986 research outputs found
Long-Term Results from Evaluation of Advanced New Construction Packages in Test Homes. Martha's Vineyard, Massachusetts
This report presents a cold climate project that examines the relationships among very energy efficient single-family residential thermal enclosures, room-to-room temperature variations, and simplified space conditioning systems. The project is located in West Tisbury, Massachusetts, on the island of Martha's Vineyard, and allowed for the comparison of room-to-room temperatures in four virtually identical houses that were all built to the same construction standard. The four homes each has a single ductless heat pump unit (DHU) located in the main living space and radiant electric resistance panels in each bedroom with individual thermostatic controls. Results indicate that temperature fluctuations in the living room due to aggressive setup and setback of the DHU may contribute to higher percentages of time where the bedroom temperatures were within +/-2 degrees F of the living room temperatures. Solar gains in the living room, door opening/closure and occupant manipulation of thermostats appear to have had a significant impact on room-to-room temperature differences, as would be expected
A systematic study of non-ideal contacts in integer quantum Hall systems
In the present article we investigate the influence of the contact region on
the distribution of the chemical potential in integer quantum Hall samples, as
well as the longitudinal and Hall resistance as a function of the magnetic
field. First we use a standard quantum Hall sample geometry and analyse the
influence of the length of the leads where current enters/leaves the sample and
the ratio of the contact width to the width of these leads. Furthermore we
investigate potential barriers in the current injecting leads and the
measurement arms in order to simulate non-ideal contacts. Second we simulate
nonlocal quantum Hall samples with applied gating voltage at the metallic
contacts. For such samples it has been found experimentally that both the
longitudinal and Hall resistance as a function of the magnetic field can change
significantly. Using the nonequilibrium network model we are able to reproduce
most qualitative features of the experiments.Comment: 29 pages, 16 Figure
Trapped two-component Fermi gases with up to six particles: Energetics, structural properties, and molecular condensate fraction
We investigate small equal-mass two-component Fermi gases under external
spherically symmetric confinement in which atoms with opposite spins interact
through a short-range two-body model potential. We employ a non-perturbative
microscopic framework, the stochastic variational approach, and determine the
system properties as functions of the interspecies s-wave scattering length a,
the orbital angular momentum L of the system, and the numbers N1 and N2 of
spin-up and spin-down atoms (with N1-N2 =0 or 1 and N < 7, where N=N1+N2). At
unitarity, we determine the energies of the five- and six-particle systems for
various ranges r0 of the underlying two-body model potential and extrapolate to
the zero-range limit. These energies serve as benchmark results that can be
used to validate and assess other numerical approaches. We also present
structural properties such as the pair distribution function and the radial
density. Furthermore, we analyze the one-body and two-body density matrices. A
measure for the molecular condensate fraction is proposed and applied. Our
calculations show explicitly that the natural orbitals and the momentum
distributions of atomic Fermi gases approach those characteristic for a
molecular Bose gas if the s-wave scattering length a, a>0, is sufficiently
small.Comment: 21 pages, 15 figures; accepted for publication in special issue of
CRA
A Comparison of Ultraviolet, Optical, and X-Ray Imagery of Selected Fields in the Cygnus Loop
During the Astro-1 and Astro-2 Space Shuttle missions in 1990 and 1995, far
ultraviolet (FUV) images of five 40' diameter fields around the rim of the
Cygnus Loop supernova remnant were observed with the Ultraviolet Imaging
Telescope (UIT). These fields sampled a broad range of conditions including
both radiative and nonradiative shocks in various geometries and physical
scales. In these shocks, the UIT B5 band samples predominantly CIV 1550 and the
hydrogen two-photon recombination continuum. Smaller contri- butions are made
by emission lines of HeII 1640 and OIII] 1665. We present these new FUV images
and compare them with optical Halpha and [OIII], and ROSAT HRI X-ray images.
Comparing the UIT images with those from the other bands provides new insights
into the spatial variations and locations of these different types of emission.
By comparing against shock model calculations and published FUV spectroscopy at
select locations, we surmise that resonance scattering in the strong FUV
permitted lines is widespread in the Cygnus Loop, especially in the bright
optical filaments typically selected for observation in most previous studies.Comment: 21 pages with 10 figures. See http://www.pha.jhu.edu/~danforth/uit/
for full-resolution figure
Long-Term Results from Evaluation of Advanced New Construction Packages in Test Homes: Lake Elsinore, California
This report presents the long-term evaluation results from a hot-dry climate project that examines the room-to-room temperature conditions that exist in a high performance envelope, the performance of a simplified air distribution system, and a comparison of modeled energy performance with measured energy use. The project, a prototype house built by K. Hovnanian Homes' Ontario Group, is located in Lake Elsinore, Riverside County, California, and achieves a 50% level of whole house source energy savings with respect to the Building America (BA) Benchmark Definition 2009 (Hendron and Engebrecht 2010). Temperature measurements in three rooms indicate that the temperature difference between the measured locations and the thermostat were within recommendations 90.3% of the time in heating mode and 99.3% of the time in cooling mode. The air distribution system is operating efficiently with average delivered temperatures adequate to facilitate proper heating and cooling and only minor average temperature differences observed between the system's plenum and farthest register. Monitored energy use results for the house indicate that it is using less energy than predicted from modeling. A breakdown of energy use according to end use determined little agreement between comparable values
Commissioning of the Fresno, California, Retrofit Unoccupied Test House
Commissioning of instrumentation and limited short-term testing have been completed on a retrofit unoccupied test house in Fresno, California. This house is intended to be used as a laboratory in which several different methods of space conditioning distribution will be evaluated. This report provides background on the project, including specifications of the house and models used in its development, along with models to be evaluated through its operation
Residential Ground Source Heat Pumps with Integrated Domestic Hot Water Generation: Performance Results from Long-Term Monitoring
This document is no longer available. Please contact [email protected] for further information
Hyperspherical Description of the Degenerate Fermi Gas: S-wave Interactions
We present a unique theoretical description of the physics of the spherically
trapped -atom degenerate Fermi gas (DFG) at zero temperature based on an
ordinary Schr\"{o}dinger equation with a microscopic, two body interaction
potential. With a careful choice of coordinates and a variational wavefunction,
the many body Schr\"{o}dinger equation can be accurately described by a
\emph{linear}, one dimensional effective Schr\"{o}dinger equation in a single
collective coordinate, the rms radius of the gas. Comparisons of the energy,
rms radius and peak density of ground state energy are made to those predicted
by Hartree-Fock (HF). Also the lowest radial excitation frequency (the
breathing mode frequency) agrees with a sum rule calculation, but deviates from
a HF prediction
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