624 research outputs found
Modulating calcium phosphate formation using CO2 laser engineering of a polymeric material
The use of simulated body fluid (SBF) is widely used as a screening technique to assess the ability of materials to promote calcium phosphate formation. This paper details the use of CO2 laser surface treatment of nylon® 6,6 to modulate calcium phosphate formation following immersion in SBF for 14 days. Through white light interferometry (WLI) it was determined that the laser surface processing gave rise to maximum Ra and Sa parameters of 1.3 and 4.4 µm, respectively. The use of X-ray photoelectron spectroscopy (XPS) enabled a maximum increase in surface oxygen content of 5.6 %at. to be identified. The laser-induced surface modifications gave rise to a modulation in the wettability characteristics such that the contact angle, θ, decreased for the whole area processed samples, as expected, and increased for the patterned samples. The increase in θ can be attributed to a transition in wetting nature to a mixed-state wetting regime. It was seen for all samples that calcium phosphate formed on each surface following 14 days. The largest increase in mass, Δg, owed to calcium phosphate formation, was brought about by the whole area processed sample irradiated with a fluence of 51 Jcm-2. No correlation between the calcium phosphate formation and the laser patterned surface properties was determined due to the likely affect of the mixed-state wetting regime. Strong correlations between θ, the surface energy parameters and the calcium phosphate formation for the whole area processed samples allow one to realize the potential for this surface treatment technique in predicting the bone forming ability of laser processed materials
Low energy transition in spectral statistics of 2D interactingfermions
We study the level spacing statistics and eigenstate properties of
spinless fermions with Coulomb interaction on a two dimensional lattice at
constant filling factor and various disorder strength. In the limit of large
lattice size, undergoes a transition from the Poisson to the
Wigner-Dyson distribution at a critical total energy independent of the number
of fermions. This implies the emergence of quantum ergodicity induced by
interaction and delocalization in the Hilbert space at zero temperature.Comment: revtex, 5 pages, 4 figures; new data for eigenfunctions are adde
On the study of oil paint adhesion on optically transparent glass: Conservation of reverse paintings on glass
Archived with thanks to Applied Surface Science, ElsevierReverse painting on glass is a technique which consists of applying a cold paint layer on the reverse-side of glass. The main challenge facing these artworks is the fragile adhesion of the pictorial layer – a simple movement can modify the appearance of the painting. This paper details a study into the adhesion parameters of pigments on glass and the comparison between different pigments. The relationships between the binder (linseed oil) with pigments and the glass with or without the use of an adhesive are studied. Physical analyses by surface characterisation have been carried out to better understand the influence of the pigment. The use of a sessile drop device, optical microscopy, scanning electron microscopy (SEM), a surface 3D profiler and a pencil hardness scratch tester were necessary to establish a comparison of the pictorial layer adhesion. A comparison of the effect of two adhesives; namely ox gall and gum arabic, has shown that the adhesion is not only linked to the physical parameters but that possible chemical reactions can influence the results. Finally, a treatment based on humidity-extreme storage has shown the weakness of some pictorial layers
The Narrow Pulse Approximation and long length scale determination in xenon gas diffusion NMR studies of model porous media
We report a systematic study of xenon gas diffusion NMR in simple model
porous media: random packs of mono-sized glass beads, and focus on three
specific areas peculiar to gas-phase diffusion. These topics are: (i) diffusion
of spins on the order of the pore dimensions during the application of the
diffusion encoding gradient pulses in a PGSE experiment (breakdown of the
'narrow pulse approximation' and imperfect background gradient cancellation),
(ii) the ability to derive long-length scale structural information, and (iii)
effects of finite sample size. We find that the time-dependent diffusion
coefficient, D(t), of the imbibed xenon gas at short diffusion times in small
beads is significantly affected by the gas pressure. In particular, as
expected, we find smaller deviations between measured D(t) and theoretical
predictions as the gas pressure is increased, resulting from reduced diffusion
during the application of the gradient pulse. The deviations are then
completely removed when water D(t) is observed in the same samples. The use of
gas also allows us to probe D(t) over a wide range of length scales, and
observe the long-time asymptotic limit which is proportional to the inverse
tortuosity of the sample, as well as the diffusion distance where this limit
takes effect (~ 1 - 1.5 bead diameters). The Pade approximation can be used as
a reference for expected xenon D(t) data between the short and long time
limits, allowing us to explore deviations from the expected behaviour at
intermediate times as a result of finite sample size effects. Finally, the
application of the Pade interpolation between the long and short time
asymptotic limits yields a fitted length scale (the "Pade length"), which is
found to be ~ 0.13b for all bead packs, where b is the bead diameter.Comment: single pdf file including figure
A complete 3D numerical study of the effects of pseudoscalar-photon mixing on quasar polarizations
We present the results of three-dimensional simulations of quasar
polarizations in the presence of pseudoscalar-photon mixing in the
intergalactic medium. The intergalactic magnetic field is assumed to be
uncorrelated in wave vector space but correlated in real space. Such a field
may be obtained if its origin is primordial. Furthermore we assume that the
quasars, located at cosmological distances, have negligible initial
polarization. In the presence of pseudoscalar-photon mixing we show, through a
direct comparison with observations, that this may explain the observed large
scale alignments in quasar polarizations within the framework of big bang
cosmology. We find that the simulation results give a reasonably good fit to
the observed data.Comment: 15 pages, 8 figures, significant changes, to appear in EPJ
Hydrodynamics and Flow
In this lecture note, we present several topics on relativistic hydrodynamics
and its application to relativistic heavy ion collisions. In the first part we
give a brief introduction to relativistic hydrodynamics in the context of heavy
ion collisions. In the second part we present the formalism and some
fundamental aspects of relativistic ideal and viscous hydrodynamics. In the
third part, we start with some basic checks of the fundamental observables
followed by discussion of collective flow, in particular elliptic flow, which
is one of the most exciting phenomenon in heavy ion collisions at relativistic
energies. Next we discuss how to formulate the hydrodynamic model to describe
dynamics of heavy ion collisions. Finally, we conclude the third part of the
lecture note by showing some results from ideal hydrodynamic calculations and
by comparing them with the experimental data.Comment: 40 pages, 35 figures; lecture given at the QGP Winter School, Jaipur,
India, Feb.1-3, 2008; to appear in Springer Lecture Notes in Physic
Electromagnetic probes
We introduce the seminal developments in the theory and experiments of
electromagnetic probes for the study of the dynamics of relativistic heavy ion
collisions and quark gluon plasma.Comment: 47 pages, 33 Figures; Lectures delivered by Dinesh K. Srivastava at
QGP Winter School (QGPWS08) at Jaipur, India, February 1-3, 200
Cosmological parameters from SDSS and WMAP
We measure cosmological parameters using the three-dimensional power spectrum
P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in
combination with WMAP and other data. Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt,
tensor modes or massive neutrinos. Adding SDSS information more than halves the
WMAP-only error bars on some parameters, tightening 1 sigma constraints on the
Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter
density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on
neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when
dropping prior assumptions about curvature, neutrinos, tensor modes and the
equation of state. Our results are in substantial agreement with the joint
analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive
consistency check with independent redshift survey data and analysis
techniques. In this paper, we place particular emphasis on clarifying the
physical origin of the constraints, i.e., what we do and do not know when using
different data sets and prior assumptions. For instance, dropping the
assumption that space is perfectly flat, the WMAP-only constraint on the
measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to
t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running
tilt, neutrino mass and equation of state in the list of free parameters, many
constraints are still quite weak, but future cosmological measurements from
SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt
figures available at http://www.hep.upenn.edu/~max/sdsspars.htm
Evolution of the differential transverse momentum correlation function with centrality in Au+Au collisions at GeV
We present first measurements of the evolution of the differential transverse
momentum correlation function, {\it C}, with collision centrality in Au+Au
interactions at GeV. {\it C} exhibits a strong dependence
on collision centrality that is qualitatively similar to that of number
correlations previously reported. We use the observed longitudinal broadening
of the near-side peak of {\it C} with increasing centrality to estimate the
ratio of the shear viscosity to entropy density, , of the matter formed
in central Au+Au interactions. We obtain an upper limit estimate of
that suggests that the produced medium has a small viscosity per unit entropy.Comment: 7 pages, 4 figures, STAR paper published in Phys. Lett.
SUSY breaking mediation mechanisms and (g-2)_\mu, B -> X_s \gamma, B -> X_{s} l^+ l^- and B_s -> \mu^+ \mu^-
We show that there are qualitative differences in correlations among
, , and in various SUSY breaking mediation mechanisms: minimal supergravity
(mSUGRA), gauge mediation (GMSB), anomaly mediation (AMSB), gaugino mediation
(MSB), weakly and strongly interacting string theories, and
brane models. After imposing the direct search limits on the Higgs boson and
SUSY particle search limits and branching ratio, we find all
the scenarios can accommodate the in the range of
(a few tens), and predict that the branching ratio for can differ from the standard model (SM) prediction by
but no more. On the other hand, the is sensitive to the
SUSY breaking mediation mechanisms through the pseudoscalar and stop masses
( and ), and the stop mixing angle. In the GMSB with a
small messenger number, the AMSB, the MSB and the noscale scenarios,
one finds that , which is
below the search limit at the Tevatron Run II. Only the mSUGRA or string
inspired models can generate a large branching ratio for this decay.Comment: 40 pages, 21 figures (to appear in JHEP
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