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181.
This paper is a sequel to our [7]. In that paper we constructed a 10 tree of avoidable points. Here we construct a 10 tree of shadow points. This tree is a tree of sharp filters, where a sharp filter is a nested sequence of basic open sets converging to a point. In the construction we assign to each basic open set on the tree an address in 2<. One interesting fact is that while our 10 tree of sharp filters (a subtree of <) is isomorphic to the tree of addresses (a subtree of 2<), the tree of addresses is recursively enumerable but not recursive. To achieve this end we use a finite injury priority argument.Mathematics Subject Classification (2000): 03D45, 03D80, 03C57, 54A20 相似文献
182.
Community detection is of great significance in understanding the structure of the network. Label propagation algorithm (LPA) is a classical and effective method, but it has the problems of randomness and instability. An improved label propagation algorithm named LPA-MNI is proposed in this study by combining the modularity function and node importance with the original LPA. LPA-MNI first identify the initial communities according to the value of modularity. Subsequently, the label propagation is used to cluster the remaining nodes that have not been assigned to initial communities. Meanwhile, node importance is used to improve the node order of label updating and the mechanism of label selecting when multiple labels are contained by the maximum number of nodes. Extensive experiments are performed on twelve real-world networks and eight groups of synthetic networks, and the results show that LPA-MNI has better accuracy, higher modularity, and more reasonable community numbers when compared with other six algorithms. In addition, LPA-MNI is shown to be more robust than the traditional LPA algorithm. 相似文献
183.
Let be Martin-Löf-random. Then there is a promptly simple set such that for each Martin-Löf-random set , . When , one obtains a c.e. non-computable set which is not weakly Martin-Löf cuppable. That is, for any Martin-Löf-random set , if , then .
184.
The lattice spin model with Q-component discrete spin variables restricted to have orientations orthogonal to the faces of Q -dimensional hypercube is considered on the Bethe lattice, the recursive graph which contains no cycles. The partition function of the model with dipole–dipole and quadrupole–quadrupole interaction for arbitrary planar graph is presented in terms of double graph expansions. The latter is calculated exactly in case of trees. The system of two recurrent relations (RR) which allows to calculate all thermodynamic characteristics of the model is obtained. The correspondence between thermodynamic phases and different types of fixed points of the RR is established. Using the technique of simple iterations the plots of the zero field magnetization and quadrupolar moment are obtained. Analyzing the regions of stability of different types of fixed points of the system of recurrent relations the phase diagrams of the model are plotted. For Q?2 the phase diagram of the model is found to have three tricritical points, whereas for Q>2 there are one triple and one tricritical points. 相似文献
185.
James H. Schmerl 《Mathematical Logic Quarterly》2000,46(4):543-548
Improving a theorem of Gasarch and Hirst, we prove that if 2 ≤ k ≤ m < ω, then the following is equivalent to WKL0 over RCA0 Every locally k‐colorable graph is m‐colorable. 相似文献
186.
Wan Shik Ha Yong Kun Chun Seung Soon Jang Do Mook Rhee Chong Rae Park 《Journal of Polymer Science.Polymer Physics》1997,35(2):309-315
Optimum conditions for the synthesis of PEI of considerable molecular weight have been established. Poly(ethylene terephthalate-co-isophthalate) (PETI) has been prepared through the ester interchange reaction of a blend of poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI). NMR analysis has indicated that the PETI changes from a block-type copolymer to a random type copolymer as the ester interchange reaction proceeds. If the reaction is limited to 20 min, the resulting PETI is crystallizable. The effects of catalysts that have been used during the synthesis of PEI on the characteristics of PETI are also discussed. © 1997 John Wiley & Sons, Inc. 相似文献
187.
James H. Schmerl 《Mathematical Logic Quarterly》2001,47(4):489-492
Let ℳ︁ be a countable, recursively saturated model of Peano Arithmetic, and let Aut(ℳ︁) be its automorphism group considered as a topological group with the pointwise stabilizers of finite sets being the basic open subgroups. Kaye proved that the closed normal subgroups are precisely the obvious ones, namely the stabilizers of invariant cuts. A proof of Kaye's theorem is given here which, although based on his proof, is different enough to yield consequences not obtainable from Kaye's proof. 相似文献
188.
A new set of Reynolds equations for predicting turbulent two-phase flows has been developed by means of Reynolds averaging method on the unsteady laminar equations of two-phase flow. These equations involve average terms of products of turbulent fluctuations in some physical parameters in a large degree. The interaction forces between two phases, the pressures for dispersed phase, extra stresses except for pressure and the expressions for energy interchange between two phases have been discussed. 相似文献
189.
铅芯橡胶隔震支座LRB (Lead Rubber Bearing)的等效水平刚度是隔震建筑物的重要力学指标,橡胶材料由于其复杂活跃的化学组分,在使用过程中极易发生老化,是LRB支座中随时间变化的活跃因素。考虑铅芯橡胶隔震支座中橡胶材料退化的时变性和随机性,引入时变变异系数。基于概率密度演化方法,得到LRB支座等效水平刚度的概率密度演化曲线和时变可靠度。结果表明,随着时间的增长,支座等效水平刚度产生增大的趋势,支座的可靠度发生非线性降低,老化对支座等效水平刚度的离散性产生了明显的影响。 相似文献
190.
In practical quantum key distribution (QKD) systems, a single photon-detector (SPD) is one of the most vulnerable components. Faint after-gate attack is a universal attack against the detector. However, the original faint after-gate attack can be discovered by monitoring the photocurrent. This paper presents a probabilistic generalization of the attack, which we refer to as probabilistic faint after-gate attack, by introducing probability control modules. Previous countermeasures for photocurrent monitoring may fail in detecting the eavesdropper under some specific probabilities. To mitigate this threat, we provide a method to determine the detectable boundary in the limitation of precision of photocurrent monitoring, and investigate the security of QKD systems under such boundaries using the weak randomness model. 相似文献