Unit Weight Ratio Research Articles

Air inclusions in the polymer melt functioning as intrinsic physical blowing agents for the generation of foams in rotational molding

In recent years, foams have experienced a major economic uprise, not least due to their lightweight construction potential. In this article, a new process variation is presented, which enables the generation of foamed structures in rotational molding by the utilization of vacuum. The novel method is based on entrapped air in the melt as an intrinsic physical blowing agent. By applying negative pressure in the cooling or solidification phase, the air bubbles expand. The crystallization freezes the existing conditions and thus forms the foamed structure. The investigations presented consider influences by different pressures as well as the temperature at which the vacuum is applied. The results with polyethylene show that by varying the pressure as well as the application temperature of the vacuum, components with different densities and cell characteristics result. The resulting foamed components excel by an improved stiffness per unit weight ratio.

Coulomb-type solutions for passive earth pressure with steady seepage

Present paper deals with the computing of passive earth pressure acting on the vertical rigid retaining wall supporting the soil mass subjected to water seepage. The basic assumptions of Coulomb’s theory and the 2-dimensional steady flow function are used. Three Coulomb-type solutions for the passive earth pressures are presented for the walls provided with three different drainage systems respectively. Based on the general solutions, the variations of the critical inclination of the failure surface and the coefficient of passive earth pressure with increasing the effective friction angle of the soil mass, the soil/structure friction angle, and the water/soil unit weight ratio are discussed. Two tables with values of the coefficients of passive earth pressure for Cases 1 and 3 respectively are also presented.

Seismic passive resistance with vertical seepage and surcharge

Present paper focuses on the computation of the seismic passive earth pressure acting on a vertical rigid retaining wall by a soil mass subjected to vertical steady-state seepage and a uniform surcharge load. Based on the basic assumptions of Coulomb's theory and a pseudo-static method of analysis, a general solution for the passive earth pressure containing two coefficients is presented. In the solution, many parameters, such as unit weight of saturated soil, soil effective internal friction angle, soil/wall friction angle, water/soil unit weight ratio, surcharge intensity coefficient, horizontal and vertical seismic acceleration coefficients, Poisson's ratio of soil mass, hydraulic gradient, and coefficients of pore water pressure, are considered. The effects of hydraulic gradient and seismic forces on passive earth pressure coefficient and passive earth pressure distribution are investigated. The results indicate that passive earth pressure increases with increasing hydraulic gradient for downward water flow case, but decreases for upward water flow case, and that the presence of seismic forces induces a reduction in passive earth pressure.

On finding approximate optimal paths in weighted regions

The main result of this paper is an approximation algorithm for the weighted region optimal path problem. In this problem, a point robot moves in a planar space composed of n triangular regions, each of which is associated with a positive unit weight. The objective is to find, for given source and destination points s and t, a path from s to t with the minimum weighted length. Our algorithm, BUSHWHACK, adopts a traditional approach (see [M. Lanthier, A. Maheshwari, J.-R. Sack, Approximating weighted shortest paths on polyhedral surfaces, in: Proceedings of the 13th Annual ACM Symposium on Coputational Geometry, 1997, pp. 274–283; L. Aleksandrov, M. Lanthier, A. Maheshwari, J.-R. Sack, An ɛ-approximation algorithm for weighted shortest paths on polyhedral surfaces, in: Proceedings of the 6th Scandinavian Workshop on Algorithm Theory, in: Lecture Notes in Comput. Sci., vol. 1432, 1998, pp. 11–22; L. Aleksandrov, A. Maheshwari, J.-R. Sack, Approximation algorithms for geometric shortest path problems, in: Proceedings of the 32nd Annual ACM Symposium on Theory of Computing, 2000, pp. 286–295]) that converts the original continuous geometric search space into a discrete graph G by placing representative points on boundary edges. However, by exploiting geometric structures that we call intervals, BUSHWHACK computes an approximate optimal path more efficiently as it accesses only a sparse subgraph of G . Combined with the logarithmic discretization scheme introduced by Aleksandrov et al. [Approximation algorithms for geometric shortest path problems, in: Proceedings of the 32nd Annual ACM Symposium on Theory of Computing, 2000, pp. 286–295], BUSHWHACK can compute an ɛ-approximation in O ( n ɛ ( log 1 ɛ + log n ) log 1 ɛ ) time. By reducing complexity dependency on ɛ, this result improves on all previous results with the same discretization approach. We also provide an improvement over the discretization scheme of [L. Aleksandrov, A. Maheshwari, J.-R. Sack, Approximation algorithms for geometric shortest path problems, in: Proceedings of the 32nd Annual ACM Symposium on Theory of Computing, 2000, pp. 286–295] so that the size of G is no longer dependent on unit weight ratio, the ratio between the maximum and minimum unit weights. This leads to the first ɛ-approximation algorithm whose time complexity does not depend on unit weight ratio.

Casein interactions as studied by gel chromatography and ultracentrifugation

Gel chromatographic and ultracentrifugal methods were employed to demonstrate structural differences in the soluble casein complexes obtained by several pathways. In solutions containing the purified κ- and α s1-casein fractions or whole acid casein at pH 6.85, I 0.26, 30 °C, an equilibrium mixture is established which promotes the formation of a unit weight ratio complex with a Stokes radius of 114 Å and M r 700 000. At the low protein concentrations obtained by zonal gel chromatography, the complex dissociates to yield free κ-casein. Whole casein isolated by high speed centrifugation and freed of calcium at pH 6.85 (first cycle casein) is shown to be an associating system with the polymeric species in rapid equilibrium. First cycle casein dissociates at low protein concentrations to a unit complex with a diameter of about 100 Å and M r approx. 270 000. The unit complex is shown by gel electrophoresis to contain κ-, α s1 - and β-caseins. The mild preparative methods employed in obtaining whole casein by centrifugation at pH 6.6 probably yield complexes more representative of their native quarternary structure than the casein complexes discussed previously. Our results, therefore, support a model of the native casein micelle built up from a 100-Å-diameter complex containing all the casein fractions.