1,208 research outputs found
The equation of state of solid nickel aluminide
The pressure-volume-temperature equation of state of the intermetallic
compound NiAl was calculated theoretically, and compared with experimental
measurements. Electron ground states were calculated for NiAl in the CsCl
structure, using density functional theory, and were used to predict the cold
compression curve and the density of phonon states. The Rose form of
compression curve was found to reproduce the ab initio calculations well in
compression but exhibited significant deviations in expansion. A
thermodynamically-complete equation of state was constructed for NiAl. Shock
waves were induced in crystals of NiAl by the impact of laser-launched Cu
flyers and by launching NiAl flyers into transparent windows of known
properties. The TRIDENT laser was used to accelerate the flyers to speeds
between 100 and 600m/s. Point and line-imaging laser Doppler velocimetry was
used to measure the acceleration of the flyer and the surface velocity history
of the target. The velocity histories were used to deduce the stress state, and
hence states on the principal Hugoniot and the flow stress. Flyers and targets
were recovered from most experiments. The effect of elasticity and plastic flow
in the sample and window was assessed. The ambient isotherm reproduced static
compression data very well, and the predicted Hugoniot was consistent with
shock compression data
The Effect of Lockdown Period during the COVID-19 Pandemic on Air Quality in Sydney Region, Australia.
In early 2020 from April to early June, the metropolitan area of Sydney as well as the rest of New South Wales (NSW, Australia) experienced a period of lockdown to prevent the spread of COVID-19 virus in the community. The effect of reducing anthropogenic activities including transportation had an impact on the urban environment in terms of air quality which is shown to have improved for a number of pollutants, such as Nitrogen Dioxides (NO2) and Carbon Monoxide (CO), based on monitoring data on the ground and from a satellite. In addition to primary pollutants CO and NOx emitted from mobile sources, PM2.5 (primary and secondary) and secondary Ozone (O3) during the lockdown period will also be analyzed using both statistical methods on air quality data and the modelling method with emission and meteorological data input to an air quality model. By estimating the decrease in traffic volume in the Sydney region, the corresponding decrease in emission input to the Weather Research and Forecasting—Community Multiscale Air Quality Modelling System (WRF-CMAQ) air quality model is then used to estimate the effect of lockdown on the air quality especially CO, NO2, O3, and PM2.5 in the Greater Metropolitan Region (GMR) of Sydney. The results from both statistical and modelling methods show that NO2, CO, and PM2.5 levels decreased during the lockdown, but O3 instead increased. However, the change in the concentration levels are small considering the large reduction of ~30% in traffic volum
Dynamic landscapes and human dispersal patterns : tectonics, coastlines, and the reconstruction of human habitats
Studies of the impact of physical environment on human evolution usually focus on climate as the main external forcing agent of evolutionary and cultural change. In this paper we focus on changes in the physical character of the landscape driven by geophysical processes as an equally potent factor. Most of the landscapes where finds of early human fossils and artefacts are concentrated are ones that have been subjected to high levels of geological instability, either because of especially active tectonic processes associated with faulting and volcanic activity or because of proximity to coastlines subject to dramatic changes of geographical position and physical character by changes of relative sea level. These processes can have both beneficial effects, creating ecologically attractive conditions for human settlement, and deleterious or disruptive ones, creating barriers to movement, disruption of ecological conditions, or hazards to survival. Both positive and negative factors can have powerful selective effects on human behaviour and patterns of settlement and dispersal. We consider both these aspects of the interaction, develop a framework for the reconstruction and comparison of landscapes and landscape change at a variety of scales, and illustrate this with selected examples drawn from Africa and Arabia
The Evolution of a Mass-Selected Sample of Early-Type Field Galaxies
We investigate the evolution of mass-selected early-type field galaxies using
a sample of 28 gravitational lenses spanning the redshift range 0 < z < 1.
Based on the redshift-dependent intercept of the fundamental plane in the rest
frame B band, we measure an evolution rate of d log (M/L)_B / dz = -0.56 +/-
0.04 (all errors are 1 sigma unless noted) if we directly compare to the local
intercept measured from the Coma cluster. Re-fitting the local intercept helps
minimize potential systematic errors, and yields an evolution rate of d log
(M/L)_B / dz = -0.54 +/- 0.09. An evolution analysis of properly-corrected
aperture mass-to-light ratios (defined by the lensed image separations) is
closely related to the Faber-Jackson relation. In rest frame B band we find an
evolution rate of d log (M/L)_B / dz = -0.41 +/- 0.21, a present-day
characteristic magnitude of M_{*0} = -19.70 + 5 log h +/- 0.29 (assuming a
characteristic velocity dispersion of sigma_{DM*} = 225 km/s), and a
Faber-Jackson slope of gamma_{FJ} = 3.29 +/- 0.58. The measured evolution rates
favor old stellar populations (mean formation redshift z_f > 1.8 at 2 sigma
confidence for a Salpeter initial mass function and a flat Omega_m =0.3
cosmology) among early-type field galaxies, and argue against significant
episodes of star formation at z < 1.Comment: 38 pages; 9 figs; ApJ accepted; REVISION: erroneous image separation
corrected for one lens, another lens removed; results recalculated and
slightly modifie
Managing lifestyle change to reduce coronary risk: a synthesis of qualitative research on peoples’ experiences
Background
Coronary heart disease is an incurable condition. The only approach known to slow its progression is healthy lifestyle change and concordance with cardio-protective medicines. Few people fully succeed in these daily activities so potential health improvements are not fully realised. Little is known about peoples’ experiences of managing lifestyle change. The aim of this study was to synthesise qualitative research to explain how participants make lifestyle change after a cardiac event and explore this within the wider illness experience.
Methods
A qualitative synthesis was conducted drawing upon the principles of meta-ethnography. Qualitative studies were identified through a systematic search of 7 databases using explicit criteria. Key concepts were identified and translated across studies. Findings were discussed and diagrammed during a series of audiotaped meetings.
Results
The final synthesis is grounded in findings from 27 studies, with over 500 participants (56% male) across 8 countries. All participants experienced a change in their self-identity from what was ‘familiar’ to ‘unfamiliar’. The transition process involved ‘finding new limits and a life worth living’ , ‘finding support for self’ and ‘finding a new normal’. Analyses of these concepts led to the generation of a third order construct, namely an ongoing process of ‘reassessing past, present and future lives’ as participants considered their changed identity. Participants experienced a strong urge to get back to ‘normal’. Support from family and friends could enable or constrain life change and lifestyle changes. Lifestyle change was but one small part of a wider ‘life’ change that occurred.
Conclusions
The final synthesis presents an interpretation, not evident in the primary studies, of a person-centred model to explain how lifestyle change is situated within ‘wider’ life changes. The magnitude of individual responses to a changed health status varied. Participants experienced distress as their notion of self identity shifted and emotions that reflected the various stages of the grief process were evident in participants’ accounts. The process of self-managing lifestyle took place through experiential learning; the level of engagement with lifestyle change reflected an individual’s unique view of the balance needed to manage ‘realistic change’ whilst leading to a life that was perceived as ‘worth living’. Findings highlight the importance of providing person centred care that aligns with both psychological and physical dimensions of recovery which are inextricably linked
The Race Between Stars and Quasars in Reionizing Cosmic Hydrogen
The cosmological background of ionizing radiation has been dominated by
quasars once the Universe aged by ~2 billion years. At earlier times (redshifts
z>3), the observed abundance of bright quasars declined sharply, implying that
cosmic hydrogen was reionized by stars instead. Here, we explain the physical
origin of the transition between the dominance of stars and quasars as a
generic feature of structure formation in the concordance LCDM cosmology. At
early times, the fraction of baryons in galaxies grows faster than the maximum
(Eddington-limited) growth rate possible for quasars. As a result, quasars were
not able to catch up with the rapid early growth of stellar mass in their host
galaxies.Comment: 5 pages, 1 figure, Accepted for publication in JCA
Constraining primordial non-Gaussianity with cosmological weak lensing: shear and flexion
We examine the cosmological constraining power of future large-scale weak
lensing surveys on the model of \emph{Euclid}, with particular reference to
primordial non-Gaussianity. Our analysis considers several different estimators
of the projected matter power spectrum, based on both shear and flexion, for
which we review the covariances and Fisher matrices. The bounds provided by
cosmic shear alone for the local bispectrum shape, marginalized over
, are at the level of . We consider
three additional bispectrum shapes, for which the cosmic shear constraints
range from (equilateral shape) up to (orthogonal shape). The competitiveness of cosmic
flexion constraints against cosmic shear ones depends on the galaxy intrinsic
flexion noise, that is still virtually unconstrained. Adopting the very high
value that has been occasionally used in the literature results in the flexion
contribution being basically negligible with respect to the shear one, and for
realistic configurations the former does not improve significantly the
constraining power of the latter. Since the flexion noise decreases with
decreasing scale, by extending the analysis up to
cosmic flexion, while being still subdominant, improves the shear constraints
by when added. However on such small scales the highly non-linear
clustering of matter and the impact of baryonic physics make any error
estimation uncertain. By considering lower, and possibly more realistic, values
of the flexion intrinsic shape noise results in flexion constraining power
being a factor of better than that of shear, and the bounds on
and being improved by a factor of upon
their combination. (abridged)Comment: 30 pages, 4 figures, 4 tables. To appear on JCA
Extending the DAMA annual-modulation region by inclusion of the uncertainties in the astrophysical velocities
The original annual-modulation region, singled out by the DAMA/NaI experiment
for direct detection of WIMPs, is extended by taking into account the
uncertainties in the galactic astrophysical velocities. Also the effect due to
a possible bulk rotation for the dark matter halo is considered. We find that
the range for the WIMP mass becomes 30 GeV < m_chi < 130 GeV at 1-sigma C.L.
with a further extension in the upper bound, when a possible bulk rotation of
the dark matter halo is taken into account. We show that the DAMA results, when
interpreted in the framework of the Minimal Supersymmetric extension of the
Standard Model, are consistent with a relic neutralino as a dominant component
of cold dark matter (on the average in our universe and in our galactic halo).
It is also discussed the discovery potential for the relevant supersymmetric
configurations at accelerators of present generation.Comment: ReVTeX, 12 pages, 1 table, 7 figure
Mammographic screening and mammographic patterns
Mammography is an effective screening modality for the early detection of breast cancer. The reduction in breast cancer mortality is greater for women aged over 50 at screening than for women aged under 50. Mammography can also contribute to an understanding of the biology of breast cancer. Screening trials provide good evidence for the dedifferentiation of a cancer as it develops over time, and the age dependency of this dedifferentiation explains much of the age difference in the effectiveness of screening. Mammographic density is an important predictor of future breast cancer risk, and has potential as an early endpoint in breast cancer prevention trials. Mammographic density is also an important determinant of mammographic screening sensitivity
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