1,406 research outputs found
Three component laser Doppler measurements in an axisymmetric jet
A three-component laser Doppler anemometer (LDA) was used to acquire a detailed set of three-dimensional mean and fluctuating velocity measurements in a low-speed air jet entering a stagnant ambient, over the first 20 jet exit diameters along the jet trajectory. These data are physically consistent with previous measurements in axisymmetric jets. The relative difficulty of obtaining three-dimensional and two-dimensional LDA data is briefly discussed
Differential localization of GABAA receptor subunits in relation to rat striatopallidal and pallidopallidal synapses
As a central integrator of basal ganglia function, the external segment of the globus pallidus (GP) plays a critical role in the control of voluntary movement. The GP is composed of a network of inhibitory GABA-containing projection neurons which receive GABAergic input from axons of the striatum (Str) and local collaterals of GP neurons. Here, using electrophysiological techniques and immunofluorescent labeling we have investigated the differential cellular distribution of a1, a2 and a3 GABAA receptor subunits in relation to striatopallidal (Str-GP) and pallidopallidal (GP-GP) synapses. Electrophysiological investigations showed that zolpidem (100 nm; selective for the a1 subunit) increased the amplitude and the decay time of both Str-GP and GP-GP IPSCs, indicating the presence of the a1 subunits at both synapses. However, the application of drugs selective for the a2, a3 and a5 subunits (zolpidem at 400 nm, L-838,417 and TP003) revealed differential effects on amplitude and decay time of IPSCs, suggesting the nonuniform distribution of non-a1 subunits. Immunofluorescence revealed widespread distribution of the a1 subunit at both soma and dendrites, while double- and triple-immunofluorescent labeling for parvalbumin, enkephalin, gephyrin and the ?2 subunit indicated strong immunoreactivity for GABAAa3 subunits in perisomatic synapses, a region mainly targeted by local axon collaterals. In contrast, immunoreactivity for synaptic GABAAa2 subunits was observed in dendritic compartments where striatal synapses are preferentially located. Due to the kinetic properties which each GABAAa subunit confers, this distribution is likely to contribute differentially to both physiological and pathological patterns of activity
Response to freshwater inflow in the Rappahannock Estuary, Virginia : Operation HIFLO \u2778
More sediment, nutrients and pollutants are discharged into an estuary during a few days of flood inflow than during many months or years of average inflow (Meade, 1972; Schubel, 1977), but few observations document the sedimentary response of an estuary to high freshwater inflow. Such inflows are usually unexpected and estuarine water charact~ristics change too rapidly to permit systematic measurements. Moreover, the expenditure of effort and number of sampling vessels required on short notice is beyond the resources of a single research group or institute. Yet, freshwater inflow observations are a key to improving water quality; especially to ameliorate the effects of high turbidity, depleted oxygen and low salinity which can cause oyster motalities (Zaborski and Haven, 1980). Many si9nificant ecological effects are noted by Snedakar, et al., 1977. Exceptional sediment deposition shoals shipping channels, fills boat basins, and blanke~ts oyster grounds. Suspended sediments adsorb toxic contaminates, nutrients and organic matter, and thus can affect plant production and the distribution of shellfish, plants and other life.
The HIFLO experiment was planned to observe and evaluate the response of an estuary to high freshwater inflow and high influx of suspended sediment. Of special interest are the questions: How far seaward does the sediment load from an event go before settling to the bed? How do the hydrodynamic conditions for sediment transport change? What is the sequence of estuarine processes triggered by a river flood
Levels of self-consistency in the GW approximation
We perform calculations on atoms and diatomic molecules at different
levels of self-consistency and investigate the effects of self-consistency on
total energies, ionization potentials and on particle number conservation. We
further propose a partially self-consistent scheme in which we keep the
correlation part of the self-energy fixed within the self-consistency cycle.
This approximation is compared to the fully self-consistent results and to
the and the approximations. Total energies, ionization
potentials and two-electron removal energies obtained with our partially
self-consistent approximation are in excellent agreement with fully
self-consistent results while requiring only a fraction of the
computational effort. We also find that self-consistent and partially
self-consistent schemes provide ionization energies of similar quality as the
values but yield better total energies and energy differences.Comment: 11 pages, 3 figures, 3 table
Large N Phases, Gravitational Instantons and the Nuts and Bolts of AdS Holography
Recent results in the literature concerning holography indicate that the
thermodynamics of quantum gravity (at least with a negative cosmological
constant) can be modeled by the large N thermodynamics of quantum field theory.
We emphasize that this suggests a completely unitary evolution of processes in
quantum gravity, including black hole formation and decay; and even more
extreme examples involving topology change. As concrete examples which show
that this correspondence holds even when the space-time is only locally
asymptotically AdS, we compute the thermodynamical phase structure of the
AdS-Taub-NUT and AdS-Taub-Bolt spacetimes, and compare them to a 2+1
dimensional conformal field theory (at large N) compactified on a squashed
three sphere, and on the twisted plane.Comment: 20 pages, three figures. (uses harvmac.tex and epsf.tex
The AdS/CFT Correspondence and a New Positive Energy Conjecture for General Relativity
We examine the AdS/CFT correspondence when the gauge theory is considered on
a compactified space with supersymmetry breaking boundary conditions. We find
that the corresponding supergravity solution has a negative energy, in
agreement with the expected negative Casimir energy in the field theory.
Stability of the gauge theory would imply that this supergravity solution has
minimum energy among all solutions with the same boundary conditions. Hence we
are lead to conjecture a new positive energy theorem for asymptotically locally
Anti-de Sitter spacetimes. We show that the candidate minimum energy solution
is stable against all quadratic fluctuations of the metric.Comment: 25 pages, harvma
D0-D4 brane tachyon condensation to a BPS state and its excitation spectrum in noncommutative super Yang-Mills theory
We investigate the D0-D4-brane system for different B-field backgrounds
including the small instanton singularity in noncommutative SYM theory. We
discuss the excitation spectrum of the unstable state as well as for the BPS
D0-D4 bound state. We compute the tachyon potential which reproduces the
complete mass defect. The relevant degrees of freedom are the massless (4,4)
strings. Both results are in contrast with existing string field theory
calculations. The excitation spectrum of the small instanton is found to be
equal to the excitation spectrum of the fluxon solution on R^2_theta x R which
we trace back to T-duality. For the effective theory of the (0,0) string
excitations we obtain a BFSS matrix model. The number of states in the
instanton background changes significantly when the B-field becomes self-dual.
This leads us to the proposal of the existence of a phase transition or cross
over at self-dual B-field.Comment: a4 11pt Latex2e 40 pages; v2: typos fixed, refined comments on
renormalisation, refs added, v3: ref added, version publishe
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