46,894 research outputs found
First principle computation of stripes in cuprates
We present a first principle computation of vertical stripes in
within the LDA+U method. We find that Cu centered
stripes are unstable toward O centered stripes. The metallic core of the stripe
is quite wide and shows reduced magnetic moments with suppressed
antiferromagnetic (AF) interactions. The system can be pictured as alternating
metallic and AF two-leg ladders the latter with strong AF interaction and a
large spin gap. The Fermi surface shows warping due to interstripe
hybridization. The periodicity and amplitude of the warping is in good
agreement with angle resolved photoemission experiment. We discuss the
connection with low-energy theories of the cuprates.Comment: 5 pages,4 figure
The phase-space structure of cold dark-matter halos: Insights into the Galactic halo
We study the formation of the Milky Way's halo in a CDM cosmology by
scaling down a high resolution simulation of the formation of a cluster of
galaxies. We determine how much phase-space substructure is left over from the
objects that merge to build up the present galaxy. We study the debris streams
originating from such objects and find that their evolution can be explained
simply in terms of the conservation of phase-space density. Analysing the mass
growth history of our halo we find that its inner regions have been in place
for more than 10 Gyr, but that the growth of the halo as a whole is more
gradual, in agreement with other high resolution simulations of dark-matter
halos. Recent accretion contributes to the inner 10 kpc of the halo only at the
10 level. Finally we determine the number of dark-matter streams as a
function of distance from the centre of the halo. In the equivalent of the
``Solar vicinity'', we find that the dark-matter is smoothly distributed in
space, and that the velocity ellipsoid is formed by hundreds of thousands of
streams, most of which have velocity dispersions of the order of 1 km/s or
less.Comment: 16 pages, 21 figures, MNRAS in press. Postscript version with high
resolution figures available from
http://www.mpa-garching.mpg.de/~ahelmi/research/lcdm_cl.html. Minor change
Anisotropic constitutive relationships in energetic materials: PETN and HMX
This paper presents results of first-principles density functional calculations of the equation of state (EOS) of PETN-I and beta-HMX. The isotropic EOS for hydrostatic compression has been extended to include uniaxial compressions in the [100], [010], [001], [110], [101], [011], and [111] directions up to compression ratio V/V0 = 0.70. Equilibrium properties, including lattice parameters and elastic constants, as well as hydrostatic EOS are in good agreement with available experimental data. The shear stresses of uniaxially compressed PETN-I and beta-HMX have been evaluated and their behavior as a function of compression ratio has been used to make predictions of shock sensitivity of these EMs. A comparison of predicted sensitivities with available experimental data has also been performed
Weak Lensing as a Calibrator of the Cluster Mass-Temperature Relation
The abundance of clusters at the present epoch and weak gravitational lensing
shear both constrain roughly the same combination of the power spectrum
normalization sigma_8 and matter energy density Omega_M. The cluster constraint
further depends on the normalization of the mass-temperature relation.
Therefore, combining the weak lensing and cluster abundance data can be used to
accurately calibrate the mass-temperature relation. We discuss this approach
and illustrate it using data from recent surveys.Comment: Matches the version in ApJL. Equation 4 corrected. Improvements in
the analysis move the cluster contours in Fig1 slightly upwards. No changes
in the conclusion
First-principles anisotropic constitutive relationships in β-cyclotetramethylene tetranitramine (β-HMX)
First-principles density functional theory calculations have been performed to obtain constitutive relationships in the crystalline energetic material β-cyclotetramethylene tetranitramine (β-HMX). In addition to hydrostatic loading, uniaxial compressions in the directions normal to the {100}, {010}, {001}, {110}, {101}, {011}, and {111} planes have been performed to investigate the anisotropic equation of state (EOS). The calculated lattice parameters and hydrostatic EOS are in reasonable agreement with the available experimental data. The uniaxial compression data show a significant anisotropy in the principal stresses, change in energy, band gap, and shear stresses, which might lead to the anisotropy of the elastic-plastic shock transition and shock sensitivity of β-HMX
All the ACEs: A Chaotic Concept for Family Policy and Decision-Making?
This paper will consider ACEs as a chaotic concept that prioritises risk and obscures the material and social conditions of the lives of its objects. It will show how the various definitions of ACEs offer no cohesive body of definitive evidence and measurement, and lead to a great deal of over-claiming. It discusses how ACEs have found their time and place, locating a variety of social ills within the child’s home, family and parenting behaviours. It argues that because ACEs are confined to intra-familial circumstances, and largely to narrow parent-child relations, issues outside of parental control are not addressed. It concludes that ACEs form a poor body of evidence for family policy and decision-making about child protection and that different and less stigmatising solutions are hiding in plain sight
Nanoscale Molecular Dynamics Simulaton of Shock Compression of Silicon
We report results of molecular dynamics simulation of shock wave propagation
in silicon in [100], [110], and [111] directions obtained using a classical
environment-dependent interatomic potential (EDIP). Several regimes of
materials response are classified as a function of shock wave intensity using
the calculated shock Hugoniot. Shock wave structure in [100] and [111]
directions exhibit usual evolution as a function of piston velocity. At piston
velocities km/s the shock wave consists of a fast elastic precursor followed by
a slower plastic front. At larger piston velocities the single overdriven
plastic wave propagates through the crystal causing amorphitization of Si.
However, the [110] shock wave exhibits an anomalous materials response at
intermediate piston velocities around km/s which is characterized by the
absence of plastic deformations
Giant Meterwave Radio Telescope observations of an M2.8 flare: insights into the initiation of a flare-coronal mass ejection event
We present the first observations of a solar flare with the GMRT. An M2.8
flare observed at 1060 MHz with the GMRT on Nov 17 2001 was associated with a
prominence eruption observed at 17 GHz by the Nobeyama radioheliograph and the
initiation of a fast partial halo CME observed with the LASCO C2 coronograph.
Towards the start of the eruption, we find evidence for reconnection above the
prominence. Subsequently, we find evidence for rapid growth of a vertical
current sheet below the erupting arcade, which is accompanied by the flare and
prominence eruption.Comment: Accepted for publication in Solar Physic
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