Dielectric properties of /Agl-xKx/NbO3 solid solutions

The possibility of the occurrence of critical point in /Ag_l-xK_x/NbO₃ solid solutions is discussed.     

The complexity of mean flow time scheduling problems with release times

We study the problem of preemptive scheduling of n} jobs with given release times on m identical parallel machines. The objective is to minimize the average flow time. In this paper, show that when all jobs have equal processing times then the problem can be solved in polynomial time using linear programming. Our algorithm can also be applied to the open-shop problem with release times and unit processing times. For the general case (when processing times are arbitrary), we show that the problem is unary NP-hard. P. Baptiste and C. Dürr: Supported by the NSF/CNRS grant 17171 and ANR/Alpage. P. Brucker: Supported by INTAS Project 00-217 and by DAAD PROCOPE Project D/0427360. M. Chrobak: Supported by NSF grants CCR-0208856 and INT-0340752. S. A. Kravchenko: Supported by the Alexander von Humboldt Foundation.     

High temperature deformation of ceramic particle composites

The particle composites Al₂O₃/(2 and 3Y)TZP and MgAl₂O₄/3Y-TZP were tested in bending at temperature of 1280 °C over strain rates from 3.4 × 10⁻⁷ to 1 × 10⁻⁴ s⁻¹ and over stresses from 23 to 85 MPa. Strain rate of the composites decreased as a volume fraction of Al₂O₃ or MgAl₂O₄ increased. MgAl₂O₄/3Y-TZP composites deformed easier under the comparable conditions than alumina/zirconia composites. Four models of composite creep behaviour were compared to the experimental data. All the models were unsuitable for MgAl₂O₄/3Y-TZP, in turn an isostress, an isostrain and a constrained isostrain models provide the good predictions for creep rates for alumina/zirconia ceramics, but the rheological model appeared not good. The threshold stresses approach seems to be useful for describing superplastic flow of MgAl₂O₄/3Y-TZP composites.     

The simplified method for transient thermal field analysis in a polymeric DC cable

The simplified method of analysis of the thermal field in the futuristic model of a DC cable is presented. The thermal conductivity of a non-conducting layer is very small comparing with the same parameter of conducting regions. The above causes very fast heat propagation in the core and coating, which in the consequences are approximated by inert elements of the first order. Spatial changes in the field in insulation cannot be neglected, because of the significantly slow heat transfer. For that reason, insulation is treated as an element of distributed parameters. The boundary-initial parabolic problem of a non-conducting region is solved by means of Duhamel’s theorem. The fundamental solutions of superposition integrals are determined by the separation of variables method. The maximal deviation of results obtained by the finite element method does not exceed 7.2%. The heating curves and results of verification are presented in a graphic form.     

Application of Lyapunov's Methods for Analyzing the Stability of a Tubular Chemical Reactor with Recycle

The first and second Lyapunov methods were adapted to analyze the stability of a tubular chemical reactor with recycle. The criterion of local stability in the form of inequalities was derived using Lyapunov's first method. It is an explicit algebraic form, despite the fact that the mathematical model of the reactor is a partial differential problem with a boundary condition. As part of the second Lyapunov method, a mathematical criterion for non-local stability was derived in the form of an increase of Lyapunov's function. Both criteria are presented on graphs.     

Nanoscale mechanical properties of polymers irradiated by UV

The application of depth sensing nanoindentation to determine mechanical properties of three different polymers is described in this work using three different techniques to calibrate the measurement system. The nano-hardness and the elastic indentation modulus of polyvinyl chloride, polyethylene oxide and polyacrylic acid were inferred from nanomechanical tests, and the influence of ultraviolet irradiation on the mechanical properties of measured polymers is studied. A multicycling test—a sequence of several loading and unloading procedures—allowed the measurement of changes in the sample viscoelasticity. The nano-hardness of the polymers is shown to increase with radiation dose while the viscoelasticity decreases.