1,631,810 research outputs found
Surface protection of graphite fabric/PMR-15 composites subjected to thermal oxidation
Graphite fabric/PMR-15 laminates develop matrix cracks during long-term exposure in air at temperatures in the range of 500 to 600 F. This study was performed to demonstrate the effectiveness of incorporating graphite mat surface plies as a means of reducing the developing of matrix cracks. Celion 3000 graphite fabric/PMR-15 laminates were fabricated with graphite or graphite mat/325-mesh boron powder surface plies. Laminates without mat surface plies were also fabricated for control purposes. Composite flexural strength, flexural modulus, and interlaminar shear strength were determined at 288 C before and after long-term exposure (up to 1500 hr) in air at 316 C. The results of this study showed that the incorporation of graphite mat surface plies reduces matrix cracking and improves the elevated temperature mechanical property retention characteristics of the composites
Josephson parametric reflection amplifier with integrated directionality
A directional superconducting parametric amplifier in the GHz frequency range
is designed and analyzed, suitable for low-power read-out of microwave kinetic
inductance detectors employed in astrophysics and when combined with a
nonreciprocal device at its input also for circuit quantum electrodynamics
(cQED). It consists of an one wavelength long nondegenerate Josephson
parametric reflection amplifier circuit. The device has two Josephson junction
oscillators, connected via a tailored impedance to an on-chip passive circuit
which directs the in- to the output port. The amplifier provides a gain of 20
dB over a bandwidth of 220 MHz on the signal as well as on the idler portion of
the amplified input and the total photon shot noise referred to the input
corresponds to maximally 1.3 photons per second per Hertz of bandwidth. We
predict a factor of four increase in dynamic range compared to conventional
Josephson parametric amplifiers.Comment: Main article (5 pages plus 2 pages references) plus supplemental
material (14 pages
The production of charm mesons from quark matter at CERN SPS and RHIC
We study the production of charm mesons and other charm baryons from quark
matter at CERN SPS and RHIC energies. Using quark coalescence models as
hadronization mechanism, we predict particle ratios, absolute yields and
transverse momentum spectra.Comment: 4 pages in Latex, 2 PS figure, to be published in the proceedings of
the SQM'2000 Conference, Berkeley, CA, July 20-25, 2000. Submitted to J.
Phys.
A characterization of the central shell-focusing singularity in spherical gravitational collapse
We give a characterization of the central shell-focusing curvature
singularity that can form in the spherical gravitational collapse of a bounded
matter distribution obeying the dominant energy condition. This
characterization is based on the limiting behaviour of the mass function in the
neighbourhood of the singularity. Depending on the rate of growth of the mass
as a function of the area radius R, the singularity may be either covered or
naked. The singularity is naked if this growth rate is slower than R, covered
if it is faster than R, and either naked or covered if the growth rate is same
as R.Comment: 12 pages, Latex, significantly revised version, including change of
title. Revised version to appear in Classical and Quantum Gravit
Novel crystal phase in suspensions of hard ellipsoids
We present a computer simulation study on the crystalline phases of hard
ellipsoids of revolution. For aspect ratios greater than or equal to 3 the
previously suggested stretched-fcc phase [D. Frenkel and B. M. Mulder, Mol.
Phys. 55, 1171 (1985)] is replaced by a novel crystalline phase. Its unit cell
contains two ellipsoids with unequal orientations. The lattice is simple
monoclinic. The angle of inclination of the lattice, beta, is a very soft
degree of freedom, while the two right angles are stiff. For one particular
value of beta, the close-packed version of this crystal is a specimen of the
family of superdense packings recently reported [Donev et al., Phys. Rev. Lett.
92, 255506 (2004)]. These results are relevant for studies of nucleation and
glassy dynamics of colloidal suspensions of ellipsoids.Comment: 4 pages, 4 figure
Observations of Diffuse EUV Emission with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS)
The Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) was designed to study
diffuse emission from hot gas in the local interstellar cavity in the
wavelength range 90 - 265 A. Between launch in January 2003 and early 2004, the
instrument was operated in narrow-slit mode, achieving a peak spectral
resolution of about 1.4 A FWHM. Observations were carried out preferentially at
high galactic latitudes; weighted by observing time, the mean absolute value of
the galactic latitude for all narrow-slit observations combined is about 45
degrees. The total integration time is about 13.2 Msec (74% day, 26% night). In
the context of a standard collisional ionization equilibrium plasma model, the
CHIPS data set tight constraints on the emission measure at temperatures
between 10^{5.55} K and 10^{6.4} K. At 10^{6.0} K, the 95% upper limit on the
emission measure is about 0.0004 cm^{-6} pc for solar abundance plasma with
foreground neutral hydrogen column of 2 x 10^{18} cm^{-2}. This constraint,
derived primarily from limits on the extreme ultraviolet emission lines of
highly ionized iron, is well below the range for the local hot bubble estimated
previously from soft X-ray studies. To support the emission measures inferred
previously from X-ray data would require depletions much higher than the
moderate values reported previously for hot gas.Comment: 13 pages, 4 figures, 1 tabl
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