16,071 research outputs found
Motion and gravitational radiation of a binary system consisting of an oscillating and rotating coplanar dusty disk and a point-like object
A binary system composed of an oscillating and rotating coplanar dusty disk
and a point mass is considered. The conservative dynamics is treated on the
Newtonian level. The effects of gravitational radiation reaction and wave
emission are studied to leading quadrupole order. The related waveforms are
given. The dynamical evolution of the system is determined semi-analytically
exploiting the Hamiltonian equations of motion which comprise the effects both
of the Newtonian tidal interaction and the radiation reaction on the motion of
the binary system in elliptic orbits. Tidal resonance effects between orbital
and oscillatory motions are considered in the presence of radiation damping.Comment: 26 pages, 8 figure
Suppression of hole-hole scattering in GaAs/AlGaAs heterostructures under uniaxial compression
Resistance, magnetoresistance and their temperature dependencies have been
investigated in the 2D hole gas at a [001] p-GaAs/AlGaAs
heterointerface under [110] uniaxial compression. Analysis performed in the
frame of hole-hole scattering between carriers in the two spin splitted
subbands of the ground heavy hole state indicates, that h-h scattering is
strongly suppressed by uniaxial compression. The decay time of the
relative momentum reveals 4.5 times increase at a uniaxial compression of 1.3
kbar.Comment: 5 pages, 3 figures. submitted to Phys.Rev.
Increased traffic exposure and negative birth outcomes: a prospective cohort in Australia
Background: Pregnant women exposed to traffic pollution have an increased risk of negative birth outcomes. We aimed to investigate the size of this risk using a prospective cohort of 970 mothers and newborns in Logan, Queensland. ----- ----- Methods: We examined two measures of traffic: distance to nearest road and number of roads around the home. To examine the effect of distance we used the number of roads around the home in radii from 50 to 500 metres. We examined three road types: freeways, highways and main roads.----- ----- Results: There were no associations with distance to road. A greater number of freeways and main roads around the home were associated with a shorter gestation time. There were no negative impacts on birth weight, birth length or head circumference after adjusting for gestation. The negative effects on gestation were largely due to main roads within 400 metres of the home. For every 10 extra main roads within 400 metres of the home, gestation time was reduced by 1.1% (95% CI: -1.7, -0.5; p-value = 0.001).----- ----- Conclusions: Our results add weight to the association between exposure to traffic and reduced gestation time. This effect may be due to the chemical toxins in traffic pollutants, or because of disturbed sleep due to traffic noise
Burst avalanches in solvable models of fibrous materials
We review limiting models for fracture in bundles of fibers, with
statistically distributed thresholds for breakdown of individual fibers. During
the breakdown process, avalanches consisting of simultaneous rupture of several
fibers occur, and the distribution of the magnitude of
such avalanches is the central characteristics in our analysis. For a bundle of
parallel fibers two limiting models of load sharing are studied and contrasted:
the global model in which the load carried by a bursting fiber is equally
distributed among the surviving members, and the local model in which the
nearest surviving neighbors take up the load. For the global model we
investigate in particular the conditions on the threshold distribution which
would lead to anomalous behavior, i.e. deviations from the asymptotics
, known to be the generic behavior. For the local
model no universal power-law asymptotics exists, but we show for a particular
threshold distribution how the avalanche distribution can nevertheless be
explicitly calculated in the large-bundle limit.Comment: 28 pages, RevTeX, 3 Postscript figure
Compartmentalized PDE4A5 signaling impairs hippocampal synaptic plasticity and long-term memory
Alterations in cAMP signaling are thought to contribute to neurocognitive and neuropsychiatric disorders. Members of the cAMP-specific phosphodiesterase 4 (PDE4) family, which contains >25 different isoforms, play a key role in determining spatial cAMP degradation so as to orchestrate compartmentalized cAMP signaling in cells. Each isoform binds to a different set of protein complexes through its unique N-terminal domain, thereby leading to targeted degradation of cAMP in specific intracellular compartments. However, the functional role of specific compartmentalized PDE4 isoforms has not been examined in vivo. Here, we show that increasing protein levels of the PDE4A5 isoform in mouse hippocampal excitatory neurons impairs a long-lasting form of hippocampal synaptic plasticity and attenuates hippocampus-dependent long-term memories without affecting anxiety. In contrast, viral expression of a truncated version of PDE4A5, which lacks the unique N-terminal targeting domain, does not affect long-term memory. Further, overexpression of the PDE4A1 isoform, which targets a different subset of signalosomes, leaves memory undisturbed. Fluorescence resonance energy transfer sensor-based cAMP measurements reveal that the full-length PDE4A5, in contrast to the truncated form, hampers forskolin-mediated increases in neuronal cAMP levels. Our study indicates that the unique N-terminal localization domain of PDE4A5 is essential for the targeting of specific cAMP-dependent signaling underlying synaptic plasticity and memory. The development of compounds to disrupt the compartmentalization of individual PDE4 isoforms by targeting their unique N-terminal domains may provide a fruitful approach to prevent cognitive deficits in neuropsychiatric and neurocognitive disorders that are associated with alterations in cAMP signaling
Long Wavelength Instability for Uniform Shear Flow
Uniform Shear Flow is a prototype nonequilibrium state admitting detailed
study at both the macroscopic and microscopic levels via theory and computer
simulation. It is shown that the hydrodynamic equations for this state have a
long wavelength instability. This result is obtained first from the
Navier-Stokes equations and shown to apply at both low and high densities.
Next, higher order rheological effects are included using a model kinetic
theory. The results are compared favorably to those from Monte Carlo
simulation.Comment: 12 pages, including 2 figure
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