507,830 research outputs found
The Star Formation Rate - Dense Gas Relation in the Nuclei of Nearby Galaxies
We investigate the relationship between the star formation rate (SFR) and
dense molecular gas mass in the nuclei of galaxies. To do this, we utilize the
observed 850 micron luminosity as a proxy for the infrared luminosity and SFR,
and correlate this with the observed CO (J=3-2) luminosity. We find tentative
evidence that the LIR-CO (J=3-2) index is similar to the Kennicutt-Schmidt (KS)
index (N ~ 1.5) in the central ~1.7 kpc of galaxies, and flattens to a roughly
linear index when including emission from the entire galaxy. This result may
imply that the volumetric Schmidt relation is the underlying driver behind the
observed SFR-dense gas correlations, and provides tentative confirmation for
recent numerical models. While the data exclude the possibility of a constant
LIR-CO (J=3-2) index for both galaxy nuclei and global measurements at the ~80%
confidence level, the considerable error bars cannot preclude alternative
interpretations.Comment: Accepted at ApJ Letter
Negative refraction with tunable absorption in an active dense gas of atoms
Applications of negative index materials (NIM) presently are severely limited
by absorption. Next to improvements of metamaterial designs, it has been
suggested that dense gases of atoms could form a NIM with negligible losses. In
such gases, the low absorption is facilitated by quantum interference. Here, we
show that additional gain mechanisms can be used to tune and effectively remove
absorption in a dense gas NIM. In our setup, the atoms are coherently prepared
by control laser fields, and further driven by a weak incoherent pump field to
induce gain. We employ nonlinear optical Bloch equations to analyze the optical
response. Metastable Neon is identified as a suitable experimental candidate at
infrared frequencies to implement a lossless active negative index material.Comment: 10 pages, 9 figure
Link between K-absorption edges and thermodynamic properties of warm-dense plasmas established by improved first-principles method
A precise calculation that translates shifts of X-ray K-absorption edges to
variations of thermodynamic properties allows quantitative characterization of
interior thermodynamic properties of warm dense plasmas by X-ray absorption
techniques, which provides essential information for inertial confinement
fusion and other astrophysical applications. We show that this interpretation
can be achieved through an improved first-principles method. Our calculation
shows that the shift of K-edges exhibits selective sensitivity to thermal
parameters and thus would be a suitable temperature index to warm dense
plasmas. We also show with a simple model that the shift of K-edges can be used
to detect inhomogeneity inside warm dense plasmas when combined with other
experimental tools
ASTE observations of nearby galaxies: A tight correlation between CO(J=3-2) emission and Halpha
Star formation rates (SFRs) obtained via extinction corrected H alpha are
compared to dense gas as traced by CO(J=3-2) emission at the centers of nearby
galaxies, observed with the ASTE telescope. It is found that, although many of
the observed positions are dusty and therefore heavily absorbed at H alpha, the
SFR shows a striking correlation with dense gas in the form of the Schmidt law
with an index 1.0. The correlation is also compared between gas traced by
CO(J=1-0) and application of H alpha extinction correction. We find that dense
gas produces a far better correlation with SFR in view of surface density
values.Comment: 6 pages, PASJ accepte
Isogenies of elliptic curves and the Morava stabilizer group
Let MS_2 be the p-primary second Morava stabilizer group, C a supersingular
elliptic curve over \br{FF}_p, O the ring of endomorphisms of C, and \ell a
topological generator of Z_p^x (respectively Z_2^x/{+-1} if p = 2). We show
that for p > 2 the group \Gamma \subseteq O[1/\ell]^x of quasi-endomorphisms of
degree a power of \ell is dense in MS_2. For p = 2, we show that \Gamma is
dense in an index 2 subgroup of MS_2.Comment: 16 pages, to appear in J. Pure Appl. Al
Fat tissue accretion in children and adolescents : interplay between food responsiveness, gender, and the home availability of snacks
The appetitive trait "food responsiveness" is assumed to be a risk factor for adiposity gain primarily in obesogenic environments. So far, the reported results are inconsistent in school-aged children, possibly because these studies did not take into account important moderators such as gender and the food-environment. In order to better inform caregivers, clinicians and the developers of targeted obesity-prevention interventions on the conditions in which food responsiveness precedes adiposity gain, the current study investigated if this relationship is stronger in girls and in children exposed to a higher home availability of energy-dense snacks. Age- and sex-independent Fat and Lean Mass Index z-scores were computed based on air-displacement plethysmography at baseline and after 2 years in a community sample of 129 children (48.8% boys) aged 7.5-14 years at baseline. Parents reported at baseline on children's food responsiveness and the home availability of energy-dense snacks. Food responsiveness was a significant predictor of increases in Fat Mass Index z-scores over 2 years in girls but not boys. The home availability of energy-dense snacks did not significantly moderate the relation of food responsiveness with Fat Mass Index z-score changes. The results suggest that food responsiveness precedes accelerated fat tissue accretion in girls, and may inform targeted obesity-prevention interventions. Further, future research should investigate to which food-environmental parameters children high in food responsiveness mainly respond
On the physical origins of the negative index of refraction
The physical origins of negative refractive index are derived from a dilute
microscopic model, producing a result that is generalized to the dense
condensed phase limit. In particular, scattering from a thin sheet of electric
and magnetic dipoles driven above resonance is used to form a fundamental
description for negative refraction. Of practical significance, loss and
dispersion are implicit in the microscopic model. While naturally occurring
negative index materials are unavailable, ferromagnetic and ferroelectric
materials provide device design opportunities.Comment: 4 pages, 1 figur
Cherenkov Radiation from Jets in Heavy-ion Collisions
The possibility of Cherenkov-like gluon bremsstrahlung in dense matter is
studied. We point out that the occurrence of Cherenkov radiation in dense
matter is sensitive to the presence of partonic bound states. This is
illustrated by a calculation of the dispersion relation of a massless particle
in a simple model in which it couples to two different massive resonance
states. We further argue that detailed spectroscopy of jet correlations can
directly probe the index of refraction of this matter, which in turn will
provide information about the mass scale of these partonic bound states.Comment: 4 pages, 5 figures, revte
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