6,096 research outputs found
An experimental investigation of two large annular diffusers with swirling and distorted inflow
Two annular diffusers downstream of a nacelle-mounted fan were tested for aerodynamic performance, measured in terms of two static pressure recovery parameters (one near the diffuser exit plane and one about three diameters downstream in the settling duct) in the presence of several inflow conditions. The two diffusers each had an inlet diameter of 1.84 m, an area ratio of 2.3, and an equivalent cone angle of 11.5, but were distinguished by centerbodies of different lengths. The dependence of diffuser performance on various combinations of swirling, radially distorted, and/or azimuthally distorted inflow was examined. Swirling flow and distortions in the axial velocity profile in the annulus upstream of the diffuser inlet were caused by the intrinsic flow patterns downstream of a fan in a duct and by artificial intensification of the distortions. Azimuthal distortions or defects were generated by the addition of four artificial devices (screens and fences). Pressure recovery data indicated beneficial effects of both radial distortion (for a limited range of distortion levels) and inflow swirl. Small amounts of azimuthal distortion created by the artificial devices produced only small effects on diffuser performance. A large artificial distortion device was required to produce enough azimuthal flow distortion to significantly degrade the diffuser static pressure recovery
The Mauna Kea Observatories Near-Infrared Filter Set. II. Specifications for a New JHKL'M' Filter Set for Infrared Astronomy
We present a description of a new 1--5 m filter set similar to the
long-used JHKLM filter set derived from that of Johnson. The new Mauna Kea
Observatories Near-Infrared (MKO-NIR) filter set is designed to reduce
background noise, improve photometric transformations from observatory to
observatory, provide greater accuracy in extrapolating to zero air mass, and
reduce the color dependence in the extinction coefficient in photometric
reductions. We have also taken into account the requirements of adaptive optics
in setting the flatness specification of the filters. A complete technical
description is presented to facilitate the production of similar filters in the
future.Comment: PASP, in press. 16 pages, 4 figures, 3 table
JWalk: a tool for lazy, systematic testing of java classes by design introspection and user interaction
Popular software testing tools, such as JUnit, allow frequent retesting of modified code; yet the manually created test scripts are often seriously incomplete. A unit-testing tool called JWalk has therefore been developed to address the need for systematic unit testing within the context of agile methods. The tool operates directly on the compiled code for Java classes and uses a new lazy method for inducing the changing design of a class on the fly. This is achieved partly through introspection, using Java’s reflection capability, and partly through interaction with the user, constructing and saving test oracles on the fly. Predictive rules reduce the number of oracle values that must be confirmed by the tester. Without human intervention, JWalk performs bounded exhaustive exploration of the class’s method protocols and may be directed to explore the space of algebraic constructions, or the intended design state-space of the tested class. With some human interaction, JWalk performs up to the equivalent of fully automated state-based testing, from a specification that was acquired incrementally
Universal parametric correlations in the transmission eigenvalue spectra of disordered conductors
We study the response of the transmission eigenvalue spectrum of disordered
metallic conductors to an arbitrary external perturbation. For systems without
time-reversal symmetry we find an exact non-perturbative solution for the
two-point correlation function, which exhibits a new kind of universal behavior
characteristic of disordered conductors. Systems with orthogonal and symplectic
symmetries are studied in the hydrodynamic regime.Comment: 10 pages, written in plain TeX, Preprint OUTP-93-36S (University of
Oxford), to appear in Phys. Rev. B (Rapid Communication
Carbon-Enhanced Metal-Poor Stars. III. Main-Sequence Turn-Off Stars from the SDSS/SEGUE Sample
The chemical compositions of seven Carbon-Enhanced Metal-Poor (CEMP) turn-off
stars are determined from high-resolution spectroscopy. Five of them are
selected from the SDSS/SEGUE sample of metal-poor stars. The effective
temperatures of these objects are all higher than 6000 K, while their
metallicities, parametrized by [Fe/H], are all below -2. Six of our program
objects exhibit high abundance ratios of barium ([Ba/H]> +1), suggesting large
contributions of the products of former AGB companions via mass transfer across
binary systems. Combining our results with previous studies provides a total of
20 CEMP main-sequence turn-off stars for which the abundances of carbon and at
least some neutron-capture elements are determined. Inspection of the [C/H]
ratios for this sample of CEMP turn-off stars show that they are generally
higher than those of CEMP giants; their dispersion in this ratio is also
smaller. We take these results to indicate that the carbon-enhanced material
provided from the companion AGB star is preserved at the surface of turn-off
stars with no significant dilution. In contrast, a large dispersion in the
observed [Ba/H] is found for the sample of CEMP turn-off stars, suggesting that
the efficiency of the s-process in very metal-poor AGB stars may differ greatly
from star to star. Four of the six stars from the SDSS/SEGUE sample exhibit
kinematics that are associated with membership in the outer-halo population, a
remarkably high fraction.Comment: 45 pages, 10 figures, 10 tables, Astrophysical Journal, in pres
A Brownian Motion Model of Parametric Correlations in Ballistic Cavities
A Brownian motion model is proposed to study parametric correlations in the
transmission eigenvalues of open ballistic cavities. We find interesting
universal properties when the eigenvalues are rescaled at the hard edge of the
spectrum. We derive a formula for the power spectrum of the fluctuations of
transport observables as a response to an external adiabatic perturbation. Our
formula correctly recovers the Lorentzian-squared behaviour obtained by
semiclassical approaches for the correlation function of conductance
fluctuations.Comment: 19 pages, written in RevTe
Random Matrix Theory of a Chaotic Andreev Quantum Dot
A new universality class distinct from the standard Wigner-Dyson ones is
identified. This class is realized by putting a metallic quantum dot in contact
with a superconductor, while applying a magnetic field so as to make the
pairing field effectively vanish on average. A random-matrix description of the
spectral and transport properties of such a quantum dot is proposed. The
weak-localization correction to the tunnel conductance is nonzero and results
from the depletion of the density of states due to the coupling with the
superconductor. Semiclassically, the depletion is caused by a a mode of
phase-coherent long-range propagation of electrons and holes.Comment: minor changes, 4 REVTeX page
Achieving Teaching, Scholarship, and Service through Community Engagement
Occupational therapy faculty currently face enormous challenges in meeting teaching load expectations, while also under pressure to participate in scholarly projects and to make administrative and service contributions. Community engagement projects may provide opportunities for faculty to effectively and efficiently meet the goals in each of these areas while imparting benefits to students and community partners as well. Faculty at the Department of Occupational Therapy (OT) at Virginia Commonwealth University (VCU) embraced this idea as consistent with the university’s mission and strategic plan, and recognized its benefits in assisting faculty to meet workload demands. Four community partnerships reflecting the range and diversity of populations currently involved are highlighted: the Children’s Museum of Richmond, Rebuilding Together-Richmond, the William Nelson Bland Literacy Center, and Gateway Homes of Richmond. The developmental process and resulting benefits are described for each of these partnerships, and the paper concludes with lessons learned from these collaborative efforts. From these examples, it appears important to be proactive about developing community partnerships and realistic about the challenges of collaboration, but also to be aware of the role community engagement plays in creatively blending the potentially conflicting demands on faculty time
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