16,062 research outputs found
Temporal tracking of mineralization and transcriptional developments of shell formation during the early life history of pearl oyster Pinctada maxima
Molluscan larval ontogeny is a highly conserved process comprising three principal developmental stages. A characteristic unique to each of these stages is shell design, termed prodissoconch I, prodissoconch II and dissoconch. These shells vary in morphology, mineralogy and microstructure. The discrete temporal transitions in shell biomineralization between these larval stages are utilized in this study to investigate transcriptional involvement in several distinct biomineralization events. Scanning electron microscopy and X-ray diffraction analysis of P. maxima larvae and juveniles collected throughout post-embryonic ontogenesis, document the mineralogy and microstructure of each shelled stage as well as establishing a timeline for transitions in biomineralization. P. maxima larval samples most representative of these biomineralization distinctions and transitions were analyzed for differential gene expression on the microarray platform PmaxArray 1.0. A number of transcripts are reported as differentially expressed in correlation to the mineralization events of P. maxima larval ontogeny. Some of those isolated are known shell matrix genes while others are novel; these are discussed in relation to potential shell formation roles. This interdisciplinary investigation has linked the shell developments of P. maxima larval ontogeny with corresponding gene expression profiles, furthering the elucidation of shell biomineralization
The Facilitation of Learning Groups: A Study of a Dairy Discussion Group Facilitator
Farm Management,
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Tafassasset: The Saga Continues
In this study, we compare data for two separate Tafassasset stones and supply new oxygen isotope data for our sample. We include a discussion of the debate surrounding the classification of Tafassasset and offer a hypothesis for its origin based upon new information
Far-Ultraviolet Number Counts of Field Galaxies
The far-ultraviolet (FUV) number counts of galaxies constrain the evolution
of the star-formation rate density of the universe. We report the FUV number
counts computed from FUV imaging of several fields including the Hubble Ultra
Deep Field, the Hubble Deep Field North, and small areas within the GOODS-North
and -South fields. These data were obtained with the Hubble Space Telescope
Solar Blind Channel of the Advance Camera for Surveys. The number counts sample
a FUV AB magnitude range from 21-29 and cover a total area of 15.9 arcmin^2, ~4
times larger than the most recent HST FUV study. Our FUV counts intersect
bright FUV GALEX counts at 22.5 mag and they show good agreement with recent
semi-analytic models based on dark matter "merger trees" by Somerville et al.
(2011). We show that the number counts are ~35% lower than in previous HST
studies that use smaller areas. The differences between these studies are
likely the result of cosmic variance; our new data cover more lines of sight
and more area than previous HST FUV studies. The integrated light from field
galaxies is found to contribute between 65.9 +/-8 - 82.6 +/-12
photons/s/cm^2/sr/angstrom to the FUV extragalactic background. These
measurements set a lower limit for the total FUV background light.Comment: Accepted for publication in ApJ, including 34 pages, 6 figures, and 2
table
Far-Ultraviolet Number Counts on Field Galaxies
The far-ultraviolet (FUV) number counts of galaxies constrain the evolution of the star formation rate density of the universe. We report the FUV number counts computed from FUV imaging of several fields including the Hubble Ultra Deep Field, the Hubble Deep Field North, and small areas within the GOODS-North and South fields. These data were obtained with the Hubble Space Telescope (HST) Solar Blind Channel of the Advance Camera for Surveys. The number counts sample an FUV AB magnitude range from 21 to 29 and cover a total area of 15.9 arcmin^2, ~4 times larger than the most recent HST FUV study. Our FUV counts intersect bright FUV Galaxy Evolution Explorer counts at 22.5 mag and they show good agreement with recent semi-analytic models based on dark matter "merger trees" by R. S. Somerville et al. We show that the number counts are ~35% lower than in previous HST studies that use smaller areas. The differences between these studies are likely the result of cosmic variance; our new data cover more lines of sight and more area than previous HST FUV studies. The integrated light from field galaxies is found to contribute between 65.9^(+8)_(–8) and 82.6^(+12)_(–)12 photons s^(–1) cm^(–2) sr^(–1) Å^(–1) to the FUV extragalactic background. These measurements set a lower limit for the total FUV background light
What is a crystal?
Almost 25 years have passed since Shechtman discovered quasicrystals, and 15
years since the Commission on Aperiodic Crystals of the International Union of
Crystallography put forth a provisional definition of the term crystal to mean
``any solid having an essentially discrete diffraction diagram.'' Have we
learned enough about crystallinity in the last 25 years, or do we need more
time to explore additional physical systems? There is much confusion and
contradiction in the literature in using the term crystal. Are we ready now to
propose a permanent definition for crystal to be used by all? I argue that time
has come to put a sense of order in all the confusion.Comment: Submitted to Zeitschrift fuer Kristallographi
Gardner optimal capacity of the diluted Blume-Emery-Griffiths neural network
The optimal capacity of a diluted Blume-Emery-Griffiths neural network is
studied as a function of the pattern activity and the embedding stability using
the Gardner entropy approach. Annealed dilution is considered, cutting some of
the couplings referring to the ternary patterns themselves and some of the
couplings related to the active patterns, both simultaneously (synchronous
dilution) or independently (asynchronous dilution). Through the de
Almeida-Thouless criterion it is found that the replica-symmetric solution is
locally unstable as soon as there is dilution. The distribution of the
couplings shows the typical gap with a width depending on the amount of
dilution, but this gap persists even in cases where a particular type of
coupling plays no role in the learning process.Comment: 9 pages Latex, 2 eps figure
Spin-exchange relaxation free magnetometry with Cs vapor
We describe a Cs atomic magnetometer operating in the spin-exchange
relaxation-free (SERF) regime. With a vapor cell temperature of
we achieve intrinsic magnetic resonance widths corresponding to an electron spin-relaxation rate of when the spin-exchange rate is . We
also observe an interesting narrowing effect due to diffusion. Signal-to-noise
measurements yield a sensitivity of about .
Based on photon shot noise, we project a sensitivity of . A theoretical optimization of the magnetometer indicates
sensitivities on the order of should be achievable in a
volume. Because Cs has a higher saturated vapor pressure than
other alkali metals, SERF magnetometers using Cs atoms are particularly
attractive in applications requiring lower temperatures.Comment: 8 pages, 6 figures. submitted to PR
Action-Angle variables for the Gel'fand-Dikii flows
Using the scattering transform for order linear scalar operators,
the Poisson bracket found by Gel'fand and Dikii, which generalizes the Gardner
Poisson bracket for the KdV hierarchy, is computed on the scattering side.
Action-angle variables are then constructed. Using this, complete integrability
is demonstrated in the strong sense. Real action-angle variables are
constructed in the self-adjoint case
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