85,450 research outputs found
Effect of environment on biological burden during spacecraft assembly
Determining effects of environment on accumulation of biological burden on spacecraft during assembl
Closed-circuit television welding- electrode guidance system
Closed-circuit TV camera is mounted parallel to electrode and moves along with it. Camera is scanned along seam so seam is viewed parallel with scan lines on TV monitor. Two fiber optics illuminators are attached to guidance system; they illuminate seam for TV camera
Asymmetry of localised states in a single quantum ring: polarization dependence of excitons and biexcitons
We performed spectroscopic studies of a single GaAs quantum ring with an
anisotropy in the rim height. The presence of an asymmetric localised state was
suggested by the adiabatic potential. The asymmetry was investigated in terms
of the polarization dependence of excitons and biexcitons, where a large energy
di erence (0.8 meV) in the exciton emission energy for perpendicular
polarizations was observed and the oscillator strengths were also compared
using the photoluminescence decay rate. For perpendicular polarizations the
biexciton exhibits twice the energy di erence seen for the exciton, a fact that
may be attributed to a possible change in the selection rules for the lowered
symmetry.Comment: accepted in Applied physics Letter
Evaluation of the utility of sediment data in NASQAN (National Stream Quality Accounting Network)
Monthly suspended sediment discharge measurements, made by the USGS as part of the National Stream Quality Accounting Network (NASQAN), are analysed to assess the adequacy in terms of spatial coverage, temporal sampling frequency, accuracy of measurements, as well as in determining the sediment yield in the nation's rivers.
It is concluded that the spatial distribution of NASQAN stations is reasonable but necessarily judgemental. The temporal variations of sediment data contain much higher frequencies than monthly. Sampling error is found to be minor when compared with other causes of data scatter which can be substantial. The usefulness of the monthly measurements of sediment transport is enhanced when combined with the daily measurements of water discharge. Increasing the sampling frequency moderately would not materially improve the accuracy of sediment yield determinations
On The Interaction Of D0-Brane Bound States And RR Photons
We consider the problem of the interaction between D0-brane bound state and
1-form RR photons by the world-line theory. Based on the fact that in the
world-line theory the RR gauge fields depend on the matrix coordinates of
D0-branes, the gauge fields also appear as matrices in the formulation. At the
classical level, we derive the Lorentz-like equations of motion for D0-branes,
and it is observed that the center-of-mass is colourless with respect to the
SU(N) sector of the background. Using the path integral method, the
perturbation theory for the interaction between the bound state and the RR
background is developed. We discuss what kind of field theory may be
corresponded to the amplitudes which are calculated by the perturbation
expansion in world-line theory. Qualitative considerations show that the
possibility of existence of a map between the world-line theory and the
non-Abelian gauge theory is very considerable.Comment: LaTeX, 28 pages, 4 eps figures. v2 and v3: eqs. (3.18) and (B.2) are
corrected, very small change
Relativistic theory of tidal Love numbers
In Newtonian gravitational theory, a tidal Love number relates the mass
multipole moment created by tidal forces on a spherical body to the applied
tidal field. The Love number is dimensionless, and it encodes information about
the body's internal structure. We present a relativistic theory of Love
numbers, which applies to compact bodies with strong internal gravities; the
theory extends and completes a recent work by Flanagan and Hinderer, which
revealed that the tidal Love number of a neutron star can be measured by
Earth-based gravitational-wave detectors. We consider a spherical body deformed
by an external tidal field, and provide precise and meaningful definitions for
electric-type and magnetic-type Love numbers; and these are computed for
polytropic equations of state. The theory applies to black holes as well, and
we find that the relativistic Love numbers of a nonrotating black hole are all
zero.Comment: 25 pages, 8 figures, many tables; final version to be published in
Physical Review
Excited exciton and biexciton localised states in a single quantum ring
We observe excited exciton and biexciton states of localised excitons in an
anisotropic quantum ring, where large polarisation asymmetry supports the
presence of a crescent-like localised structure. We also find that saturation
of the localised ground state exciton with increasing excitation can be
attributed to relatively fast dissociation of biexcitons (? 430 ps) compared to
slow relaxation from the excited state to the ground state (? 1000 ps). As no
significant excitonic Aharonov-Bohm oscillations occur up to 14 T, we conclude
that phase coherence around the rim is inhibited as a consequence of height
anisotropy in the quantum ring.Comment: 4 pages, 4 figure
Recommended from our members
An atlas of CO2 storage potential in the nearshore waters of the Texas coast â American Recovery and Reinvestment Act â âGulf of Mexico Miocene CO2 site characterization mega-transectâ
Bureau of Economic Geolog
Gauge Invariant Effective Stress-Energy Tensors for Gravitational Waves
It is shown that if a generalized definition of gauge invariance is used,
gauge invariant effective stress-energy tensors for gravitational waves and
other gravitational perturbations can be defined in a much larger variety of
circumstances than has previously been possible. In particular it is no longer
necessary to average the stress-energy tensor over a region of spacetime which
is larger in scale than the wavelengths of the waves and it is no longer
necessary to restrict attention to high frequency gravitational waves.Comment: 11 pages, RevTe
Critical X-ray Scattering Studies of Jahn-Teller Phase Transitions in TbVAsO
The critical behaviour associated with cooperative Jahn-Teller phase
transitions in TbVAsO (where \textit{x} = 0, 0.17, 1)
single crystals have been studied using high resolution x-ray scattering. These
materials undergo continuous tetragonal orthorhombic structural phase
transitions driven by Jahn-Teller physics at T = 33.26(2) K, 30.32(2) K and
27.30(2) K for \textit{x} = 0, 0.17 and 1 respectively. The orthorhombic strain
was measured close to the phase transition and is shown to display mean field
behavior in all three samples. Pronounced fluctuation effects are manifest in
the longitudinal width of the Bragg scattering, which diverges as a power law,
with an exponent given by , on approaching the transition from
either above or below. All samples exhibited twinning; however the disordered x
= 0.17 sample showed a broad distribution of twins which were stable to
relatively low temperatures, well below T. This indicates that while the
orthorhombic strain continues to develop in a conventional mean field manner in
the presence of disorder, twin domains are easily pinned by the quenched
impurities and their associated random strains.Comment: 8 pages, 6 figure
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