6,929 research outputs found
Observations of time delayed all-optical routing in a slow light regime
We report an observation of a delayed all-optical routing/switching
phenomenon based on ultraslow group velocity of light via nondegenerate
four-wave mixing processes in a defected solid medium. Unlike previous
demonstrations of enhanced four-wave mixing processes using the slow light
effects, the present observation demonstrates a direct retrieval of the
resonant Raman-pulse excited spin coherence into photon coherence through
coherence conversion processes.Comment: 5 pages with 3 figures include
The Mass-Loss Return From Evolved Stars to The Large Magellanic Cloud VI: Luminosities and Mass-Loss Rates on Population Scales
We present results from the first application of the Grid of Red Supergiant
and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved
stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed
grid of 80,843 radiative transfer (RT) models of evolved stars and
circumstellar dust shells composed of either silicate or carbonaceous dust. We
fit GRAMS models to ~30,000 Asymptotic Giant Branch (AGB) and Red Supergiant
(RSG) stars in the LMC, using 12 bands of photometry from the optical to the
mid-infrared. Our published dataset consists of thousands of evolved stars with
individually determined evolutionary parameters such as luminosity and
mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate
discriminating between Oxygen- and Carbon-rich chemistry. The global dust
injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB
stars is on the order of 1.5x10^(-5) solar masses/yr, equivalent to a total
mass injection rate (including the gas) into the ISM of ~5x10^(-3) solar
masses/yr. Carbon stars inject two and a half times as much dust into the ISM
as do O-rich AGB stars, but the same amount of mass. We determine a bolometric
correction factor for C-rich AGB stars in the K band as a function of J - K
color, BC(K) = -0.40(J-K)^2 + 1.83(J-K) + 1.29. We determine several IR color
proxies for the dust mass-loss rate (MLR) from C-rich AGB stars, such as log
(MLR) = (-18.90)/((K-[8.0])+3.37)-5.93. We find that a larger fraction of AGB
stars exhibiting the `long-secondary period' phenomenon are O-rich than stars
dominated by radial pulsations, and AGB stars without detectable mass-loss do
not appear on either the first-overtone or fundamental-mode pulsation
sequences.Comment: 19 pages, 19 figure
Effect of disorder on transport properties in a tight-binding model for lead halide perovskites
The hybrid organic-inorganic lead halide perovskite materials have emerged as
remarkable materials for photovoltaic applications. Their strengths include
good electric transport properties in spite of the disorder inherent in them.
Motivated by this observation, we analyze the effects of disorder on the energy
eigenstates of a tight-binding model of these materials. In particular, we
analyze the spatial extension of the energy eigenstates, which is quantified by
the inverse participation ratio. This parameter exhibits a tendency, and
possibly a phase transition, to localization as the on-site energy disorder
strength is increased. However, we argue that the disorder in the lead halide
perovskites corresponds to a point in the regime of highly delocalized states.
Our results also suggest that the electronic states of mixed-halide materials
tend to be more localized than those of pure materials, which suggests a weaker
tendency to form extended bonding states in the mixed-halide materials and is
therefore not favourable for halide mixing.Comment: 24 pages (preprint), 11 figure
The morphology of the cellular constituents of the blood of Salmo trutta
Thesis (M.A.)--Boston UniversityThe morphology of the cellular constituents of the blood of Salmo trutta was investigated. Blood cell counts and differential counts were included. Cellular elements of the blood were found to be nucleated erythrocytes, lymphocytes, neutrophils, monocytes and thrombocytes. Dried smears of blood which had been stained with Wright's stain indicated the erythrocytes were flat elliptical cells . However, the phase microscope revealed the biconcave shape of the mature erythrocyte, the concavity being interrupted by the central nucleus. Average cell rreasurements were 16.5 microns in length and 10.2 microns in width. [TRUNCATED
Exploring mental dungeons and slaying psychic dragons : an exploratory study
This qualitative study examined the experiences of participants with table-top roleplaying and with the gaming community. Specifically this study asked: In what ways do fantasy play and participation in the role-playing community benefit participants? This study aimed to address the lack of social work literature regarding the emotional and social benefits that roleplaying games provide consumers. Data were collected from interviews with six individuals who regularly engage in tabletop role-playing games. The study asked open ended questions regarding participants\u27 experiences with the role-playing community, thematic and emotional content experienced within the fantasy setting, and benefits participants felt they\u27d gained from role-playing games and access to that community. The key findings of this study were that community access and feelings of belonging were an important part of the role-playing experience, that participants reported the context of fantasy play decreased their social anxiety which allowed them to interact with their own emotional content meaningful ways, and that role experimentation through their characters led to improved social skills in all participants
Variation of Molecular Line Ratios and Cloud Properties in the Arp 299 Galaxy Merger
High resolution observations of 12CO (2.''3), 13CO (3.''9), and HCN (5.''4)
J=1--0 in the galaxy merger Arp 299 (IC 694 and NGC 3690) show the line ratios
vary dramatically across the system. The 12CO/13CO ratio is unusually large, 60
+- 15, at the IC 694 nucleus, where 12CO emission is very strong, and much
smaller, 10 +- 3, in the southern extended disk of that galaxy. Elsewhere, the
12CO/13CO line ratio is 5-20, typical of spiral galaxies. The line ratio
variation in the overlap between the two galaxies is smaller, ranging from 10
+- 3 in the east to 20 +- 4 in the west.
The 12CO/HCN line ratio also varies across Arp 299, although to a lesser
degree. HCN emission is bright towards each galaxy nucleus and in the
extranuclear region of active star formation; it was not detected in the IC 694
disk, or the eastern part of the overlap region, leading to lower limits of 25
and 20 respectively. By contrast, at the nuclei of IC 694 and NGC 3690 the
ratios are 9 +- 1 and 14 +- 3 respectively. In the western part of the overlap
region it is 11 +- 3.Comment: 16 pages, 4 postscript figures, to appear in ApJ Letter
An analysis of the peculiar A star HD 204411
Spectrum analysis of cool Ap star HD 20441
The Lyman-alpha Forest at z~4: Keck HIRES Observations of Q 0000-26
This paper describes a study of the Lyman-alpha forest absorption clouds
along the quasar sightline Q0000-26 (zem=4.1). The spectrum was obtained with
the High Resolution Spectrometer on the 10m Keck telescope. We derive accurate
H I column density and Doppler width distributions for the clouds from Voigt
profile fitting. We also analyze simulated Lyman-alpha forest spectra of
matching characteristics in order to gauge the effects of line
blending/blanketing and noise in the data. The results are compared with
similar studies at lower redshifts in order to study any possible evolution in
the clouds' properties. We also estimate the mean intensity of the UV
background at z=4 from an analysis of the proximity effect.Comment: plain TeX containing 23 PS pages, 3 PS tables, and 9 PS figures, ApJ,
Dec 1, 1996 issue replacing an earlier version which contains an corrupted
table
CO J = 2 - 1 Emission from Evolved Stars in the Galactic Bulge
We observe a sample of 8 evolved stars in the Galactic Bulge in the CO J = 2
- 1 line using the Submillimeter Array (SMA) with angular resolution of 1 - 4
arcseconds. These stars have been detected previously at infrared wavelengths,
and several of them have OH maser emission. We detect CO J = 2 - 1 emission
from three of the sources in the sample: OH 359.943 +0.260, [SLO2003] A12, and
[SLO2003] A51. We do not detect the remaining 5 stars in the sample because of
heavy contamination from the galactic foreground CO emission. Combining CO data
with observations at infrared wavelengths constraining dust mass loss from
these stars, we determine the gas-to-dust ratios of the Galactic Bulge stars
for which CO emission is detected. For OH 359.943 +0.260, we determine a gas
mass-loss rate of 7.9 (+/- 2.2) x 10^-5 M_Sun/year and a gas-to-dust ratio of
310 (+/- 89). For [SLO2003] A12, we find a gas mass-loss rate of 5.4 (+/- 2.8)
x 10^-5 M_Sun/year and a gas-to-dust ratio of 220 (+/- 110). For [SLO2003] A51,
we find a gas mass-loss rate of 3.4 (+/- 3.0) x 10^-5 M_Sun/year and a
gas-to-dust ratio of 160 (+/- 140), reflecting the low quality of our tentative
detection of the CO J = 2 - 1 emission from A51. We find the CO J = 2 - 1
detections of OH/IR stars in the Galactic Bulge require lower average CO J = 2
- 1 backgrounds.Comment: 40 pages, 16 figures, appeared in the 1 March 2013 issue of the
Astrophysical Journa
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