1,933 research outputs found
The temperature dependence of photo-elastic properties of cross-linked amorphous polyethylenes
Cross-linked samples of polyethylene were prepared by electron
irradiation of both high and low density polymers in the crystalline state.
A further cross-linked sample was obtained by curing a high density polyethylene
by reaction with dicumyl peroxide at 180°C. The stress-strain birefringence
relations were obtained, on specimens cut from these samples, at temperatures
between 130 and 250°C.
All samples showed a substantial decrease in stress-optical coefficient
with increasing degree of cross-linking and with increasing temperature. The
stress-optical properties at each temperature were extrapolated to zero degree
of cross-linking to give quantities characteristic of the Guassian network.
Comparison of these properties with Gaussian theory of the network leads to a
value of ca.1150 cals/mole for the difference in energy between trans and
gauche conformations of successive links of the polyethylene chain and also
indicates that the optical anisotropy of a - CH2 group in the elastomeric
state is more nearly given by Denbigh’s than by Bunn and Daubeny's polaris-abilities
Infrared scintillation yield in gaseous and liquid argon
The study of primary and secondary scintillations in noble gases and liquids
is of paramount importance to rare-event experiments using noble gas media. In
the present work, the scintillation yield in gaseous and liquid Ar has for the
first time been measured in the near infrared (NIR) and visible region, both
for primary and secondary (proportional) scintillations, using Geiger-mode
avalanche photodiodes (G-APDs) and pulsed X-ray irradiation. The primary
scintillation yield of the fast component was measured to be 17000 photon/MeV
in gaseous Ar in the NIR, in the range of 690-1000 nm, and 510 photon/MeV in
liquid Ar, in the range of 400-1000 nm. Proportional NIR scintillations
(electroluminescence) in gaseous Ar have been also observed; their
amplification parameter at 163 K was measured to be 13 photons per drifting
electron per kV. Possible applications of NIR scintillations in high energy
physics experiments are discussed.Comment: 6 pages, 5 figures. Submitted to Europhysics Letter. Revised Figs. 3
and
Metabolite Fingerprinting in Transgenic Nicotiana tabacum Altered by the Escherichia coli Glutamate Dehydrogenase Gene
With about 200 000 phytochemicals in existence, identifying those of biomedical significance is a mammoth task. In the postgenomic era, relating metabolite fingerprints, abundances, and profiles to genotype is also a large task. Ion analysis using Fourier transformed ion cyclotron resonance mass spectrometry (FT-ICR-MS) may provide a high-throughput approach to measure genotype dependency of the inferred metabolome if reproducible techniques can be established. Ion profile inferred metabolite fingerprints are coproducts. We used FT-ICR-MS-derived ion analysis to examine gdhA (glutamate dehydrogenase (GDH; EC 1.4.1.1)) transgenic Nicotiana tabacum (tobacco) carrying out altered glutamate, amino acid, and carbon metabolisms, that fundamentally alter plant productivity. Cause and effect between gdhA expression, glutamate metabolism, and plant phenotypes was analyzed by [Formula: see text] labeling of amino acid fractions, and by FT-ICR-MS analysis of metabolites. The gdhA transgenic plants increased (13)N labeling of glutamate and glutamine significantly. FT-ICR-MS detected 2 012 ions reproducible in 2 to 4 ionization protocols. There were 283 ions in roots and 98 ions in leaves that appeared to significantly change abundance due to the measured GDH activity. About 58% percent of ions could not be used to infer a corresponding metabolite. From the 42% of ions that inferred known metabolites we found that certain amino acids, organic acids, and sugars increased and some fatty acids decreased. The transgene caused increased ammonium assimilation and detectable ion variation. Thirty-two compounds with biomedical significance were altered in abundance by GDH including 9 known carcinogens and 14 potential drugs. Therefore, the GDH transgene may lead to new uses for crops like tobacco
A sequence based synteny map between soybean and Arabidopsis thaliana
BACKGROUND: Soybean (Glycine max, L. Merr.) is one of the world's most important crops, however, its complete genomic sequence has yet to be determined. Nonetheless, a large body of sequence information exists, particularly in the form of expressed sequence tags (ESTs). Herein, we report the use of the model organism Arabidopsis thaliana (thale cress) for which the entire genomic sequence is available as a framework to align thousands of short soybean sequences. RESULTS: A series of JAVA-based programs were created that processed and compared 341,619 soybean DNA sequences against A. thaliana chromosomal DNA. A. thaliana DNA was probed for short, exact matches (15 bp) to each soybean sequence, and then checked for the number of additional 7 bp matches in the adjacent 400 bp region. The position of these matches was used to order soybean sequences in relation to the A. thaliana genome. CONCLUSION: Reported associations between soybean sequences and A. thaliana were within a 95% confidence interval of e(-30 )– e(-100). In addition, the clustering of soybean expressed sequence tags (ESTs) based on A. thaliana sequence was accurate enough to identify potential single nucleotide polymorphisms (SNPs) within the soybean sequence clusters. An EST, bacterial artificial chromosome (BAC) end sequence and marker amplicon sequence synteny map of soybean and A. thaliana is presented. In addition, all JAVA programs used to create this map are available upon request and on the WEB
Resolving the Submillimeter Background: the 850-micron Galaxy Counts
Recent deep blank field submillimeter surveys have revealed a population of
luminous high redshift galaxies that emit most of their energy in the
submillimeter. The results suggest that much of the star formation at high
redshift may be hidden to optical observations. In this paper we present
wide-area 850-micron SCUBA data on the Hawaii Survey Fields SSA13, SSA17, and
SSA22. Combining these new data with our previous deep field data, we establish
the 850-micron galaxy counts from 2 mJy to 10 mJy with a >3-sigma detection
limit. The area coverage is 104 square arcmin to 8 mJy and 7.7 square arcmin to
2.3 mJy. The differential 850-micron counts are well described by the function
n(S)=N_0/(a+S^3.2), where S is the flux in mJy, N_0=3.0 x 10^4 per square
degree per mJy, and a=0.4-1.0 is chosen to match the 850-micron extragalactic
background light. Between 20 to 30 per cent of the 850-micron background
resides in sources brighter than 2 mJy. Using an empirical fit to our >2 mJy
data constrained by the EBL at lower fluxes, we argue that the bulk of the
850-micron extragalactic background light resides in sources with fluxes near 1
mJy. The submillimeter sources are plausible progenitors of the present-day
spheroidal population.Comment: 5 pages, accepted by The Astrophysical Journal Letter
On the low-temperature performances of THGEM and THGEM/G-APD multipliers in gaseous and two-phase Xe
The performances of THGEM multipliers in two-phase Xe avalanche mode are
presented for the first time. Additional results on THGEM operation in gaseous
Xe at cryogenic temperatures are provided. Stable operation of a double-THGEM
multiplier was demonstrated in two-phase Xe with gains reaching 600. These are
compared to existing data, summarized here for two-phase Ar, Kr and Xe
avalanche detectors incorporating GEM and THGEM multipliers. The optical
readout of THGEMs with Geiger-mode Avalanche Photodiodes (G-APDs) has been
investigated in gaseous Xe at cryogenic temperature; avalanche scintillations
were recorded in the Near Infrared (NIR) at wavelengths of up to 950 nm. At
avalanche charge gain of 350, the double-THGEM/G-APD multiplier yielded 0.07
photoelectrons per initial ionization electron, corresponding to an avalanche
scintillation yield of 0.7 NIR photons per avalanche electron over 4pi. The
results are compared with those of two-phase Ar avalanche detectors. The
advantages, limitations and possible applications are discussed.Comment: 22 pages, 14 figures. Revised Figs. 10,11 and Table 1. To be
published in JINS
Direct observation of avalanche scintillations in a THGEM-based two-phase Ar avalanche detector using Geiger-mode APD
A novel concept of optical signal recording in two-phase avalanche detectors,
with Geiger-mode Avalanche Photodiodes (G-APD) is described.
Avalanche-scintillation photons were measured in a thick Gas Electron
Multiplier (THGEM) in view of potential applications in rare-event experiments.
The effective detection of avalanche scintillations in THGEM holes has been
demonstrated in two-phase Ar with a bare G-APD without wavelength shifter, i.e.
insensitive to VUV emission of Ar. At gas-avalanche gain of 400 and under \pm
70^\circ viewing-angle, the G-APD yielded 640 photoelectrons (pe) per 60 keV
X-ray converted in liquid Ar; this corresponds to 0.7 pe per initial (prior to
multiplication) electron. The avalanche-scintillation light yield measured by
the G-APD was about 0.7 pe per avalanche electron, extrapolated to 4pi
acceptance. The avalanche scintillations observed occurred presumably in the
near infrared (NIR) where G-APDs may have high sensitivity. The measured
scintillation yield is similar to that observed by others in the VUV. Other
related topics discussed in this work are the G-APD's single-pixel and
quenching resistor characteristics at cryogenic temperatures.Comment: 21 pages, 18 figures. Submitted to JINS
HST/ACS Images of the GG Tauri Circumbinary Disk
Hubble Space Telescope Advanced Camera for Surveys images of the young binary
GG Tauri and its circumbinary disk in V and I bandpasses were obtained in 2002
and are the most detailed of this system to date. The confirm features
previously seen in the disk including: a "gap" apparently caused by shadowing
from circumstellar material; an asymmetrical distribution of light about the
line of sight on the near edge of the disk; enhanced brightness along the near
edge of the disk due to forward scattering; and a compact reflection nebula
near the secondary star. New features are seen in the ACS images: two short
filaments along the disk; localized but strong variations in disk intensity
("gaplets"); and a "spur" or filament extending from the reflection nebulosity
near the secondary. The back side of the disk is detected in the V band for the
first time. The disk appears redder than the combined light from the stars,
which may be explained by a varied distribution of grain sizes. The brightness
asymmetries along the disk suggest that it is asymmetrically illuminated by the
stars due to extinction by nonuniform circumstellar material or the illuminated
surface of the disk is warped by tidal effects (or perhaps both). Localized,
time-dependent brightness variations in the disk are also seen.Comment: 28 pages, 7 figures, accepted for publication in the Astronomical
Journa
Study of infrared scintillations in gaseous and liquid argon - Part I: methodology and time measurements
A methodology to measure Near Infrared (NIR) scintillations in gaseous and
liquid Ar, using Geiger-mode APDs (GAPDs) sensitive in the NIR and pulsed X-ray
irradiation, is described. This study has been triggered by the development of
Cryogenic Avalanche Detectors (CRADs) with optical readout in the NIR using
combined THGEM/GAPD multiplier, which may come to be in demand in coherent
neutrino-nucleus scattering and dark matter search experiments. A new approach
to measure the NIR scintillation yield at cryogenic temperatures has been
developed, namely using GAPDs in single photoelectron counting mode with time
resolution. The time structure of NIR scintillations and their light yield were
measured both for primary scintillations and that of secondary at moderate
electric fields (electroluminescence), in gaseous and liquid Ar.Comment: 17 pages, 15 figures. Submitted to JINS
Definition of Soybean Genomic Regions That Control Seed Phytoestrogen Amounts
Soybean seeds contain large amounts of isoflavones or phytoestrogens such as genistein, daidzein, and glycitein that display biological effects when ingested by humans and animals. In seeds, the total amount, and amount of each type, of isoflavone varies by 5 fold between cultivars and locations. Isoflavone content and quality are one key to the biological effects of soy foods, dietary supplements, and nutraceuticals. Previously we had identified 6 loci (QTL) controlling isoflavone content using 150 DNA markers. This study aimed to identify and delimit loci underlying heritable variation in isoflavone content with additional DNA markers. We used a recombinant inbred line (RIL) population ([Formula: see text]) derived from the cross of “Essex” by “Forrest,” two cultivars that contrast for isoflavone content. Seed isoflavone content of each RIL was determined by HPLC and compared against 240 polymorphic microsatellite markers by one-way analysis of variance. Two QTL that underlie seed isoflavone content were newly discovered. The additional markers confirmed and refined the positions of the six QTL already reported. The first new region anchored by the marker BARC_Satt063 was significantly associated with genistein ([Formula: see text] , [Formula: see text]) and daidzein ([Formula: see text] , [Formula: see text]). The region is located on linkage group B2 and derived the beneficial allele from Essex. The second new region defined by the marker BARC_Satt129 was significantly associated with total glycitein ([Formula: see text] , [Formula: see text]). The region is located on linkage group D1a+Q and also derived the beneficial allele from Essex. Jointly the eight loci can explain the heritable variation in isoflavone content. The loci may be used to stabilize seed isoflavone content by selection and to isolate the underlying genes
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