2,695 research outputs found
Statistical mechanics of a colloidal suspension in contact with a fluctuating membrane
Surface effects are generally prevailing in confined colloidal systems. Here
we report on dispersed nanoparticles close to a fluid membrane. Exact results
regarding the static organization are derived for a dilute solution of
non-adhesive colloids. It is shown that thermal fluctuations of the membrane
broaden the density profile, but on average colloids are neither accumulated
nor depleted near the surface. The radial correlation function is also
evaluated, from which we obtain the effective pair-potential between colloids.
This entropically-driven interaction shares many similarities with the familiar
depletion interaction. It is shown to be always attractive with range
controlled by the membrane correlation length. The depth of the potential well
is comparable to the thermal energy, but depends only indirectly upon membrane
rigidity. Consequenses for stability of the suspension are also discussed
Butterfly richness and abundance along a gradient of imperviousness and the importance of matrix quality
Heterogeneity in quantity and quality of resources provided in the urban matrix may mitigate adverse effects of urbanization intensity on the structure of biotic communities. To assess this we quantified the spatial variation in butterfly richness and abundance along an impervious surface gradient using three measures of urban matrix quality: floral resource availability and origin (native vs exotic plants), tree cover, and the occurrence of remnant habitat patches. Butterfly richness and abundance were surveyed in 100 cells (500 x 500‐m), selected using a random‐stratified sampling design, across a continuous gradient of imperviousness in Melbourne, Australia. Sampling occurred twice during the butterfly flight season. Occurrence data were analyzed using generalized linear models at local and meso‐ scales. Despite high sampling completeness we did not detect 75% of species from the regional species pool in the urban area, suggesting that urbanization has caused a large proportion of the region’s butterflies to become absent or extremely rare within Melbourne’s metro‐area. Those species that do remain are largely very generalist in their choice of larval host plants. Butterfly species richness and abundance declined with increasing impervious surface cover and, contrary to evidence for other taxa, there was no evidence that richness peaked at intermediate levels of urbanization. Declines in abundance appeared to be more noticeable when impervious surface cover exceeded 25%, while richness declined linearly with increasing impervious surface cover. We find evidence that the quality of the urban matrix (floral resources and remnant vegetation) influenced butterfly richness and abundance although the effects were small. Total butterfly abundance responded negatively to exotic floral abundance early in the sampling season and positively to total floral abundance later in the sampling season. Butterfly species richness increased with tree cover. Negative impacts of increased urbanization intensity on butterfly species richness and abundance may be mitigated to some extent by improving the quality of the urban matrix by enhancing tree cover and the provision of floral resources – with some evidence that native plants are more effective
The liquid-vapor interface of an ionic fluid
We investigate the liquid-vapor interface of the restricted primitive model
(RPM) for an ionic fluid using a density-functional approximation based on
correlation functions of the homogeneous fluid as obtained from the
mean-spherical approximation (MSA). In the limit of a homogeneous fluid our
approach yields the well-known MSA (energy) equation of state. The ionic
interfacial density profiles, which for the RPM are identical for both species,
have a shape similar to those of simple atomic fluids in that the decay towards
the bulk values is more rapid on the vapor side than on the liquid side. This
is the opposite asymmetry of the decay to that found in earlier calculations
for the RPM based on a square-gradient theory. The width of the interface is,
for a wide range of temperatures, approximately four times the second moment
correlation length of the liquid phase. We discuss the magnitude and
temperature dependence of the surface tension, and argue that for temperatures
near the triple point the ratio of the dimensionless surface tension and
critical temperature is much smaller for the RPM than for simple atomic fluids.Comment: 6 postscript figures, submitted to Phys. Rev.
Action at a distance as a full-value solution of Maxwell equations: basis and application of separated potential's method
The inadequacy of Li\'{e}nard-Wiechert potentials is demonstrated as one of
the examples related to the inconsistency of the conventional classical
electrodynamics. The insufficiency of the Faraday-Maxwell concept to describe
the whole electromagnetic phenomena and the incompleteness of a set of
solutions of Maxwell equations are discussed and mathematically proved. Reasons
of the introduction of the so-called ``electrodynamics dualism concept"
(simultaneous coexistence of instantaneous Newton long-range and
Faraday-Maxwell short-range interactions) have been displayed. It is strictly
shown that the new concept presents itself as the direct consequence of the
complete set of Maxwell equations and makes it possible to consider classical
electrodynamics as a self-consistent and complete theory, devoid of inward
contradictions. In the framework of the new approach, all main concepts of
classical electrodynamics are reconsidered. In particular, a limited class of
motion is revealed when accelerated charges do not radiate electromagnetic
field.Comment: ReVTeX file, 24pp. Small corrections which do not have influence
results of the paper. Journal reference is adde
Short-term rhGH increases PIIINP, a biomarker of endothelial dysfunction
Objectives: In arterial hypertension, amino-terminal propeptide of type III procollagen (PIIINP) is elevated in arterial aneurysm tissue and associated with a poor prognosis following acute myocardial infarction (MI). Recombinant human growth hormone (rhGH) administration attenuates endothelial dysfunction but increases PIIINP. This study was conducted to establish if short-term rhGH administration affects PIIINP, endothelial function and selected cardiovascular disease (CVD) risk factors, in healthy males. Design: Method: Male subjects (n=48) were randomly assigned into two groups: (1): control group (C) n=24, mean ± SD, age 32 ± 11 years; height 1.8 ± 0.06 metres; (2): rhGH administration group (rhGH) n=24, mean ± SD, age 32 ± 9 years; height 1.8 ± 0.07 metres. Blood pressure (BP), heart rate (HR), arterial pulse wave velocity (APWV), and biochemical indices were investigated. Results: PIIINP (0.28±0.1 vs. 0.42±0.2, U/ml); Insulin like growth factor-I (159±54 vs. 323±93, ng.mL-1); resting HR (72±14 vs. 78±11, b.p.m.) and rate pressure product (RPP) (90±18 vs. 97±14, bpm x mm.Hg x 10-2) all significantly increased (P<0.05). Total cholesterol (4.7±0.9 vs. 4.4±0.7, mmol.L-1); high sensitivity C-reactive protein (1.77±2.1 vs. 1.29±1.6, mg.L-1); serum homocysteine (13.2±4.0 vs. 11.7±3.1, μmol.L-1) and APWV (9.97±1.38 vs. 9.18±1.6, m.s-1) all significantly decreased (P<0.05). Conclusion: Paradoxically, there was an improvement in CVD inflammatory markers and APWV; but PIIINP and resting RPP increased. Elevated PIIINP may have a confounding adverse effect on the endothelium, but may also provide clinical prognostic information in monitoring arterial hypertension, left ventricular function in the sub-acute phase following MI and endothelial function in aortic aneurysms
The VLT-FLAMES survey of massive stars: Wind properties and evolution of hot massive stars in the LMC
[Abridged] We have studied the optical spectra of 28 O- and early B-type
stars in the Large Magellanic Cloud, 22 of which are associated with the young
star-forming region N11. Stellar parameters are determined using an automated
fitting method, combining the stellar atmosphere code FASTWIND with the
genetic-algorithm optimisation routine PIKAIA. Results for stars in the LH9 and
LH10 associations of N11 are consistent with a sequential star formation
scenario, in which activity in LH9 triggered the formation of LH10. Our sample
contains four stars of spectral type O2, of which the hottest is found to be
~49-54 kK (cf. ~45-46 kK for O3 stars). The masses of helium-enriched dwarfs
and giants are systematically lower than those implied by non-rotating
evolutionary tracks. We interpret this as evidence for efficient
rotationally-enhanced mixing, leading to the surfacing of primary helium and to
an increase of the stellar luminosity. This result is consistent with findings
for SMC stars by Mokiem et al. For bright giants and supergiants no such
mass-discrepancy is found, implying that these stars follow tracks of modestly
(or non-)rotating objects. Stellar mass-loss properties were found to be
intermediate to those found in massive stars in the Galaxy and the SMC, and
comparisons with theoretical predictions at LMC metallicity yielded good
agreement over the luminosity range of our targets, i.e. 5.0 < log L/L(sun) <
6.1
Process mapping of laser surface modification of AISI 316L stainless steel for biomedical applications
A 1.5-kW CO2 laser in pulsed mode at 3 kHz was used to investigate the effects of varied laser process parameters and resulting morphology of AISI 316L stainless steel. Irradiance and residence time were varied between 7.9 to 23.6 MW/cm2 and 50 to 167 µs respectively. A strong correlation between irradiance, residence time, depth of processing and roughness of processed steel was established. The high depth of altered microstructure and increased roughness were linked to higher levels of both irradiance and residence times. Energy fluence and surface temperature models were used to predict levels of melting occurring on the surface through the analysis of roughness and depth of the region processed. Microstructural images captured by the SEM revealed significant grain structure changes at higher irradiances, but due to increased residence times, limited to the laser in use, the hardness values were not improved
A lattice model for the kinetics of rupture of fluid bilayer membranes
We have constructed a model for the kinetics of rupture of membranes under
tension, applying physical principles relevant to lipid bilayers held together
by hydrophobic interactions. The membrane is characterized by the bulk
compressibility (for expansion), the thickness of the hydrophobic part of the
bilayer, the hydrophobicity and a parameter characterizing the tail rigidity of
the lipids. The model is a lattice model which incorporates strain relaxation,
and considers the nucleation of pores at constant area, constant temperature,
and constant particle number. The particle number is conserved by allowing
multiple occupancy of the sites. An equilibrium ``phase diagram'' is
constructed as a function of temperature and strain with the total pore surface
and distribution as the order parameters. A first order rupture line is found
with increasing tension, and a continuous increase in proto-pore concentration
with rising temperature till instability. The model explains current results on
saturated and unsaturated PC lipid bilayers and thicker artificial bilayers
made of diblock copolymers. Pore size distributions are presented for various
values of area expansion and temperature, and the fractal dimension of the pore
edge is evaluated.Comment: 15 pages, 8 figure
The Pathways for Intelligible Speech: Multivariate and Univariate Perspectives
An anterior pathway, concerned with extracting meaning from sound, has been identified in nonhuman primates. An analogous pathway has been suggested in humans, but controversy exists concerning the degree of lateralization and the precise location where responses to intelligible speech emerge. We have demonstrated that the left anterior superior temporal sulcus (STS) responds preferentially to intelligible speech (Scott SK, Blank CC, Rosen S, Wise RJS. 2000. Identification of a pathway for intelligible speech in the left temporal lobe. Brain. 123:2400-2406.). A functional magnetic resonance imaging study in Cerebral Cortex used equivalent stimuli and univariate and multivariate analyses to argue for the greater importance of bilateral posterior when compared with the left anterior STS in responding to intelligible speech (Okada K, Rong F, Venezia J, Matchin W, Hsieh IH, Saberi K, Serences JT,Hickok G. 2010. Hierarchical organization of human auditory cortex: evidence from acoustic invariance in the response to intelligible speech. 20: 2486-2495.). Here, we also replicate our original study, demonstrating that the left anterior STS exhibits the strongest univariate response and, in decoding using the bilateral temporal cortex, contains the most informative voxels showing an increased response to intelligible speech. In contrast, in classifications using local "searchlights” and a whole brain analysis, we find greater classification accuracy in posterior rather than anterior temporal regions. Thus, we show that the precise nature of the multivariate analysis used will emphasize different response profiles associated with complex sound to speech processin
High-latitude ocean ventilation and its role in Earth's climate transitions
The processes regulating ocean ventilation at high latitudes are re-examined based on a range of observations spanning all scales of ocean circulation, from the centimetre scales of turbulence to the basin scales of gyres. It is argued that high-latitude ocean ventilation is controlled by mechanisms that differ in fundamental ways from those that set the overturning circulation. This is contrary to the assumption of broad equivalence between the two that is commonly adopted in interpreting the role of the high-latitude oceans in Earth's climate transitions. Illustrations of how recognizing this distinction may change our view of the ocean's role in the climate system are offered
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