6,467 research outputs found
Kaluza-Klein and H-Dyons in String Theory
Kaluza-Klein monopole and H-monopole solutions, which are T-dual to each
other, are the well-known solutions of string theory compactified on .
Since string theory in this case has an S-duality symmetry, we explicitly
construct the corresponding dyonic solutions by expressing the string
effective action in a manifestly invariant form with an
invariant constraint. The Schwarz-Sen charge spectrum, the BPS saturated mass
formula as well as the stability of these states are discussed briefly.Comment: 15 pages, LaTeX, No figures, improved version to appear in Phys. Rev.
Setting school-level outcome standards
To establish international standards for medical schools, an appropriate panel of experts must decide on performance standards. A pilot test of such standards was set in the context of a multidimensional (multiple-choice question examination, objective structured clinical examination, faculty observation) examination at 8 leading schools in China. Methodsâ A group of 16 medical education leaders from a broad array of countries met over a 3-day period. These individuals considered competency domains, examination items, and the percentage of students who could fall below a cut-off score if the school was still to be considered as meeting competencies. This 2-step process started with a discussion of the borderline school and the relative difficulty of a borderline school in achieving acceptable standards in a given competency domain. Committee members then estimated the percentage of students falling below the standard that is tolerable at a borderline school and were allowed to revise their ratings after viewing pilot data. Resultsâ Tolerable failure rates ranged from 10% to 26% across competency domains and examination types. As with other standard-setting exercises, standard deviations from initial to final estimates of the tolerable failure rates fell, but the cut-off scores did not change significantly. Final, but not initial cut-off scores were correlated with student failure rates ( râ= â0.59, P â=â0.03). Discussionâ This paper describes a method to set school-level outcome standards at an international level based on prior established standard-setting methods. Further refinement of this process and validation using other examinations in other countries will be needed to achieve accurate international standards.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71572/1/j.1365-2929.2005.02374.x.pd
Some anisotropic universes in the presence of imperfect fluid coupling with spatial curvature
We consider Bianchi VI spacetime, which also can be reduced to Bianchi types
VI0-V-III-I. We initially consider the most general form of the energy-momentum
tensor which yields anisotropic stress and heat flow. We then derive an
energy-momentum tensor that couples with the spatial curvature in a way so as
to cancel out the terms that arise due to the spatial curvature in the
evolution equations of the Einstein field equations. We obtain exact solutions
for the universes indefinetly expanding with constant mean deceleration
parameter. The solutions are beriefly discussed for each Bianchi type. The
dynamics of the models and fluid are examined briefly, and the models that can
approach to isotropy are determined. We conclude that even if the observed
universe is almost isotropic, this does not necessarily imply the isotropy of
the fluid (e.g., dark energy) affecting the evolution of the universe within
the context of general relativity.Comment: 17 pages, no figures; to appear in International Journal of
Theoretical Physics; in this version (which is more concise) an equation
added, some references updated and adde
Weighed scalar averaging in LTB dust models, part I: statistical fluctuations and gravitational entropy
We introduce a weighed scalar average formalism ("q-average") for the study
of the theoretical properties and the dynamics of spherically symmetric
Lemaitre-Tolman-Bondi (LTB) dust models models. The "q-scalars" that emerge by
applying the q-averages to the density, Hubble expansion and spatial curvature
(which are common to FLRW models) are directly expressible in terms of
curvature and kinematic invariants and identically satisfy FLRW evolution laws
without the back-reaction terms that characterize Buchert's average. The local
and non-local fluctuations and perturbations with respect to the q-average
convey the effects of inhomogeneity through the ratio of curvature and
kinematic invariants and the magnitude of radial gradients. All curvature and
kinematic proper tensors that characterize the models are expressible as
irreducible algebraic expansions on the metric and 4-velocity, whose
coefficients are the q-scalars and their linear and quadratic local
fluctuations. All invariant contractions of these tensors are quadratic
fluctuations, whose q-averages are directly and exactly related to statistical
correlation moments of the density and Hubble expansion scalar. We explore the
application of this formalism to a definition of a gravitational entropy
functional proposed by Hosoya et al (2004 Phys. Rev. Lett. 92 141302). We show
that a positive entropy production follows from a negative correlation between
fluctuations of the density and Hubble scalar, providing a brief outline on its
fulfillment in various LTB models and regions. While the q-average formalism is
specially suited for LTB and Szekeres models, it may provide a valuable
theoretical insight on the properties of scalar averaging in inhomogeneous
spacetimes in general.Comment: 27 pages in IOP format, 1 figure. Matches version accepted for
publication in Classical and Quantum Gravit
Intravenous sodium nitrite in acute ST-elevation myocardial infarction: a randomized controlled trial (NIAMI).
AIM: Despite prompt revascularization of acute myocardial infarction (AMI), substantial myocardial injury may occur, in part a consequence of ischaemia reperfusion injury (IRI). There has been considerable interest in therapies that may reduce IRI. In experimental models of AMI, sodium nitrite substantially reduces IRI. In this double-blind randomized placebo controlled parallel-group trial, we investigated the effects of sodium nitrite administered immediately prior to reperfusion in patients with acute ST-elevation myocardial infarction (STEMI).
METHODS AND RESULTS: A total of 229 patients presenting with acute STEMI were randomized to receive either an i.v. infusion of 70 ÎŒmol sodium nitrite (n = 118) or matching placebo (n = 111) over 5 min immediately before primary percutaneous intervention (PPCI). Patients underwent cardiac magnetic resonance imaging (CMR) at 6-8 days and at 6 months and serial blood sampling was performed over 72 h for the measurement of plasma creatine kinase (CK) and Troponin I. Myocardial infarct size (extent of late gadolinium enhancement at 6-8 days by CMR-the primary endpoint) did not differ between nitrite and placebo groups after adjustment for area at risk, diabetes status, and centre (effect size -0.7% 95% CI: -2.2%, +0.7%; P = 0.34). There were no significant differences in any of the secondary endpoints, including plasma troponin I and CK area under the curve, left ventricular volumes (LV), and ejection fraction (EF) measured at 6-8 days and at 6 months and final infarct size (FIS) measured at 6 months.
CONCLUSIONS: Sodium nitrite administered intravenously immediately prior to reperfusion in patients with acute STEMI does not reduce infarct size
Pathway to the Square Kilometre Array - The German White Paper -
The Square Kilometre Array (SKA) is the most ambitious radio telescope ever
planned. With a collecting area of about a square kilometre, the SKA will be
far superior in sensitivity and observing speed to all current radio
facilities. The scientific capability promised by the SKA and its technological
challenges provide an ideal base for interdisciplinary research, technology
transfer, and collaboration between universities, research centres and
industry. The SKA in the radio regime and the European Extreme Large Telescope
(E-ELT) in the optical band are on the roadmap of the European Strategy Forum
for Research Infrastructures (ESFRI) and have been recognised as the essential
facilities for European research in astronomy.
This "White Paper" outlines the German science and R&D interests in the SKA
project and will provide the basis for future funding applications to secure
German involvement in the Square Kilometre Array.Comment: Editors: H. R. Kl\"ockner, M. Kramer, H. Falcke, D.J. Schwarz, A.
Eckart, G. Kauffmann, A. Zensus; 150 pages (low resolution- and colour-scale
images), published in July 2012, language English (including a foreword and
an executive summary in German), the original file is available via the MPIfR
homepag
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