3,549 research outputs found
The changes in chemical composition during development of the bovine nuchal ligament
Whole bovine nuchal ligaments, or portions thereof (in the case of commercially valuable animals), were obtained from 45 animals (28 fetal and 17 postnatal) ranging in age from 110 days of gestation to 10 yr. Insoluble elastin was quantitatively prepared from the fresh ligaments by extraction with hot alkali and by a combination of multiple extractions with alkaline buffer and then repeated autoclaving. When adult samples were examined, the yields of insoluble residue by these two methods were very similar, but with young fetal samples the second method gave significantly higher values, because of incomplete purification of the elastin residue. The changes in the concentration of collagen, alkali-insoluble elastin, and DNA have been examined. DNA concentration, and, thus, cell population density, fell progressively during the fetal period of development, to reach a steady value soon after birth. Collagen appeared in appreciable quantities before elastin, but its concentration was rapidly halved at about the time of birth. Insoluble elastin concentration was low until the end of the 7th fetal month, at which time it began to rise rapidly. The rate of increase in elastin concentration remained high throughout the next 10â12 wk, by which time the adult value had been reached. Quantitative studies, on the basis of the whole ligament, showed that the total cell content rises to a maximum at birth, but falls soon after to a level about half that at birth. Total collagen production and elastin deposition continue at a steady, maximal rate over the interval from 235 days of gestation to the end of the 1st postnatal month. It is concluded that the immediate postnatal period would be the most favorable phase in which to attempt the isolation of the soluble precursor elastin
Trident: A three-pronged galaxy survey. I. Lyman alpha emitting galaxies at z~2 in GOODS North
Context. Lyman alpha emitting galaxies (LAEs) are used to probe the distant
universe and are therefore important for galaxy evolution studies and for
providing clues to the nature of the epoch of reionization, but the exact
circumstances under which Lyman alpha escapes a galaxy are still not fully
understood.
Aims. The Trident project is designed to simultaneously examine Lyman alpha,
H-alpha and Lyman Continuum emission from galaxies at redshift z~2, thus
linking together these three aspects of ionising radiation in galaxies. In this
paper, we outline the strategy of this project and examine the properties of
LAEs in the GOODS North field.
Methods. We performed a narrowband LAE survey in GOODS North using existing
and two custom made filters at the Nordic Optical Telescope with MOSCA. We use
complementary broad band archival data in the field to make a careful candidate
selection and perform optical to near-IR SED fitting. We also estimate
far-infrared luminosities by matching our candidates to detections in
Spitzer/MIPS 24{\mu}m and Herschel/PACS catalogs.
Results. We find a total of 25 LAE candidates, probing mainly the bright end
of the LAE luminosity function with L_Ly {\alpha} ~ 1-15e42 erg/s. They display
a range of masses of ~0.5-50e9 M_solar, and average ages from a few tens of Myr
to 1 Gyr when assuming a constant star formation history. The majority of our
candidates also show signs of recent elevated star formation. Three candidates
have counterparts in the GOODS-Herschel far-IR catalogue, with luminosities
consistent with ultra-luminous infrared galaxies (ULIRGs).
Conclusions. The wide range of parameters derived from our SED fitting, as
well as part of our sample being detected as ULIRGs, seems to indicate that at
these Lyman alpha luminosities, LAEs do not necessarily have to be young
dwarfs, and that a lack of dust is not required for Lyman alpha to escape.Comment: 16 pages, 12 figures. Accepted version for publication in A&
CARICOM Bilateral Trade: A Preliminary Analysis Using the Gravity Model
This paper investigates the determinants of intra-CARICOM bilateral trade and the CARICOM member's trade with the North American and European countries using the gravity model. Seventeen annual cross-sections are estimated for the period 1980 through 1996. Overall, the empirical results indicate that the gravity model has considerable potential to explain intra-CARICOM bilateral trade as well as trade between CARICOM members and non-members. The evidence suggests that both the importer's GDP per capita and the exporter's GDP per capita exert strong positive effects on CARICOM trade levels. Since these effects are found to be statistically the same, we conclude that the gravity model is symmetric with respect to GDP per capita. Further, sharing a common language, colonial ties, or membership in the CARICOM all significantly contribute to larger volumes of bilateral trade, while geographic distance has the opposite effect. Both the exporting and the importing countries' populations have a positive effect on trade levels, indicating that larger economies have a wider production base and thus export and import more than would smaller economies.Caribbean economies, CARICOM, FTAA, gravity model, regional integration, International Relations/Trade,
Butt Joint Reinforcement in Parallel-Laminated Veneer (PLV) Lumber
Parallel-laminated veneer (PLV) is a high-strength structural material consisting of thin parallel-laminated wood veneers. The use of graphite-cloth reinforcement, placed on either side of a butt joint in 1 1/2- by 3 1/2- by 32-inch Douglas-fir PLV tensile members, was assessed. The finite-element method of analysis was used to predict the behavior in different unreinforced and reinforced butt-jointed PLV tensile members. Relationships between the reinforcing parametersâlength, modulus of elasticity, and thicknessâand the stresses in the wood and reinforcement components were developed by regression analysis techniques. The reinforcing mechanism reduced the peak stresses at the butt joint and hence increased the ultimate strength of the member. Design of PLV material whose strength is limited by shear stresses that develop at the butt joint is facilitated by use of the proposed relationships.Experimental testing confirmed the predictions of the finite-element analysis. Failure initiated at the unreinforced joint in the specimens. Average tensile strength increased and variability decreased in reinforced specimens. Application of a small amount of reinforcement at the butt joint has been shown to enhance PLV performance
Theoretical Properties of Projection Based Multilayer Perceptrons with Functional Inputs
Many real world data are sampled functions. As shown by Functional Data
Analysis (FDA) methods, spectra, time series, images, gesture recognition data,
etc. can be processed more efficiently if their functional nature is taken into
account during the data analysis process. This is done by extending standard
data analysis methods so that they can apply to functional inputs. A general
way to achieve this goal is to compute projections of the functional data onto
a finite dimensional sub-space of the functional space. The coordinates of the
data on a basis of this sub-space provide standard vector representations of
the functions. The obtained vectors can be processed by any standard method. In
our previous work, this general approach has been used to define projection
based Multilayer Perceptrons (MLPs) with functional inputs. We study in this
paper important theoretical properties of the proposed model. We show in
particular that MLPs with functional inputs are universal approximators: they
can approximate to arbitrary accuracy any continuous mapping from a compact
sub-space of a functional space to R. Moreover, we provide a consistency result
that shows that any mapping from a functional space to R can be learned thanks
to examples by a projection based MLP: the generalization mean square error of
the MLP decreases to the smallest possible mean square error on the data when
the number of examples goes to infinity
NASC-seq monitors RNA synthesis in single cells.
Sequencing of newly synthesised RNA can monitor transcriptional dynamics with great sensitivity and high temporal resolution, but is currently restricted to populations of cells. Here, we develop new transcriptome alkylation-dependent single-cell RNA sequencing (NASC-seq), to monitor newly synthesised and pre-existing RNA simultaneously in single cells. We validate the method on pre-labelled RNA, and by demonstrating that more newly synthesised RNA was detected for genes with known high mRNA turnover. Monitoring RNA synthesis during Jurkat T-cell activation with NASC-seq reveals both rapidly up- and down-regulated genes, and that induced genes are almost exclusively detected as newly transcribed. Moreover, the newly synthesised and pre-existing transcriptomes after T-cell activation are distinct, confirming that NASC-seq simultaneously measures gene expression corresponding to two time points in single cells. Altogether, NASC-seq enables precise temporal monitoring of RNA synthesis at single-cell resolution during homoeostasis, perturbation responses and cellular differentiation
Women, know your limits: Cultural sexism in academia
Despite the considerable advances of the feminist movement across Western societies, in Universities women are less likely to be promoted, or paid as much as their male colleagues, or even get jobs in the first place. One way in which we can start to reflect on why this might be the case is through hearing the experiences of women academics themselves. Using feminist methodology, this article attempts to unpack and explore just some examples of
âcultural sexismâ which characterise the working lives of many women in British academia.This article uses qualitative methods to describe and make sense of just some of those experiences. In so doing, the argument is also made that the activity of academia is profoundly gendered and this explicit acknowledgement may contribute to our
understanding of the under-representation of women in senior positions
Tests of Lorentz violation in muon antineutrino to electron antineutrino oscillations
A recently developed Standard-Model Extension (SME) formalism for neutrino
oscillations that includes Lorentz and CPT violation is used to analyze the
sidereal time variation of the neutrino event excess measured by the Liquid
Scintillator Neutrino Detector (LSND) experiment. The LSND experiment,
performed at Los Alamos National Laboratory, observed an excess, consistent
with neutrino oscillations, of in a beam of . It
is determined that the LSND oscillation signal is consistent with no sidereal
variation. However, there are several combinations of SME coefficients that
describe the LSND data; both with and without sidereal variations. The scale of
Lorentz and CPT violation extracted from the LSND data is of order
GeV for the SME coefficients and . This solution for
Lorentz and CPT violating neutrino oscillations may be tested by other short
baseline neutrino oscillation experiments, such as the MiniBooNE experiment.Comment: 10 pages, 10 figures, 2 tables, uses revtex4 replaced with version to
be published in Physical Review D, 11 pages, 11 figures, 2 tables, uses
revtex
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