33,972 research outputs found
Competing interactions in two dimensional Coulomb systems: Surface charge heterogeneities in co-assembled cationic-anionic incompatible mixtures
A binary mixture of oppositely charged components confined to a plane such as
cationic and anionic lipid bilayers may exhibit local segregation. The relative
strength of the net short range interactions, which favors macroscopic
segregation, and the long range electrostatic interactions, which favors
mixing, determines the length scale of the finite size or microphase
segregation. The free energy of the system can be examined analytically in two
separate regimes, when considering small density fluctuations at high
temperatures, and when considering the periodic ordering of the system at low
temperatures (F. J. Solis and M. Olvera de la Cruz, J. Chem. Phys. 122, 054905
(2000)). A simple Molecular Dynamics simulation of oppositely charged monomers,
interacting with a short range Lennard Jones potential and confined to a two
dimensional plane, is examined at different strengths of short and long range
interactions. The system exhibits well-defined domains that can be
characterized by their periodic length-scale as well as the orientational
ordering of their interfaces. By adding salt, the ordering of the domains
disappears and the mixture macroscopically phase segregates in agreement with
analytical predictions.Comment: 8 pages, 5 figures, accepted for publication in J. Chem. Phys, Figure
1 include
Simulations of the IMF in Clusters
We review computational approaches to understanding the origin of the Initial
Mass Function (IMF) during the formation of star clusters. We examine the role
of turbulence, gravity and accretion, equations of state, and magnetic fields
in producing the distribution of core masses - the Core Mass Function (CMF).
Observations show that the CMF is similar in form to the IMF. We focus on
feedback processes such as stellar dynamics, radiation, and outflows can reduce
the accreted mass to give rise to the IMF. Numerical work suggests that
filamentary accretion may play a key role in the origin of the IMF.Comment: 8 pages, 1 (4 part) figure, refereed conference proceedings - invited
review, to appear in Proceedings of IAU Symposium 270, 2010 "Computational
Star Formation", J. Alves, B.G. Elmegreen, J. Miquel, & V. Trimble (eds.
Exposure of ciprofloxacin-resistant Escherichia coli broiler isolates to subinhibitory concentrations of a quaternary ammonium compound does not increase antibiotic resistance gene transfer
Resistance to antibiotics threatens to become a worldwide health problem. An important attributing phenomenon in this context is that pathogens can acquire antibiotic resistance genes through conjugative transfer of plasmids. To prevent bacterial infections in agricultural settings, the use of veterinary hygiene products, such as disinfectants, has gained popularity and questions have been raised about their contribution to such spreading of antibiotic resistance. Therefore, this study investigated the effect of subinhibitory concentrations of benzalkoniumchloride (BKC), a quaternary ammonium compound (QAC), on the conjugative transfer of antibiotic resistance genes. Five Escherichia coli field strains originating from broiler chickens and with known transferable plasmid-mediated ciprofloxacin resistance were exposed to subinhibitory BKC concentrations: 1/3, 1/10 and 1/30 of the minimum bactericidal concentration. Antibiotic resistance transfer was assessed by liquid mating for 4 h at 25 degrees C using E. coli K12 MG1655 as recipient strain. The transfer ratio was calculated as the number of transconjugants divided by the number of recipients. Without exposure to BKC, the strains showed a ciprofloxacin resistance transfer ratio ranging from 10(-4) to 10(-7). No significant effect of exposure to subinhibitory concentrations of BKC was observed on this transfer ratio
Why Local Party Leaders Don't Support Nominating Centrists
Would giving party leaders more influence in primary elections in the United States decrease elite polarization? Some scholars have argued that political party leaders tend to support centrist candidates in the hopes of winning general elections. In contrast, the authors argue that many local party leaders - especially Republicans - may not believe that centrists perform better in elections and therefore may not support nominating them. They test this argument using data from an original survey of 1,118 county-level party leaders. In experiments, they find that local party leaders most prefer nominating candidates who are similar to typical co-partisans, not centrists. Moreover, given the choice between a more centrist and more extreme candidate, they strongly prefer extremists: Democrats do so by about 2 to 1 and Republicans by 10 to 1. Likewise, in open-ended questions, Democratic Party leaders are twice as likely to say they look for extreme candidates relative to centrists; Republican Party leaders are five times as likely. Potentially driving these partisan differences, Republican leaders are especially likely to believe that extremists can win general elections and overestimate the electorate's conservatism by double digits
Noise Prevents Singularities in Linear Transport Equations
A stochastic linear transport equation with multiplicative noise is
considered and the question of no-blow-up is investigated. The drift is assumed
only integrable to a certain power. Opposite to the deterministic case where
smooth initial conditions may develop discontinuities, we prove that a certain
Sobolev degree of regularity is maintained, which implies H\"older continuity
of solutions. The proof is based on a careful analysis of the associated
stochastic flow of characteristics
Untwisting of a cholesteric elastomer by a mechanical field
A mechanical strain field applied to a monodomain cholesteric elastomer will
unwind the helical director distribution. There is an analogy with the
classical problem of an electric field applied to a cholesteric liquid crystal,
but with important differences. Frank elasticity is of minor importance unless
the gel is very weak. The interplay is between director anchoring to the rubber
elastic matrix and the external mechanical field. Stretching perpendicular to
the helix axis induces the uniform unwound state via the elimination of sharp,
pinned twist walls above a critical strain. Unwinding through conical director
states occurs when the elastomer is stretched along the helical axis.Comment: 4 pages, RevTeX 3 style, 3 EPS figure
Decreasing initial telomere length in humans intergenerationally understates age-associated telomere shortening
Telomere length shortens with aging, and short telomeres have been linked to a wide variety of pathologies. Previous studies suggested a discrepancy in age-associated telomere shortening rate estimated by cross-sectional studies versus the rate measured in longitudinal studies, indicating a potential bias in cross-sectional estimates. Intergenerational changes in initial telomere length, such as that predicted by the previously described effect of a father's age at birth of his offspring (FAB), could explain the discrepancy in shortening rate measurements. We evaluated whether changes occur in initial telomere length over multiple generations in three large datasets and identified paternal birth year (PBY) as a variable that reconciles the difference between longitudinal and cross-sectional measurements. We also clarify the association between FAB and offspring telomere length, demonstrating that this effect is substantially larger than reported in the past. These results indicate the presence of a downward secular trend in telomere length at birth over generational time with potential public health implications
Information dynamics: patterns of expectation and surprise in the perception of music
This is a postprint of an article submitted for consideration in Connection Science © 2009 [copyright Taylor & Francis]; Connection Science is available online at:http://www.tandfonline.com/openurl?genre=article&issn=0954-0091&volume=21&issue=2-3&spage=8
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