28,460 research outputs found
Abundance analysis of a CEMP-no star in the Carina dwarf spheroidal galaxy
Carbon-enhanced metal-poor (CEMP) stars bear important imprints of the early
chemical enrichment of any stellar system. While these stars are known to exist
in copious amounts in the Milky Way halo, detailed chemical abundance data from
the faint dwarf spheroidal (dSph) satellites are still sparse, although the
relative fraction of these stars increases with decreasing metallicity. Here,
we report the abundance analysis of a metal-poor ([Fe/H]= dex),
carbon-rich ([C/Fe]=1.4 dex) star, ALW-8, in the Carina dSph using
high-resolution spectroscopy obtained with the ESO/UVES instrument. Its
spectrum does not indicate any over-enhancements of neutron capture elements.
Thus classified as a CEMP-no star, this is the first detection of this kind of
star in Carina. Another of our sample stars, ALW-1, is shown to be a CEMP-
star, but its immediate binarity prompted us to discard it from a detailed
analysis. The majority of the 18 chemical elements we measured are typical of
Carina's field star population and also agree with CEMP stars in other dSph
galaxies. Similar to the only known CEMP-no star in the Sculptor dSph and the
weak--process star HD 122563, the lack of any strong barium-enhancement is
accompanied by a moderate overabundance in yttrium, indicating a weak
-process activity. The overall abundance pattern confirms that, also in
Carina, the formation site for CEMP-no stars has been affected by both faint
supernovae and by standard core collapse supernovae. Whichever process was
responsible for the heavy element production in ALW-8 must be a ubiquitous
source to pollute the CEMP-no stars, acting independently of the environment
such as in the Galactic halo or in dSphs.Comment: Accepted for publication in A&
Analysis And Performance Of A Picosecond Dye Laser Amplifier Chain
Design considerations are discussed for a simple, easy to use and relatively efficient high gain dye laser amplifier chain for CW mode-locked dye lasers. The amplifier boosts the output of a synchronously mode-locked dye laser to obtain ≈005 mj, ≤ 1 psec pulses over a ≈ 400 Å bandwidth. These pulses are suitable for efficient Raman Shifting, frequency mixing and continuum generation to vastly extend the spectral range of the system. Our amplifier is pumped by a frequency doubled Nd:YAG oscillator only, which longitudinally pumps three identical brewster cells with the same flowing dye solution in each. Contrary to popular belief, high small signal gains (≥ 105) are easily attained in a single stage with longitudinal pumping, with better beam homogeneity and easier alignment than transverse pumping. Gain saturation measurements are presented which agree well with calculations. Factors which relax the pump timing sensitivity are examined. The importance of gain saturation for both efficient amplification and for amplitude stability is also discussed. The need for isolated amplifier stages is stressed and optimal amplifier cell areas for a given stage are calculated
AND Protocols Using Only Uniform Shuffles
Secure multi-party computation using a deck of playing cards has been a
subject of research since the "five-card trick" introduced by den Boer in 1989.
One of the main problems in card-based cryptography is to design
committed-format protocols to compute a Boolean AND operation subject to
different runtime and shuffle restrictions by using as few cards as possible.
In this paper, we introduce two AND protocols that use only uniform shuffles.
The first one requires four cards and is a restart-free Las Vegas protocol with
finite expected runtime. The second one requires five cards and always
terminates in finite time.Comment: This paper has appeared at CSR 201
Ultrafast magnetophotoconductivity of semi-insulating gallium arsenide
The speed of opto-electronic switches is increased or decreased by the application of a magnetic field. This is achieved by inducing a carrier drift toward or away from the semiconductor surface, resulting in the enhancement or suppression of surface recombination. We establish that surface recombination plays a major role in determining the speed of the opto-electronic switch
Advanced indium antimonide monolithic charge coupled infrared imaging arrays
The continued process development of SiO2 insulators for use in advanced InSb monolithic charge coupled infrared imaging arrays is described. Specific investigations into the use of plasma enhanced chemical vapor deposited (PECVD) SiO2 as a gate insulator for InSb charge coupled devices is discussed, as are investigations of other chemical vapor deposited SiO2 materials
Guyanese expatriate women ask: “is it a touch of sugar?”
Eight Guyanese expatriate women, who had been living in and around London for decades, came together driven by a participatory inquiry approach. Do we just have ‘a touch of sugar’ or is diabetes a serious affliction were questions asked. The study’s objective was to find answers to these questions. Three nurse academics, one a Guyanese / English woman herself, researched alongside participants. After several years of storytelling and group discussion (2010-2015), the women recognised that when they connected socially, the practical effect of togetherness was empowerment. Researching with participants fostered new understandings of diabetes and improved self-management of this chronic condition. This was achieved through the collaborative character of the inquiry and as a practical response to the problems women were facing. They continue to engage with each other and are reaching out to the wider UK Guyanese community. They have a strong voice about living well with diabetes and strongly reject the myth that diabetes is only ‘a touch of sugar.
Emergence of slow-switching assemblies in structured neuronal networks
Unraveling the interplay between connectivity and spatio-temporal dynamics in
neuronal networks is a key step to advance our understanding of neuronal
information processing. Here we investigate how particular features of network
connectivity underpin the propensity of neural networks to generate
slow-switching assembly (SSA) dynamics, i.e., sustained epochs of increased
firing within assemblies of neurons which transition slowly between different
assemblies throughout the network. We show that the emergence of SSA activity
is linked to spectral properties of the asymmetric synaptic weight matrix. In
particular, the leading eigenvalues that dictate the slow dynamics exhibit a
gap with respect to the bulk of the spectrum, and the associated Schur vectors
exhibit a measure of block-localization on groups of neurons, thus resulting in
coherent dynamical activity on those groups. Through simple rate models, we
gain analytical understanding of the origin and importance of the spectral gap,
and use these insights to develop new network topologies with alternative
connectivity paradigms which also display SSA activity. Specifically, SSA
dynamics involving excitatory and inhibitory neurons can be achieved by
modifying the connectivity patterns between both types of neurons. We also show
that SSA activity can occur at multiple timescales reflecting a hierarchy in
the connectivity, and demonstrate the emergence of SSA in small-world like
networks. Our work provides a step towards understanding how network structure
(uncovered through advancements in neuroanatomy and connectomics) can impact on
spatio-temporal neural activity and constrain the resulting dynamics.Comment: The first two authors contributed equally -- 18 pages, including
supplementary material, 10 Figures + 2 SI Figure
First Order Calculation of the Inclusive Cross Section pp to ZZ by Graviton Exchange in Large Extra Dimensions
We calculate the inclusive cross section of double Z-boson production within
large extra dimensions at the Large Hadron Collider (LHC). Using perturbatively
quantized gravity in the ADD model we perform a first order calculation of the
graviton mediated contribution to the pp to ZZ cross section. At low energies
(e.g. Tevatron) this additional contribution is very small, making it virtually
unobservable, for a fundamental mass scale above 2500 GeV. At LHC energies
however, the calculation indicates that the ZZ-production rate within the ADD
model should differ significantly from the Standard Model if the new
fundamental mass scale would be below 15000 GeV. A comparison with the observed
production rate at the LHC might therefore provide direct hints on the number
and structure of the extra dimensions.Comment: 7 pages, 7 figures, accepted for publication in Phys. Rev.
Expansion dynamics of a dipolar Bose-Einstein condensate
Our recent measurements on the expansion of a chromium dipolar condensate
after release from an optical trapping potential are in good agreement with an
exact solution of the hydrodynamic equations for dipolar Bose gases. We report
here the theoretical method used to interpret the measurement data as well as
more details of the experiment and its analysis. The theory reported here is a
tool for the investigation of different dynamical situations in time-dependent
harmonic traps.Comment: 12 pages. Submitted to PR
Secure Grouping Protocol Using a Deck of Cards
We consider a problem, which we call secure grouping, of dividing a number of
parties into some subsets (groups) in the following manner: Each party has to
know the other members of his/her group, while he/she may not know anything
about how the remaining parties are divided (except for certain public
predetermined constraints, such as the number of parties in each group). In
this paper, we construct an information-theoretically secure protocol using a
deck of physical cards to solve the problem, which is jointly executable by the
parties themselves without a trusted third party. Despite the non-triviality
and the potential usefulness of the secure grouping, our proposed protocol is
fairly simple to describe and execute. Our protocol is based on algebraic
properties of conjugate permutations. A key ingredient of our protocol is our
new techniques to apply multiplication and inverse operations to hidden
permutations (i.e., those encoded by using face-down cards), which would be of
independent interest and would have various potential applications
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