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 $G$ and an integer $D$, whether it is possible to add edges to $G$ in a way that the resulting graph is outerplanar and has diameter at most $D$. 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