3,020 research outputs found
An absorption spectrum amplifier for determining gas composition
Compositions of gas samples are frequently studied by laser absorption spectroscopy. Sensitivity is improved by two orders of magnitude when absorption cell is placed inside an organic-dye laser cavity
How universal is the fractional-quantum-Hall edge Luttinger liquid?
This article reports on our microscopic investigations of the edge of the
fractional quantum Hall state at filling factor . We show that the
interaction dependence of the wave function is well described in an
approximation that includes mixing with higher composite-fermion Landau levels
in the lowest order. We then proceed to calculate the equal time edge Green
function, which provides evidence that the Luttinger exponent characterizing
the decay of the Green function at long distances is interaction dependent. The
relevance of this result to tunneling experiments is discussed.Comment: 5 page
Distant field BHB stars and the mass of the Galaxy II: Photometry and spectroscopy of UKST candidates 16<B<19.5, 11<R<52 kpc
This is the second in a series of papers presenting a new calculation of the
mass of the Galaxy based on radial velocities and distances for a sample of
faint 16 < B < 21.3 field blue horizontal-branch (BHB) stars. We present
accurate BV CCD photometry and spectra for 142 candidate A-type stars selected
from ub_jr photometry of UK Schmidt telescope plates in six
high-Galactic-latitude fields. Classification of these candidates produces a
sample of 60 BHB stars at distances of 11-52 kpc from the Sun (mean 28 kpc),
with heliocentric line-of-sight velocities accurate to 15 km/s, and distance
errors < 10%. We provide a summary table listing coordinates and velocities of
these stars. The measured dispersion of the radial component of the
Galactocentric velocity for this sample is 108+-10 km/s, in agreement with a
recent study of the distant halo by Sirko and coworkers. Measurements of the Ca
II K line indicate that nearly all the stars are metal-poor with a mean [Fe/H]
= -1.8 with dispersion 0.5. Subsequent papers will describe a second survey of
BHBs to heliocentric distances 70 < R < 125 kpc and present a new estimate of
the mass of the Galaxy.Comment: 16 pages, 15 figures. Accepted for publication in MNRA
Curvature perturbation in multi-field inflation with non-minimal coupling
In this paper we discuss a multi-field model of inflation in which generally
all fields are non-minimally coupled to the Ricci scalar and have non-canonical
kinetic terms. The background evolution and first-order perturbations for the
model are evaluated in both the Jordan and Einstein frames, and the respective
curvature perturbations compared. We confirm that they are indeed not the same
- unlike in the single-field case - and also that the difference is a direct
consequence of the isocurvature perturbations inherent to multi-field models.
This result leads us to conclude that the notion of adiabaticity is not
invariant under conformal transformations. Using a two-field example we show
that even if in one frame the evolution is adiabatic, meaning that the
curvature perturbation is conserved on super-horizon scales, in general in the
other frame isocurvature perturbations continue to source the curvature
perturbation. We also find that it is possible to realise a particular model in
which curvature perturbations in both frames are conserved but with each being
of different magnitude. These examples highlight that the curvature
perturbation itself, despite being gauge-invariant, does not correspond
directly to an observable. The non-equivalence of the two curvature
perturbations would also be important when considering the addition of Standard
Model matter into the system.Comment: 21 pages, 2 figures, references added, typos corrected, version to
appear in JCA
Kinetic energy of solid neon by Monte Carlo with improved Trotter- and finite-size extrapolation
The kinetic energy of solid neon is calculated by a path-integral Monte Carlo
approach with a refined Trotter- and finite-size extrapolation. These accurate
data present significant quantum effects up to temperature T=20 K. They confirm
previous simulations and are consistent with recent experiments.Comment: Text and figures revised for minor corrections (4 pages, 3 figures
included by psfig
Sex-Specific Growth and Reproductive Dynamics of Red Drum in the Northern Gulf of Mexico
The Red Drum Sciaenops ocellatus stock is heavily targeted in the Gulf of Mexico (GOM) by recreational fishers and supports a small commercial fishery in Mississippi. Despite their popularity, little recent work has been done to describe their life history. In this work, we describe sexâspecific growth and reproductive dynamics of Red Drum collected from the northern GOM from September 2016 through October 2017. We evaluated seven candidate growth models and found that the threeâparameter von Bertalanffy growth function (VBGF) was the best candidate lengthâatâage model. No significant difference in growth between sexes was observed with the threeâparameter VBGF, despite the femaleâspecific curve having a larger mean asymptotic length than the maleâspecific curve. All seven candidate growth models predicted similar mean lengthâatâage estimates, and four of them exhibited significant differences in sexâspecific mean length at age, with females reaching a larger length at age than males after age 5. There was no significant difference between the sexâspecific weightâatâlength relationships. Red Drum are batch spawners that spawn in northern GOM coastal waters during August and September. We estimated 3.7 d between spawns and 10.5 spawning events per female in 2017. Nearly 20% of fish collected during the spawning season were sexually mature but reproductively inactive, indicating the possibility of skipped spawning. The age at 50% maturity was around 3 years (length at 50% maturity = 670 mm TL) in both sexes, but fish were not spawning capable until age 4.5 (703 mm TL) in males and age 5.8 (840 mm TL) in females. Furthermore, elevated gonadosomatic indices were not observed until around age 5â6. The updated life history information presented in this work helps to address current data limitations and provides critical information for future assessments of Red Drum stocks in the northern GOM
A standardized terminology for describing reproductive development in fishes
19 pĂĄginas, 12 figuras, 3 tablas.-- Open access journalAs the number of fish reproduction studies has proliferated, so has the number of gonadal classification schemes
and terms. This has made it difficult for both scientists and resource managers to communicate and for comparisons to
be made among studies.We propose the adoption of a simple, universal terminology for the phases in the reproductive
cycle, which can be applied to all male and female elasmobranch and teleost fishes. These phases were chosen because
they define key milestones in the reproductive cycle; the phases include immature, developing, spawning capable,
regressing, and regenerating. Although the temporal sequence of events during gamete development in each phase
may vary among species, each phase has specific histological and physiological markers and is conceptually universal.
The immature phase can occur only once. The developing phase signals entry into the gonadotropin-dependent stage
of oogenesis and spermatogenesis and ultimately results in gonadal growth. The spawning capable phase includes (1)
those fish with gamete development that is sufficiently advanced to allow for spawning within the current reproductive
cycle and (2) batch-spawning females that show signs of previous spawns (i.e., postovulatory follicle complex) and
that are also capable of additional spawns during the current cycle. Within the spawning capable phase, an actively
spawning subphase is defined that corresponds to hydration and ovulation in females and spermiation in males. The
regressing phase indicates completion of the reproductive cycle and, for many fish, completion of the spawning season.
Fish in the regenerating phase are sexually mature but reproductively inactive. Species-specific histological criteria
or classes can be incorporated within each of the universal phases, allowing for more specific divisions (subphases) while preserving the overall reproductive terminology for comparative purposes. This terminology can easily be
modified for fishes with alternate reproductive strategies, such as hermaphrodites (addition of a transition phase) and
livebearers (addition of a gestation phase)Fish Reproduction and Fisheries (FRESH; European
Cooperation in Science and Technology Action FA0601)
and theWest Palm Beach Fishing Club (Florida) provided funding
for the gonadal histology workshops where this terminology
was developed and refined. Additionally, we thank FRESH for
travel and publication fundsPeer reviewe
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