Surface-wave damping in a brimful circular cylinder

The natural frequencies and damping rates of surface waves in a circular cylinder with pinned-end boundary conditions are calculated in terms of the gravitational Reynolds and Bond numbers, C[minus sign]1 and B, and the slenderness of the cylinder [Lambda], in the limit C[rightward arrow]0. We consider higher-order approximations that include the effect of viscous dissipation in the Stokes boundary layers and the bulk. A comparison with clean-surface experiments by Henderson & Miles (1994) shows a satisfactory agreement except for the first axisymmetric mode, which exhibits a 26% discrepancy. The much larger dramatic discrepancy of former theoretical predictions is hereby improved and explained

Description of the inelastic collision of two solitary waves for the BBM equation

We prove that the collision of two solitary waves of the BBM equation is inelastic but almost elastic in the case where one solitary wave is small in the energy space. We show precise estimates of the nonzero residue due to the collision. Moreover, we give a precise description of the collision phenomenon (change of size of the solitary waves).Comment: submitted for publication. Corrected typo in Theorem 1.

Regular coordinate systems for Schwarzschild and other spherical spacetimes

The continuation of the Schwarzschild metric across the event horizon is almost always (in textbooks) carried out using the Kruskal-Szekeres coordinates, in terms of which the areal radius r is defined only implicitly. We argue that from a pedagogical point of view, using these coordinates comes with several drawbacks, and we advocate the use of simpler, but equally effective, coordinate systems. One such system, introduced by Painleve and Gullstrand in the 1920's, is especially simple and pedagogically powerful; it is, however, still poorly known today. One of our purposes here is therefore to popularize these coordinates. Our other purpose is to provide generalizations to the Painleve-Gullstrand coordinates, first within the specific context of Schwarzschild spacetime, and then in the context of more general spherical spacetimes.Comment: 5 pages, 2 figures, ReVTeX; minor changes were made, new references were include

Vacuum Energy: If Not Now, Then When?

We review the cosmological evidence for a low matter density universe and a cosmological constant or dynamical vacuum energy and address the cosmolog$ coincidence problem: why is the matter density about one-half the vacuum energy {\em now}. This is reasonble, following the anthropic argument of Efstathiou and of Martel, Schapiro & Weinberg.Comment: 4 pages (latex

Light Propagation in inhomogeneous Universes

Using a multi-plane lensing method that we have developed, we follow the evolution of light beams as they propagate through inhomogeneous universes. We use a P3M code to simulate the formation and evolution of large-scale structure. The resolution of the simulations is increased to sub-Megaparsec scales by using a Monte Carlo method to locate galaxies inside the computational volume according to the underlying particle distribution. The galaxies are approximated by isothermal spheres, with each morphological type having its own distribution of masses and core radii. The morphological types are chosen in order to reproduce the observed morphology-density relation. This algorithm has an effective resolution of 9 orders of magnitudes in length, from the size of superclusters down to the core radii of the smallest galaxies. We consider cold dark matter models normalized to COBE, and perform a large parameter survey by varying the cosmological parameters Omega_0, lambda_0, H_0, and n (the tilt of the primordial power spectrum). The values of n are chosen by imposing particular values or sigma_8, the rms mass fluctuation at a scale of 8/h Mpc. We use the power spectrum given by Bunn & White. This is the largest parameter survey ever done is this field.Comment: 3 pages, gzip'ed tar file, including TeX source (not Latex). To be published in a periodical of the Yukawa Institute for Theoretical Physics (1998

Aharonov-Bohm effect in circular carbon nanotubes

We study the interference of interacting electrons in toroidal single-wall carbon nanotubes coupled to metallic electrodes by tunnel junctions. The dc conductance shows resonant features as a function of the gate voltage and the magnetic field. The conductance pattern is determined by the interaction parameter, which in turn can be cross-checked against the exponents governing the transport at high temperatures. The coordinate dependence of the conductance reflects electron correlations in one-dimensional space.Comment: 2 pages, contributed paper to LT-22, style file phbauth.cls is include

Microfluidic-SANS: flow processing of complex fluids

Understanding and engineering the flow-response of complex and non-Newtonian fluids at a molecular level is a key challenge for their practical utilisation. Here we demonstrate the coupling of microfluidics with small angle neutron scattering (SANS). Microdevices with high neutron transmission (up to 98%), low scattering background ([Image: see text]), broad solvent compatibility and high pressure tolerance (≈3–15 bar) are rapidly prototyped via frontal photo polymerisation. Scattering from single microchannels of widths down to 60 μm, with beam footprint of 500 μm diameter, was successfully obtained in the scattering vector range 0.01–0.3 Å(−1), corresponding to real space dimensions of [Image: see text]. We demonstrate our approach by investigating the molecular re-orientation and alignment underpinning the flow response of two model complex fluids, namely cetyl trimethylammonium chloride/pentanol/D(2)O and sodium lauryl sulfate/octanol/brine lamellar systems. Finally, we assess the applicability and outlook of microfluidic-SANS for high-throughput and flow processing studies, with emphasis of soft matter

Effective strategies for general and special education teachers

Today’s teachers are asked to educate ALL students using research-based strategies in inclusive classrooms. The following review will include three research based instructional strategies and one teaching model all of which are elements that can increase the success of students at risk for learning problems. Instructional strategies explored in this review are class-wide peer tutoring, direct instruction and the behavioral strategy of self-monitoring. The teaching model is known as co-teaching, a model which is becoming the norm in schools in southeast Michigan. It is hypothesized that concrete knowledge of research based instructional methods that can be used in co-teaching situations may reduce rates of teacher frustration and attrition, and will improve academic and behavioral performance of students in a variety of settings