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Search Results: 1 - 10 of 130189 matches for " LIU Ming-jun "
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 Mathematics , 2007, Abstract: Finite element method is one of powerful numerical methods to solve PDE. Usually, if a finite element solution to a Poisson equation based on a triangulation of the underlying domain is not accurate enough, one will discard the solution and then refine the triangulation uniformly and compute a new finite element solution over the refined triangulation. It is wasteful to discard the original finite element solution. We propose a prewavelet method to save the original solution by adding a prewavelet subsolution to obtain the refined level finite element solution. To increase the accuracy of numerical solution to Poisson equations, we can keep adding prewavelet subsolutions. Our prewavelets are orthogonal in the \$H^1\$ norm and they are compactly supported except for one globally supported basis function in a rectangular domain. We have implemented these prewavelet basis functions in MATLAB and used them for numerical solution of Poisson equation with Dirichlet boundary conditions. Numerical simulation demonstrates that our prewavelet solution is much more efficient than the standard finite element method.
 Statistics , 2015, Abstract: Gaussian fields (GFs) are frequently used in spatial statistics for their versatility. The associated computational cost can be a bottleneck, especially in realistic applications. It has been shown that computational efficiency can be gained by doing the computations using Gaussian Markov random fields (GMRFs) as the GFs can be seen as weak solutions to corresponding stochastic partial differential equations (SPDEs) using piecewise linear finite elements. We introduce a new class of representations of GFs with bivariate splines instead of finite elements. This allows an easier implementation of piecewise polynomial representations of various degrees. It leads to GMRFs that can be inferred efficiently and can be easily extended to non-stationary fields. The solutions approximated with higher order bivariate splines converge faster, hence the computational cost can be alleviated. Numerical simulations using both real and simulated data also demonstrate that our framework increases the flexibility and efficiency.
 计算机科学技术学报 , 2009, Abstract: Delay tolerant networks (DTNs) experience frequent and long lasting network disconnection due to various reasons such as mobility, power management, and scheduling. One primary concern in DTNs is to route messages to keep the end-to-end delivery delay as low as possible. In this paper, we study the single-copy message routing problem and propose an optimal opportunistic routing strategy – Leapfrog Routing – for probabilistically contacted DTNs where nodes encounter or contact in some fixed probabilities. We deduce the iterative computation formulate of minimum expected opportunistic delivery delay from each node to the destination, and discover that under the optimal opportunistic routing strategy, messages would be delivered from high-delay node to low-delay node in the leapfrog manner. Rigorous theoretical analysis shows that such a routing strategy is exactly the optimal among all possible ones. Moreover, we apply the idea of Reverse Dijkstra algorithm to design an algorithm. When a destination is given, this algorithm can determine for each node the routing selection function under the Leapfrog Routing strategy. The computation overhead of this algorithm is only O(n 2) where n is the number of nodes in the network. In addition, through extensive simulations based on real DTN traces, we demonstrate that our algorithm can significantly outperform the previous ones.
 计算机科学技术学报 , 2009, Abstract: Composite Web services need transactional support to guarantee their consistent and reliable execution.Due to the long running and inter-organizational characteristics of Web services,current approaches for transactional Web services composition adopt compensation mechanism to maintain atomicity.A common assumption is that a compensation operation can be applied at any time with no cost.However,compensation operations are typically associated with temporal and cost constraints,which make compensation mechan...
 中国生物工程杂志 , 2009, Abstract: Mutants of recombinant hIL-2 (rhIL-2), generated by using site-directed mutagenesis strategy, can increase anti-tumor activity and decrease toxicity. We have used site-directed mutagenesis of hIL-2 to generate a mutant of hIL-2(MhIL-2) in which Asn88 was substituted by Arg88. To reduce the undesirable formation of inclusion body and maximize the yield of soluble MhIL-2 fusion protein, we adapted a protocol for the expression of soluble MhIL-2 fusion protein. Our results have indicated that soluble form of the MhIL-2 fusion protein is expressed from E. coli.. Moreover, it also has facilitated purification of the MhIL-2. SDS-PAGE analysis revealed that the MhIL-2 protein was efficiently purified to 95% purity by the combination of nickel ion Chelating column chromatography, Desalting column chromatography, thrombin cleavage and Superdex 75 gel filtration column chromatography. Proliferation assay of T lymphocyte of purified MhIL-2 showed that the biological activity of MhIL-2 was higher than that of standard hIL-2 in vitro. This work not only describes an efficient preparation strategy of MhIL-2, but also introduces a highly active MhIL-2 that may have important clinical applicability.
 Acta Crystallographica Section E , 2012, DOI: 10.1107/s1600536812017345 Abstract: In the title compound, C20H11Cl2F4N3, the central pyrazolo[1,5-a]pyrimidine unit is almost planar [the mean deviation from the best least-square plane through the nine atoms is 0.006 (2) ]. The fluorobenzene ring is rotated out of this plane by 10.3 (3)°, whereas the dichlorobenzene ring is rotated by 46.2 (3)°. The crystal packing is dominated by Cl...Cl interactions of 3.475 (3) and van der Waals interactions.
 地球物理学报 , 2008, Abstract: 依据穿过巴颜喀拉地块的北部、秦岭地块、祁连地块、海原弧形构造区和鄂尔多斯地块的玛沁-兰州-靖边人工地震剖面的P波、S波的速度结构和泊松比结构,对青藏高原东北缘的地壳组成进行研究,并探讨其动力学过程.首先,系统地归纳总结出一套将地震测深得到的原位P波速度校正到实验室温压条件下波速的具体可行的方法,利用大地热流值求取地壳不同深度的温度是该方法的关键.然后,将上述剖面的原位P波速度校正到600MPa和室温条件下,结合泊松比与相同温压条件下的实验室岩石波速测量结果进行对比,确定研究区的岩性组成.结果表明,青藏高原东北缘地壳平均P波校正波速为6.43 km/s,地壳整体像上地壳一样呈酸性.巴颜喀拉地块和秦岭地块南部的下地壳底部缺失校正速度VP6.9 km/s的基性岩,下地壳中酸性互层,下地壳整体呈酸性.其他地块下地壳底部有2～10 km厚的校正速度VP6.9 km/s的基性岩,下地壳整体呈中性.最后,根据青藏高原东北缘地壳结构和组成的研究成果,支持地壳增厚主要发生在下地壳的观点;提出巴颜喀拉地块和秦岭地块南部曾发生过下地壳拆沉作用,并导致高原的加速隆升.
 计算机应用研究 , 2010, Abstract: The efficient scheduling of workflow applications represented by DAG(directed acrylic graph) with the objective of time-cost optimization is fundamental and intractable in computational grid.To solve this problem,this paper put forward two new algorithms GSA-GW and IGSA-GW.Under the current distribution,this paper converted deadline into slot time SLOT for every task,then greedily replaced the distribution in the limitation of SLOT. The results show that the algorithms can optimize workflow costs better,and...
 遥感学报 , 2007, Abstract: 星载合成孔径雷达构像方程是地理编码、立体测量、影像定位等几何处理的基础。本文首先讨论了构像方程的参数选择,在充分考虑轨道物理模型及摄动力影响的基础上,提出了一套改进的轨道模型参数。从距离方程及多普勒方程出发,详细推导了包含轨道模型参数及成像处理参数的星载SAR构像方程。作为构像方程的一个具体应用,本文研究了星载SAR影像的轨道精化问题。将构像方程线性化,对每个地面控制点列出误差方程,可以用类似于航空影像的空间后方交会的方式精确求解轨道模型参数。试验中从1∶5万地形图上量取了5个地面控制点,对一景Radarsat SAR影像进行了轨道精化。比较发现,头文件提供的轨道与精化的轨道之间有约2km的位置差异,用精化的轨道数据得到了高精度的几何校正结果。它间接地表明了轨道精化算法的正确可行。
 中国物理 B , 2007, Abstract: This paper proposes a model of direct current (DC) electron hopping transport in DNA, in which DNA is considered as a binary one-dimensional disordered system. To quantitatively study the DC conductivity in DNA, it numerically calculates the DC conductivity of DNA chains with different parameter values. The result shows that the DC conductivity of DNA chain increases with the increase of temperature. And the conductivity of DNA chain is depended on the probability p, which represents the degree of compositional disorder in a DNA sequence to some extent. For p<0.5, the conductivity of DNA chain decreases with the increase of p, while for p\geq0.5, the conductivity increases with the increase of p. The DC conductivity in DNA chain also varies with the change of the electric field, it presents non-Ohm's law conductivity characteristics.
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