Lehigh University

About: Lehigh University is a education organization based out in Bethlehem, Pennsylvania, United States. It is known for research contribution in the topics: Catalysis & Fracture mechanics. The organization has 12684 authors who have published 26550 publications receiving 770061 citations.

Secondary vortices in the wake of circular cylinders

Abstract: Using both the hydrogen-bubble flow-visualization technique and hot-wire-anemometry measurements, secondary vortices have been detected in the near-wake of circular cylinders and their characteristics studied over a Reynolds-number range of 1200–11000. The vortex-shedding characteristics of these secondary vortices clearly indicate that ‘transition waves’, detected in the cylinder near wake by Bloor (1964), and secondary vortices are identical phenomena. It is established that the non-dimensional shedding frequency of the secondary vortices demonstrates a 0.87 power-law relationship relative to Reynolds number, contrary to the 0.5 power-law reported by Bloor. The results suggest that the vortices result from a near-wake, free-shear instability which causes the separated cylinder boundary layer to roll up into the secondary vortices. Visual observations indicate that immediately following their formation the vortices undergo a strong three-dimensional distortion, which may provide the mechanism for the transition from laminar to turbulent Strouhal vortices.

Energy-Flux Operator for a Lattice

Abstract: A systematic derivation of the energy-flux operator for a three-dimensional lattice is given. The treatment is based on the general expressions for the energy flux which are valid for all phases of matter; a short derivation of these expressions, making no restrictions to two-body forces, is presented. The average energy flux is transformed to the phonon representation, and it is shown that the diagonal contribution from the harmonic forces has the familiar form $\ensuremath{\Sigma}{\mathrm{k}s}^{}{N}_{\mathrm{k}s}\ensuremath{\hbar}{\ensuremath{\omega}}_{\mathrm{k}s}{\mathrm{v}}_{\mathrm{k}s}$. There are, in addition, nondiagonal contributions to the energy flux, even in the harmonic approximation. The significance of these corrections is discussed. The contributions to the average flux from the anharmonic forces and from lattice imperfections are also treated. Finally, the problem of forming wave packets of the plane-wave normal modes to obtain an expression for the local energy flux is considered.

When All Else Fails: Ethnic Population Transfers and Partitions in the Twentieth Century

Abstract: ~ U n t i l recently, there has been a near consensus among policymakers and scholars that the objective of ethnic conflict management should be to support and preserve integrated, multiethnic societies. In the last few years, however, the idea that separating the warring populations may be the best solution to many of the most intense ethnic conflicts has been gaining ground. Events in Bosnia have supported this trend, as observers note that the more the warring groups have separated, the more peaceful their relations have become, while proposals to thoroughly reintegrate them command less and less support.' In addition, a growing body of scholarship that focuses on the role of intergroup security dilemmas in ethnic conflicts argues that intermixed population settlement patterns can promote escalation of violence, implying that separation of warring groups may dampen conflict2

The current status of interpenetrating polymer networks

Abstract: An interpenetrating polymer network, IPN, is defined as a combination of two or more polymers in network form, at least one of which is polymerized and/or crosslinked in the immediate presence of the other(s). The synthesis, morphology and mechanical properties of recent works are reviewed, with special emphasis on dual phase continuity, and the number of physical entanglements that arise in homo-IPNs. The concepts of phase diagrams are applied, especially to simultaneous interpenetrating network phase separations and gelations. Recent engineering applications are discussed.