22,805,882 research outputs found
Rock-salt SnS and SnSe: Native Topological Crystalline Insulators
Unlike time-reversal topological insulators, surface metallic states with
Dirac cone dispersion in the recently discovered topological crystalline
insulators (TCIs) are protected by crystal symmetry. To date, TCI behaviors
have been observed in SnTe and the related alloys PbSnSe/Te,
which incorporate heavy elements with large spin-orbit coupling (SOC). Here, by
combining first-principles and {\it ab initio} tight-binding calculations, we
report the formation of a TCI in the relatively lighter rock-salt SnS and SnSe.
This TCI is characterized by an even number of Dirac cones at the high-symmetry
(001), (110) and (111) surfaces, which are protected by the reflection symmetry
with respect to the (10) mirror plane. We find that both SnS and SnSe
have an intrinsically inverted band structure and the SOC is necessary only to
open the bulk band gap. The bulk band gap evolution upon volume expansion
reveals a topological transition from an ambient pressure TCI to a
topologically trivial insulator. Our results indicate that the SOC alone is not
sufficient to drive the topological transition.Comment: 5 pages, 5 figure
Recurrence in 2D Inviscid Channel Flow
I will prove a recurrence theorem which says that any () solution
to the 2D inviscid channel flow returns repeatedly to an arbitrarily small
neighborhood. Periodic boundary condition is imposed along the
stream-wise direction. The result is an extension of an early result of the
author [Li, 09] on 2D Euler equation under periodic boundary conditions along
both directions
Antimicrobials: a global alliance for optimizing their rational use in intra-abdominal infections (AGORA)
Intra-abdominal infections (IAI) are an important cause of morbidity and are frequently associated with poor prognosis, particularly in high-risk patients. The cornerstones in the management of complicated IAIs are timely effective source control with appropriate antimicrobial therapy. Empiric antimicrobial therapy is important in the management of intra-abdominal infections and must be broad enough to cover all likely organisms because inappropriate initial antimicrobial therapy is associated with poor patient outcomes and the development of bacterial resistance. The overuse of antimicrobials is widely accepted as a major driver of some emerging infections (such as C. difficile), the selection of resistant pathogens in individual patients, and for the continued development of antimicrobial resistance globally. The growing emergence of multi-drug resistant organisms and the limited development of new agents available to counteract them have caused an impending crisis with alarming implications, especially with regards to Gram-negative bacteria. An international task force from 79 different countries has joined this project by sharing a document on the rational use of antimicrobials for patients with IAIs. The project has been termed AGORA (Antimicrobials: A Global Alliance for Optimizing their Rational Use in Intra-Abdominal Infections). The authors hope that AGORA, involving many of the world's leading experts, can actively raise awareness in health workers and can improve prescribing behavior in treating IAIs
Evaluation and application of the Baldwin-Lomax turbulence model in two-dimensional, unsteady, compressible boundary layers with and without separation in engine inlets
There is a practical need to model high speed flows that exist in jet engine inlets. The boundary layers that form in these inlets may be turbulent or laminar and either separated or attached. Also, unsteady supersonic inlets may be subject to frequent changes in operating conditions. Some changes in the operating conditions of the inlets may include varying the inlet geometry, bleeds and bypasses, and rotating or translating the centerbody. In addition, the inlet may be either started or unstarted. Therefore, a CFD code, used to model these inlets, may have to run for several different cases. Also, since the flow conditions through an unsteady inlet may be continually fluctuating, the CFD code which models these flows may have to be run over many time steps. Therefore, it would be beneficial that the code run quickly. Many turbulence models, however, are cumbersome to implement and require a lot of computer time to run, since they add to the number of differential equations to be solved to model a flow. The Baldwin-Lomax turbulence model is a popular model. It is an algebraic, eddy viscosity model. The Baldwin-Lomax model is used in many CFD codes because it is quick and easy to implement. In this paper, we will discuss implementing the Baldwin-Lomax turbulence model for both steady and unsteady compressible flows. In addition, these flows may be either separated or attached. In order to apply this turbulence model to flows which may be subjected to these conditions, certain modifications should be made to the original Baldwin-Lomax model. We will discuss these modifications and determine whether the Baldwin-Lomax model is a viable turbulence model that produces reasonably accurate results for high speed flows that can be found in engine inlets
Cosmological Constraints on Neutrino Masses and Mixings
The bounds on neutrino masses and mixing that follows from the data on light
element abundances, large scale structure formation, and angular fluctuations
of cosmic microwave background radiation are analyzed. The role of neutrino
oscillations in BBN and the bounds on cosmological lepton asymmetry are
discussed.Comment: Talk presented at the NOON 2003 workshop, February 10-14, 2003,
Kanazawa, Japan (to be published in the Proceedings), 10 page
Status of Evidence for Neutrinoless Double Beta Decay, and the Future: GENIUS and GENIUS-TF
The first evidence for neutrinoless double beta decay has been observed in
the HEIDELBERG-MOSCOW experiment, which is the most sensitive double beta decay
experiment since ten years. This is the first evidence for lepton number
violation and proves that the neutrino is a Majorana particle. It further shows
that neutrino masses are degenerate. In addition it puts several stringent
constraints on other physics beyond the Standard Model. The result from the
HEIDELBERG-MOSCOW experiment is consistent with recent results from CMB
investigations, with high energy cosmic rays, with the result from the g-2
experiment and with recent theoretical work. It is indirectly supported by the
analysis of other Ge double beta experiments.
The new project GENIUS will cover a wide range of the parameter space of
predictions of SUSY for neutralinos as cold dark matter. Further it has the
potential to be a real-time detector for low-energy ( and Be) solar
neutrinos.
A GENIUS Test Facility has come into operation on May 5, 2003. This is the
first time that this novel technique for extreme background reduction in search
for rare decays is applied under the background conditions of an underground
laboratory.Comment: 20 pages, 13 figure
A Unique Oscillation Solution to the Solar Neutrino Problem?
A global two-neutrino oscillation fit combining Super-Kamiokande solar
neutrino data with the solar neutrino rates measured by Homestake, Gallex/GNO,
SAGE and SNO prefers a single allowed area, the Large Mixing Angle solution, at
about 95% confidence level. The mass^2 difference between the two mass
eigenstates is Delta m^2 approx 3-25 x 10^-5 eV^2, the mixing angle theta is
tan^2 theta approx 0.21-0.67.Comment: 10 pages, 3 figures, to be published in the proceedings of the NOON
2001 worksho
Kamland Results
The LMA solution of the solar neutrino problem has been explored with the
1,000 ton liquid scinatillator detector, KamLAND. It utilizes nuclear power
reactors distributing effectively 180km from the experimental site. Comparing
observed neutrino rate with the calculation of reactor operation histories, an
evidence for reactor neutrino disapearance has been obtained from 162 ton-year
exposure data. This deficit is only compatible with the LMA solution and the
other solutions in the two neutrino oscillation hypotheisis are excluded at
99.95% confidence level.Comment: 8 pages, 5 figures, proceeding of the Moriond Conference "Electroweak
Interactions and Unified Thories
Universal Texture of Quark and Lepton Mass Matrices
Against the conventional picture that the mass matrix forms in the quark
sectors will take somewhat different structures from those in the lepton
sectors, a possibility that all the mass matrices of quarks and leptons have
the same form as in the neutrinos is investigated. For the lepton sectors, the
model leads to a nearly bimaximal mixing with the prediction
|U_{e3}|^2=m_e/2m_\mu=0.0024 and \tan^2\theta_{sol} \simeq m_{\nu 1}/m_{\nu 2},
and so on. For the quark sectors, it can lead to reasonable values of the CKM
mixing matrix and masses: |V_{us}|\simeq \sqrt{m_d/m_s}, |V_{ub}| \simeq
|V_{cb}|\sqrt{m_u/m_c}, |V_{td}| \simeq |V_{cb}|\cdot |V_{us}|, and so on.Comment: 9 pages, Latex, talk given at The 4th workshop on "Neutrino
Oscillations and their Origin" (NOON2003) (Kanazawa, Japan, 10--14 Feb.
2002). To appear in the Proceeding
Models of maximal atmospheric neutrino mixing and leptogenesis
We discuss two extensions of the Standard Model based on the seesaw mechanism
and on non-abelian family symmetry groups O(2) and , respectively. Both
models have a twofold-degenerate neutrino Dirac mass matrix , a Majorana
mass matrix invariant under a -- interchange symmetry and the
predictions of maximal atmospheric neutrino mixing and vanishing mixing angle
. Leptogenesis can naturally be incorporated if eV where the mass of the lightest neutrino and if
the relevant heavy neutrinos are in the range to GeV. The
model is more constrained and leptogenesis requires to be in the
vicinity of eV.Comment: 8 pages, one figure, talk presented at NOON2004, February 11-15,
2004, Tokyo, Japa
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