19,295 research outputs found
Analysis of interior noise ground and flight test data for advanced turboprop aircraft applications
Interior noise ground tests conducted on a DC-9 aircraft test section are described. The objectives were to study ground test and analysis techniques for evaluating the effectiveness of interior noise control treatments for advanced turboprop aircraft, and to study the sensitivity of the ground test results to changes in various test conditions. Noise and vibration measurements were conducted under simulated advanced turboprop excitation, for two interior noise control treatment configurations. These ground measurement results were compared with results of earlier UHB (Ultra High Bypass) Demonstrator flight tests with comparable interior treatment configurations. The Demonstrator is an MD-80 test aircraft with the left JT8D engine replaced with a prototype UHB advanced turboprop engine
A tight coupling between β\u3csub\u3e2\u3c/sub\u3eY97 and β\u3csub\u3e2\u3c/sub\u3eF200 of the GABA\u3csub\u3eA\u3c/sub\u3e receptor mediates GABA binding
The GABAA receptor is an oligopentameric chloride channel that is activated via conformation changes induced upon the binding of the endogenous ligand, GABA, to the extracellular inter-subunit interfaces. Although dozens of amino acid residues at the α/β interface have been implicated in ligand binding, the structural elements that mediate ligand binding and receptor activation are not yet fully described. In this study, double-mutant cycle analysis was employed to test for possible interactions between several arginines (α1R67, α1R120, α1R132, and β2R207) and two aromatic residues (β2Y97 and β2F200) that are present in the ligand-binding pocket and are known to influence GABA affinity. Our results show that neither α1R67 nor α1R120 is functionally coupled to either of the aromatics, whereas a moderate coupling exists between α1R132 and both aromatic residues. Significant functional coupling between β2R207 and both β2Y97 and β2F200 was found. Furthermore, we identified an even stronger coupling between the two aromatics, β2Y97 and β2F200, and for the first time provided direct evidence for the involvement of β2Y97 and β2F200 in GABA binding. As these residues are tightly linked, and mutation of either has similar, severe effects on GABA binding and receptor kinetics, we believe they form a single functional unit that may directly coordinate GABA
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The Recurrent Temporal Discriminative Restricted Boltzmann Machines
Classification of sequence data is the topic of interest for dynamic Bayesian models and Recurrent Neural Networks (RNNs). While the former can explicitly model the temporal dependencies between class variables, the latter have a capability of learning representations. Several attempts have been made to improve performance by combining these two approaches or increasing the processing capability of the hidden units in RNNs. This often results in complex models with a large number of learning parameters. In this paper, a compact model is proposed which offers both representation learning and temporal inference of class variables by rolling Restricted Boltzmann Machines (RBMs) and class variables over time. We address the key issue of intractability in this variant of RBMs by optimising a conditional distribution, instead of a joint distribution. Experiments reported in the paper on melody modelling and optical character recognition show that the proposed model can outperform the state-of-the-art. Also, the experimental results on optical character recognition, part-of-speech tagging and text chunking demonstrate that our model is comparable to recurrent neural networks with complex memory gates while requiring far fewer parameters
Closed-form Absorption Probability of Certain D=5 and D=4 Black Holes and Leading-Order Cross-Section of Generic Extremal p-branes
We obtain the closed-form absorption probabilities for minimally-coupled
massless scalars propagating in the background of D=5 single-charge and D=4
two-charge black holes. These are the only two examples of extremal black holes
with non-vanishing absorption probabilities that can be solved in closed form
for arbitrary incident frequencies. In both cases, the absorption probability
vanishes when the frequency is below a certain threshold, and we discuss the
connection between this phenomenon and the behaviour of geodesics in these
black hole backgrounds. We also obtain leading-order absorption cross-sections
for generic extremal p-branes, and show that the expression for the
cross-section as a function of frequency coincides with the leading-order
dependence of the entropy on the temperature in the corresponding near-extremal
p-branes.Comment: Latex (3 times), 20 page
Probing topology by "heating": Quantized circular dichroism in ultracold atoms
We reveal an intriguing manifestation of topology, which appears in the
depletion rate of topological states of matter in response to an external
drive. This phenomenon is presented by analyzing the response of a generic 2D
Chern insulator subjected to a circular time-periodic perturbation: due to the
system's chiral nature, the depletion rate is shown to depend on the
orientation of the circular shake. Most importantly, taking the difference
between the rates obtained from two opposite orientations of the drive, and
integrating over a proper drive-frequency range, provides a direct measure of
the topological Chern number of the populated band (): this "differential
integrated rate" is directly related to the strength of the driving field
through the quantized coefficient . Contrary to the
integer quantum Hall effect, this quantized response is found to be non-linear
with respect to the strength of the driving field and it explicitly involves
inter-band transitions. We investigate the possibility of probing this
phenomenon in ultracold gases and highlight the crucial role played by edge
states in this effect. We extend our results to 3D lattices, establishing a
link between depletion rates and the non-linear photogalvanic effect predicted
for Weyl semimetals. The quantized circular dichroism revealed in this work
designates depletion-rate measurements as a universal probe for topological
order in quantum matter.Comment: 10 pages, 5 figures (including Sup. Mat.). Revised version, accepted
for publicatio
On the Microcanonical Entropy of a Black Hole
It has been suggested recently that the microcanonical entropy of a system
may be accurately reproduced by including a logarithmic correction to the
canonical entropy. In this paper we test this claim both analytically and
numerically by considering three simple thermodynamic models whose energy
spectrum may be defined in terms of one quantum number only, as in a
non-rotating black hole. The first two pertain to collections of noninteracting
bosons, with logarithmic and power-law spectra. The last is an area ensemble
for a black hole with equi-spaced area spectrum. In this case, the many-body
degeneracy factor can be obtained analytically in a closed form. We also show
that in this model, the leading term in the entropy is proportional to the
horizon area A, and the next term is ln A with a negative coefficient.Comment: 15 pages, 1 figur
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