1,508 research outputs found
Giant Gravitons with NSNS B field
We study the motion of a D(8-p)-brane probe in the background created by a
stack of non-threshold (D(p-2), Dp) bound states for . The brane
probe and the branes of the background have two common directions. We show that
for a particular value of the worldvolume gauge field there exist
configurations of the probe brane which behave as massless particles and can be
interpreted as gravitons blown up into a fuzzy sphere and a noncommutative
plane. We check this behaviour by studying the motion and energy of the brane
and by determining how supersymmetry is broken by the probe as it moves under
the action of the background.Comment: 24 pages, LaTe
Flux Stabilization of D-branes in a non-threshold bound state background
We study some configurations of brane probes which are partially wrapped on
spheres transverse to a stack of non-threshold bound states. The latter are
represented by the corresponding supergravity background. Two cases are
studied: D(10-p)-branes in the background of (D(p-2), Dp) bound states and
D(8-p)-branes in the (NS5, Dp) geometry. By using suitable flux quantization
rules of the worldvolume gauge field, we determine the stable configurations of
the probe. The analysis of the energy and supersymmetry of these configurations
reveals that they can be interpreted as bound states of lower dimensional
objects polarized into a D-brane.Comment: 11 pages, LaTe
Cholesterol modulates acetylcholine receptor diffusion by tuning confinement sojourns and nanocluster stability
Translational motion of neurotransmitter receptors is key for determining receptor number at the synapse and hence, synaptic efficacy. We combine live-cell STORM superresolution microscopy of nicotinic acetylcholine receptor (nAChR) with single-particle tracking, mean-squared displacement (MSD), turning angle, ergodicity, and clustering analyses to characterize the lateral motion of individual molecules and their collective behaviour. nAChR diffusion is highly heterogeneous: subdiffusive, Brownian and, less frequently, superdiffusive. At the single-track level, free walks are transiently interrupted by ms-long confinement sojourns occurring in nanodomains of ~36 nm radius. Cholesterol modulates the time and the area spent in confinement. Turning angle analysis reveals anticorrelated steps with time-lag dependence, in good agreement with the permeable fence model. At the ensemble level, nanocluster assembly occurs in second-long bursts separated by periods of cluster disassembly. Thus, millisecond-long confinement sojourns and second-long reversible nanoclustering with similar cholesterol sensitivities affect all trajectories; the proportion of the two regimes determines the resulting macroscopic motional mode and breadth of heterogeneity in the ensemble population.Fil: Mosqueira, Alejo. Pontificia Universidad Católica Argentina "Santa MarÃa de los Buenos Aires". Instituto de Investigaciones Biomédicas. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas; ArgentinaFil: Camino, Pablo A.. Pontificia Universidad Católica Argentina "Santa MarÃa de los Buenos Aires". Instituto de Investigaciones Biomédicas. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas; ArgentinaFil: Barrantes, Francisco Jose. Pontificia Universidad Católica Argentina "Santa MarÃa de los Buenos Aires". Instituto de Investigaciones Biomédicas. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Biomédicas; Argentin
Improving Missing Data Imputation with Deep Generative Models
Datasets with missing values are very common on industry applications, and
they can have a negative impact on machine learning models. Recent studies
introduced solutions to the problem of imputing missing values based on deep
generative models. Previous experiments with Generative Adversarial Networks
and Variational Autoencoders showed interesting results in this domain, but it
is not clear which method is preferable for different use cases. The goal of
this work is twofold: we present a comparison between missing data imputation
solutions based on deep generative models, and we propose improvements over
those methodologies. We run our experiments using known real life datasets with
different characteristics, removing values at random and reconstructing them
with several imputation techniques. Our results show that the presence or
absence of categorical variables can alter the selection of the best model, and
that some models are more stable than others after similar runs with different
random number generator seeds
Spatial Distribution of the Incompressible Strips at Aharonov-Bohm Interferometer
In this work, the edge physics of an Aharonov-Bohm interferometer (ABI)
defined on a two dimensional electron gas, subject to strong perpendicular
magnetic field B, is investigated. We solve the three dimensional Poisson
equation using numerical techniques starting from the crystal growth parameters
and surface image of the sample. The potential profiles of etched and gate
defined geometries are compared and it is found that the etching yields a
steeper landscape. The spatial distribution of the incompressible strips is
investigated as a function of the gate voltage and applied magnetic field,
where the imposed current is confined to. AB interference is investigated due
to scattering processes between two incompressible "edge-states".Comment: 5 pages, 3 figure
Synergistic effects of zinc borate and aluminiumtrihydroxide on flammability behaviour of aerospaceepoxy system
The flame retardancy of mono-component epoxy resin (RTM6), widely used for aerospace composites, treated with zinc borate (ZB), aluminium trihydroxide (ATH) and their mixtures at different concentrations have been investigated by morphological and thermal characterization. Cone calorimeter data reveal that combustion behaviour, heat release rate peak (PHRR) and heat release rate average (HRR Average) of RTM6 resin decrease substantially when synergistic effects of zinc borate and aluminium trihydroxide intervene. Thermogravimetric (TGA) results and analysis of the residue show that addition higher than 20% w/w of ZB, ATH, and their mixture greatly promotes RTM6 char formation acting as a barrier layer for the fire development. Depending upon the different used flame additives, SEM micrographs indicate that the morphology of residual char could vary from a compact amalgam-like structure, for the RTM6+ZB system, to a granular structure, characterized by very small particles of degraded resin and additive for the AT
Non-Abelian statistics in the interference noise of the Moore-Read quantum Hall state
We propose noise oscillation measurements in a double point contact,
accessible with current technology, to seek for a signature of the non-abelian
nature of the \nu=5/2 quantum Hall state. Calculating the voltage and
temperature dependence of the current and noise oscillations, we predict the
non-abelian nature to materialize through a multiplicity of the possible
outcomes: two qualitatively different frequency dependences of the nonzero
interference noise. Comparison between our predictions for the Moore-Read state
with experiments on \nu=5/2 will serve as a much needed test for the nature of
the \nu=5/2 quantum Hall state.Comment: 4 pages, 4 figures v2: typo's corrected, discussions clarified,
references adde
Seismic site classification from the horizontal-to-vertical response spectral ratios: use of the Spanish strong-motion database
Normally, the average of the horizontal-to-vertical (H/V) ratios of the 5% damped response spectra of ground motions is used to classify the site of strong-motion stations. In these cases, only the three-orthogonal as-recorded acceleration components are used in the analysis, and all the vector compositions that can generate a different response for each period oscillator are excluded. In this study, the Spanish strong-motion database was used to classify the sites of accelerometric stations based on the predominant periods through the average horizontal-to-vertical spectral ratios (HVSR) of recorded ground motions. Moreover, the directionality effects using the vector composition of the horizontal components of ground motions were also considered in the estimations of H/V ratios. This consideration is a relevant novelty compared to the traditional H/V ratios methods. Only earthquakes with magnitudes above 3.5 and hypocentral distances below 200 km were selected, which resulted in 692 ground-motion records, corresponding to 86 stations, from events in the period between 1993 and 2017. After the analysis, a predominant-period site classification was assigned to each station. On the whole, the obtained mean and standard deviation values of the spectral ratios are comparable to those shown by other researchers. Therefore, the advantages of the proposed procedure, which takes the directionality effects into account, can be summarized as follows: (a) The obtained information is richer and gives enables more sophisticated and realistic analyses on the basis of percentiles and (b) it is easier to detect anomalous stations, sites, and/or accelerograms. Moreover, the method eliminates the effect of directionality as a contributor to epistemic uncertainty.Peer ReviewedPostprint (published version
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