51,685 research outputs found
Study of providing omnidirectional vibration isolation to entire space shuttle payload packages
Techniques to provide omnidirectional vibration isolation for a space shuttle payload package were investigated via a reduced-scale model. Development, design, fabrication, assembly and test evaluation of a 0.125-scale isolation model are described. Final drawings for fabricated mechanical components are identified, and prints of all drawings are included
Cooling of Sr to high phase-space density by laser and sympathetic cooling in isotopic mixtures
Based on an experimental study of two-body and three-body collisions in
ultracold strontium samples, a novel optical-sympathetic cooling method in
isotopic mixtures is demonstrated. Without evaporative cooling, a phase-space
density of is obtained with a high spatial density that should
allow to overcome the difficulties encountered so far to reach quantum
degeneracy for Sr atoms.Comment: 5 pages, 4 figure
Higher charges and regularized quantum trace identities in su(1,1) Landau-Lifshitz model
We solve the operator ordering problem for the quantum continuous integrable
su(1,1) Landau-Lifshitz model, and give a prescription to obtain the quantum
trace identities, and the spectrum for the higher-order local charges. We also
show that this method, based on operator regularization and renormalization,
which guarantees quantum integrability, as well as the construction of
self-adjoint extensions, can be used as an alternative to the discretization
procedure, and unlike the latter, is based only on integrable representations.Comment: 27 pages; misprints corrected, references adde
Exact and Quasi-exact Models of Strange Stars
We construct and compare a variety of simple models for strange stars,
namely, hypothetical self-bound objects made of a cold stable version of the
quark-gluon plasma. Exact, quasi-exact and numerical models are examined to
find the most economical description for these objects. A simple and successful
parametrization of them is given in terms of the central density, and many
differences among the models are explicitly shown and discussed.Comment: 20 pp. 15 figures, to appear in IJMP
Gravitational Waves Astronomy: a cornerstone for gravitational theories
Realizing a gravitational wave (GW) astronomy in next years is a great
challenge for the scientific community. By giving a significant amount of new
information, GWs will be a cornerstone for a better understanding of
gravitational physics. In this paper we re-discuss that the GW astronomy will
permit to solve a captivating issue of gravitation. In fact, it will be the
definitive test for Einstein's general relativity (GR), or, alternatively, a
strong endorsement for extended theories of gravity (ETG).Comment: To appear in Proceedings of the Workshop "Cosmology, the Quantum
Vacuum and Zeta Functions" for the celebration of Emilio Elizalde's sixtieth
birthday, Barcelona, March 8-10, 201
[OII] emitters in the GOODS field at z~1.85: a homogeneous measure of evolving star formation
We present the results of a deep, near-infrared, narrow band imaging survey
at a central wavelength of 1.062 microns (FWHM=0.01 microns) in the GOODS-South
field using the ESO VLT instrument, HAWK-I. The data are used to carry out the
highest redshift search for [OII]3727 emission line galaxies to date. The
images reach an emission line flux limit (5 sigma) of 1.5 x 10^-17 erg cm^-2
s^-1, additionally making the survey the deepest of its kind at high redshift.
In this paper we identify a sample of [OII]3727 emission line objects at
redshift z~1.85 in a co-moving volume of ~4100 Mpc^3. Objects are selected
using an observed equivalent width (EW_obs) threshold of EW_obs = 50 angstroms.
The sample is used to derive the space density and constrain the luminosity
function of [OII] emitters at z=1.85. We find that the space density of objects
with observed [OII] luminosities in the range log(L_[OII]) > 41.74 erg s^-1 is
log(rho)=-2.45+/-0.14 Mpc^-3, a factor of 2 greater than the observed space
density of [OII] emitters reported at z~1.4. After accounting for completeness
and assuming an internal extinction correction of A_Halpha=1 mag (equivalent to
A_[OII]=1.87), we report a star formation rate density of rho* ~0.38+/-0.06
Msun yr^-1 Mpc^-3. We independently derive the dust extinction of the sample
using 24 micron fluxes and find a mean extinction of A_[OII]=0.98+/-0.11
magnitudes (A_Halpha=0.52). This is significantly lower than the A_Halpha=1
(A[OII]=1.86) mag value widely used in the literature. Finally we incorporate
this improved extinction correction into the star formation rate density
measurement and report rho*~0.24+/-0.06 Msun yr^-1 Mpc^-3.Comment: 11 pages, 10 figures, accepted for publication in MNRA
A Three-Dimensional Solution of Flows over Wings with Leading-Edge Vortex Separation. Part 1: Engineering Document
A method of predicting forces, moments, and detailed surface pressures on thin, sharp-edged wings with leading-edge vortex separation in incompressible flow is presented. The method employs an inviscid flow model in which the wing and the rolled-up vortex sheets are represented by piecewise, continuous quadratic doublet sheet distributions. The Kutta condition is imposed on all wing edges. Computed results are compared with experimental data and with the predictions of the leading-edge suction analogy for a selected number of wing planforms over a wide range of angle of attack. These comparisons show the method to be very promising, capable of producing not only force predictions, but also accurate predictions of detailed surface pressure distributions, loads, and moments
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