3,490 research outputs found
On the origin of \gamma-ray emission in \eta\ Carina
\eta\ Car is the only colliding-wind binary for which high-energy \gamma\
rays are detected. Although the physical conditions in the shock region change
on timescales of hours to days, the variability seen at GeV energies is weak
and on significantly longer timescales. The \gamma-ray spectrum exhibits two
features that can be interpreted as emission from the shocks on either side of
the contact discontinuity. Here we report on the first time-dependent modelling
of the non-thermal emission in \eta\ Car. We find that emission from primary
electrons is likely not responsible for the \gamma-ray emission, but
accelerated protons interacting with the dense wind material can explain the
observations. In our model, efficient acceleration is required at both shocks,
with the primary side acting as a hadron calorimeter, whilst on the companion
side acceleration is limited by the flow time out of the system, resulting in
changing acceleration conditions. The system therefore represents a unique
laboratory for the exploration of hadronic particle acceleration in
non-relativistic shocks.Comment: 5 pages, 4 figures, 1 table, accepted for publication in MNRAS
Letter
Potential Neutrino Signals from Galactic Gamma-Ray Sources
The recent progress made in Galactic gamma-ray astronomy using the High
Energy Stereoskopic System (H.E.S.S.) instrument provides for the first time a
population of Galactic TeV gamma-rays, and hence potential neutrino sources,
for which the neutrino flux can be estimated. Using the energy spectra and
source morphologies measured by H.E.S.S., together with new parameterisations
of pion production and decay in hadronic interactions, we estimate the signal
and background rates expected for these sources in a first-generation water
Cherenkov detector (ANTARES) and a next-generation neutrino telescope in the
Mediterranean Sea, KM3NeT, with an instrumented volume of 1 km^3. We find that
the brightest gamma-ray sources produce neutrino rates above 1 TeV, comparable
to the background from atmospheric neutrinos. The expected event rates of the
brightest sources in the ANTARES detector make a detection unlikely. However,
for a 1 km^3 KM3NeT detector, event rates of a few neutrinos per year from
these sources are expected, and the detection of individual sources seems
possible. Although generally these estimates should be taken as flux upper
limits, we discuss the conditions and type of gamma-ray sources for which the
neutrino flux predictions can be considered robust.Comment: 20 pages, 4 figures; v2: ERROR in energy scale of KM3NeT effective
neutrino area corrected which resulted in event rates being about a factor 3
too low; v3: grammatical changes and update of references after receiving
proof
Comparing Probabilistic Models for Melodic Sequences
Modelling the real world complexity of music is a challenge for machine
learning. We address the task of modeling melodic sequences from the same music
genre. We perform a comparative analysis of two probabilistic models; a
Dirichlet Variable Length Markov Model (Dirichlet-VMM) and a Time Convolutional
Restricted Boltzmann Machine (TC-RBM). We show that the TC-RBM learns
descriptive music features, such as underlying chords and typical melody
transitions and dynamics. We assess the models for future prediction and
compare their performance to a VMM, which is the current state of the art in
melody generation. We show that both models perform significantly better than
the VMM, with the Dirichlet-VMM marginally outperforming the TC-RBM. Finally,
we evaluate the short order statistics of the models, using the
Kullback-Leibler divergence between test sequences and model samples, and show
that our proposed methods match the statistics of the music genre significantly
better than the VMM.Comment: in Proceedings of the ECML-PKDD 2011. Lecture Notes in Computer
Science, vol. 6913, pp. 289-304. Springer (2011
Evidence for shape coexistence in Mo
A angular correlation experiment has been performed to
investigate the low-energy states of the nucleus Mo. The new data,
including spin assignments, multipole mixing ratios and lifetimes reveal
evidence for shape coexistence and mixing in Mo, arising from a proton
intruder configuration. This result is reproduced by a theoretical calculation
within the proton-neutron interacting boson model with configuration mixing,
based on microscopic energy density functional theory. The microscopic
calculation indicates the importance of the proton particle-hole excitation
across the Z=40 sub-shell closure and the subsequent mixing between spherical
vibrational and the -soft equilibrium shapes in Mo.Comment: 6 pages, 5 figures, 3 tables; published in Phys. Rev.
Anomalous Noise in the Pseudogap Regime of YBaCuO
An unusual noise component is found near and below about 250 K in the normal
state of underdoped YBCO and Ca-YBCO films. This noise regime, unlike the more
typical noise above 250 K, has features expected for a symmetry-breaking
collective electronic state. These include large individual fluctuators, a
magnetic sensitivity, and aging effects. A possible interpretation in terms of
fluctuating charge nematic order is presented.Comment: 4 pages, 4 figure
Dark matter annihilation and decay in dwarf spheroidal galaxies: The classical and ultrafaint dSphs
Dwarf spheroidal (dSph) galaxies are prime targets for present and future
gamma-ray telescopes hunting for indirect signals of particle dark matter. The
interpretation of the data requires careful assessment of their dark matter
content in order to derive robust constraints on candidate relic particles.
Here, we use an optimised spherical Jeans analysis to reconstruct the
`astrophysical factor' for both annihilating and decaying dark matter in 21
known dSphs. Improvements with respect to previous works are: (i) the use of
more flexible luminosity and anisotropy profiles to minimise biases, (ii) the
use of weak priors tailored on extensive sets of contamination-free mock data
to improve the confidence intervals, (iii) systematic cross-checks of binned
and unbinned analyses on mock and real data, and (iv) the use of mock data
including stellar contamination to test the impact on reconstructed signals.
Our analysis provides updated values for the dark matter content of 8
`classical' and 13 `ultrafaint' dSphs, with the quoted uncertainties directly
linked to the sample size; the more flexible parametrisation we use results in
changes compared to previous calculations. This translates into our ranking of
potentially-brightest and most robust targets---viz., Ursa Minor, Draco,
Sculptor---, and of the more promising, but uncertain targets---viz., Ursa
Major 2, Coma---for annihilating dark matter. Our analysis of Segue 1 is
extremely sensitive to whether we include or exclude a few marginal member
stars, making this target one of the most uncertain. Our analysis illustrates
challenges that will need to be addressed when inferring the dark matter
content of new `ultrafaint' satellites that are beginning to be discovered in
southern sky surveys.Comment: 19 pages, 14 figures, submitted to MNRAS. Supplementary material
available on reques
How to build nanoblocks using DNA scaffolds
In recent years there have been a number of proposals to utilize the
specificity of DNA based interactions for potential applications in
nanoscience. One interesting direction is the self-assembly of micro- and
nanoparticle clusters using DNA scaffolds. In this letter we consider a DNA
scaffold method to self-assemble clusters of "colored" particles. Stable
clusters of microspheres have recently been produced by an entirely different
method. Our DNA based approach self-assembles clusters with additional degrees
of freedom associated with particle permutation. We demonstrate that in the
non-equilibrium regime of irreversible binding the self-assembly process is
experimentally feasible. These color degrees of freedom may allow for more
diverse intercluster interactions essential for hierarchical self-assembly of
larger structures.Comment: 4 pages, 2 figures ; epl forma
Pathways to Juvenile Detention Reform: Reducing Racial Disparities in Juvenile Detention
Many years ago, Jim Casey, a founder and long-time CEO of the United Parcel Service, observed that his least prepared and least effective employees were those unfortunate individuals who, for various reasons, had spent much of their youth in institutions or who had been passed through multiple foster care placements. When his success in business enabled him and his siblings to establish a philanthropy (named in honor of their mother, Annie E. Casey), Mr. Casey focused his charitable work on improving the circumstances of disadvantaged children, in particular by increasing their chances of being raised in stable, nurturing family settings. His insight about what kids need to become healthy, productive citizens helps to explain the Casey Foundation’s historical commitment to juvenile justice reform. Over the past two decades, we have organized and funded a series of projects aimed at safely minimizing populations in juvenile correctional facilities through fairer, better informed system policies and practices and the use of effective community-based alternatives.
In December 1992, the Annie E. Casey Foundation launched a multi-year, multi-site project known as the Juvenile Detention Alternatives Initiative (JDAI). JDAI’s purpose was straightforward: to demonstrate that jurisdictions can establish more effective and efficient systems to accomplish the purposes of juvenile detention. The initiative was inspired by work that we had previously funded in Broward County, Florida, where an extremely crowded, dangerous, and costly detention operation had been radically transformed. Broward County’s experience demonstrated that interagency collaboration and data-driven policies and programs could reduce the numbers of kids behind bars without sacrificing public safety or court appearance rates
Development of a high-altitude airborne dial system: The Lidar Atmospheric Sensing Experiment (LASE)
The ability of a Differential Absorption Lidar (DIAL) system to measure vertical profiles of H2O in the lower atmosphere was demonstrated both in ground-based and airborne experiments. In these experiments, tunable lasers were used that required real-time experimenter control to locate and lock onto the atmospheric H2O absorption line for the DIAL measurements. The Lidar Atmospheric Sensing Experiment (LASE) is the first step in a long-range effort to develop and demonstrate an autonomous DIAL system for airborne and spaceborne flight experiments. The LASE instrument is being developed to measure H2O, aerosol, and cloud profiles from a high-altitude ER-2 (extended range U-2) aircraft. The science of the LASE program, the LASE system design, and the expected measurement capability of the system are discussed
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