Experimental investigation of a magnetically balanced arc in a transverse argon flow

"Reprinted from Journal of Engineering for Power January, 1966.""An experimental study of an electric arc in crossed convective and magnetic fields has been made. An electric arc was established across a rectangular test section through which argon gas was flowing at approximately atmospheric pressure and velocities up to 100 m/sec. Magnetic field strengths up to 3 webers/m2, oriented so that the Lorentz force opposed the convective force on the arc, were applied perpendicular lo both the arc and the direction of the argon gas flow. The test apparatus and the procedure used to obtain the experimental relationship between the velocity of the argon flow and the balancing magnetic field are described. An analysis which assumed the magnetically balanced arc lo be a gaseous cylinder positioned between the electrodes and with a diameter varying directly as the arc current satisfactorily explained the observed dependence of the balancing magnetic field on the gas velocity."--Page 1

D--branes and Spinning Black Holes

We obtain a new class of spinning charged extremal black holes in five dimensions, considered both as classical configurations and in the Dirichlet(D)--brane representation. The degeneracy of states is computed from the D--brane side and the entropy agrees perfectly with that obtained from the black hole side.Comment: 10 pages, harvmac ``b'' mode (minor changes

A case of post-fundoplication dysphagia: another possible interpretation of the manometric findings

Jennifer C Myers, and John Den

Achalasia subtypes are front and center of the Chicago classification-strategies to overcome limitations in clinical application

Published: 25 September 2020.High-resolution manometry (HRM) with closely spaced pressure sensors, enhances visualization and interpretation of esophageal pressures. HRM software displays two key physiological features of achalasia: inadequate swallow-induced lower esophageal sphincter (LES) relaxation, and the absence of normal esophageal primary peristalsis. HRM metrics quantify these features, by determining: (I) integrated relaxation pressure (IRP) of the esophagogastric junction (EGJ) during swallowing; and (II) esophageal body pressure patterns of absent or abnormal peristalsis, with high sensitivity for diagnosis of achalasia. These measures guide identification of three achalasia subtypes, through the Chicago classification of motility disorders. Achalasia subtypes stratify prevalent esophageal body pressure patterns with: subtype I, absent pressures (aperistalsis); subtype II, uniform pressures (esophageal pan pressurization); and subtype III, spasm pressures (spastic, premature or abnormal contractions). Whenever HRM reveals a non-relaxing EGJ, achalasia subtypes are front and center of the hierarchical classification process, with relevance to treatment outcomes. Exploration of pathophysiology suggests esophageal circular and longitudinal muscle function varies with achalasia subtype. Beyond the classification, an achalasia-like syndrome refers to a minority of patients where pressures do not meet criteria for achalasia subtypes, necessitating adjunct tests. Application of HRM in patients with achalasia can be challenging. Limitations during acquisition may occur with resistance at the EGJ or catheter curling, and esophageal pooling with successive water swallows. Interpretation requires care when EGJ relaxation pressure is within the normal range or affected by longitudinal muscle contraction. To overcome inconclusive HRM findings, strategies to clarify dysmotility include adjunct swallow challenge tests or additional investigations. Evolving manometric protocols, additional HRM metrics, and incorporation of intraluminal impedance will maximize HRM utility for achalasia.Jennifer C. Myers, Charles Coc

Index theorem for topological excitations on R^3 * S^1 and Chern-Simons theory

We derive an index theorem for the Dirac operator in the background of various topological excitations on an R^3 \times S^1 geometry. The index theorem provides more refined data than the APS index for an instanton on R^4 and reproduces it in decompactification limit. In the R^3 limit, it reduces to the Callias index theorem. The index is expressed in terms of topological charge and the eta-invariant associated with the boundary Dirac operator. Neither topological charge nor eta-invariant is typically an integer, however, the non-integer parts cancel to give an integer-valued index. Our derivation is based on axial current non-conservation--an exact operator identity valid on any four-manifold--and on the existence of a center symmetric, or approximately center symmetric, boundary holonomy (Wilson line). We expect the index theorem to usefully apply to many physical systems of interest, such as low temperature (large S^1, confined) phases of gauge theories, center stabilized Yang-Mills theories with vector-like or chiral matter (at S^1 of any size), and supersymmetric gauge theories with supersymmetry-preserving boundary conditions (also at any S^1). In QCD-like and chiral gauge theories, the index theorem should shed light into the nature of topological excitations responsible for chiral symmetry breaking and the generation of mass gap in the gauge sector. We also show that imposing chirally-twisted boundary condition in gauge theories with fermions induces a Chern-Simons term in the infrared. This suggests that some QCD-like gauge theories should possess components with a topological Chern-Simons phase in the small S^1 regime.Comment: 29 pages, refs added, published versio

Dictionary Matching with One Gap

The dictionary matching with gaps problem is to preprocess a dictionary $D$ of $d$ gapped patterns $P_1,\ldots,P_d$ over alphabet $\Sigma$, where each gapped pattern $P_i$ is a sequence of subpatterns separated by bounded sequences of don't cares. Then, given a query text $T$ of length $n$ over alphabet $\Sigma$, the goal is to output all locations in $T$ in which a pattern $P_i\in D$, $1\leq i\leq d$, ends. There is a renewed current interest in the gapped matching problem stemming from cyber security. In this paper we solve the problem where all patterns in the dictionary have one gap with at least $\alpha$ and at most $\beta$ don't cares, where $\alpha$ and $\beta$ are given parameters. Specifically, we show that the dictionary matching with a single gap problem can be solved in either $O(d\log d + |D|)$ time and $O(d\log^{\varepsilon} d + |D|)$ space, and query time $O(n(\beta -\alpha )\log\log d \log ^2 \min \{ d, \log |D| \} + occ)$, where $occ$ is the number of patterns found, or preprocessing time and space: $O(d^2 + |D|)$, and query time $O(n(\beta -\alpha ) + occ)$, where $occ$ is the number of patterns found. As far as we know, this is the best solution for this setting of the problem, where many overlaps may exist in the dictionary.Comment: A preliminary version was published at CPM 201

Macroscopic and Microscopic Entropy of Near-Extremal Spinning Black Holes

A seven parameter family of five-dimensional black hole solutions depending on mass, two angular momenta, three charges and the asymptotic value of a scalar field is constructed. The entropy is computed as a function of these parameters both from the Bekenstein-Hawking formula and from the degeneracies of the corresponding D-brane states in string theory. The expressions agree at and to leading order away from extremality.Comment: 7 pages, harvma

Current driven switching of magnetic layers

The switching of magnetic layers is studied under the action of a spin current in a ferromagnetic metal/non-magnetic metal/ferromagnetic metal spin valve. We find that the main contribution to the switching comes from the non-equilibrium exchange interaction between the ferromagnetic layers. This interaction defines the magnetic configuration of the layers with minimum energy and establishes the threshold for a critical switching current. Depending on the direction of the critical current, the interaction changes sign and a given magnetic configuration becomes unstable. To model the time dependence of the switching process, we derive a set of coupled Landau-Lifshitz equations for the ferromagnetic layers. Higher order terms in the non-equilibrium exchange coupling allow the system to evolve to its steady-state configuration.Comment: 8 pages, 2 figure. Submitted to Phys. Rev.

Reduction of the Three Dimensional Schrodinger Equation for Multilayered Films

In this paper, we present a method for reducing the three dimensional Schrodinger equation to study confined metallic states, such as quantum well states, in a multilayer film geometry. While discussing some approximations that are employed when dealing with the three dimensionality of the problem, we derive a one dimensional equation suitable for studying such states using an envelope function approach. Some applications to the Cu/Co multilayer system with regard to spin tunneling/rotations and angle resolved photoemission are discussed.Comment: 14 pages, 1 figur