616 research outputs found
Constraints on Dimensional Warped Spaces
In order to investigate the phenomenological implications of allowing gauge
fields to propagate in warped spaces of more than five dimensions, we consider
a toy model of a space warped by the presence of a anisotropic bulk
cosmological constant. After solving the Einstein equation, three classes of
solutions are found, those in which the additional () dimensions are
growing, shrinking or remaining constant. It is found that gauge fields
propagating in these spaces have a significantly different Kaluza Klein (KK)
mass spectrum and couplings from that of the Randall and Sundrum model. This
leads to a greatly reduced lower bound on the KK scale, arising from
electroweak constraints, for spaces growing towards the IR brane.Comment: 6 pages, 5 figures PASCOS2010 International Symposium proceedin
The van Hove distribution function for Brownian hard spheres: dynamical test particle theory and computer simulations for bulk dynamics
We describe a test particle approach based on dynamical density functional
theory (DDFT) for studying the correlated time evolution of the particles that
constitute a fluid. Our theory provides a means of calculating the van Hove
distribution function by treating its self and distinct parts as the two
components of a binary fluid mixture, with the `self' component having only one
particle, the `distinct' component consisting of all the other particles, and
using DDFT to calculate the time evolution of the density profiles for the two
components. We apply this approach to a bulk fluid of Brownian hard spheres and
compare to results for the van Hove function and the intermediate scattering
function from Brownian dynamics computer simulations. We find good agreement at
low and intermediate densities using the very simple Ramakrishnan-Yussouff
[Phys. Rev. B 19, 2775 (1979)] approximation for the excess free energy
functional. Since the DDFT is based on the equilibrium Helmholtz free energy
functional, we can probe a free energy landscape that underlies the dynamics.
Within the mean-field approximation we find that as the particle density
increases, this landscape develops a minimum, while an exact treatment of a
model confined situation shows that for an ergodic fluid this landscape should
be monotonic. We discuss possible implications for slow, glassy and arrested
dynamics at high densities.Comment: Submitted to Journal of Chemical Physic
Dynamics in inhomogeneous liquids and glasses via the test particle limit
We show that one may view the self and the distinct part of the van Hove
dynamic correlation function of a simple fluid as the one-body density
distributions of a binary mixture that evolve in time according to dynamical
density functional theory. For a test case of soft core Brownian particles the
theory yields results for the van Hove function that agree quantitatively with
those of our Brownian dynamics computer simulations. At sufficiently high
densities the free energy landscape underlying the dynamics exhibits a barrier
as a function of the mean particle displacement, shedding new light on the
nature of glass formation. For hard spheres confined between parallel planar
walls the barrier height oscillates in-phase with the local density, implying
that the mobility is maximal between layers, which should be experimentally
observable in confined colloidal dispersions.Comment: 4 pages, 3 figure
Solvent mediated interactions between model colloids and interfaces: A microscopic approach
We determine the solvent mediated contribution to the effective potentials
for model colloidal or nano- particles dispersed in a binary solvent that
exhibits fluid-fluid phase separation. Using a simple density functional theory
we calculate the density profiles of both solvent species in the presence of
the `colloids', which are treated as external potentials, and determine the
solvent mediated (SM) potentials. Specifically, we calculate SM potentials
between (i) two colloids, (ii) a colloid and a planar fluid-fluid interface,
and (iii) a colloid and a planar wall with an adsorbed wetting film. We
consider three different types of colloidal particles: colloid A which prefers
the bulk solvent phase rich in species 2, colloid C which prefers the solvent
phase rich in species 1, and `neutral' colloid B which has no strong preference
for either phase, i.e. the free energies to insert the colloid into either of
the coexisting bulk phases are almost equal. When a colloid which has a
preference for one of the two solvent phases is inserted into the disfavored
phase at statepoints close to coexistence a thick adsorbed `wetting' film of
the preferred phase may form around the colloids. The presence of the adsorbed
film has a profound influence on the form of the SM potentials.Comment: 17 Pages, 13 Figures. Accepted for publication in Journal of Chemical
Physic
Interfacial and wetting properties of a binary point Yukawa fluid
We investigate the interfacial phase behavior of a binary fluid mixture
composed of repulsive point Yukawa particles. Using a simple approximation for
the Helmholtz free energy functional, which yields the random phase
approximation (RPA) for the pair direct correlation functions, we calculate the
equilibrium fluid density profiles of the two species of particles adsorbed at
a planar wall. We show that for a particular choice (repulsive exponential) of
the wall potentials and the fluid pair-potential parameters, the Euler-Lagrange
equations for the equilibrium fluid density profiles may be transformed into a
single ordinary differential equation and the profiles obtained by a simple
quadrature. For certain other choices of the fluid pair-potential parameters
fluid-fluid phase separation of the bulk fluid is observed. We find that when
such a mixture is exposed to a planar hard-wall, the fluid exhibits complete
wetting on the species 2 poor side of the binodal, i.e. we observe a thick film
of fluid rich in species 2 adsorbed at the hard-wall. The thickness of the
wetting film grows logarithmically with the concentration difference between
the fluid state-point and the binodal and is proportional to the bulk
correlation length of the intruding (wetting) fluid phase. However, for state
points on the binodal that are further from the critical point, we find there
is no thick wetting film. We determine the accompanying line of first-order
(pre-wetting) surface phase transitions which separate a thin and thick
adsorbed film. We show that for some other choices of repulsive wall potentials
the pre-wetting line is still present, but its location and extent in the phase
diagram is strongly dependent on the wall-fluid interaction parameters.Comment: 11 pages, 7 figures. Accepted for publication in Journal of Chemical
Physic
Aqueous Processes and Microbial Habitability of Gale Crater Sediments from the Blunts Point to the Glenn Torridon Clay Unit
A driving factor for sending the Mars Science Laboratory, Curiosity rover to Gale Crater was the orbital detection of clay minerals in the Glen Torridon (GT) clay unit. Clay mineral detections in GT suggested a past aqueous environment that was habitable, and could contain organic evidence of past microbiology. The mission of the Sample Analysis at Mars (SAM) instrument onboard Curiosity was to detect organic evidence of past microbiology and to detect volatile bearing mineralogy that can inform on whether past geochemical conditions would have supported microbiological activity. The objective of this work was to 1) evaluate the depositional/alteration conditions of Blunts Point (BP) to GT sediments 2) search for evidence of organics, and 3) evaluate microbial habitability in the BP, Vera Rubin Ridge (VRR), and GT sedimentary rock
Evidence for Smectite Clays from MSL SAM Analyses of Mudstone at Yellowknife Bay, Gale Crater, Mars
Drilled samples of mudstone from the Sheepbed unit at Yellowknife Bay were analyzed by MSL instruments including the Sample Analysis at Mars (SAM) and Chemistry and Mineralogy (CheMin) instruments in MSL's Analytical Laboratory. CheMin analyses revealed the first in situ X-ray diffraction based evidence of clay minerals on Mars, which are likely trioctahedral smectites (e.g., saponite) and comprise approx 20% of the mudstone sample (e.g., Bristow et al., this meeting). SAM analyses, which heated the mudstone samples to 1000 C and monitored volatiles evolved to perform in situ evolved gas analysis mass spectrometry (EGA-MS), resulted in a H2O trace exhibiting a wide evolution at temperatures < 500 C, and an evolution peak at higher temperatures near approx 750 C. The low temperature H2O evolution has many potential contributors, including adsorbed H2O, smectite interlayer H2O, and structural H2O/OH from bassanite and akaganeite (identified by CheMin) and H2O/OH from amorphous phases in the sample. The high temperature H2O is consistent with the evolution of H2O from the dehydroxylation of the smectite clay mineral. Comparison to EGA-MS data collected under SAM-like conditions on a variety of clay mineral reference materials indicate that a trioctahedral smectite, such as saponite, is most consistent with the high temperature H2O evolution observed. There may also be SAM EGA-MS evidence for a small high temperature H2O evolution from scoop samples from the Yellowknife Bay Rocknest sand shadow bedform. As in the mudstone samples, this evolution may indicate the detection of smectite clays, and the idea that minor clays may be present in Rocknest materials that could be expected to be at least partially derived from local sources is reasonable. But, because smectite clays were not definitively observed in CheMin analyses of Rocknest materials, they must be present at much lower abundances than the approx 20% observed in the mudstone samples. This potential detection underscores the complementary nature of the MSL CheMin and SAM instruments for investigations of martian sample mineralogy. Information on the nature of Yellowknife Bay clay minerals may also be available from the detection of H2 evolved during SAM EGA-MS at high temperature. A likely source of at least some of this H2 is H2O evolved from the smectite clays at high temperature, and it is possible these evolutions can be used in a similar fashion to high temperature H2O releases to provide constraints on the clay minerals in a sample. In addition, the D/H of this high temperature H2, as well as the H2O, can be derived from SAM MS and Tunable Laser Spectrometer (TLS) data, respectively. These D/H values may help to inform the provenance of high and low temperature water evolved from martian sample
Comparison of a novel incubator with standard incubator care: A randomised multi-centre, cross-over study
Objective: To test the performance, efficacy and usability of the mOm Essential Incubator, a novel, spacesaving infant incubator designed for use in high and low-resource settings. Design and Setting: Prospective, randomised, multi-centre, cross-over design pilot study. Neonatal Units at three UK centres participated. Patients: Stable premature infants of =30 weeks corrected gestational age who required incubator care were eligible to participate. Intervention: Babies were randomised to 24-hour care episodes in either standard or mOm incubators with cross-over after 24 hours. Primary Outcome: Efficacy of temperature maintenance within the normothermic range 36.5°C to 37.5°C. Staff feedback on the usability of the mOm incubator was collected as a secondary outcome. Results: There was no significant difference between the performance of the mOm and standard incubators in maintaining normothermia and no adverse incidents were observed. User feedback was positive, with staff reporting the mOm incubator to be easy to use and quicker to clean between patient uses. Conclusion: For the care of infants =6kg who do not require humidification, the mOm Essential Incubator can be considered as an alternative to standard incubators
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