9,172 research outputs found
Understanding Perceptions about Contraceptive Responsibility Among Adolescents
Invited Commentary on Attitudes Surrounding Contraceptive Responsibility: Do Latino Adolescents Differ From Other Groups
Spitzer-IRS high resolution spectroscopy of the 12\mu m Seyfert galaxies: I. First results
The first high resolution Spitzer IRS 9-37um spectra of 29 Seyfert galaxies
(about one quarter) of the 12um Active Galaxy Sample are presented and
discussed. The high resolution spectroscopy was obtained with corresponding
off-source observations. This allows excellent background subtraction, so that
the continuum levels and strengths of weak emission lines are accurately
measured. The result is several new combinations of emission line ratios,
line/continuum and continuum/continuum ratios that turn out to be effective
diagnostics of the strength of the AGN component in the IR emission of these
galaxies. The line ratios [NeV]/[NeII], [OIV]/[NeII], already known, but also
[NeIII]/[NeII] and [NeV]/[SiII] can all be effectively used to measure the
dominance of the AGN. We extend the analysis, already done using the 6.2um PAH
emission feature, to the equivalent width of the 11.25um PAH feature, which
also anti-correlates with the dominance of the AGN. We measure that the 11.25um
PAH feature has a constant ratio with the H_2 S(1) irrespective of Seyfert
type, approximately 10 to 1. Using the ratio of accurate flux measurements at
about 19um with the two spectrometer channels, having aperture areas differing
by a factor 4, we measured the source extendness and correlated it with the
emission line and PAH feature equivalent widths. The extendness of the source
gives another measure of the AGN dominance and correlates both with the EWs of
[NeII] and PAH emission. Using the rotational transitions of H we were able
to estimate temperatures (200-300K) and masses (1-10 x 10^6 M_sun), or
significant limits on them, for the warm molecular component in the galaxies
observed.Comment: submitted to ApJ, Aug.2007, revised, in the refereeing proces
Single-photon excitation of a coherent state: catching the elementary step of stimulated light emission
When a single quantum of electromagnetic field excitation is added to the
same spatio-temporal mode of a coherent state, a new field state is generated
that exhibits intermediate properties between those of the two parents. Such a
single-photon-added coherent state is obtained by the action of the photon
creation operator on a coherent state and can thus be regarded as the result of
the most elementary excitation process of a classical light field. Here we
present and describe in depth the experimental realization of such states and
their complete analysis by means of a novel ultrafast, time-domain, quantum
homodyne tomography technique clearly revealing their non-classical character.Comment: 9 pages, 9 figures. Accepted for publication in Phys. Rev.
Influence of impurity spin dynamics on quantum transport in epitaxial graphene
Experimental evidence from both spin-valve and quantum transport measurements
points towards unexpectedly fast spin relaxation in graphene. We report
magnetotransport studies of epitaxial graphene on SiC in a vector magnetic
field showing that spin relaxation, detected using weak-localisation analysis,
is suppressed by an in-plane magnetic field, , and thereby
proving that it is caused at least in part by spinful scatterers. A
non-monotonic dependence of effective decoherence rate on
reveals the intricate role of scatterers' spin dynamics in forming the
interference correction to conductivity, an effect that has gone unnoticed in
earlier weak localisation studie
Physical consequences of PNP and the DMRG-annealing conjecture
Computational complexity theory contains a corpus of theorems and conjectures
regarding the time a Turing machine will need to solve certain types of
problems as a function of the input size. Nature {\em need not} be a Turing
machine and, thus, these theorems do not apply directly to it. But {\em
classical simulations} of physical processes are programs running on Turing
machines and, as such, are subject to them. In this work, computational
complexity theory is applied to classical simulations of systems performing an
adiabatic quantum computation (AQC), based on an annealed extension of the
density matrix renormalization group (DMRG). We conjecture that the
computational time required for those classical simulations is controlled
solely by the {\em maximal entanglement} found during the process. Thus, lower
bounds on the growth of entanglement with the system size can be provided. In
some cases, quantum phase transitions can be predicted to take place in certain
inhomogeneous systems. Concretely, physical conclusions are drawn from the
assumption that the complexity classes {\bf P} and {\bf NP} differ. As a
by-product, an alternative measure of entanglement is proposed which, via
Chebyshev's inequality, allows to establish strict bounds on the required
computational time.Comment: Accepted for publication in JSTA
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Patterns of drug use and HIV infection among adults in a nationally representative sample
Background: Little is known about drug use patterns among people living with HIV in comparison to an uninfected group in the general population. The aim of this study was to investigate the association between legal and illegal drug use and HIV infection in a nationally representative sample of adults in the United States. Methods: Public use data files (2005â2014) from the National Survey on Drug Use and Health (NSDUH) were used. Respondents were asked whether a medical professional had ever told them that they had HIV/AIDS. Ever (lifetime), past-year, and past month use of cigarettes, alcohol, marijuana, cocaine, heroin, hallucinogens, inhalants, and nonmedical use of psychotherapeutics was assessed. Logistic regression was used to estimate adjusted odds ratios (aOR) of the relationship between drug use and HIV infection, adjusting for demographics. Results: Of 377,787 respondents age 18 and older, 548 (0.19%) were categorized as HIV-infected. Ever use of cigarettes, tobacco, marijuana, cocaine, heroin, hallucinogens, inhalants, and psychotherapeutics was higher in HIV-infected individuals compared to HIV-uninfected individuals after adjustment for sex, age, race/ethnicity, education, total family income, and marital status. Past year and past month use was also higher for HIV-infected individuals for all substances aside from alcohol. Conclusions: In a nationally representative sample, there are higher levels of drug use and DSM-IV dependence among the HIV-infected population compared to the HIV-uninfected population. This is of concern because drug use and dependence can impede engagement in HIV care and adherence to antiretroviral therapy
The accretion environment in Vela X-1 during a flaring period using XMM-Newton
We present analysis of 100 ks contiguous XMM-Newton data of the prototypical
wind accretor Vela X-1. The observation covered eclipse egress between orbital
phases 0.134 and 0.265, during which a giant flare took place, enabling us to
study the spectral properties both outside and during the flare. This giant
flare with a peak luminosity of erg
s allows estimates of the physical parameters of the accreted structure
with a mass of g.
We have been able to model several contributions to the observed spectrum
with a phenomenological model formed by three absorbed power laws plus three
emission lines. After analysing the variations with orbital phase of the column
density of each component, as well as those in the Fe and Ni fluorescence
lines, we provide a physical interpretation for each spectral component.
Meanwhile, the first two components are two aspects of the principal accretion
component from the surface of the neutron star, and the third component seems
to be the \textit{X-ray light echo} formed in the stellar wind of the
companion.Comment: Accepted. Astronomy and Astrophysics, 201
coupling determined beyond the chiral limit
Within the conventional QCD sum rules, we calculate the coupling
constant, , beyond the chiral limit using two-point correlation
function with a pion. We consider the Dirac structure, , at
order, which has clear dependence on the PS and PV coupling schemes
for the pion-nucleon interactions. For a consistent treatment of the sum rule,
we include the linear terms in quark mass as they constitute the same chiral
order as . Using the PS coupling scheme for the pion-nucleon
interaction, we obtain , which is very close to the
empirical coupling. This demonstrates that going beyond the chiral
limit is crucial in determining the coupling and the pseudoscalar coupling
scheme is preferable from the QCD point of view.Comment: 8 pages, revtex, some errors are corrected, substantially revise
Decaying neutron propagation in the Galaxy and the Cosmic Ray anisotropy at 1 EeV
We study the cosmic ray arrival distribution expected from a source of
neutrons in the galactic center at energies around 1 EeV and compare it with
the anisotropy detected by AGASA and SUGAR. Besides the point-like signal in
the source direction produced by the direct neutrons, an extended signal due to
the protons produced in neutron decays is expected. This associated proton
signal also leads to an excess in the direction of the spiral arm. For
realistic models of the regular and random galactic magnetic fields, the
resulting anisotropy as a function of the energy is obtained. We find that for
the anisotropy to become sufficiently suppressed below E\sim 10^{17.9}eV, a
significant random magnetic field component is required, while on the other
hand, this also tends to increase the angular spread of the associated proton
signal and to reduce the excess in the spiral arm direction. The source
luminosity required in order that the right ascension anisotropy be 4% for the
AGASA angular exposure corresponds to a prediction for the point-like flux from
direct neutrons compatible with the flux detected by SUGAR. We also analyse the
distinguishing features predicted for a large statistics southern observatory.Comment: 14 pages, 6 figures, minor changes to match published versio
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