527 research outputs found
Observation of negative refraction and negative phase velocity in left-handed metamaterials
Cataloged from PDF version of article.We report the transmission characteristics of a two-dimensional (2D) composite metamaterial (CMM) structure in free space. At the frequencies where left-handed transmission takes place, we experimentally confirmed that the CMM structure has effective negative refractive index. Phase shift between consecutive numbers of layers of CMM is measured and phase velocity is shown to be negative at the relevant frequency range. Refractive index values obtained from the refraction experiments and the phase measurements are in good agreement. (C) 2005 American Institute of Physics
Experimental observation of true left-handed transmission peaks in metamaterials
Cataloged from PDF version of article.We report true left-handed (LH) behavior in a composite metamaterial consisting of a periodically arranged split ring resonator (SRR) and wire structures. We demonstrate the magnetic resonance of the SRR structure by comparing the transmission spectra of SRRs with those of closed SRRs. We have confirmed experimentally that the effective plasma frequency of the LH material composed of SRRs and wires is lower than the plasma frequency of the wires. A well-defined LH transmission band with a peak value of -1.2 dB (-0.3 dB/cm) was obtained. The experimental results agree extremely well with the theoretical calculations. (C) 2004 Optical Society of America
Geometry of Deformations of Relativistic Membranes
A kinematical description of infinitesimal deformations of the worldsheet
spanned in spacetime by a relativistic membrane is presented. This provides a
framework for obtaining both the classical equations of motion and the
equations describing infinitesimal deformations about solutions of these
equations when the action describing the dynamics of this membrane is
constructed using {\it any} local geometrical worldsheet scalars. As examples,
we consider a Nambu membrane, and an action quadratic in the extrinsic
curvature of the worldsheet.Comment: 20 pages, Plain Tex, sign errors corrected, many new references
added. To appear in Physical Review
Perturbations of a topological defect as a theory of scalar fields interacting with an external vector potential
This is a revised version of gr-qc/930403
A retrospective evaluation of critically ill patients infected with H1N1 influenza A virus in Bursa, Turkey, during the 2009–2010 pandemic
Background: H1N1 influenza A virus infections were first reported in April 2009 and spread rapidly, resulting in mortality worldwide. The aim of this study was to evaluate patients with H1N1 infection treated in the intensive care unit (ICU) in Bursa, Turkey.Methods: Demographic characteristics, clinical features, and outcome relating to H1N1 infection were retrospectively analysed in patients treated in the ICU.Results: Twenty-three cases of H1N1 infection were treated in the ICU. The mean age of patients was 37 years range: (17– 82). Fifteen patients were female (65.2%). The mean Acute Physiology and Chronic Health Evaluation (APACHE) II score was 19 range: (5–39). The most common symptoms were dyspnea (73.9%), fever (69.6%), and cough (60.9%). Mechanical ventilation was required for all patients. Oseltamivir and antibiotics were administered to all patients. Six (26.1%) patients died. APACHE II scores were higher in the deceased 28.5 range: [16–39] vs. 14 range: [5–28] in survivors; p = 0.013).Conclusion: When compared to the literature, the demographic, epidemiological, and clinical characteristics were similar in the cases we encountered. The mortality rate was high despite the use of appropriate treatment. We believe that the high mortality is related to higher APACHE II scores. The H1N1 virus should be considered in community acquired pneumonia, especially in younger patients presenting with severe pneumonia.Key words: pandemic influenza, H1N1 infection, critically ill patient, intensive care uni
Heisenberg-picture approach to the evolution of the scalar fields in an expanding universe
We present the Heisenberg-picture approach to the quantum evolution of the
scalar fields in an expanding FRW universe which incorporates relatively simply
the initial quantum conditions such as the vacuum state, the thermal
equilibrium state, and the coherent state. We calculate the Wightman function,
two-point function, and correlation function of a massive scalar field. We find
the quantum evolution of fluctuations of a self-interacting field
perturbatively and discuss the renormalization of field equations.Comment: 15 pages, RevTeX, no figure
p-Brane Solutions in Diverse Dimensions
A generic Lagrangian, in arbitrary spacetime dimension, describing the
interaction of a graviton, a dilaton and two antisymmetric tensors is
considered. An isotropic p-brane solution consisting of three blocks and
depending on four parameters in the Lagrangian and two arbitrary harmonic
functions is obtained. For specific values of parameters in the Lagrangian the
solution may be identified with previously known superstring solutions.Comment: 15 pages, latex, no figure
Stable and Unstable Circular Strings in Inflationary Universes
It was shown by Garriga and Vilenkin that the circular shape of nucleated
cosmic strings, of zero loop-energy in de Sitter space, is stable in the sense
that the ratio of the mean fluctuation amplitude to the loop radius is
constant. This result can be generalized to all expanding strings (of non-zero
loop-energy) in de Sitter space. In other curved spacetimes the situation,
however, may be different.
In this paper we develop a general formalism treating fluctuations around
circular strings embedded in arbitrary spatially flat FRW spacetimes. As
examples we consider Minkowski space, de Sitter space and power law expanding
universes. In the special case of power law inflation we find that in certain
cases the fluctuations grow much slower that the radius of the underlying
unperturbed circular string. The inflation of the universe thus tends to wash
out the fluctuations and to stabilize these strings.Comment: 15 pages Latex, NORDITA 94/14-
Perturbations on a moving D3-brane and mirage cosmology
We study the evolution of perturbations on a moving probe D3-brane coupled to
a 4-form field in an AdS-Schwarzschild bulk. The unperturbed dynamics are
parametrised by a conserved energy and lead to Friedmann-Robertson-Walker
`mirage' cosmology on the brane with scale factor . The fluctuations
about the unperturbed worldsheet are then described by a scalar field
. We derive an equation of motion for , and find that
in certain regimes of the effective mass squared is negative. On an
expanding BPS brane with E=0 superhorizon modes grow as whilst subhorizon
modes are stable. When the brane contracts, all modes grow. We also briefly
discuss the case when , BPS anti-branes as well as non-BPS branes.
Finally, the perturbed brane embedding gives rise to scalar perturbations in
the FRW universe. We show that is proportional to the gauge invariant
Bardeen potentials on the brane.Comment: 26 pages, 5 figures, to appear in Phys.Rev.D, comments and minor
corrections adde
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