Response of Fishes to Revetment Placement

Routine fish sampling with hoop nets was conducted monthly from April through December 1978 along natural and revetted riverbanks on the lower Mississippi River near Eudora, Arkansas, to monitor changes in fish populations affected by placement of new revetment for bank protection. Eighteen species of fish were collected with four species comprising over 75% of the total catch. During the months prior to revetment placement, freshwater drum, Aplodinotus grunniens, was the most abundant (32.7% of the catch) species collected. Following in abundance were the flathead catfish, Pylodictis olivaris, (9.8%), common carp, Cyprinus carpio, (7.8%), and blue catfish, Ictalurus furcatus, (3.3%). After revetment placement in August 1978, the freshwater drum was again the most abundant component, comprising 9.7% of the catch. Gizzard shad, Dorosoma cepedianum, flathead catfish, and blue catfish followed in abundance and comprised 8.9, 4.1, and 3.4% of the total catch, respectively. Catch per effort data indicated that fish were generally more abundant at natural bank stations than revetted bank stations but the difference was not significant. The study suggests that fish inhabiting natural riverbank habitat recover quite rapidly from bank perturbation caused by the placement of revetment

A rotor-mounted digital instrumentation system for helicopter blade flight research measurements

A rotor mounted flight instrumentation system developed for helicopter rotor blade research is described. The system utilizes high speed digital techniques to acquire research data from miniature pressure transducers on advanced rotor airfoils which are flight tested on an AH-1G helicopter. The system employs microelectronic pulse code modulation (PCM) multiplexer digitizer stations located remotely on the blade and in a hub mounted metal canister. As many as 25 sensors can be remotely digitized by a 2.5 mm thick electronics package mounted on the blade near the tip to reduce blade wiring. The electronics contained in the canister digitizes up to 16 sensors, formats these data with serial PCM data from the remote stations, and transmits the data from the canister which is above the plane of the rotor. Data are transmitted over an RF link to the ground for real time monitoring and to the helicopter fuselage for tape recording. The complete system is powered by batteries located in the canister and requires no slip rings on the rotor shaft

A Study of Giant Pulses from PSR J1824-2452A

We have searched for microsecond bursts of emission from millisecond pulsars in the globular cluster M28 using the Parkes radio telescope. We detected a total of 27 giant pulses from the known emitter PSR J1824-2452A. At wavelengths around 20 cm the giant pulses are scatter-broadened to widths of around 2 microseconds and follow power-law statistics. The pulses occur in two narrow phase-windows which correlate in phase with X-ray emission and trail the peaks of the integrated radio pulse-components. Notably, the integrated radio emission at these phase windows has a steeper spectral index than other emission. The giant pulses exhibit a high degree of polarization, with many being 100% elliptically polarized. Their position angles appear random. Although the integrated emission of PSR J1824-2452A is relatively stable for the frequencies and bandwidths observed, the intensities of individual giant pulses vary considerably across our bands. Two pulses were detected at both 2700 and 3500 MHz. The narrower of the two pulses is 20 ns wide at 3500 MHz. At 2700 MHz this pulse has an inferred brightness temperature at maximum of 5 x 10^37 K. Our observations suggest the giant pulses of PSR J1824-2452A are generated in the same part of the magnetosphere as X-ray emission through a different emission process to that of ordinary pulses.Comment: Accepted by Ap

Nonclassicality of a photon-subtracted Gaussian field

Published versio

Thermal convection in fluidized granular systems

Thermal convection is observed in molecular dynamic simulation of a fluidized granular system of nearly elastic hard disks moving under gravity, inside a rectangular box. Boundaries introduce no shearing or time dependence, but the energy injection comes from a slip (shear-free) thermalizing base. The top wall is perfectly elastic and lateral boundaries are either elastic or periodic. The observed convection comes from the effect of gravity and the spontaneous granular temperature gradient that the system dynamically develops.Comment: 4 pages, 5 figure

Continued fraction solution of Krein's inverse problem

The spectral data of a vibrating string are encoded in its so-called characteristic function. We consider the problem of recovering the distribution of mass along the string from its characteristic function. It is well-known that Stieltjes' continued fraction provides a solution of this inverse problem in the particular case where the distribution of mass is purely discrete. We show how to adapt Stieltjes' method to solve the inverse problem for a related class of strings. An application to the excursion theory of diffusion processes is presented.Comment: 18 pages, 2 figure

Self-consistency of relativistic observables with general relativity in the white dwarf-neutron star binary pulsar PSR J1141-6545

Here we report timing measurements of the relativistic binary pulsar PSR J1141-6545 that constrain the component masses and demonstrate that the orbital period derivative \dot Pb = (-4+/-1)x10^-13 is consistent with gravitational wave emission as described by the general theory of relativity. The mass of the neutron star and its companion are 1.30+/-0.02 Mo and 0.986+/-0.020 Mo respectively, suggesting a white dwarf companion, and extending the range of systems for which general relativity provides a correct description. On evolutionary grounds, the progenitor mass of PSR J1141-6545 should be near the minimum for neutron star production. Its mass is two standard deviations below the mean of the other neutron stars, suggesting a relationship between progenitor and remnant masses.Comment: 10 pages, 2 figures, revised version to Ap J Letter

Introduction to the computational structural mechanics testbed

The Computational Structural Mechanics (CSM) testbed software system based on the SPAR finite element code and the NICE system is described. This software is denoted NICE/SPAR. NICE was developed at Lockheed Palo Alto Research Laboratory and contains data management utilities, a command language interpreter, and a command language definition for integrating engineering computational modules. SPAR is a system of programs used for finite element structural analysis developed for NASA by Lockheed and Engineering Information Systems, Inc. It includes many complementary structural analysis, thermal analysis, utility functions which communicate through a common database. The work on NICE/SPAR was motivated by requirements for a highly modular and flexible structural analysis system to use as a tool in carrying out research in computational methods and exploring computer hardware. Analysis examples are presented which demonstrate the benefits gained from a combination of the NICE command language with a SPAR computational modules