36,041 research outputs found
A dynamical symmetry breaking model in Weyl space
The dynamical process following the breaking of Weyl geometry to Riemannian
geometry is considered by studying the motion of de Sitter bubbles in a Weyl
vacuum. The bubbles are given in terms of an exact, spherically symmetric thin
shell solution to the Einstein equations in a Weyl-Dirac theory with a
time-dependent scalar field of the form beta = f(t)/r. The dynamical solutions
obtained lead to a number of possible applications. An important feature of the
thin shell model is the manner in which beta provides a connection between the
interior and exterior geometries since information about the exterior geometry
is contained in the boundary conditions for beta.Comment: 18 pages, RevTex, to be published in J. Math. Phy
NASA Low-Speed Centrifugal Compressor for Fundamental Research
A centrifugal compressor facility being built by the NASA Lewis Research Center is described; its purpose is to obtain benchmark experimental data for internal flow code verification and modeling. The facility will be heavily instrumented with standard pressure and temperature probes and have provisions for flow visualization and laser Doppler velocimetry. The facility will accommodate rotational speeds to 2400 rpm and will be rated at pressures to 1.25 atm. The initial compressor stage for testing is geometrically and dynamically representative of modern high-performance stages with the exception of Mach number levels. Design exit tip speed for the initial stage is 500 ft/sec with a pressure ratio of 1.17. The rotor exit backsweep is 55 deg from radial
Development and initial operating characteristics of the 20 megawatt linear plasma accelerator facility
A 20-megawatt linear plasma accelerator facility, a steady flow, Faraday-type plasma accelerator facility for high velocity aerodynamic testing, was constructed, developed, and brought to an operational status. The accelerator has a 63.5-mm-square and 0.5-meter-long channel and utilizes nitrogen-seeded with 2 % mole fraction of cesium vapor. Modification of the original accelerator design characteristics and the improvements necessary to make the arc heater a suitable plasma source are described. The measured accelerator electrode current distribution and the electrode-wall potential distributions are given. The computed and the measured values are in good agreement. Measured pitot pressure indicates that an accelerator exit velocity of 9.2 km/sec, is obtained with 30 of the 36 electrode pairs powered and corresponds to a velocity increase to about 2 1/4 times the computed entrance velocity. The computed stagnation enthalpy at the accelerator exit is 92 MJ/kg, and the mass density corresponds to an altitude of about 58 km. The 92 MJ/kg stagnation enthalpy corresponds to a kinetic energy content at low temperature equivalent to a velocity of 13.6 km/sec
Communications of the lunar planetary laboratory, volume 3, no. 40- the system of lunar craters, quadrant ii
Observable properties of craters in second lunar quadran
Research on a one-inch-square linear d-c plasma accelerator
One-inch-square linear d-c plasma accelerator using cesium seeded nitroge
Surface shape resonances in lamellar metallic gratings
The specular reflectivity of lamellar gratings of gold with grooves 0.5
microns wide separated by a distance of 3.5 microns was measured on the 2000
cm - 7000 cm spectral range for p-polarized light. For the first
time, experimental evidence of the excitation of electromagnetic surface shape
resonances for optical frequencies is given. In these resonances the electric
field is highly localized inside the grooves and is almost zero in all other
regions. For grooves of depth equal to 0.6 microns, we have analyzed one of
these modes whose wavelength (3.3 microns) is much greater than the lateral
dimension of the grooves.Comment: 4 pages (LaTex), 5 postscript figures, to be published in Physical
Review Letter
Weyl geometry approach to describe planetary systems
In the present work we show that planetary mean distances can be calculated
through considering the Weyl geometry. We interpret the Weyl gauge field as a
vector field associated with the hypercharge of the particles and apply the
gauge concept of the Weyl geometry. The results obtained are shown to agree
with the observed orbits of all the planets and of the asteroid belt in the
solar system, with some empty states.Comment: 7 pages, no figure
The infall of the Virgo elliptical galaxy M60 toward M87 and the gaseous structures produced by Kelvin-Helmholtz instabilities
We present Chandra observations of hot gas structures, characteristic of gas stripping during infall, in the Virgo cluster elliptical galaxy M60 (NGC4649) located 1 Mpc east of M87. 0.5−2 keV Chandra X-ray images show a sharp leading edge in the surface brightness 12.4±0.1 kpc north and west of the galaxy center in the direction of M87 characteristic of a merger cold front due to M60's motion through the Virgo ICM. We measured a temperature of 1.00±0.02 keV for abundance 0.5Z⊙ inside the edge and 1.37+0.35−0.19 keV for abundance 0.1Z⊙ in the Virgo ICM free stream region. We find that the observed jump in surface brightness yields a density ratio of 6.44+1.04−0.67 between gas inside the edge and in the cluster free stream region. If the edge is a cold front due solely to the infall of M60 in the direction of M87, we find a pressure ratio of 4.7+1.7−1.4 and Mach number 1.7±0.3. For 1.37 keV Virgo gas we find a total infall velocity for M60 of 1030±180 kms−1. We calculate the motion in the plane of the sky to be 1012+183−192 km−1 implying an inclination angle ξ=11±3 degrees. Surface brightness profiles show the presence of a faint diffuse gaseous tail. We identify filamentary, gaseous wing structures caused by the galaxy's motion through the ICM. The structure and dimensions of these wings are consistent with simulations of Kelvin-Helmholtz instabilities as expected if the gas stripping is close to inviscid
Novae as a Mechanism for Producing Cavities around the Progenitors of SN 2002ic and Other SNe Ia
We propose that a nova shell ejected from a recurrent nova progenitor system
created the evacuated region around the explosion center of SN 2002ic. In this
picture, periodic shell ejections due to nova explosions on a white dwarf sweep
up the slow wind from the binary companion, creating density variations and
instabilities that lead to structure in the circumstellar medium (CSM). Our
model naturally explains the observed gap between the supernova explosion
center and the CSM in SN 2002ic, accounts for the density variations observed
in the CSM, and resolves the coincidence problem of the timing of the explosion
of SN 2002ic with respect to the apparent cessation of mass-loss in the
progenitor system. We also consider such nova outburst sweeping as a generic
feature of Type Ia supernovae with recurrent nova progenitors.Comment: Accepted to ApJL. 11 pages, 1 tabl
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