28,424 research outputs found
Development of a sensitive superconducting gravity gradiometer for geological and navigational applications
A sensitive and stable gravity gradiometer would provide high resolution gravity measurements from space. The instrument could also provide precision tests of fundamental laws of physics and be applied to inertial guidance systems of the future. This report describes research on the superconducting gravity gradiometer program at the University of Maryland from July 1980 to July 1985. The report describes the theoretical and experimental work on a prototype superconducting gravity gradiometer. The design of an advanced three-axis superconducting gravity gradiometer is also discussed
Subroutines GEORGE and DRASTC simplify operation of automatic digital plotter
FORTRAN language subroutines enable the production of a tape for a 360-30 tape unit that controls the CALCOMP 566 Digital Incremental Plotter. This provides the plotter with instructions for graphically displaying data points with the proper scaling of axes, numbering, lettering, and tic marking
Ideal Linear Chain Polymers with Fixed Angular Momentum
The statistical mechanics of a linear non-interacting polymer chain with a
large number of monomers is considered with fixed angular momentum. The radius
of gyration for a linear polymer is derived exactly by functional integration.
This result is then compared to simulations done with a large number of
non-interacting rigid links at fixed angular momentum. The simulation agrees
with the theory up to finite size corrections. The simulations are also used to
investigate the anisotropic nature of a spinning polymer. We find universal
scaling of the polymer size along the direction of the angular momentum, as a
function of rescaled angular momentum.Comment: 7 pages, 3 figure
One-dimensional behavior of elongated Bose-Einstein condensates
We study the properties of elongated Bose-Einstein condensates. First, we
show that the dimensions of the condensate after expansion differs from the 3D
Thomas-Fermi regime. We also study the coherence length of such elongated
condensates.Comment: proceeding of Quantum Gases in Low Dimension, Les Houches 2003, 8
pages, 5 figure
Optimal Prandtl number for heat transfer in rotating Rayleigh-Benard convection
Numerical data for the heat transfer as a function of the Prandtl (Pr) and
Rossby (Ro) numbers in turbulent rotating Rayleigh-Benard convection are
presented for Rayleigh number Ra = 10^8. When Ro is fixed the heat transfer
enhancement with respect to the non-rotating value shows a maximum as function
of Pr. This maximum is due to the reduced efficiency of Ekman pumping when Pr
becomes too small or too large. When Pr becomes small, i.e. for large thermal
diffusivity, the heat that is carried by the vertical vortices spreads out in
the middle of the cell, and Ekman pumping thus becomes less efficient. For
higher Pr the thermal boundary layers (BLs) are thinner than the kinetic BLs
and therefore the Ekman vortices do not reach the thermal BL. This means that
the fluid that is sucked into the vertical vortices is colder than for lower Pr
which limits the efficiency of the upwards heat transfer.Comment: 5 pages, 6 figure
A chromomagnetic mechanism for the X(3872) resonance
The chromomagnetic interaction, with proper account for flavour-symmetry
breaking, is shown to explain the mass and coupling properties of the X(3872)
resonance as a = 1 state consisting of a heavy quark-antiquark
pair and a light one. It is crucial to introduce all the spin-colour
configurations compatible with these quantum numbers and diagonalise the
chromomagnetic interaction in this basis. This approach thus differs from the
molecular picture and from the diquark-antidiquark picture.Comment: 4 pages - revtex4 - Typos corrected, refs. added, to be published in
Phys. Rev.
The new radiation-hard optical links for the ATLAS pixel detector
The ATLAS detector is currently being upgraded with a new layer of pixel
based charged particle tracking and a new arrangement of the services for the
pixel detector. These upgrades require the replacement of the opto-boards
previously used by the pixel detector. In this report we give details on the
design and production of the new opto-boards.Comment: Presentation at the DPF 2013 Meeting of the American Physical Society
Division of Particles and Fields, Santa Cruz, California, August 13-17, 201
Disentangling the surface and bulk electronic structures of LaOFeAs
We performed a comprehensive angle-resolved photoemission spectroscopy study
of the electronic band structure of LaOFeAs single crystals. We found that
samples cleaved at low temperature show an unstable and highly complicated band
structure, whereas samples cleaved at high temperature exhibit a stable and
clearer electronic structure. Using \emph{in-situ} surface doping with K and
supported by first-principles calculations, we identify both surface and bulk
bands. Our assignments are confirmed by the difference in the temperature
dependence of the bulk and surface states.Comment: 5 pages, 5 figure
Tidal Evolution of Close-in Extra-Solar Planets
The distribution of eccentricities e of extra-solar planets with semi-major
axes a > 0.2 AU is very uniform, and values for e are relatively large,
averaging 0.3 and broadly distributed up to near 1. For a < 0.2 AU,
eccentricities are much smaller (most e < 0.2), a characteristic widely
attributed to damping by tides after the planets formed and the protoplanetary
gas disk dissipated. Most previous estimates of the tidal damping considered
the tides raised on the planets, but ignored the tides raised on the stars.
Most also assumed specific values for the planets' poorly constrained tidal
dissipation parameter Qp. Perhaps most important, in many studies, the strongly
coupled evolution between e and a was ignored. We have now integrated the
coupled tidal evolution equations for e and a over the estimated age of each
planet, and confirmed that the distribution of initial e values of close-in
planets matches that of the general population for reasonable Q values, with
the best fits for stellar and planetary Q being ~10^5.5 and ~10^6.5,
respectively. The accompanying evolution of a values shows most close-in
planets had significantly larger a at the start of tidal migration. The earlier
gas disk migration did not bring all planets to their current orbits. The
current small values of a were only reached gradually due to tides over the
lifetimes of the planets. These results may have important implications for
planet formation models, atmospheric models of "hot Jupiters", and the success
of transit surveys.Comment: accepted to Ap
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