6,034 research outputs found
Asymmetric Dark Matter from a GeV Hidden Sector
Asymmetric Dark Matter (ADM) models relate the dark matter density to the
baryon asymmetry, so that a natural mass scale for ADM is around a few GeV. In
existing models of ADM, this mass scale is unexplained; here we generate this
GeV scale for dark matter (DM) from the weak scale via gauge kinetic mixing
with a new Abelian dark force. In addition, this dark sector provides an
efficient mechanism for suppressing the symmetric abundance of DM through
annihilations to the dark photon. We augment this sector with a higher
dimensional operator responsible for communicating the baryon asymmetry to the
dark sector. Our framework also provides DM candidate for gauge mediation
models. It results in a direct detection cross section of interest for current
experiments: sigma less than or similar to 10^{-42} cm^2 for DM masses in the
range 1 - 15 GeV.Comment: 21 pages, 4 figure
Analgesia and Sedation of Pediatric Patients with Major Trauma in Pre-Hospital and Emergency Department Settings-A Narrative Review
Children who sustain major injuries are at risk of receiving insufficient pain relief and sedation, which can have physical and psychological repercussions. Heightened emotional distress can increase the likelihood of developing symptoms of post-traumatic stress. Providing sufficient analgesia and sedation for children with major trauma presents specific challenges, given the potential for drug-related adverse events, particularly in non-intubated patients. The current literature suggests that a relatively low percentage of pediatric patients receive adequate analgesia in pre-hospital and emergency department settings following major trauma. There are only sparse data on the safety of the provision of analgesia and sedation in children with major trauma in the pre-hospital and ED settings. The few studies that examined sedation protocols in this context highlight the importance of physician training and competency in managing pediatric airways. There is a pressing need for prospective studies that focus upon pediatric major trauma in the pre-hospital and emergency department setting to evaluate the benefits and risks of administering analgesia and sedation to these patients. The aim of this narrative review was to offer an updated overview of analgesia and sedation management in children with major trauma in pre-hospital and ED settings
Vertical Orientation in a New Gobioid Fish from New Britain
While visiting Rabaul, New Britain, during
Cruise 6 of the Stanford University vessel "Te
Vega" we observed and collected specimens of
a small gobioid fish that swam and hovered
vertically, with its head up, in midwater close to
pockets in the wall of an underwater cliff at
depths below 30 feet. Many kinds of fishes, for
example scorpaenids and cottoids, are known to
orient vertically in contact with a substrate.
There are fewer examples of vertically oriented
fishes in midwater; among the best known are
the seahorses and centriscids. Observations have
also been made on vertically oriented mesopelagic
fishes. Barham (1966) has seen myctophids
hovering vertically, as well as swimming
upward and downward. Paralepidids are also
known to be vertical swimmers (Peres, 1958;
Bernard, 1958; Cohen, personal observations).
We have found, however, no previous record of
this habit in gobioid fishes and our observations
are presented herewith. We have been unable to
identify the fish with any known form, and we
describe it as a ne
High sensitivity of 17O NMR to p-d hybridization in transition metal perovskites: first principles calculations of large anisotropic chemical shielding
A first principles embedded cluster approach is used to calculate O chemical
shielding tensors, sigma, in prototypical transition metal oxide ABO_3
perovskite crystals. Our principal findings are 1) a large anisotropy of sigma
between deshielded sigma_x ~ sigma_y and shielded sigma_z components (z along
the Ti-O bond); 2) a nearly linear variation, across all the systems studied,
of the isotropic sigma_iso and uniaxial sigma_ax components, as a function of
the B-O-B bond asymmetry. We show that the anisotropy and linear variation
arise from large paramagnetic contributions to sigma_x and sigma_y due to
virtual transitions between O(2p) and unoccupied B(nd) states. The calculated
isotropic delta_iso and uniaxial delta_ax chemical shifts are in good agreement
with recent BaTiO_3 and SrTiO_3 single crystal 17O NMR measurements. In PbTiO_3
and PbZrO_3, calculated delta_iso are also in good agreement with NMR powder
spectrum measurements. In PbZrO_3, delta_iso calculations of the five
chemically distinct sites indicate a correction of the experimental
assignments. The strong dependence of sigma on covalent O(2p)-B(nd)
interactions seen in our calculations indicates that 17O NMR spectroscopy,
coupled with first principles calculations, can be an especially useful tool to
study the local structure in complex perovskite alloys.Comment: 12 pages, 3 figures, and 3 Table
A Polynomial-time Algorithm for Outerplanar Diameter Improvement
The Outerplanar Diameter Improvement problem asks, given a graph and an
integer , whether it is possible to add edges to in a way that the
resulting graph is outerplanar and has diameter at most . We provide a
dynamic programming algorithm that solves this problem in polynomial time.
Outerplanar Diameter Improvement demonstrates several structural analogues to
the celebrated and challenging Planar Diameter Improvement problem, where the
resulting graph should, instead, be planar. The complexity status of this
latter problem is open.Comment: 24 page
Efficient Immunization Strategies for Computer Networks and Populations
We present an effective immunization strategy for computer networks and
populations with broad and, in particular, scale-free degree distributions. The
proposed strategy, acquaintance immunization, calls for the immunization of
random acquaintances of random nodes (individuals). The strategy requires no
knowledge of the node degrees or any other global knowledge, as do targeted
immunization strategies. We study analytically the critical threshold for
complete immunization. We also study the strategy with respect to the
susceptible-infected-removed epidemiological model. We show that the
immunization threshold is dramatically reduced with the suggested strategy, for
all studied cases.Comment: Revtex, 5 pages, 4 ps fig
Percolation Critical Exponents in Scale-Free Networks
We study the behavior of scale-free networks, having connectivity
distribution P(k) k^-a, close to the percolation threshold. We show that for
networks with 3<a<4, known to undergo a transition at a finite threshold of
dilution, the critical exponents are different than the expected mean-field
values of regular percolation in infinite dimensions. Networks with 2<a<3
possess only a percolative phase. Nevertheless, we show that in this case
percolation critical exponents are well defined, near the limit of extreme
dilution (where all sites are removed), and that also then the exponents bear a
strong a-dependence. The regular mean-field values are recovered only for a>4.Comment: Latex, 4 page
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