12,555 research outputs found
A vapor barrier for cold testing printed circuit cards
Cold testing method prevents formation of frost on printed circuit boards and part holders during testing at sub-zero temperatures. Freon permits rapid attainment of the required testing temperature
Heat Transport in Mesoscopic Systems
Phonon heat transport in mesoscopic systems is investigated using methods
analogous to the Landauer description of electrical conductance. A "universal
heat conductance" expression that depends on the properties of the conducting
pathway only through the mode cutoff frequencies is derived. Corrections due to
reflections at the junction between the thermal body and the conducting bridge
are found to be small except at very low temperatures where only the lowest few
bridge modes are excited. Various non-equilibrium phonon distributions are
studied: a narrow band distribution leads to clear steps in the cooling curve,
analogous to the quantized resistance values in narrow wires, but a thermal
distribution is too broad to show such features.Comment: To be published in Superlattices and Microstructures, special issue
in honor of Rolf Landauer, March 198
Domain Coarsening in Systems Far from Equilibrium
The growth of domains of stripes evolving from random initial conditions is
studied in numerical simulations of models of systems far from equilibrium such
as Rayleigh-Benard convection. The scaling of the size of the domains deduced
from the inverse width of the Fourier spectrum is studied for both potential
and nonpotential models. The morphology of the domains and the defect
structures are however quite different in the two cases, and evidence is
presented for a second length scale in the nonpotential case.Comment: 11 pages, RevTeX; 3 uufiles encoded postscript figures appende
Flight test evaluation of a method to determine the level flight performance of a propeller-driven aircraft
The overall drag of the aircraft is expressed in terms of the measured increment of power required to overcome a corresponding known increment of drag, which is generated by a towed drogue. The simplest form of the governing equations, D = delta D SHP/delta SHP, is such that all of the parameters on the right side of the equation can be measured in flight. An evaluation of the governing equations has been performed using data generated by flight test of a Beechcraft T-34B. The simplicity of this technique and its proven applicability to sailplanes and small aircraft is well known. However, the method fails to account for airframe-propulsion system
The monoclinic phase in PZT: new light on morphotropic phase boundaries
A summary of the work recently carried out on the morphotropic phase boundary
(MPB) of PZT is presented. By means of x-ray powder diffraction on ceramic
samples of excellent quality, the MPB has been successfully characterized by
changing temperature in a series of closely spaced compositions. As a result,
an unexpected monoclinic phase has been found to exist in between the
well-known tetragonal and rhombohedral PZT phases. A detailed structural
analysis, together with the investigation of the field effect in this region of
compositions, have led to an important advance in understanding the mechanisms
responsible for the physical properties of PZT as well as other piezoelectric
materials with similar morphotropic phase boundaries.Comment: 5 pages REVTeX file, 6 figures embedded. Presented at the Workshop on
"Fundamental Physics of Ferroelectrics" held in Aspen, February 00. To appear
in the proceeding
An experimental investigation of the aerodynamics and cooling of a horizontally-opposed air-cooled aircraft engine installation
A flight-test based research program was performed to investigate the aerodynamics and cooling of a horizontally-opposed engine installation. Specific areas investigated were the internal aerodynamics and cooling mechanics of the installation, inlet aerodynamics, and exit aerodynamics. The applicable theory and current state of the art are discussed for each area. Flight-test and ground-test techniques for the development of the cooling installation and the solution of cooling problems are presented. The results show that much of the internal aerodynamics and cooling technology developed for radial engines are applicable to horizontally opposed engines. Correlation is established between engine manufacturer's cooling design data and flight measurements of the particular installation. Also, a flight-test method for the development of cooling requirements in terms of easily measurable parameters is presented. The impact of inlet and exit design on cooling and cooling drag is shown to be of major significance
Full scale visualization of the wing tip vortices generated by a typical agricultural aircraft
The trajectories of the wing tip vortices of a typical agricultural aircraft were experimentally determined by flight test. A flow visualization method, similar to the vapor screen method used in wind tunnels, was used to obtain trajectory data for a range of flight speeds, airplane configurations, and wing loadings. Detailed measurements of the spanwise surface pressure distribution were made for all test points. Further, a powered 1/8 scale model of the aircraft was designed, built, and used to obtain tip vortex trajectory data under conditions similar to that of the full scale test. The effects of light wind on the vortices were demonstrated, and the interaction of the flap vortex and the tip vortex was clearly shown in photographs and plotted trajectory data
Laboratory Tests of Gravitational Physics Using a Cryogenic Torsion Pendulum
Progress and plans are reported for a program of gravitational physics
experiments using cryogenic torsion pendula undergoing large amplitude
torsional oscillation. The program includes a UC Irvine project to measure the
gravitational constant G and joint UC Irvine - U. Washington projects to test
the gravitational inverse square law at a range of about 10 cm and to test the
weak equivalence principle.Comment: 17 pages, 11 figures, contribution to the 10th Marcel Grossman
Conference Proceedings (Rio de Janeiro, July 20 - 26, 2003) - changed wording
in first paragraph of section
Finite Size Scaling of Domain Chaos
Numerical studies of the domain chaos state in a model of rotating
Rayleigh-Benard convection suggest that finite size effects may account for the
discrepancy between experimentally measured values of the correlation length
and the predicted divergence near onset
Prevalence and Antimicrobial Agent Susceptibility of Methicillin-resistant Staphylococcus aureus in Healthy Pediatric Outpatients in Las Vegas
Colonization and infection by community-associated resistant strains of Staphylococcus aureus are being reported in epidemic proportions. The purpose of this study was to determine the local prevalence of methicillin-resistant Staphylococcus aureus (MRSA) colonization in children and to characterize the MRSA isolates in the laboratory with regard to antimicrobial agent susceptibility patterns, and the presence of the mecA and the Panton-Valentine leukocidin (PVL) genes. Nasal swabs were collected at two pediatric clinics from a total of 505 children during health maintenance visits. A brief questionnaire was administered to collect demographic data and pertinent medical, family, and social history. Samples were cultured onto 2 selective media for S. aureus and MRSA. Potential MRSA isolates were further evaluated by real-time polymerase chain reaction (PCR), and for susceptibility to eight antibiotics by disk diffusion. Culture results showed that MRSA was present in 15 of the 505 specimens (3.0%). Six different antimicrobial susceptibility profiles were observed among the MRSA isolates. PCR amplification results showed that all 15 MRSA isolates were positive for the presence of the mecA gene, and 10 MRSA isolates contained the PVL gene. Understanding local prevalence rates and the role of colonization in infection are needed to develop effective interventions to reduce MRSA infections
- …