Liénard方程极限环存在定理

讨论了非线性振动方程:(x:)+f(x)(x.)+g(x)=0在G(±∞)=+∞的限制被取消时,其极限环的存在性.     

On the Hamilton–Waterloo Problem with cycle lengths of distinct parities

Let $K_v^1$ denote the complete graph $K_v$ if $v$ is odd and $K_v?I$, the complete graph with the edges of a 1-factor removed, if $v$ is even. Given non-negative integers $v,M,N,\alpha ,\beta$, the Hamilton–Waterloo problem asks for a 2-factorization of $K_v^1$ into $\alpha$$C_M$-factors and $\beta$$C_N$-factors. Clearly, $M,N\ge 3$, $M\mid v$, $N\mid v$ and $\alpha +\beta =?\frac{v?1}{2}?$ are necessary conditions.Very little is known on the case where $M$ and $N$ have different parities. In this paper, we make some progress on this case by showing, among other things, that the above necessary conditions are sufficient whenever $M|N$, $v>6N>36M$, and $\beta \ge 3$.     

Existence and Uniqueness of Limit Cycles for a Polynomial System

§１．ＩｎｔｒｏｄｕｃｔｉｏｎＦｏｒｔｈｅｆｏｌｏｗｉｎｇｐｏｌｙｎｏｍｉａｌｓｙｓｔｅｍｏｆｄｅｇｒｅｅｍ：ｄｘｄｔ＝ｆ１（ｘ,ｙ）,ｄｙｄｔ＝ｆ２（ｘ,ｙ）,（Ｅ）ｗｈｅｒｅｆ１（ｘ,ｙ）ａｎｄｆ２（ｘ,ｙ）ａｒｅｐｏｌｙｎｏｍｉａｌｓｉｎｘａｎ...     

The confirmation of a conjecture on disjoint cycles in a graph

Let $t$ and $k$ be two integers with $t\ge 5$ and $k\ge 2$. For a graph $G$ and a vertex $x$ of $G$, we use $d_G\left(x\right)$ to denote the degree of $x$ in $G$. Define ${\sigma }_t\left(G\right)$ to be the minimum value of ${\sum }_{x\in X}{d}_G\left(x\right)$, where $X$ is an independent set of $G$ with $\left|X\right|=t$. This paper proves the following conjecture proposed by Gould et al. (2018). If $G$ is a graph of sufficiently large order with ${\sigma }_t\left(G\right)\ge 2kt?t+1$, then $G$ contains $k$ vertex-disjoint cycles.     

On Edge-Colored Graphs Covered by Properly Colored Cycles

We characterize edge-colored graphs in which every edge belongs to some properly colored cycle. We obtain our result by applying a characterization of 1-extendable graphs. Received: April, 2003     

On 3-colorable planar graphs without prescribed cycles

In this paper we prove that every planar graph without cycles of length 4, 5, 6 and 8 is 3-colorable.     

On cycle lengths in claw-free graphs with complete closure

We show a construction that gives an infinite family of claw-free graphs of connectivity κ=2,3,4,5 with complete closure and without a cycle of a given fixed length. This construction disproves a conjecture by the first author, A. Saito and R.H. Schelp.     

Acyclic 4-choosability of planar graphs

A proper vertex coloring of a graph G=(V,E) is acyclic if G contains no bicolored cycle. Given a list assignment L={L(v)∣v∈V} of G, we say G is acyclically L-list colorable if there exists a proper acyclic coloring π of G such that π(v)∈L(v) for all v∈V. If G is acyclically L-list colorable for any list assignment with |L(v)|≥k for all v∈V, then G is acyclically k-choosable. In this paper we prove that planar graphs without 4, 7, and 8-cycles are acyclically 4-choosable.     

Busy period analysis for the GI/M/1 queue with exponential vacations

We consider the busy period in the GI/M/1 queue with multiple exponential vacations. We derive the transform of the joint distribution of the length of a busy period, the number of customers served during the busy period, and the residual interarrival time at the instant the busy period ends.     

钠掺杂磷酸铁锂晶格变化和电化学性能

利用固相法合成了钠掺杂的LiFePO₄,结构表征显示钠离子成功地掺入到了晶格中．SEM显示其粒径在1～3 μm．XRD显示钠掺杂样品晶胞变大．电池测试表明样品0.1 C放电150 mAh/g,5和7.5 C下分别放电109和107 mAh/g．1和5 C循环时,与初始放电容量相比,样品容量保持率分别为84%(1000次循环后)和86%(350次循环后),表现了优异的结构稳定性和循环性能．研究表明钠离子掺杂可以有效地提高磷酸铁锂的电化学活性,尤其是循环性能．