625 research outputs found
Hydration interactions: aqueous solvent effects in electric double layers
A model for ionic solutions with an attractive short-range pair interaction
between the ions is presented. The short-range interaction is accounted for by
adding a quadratic non-local term to the Poisson-Boltzmann free energy. The
model is used to study solvent effects in a planar electric double layer. The
counter-ion density is found to increase near the charged surface, as compared
with the Poisson-Boltzmann theory, and to decrease at larger distances. The ion
density profile is studied analytically in the case where the ion distribution
near the plate is dominated only by counter-ions. Further away from the plate
the density distribution can be described using a Poisson-Boltzmann theory with
an effective surface charge that is smaller than the actual one.Comment: 11 Figures in 13 files + LaTex file. 20 pages. Accepted to Phys. Rev.
E. Corrected typos and reference
Novel methodology for predicting the critical salt concentration of bubble coalescence inhibition
Bubble coalescence in some salt solutions can be inhibited if the salt concentration reaches a critical concentration Ccr. There are three models available for Ccr in the literature, but they fail to predict Ccr correctly. The first two models employ the van der Waals attraction power laws to establish Ccr from the discriminant of quadratic or cubic polynomials. To improve the two models, the third model uses the same momentum balance equation of the previous models but different intermolecular force generated by water hydration with exponential decaying. The third prediction for Ccr requires the experimental input for film rupture thickness and is incomplete. We show further in this paper that the third model is incorrect. We propose a novel methodology for determining C cr which resolves the mathematical uncertainties in modeling C cr and can explicitly predict it from any relevant intermolecular forces. The methodology is based on the discovery that Ccr occurs at the local maximum of the balance equation for the capillary pressure, disjoining pressure, and pressure of the Gibbs-Marangoni stress. The novel generic approach is successfully validated using nonlinear equations for complicated disjoining pressure
A lattice gas model of II-VI(001) semiconductor surfaces
We introduce an anisotropic two-dimensional lattice gas model of metal
terminated II-IV(001) seminconductor surfaces. Important properties of this
class of materials are represented by effective NN and NNN interactions, which
result in the competition of two vacancy structures on the surface. We
demonstrate that the experimentally observed c(2x2)-(2x1) transition of the
CdTe(001) surface can be understood as a phase transition in thermal
equilbrium. The model is studied by means of transfer matrix and Monte Carlo
techniques. The analysis shows that the small energy difference of the
competing reconstructions determines to a large extent the nature of the
different phases. Possible implications for further experimental research are
discussed.Comment: 7 pages, 2 figure
Unintentional high density p-type modulation doping of a GaAs/AlAs core-multi-shell nanowire
Achieving significant doping in GaAs/AlAs core/shell nanowires (NWs) is of
considerable technological importance but remains a challenge due to the
amphoteric behavior of the dopant atoms. Here we show that placing a narrow
GaAs quantum well in the AlAs shell effectively getters residual carbon
acceptors leading to an \emph{unintentional} p-type doping. Magneto-optical
studies of such a GaAs/AlAs core multi-shell NW reveal quantum confined
emission. Theoretical calculations of NW electronic structure confirm quantum
confinement of carriers at the core/shell interface due to the presence of
ionized carbon acceptors in the 1~nm GaAs layer in the shell.
Micro-photoluminescence in high magnetic field shows a clear signature of
avoided crossings of the Landau level emission line with the Landau
level TO phonon replica. The coupling is caused by the resonant hole-phonon
interaction, which points to a large 2D hole density in the structure.Comment: just published in Nano Letters
(http://pubs.acs.org/doi/full/10.1021/nl500818k
Mycobacterium tuberculosis ClpP Proteases Are Co-transcribed but Exhibit Different Substrate Specificities
PMCID: PMC3613350This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Environmental variables, habitat discontinuity and life history shaping the genetic structure of Pomatoschistus marmoratus
Coastal lagoons are semi-isolated ecosystems
exposed to wide fluctuations of environmental conditions
and showing habitat fragmentation. These features may
play an important role in separating species into different
populations, even at small spatial scales. In this study, we
evaluate the concordance between mitochondrial (previous
published data) and nuclear data analyzing the genetic
variability of Pomatoschistus marmoratus in five localities,
inside and outside the Mar Menor coastal lagoon (SE
Spain) using eight microsatellites. High genetic diversity
and similar levels of allele richness were observed across
all loci and localities, although significant genic and
genotypic differentiation was found between populations
inside and outside the lagoon. In contrast to the FST values
obtained from previous mitochondrial DNA analyses
(control region), the microsatellite data exhibited significant
differentiation among samples inside the Mar Menor
and between lagoonal and marine samples. This pattern
was corroborated using Cavalli-Sforza genetic distances.
The habitat fragmentation inside the coastal lagoon and
among lagoon and marine localities could be acting as a
barrier to gene flow and contributing to the observed
genetic structure. Our results from generalized additive
models point a significant link between extreme lagoonal
environmental conditions (mainly maximum salinity) and
P. marmoratus genetic composition. Thereby, these environmental
features could be also acting on genetic structure
of coastal lagoon populations of P. marmoratus favoring
their genetic divergence. The mating strategy of P. marmoratus
could be also influencing our results obtained from
mitochondrial and nuclear DNA. Therefore, a special
consideration must be done in the selection of the DNA
markers depending on the reproductive strategy of the
species
Protein disorder-order interplay to guide the growth of hierarchical mineralized structures
A major goal in materials science is to develop bioinspired functional materials based on the precise control of molecular building blocks across length scales. Here we report a protein-mediated mineralization process that takes advantage of disorder–order interplay using elastin-like recombinamers to program organic–inorganic interactions into hierarchically ordered mineralized structures. The materials comprise elongated apatite nanocrystals that are aligned and organized into microscopic prisms, which grow together into spherulite-like structures hundreds of micrometers in diameter that come together to fill macroscopic areas. The structures can be grown over large uneven surfaces and native tissues as acid-resistant membranes or coatings with tuneable hierarchy, stiffness, and hardness. Our study represents a potential strategy for complex materials design that may open opportunities for hard tissue repair and provide insights into the role of molecular disorder in human physiology and pathology
Two years survival rate of class II composite resin restorations prepared by ART with and without a chemomechanical caries removal gel in primary molars
The aim was to test the null hypotheses that there is no difference: (1) in carious lesion development at the restoration margin between class II composite resin restorations in primary molars produced through the atraumatic restorative treatment (ART) with and without a chemomechanical caries removal gel and (2) in the survival rate of class II composite resin restorations between two treatment groups after 2 years. Three hundred twenty-seven children with 568 class II cavitated lesions were included in a parallel mouth study design. Four operators placed resin composite (Filtek Z 250) restorations bonded with a self-etch adhesive (Adper prompt L pop). Two independent examiners evaluated the restorations after 0.5, 1, and 2 years using the modified Ryge criteria. The Kaplan–Meier survival method was applied to estimate survival percentages. A high proportion of restorations were lost during the study period. Therefore, the first hypothesis could not be tested. No statistically significant difference was observed between the cumulative survival percentages of restorations produced by the two treatment approaches over the 2-year period (ART, 54.1 ± 3.4%; ART with Carisolv™, 46.0 ± 3.4%). This hypothesis was accepted. ART with chemomechanical gel might not provide an added benefit increasing the survival percentages of ART class II composite resin restorations in primary teeth
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