8,892 research outputs found
Direct observation of size scaling and elastic interaction between nano-scale defects in collision cascades
Using in-situ transmission electron microscopy, we have directly observed
nano-scale defects formed in ultra-high purity tungsten by low-dose high energy
self-ion irradiation at 30K. At cryogenic temperature lattice defects have
reduced mobility, so these microscope observations offer a window on the
initial, primary damage caused by individual collision cascade events. Electron
microscope images provide direct evidence for a power-law size distribution of
nano-scale defects formed in high-energy cascades, with an upper size limit
independent of the incident ion energy, as predicted by Sand et al. [Eur. Phys.
Lett., 103:46003, (2013)]. Furthermore, the analysis of pair distribution
functions of defects observed in the micrographs shows significant
intra-cascade spatial correlations consistent with strong elastic interaction
between the defects
The Luminosity Function Evolution of Soft X--ray selected AGN in the RIXOS survey
A sample of 198 soft X--ray selected active galactic nuclei (AGN) from the
ROSAT International X--ray Optical Survey (RIXOS), is used to investigate the
X--ray luminosity function and its evolution. RIXOS, with a flux limit of 3E-14
erg s-1 cm-2 (0.5 to 2.0 keV), samples a broad range in redshift over 20 deg^2
of sky, and is almost completely identified; it is used in combination with the
Einstein Extended Medium Sensitivity Survey (EMSS), to give a total sample of
over 600 AGN. We find the evolution of AGN with redshift to be consistent with
pure luminosity evolution (PLE) models in which the rate of evolution slows
markedly or stops at high redshifts z>1.8. We find that this result is not
affected by the inclusion, or exclusion, of narrow emission line galaxies at
low redshift in the RIXOS and EMSS samples, and is insensitive to uncertainties
in the conversion between flux values measured with ROSAT and Einstein. We
confirm, using a model independent Ve/Va test, that our survey is consistent
with no evolution at high redshifts.Comment: 10 pages, LaTeX file, PS figures and mn.sty. Accepted in MNRA
On primordial trispectrum from exchanging scalar modes in general multiple field inflationary models
We make an complementary investigation of the primordial trispectrum from
exchanging intermediate scalar modes in multi-field inflation models with
generalized kinetic terms. Together with the calculation of irreducible
contributions to the primordial trispectrum in Ref.[103], we give the full
leading-order primordial trispectrum in generalized multi-field models.Comment: 15 pages, 1 figure; v2 references adde
Cascade fragmentation : deviation from power law in primary radiation damage
The sizes of defect clusters, produced in materials by energetic ion or neutron impacts, are critically important input for models describing microstructural evolution of irradiated materials. We propose a model for the distribution of sizes of vacancy and self-interstitial defect clusters formed by high-energy impacts in tungsten, and provide new data from in situ ion irradiation experiments to validate the model. The model predicts the statistics of sub-cascade splitting and the resulting distribution of primary defects extending over the entire range of cluster sizes, and is able to provide initial conditions for quantitative multi-scale simulations of microstructural evolution. [GRAPHICS] .Peer reviewe
Recommended from our members
Corrigendum to 'Homage to Professor Maria Petrou' [ Pattern Recognition Letters 48 (2014) 2-7].
Universality in movie rating distributions
In this paper histograms of user ratings for movies (1,...,10) are analysed.
The evolving stabilised shapes of histograms follow the rule that all are
either double- or triple-peaked. Moreover, at most one peak can be on the
central bins 2,...,9 and the distribution in these bins looks smooth
`Gaussian-like' while changes at the extremes (1 and 10) often look abrupt. It
is shown that this is well approximated under the assumption that histograms
are confined and discretised probability density functions of L\'evy skew
alpha-stable distributions. These distributions are the only stable
distributions which could emerge due to a generalized central limit theorem
from averaging of various independent random avriables as which one can see the
initial opinions of users. Averaging is also an appropriate assumption about
the social process which underlies the process of continuous opinion formation.
Surprisingly, not the normal distribution achieves the best fit over histograms
obseved on the web, but distributions with fat tails which decay as power-laws
with exponent -(1+alpha) (alpha=4/3). The scale and skewness parameters of the
Levy skew alpha-stable distributions seem to depend on the deviation from an
average movie (with mean about 7.6). The histogram of such an average movie has
no skewness and is the most narrow one. If a movie deviates from average the
distribution gets broader and skew. The skewness pronounces the deviation. This
is used to construct a one parameter fit which gives some evidence of
universality in processes of continuous opinion dynamics about taste.Comment: 8 pages, 5 figures, accepted for publicatio
Discovery of a Cyclotron Resonant Scattering Feature in the RXTE Spectrum of 4U 0352+309 (X Per)
We have discovered a ~29 keV Cyclotron Resonant Scattering Feature (CRSF) in
the X-Ray spectrum of 4U 0352+309 (X Per) using observations taken with the
Rossi X-Ray Timing Explorer. 4U 0352+309 is a persistent low luminosity (L_x =
4.2x10^34 ergs/s) X-ray pulsar, with a 837 s period and which accretes material
from the Be star X Per. The X-Ray spectrum, unusual when compared to brighter
accreting pulsars, may be due to the low mass accretion rate and could be
typical of the new class of persistent low luminosity Be/X-Ray binary pulsars.
We attempted spectral fits with continuum models used historically for 4U
0352+309, and found that all were improved by the addition of a CRSF at ~29
keV. The model that best fit the observations is a combination of a 1.45+/-0.02
keV blackbody with a 5.4x10^8 cm^2 area, and a power-law with a 1.83+/-0.03
photon index modified by the CRSF. In these fits the CRSF energy is
28.6+1.5-1.7 keV, implying a magnetic field strength of 2.5(1+z)x10^12 G in the
scattering region (where z is the gravitational redshift). Phase resolved
analysis shows that the blackbody and cyclotron line energies are consistent
with being constant through the pulse.Comment: 34 pages, 6 figures, 3 tables, Accepted by Ap
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