166 research outputs found
Investigation of phase separation within the generalized Lin-Taylor model for a binary liquid mixture of large hexagonal and small triangular particles
The generalized Lin-Taylor model defined on the hexagonal lattice is used to
investigate the phase separation in an asymmetric binary liquid mixture
consisting of large A (hexagons) and small B (triangles) particles. By
considering interaction energies between A-A and A-B pairs of particles that
occupy nearest-neighbour cells of the hexagonal lattice, we have derived an
exact solution for the considered model system having established a mapping
correspondence with the two-dimensional Ising model on its dual triangular
lattice. Altogether, six different types of coexistence curves including those
with reentrant miscibility regions (i.e. closed-loop coexistence curves) were
found in dependence on the relative strength between both coupling constants.Comment: 8 pages, 4 figures, presented at 7th Liblice conference on the
Statistical Mechanics of Liquids to be held in Lednice on June 11-16, 200
From Isotropic to Anisotropic Side Chain Representations: Comparison of Three Models for Residue Contact Estimation
The criterion to determine residue contact is a fundamental problem in deriving knowledge-based mean-force potential energy calculations for protein structures. A frequently used criterion is to require the side chain center-to-center distance or the -to- atom distance to be within a pre-determined cutoff distance. However, the spatially anisotropic nature of the side chain determines that it is challenging to identify the contact pairs. This study compares three side chain contact models: the Atom Distance criteria (ADC) model, the Isotropic Sphere Side chain (ISS) model and the Anisotropic Ellipsoid Side chain (AES) model using 424 high resolution protein structures in the Protein Data Bank. The results indicate that the ADC model is the most accurate and ISS is the worst. The AES model eliminates about 95% of the incorrectly counted contact-pairs in the ISS model. Algorithm analysis shows that AES model is the most computational intensive while ADC model has moderate computational cost. We derived a dataset of the mis-estimated contact pairs by AES model. The most misjudged pairs are Arg-Glu, Arg-Asp and Arg-Tyr. Such a dataset can be useful for developing the improved AES model by incorporating the pair-specific information for the cutoff distance
Thermodynamics of the system Fe-Si-O under high pressure and temperature and its implications for Earth's core
Six Year Refractive Change among White Children and Young Adults: Evidence for Significant Increase in Myopia among White UK Children
OBJECTIVE:To determine six-year spherical refractive error change among white children and young adults in the UK and evaluate differences in refractive profiles between contemporary Australian children and historical UK data. DESIGN:Population-based prospective study. PARTICIPANTS:The Northern Ireland Childhood Errors of Refraction (NICER) study Phase 1 examined 1068 children in two cohorts aged 6-7 years and 12-13 years. Prospective data for six-year follow-up (Phase 3) are available for 212 12-13 year olds and 226 18-20 year olds in each cohort respectively. METHODS:Cycloplegic refractive error was determined using binocular open-field autorefraction (Shin-Nippon NVision-K 5001, cyclopentolate 1%). Participants were defined by spherical equivalent refraction (SER) as myopic SER ≤-0.50D, emmetropic -0.50D<SER<+2.00 or hyperopic SER≥+2.00D. MAIN OUTCOME MEASURES:Proportion and incidence of myopia. RESULTS:The proportion of myopes significantly increased between 6-7 years (1.9%) and 12-13 years (14.6%) (p<0.001) but not between 12-13 and 18-20 years (16.4% to 18.6%, p = 0.51). The estimated annual incidence of myopia was 2.2% and 0.7% for the younger and older cohorts respectively. There were significantly more myopic children in the UK at age 12-13 years in the NICER study (16.4%) than reported in Australia (4.4%) (p<0.001). However by 17 years the proportion of myopia neared equivalence in the two populations (NICER 18.6%, Australia 17.7%, p = 0.75). The proportion of myopic children aged 12-13 years in the present study (2006-2008) was 16.4%, significantly greater than that reported for children aged 10-16 years in the 1960's (7.2%, p = 0.01). The proportion of hyperopes in the younger NICER cohort decreased significantly over the six year period (from 21.7% to 14.2%, p = 0.04). Hyperopes with SER ≥+3.50D in both NICER age cohorts demonstrated persistent hyperopia. CONCLUSIONS:The incidence and proportion of myopia are relatively low in this contemporary white UK population in comparison to other worldwide studies. The proportion of myopes in the UK has more than doubled over the last 50 years in children aged between 10-16 years and children are becoming myopic at a younger age. Differences between the proportion of myopes in the UK and in Australia apparent at 12-13 years were eliminated by 17 years of age
A Natural Supersymmetric Model with MeV Dark Matter
It has previously been proposed that annihilating dark matter particles with
MeV-scale masses could be responsible for the flux of 511 keV photons observed
from the region of the Galactic Bulge. The conventional wisdom, however, is
that it is very challenging to construct a viable particle physics model
containing MeV dark matter. In this letter, we challenge this conclusion by
describing a simple and natural supersymmetric model in which the lightest
supersymmetric particle naturally has a MeV-scale mass and the other
phenomenological properties required to generate the 511 keV emission. In
particular, the small ( ) effective couplings between dark
matter and the Standard Model fermions required in this scenario naturally lead
to radiative corrections that generate MeV-scale masses for both the dark
matter candidate and the mediator particle.Comment: 4 pages, 1 figure. v2: Small modification to discussion of spectru
Density, Viscosity and Surface Tension of Binary Mixtures of 1-Butyl-1-Methylpyrrolidinium Tricyanomethanide with Benzothiophene
Low serum vitamin D is associated with axial length and risk of myopia in young children
Probability Theory in Statistical Physics, Percolation, and Other Random Topics: The Work of C. Newman
In the introduction to this volume, we discuss some of the highlights of the
research career of Chuck Newman. This introduction is divided into two main
sections, the first covering Chuck's work in statistical mechanics and the
second his work in percolation theory, continuum scaling limits, and related
topics.Comment: 38 pages (including many references), introduction to Festschrift in
honor of C.M. Newma
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