16,708 research outputs found
An experimental survey of the production of alpha decaying heavy elements in the reactions of U +Th at 7.5-6.1 MeV/nucleon
The production of alpha particle decaying heavy nuclei in reactions of
7.5-6.1 MeV/nucleon U +Th has been explored using an in-beam
detection array composed of YAP scintillators and gas ionization chamber-Si
telescopes. Comparisons of alpha energies and half-lives for the observed
products with those of the previously known isotopes and with theoretically
predicted values indicate the observation of a number of previously unreported
alpha emitters. Alpha particle decay energies reaching as high as 12 MeV are
observed. Many of these are expected to be from decay of previously unseen
relatively neutron rich products. While the contributions of isomeric states
require further exploration and specific isotope identifications need to be
made, the production of heavy isotopes with quite high atomic numbers is
suggested by the data.Comment: 12 pages, 12 figure
Updated cosmic-ray and radio constraints on light dark matter: Implications for the GeV gamma-ray excess at the Galactic center
The apparent gamma-ray excess in the Galactic center region and inner Galaxy
has attracted considerable interest, notably because both its spectrum and
radial distribution are consistent with an interpretation in terms of
annihilating dark matter particles with a mass of about 10-40 GeV. We confront
such an interpretation with an updated compilation of various indirect dark
matter detection bounds, which we adapt to the specific form required by the
observed signal. We find that cosmic-ray positron data strongly rule out dark
matter annihilating to light leptons, or 'democratically' to all leptons, as an
explanation of the signal. Cosmic-ray antiprotons, for which we present
independent and significantly improved limits with respect to previous
estimates, are already in considerable tension with DM annihilation to any
combination of quark final states; the first set of AMS-02 data will thus be
able to rule out or confirm the DM hypothesis with high confidence. For
reasonable assumptions about the magnetic field in the Galactic center region,
radio observations independently put very severe constraints on a DM
interpretation of the excess, in particular for all leptonic annihilation
channels.Comment: 23 pages revtex, 19 figures, 1 table. Extended discussion of
antiproton limits and added references. Matches published versio
Thermo-visual feature fusion for object tracking using multiple spatiogram trackers
In this paper, we propose a framework that can efficiently combine features for robust tracking based on fusing the outputs of multiple spatiogram trackers. This is achieved without the exponential increase in storage and processing that other multimodal tracking approaches suffer from. The framework allows the features to be split arbitrarily between the trackers, as well as providing the flexibility to add, remove or dynamically weight features. We derive a mean-shift type algorithm for the framework that allows efficient object tracking with very low computational overhead. We especially target the fusion of thermal infrared and visible spectrum features as the most useful features for automated surveillance applications. Results are shown on multimodal video sequences clearly illustrating the benefits of combining multiple features using our framework
A Comprehensive Survey of Deep Learning in Remote Sensing: Theories, Tools and Challenges for the Community
In recent years, deep learning (DL), a re-branding of neural networks (NNs),
has risen to the top in numerous areas, namely computer vision (CV), speech
recognition, natural language processing, etc. Whereas remote sensing (RS)
possesses a number of unique challenges, primarily related to sensors and
applications, inevitably RS draws from many of the same theories as CV; e.g.,
statistics, fusion, and machine learning, to name a few. This means that the RS
community should be aware of, if not at the leading edge of, of advancements
like DL. Herein, we provide the most comprehensive survey of state-of-the-art
RS DL research. We also review recent new developments in the DL field that can
be used in DL for RS. Namely, we focus on theories, tools and challenges for
the RS community. Specifically, we focus on unsolved challenges and
opportunities as it relates to (i) inadequate data sets, (ii)
human-understandable solutions for modelling physical phenomena, (iii) Big
Data, (iv) non-traditional heterogeneous data sources, (v) DL architectures and
learning algorithms for spectral, spatial and temporal data, (vi) transfer
learning, (vii) an improved theoretical understanding of DL systems, (viii)
high barriers to entry, and (ix) training and optimizing the DL.Comment: 64 pages, 411 references. To appear in Journal of Applied Remote
Sensin
Simple method for sub-diffraction resolution imaging of cellular structures on standard confocal microscopes by three-photon absorption of quantum dots
This study describes a simple technique that improves a recently developed 3D sub-diffraction imaging method based on three-photon absorption of commercially available quantum dots. The method combines imaging of biological samples via tri-exciton generation in quantum dots with deconvolution and spectral multiplexing, resulting in a novel approach for multi-color imaging of even thick biological samples at a 1.4 to 1.9-fold better spatial resolution. This approach is realized on a conventional confocal microscope equipped with standard continuous-wave lasers. We demonstrate the potential of multi-color tri-exciton imaging of quantum dots combined with deconvolution on viral vesicles in lentivirally transduced cells as well as intermediate filaments in three-dimensional clusters of mouse-derived neural stem cells (neurospheres) and dense microtubuli arrays in myotubes formed by stacks of differentiated C2C12 myoblasts
On the DM interpretation of the origin of non-thermal phenomena in galaxy clusters
(Abridged) We study the predictions of various annihilating Dark Matter (DM)
models in order to interpret the origin of non-thermal phenomena in galaxy
clusters. We consider three neutralino DM models with light (9 GeV),
intermediate (60 GeV) and high (500 GeV) mass. The secondary particles created
by neutralino annihilation produce a multi-frequency Spectral Energy
Distribution (SED), as well as heating of the intracluster gas, that are tested
against the observations available for the Coma cluster. The DM produced SEDs
are normalized to the Coma radio halo spectrum. We find that it is not possible
to interpret all non-thermal phenomena observed in Coma in terms of DM
annihilation. The DM model with 9 GeV mass produces too small power at all
frequencies, while the DM model with 500 GeV produces a large excess power at
all frequencies. The DM model with 60 GeV and composition is
consistent with the HXR and gamma-ray data but fails to reproduce the EUV and
soft X-ray data. The DM model with 60 GeV and composition is always
below the observed fluxes. The radio halo spectrum of Coma is well fitted only
in the or light and intermediate mass DM models. The heating
produced by DM annihilation in the center of Coma is always larger than the
intracluster gas cooling rate for an NFW DM density profile and it is
substantially smaller than the cooling rate only for a cored DM density profile
in DM model with 9 GeV. We conclude that the possibility of interpreting the
origin of non-thermal phenomena in galaxy clusters with DM annihilation models
requires a low neutralino mass and a cored DM density profile. If we then
consider the multimessenger constraints to the neutralino annihilation
cross-section, it turns out that such scenario would also be excluded unless we
introduce a substantial boost factor due to the presence of DM substructures.Comment: 9 pages, 6 figures, 2 Tables. Submitted to A&
Decay modes of 250No
The Fragment Mass Analyzer at the ATLAS facility has been used to
unambiguously identify the mass number associated with different decay modes of
the nobelium isotopes produced via 204Pb(48Ca,xn)(252-x)No reactions.
Isotopically pure (>99.7%) 204Pb targets were used to reduce background from
more favored reactions on heavier lead isotopes. Two spontaneous fission
half-lives (t_1/2 = 3.7+1.1-0.8 us and 43+22-15 us) were deduced from a total
of 158 fission events. Both decays originate from 250No rather than from
neighboring isotopes as previously suggested. The longer activity most likely
corresponds to a K-isomer in this nucleus. No conclusive evidence for an alpha
branch was observed, resulting in upper limits of 2.1% for the shorter lifetime
and 3.4% for the longer activity.Comment: RevTex4, 10 pages, 5 figures, submitted to PR
Frequency-encoded linear cluster states with coherent Raman photons
Entangled multi-qubit states are an essential resource for quantum
information and computation. Solid-state emitters can mediate interactions
between subsequently emitted photons via their spin, thus offering a route
towards generating entangled multi-photon states. However, existing schemes
typically rely on the incoherent emission of single photons and suffer from
severe practical limitations, for self-assembled quantum dots most notably the
limited spin coherence time due to Overhauser magnetic field fluctuations. We
here propose an alternative approach of employing spin-flip Raman scattering
events of self-assembled quantum dots in Voigt geometry. We argue that weakly
driven hole spins constitute a promising platform for the practical generation
of frequency-entangled photonic cluster states
- âŠ