8,395 research outputs found
A Supersymmetric Solution in M-theory with Purely Magnetic Flux
We find a new solution in M-theory supported by
purely magnetic flux via a sequence of abelian and non-abelian T-dualities.
This provides the second known example in this class besides the uplift of the
Pernici and Sezgin solution to 7d gauged supergravity constructed in the
eighties. We compute the free energy of the solution, and show that it scales
as . It is intriguing that even though the natural holographic
interpretation is in terms of M5-branes wrapped on a special Lagrangian
3-cycle, this solution does not exhibit the expected behavior.Comment: 19 pages plus appendices. v2 metadata amended, reference adde
Temporal Correlations and Persistence in the Kinetic Ising Model: the Role of Temperature
We study the statistical properties of the sum , that is the difference of time spent positive or negative by the
spin , located at a given site of a -dimensional Ising model
evolving under Glauber dynamics from a random initial configuration. We
investigate the distribution of and the first-passage statistics
(persistence) of this quantity. We discuss successively the three regimes of
high temperature (), criticality (), and low temperature
(). We discuss in particular the question of the temperature
dependence of the persistence exponent , as well as that of the
spectrum of exponents , in the low temperature phase. The
probability that the temporal mean was always larger than the
equilibrium magnetization is found to decay as . This
yields a numerical determination of the persistence exponent in the
whole low temperature phase, in two dimensions, and above the roughening
transition, in the low-temperature phase of the three-dimensional Ising model.Comment: 21 pages, 11 PostScript figures included (1 color figure
Supersymmetry and non-Abelian T-duality in type II supergravity
We study the effect of T-duality on supersymmetry in the context of type II
supergravity. For both U(1) Abelian and SU(2) non-Abelian T-duality, we
demonstrate that the supersymmetry variations after T-duality are related to
the variations before T-duality through the Kosmann spinorial Lie derivative,
which vanishes when the Killing spinors are independent of the T-duality
directions. As a byproduct of our analysis, we present closed expressions for
SU(2) T-duality in a class of spacetimes with diagonal Bianchi IX symmetry and
comment on specific examples of T-dual geometries, including a novel AdS3
geometry with large N = (0,4) superconformal symmetry.Comment: 34 pages, v2, wording improved, references updated, v3 references
added, matches published version; v4 signs in section 6 changed to make
consistent with earlier sections, erroneous statement about supersymmetry of
AdS3 S3 S3 S1 non-Abelian T-dual corrected, reference adde
Duality of Super D-brane Actions in General Type IIB Supergravity Background
We examine duality transformations of supersymmetric and -symmetric
Dp-brane actions in a general type II supergravity background where in
particular the dilaton and the axion are supposed to not be zero or a constant
but a general superfield. Due to non-constant dilaton and axion, we can
explicitly show that the dilaton and the axion as well as the two 2-form gauge
potentials transform as doublets under the transformation from the
point of view of the world-volume field theory.Comment: 32 pages, LaTex 2
CP violation in semileptonic tau lepton decays
The leading order contribution to the direct CP asymmetry in tau^{+/-} ->
K^{+/-} pi^0 nu_{tau} decay rates is evaluated within the Standard Model. The
weak phase required for CP violation is introduced through an interesting
mechanism involving second order weak interactions, which is also responsible
for tiny violations of the Delta S= Delta Q rule in K_{l3} decays. The
calculated CP asymmetry turns out to be of order 10^{-12}, leaving a large
window for studying effects of non-standard sources of CP violation in this
observable.Comment: 5 pages, 3 figures, version published in Phys.Rev.
Exploring convolutional, recurrent, and hybrid deep neural networks for speech and music detection in a large audio dataset
Audio signals represent a wide diversity of acoustic events, from background environmental noise to spoken
communication. Machine learning models such as neural networks have already been proposed for audio signal
modeling, where recurrent structures can take advantage of temporal dependencies. This work aims to study the
implementation of several neural network-based systems for speech and music event detection over a collection of
77,937 10-second audio segments (216 h), selected from the Google AudioSet dataset. These segments belong to
YouTube videos and have been represented as mel-spectrograms. We propose and compare two approaches. The
first one is the training of two different neural networks, one for speech detection and another for music detection.
The second approach consists on training a single neural network to tackle both tasks at the same time. The studied
architectures include fully connected, convolutional and LSTM (long short-term memory) recurrent networks.
Comparative results are provided in terms of classification performance and model complexity. We would like to
highlight the performance of convolutional architectures, specially in combination with an LSTM stage. The hybrid
convolutional-LSTM models achieve the best overall results (85% accuracy) in the three proposed tasks. Furthermore,
a distractor analysis of the results has been carried out in order to identify which events in the ontology are the most
harmful for the performance of the models, showing some difficult scenarios for the detection of music and speechThis work has been supported by project “DSSL: Redes Profundas y Modelos
de Subespacios para Deteccion y Seguimiento de Locutor, Idioma y
Enfermedades Degenerativas a partir de la Voz” (TEC2015-68172-C2-1-P),
funded by the Ministry of Economy and Competitivity of Spain and FEDE
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Greenhouse Gas Reduction Opportunities for Local Governments: A Quantification and Prioritization Framework
Local governments have steadily increased their initiative to address global climate change, and many present their proposed strategies through climate action plans (CAPs). This study conducts a literature review on current local approaches to greenhouse gas (GHG) reduction strategies by assessing CAPs in California and presents common strategies in the transportation sector along with useful tools. One identified limitation of many CAPs is the omission of quantitative economic cost and emissions data for decision-making on the basis of cost-effectiveness. Therefore, this study proposes a framework for comparing strategies based on their life cycle emissions mitigation potential and costs. The results data can be presented in a marginal abatement cost curve (MACC) to allow for side-by-side comparison of considered strategies. Researchers partnered with Yolo and Unincorporated Los Angeles Counties to analyze 7 strategies in the transportation and energy sectors (five and two, respectively). A MACC was subsequently developed for each county. Applying the life cycle approach revealed strategies that had net cost savings over their life cycle, indicating there are opportunities for reducing emissions and costs. The MACC also revealed that some emissions reduction strategies in fact increased emissions on a life cycle basis. Applying the MACC framework to two case study jurisdictions illustrated both the feasibility and challenges of including quantitative analysis in their decision-making process. An additional barrier to using the MACC framework in the context of CAPs, is the mismatch between a life cycle and annual accounting basis for GHG emissions. Future work could explore more efficient data collection, alternative scopes of emissions for reporting, and environmental justice concerns.View the NCST Project Webpag
Breaking arches with vibrations: the role of defects
We present experimental results about the stability of arches against
external vibrations. Two dimensional strings of mutually stabilizing grains are
geometrically analyzed and subsequently submitted to a periodic forcing at
fixed frequency and increasing amplitude. The main factor that determines the
granular arch resistance against vibrations is the maximum angle among those
formed between any particle of the arch and its two neighbors: the higher the
maximum angle is, the easier to break the arch. Based in an analysis of the
forces, a simple explanation is given for this dependence. From this,
interesting information can be extracted about the expected magnitudes of
normal forces and friction coefficients of the particles conforming the arches
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