Broadband arrayed waveguide gratings on InP

Broadband arrayed waveguide gratings on InP are presented using a novel S-shape design. This design was utilized to accommodate the large free spectral range required for broadband operation. Four and eight channel AWGs with a wavelength channel spacing of 18 nm are discussed. The output peaks of the AWGs have a wide FWHM of 11 nm which provides insensitive operation to polarization, temperature fluctuations, and chromatic dispersion.     

Three-parameter Lorentz-violating texture for neutrino mixing

A three-parameter model of neutrino oscillations based on a simple Lorentz- and CPT-violating texture is presented. The model is consistent with established data and naturally generates low-energy and neutrino–antineutrino anomalies of the MiniBooNE type. A one-parameter extension incorporates the MINOS anomaly, while a simple texture enhancement accommodates the LSND signal.     

High-power and high-temperature THz quantum-cascade lasers based on lens-coupled metal-metal waveguides

A metal-metal waveguide quantum cascade laser with an abutted silicon hyperhemispherical lens is demonstrated at ~4.1 THz. The device produced 145 mW of peak pulsed power at 5 K with a wall-plug power efficiency of 0.7%, lasing up to a maximum operating temperature of 160 K. The far-field beam pattern has a full width at half-maximum value of ~4.8 degrees in the H plane. The same device produced ~26 mW of peak power using a Winston cone instead of a lens, lasing up to 165 K. The large increase in output power is mainly attributed to an increase in collection efficiency.     

Antiferromagnetic Potts Models on the Square Lattice: A High-Precision Monte Carlo Study

We study the antiferromagnetic q-state Potts model on the square lattice for q=3 and q=4, using the Wang–Swendsen–Kotecký (WSK) Monte Carlo algorithm and a powerful finite-size-scaling extrapolation method. For q=3 we obtain good control up to correlation length 5000; the data are consistent with ()=Ae ^{2 p} (1+a ₁ e ^– + ...) as , with p1. The staggered susceptibility behaves as _stagg ^5/3. For q=4 the model is disordered (2) even at zero temperature. In appendices we prove a correlation inequality for Potts antiferromagnets on a bipartite lattice, and we prove ergodicity of the WSK algorithm at zero temperature for Potts antiferromagnets on a bipartite lattice.     

Loop Groups, Anyons and the Calogero–Sutherland Model

The positive energy representations of the loop group of U(1) are used to construct a boson-anyon correspondence. We compute all the correlation functions of our anyon fields and study an anyonic W-algebra of unbounded operators with a common dense domain. This algebra contains an operator with peculiar exchange relations with the anyon fields. This operator can be interpreted as a second quantized Calogero–Sutherland (CS) Hamiltonian and may be used to solve the CS model. In particular, we inductively construct all eigenfunctions of the CS model from anyon correlation functions, for all particle numbers and positive couplings. Received: 12 May 1998 / Accepted: 4 August 1998     

A linear time implementation of the reverse Cuthill-McKee algorithm

The Reverse Cuthill-McKee (RCM) algorithm is a method for reordering a sparse matrix so that it has a small envelope. Given a starting node, we provide an implementation of the algorithm whose run-time complexity is proved to be linear in the number of nonzeros in the matrix. Numerical experiments are provided which compare the performance of the new implementation to a good conventional implementation.     

Computer Scheduling of Vehicles from One or More Depots to a Number of Delivery Points

The problem of scheduling delivery vehicles from a number of depots to customers, subject to constraints on load and distance or time, is considered. A new algorithm is presented; this allows routes from several depots to be constructed simultaneously, subject to restrictions on numbers of vehicles at individual depots. Where too many customers require service, a flexible priority rule will select those to be served. Results for the single depot case are compared with other known algorithms; further results are given and discussed for cases of several depots.     

On the dynamics of turbulent vortical flow

Zusammenfassung Die Wirbelströmung in einer turbulenten kompressiblen Flüssigkeit wird behandelt. Die Bewegungsgleichungen werden durch die Vernachlässigung der kleineren Glieder vereinfacht. Die experimentellen Ergebnisse erlauben eine Fehlerrechnung für einen Fall. Ein wichtiger Schritt in der Vereinfachung ist die Voraussetzung, dass die Radialgradienten viel grösser sind als die Axialgradienten. Für die kräftigen Wirbel erwies sich diese Annahme sowohl durch die Erfahrung als auch aus den wesentlichen theoretischen Betrachtungen heraus als begründet. Die vereinfachten Gleichungen zeigen einige wichtige Aspekte der schnelldrehenden Strömungen und geben einen Anhaltspunkt für die ausführlicheren Studien.

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Notation r radial co-ordinate - z axial co-ordinate - u, U, u radial velocity component, its time-mean value, and the turbulent perturbation to it - v, V, v tangential or swirl velocity component, etc. - w, W, w axial velocity component, etc. - p, P, p fluid pressure, etc. - ,R, fluid density, etc. - , , , numbers small with respect to unity - C, F, G, G ₀ constants of integration     

Uniquely colorable perfect graphs

This paper defines the concept of sequential coloring. If G or its complement is one of four major types of perfect graphs, G is shown to be uniquely k-colorable it and only if it is sequentially k-colorable. It is conjectured that this equivalence is true for all perfect graphs. A potential role for sequential coloring in verifying the Strong Perfect Graph Conjecture is discussed. This conjecture is shown to be true for strongly sequentially colorable graphs.