Partitioning edge-coloured complete symmetric digraphs into monochromatic complete subgraphs

Let ${\overrightarrow{K}}_{\mathbb{N}}$ be the complete symmetric digraph on the positive integers. Answering a question of DeBiasio and McKenney, we construct a 2-colouring of the edges of ${\overrightarrow{K}}_{\mathbb{N}}$ in which every monochromatic path has density 0.However, if we restrict the length of monochromatic paths in one colour, then no example as above can exist: We show that every $(r+1)$-edge-coloured complete symmetric digraph (of arbitrary infinite cardinality) containing no directed paths of edge-length ${?}_i$ for any colour $i\le r$ can be covered by ${\prod }_{i\in \left[r\right]}{?}_i$ pairwise disjoint monochromatic complete symmetric digraphs in colour $r+1$.Furthermore, we present a stability version for the countable case of the latter result: We prove that the edge-colouring is uniquely determined on a large subgraph, as soon as the upper density of monochromatic paths in colour $r+1$ is bounded by ${\prod }_{i\in \left[r\right]}\frac{1}{{?}_i}$.     

Accurate step wedge calibration for densitometry of electrophoresis gels

Accurate step wedge calibration is important for reliable quantitative densitometry of electrophoresis gels. In this work, we outline the theory and verified by experiment, the effect that the nonlinear response of detectors at low irradiance levels has on accurate optical density (OD) calibration of step wedges. It was found that OD value departures from stated do exist and thus supports the case of calibration. Halogen broadband light was shown to be generally unsuited as light source for step wedge calibration even though applied at highest illumination before saturation, unless correction approaches which add complexity to the process are applied. Monochromatic light was determined best suited for use, provided that the irradiance level was high enough for the calibration to be conducted fully in the detector’s linear range.     

Covering complete partite hypergraphs by monochromatic components

A well-known special case of a conjecture attributed to Ryser (actually appeared in the thesis of Henderson (1971)) states that $k$-partite intersecting hypergraphs have transversals of at most $k?1$ vertices. An equivalent form of the conjecture in terms of coloring of complete graphs is formulated in Gyárfás (1977): if the edges of a complete graph $K$ are colored with $k$ colors then the vertex set of $K$ can be covered by at most $k?1$ sets, each forming a connected graph in some color. It turned out that the analogue of the conjecture for hypergraphs can be answered: it was proved in Király (2013) that in every $k$-coloring of the edges of the $r$-uniform complete hypergraph $K^r$ ($r\ge 3$), the vertex set of $K^r$ can be covered by at most $?k∕r?$ sets, each forming a connected hypergraph in some color.Here we investigate the analogue problem for complete $r$-uniform $r$-partite hypergraphs. An edge coloring of a hypergraph is called spanning if every vertex is incident to edges of every color used in the coloring. We propose the following analogue of Ryser’s conjecture.In every spanning $(r+t)$-coloring of the edges of a complete $r$-uniform $r$-partite hypergraph, the vertex set can be covered by at most $t+1$ sets, each forming a connected hypergraph in some color.We show that the conjecture (if true) is best possible. Our main result is that the conjecture is true for $1\le t\le r?1$. We also prove a slightly weaker result for $t\ge r$, namely that $t+2$ sets, each forming a connected hypergraph in some color, are enough to cover the vertex set.To build a bridge between complete $r$-uniform and complete $r$-uniform $r$-partite hypergraphs, we introduce a new notion. A hypergraph is complete $r$-uniform $(r,?)$-partite if it has all $r$-sets that intersect each partite class in at most $?$ vertices (where $1\le ?\le r$).Extending our results achieved for $?=1$, we prove that for any $r\ge 3,2\le ?\le r,k\ge 1+r??$, in every spanning $k$-coloring of the edges of a complete $r$-uniform $(r,?)$-partite hypergraph, the vertex set can be covered by at most $1+?\frac{k?r+??1}{?}?$ sets, each forming a connected hypergraph in some color.     

Monochromatic loose path partitions in k-uniform hypergraphs

A conjecture of Gyárfás and Sárközy says that in every $2$-coloring of the edges of the complete $k$-uniform hypergraph $K_n^k$, there are two disjoint monochromatic loose paths of distinct colors such that they cover all but at most $k?2$ vertices. A weaker form of this conjecture with $2k?5$ uncovered vertices instead of $k?2$ is proved. Thus the conjecture holds for $k=3$. The main result of this paper states that the conjecture is true for all $k\ge 3$.     

The development of a high-power bremsstrahlung radiator for the production of monochromatic X-rays

An experimental set-up for the production of monochromatic X-ray beams tuneable in the energy region between 40 and 700 keV was built at our facility. This paper describes the design of a bremsstrahlung radiator to create a suitable photon field for monochromatisation by Laue diffraction on a curved single-crystal.     

三阶Ramsey数的性质和下界

本文得出了三个关于三阶Ｒａｍｓｅｙ数性质的结论，由这三个结论直接导出了若干三阶Ｒａｍｓｅｙ数的下界结果．     

On some Rado numbers for generalized arithmetic progressions

The 2-color Rado number for the equation x₁+x₂−2x₃=c, which for each constant we denote by S₁(c), is the least integer, if it exists, such that every 2-coloring, Δ : [1,S₁(c)]→{0,1}, of the natural numbers admits a monochromatic solution to x₁+x₂−2x₃=c, and otherwise S₁(c)=∞. We determine the 2-color Rado number for the equation x₁+x₂−2x₃=c, when additional inequality restraints on the variables are added. In particular, the case where we require x₂<x₃<x₁, is a generalization of the 3-term arithmetic progression; and the work done here improves previously established upper bounds to an exact value.     

透镜单色焦距的测量

本文根据夫朗和费单缝衍射原理，结合光电扫描技术，给出了测量透镜单色焦距的原理和测量装置，并以凸透镜为例给出了详细的测量方法和测量结果，计算了测量中的相对误差约为０．７％，最后讨论了减小测量误差的技术途径以及对凹透镜的测量方法。该方法不仅适用于可见光区，也适用于不可见光区的测量。测量方法简便，精度高。