On a family of minimal blocking sets of the Hermitian surface

An infinite family of minimal blocking sets of ??(3, q²) is constructed for even q, with links to Ceva configurations. Copyright © 2011 John Wiley & Sons, Ltd 19:313‐316, 2011.     

Resolvable candelabra quadruple systems with three groups

Candelabra quadruple systems play an important role in the construction of Steiner 3‐designs. In this article, we consider resolvable candelabra quadruple systems with three groups and show that the necessary conditions on the existence of RCQS(g³: s) when g is even are also sufficient. © 2011 Wiley Periodicals, Inc. J Combin Designs 19:247‐267, 2011     

An optimization technique based on a vector autoregression model with state space representation: application to Ukrainian cargo transport data

This paper proposes to forecast indicators of the Ukrainian cargo transport system, taking into account their relations with macroeconomic indicators. Increased forecast accuracy at a priori information uncertainty is attained through an optimization technique, starting with a Vector Autoregression (VAR) model of observed multiple time series, its state space representation and subsequent adaptive filtering. The adaptive filter, earlier proposed by the authors, minimizes forecasting errors. Under an optimization criterion, the information divergence of Kullback–Leibler between probability distributions of real values and their estimations is established. The main advantage of the proposed technique is connected with the opportunity to estimate future values of multiple time series even in presence of structural breaks (describing the changes of the status ‘before crisis’ / ‘after crisis’). The observations are available from 2003:1–2011:12, the analysis is performed for the period 2003:1–2011:9. In-sample forecasting of multiple time series of cargo volumes transferred by different transport modes and two macro indicators is compared with the forecast based on a VAR model. In-sample forecast is realized for the last three months 2011:10–2011:12.     

Polynomial preserving recovery for quadratic elements on anisotropic meshes

Polynomial preserving gradient recovery technique under anisotropic meshes is further studied for quadratic elements. The analysis is performed for highly anisotropic meshes where the aspect ratios of element sides are unbounded. When the mesh is adapted to the solution that has significant changes in one direction but very little, if any, in another direction, the recovered gradient can be superconvergent. The results further explain why recovery type error estimator is robust even under nonstandard and highly distorted meshes. © 2011 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2011     

Decomposing complete equipartite graphs into short even cycles

In this article we find necessary and sufficient conditions to decompose a complete equipartite graph into cycles of uniform length, in the case that the length is both even and short relative to the number of parts. © 2010 Wiley Periodicals, Inc. J Combin Designs 19:131‐143, 2011     

A short proof for the polyhedrality of the Chvátal–Gomory closure of a compact convex set

Recently Schrijver’s open problem, whether the Chvátal–Gomory closure of an irrational polytope is polyhedral was answered independently in the seminal works of Dadush et al. (2011) and Dunkel and Schulz (2010); the former even applies to general compact convex sets. We present a very short, easily accessible proof.     

Cyclic even cycle systems of the complete graph

In this article, it is proved that for each even integer m?4 and each admissible value n with n>2m, there exists a cyclic m‐cycle system of K_n, which almost resolves the existence problem for cyclic m‐cycle systems of K_n with m even. © 2011 Wiley Periodicals, Inc. J Combin Designs 20:23–39, 2012     

Integral trees of odd diameters

A graph is called integral if all eigenvalues of its adjacency matrix consist entirely of integers. Recently, Csikvári proved the existence of integral trees of any even diameter. In the odd case, integral trees have been constructed with diameter at most 7. In this article, we show that for every odd integer n>1, there are infinitely many integral trees of diameter n. © 2011 Wiley Periodicals, Inc. J Graph Theory     

Combinatorial theorems about embedding trees on the real line

We consider the combinatorial problem of embedding the metric defined by an unweighted graph into the real line, so as to minimize the distortion of the embedding. This problem is inspired by connections to Banach space theory and to computer science. After establishing a framework in which to study line embeddings, we focus on metrics defined by three specific families of trees: complete binary trees, fans, and combs. We construct asymptotically optimal (i.e., distortion‐minimizing) line embeddings for these metrics and prove their optimality via suitable lower bound arguments. It appears that even such specialized metrics require nontrivial constructions and proofs of optimality require sophisticated combinatorial arguments. The combinatorial techniques from our work might prove useful in further algorithmic research on low distortion metric embeddings. © 2011 Wiley Periodicals, Inc. J Graph Theory 67: 153–168, 2011     

The application of the Ehrlich-Aberth method to structured polynomial eigenvalue problems

An algorithm for the application of the Ehrlich-Aberth method to polynomial eigenvalue problems (PEPs) is proposed. The computational complexity of the algorithm is only quadratic with respect to the degree of the polynomial, where customary matrix methods have cubic complexity. For the case of some structured PEPs a strategy is given in order to exploit the structure and obtain the induced coupling in the spectrum. Numerical experiments are provided for the particular case of even/odd PEPs. This communication is based on joint work with Dario A. Bini and Luca Gemignani. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonlinear self-adjointness through differential substitutions

It is known (Ibragimov, 2011; Galiakberova and Ibragimov, 2013) [14,18] that the property of nonlinear self-adjointness allows to associate conservation laws of the equations under study, with their symmetries. In this paper we show that, even when the equation is nonlinearly self-adjoint with a non differential substitution, finding the explicit form of the differential substitution can provide new conservation laws associated to its symmetries. By using the general theorem on conservation laws (Ibragimov, 2007) [11] and the property of nonlinear self-adjointness we find some new conservation laws for the modified Harry-Dym equation. By using a differential substitution we construct a conservation law for the Harry-Dym equation, which has not been derived before using Ibragimov method.     

基金风险改变了投资者的业绩敏感程度吗？——基于基金业绩波动与资金净流量关系的实证研究

本文利用我国2005年至2011年期间开放式基金的面板数据,研究了基金业绩波动对投资者业绩敏感程度的影响。在验证了基金资金净流量与基金业绩的正相关关系后,实证研究发现:(1)基金业绩波动降低了投资者对基金业绩的敏感程度:基金业绩波动越大,相同业绩提升带来的资金净流量越少;(2)对于不同业绩类型的基金,业绩波动对基金“业绩—资金净流量”关系的反向影响程度也有所不同:这一影响主要体现在绩劣基金中,中等业绩基金次之,在明星基金中反而体现为正向影响。     

Model reduction for nonlinear biomechanical structural analysis

For surgery training and on-line support during surgeries a method is required which is able to reduce simulation time possibly even to realtime. This contribution compares the effectiveness of three model reduction methods, all of which are widely used for linear problems, in the context of nonlinear structural mechanics. Three reduction methods will be extended to nonlinear elasticity including large deformations. The performance of the extended concepts is investigated for a simplified model of a human inferior turbinate in the context of the functional endoscopic sinus surgery. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A single‐node characteristic collocation method for unsteady‐state convection‐diffusion equations in three‐dimensional spaces

We develop a nonconventional single‐node characteristic collocation method with piecewise‐cubic Hermite polynomials for the numerical simulation to unsteady‐state advection‐diffusion transport partial differential equations. This method greatly reduces the number of unknowns in the conventional collocation method, and generates accurate numerical solutions even if very large time steps are taken. The reduction of number of nodes has great potential for problems defined on high space dimensions, which appears in such problems as quantification of uncertainties in subsurface porous media. The method developed here is easy to formulate. Numerical experiments are presented to show the strong potential of the method. © 2009 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 27: 786–802, 2011     

Energy partition for the linear radial wave equation

We consider the radial free wave equation in all dimensions and derive asymptotic formulas for the space partition of the energy, as time goes to infinity. We show that the exterior energy estimate, which Duyckaerts et al. obtained in odd dimensions (Duyckaerts et al., J Eur Math Soc 13:533–599, 2011; J Eur Math Soc, 2013) fails in even dimensions. Positive results for restricted classes of data are obtained.     

The Cartesian product of hypergraphs

We show that every simple, (weakly) connected, possibly directed and infinite, hypergraph has a unique prime factor decomposition with respect to the (weak) Cartesian product, even if it has infinitely many factors. This generalizes previous results for graphs and undirected hypergraphs to directed and infinite hypergraphs. The proof adopts the strategy outlined by Imrich and ?erovnik for the case of graphs and introduces the notion of diagonal‐free grids as a replacement of the chord‐free 4‐cycles that play a crucial role in the case of graphs. This leads to a generalization of relation Δ on the arc set, whose convex hull is shown to coincide with the product relation of the prime factorization. © 2011 Wiley Periodicals, Inc. J Graph Theory     

Efficient parallel solution to large‐size sparse eigenproblems with block FSAI preconditioning

The choice of the preconditioner is a key factor to accelerate the convergence of eigensolvers for large‐size sparse eigenproblems. Although incomplete factorizations with partial fill‐in prove generally effective in sequential computations, the efficient preconditioning of parallel eigensolvers is still an open issue. The present paper describes the use of block factorized sparse approximate inverse (BFSAI) preconditioning for the parallel solution of large‐size symmetric positive definite eigenproblems with both a simultaneous Rayleigh quotient minimization and the Jacobi–Davidson algorithm. BFSAI coupled with a block diagonal incomplete decomposition proves a robust and efficient parallel preconditioner in a number of test cases arising from the finite element discretization of 3D fluid‐dynamical and mechanical engineering applications, outperforming FSAI even by a factor of 8 and exhibiting a satisfactory scalability. Copyright © 2011 John Wiley & Sons, Ltd.     

CEO权力影响公司股价特质波动吗？——基于公司治理和风险承担双重视角

影响股价特质波动的因素是当前的热点研究问题。本文认为CEO权力通过降低公司风险承担水平、弱化公司治理机制有效性两条途径降低股价特质波动。为验证该基本假设,本文以2011~2017年中国A 股 上市公司为样本进行实证检验,发现在控制相关影响因素后,CEO权力对股价特质波动呈现出显著的负向影响,在非国有上市公司和小型企业中,这种关系更加显著。本研究丰富了有关CEO权力经济后果及股价特质波动影响因素的研究,对CEO权力的合理配置和公司风险管理均具有一定启示。     

Applications of Rosenbrock-type methods to the p-version of finite elements

In quasistatic solid mechanics the spatial as well as the temporal domain need to be discetized. For the spatial discretization usually elements with linear shape functions are used even though it has been shown that generally the p-version of the finite elemente method yields more effective discretizations, see e.g. [1], [2]. For the temporal discretization diagonal-implicit, see e.g. [4], and especially linear-implicit Runge-Kutta schemes, see e.g. [5], [6], have for smooth problems proven to be superior to the frequently applied Backward-Euler scheme (BE). Thus an approach combining the p-version of the finite element method with linear-implicit Runge-Kutta schemes, so-called Rosenbrock-type methods, is presented. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)