Solving large scale linear programming

The interior point method (IPM) is now well established as a competitive technique for solving very large scale linear programming problems. The leading variant of the interior point method is the primal dual - predictor corrector algorithm due to Mehrotra. The main computational steps of this algorithm are the repeated calculation and solution of a large sparse positive definite system of equations. We describe an implementation of the predictor corrector IPM algorithm on MasPar, a massively parallel SIMD computer. At the heart of the implemen-tation is a parallel Cholesky factorization algorithm for sparse matrices. Our implementation uses a new scheme of mapping the matrix onto the processor grid of the MasPar, that results in a more efficient Cholesky factorization than previously suggested schemes. The IPM implementation uses the parallel unit of MasPar to speed up the factorization and other computationally intensive parts of the IPM. An impor-tant part of this implementation is the judicious division of data and computation between the front-end computer, that runs the main IPM algorithm, and the par-allel unit. Performanc

Protocols for calibrating multibeam sonar

Author Posting. © Acoustical Society of America, 2005. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 117 (2005): 2013-2027, doi:10.1121/1.1869073.Development of protocols for calibrating multibeam sonar by means of the standard-target method is documented. Particular systems used in the development work included three that provide the water-column signals, namely the SIMRAD SM2000/90- and 200-kHz sonars and RESON SeaBat 8101 sonar, with operating frequency of 240 kHz. Two facilities were instrumented specifically for the work: a sea well at the Woods Hole Oceanographic Institution and a large, indoor freshwater tank at the University of New Hampshire. Methods for measuring the transfer characteristics of each sonar, with transducers attached, are described and illustrated with measurement results. The principal results, however, are the protocols themselves. These are elaborated for positioning the target, choosing the receiver gain function, quantifying the system stability, mapping the directionality in the plane of the receiving array and in the plane normal to the central axis, measuring the directionality of individual beams, and measuring the nearfield response. General preparations for calibrating multibeam sonars and a method for measuring the receiver response electronically are outlined. Advantages of multibeam sonar calibration and outstanding problems, such as that of validation of the performance of multibeam sonars as configured for use, are mentioned.Support by the National Science Foundation through Award No. OCE-0002664, NOAA through Grant No. NA97OG0241, and the Cooperative Institute for Climate and Ocean Research (CICOR) through NOAA Contract No. NA17RJ1223 is acknowledged

Nippers stand ready to compete, 1990 [picture] /

Condition: Good.; Title supplied by photographer.; Also available in an electronic version via the Internet at: http://nla.gov.au/nla.pic-vn3970586; Purchased from Jeff Carter, 2007

Exploration of temperature effects on the far-field acoustic radiation from a supersonic jet

Jet engines designed for high-speed aircraft commonly include C-D nozzles to obtain supersonic speeds. The radiated noise from the jet exhaust reaches acoustic levels which may cause hearing damage to the pilot and the air-field personnel even though state of the art noise protection such as noise-canceling ear muffs are employed. It is therefore extremely important to keep the noise levels as low as possible. Understanding the noise generation mechanism is of great importance in order to reduce strength of the noise sources. Typical far-field noise spectral characteristics from the supersonic jet exhaust consist of turbulent mixing noise and shock-associated noise. Another noise component named'crackle' is radiated from the jet under certain circumstances. Although it does not appear in the noise spectra due to its characteristics, its rasping character is perceived as a dominant annoyance factor by the human ear. Since it does not appear in the spectrum other measures are needed to identify the existence of'crackle'. Statistical tools like Skewness and Kurtosis applied to the far- and near-field pressure signals and the time derivate of the pressure signal have been shown in literature to be useful for identification of'crackle' events. In this paper the near-field and far-field acoustic radiation from a supersonic jet is analyzed using LES with a code developed at Chalmers University of Technology. The code has previously shown to accurately capture far-field noise spectra of supersonic jets under a variety of moderately cool jet conditions. In the present study we move towards more realistic high-speed aircraft conditions with higher jet exhaust temperatures. The nozzle is operated at slightly underexpanded conditions (NPR = 4.0) and three different stagnation temperature ratios NTR = 1.0, NTR = 2.0 and NTR = 3.0. The LES results are compared with experiments conducted at the Gas Dynamics and Propulsion Laboratory at the University of Cincinnati

An analysis of Turkish high school students' metacognition and motivation

The present study aimed at investigating Turkish high school students' metacognition and its relation to achievement goals (mastery approach goals, mastery avoidance goals, performance approach goals, performance avoidance goals), perceived competence, and perceived classroom environment (challenge and threat). Metacognition was examined in terms of knowledge of cognition (declarative knowledge, procedural knowledge, and conditional knowledge) and regulation of cognition (planning, information management, monitoring, debugging, and evaluating). Self-report instruments were administered to 141 high school students with a mean age of 15.29 to assess variables of the study. Results reveal that Turkish high school students have more declarative and conditional knowledge than procedural knowledge and mostly use debugging strategies. All motivational variables except threat were found to be positively linked to students' metacognition. The students also appear to adopt approach goals more than avoidance goals. Results were interpreted taking the Turkish educational system into consideration