On the field of a line charge in magnetized plasma

The field of a line charge in magnetized plasma is determined. It is shown that the Debye shielding doesn't occur in situations where we can neglect the plasma drift. Our approach can justify the use of a simple model of a sheath around an antenna or a tether mounted on a spacecraft moving through ionospheric plasma.     

NP completeness of the edge precoloring extension problem on bipartite graphs

We show that the following problem is NP complete: Let G be a cubic bipartite graph and f be a precoloring of a subset of edges of G using at most three colors. Can f be extended to a proper edge 3‐coloring of the entire graph G? This result provides a natural counterpart to classical Holyer's result on edge 3‐colorability of cubic graphs and a strengthening of results on precoloring extension of perfect graphs. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 156–160, 2003     

Thermodynamics of the Farey Fraction Spin Chain

We consider the Farey fraction spin chain, a one-dimensional model defined on (the matrices generating) the Farey fractions. We extend previous work on the thermodynamics of this model by introducing an external field h. From rigorous and more heuristic arguments, we determine the phase diagram and phase transition behavior of the extended model. Our results are fully consistent with scaling theory (for the case when a “marginal” field is present) despite the unusual nature of the transition for h = 0, and the presence of long-range forces.     

Investigations of the inhibition of copper corrosion in nitric acid solutions by ketene dithioacetal derivatives

Ketene dithioacetal derivatives, namely 3-[bis(methylthio)methylene] pentane-2,4-dione (1), 3-(1,3-dithian-2-ylidene) pentane-2,4-dione (2) and 3-(1,3-dithiolan-2-ylidene) pentane-2,4-dione (3) were synthesized and their respective capacity to inhibit copper corrosion in 3 M HNO₃ was investigated by means of weight loss, potentiodynamic polarization, scanning electron microscopy (SEM) and energy dispersive X-ray fluorescence (XRF). The obtained results indicate that the addition of these compounds significantly decreases the corrosion rate. Potentiodynamic polarization studies clearly showed that the inhibition efficiency increases with increasing concentration of the investigated compounds at a fixed temperature, but decreases with increasing temperature. These results on the whole showed that the studied substances are good cathodic inhibitors for copper corrosion in nitric acid medium. SEM and energy dispersive X-ray (EDAX) examination of the copper surface revealed that these compounds prevented copper from corrosion by adsorption on its surface to form a protective film, which acts as a barrier to aggressive agents. The presence of these organic compounds adsorbed on the electrode surface was confirmed by XRF investigations.     

JINR (Dubna) and Prague Tier2 sites: Common experience in the WLCG grid infrastructure

The paper describes the cooperation of JINR specialists and Czech colleagues in the field of deployment and development of modern grid technologies within the framework of the WLCG global infrastructure project. Special attention is paid to the development and usage of monitoring systems.     

Geometrical setting of solid mechanics

The starting point in the geometrical setting of solid mechanics is to represent deformation process of a solid body as a trajectory in a convenient space with Riemannian geometry, and then to use the corresponding tools for its analysis. Based on virtual power of internal stresses, we show that such a configuration space is the (globally) symmetric space of symmetric positive-definite real matrices. From this unifying point of view, we shall analyse the logarithmic strain, the stress rate, as well as linearization and intrinsic integration of corresponding evolution equation.     

Project portfolio designing using data envelopment analysis and De Novo optimisation

In a rapidly evolving economic world, projects become tools to support organization goals. Project portfolio is set of all projects that are implemented in the organisation at a time. Possible projects are characterized by sets of inputs and outputs, where inputs are resources for project realisation and outputs measure multiple goals of the organisation. The data envelopment analysis (DEA) is an appropriate approach to select efficient projects. The organisation has its total resources in limited quantities. Designing a portfolio of efficient projects not exceeding the limited resources does not always lead to the most efficient portfolio. De Novo optimisation is an approach for designing optimal systems by reshaping the feasible set. The paper proposes a new approach for project portfolio designing based on a systemic combination of DEA model and De Novo optimisation approach. A total available budget is a restriction on project portfolio. The proposed concept provides designing of optimal project portfolio with the minimal budget. Performance measures of the designed project portfolio are the efficiency of the portfolio and the effectiveness of outputs. Possible extensions of the concept are formulated and discussed.