151 research outputs found
Compression failure of angle-ply laminates
The present work deals with modes and mechanisms of failure in compression of angle-ply laminates. Experimental results were obtained from 42 angle-ply IM7/8551-7a specimens with a lay-up of ((plus or minus theta)/(plus or minus theta)) sub 6s where theta, the off-axis angle, ranged from 0 degrees to 90 degrees. The results showed four failure modes, these modes being a function of off-axis angle. Failure modes include fiber compression, inplane transverse tension, inplane shear, and inplane transverse compression. Excessive interlaminar shear strain was also considered as an important mode of failure. At low off-axis angles, experimentally observed values were considerably lower than published strengths. It was determined that laminate imperfections in the form of layer waviness could be a major factor in reducing compression strength. Previously developed linear buckling and geometrically nonlinear theories were used, with modifications and enhancements, to examine the influence of layer waviness on compression response. The wavy layer is described by a wave amplitude and a wave length. Linear elastic stress-strain response is assumed. The geometrically nonlinear theory, in conjunction with the maximum stress failure criterion, was used to predict compression failure and failure modes for the angle-ply laminates. A range of wave length and amplitudes were used. It was found that for 0 less than or equal to theta less than or equal to 15 degrees failure was most likely due to fiber compression. For 15 degrees less than theta less than or equal to 35 degrees, failure was most likely due to inplane transverse tension. For 35 degrees less than theta less than or equal to 70 degrees, failure was most likely due to inplane shear. For theta less than 70 degrees, failure was most likely due to inplane transverse compression. The fiber compression and transverse tension failure modes depended more heavily on wave length than on wave amplitude. Thus using a single parameter, such as a ratio of wave amplitude to wave length, to describe waviness in a laminate would be inaccurate. Throughout, results for AS4/3502, studied previously, are included for comparison. At low off-axis angles, the AS4/3502 material system was found to be less sensitive to layer waviness than IM7/8551-7a. Analytical predictions were also obtained for laminates with waviness in only some of the layers. For this type of waviness, laminate compression strength could also be considered a function of which layers in the laminate were wavy, and where those wavy layers were. Overall, the geometrically nonlinear model correlates well with experimental results
Physiological and Molecular Characterisation of Lucerne (Medicago sativa L.) Germplasm with Improved Seedling Freezing Tolerance
We conducted greenhouse experiments to compare 14 lucerne (alfalfa, Medicago sativa L.) germplasms for their survival following freezing. Some are collections adapted to the Grand River National Grasslands in South Dakota. We hypothesised that these collections might have developed a tolerance to survive the frigid growth conditions common there. Two of these collections, River side (RS) and Foster ranch (FR), showed greater freezing tolerance than the other germplasms tested, based on their consistent survival rates with or without cold acclimation. In multiple freezing studies, RS and FR had average survival rates of 74% and 79%, respectively, in contrast to the commercial cultivars Apica and CUF-101 (CUF) (64% and 24%, respectively). The average temperature at which 50% of ions in plant tissues leak out (LT50) by freezing based on leaf electrolyte leakage was closely correlated with survival rates. Leaf LT50 improved 2–3-fold after 3 days of cold acclimation, based on leaf electrolyte leakage analysis, reaching −18°C, –9.6°C, –8.5°C, and −5°C for RS, FR, Apica, and CUF, respectively. Comparison of total soluble sugars and relative water content in shoots before and after cold acclimation showed that they were not well correlated with freezing tolerance and could not explain the superior responses of RS and FR during cold acclimation. Transcript analysis of cold-responsive MsCBF1, MsCBF2 and CAS15B genes showed that RS, FR, Apica and CUF exhibited distinct patterns of cold induction. Although RS, FR and Apica showed a rapid or greater increase in expression level of one or two of these genes, CUF showed only a moderate induction in MsCBF2 and CAS15B transcripts, suggesting that expression of these genes may be a good molecular marker for freezing tolerance in lucerne. The findings provide evidence that freezing tolerance in lucerne is a complex trait and that a combination of different mechanisms may greatly improve freezing tolerance. RS and FR are potential resources in breeding for improving freezing tolerance in lucerne
Salinity Reduces the Forage Quality of Forage Kochia: A Halophytic Chenopodiaceae Shrub
Forage kochia (Bassia prostrata [L.] A.J. Scott) is a perennial, halophytic Chenopodiaceae shrub adapted to semiarid rangelands and steppes. It is noted for its ability to produce edible forage in saline environments, but the effect of salinity on its nutritive value has not been determined. Therefore, this study evaluated the dose-response of increasing salinity on the forage quality of forage kochia and Gardner’s saltbush (Atriplex gardneri [Moq.] D. Dietr., a chenopod forage shrub indigenous to the United States). Individual plants were evaluated in hydroponics for 28 days at 0, 150, 300, and 600 mM NaCl. Salt from accumulated ions, minerals, and forage nutritive value were determined using ground shoot samples. Analysis of forage nutritive value is problematic in plants with high salt concentrations, so neutral detergent fiber (NDF) and in vitro true digestibility (IVTD) were also predicted on an ash-corrected dry matter (DM) basis (NDFcorrected and IVTDcorrected). Forage kochia exhibited a dose-response for salt concentration, IVTDcorrected, and crude protein (CP) as salinity increased. Salt concentrations increased to 19% of DM at 600 mM NaCl, which may reduce voluntary intake by ruminants grazing forage kochia. Results indicated that uncorrected IVTD estimates were inflated as forage kochia IVTDcorrected decreased from 65% to 56% with the major change between 300 and 600 mM NaCl. Crude protein did not differ between two forage kochia cultivars but decreased from 26% to 15% between 0 and 600 mM NaCl, whereas Gardner’s saltbush CP decreased by only five percentage points as salinity increased. Nonetheless, despite the greater CP sensitivity to salinity level, forage kochia salt concentration was less and digestibility and metabolizable energy (ME) were greater than Gardner’s saltbush. Overall, salinity reduced the forage quality of forage kochia, though not as dramatically as for Gardner’s saltbush, thus supporting use of forage kochia to improve the forage base of saline rangelands
Selective lability of ruthenium(II) arene amino acid complexes.
A series of organometallic complexes of the form [(PhH)Ru(amino acid)](+) have been synthesized using amino acids able to act as tridentate ligands. The straightforward syntheses gave enantiomerically pure complexes with two stereogenic centers due to the enantiopurity of the chelating ligands. Complexes were characterized in the solid-state and/or solution-state where the stability of the complex allowed. The propensity toward labilization of the coordinatively saturated complexes was investigated. The links between complex stability and structural features are very subtle. Nonetheless, H/D exchange rates of coordinated amino groups reveal more significant differences in reactivity linked to metallocycle ring size resulting in decreasing stability of the metallocycle as the amino acid side-chain length increases. The behavior of these systems in acid is unusual, apparently labilizing the carboxylate residue of the amino acid. This acid-catalyzed hemilability in an organometallic is relevant to the use of Ru(II) arenes in medicinal contexts due to the relatively low pH of cancerous cells.TGS and MO thank the EPSRC for Studentships EP/P505445/1 and EP/K503/009/1, respectively.This is the final version of the article. It was first published by ACS at http://pubs.acs.org/doi/abs/10.1021/ic502051
The C-Band All-Sky Survey (C-BASS): Constraining diffuse Galactic radio emission in the North Celestial Pole region
The C-Band All-Sky Survey C-BASS is a high-sensitivity all-sky radio survey
at an angular resolution of 45 arcmin and a frequency of 4.7 GHz. We present a
total intensity 4.7 GHz map of the North Celestial Pole (NCP) region of sky,
above declination +80 deg, which is limited by source confusion at a level of
~0.6 mK rms. We apply the template-fitting (cross-correlation) technique to
WMAP and Planck data, using the C-BASS map as the synchrotron template, to
investigate the contribution of diffuse foreground emission at frequencies
~20-40 GHz. We quantify the anomalous microwave emission (AME) that is
correlated with far-infrared dust emission. The AME amplitude does not change
significantly (<10%) when using the higher frequency C-BASS 4.7 GHz template
instead of the traditional Haslam 408 MHz map as a tracer of synchrotron
radiation. We measure template coefficients of and
K per unit when using the Haslam and C-BASS synchrotron templates,
respectively. The AME contributes K rms at 22.8 GHz and accounts
for ~60% of the total foreground emission. Our results suggest that a harder
(flatter spectrum) component of synchrotron emission is not dominant at
frequencies >5 GHz; the best-fitting synchrotron temperature spectral index is
from 4.7 to 22.8 GHz and from 22.8 to
44.1 GHz. Free-free emission is weak, contributing ~K rms (~7%) at 22.8
GHz. The best explanation for the AME is still electric dipole emission from
small spinning dust grains.Comment: 18 pages, 6 figures, version matches version accepted by MNRA
C-Band All-Sky Survey: A First Look at the Galaxy
We present an analysis of the diffuse emission at 5 GHz in the first quadrant
of the Galactic plane using two months of preliminary intensity data taken with
the C-Band All Sky Survey (C-BASS) northern instrument at the Owens Valley
Radio Observatory, California. Combining C-BASS maps with ancillary data to
make temperature-temperature plots we find synchrotron spectral indices of
between 0.408 GHz and 5 GHz and between 1.420 GHz and 5 GHz for ,
. Through the subtraction of a radio recombination
line (RRL) free-free template we determine the synchrotron spectral index in
the Galactic plane () to be between
0.408 GHz and 5 GHz, with a contribution of per cent from free-free
emission at 5\,GHz. These results are consistent with previous low frequency
measurements in the Galactic plane. By including C-BASS data in spectral fits
we demonstrate the presence of anomalous microwave emission (AME) associated
with the HII complexes W43, W44 and W47 near 30 GHz, at 4.4 sigma, 3.1 sigma
and 2.5 sigma respectively. The CORNISH VLA 5 GHz source catalogue rules out
the possibility that the excess emission detected around 30\;GHz may be due to
ultra-compact HII regions. Diffuse AME was also identified at a 4 sigma level
within , between 5
GHz and 22.8 GHz.Comment: 16 pages, 9 figures, submitted to MNRAS, referee's corrections made,
awaiting for final approval for publicatio
Stand Establishment and Persistence of Perennial Cool-Season Grasses in the Intermountain West and the Central and Northern Great Plains
The choice of plant materials is an important component of revegetation following disturbance. To determine the utility and effectiveness of various perennial grass species for revegetation on varied landscapes, a meta analysis was used to evaluate the stand establishment and persistence of 18 perennial cool-season grass species in 34 field studies in the Intermountain and Great Plains regions of the United States under monoculture conditions. Combined across the 34 studies, stand establishment values ranged from 79% to 43% and stand persistence values ranged from 70% to 0%. Intermediate wheatgrass (Thinopyrum intermedium [Host] Barkworth & D. R. Dewey), tall wheatgrass (Thinopyrum ponticum [Podp.] Z.-W. Liu & R.-C. Wang), crested wheatgrass (Agropyron spp.), Siberian wheatgrass (Agropyron fragile [Roth] P. Candargy), and meadow brome (Bromus riparius Rehmann) possessed the highest stand establishment (≥69%). There were no significant differences among the 12 species with the largest stand persistence values. Basin wildrye (Leymus cinereus (Scribn. & Merr.) A. Love), Altai wildrye (Leymus angustus [Trin.] Pilg.), slender wheatgrass (Elymus trachycaulus [Link] Gould ex Shinners), squirreltail (Elymus spp.), and Indian ricegrass (Achnatherum hymenoides [Roem. & Schult.] Barkworth) possessed lower stand persistence (≤32%) than the majority of the other species, and Indian ricegrass (0%) possessed the lowest stand persistence of any of the species. Correlations between environmental conditions and stand establishment and persistence showed mean annual study precipitation to have the most consistent, although moderate effect (r=~0.40) for establishment and persistence. This relationship was shown by the relatively poor stand establishment and persistence of most species at sites receiving less than 310 mm of annual precipitation. These results will be a tool for land managers to make decisions concerning the importance of stand establishment, stand persistence, and annual precipitation for revegetation projects on disturbed sites
The C-Band All-Sky Survey (C-BASS): New Constraints on the Integrated Radio Spectrum of M 31
The Andromeda galaxy (M31) is our closest neighbouring spiral galaxy, making
it an ideal target for studying the physics of the interstellar medium in a
galaxy very similar to our own. Using new observations of M31 at 4.76GHz by the
C-Band All-Sky Survey (C-BASS), and all available radio data at
resolution, we produce the integrated spectrum and put new constraints on the
synchrotron spectral index and anomalous microwave emission (AME) from M31. We
use aperture photometry and spectral modelling to fit for the integrated
spectrum of M31, and subtract a comprehensive model of nearby background radio
sources. The AME in M31 is detected at significance with a peak near
30GHz and flux density Jy. The synchrotron spectral index of M31
is flatter than our own Galaxy at with no strong
evidence of spectral curvature. The emissivity of AME, averaged over the total
emission from M31 is lower than typical AME sources in our Galaxy, implying
that AME is not uniformly distributed throughout M31 and instead is likely
confined to sub-regions -- this will need to be confirmed using future higher
resolution observations around 20--30GHz.Comment: 16 pages, 6 figures, submitted to MNRA
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