2,068 research outputs found
Manipulation of Giant Faraday Rotation in Graphene Metasurfaces
Faraday rotation is a fundamental magneto-optical phenomenon used in various
optical control and magnetic field sensing techniques. Recently, it was shown
that a giant Faraday rotation can be achieved in the low-THz regime by a single
monoatomic graphene layer. Here, we demonstrate that this exceptional property
can be manipulated through adequate nano-patterning, notably achieving giant
rotation up to 6THz with features no smaller than 100nm. The effect of the
periodic patterning on the Faraday rotation is predicted by a simple physical
model, which is then verified and refined through accurate full-wave
simulations.Comment: 4 pages, 5 figures, submitted to Applied Physics Letter
Depression in reproductive-age women : assessment of infectious, endocrinological, and immunological correlates from an evolutionary perspective.
Depression is one of the most frequent causes of disability worldwide. It can affect the psychological, social, and physical wellbeing of those that suffer from it, the majority of which are women. Depression has been linked to immune activation as well as serotonin depletion through a reduction in its precursor, tryptophan. Chlamydia trachomatis infection and estrogen can influence both the immune system and tryptophan levels, thereby biochemically inducing a depressive state. If this is the case, the use of exogenous estrogen through oral contraceptive pills (OCPs) could increase depressive symptoms, while the use of antibiotics to treat C. trachomatis infection could decrease depression. This thesis examined whether depression status in subjects was correlated with infection and medication use. Women were screened for depression at their annual gynecological exam, during which time they would receive an STI screen as standard of care. The study was conducted at the University of Louisville GYN/OB Foundation clinic and Campus Health Services from 2009-2011. Subjects were given a Beck Depression Inventory (BDI) to assess depressive symptoms and asked to keep a calendar of medication use. Subjects returned after one month to take a second BDI and their scores and medication calendars were compared with their medical records, specifically infection status and existing medical conditions. BDI scores decreased significantly in the follow-up assessment relative to the initial assessment. This decrease was correlated with the extent to which the subjects used mood-altering medications. Birth control use was correlated with an increase in depressive symptoms, but subjects who took mood-altering medication in addition to birth control were not more depressed than those that did not take birth control. There were insufficient data to correlate sexually transmitted infections, particularly C. trachomatis, with depressive symptoms. These findings show that increased hormonal birth control use is correlated with an increase in depression, but this depression is ameliorated with the use of mood-altering medication. These results imply that antidepressive medication may be particularly effective in treating depression associated with estrogen or oral contraceptive pills
Binaries among Ap and Am stars
The results of long-term surveys of radial velocities of cool Ap and Am stars
are presented. There are two samples, one of about 100 Ap stars and the other
of 86 Am stars. Both have been observed with the CORAVEL scanner from
Observatoire de Haute-Provence (CNRS), France.
The conspicuous lack of short-period binaries among cool Ap stars seems
confirmed, although this may be the result of an observational bias; one system
has a period as short as 1.6 days. A dozen new orbits could be determined,
including that of one SB2 system. Considering the mass functions of 68 binaries
from the literature and from our work, we conclude that the distribution of the
mass ratios is the same for the Bp-Ap stars than for normal G dwarfs.
Among the Am stars, we found 52 binaries, i.e. 60%; an orbit could be
computed for 29 of them. Among these 29, there are 7 SB2 systems, one triple
and one quadruple system. The 21 stars with an apparently constant radial
velocity may show up later as long-period binaries with a high eccentricity.
The mass functions of the SB1 systems are compatible with cool main-sequence
companions, also suggested by ongoing spectral observations.Comment: 5 pages, 2 figures, to appear in: Proc. of the 26th workshop of the
European Working Group on CP stars, Contrib. Astr. Obs. Skalnate Pleso Vol.
27, No
Efficient MIMO Transmission of PSK Signals With a Single-Radio Reconfigurable Antenna
Crucial developments to the recently introduced signal-space approach for
multiplexing multiple data symbols using a single-radio switched antenna are
presented. First, we introduce a general framework for expressing the spatial
multiplexing relation of the transmit signals only from the antenna scattering
parameters and the modulating reactive loading. This not only avoids tedious
far-field calculations, but more importantly provides an efficient and
practical strategy for spatially multiplexing PSK signals of any modulation
order. The proposed approach allows ensuring a constant impedance matching at
the input of the driving antenna for all symbol combinations, and as
importantly uses only passive reconfigurable loads. This obviates the use of
reconfigurable matching networks and active loads, respectively, thereby
overcoming stringent limitations of previous single-feed MIMO techniques in
terms of complexity, efficiency, and power consumption. The proposed approach
is illustrated by the design of a realistic very compact antenna system
optimized for multiplexing QPSK signals. The results show that the proposed
approach can bring the MIMO benefits to the low-end user terminals at a reduced
RF complexity.Comment: 30 pages, 6 figures. IEEE Transactions on Communications, 201
Quasiharmonic elastic constants corrected for deviatoric thermal stresses
The quasiharmonic approximation (QHA), in its simplest form also called the
statically constrained (SC) QHA, has been shown to be a straightforward method
to compute thermoelastic properties of crystals. Recently we showed that for
non-cubic solids SC-QHA calculations develop deviatoric thermal stresses at
high temperatures. Relaxation of these stresses leads to a series of
corrections to the free energy that may be taken to any desired order, up to
self-consistency. Here we show how to correct the elastic constants obtained
using the SC-QHA. We exemplify the procedure by correcting to first order the
elastic constants of MgSiO-perovskite and MgSiO-post-perovskite, the
major phases of the Earth's lower mantle. We show that this first order
correction is quite satisfactory for obtaining the aggregated elastic averages
of these minerals and their velocities in the lower mantle. This type of
correction is also shown to be applicable to experimental measurements of
elastic constants in situations where deviatoric stresses can develop, such as
in diamond anvil cells.Comment: 4 figures, 1 table, submitted to Phys. Rev. B, July 200
Analysis of 70 Ophiuchi AB including seismic constraints
The analysis of solar-like oscillations for stars belonging to a binary
system provides a unique opportunity to probe the internal stellar structure
and to test our knowledge of stellar physics. Such oscillations have been
recently observed and characterized for the A component of the 70 Ophiuchi
system. A model of 70 Ophiuchi AB that correctly reproduces all observational
constraints available for both stars is determined. An age of 6.2 +- 1.0 Gyr is
found with an initial helium mass fraction Y_i=0.266 +- 0.015 and an initial
metallicity (Z/X)_i=0.0300 +- 0.0025 when atomic diffusion is included and a
solar value of the mixing-length parameter assumed. A precise and independent
determination of the value of the mixing-length parameter needed to model 70
Oph A requires accurate measurement of the mean small separation, which is not
available yet. Current asteroseismic observations, however, suggest that the
value of the mixing-length parameter of 70 Oph A is lower or equal to the solar
calibrated value. The effects of atomic diffusion and of the choice of the
adopted solar mixture were also studied. We also tested and compared the
theoretical tools used for the modeling of stars for which p-modes frequencies
are detected by performing this analysis with three different stellar evolution
codes and two different calibration methods. We found that the different
evolution codes and calibration methods we used led to perfectly coherent
results.Comment: 9 pages, 8 figures, accepted for publication in A&
Multiplicity among peculiar A stars I. The Ap stars HD 8441 and HD 137909, and the Am stars HD 43478 and HD 96391
We present the first results of a radial-velocity survey of cool Ap and Am
stars. HD 8441 is not only a double system with P = 106.357 days, but is a
triple one, the third companion having an orbital period larger than 5000 days.
Improved orbital elements are given for the classical Ap star HD 137909 = beta
CrB by combining our radial velocities with published ones. We yield new
orbital elements of the two Am, SB2 binaries HD 43478 and HD 96391. Good
estimates of the individual masses of the components of HD 43478 can be given
thanks to the eclipses of this system, for which an approximate photometric
solution is also proposed.Comment: 10 pages, 10 figures, accepted for publication in A&A
Counteracting Interfacial Energetics for Wetting of Hydrophobic Surfaces in the Presence of Surfactants
Ni/HZSM-5 catalyst preparation by deposition-precipitation. Part 1. Effect of nickel loading and preparation conditions on catalyst properties
Nickel metal supported on HZSM-5 (zeolite) is a promising catalyst for lignin depolymerization. In this work, Ni/HZSM-5 catalysts were synthesized via deposition-precipitation (DP) and characterized. The effect of synthesis parameters; including nickel loading, DP time (synthesis contact time), and calcination temperature, on catalyst properties were studied. N2 and CO2 adsorption techniques were used to look at textural properties and confirmed the existence of lamellar species generated from DP. X-ray diffraction (XRD) confirmed that nickel metal was present on the support after reduction and passivation of the catalyst. Temperature programmed reduction showed that all the catalyst preparations were reducible at 733 K after 4 h, and that the DP method formed a mixture of Ni2+ species on the support. Transmission electron microscopy, XRD, and H2 chemisorption were used to determine approximate particle size and dispersion of nickel metal. From all the preparations, the 15 wt% Ni/HZSM-5 catalyst with long DP time (16 h) and low calcination temperature (673 K), exhibited the most favorable particle size (~5 nm) and dispersion (7%)
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