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991.
Let β(n,M,w) denote the minimum average Hamming distance of a binary constant weight code with length n, size M and weight w. In this paper, we study the problem of determining β(n,M,w). Using the methods from coding theory and linear programming, we derive several lower bounds on the average Hamming distance of a binary constant weight code. These lower bounds enable us to determine the exact value for β(n,M,w) in several cases. 相似文献
992.
The effects of surface-induced evaporative cooling on an atom chip
are investigated. The evolutions of temperature, number and
phase-space density of the atom cloud are measured when the atom
cloud is brought close to the surface. Rapid decrease of the
temperature and number of the atoms is found when the atom-surface
distance is < 100~μm. A gain of about a factor of five on the
phase-space density is obtained. It is found that the efficiency
of the surface-induced evaporative cooling depends on the
atom-surface distance and the shape of the evaporative trap. When
the atoms are moved very close to the surface, severe heating is
observed, which dominates when the holding time is >8~ms. It is
important that the surface-induced evaporative cooling offers novel
possibilities for the realization of a continuous condensation,
where a spatially varying evaporative cooling is required. 相似文献
993.
卫星编队飞行中C-W方程与轨道根数法的比较 总被引:16,自引:0,他引:16
目前卫星编队飞行动力学与控制的研究得到了广泛的重视,这些研究的理论主要是基于描述卫星相对运动的Clohessy-Wiltshire(C-W)方程。但根据特例及定性分析,表明C-W方程在初始条件的选取、解的周期性等方面与实际情况不符,从星的能量也不守恒。以卫星轨道根数为基础,提出了卫星编队飞行中的相对轨道根数法,克服了C-W方程的局限性,物理概念清楚,应用范围广,解的周期性成为自然结论。在主星为小偏心率的情况下,得到了简化的相对运动方程。最后对两种方法进行了比较,指出了C-W方程的局限性及其原因。 相似文献
994.
The hypersonic flow field over a sphere flying in a ballistic-range is numerically simulated for the purpose of validating
a hypersonic chemical equilibrium flow solver. The numerical results obtained are compared with available experimental data
on the stand-off distance and the shape of the detached bow shock wave. In the calculation, an adaptive mesh is employed for
a crisp capturing of the shock wave. Comparison with the experimental data reveals that the equilibrium flow solver can yield
a fairly accurate prediction of the flow field.
Received 18 November 1997 / Accepted 10 November 1998 相似文献
995.
It is proved that any subset of an (m-1)-dimensional sphere of volume larger than l(m+ 1) of the volume of the entire sphere contains l+ 1 points forming a regular l-dimensional simplex. As a corollary, it is obtained that, if the exterior of a given m-dimensional filled ellipsoid contains no more than the 1/(m+ 1) fraction of some sphere, then the volume of the ellipsoid is no less than the volume of the corresponding ball. The existence of a pair of points a given spherical distance apart in a set of positive measure is examined. 相似文献
996.
1 IntroductionThroughout this paperl {X., n 2 1} is assumed to be a sequence of independent randomvariables. Fn denotes the distribution function of the partial surns S. = Z Xk. As is known,k = 1oothe series Z X. is said to be essentially convergent (a.s.) if there exists a sequence of constantsn = 1oo{b., n 2 1} such that Z (X. -- 6.) a.s. converges. When this happens we writeClearlyFn(x) = G.(x -- B.). (l.2)Our problem stems from an old conjecture in Probabilistic Number Theory sugges… 相似文献
997.
998.
The Wiener index of a connected k-uniform hypergraph is defined as the summation of distances between all pairs of vertices. We determine the unique k-uniform unicyclic hypergraphs with maximum and second maximum, minimum and second minimum Wiener indices, respectively. 相似文献
999.
With the upper bound of Kullback-Leibler distance between a matrix variate Beta-distribution and a normal distribution, this paper gives the conditions under which a matrix-variate Beta-distribution will approach uniformly and asymptotically a normal distribution. 相似文献
1000.
Protein structure prediction from inaccurate and sparse NMR data using an enhanced genetic algorithm
Nuclear Magnetic Resonance Spectroscopy (most commonly known as NMR Spectroscopy) is used to generate approximate and partial distances between pairs of atoms of the native structure of a protein. To predict protein structure from these partial distances by solving the Euclidean distance geometry problem from the partial distances obtained from NMR Spectroscopy, we can predict three-dimensional (3D) structure of a protein. In this paper, a new genetic algorithm is proposed to efficiently address the Euclidean distance geometry problem towards building 3D structure of a given protein applying NMR's sparse data. Our genetic algorithm uses (i) a greedy mutation and crossover operator to intensify the search; (ii) a twin removal technique for diversification in the population; (iii) a random restart method to recover from stagnation; and (iv) a compaction factor to reduce the search space. Reducing the search space drastically, our approach improves the quality of the search. We tested our algorithms on a set of standard benchmarks. Experimentally, we show that our enhanced genetic algorithms significantly outperforms the traditional genetic algorithms and a previously proposed state-of-the-art method. Our method is capable of producing structures that are very close to the native structures and hence, the experimental biologists could adopt it to determine more accurate protein structures from NMR data. 相似文献