305 research outputs found
Impact fragmentation of aluminum reactive materials
The article of record as published may be found at http://dx.doi.org/10.1063/1.4746788We report the fragmentation of brittle, granular aluminum spheres following high velocity impact
(0.5-2.0 km/s) on thin steel plates. These spheres, machined from isostatically pressed aluminum
powder, represent a prototypical metallic reactive material. The fragments generated by the impacts
are collected in a soft-catch apparatus and analyzed down to a length scale of 44
l
m. With increasing
velocity, there is a transition from an exponential Poisson-process fragment distribution with a
characteristic length scale to a power-law behavior indicative of scale-invariance. A normalized
power-law distribution with a finite size cutoff is introduced and used to analyze the number and
mass distributions of the recovered fragments. At high impact velocities, the power-law behavior
dominates the distribution and the power-law exponent is identical to the universal value for brittle
fragmentation discussed in recent works. The length scale at which the power-law behavior decays is
consistent with the idea that the length of side microbranches or damage zones from primary cracks
is governing this cutoff. The transition in fragment distribution at high strain-rates also implies
a significant increase in small fragments that can rapidly combust in an ambient atmosphere
Ab initio metadynamics simulations of oxygen/ligand interactions in organoaluminum clusters
The article of record as published may be found at http://dx.doi.org/10.1063/1.4897256Car-Parrinello molecular dynamics combined with a metadynamics algorithm is used to study the
initial interaction of O
2
with the low-valence organoaluminum clusters Al
4
Cp
4
(Cp
=
C
5
H
5
)and
Al
4
Cp
â
4
(Cp
â
=
C5[CH3]5). Prior to reaction with the aluminum core, simulations suggest that the
oxygen undergoes a hindered crossing of the steric barrier presented by the outer ligand monolayer.
Acombinationoftwocollectivevariablesbasedonaluminum/oxygendistanceandlateraloxygen
displacement was found to produce distinct reactant, product, and transition states for this process.
In the methylated cluster with Cp
â
ligands, a broad transition state of 45 kJ/mol was observed due
to direct steric interactions with the ligand groups and considerable oxygen reorientation. In the
non-methylated cluster the ligands distort away from the oxidizer, resulting in a barrier of roughly
34 kJ/mol with minimal O
2
reorientation. A study of the oxygen/cluster system fixed in a triplet
multiplicity suggests that the spin state does not affect the initial steric interaction with the ligands.
The metadynamics approach appears to be a promising means of analyzing the initial steps of such
oxidation reactions for ligand-protected clusters
Dynamic response of full-scale sandwich composite structures subject to air-blast loading
Glass-fibre reinforced polymer (GFRP) sandwich structures (1.6 m Ă 1.3 m) were subject to 30 kg charges of C4 explosive at stand-off distances 8â14 m. Experiments provide detailed data for sandwich panel response, which are often used in civil and military structures, where air-blast loading represents a serious threat. High-speed photography, with digital image correlation (DIC), was employed to monitor the deformation of these structures during the blasts. Failure mechanisms were revealed in the DIC data, confirmed in post-test sectioning. The experimental data provides for the development of analytical and computational models. Moreover, it underlines the importance of support boundary conditions with regards to blast mitigation. These findings were analysed further in finite element simulations, where boundary stiffness was, as expected, shown to strongly influence the panel deformation. In-depth parametric studies are ongoing to establish the hierarchy of the various factors that influence the blast response of sandwich composite structures
Uniaxial compression of single crystal and polycrystalline tantalum
A series of compression experiments characterising the elastic-plastic response of single crystal and polycrystalline tantalum from quasi-static to intermediate strain-rates (10^â3 â 10^3 sâ1) over a range of temperatures (233â438âŻK) are reported in this paper. The single crystal experiments show significant differences in the response of the three principle crystal orientations of tantalum in terms of yield, work hardening and ultimate deformed shapes. Modelling is undertaken using a dislocation mechanics based crystal plasticity finite element model giving insight into the underlying microscopic processes that govern the macroscopic response. The simulations show the importance of the dislocation mobility relations and laws governing the evolution of the mobile dislocation density for capturing the correct behaviours. The inclusion of the twinning/anti-twinning asymmetry is found to influence [100] orientation most strongly, and is shown to be critical for matching the relative yield strengths. In general the simulations are able to adequately match experimental trends although some specific details such as exact strain hardening evolution are not reproduced suggesting a more complex hardening model is required. 3D finite element simulations approximating the tests are also undertaken and are able to predict the final deformed sample shapes well once the twinning/anti-twinning asymmetry is included (particularly for the [100] orientation). The polycrystalline data in both as-received and cold rolled conditions shows the initial yield strength is highest and work hardening rate is lowest for the cold-rolled material due to the increase in mobile dislocation density caused by the prior work. The general behavioural trends with temperature and strain-rate of the polycrystalline materials are reproduced in the single crystal data however the specific form of stress versus strain curves are significantly different. This is discussed in terms of the similar active slip systems in polycrystalline material to high symmetry single crystals but with the significant added effect of grain boundary interactions
Reaction forces of laminated glass windows subject to blast loads
Several blast trials on laminated glass windows have been performed in the past, using both full field 3D Digital Image Correlation and strain gauges located on the supporting structure to collect information on the glass pane behaviour. The data obtained during three blast experiments were employed to calculate reaction forces throughout the perimeter supports both before and after the fracture of the glass layers. The pre-crack experimental data were combined with finite element modelling results to achieve this, whilst solely experimental results were employed for post-cracked reactions. The results for the three blast experiments were compared to identify similarities in their behaviour. It is intended that the results can be used to improve the existing springâmass systems used for the design of blast resistant windows
Metastable Vacua in Flux Compactifications and Their Phenomenology
In the context of flux compactifications, metastable vacua with a small
positive cosmological constant are obtained by combining a sector where
supersymmetry is broken dynamically with the sector responsible for moduli
stabilization, which is known as the F-uplifting. We analyze this procedure in
a model-independent way and study phenomenological properties of the resulting
vacua.Comment: 21 pages, 19 figures; v2: matches version published in JHE
Gamma-ray and radio tests of the e+e- excess from DM annihilations
PAMELA and ATIC recently reported an excess in e+e- cosmic rays. We show that
if it is due to Dark Matter annihilations, the associated gamma-ray flux and
the synchrotron emission produced by e+e- in the galactic magnetic field
violate HESS and radio observations of the galactic center and HESS
observations of dwarf Spheroidals, unless the DM density profile is
significantly less steep than the benchmark NFW and Einasto profiles.Comment: 16 pages, 4 figures; v2: normalizations fixed in Table 2 and typos
corrected (no changes in the analysis nor the results), some references and
comments added; v3: minor additions, matches published versio
LB01: Cell Salvage during Caesarean Section: A Randomised Controlled Trial (The SALVO Trial)
Objective
Excessive haemorrhage at caesarean section requires the use of donor (allogeneic) blood transfusion. The SALVO trial assessed whether the routine use of cell salvage during caesarean section can reduce the need for donor blood transfusion.
Study Design
We conducted a randomised controlled trial (26 UK obstetric units; June 2013 through April 2016) of routine cell salvage use (intervention) vs. current standard of care without routine salvage use (control) in caesarean section among women at risk of haemorrhage. We used multivariable models, adjusting for stratification variables and prognostic factors identified a priori, to compare rates of donor blood transfusion (primary outcome) and fetomaternal haemorrhage â„2ml in RhD-negative women with RhD-positive baby (one of the secondary outcomes) between groups.
Results
Of 3028 women randomised, 2990 were analysed (after exclusions for vaginal delivery or hospital transfer after randomisation). Of 1498 assigned to intervention, 95.6% had cell salvage deployed (50.8% had salvaged blood returned; mean 259.9 ml) vs. 3.9% of 1492 assigned to control. Donor blood transfusion rates were lower in the intervention group than in control (2.5% vs. 3.5%, adjusted odds ratio [OR] 0.65, 95% confidence interval [CI] 0.42 to 1.01). No case of amniotic fluid embolism was observed. Fetomaternal haemorrhage was higher with intervention vs. control (25.6% vs. 10.5%, adjusted OR 5.63, 95% CI 1.43 to 22.14).
Conclusion
There was modest evidence for an effect of routine use of cell salvage during caesarean section on donor blood transfusion. The increased fetomaternal haemorrhage emphasises the need for adherence to guidance on anti-D prophylaxis and for research on risks of alloimmunisation to RhD and other red cell antigens following cell salvage. (Funder: UK National Institute of Health Research Health Technology Assessment programme, ISRCTN66118656)
Galactic-Centre Gamma Rays in CMSSM Dark Matter Scenarios
We study the production of gamma rays via LSP annihilations in the core of
the Galaxy as a possible experimental signature of the constrained minimal
supersymmetric extension of the Standard Model (CMSSM), in which
supersymmetry-breaking parameters are assumed to be universal at the GUT scale,
assuming also that the LSP is the lightest neutralino chi. The part of the
CMSSM parameter space that is compatible with the measured astrophysical
density of cold dark matter is known to include a stau_1 - chi coannihilation
strip, a focus-point strip where chi has an enhanced Higgsino component, and a
funnel at large tanb where the annihilation rate is enhanced by the poles of
nearby heavy MSSM Higgs bosons, A/H. We calculate the total annihilation rates,
the fractions of annihilations into different Standard Model final states and
the resulting fluxes of gamma rays for CMSSM scenarios along these strips. We
observe that typical annihilation rates are much smaller in the coannihilation
strip for tanb = 10 than along the focus-point strip or for tanb = 55, and that
the annihilation branching ratios differ greatly between the different dark
matter strips. Whereas the current Fermi-LAT data are not sensitive to any of
the CMSSM scenarios studied, and the calculated gamma-ray fluxes are probably
unobservably low along the coannihilation strip for tanb = 10, we find that
substantial portions of the focus-point strips and rapid-annihilation funnel
regions could be pressured by several more years of Fermi-LAT data, if
understanding of the astrophysical background and/or systematic uncertainties
can be improved in parallel.Comment: 33 pages, 12 figures, comments and references added, version to
appear in JCA
Exploring the Concepts of Recognition and Shame for Social Work
© 2016 GAPS. Recognition and shame are both concepts that potentially offer social workers a structure to build practice on; two states experienced by both social workers and service users. âRecognitionâ, within social, political and economic thought, has been established as a field in which inequality and exclusion can be analysed. Social work theorists have also made inroads into exploring its reach. âShameâ in twentieth century and contemporary sociological and psychoanalytical accounts, is understood as a force in limiting human agency, well-being and capacity This paper briefly outlines some of the defining ideas in circulation in relation to recognition and shame, and then briefly considers how psychoanalytical and contemporary social structural analysis builds on this, making links to contemporary social work thinking throughout. The paper also specifically considers some of the uses of recognition and shame for thinking about social worker and service user âwell-beingâ, and the connections, through both the relational and the socio-political, which inflect social work practice
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