836 research outputs found
Giant directional dichroism of terahertz light in resonance with magnetic excitations of the multiferroic oxide BaCoGeO
We propose that concurrently magnetic and ferroelectric, i.e. multiferroic,
compounds endowed with electrically-active magnetic excitations
(electromagnons) provide a key to produce large directional dichroism for long
wavelengths of light. By exploiting the control of ferroelectric polarization
and magnetization in a multiferroic oxide BaCoGeO, we demonstrate
the realization of such a directional light-switch function at terahertz
frequecies in resonance with the electromagnon absorption. Our results imply
that this hidden potential is present in a broad variety of multiferroics
Partial and macroscopic phase coherences in underdoped BiSrCaCuO thin film
A combined study with use of time-domain pump-probe spectroscopy and
time-domain terahertz transmission spectroscopy have been carried out on an
underdoped BiSrCaCuO thin film. It was observed that
the low energy multi-excitation states were decomposed into superconducting gap
and pseudogap. The pseudogap locally opens below K
simultaneously with the appearance of the high-frequency partial pairs around
1.3 THz. With decreasing temperature, the number of the local domains with the
partial phase coherence increased and saturated near 100 K, and the macroscopic
superconductivity appeared below 76 K through the superconductivity fluctuation
state below 100 K. These experimental results indicate that the pseudogap makes
an important role for realization of the superconductivity as a precursor to
switch from the partial to the macroscopic phase coherence.Comment: Revtex4, 4 pages, 4 figure
Fast Arc-Annotated Subsequence Matching in Linear Space
An arc-annotated string is a string of characters, called bases, augmented
with a set of pairs, called arcs, each connecting two bases. Given
arc-annotated strings and the arc-preserving subsequence problem is to
determine if can be obtained from by deleting bases from . Whenever
a base is deleted any arc with an endpoint in that base is also deleted.
Arc-annotated strings where the arcs are ``nested'' are a natural model of RNA
molecules that captures both the primary and secondary structure of these. The
arc-preserving subsequence problem for nested arc-annotated strings is basic
primitive for investigating the function of RNA molecules. Gramm et al. [ACM
Trans. Algorithms 2006] gave an algorithm for this problem using time
and space, where and are the lengths of and , respectively. In
this paper we present a new algorithm using time and space,
thereby matching the previous time bound while significantly reducing the space
from a quadratic term to linear. This is essential to process large RNA
molecules where the space is likely to be a bottleneck. To obtain our result we
introduce several novel ideas which may be of independent interest for related
problems on arc-annotated strings.Comment: To appear in Algoritmic
Sputum smear positivity among patients presenting to the dots clinic with chronic cough
Cough is one of the cardinal features of Pulmonary Tuberculosis (PTB). However, even in communities with high prevalence of TB, lung diseases other than TB appear to account for this symptom. Objective: To estimate the prevalence of sputum smear positivity among patients with TB who presented with complaints of chronic cough to the Directly Observed Therapy Short Course (DOTS) clinic at the University of Maiduguri Teaching Hospital, North Eastern Nigeria. Methodology: A cross sectional study was conducted at the University of Maiduguri Teaching Hospital (UMTH) Borno state, Northeastern Nigeria between September 2014 and January 2017. All patients (new or previously treated) who presented to the DOTS clinic of the UMTH with complaints of chronic cough and had screening for pulmonary TB using sputum smear microscopy were reviewed. The minimum and the maximum ages were 1 year and 85 years, respectively, and the mean age was 36.0 (SD=14.0) years. The mean age did not differ among the male and female patients (i.e.37.3 ± 14.4 vs 34.1 ± 13.2, p=0.78). The overall prevalence of sputum smear positivity for TB was 26.5%. Although majority of patients who were sputum smear positive for TB fell within the age groups 30-39 and 20-29 thus accounting for 42.6% and 28.7% respectively, however, there was no significant association between age of those with chronic cough and sputum smear positivity TB (p=0.80). Among those who were sputum smear positive, 24.3% were new cases and 2.2% were previously treated. Conclusions: Data were entered into a computer database and analyzed with SPSS version 20.0 statistical software. Results: This study showed a high prevalence of sputum smear positivity among suspected TB patients with complaints of chronic cough This could be explained by the fact that the DOTS strategy has improved the case detection of PTB in this community. All patients with chronic cough should be evaluated for PTB
Nonreciprocal Directional Dichroism and Toroidalmagnons in Helical Magnets
We investigate a dynamical magnetoelectric effect due to a magnetic resonance
in helical spin structures through the coupling between magnetization and
electric polarization via a spin current mechanism. We show that the magnon has
both the dynamical magnetic moment and the electric moment
(), i.e., a dynamical toroidal moment,
under external magnetic fields, and thus it is named the {\em toroidalmagnon}.
The toroidalmagnon exists in most conical spin structures owing to the
generality of the spin current mechanism. In the absorption of electromagnetic
waves, the toroidalmagnon excitation process generally induces a nonreciprocal
directional dichroism as a consequence of an interference of the magnetic and
electric responses.Comment: 5 pages, 2 figure
Theory of magnetoelectric resonance in two-dimensional antiferromagnet via spin-dependent metal-ligand hybridization mechanism
We investigate magnetic excitations in an Heisenberg model
representing two-dimensional antiferromagnet . In
terahertz absorption experiment of the compound, Goldstone mode as well as
novel magnetic excitations, conventional magnetic resonance at 2 meV and both
electric- and magnetic-active excitation at 4 meV, have been observed. By
introducing a hard uniaxial anisotropy term , three modes can
be explained naturally. We also indicate that, via the spin-dependent
metal-ligand hybridization mechanism, the 4 meV excitation is an
electric-active mode through the coupling between spin and electric-dipole.
Moreover, at 4 meV excitation, an interference between magnetic and electric
responses emerges as a cross correlated effect. Such cross correlation effects
explain the non-reciprocal linear directional dichroism observed in .Comment: 5 pages, 3 figure
Universal decay of scalar turbulence
The asymptotic decay of passive scalar fields is solved analytically for the
Kraichnan model, where the velocity has a short correlation time. At long
times, two universality classes are found, both characterized by a distribution
of the scalar -- generally non-Gaussian -- with global self-similar evolution
in time. Analogous behavior is found numerically with a more realistic flow
resulting from an inverse energy cascade.Comment: 4 pages, 3 Postscript figures, submitted to PR
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