systems. These processes
generalize a wide range of both quantum and classical space-bounded
computations, including unbounded error computations given by machines
having algebraic number transition amplitudes or probabilities.
It is proved that any space s quantum stochastic process from this class
can be simulated probabilistically with unbounded error in space O(s),
and therefore deterministically in space O(s2). 相似文献
1000.
Solidification time and heat treatment are known to have a large effect on the microstructure of cast aluminum alloys. This
study was conducted to quantify how the fatigue properties of a 319-type aluminum alloy are affected by solidification time
and heat treatment. Both porosity-containing (non-hot isostatically pressed (HIP)) and porosity-free (HIP) samples in the
T6 (“peak aged”) or T7 (“overaged”) heattreated conditions were tested. As the solidification time increased, the average
initiating pore diameter increased and stress-controlled fatigue life decreased. Heat treatment was observed to have a large
effect on fatigue properties of the HIP samples. However, in the non-HIP fatigue samples, heat treatment did not significantly
change the fatigue life or fatigue strength of the cast 319-type alloy. The absence of an influence of heat treatment on fatigue
response is attributed to the predominance of the microporosity in fatigue crack initiation in cast aluminum. 相似文献