1,518 research outputs found
New class of 3D topological insulator in double perovskite
We predict a new class of three-dimensional topological insulators (TIs) in
which the spin-orbit coupling (SOC) can more effectively generate a large band
gap at point. The band gap of conventional TI such as BiSe is
mainly limited by two factors, the strength of SOC and, from electronic
structure perspective, the band gap when SOC is absent. While the former is an
atomic property, we find that the latter can be minimized in a generic
rock-salt lattice model in which a stable crossing of bands {\it at} the Fermi
level along with band character inversion occurs for a range of parameters in
the absence of SOC. Thus, large-gap TI's or TI's comprised of lighter elements
can be expected. In fact, we find by performing first-principle calculations
that the model applies to a class of double perovskites ABiXO (A = Ca,
Sr, Ba; X = Br, I) and the band gap is predicted up to 0.55 eV. Besides, more
detailed calculations considering realistic surface structure indicate that the
Dirac cones are robust against the presence of dangling bond at the boundary
with a specific termination.Comment: submitted; title changed and new references added; see DOI for
published versio
Updated constraints on Georgi-Machacek model, and its electroweak phase transition and associated gravitational waves
With theoretical constraints such as perturbative unitarity and vacuum
stability conditions and updated experimental data of Higgs measurements and
direct searches for exotic scalars at the LHC, we perform an updated scan of
the allowed parameter space of the Georgi-Machacek (GM) model. With the refined
global fit, we examine the allowed parameter space for inducing strong
first-order electroweak phase transitions (EWPTs) and find only the one-step
phase transition is phenomenologically viable. Based upon the result, we study
the associated gravitational wave (GW) signals and find most of which can be
detected by several proposed experiments. We also make predictions on processes
that may serve as promising probes to the GM model in the near future at the
LHC, including the di-Higgs productions and several exotic scalar production
channels.Comment: 42 pages, 11 figures, 9 table
Empiric antibiotic choices for community-acquired biliary tract infections
SummaryBackgroundThe study was conducted to reveal the most appropriate empiric antibiotics for the treatment of community-acquired biliary tract infections (CA-BTI) at a regional hospital in Taiwan.MethodsThe study was performed between October 1, 2010 and October 31, 2012. All positive bile culture results of presumptive community-acquired origins were collected. The associated etiologic microorganisms and their antimicrobial susceptibilities were analyzed. The appropriateness of empiric therapy (defined as the effectiveness of the antibiotics against the etiologic agents) and the subsequent treatment response were examined through the review of medical records.ResultsA total of 115 patients (cholecystitis, 83 cases, 72.2%; cholangitis, 32 cases, 27.8%) and 189 isolates (136 Gram-negative bacilli, 37 Gram-positive cocci, and 16 anaerobes) were analyzed. The most frequent pathogens were Escherichia coli (n = 69, 36.5%), Klebsiella spp. (n = 37, 19.6%), enterococci (n = 29, 15.3%), and Bacteroides spp. (n = 11, 5.8%). Penicillin resistance (5.4%) was low in Gram-positive cocci, whereas higher resistance (>20%) to cefazolin, cefuroxime, and ampicillin–sulbactam was found in Gram-negative bacilli. Anaerobes also demonstrated high resistance to clindamycin (37.5%) but less to metronidazole (12.5%). Appropriate empiric therapy was found in 92 (80%) cases, and among them, 83 (90.2%) were treated successfully. The treatment success rate (69.6%) was significantly lower among the remaining 23 cases with inappropriate empiric therapy (16 of 23 vs. 83 of 92, p < 0.05). A high treatment success rate (97.2%) was observed among cases empirically treated with ceftriaxone plus metronidazole.ConclusionThe combination of ceftriaxone plus metronidazole appears to be the most appropriate empiric antibiotics for the treatment of CA-BTI at this hospital. Because different hospitals may encounter microorganisms of different antimicrobial susceptibilities, similar approaches may be followed by other hospitals where appropriate empiric therapy has not yet been established for the treatment of CA-BTI
Acute Myeloid Leukemia Presenting with Sweet Syndrome: A Case Report and Review of the Literature
Angular-Resolved Optical Characteristics and Threshold Gain Analysis of GaN-Based 2-D Photonics Crystal Surface Emitting Lasers
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