2,230 research outputs found

    Polymer translocation through a nanopore under an applied external field

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    We investigate the dynamics of polymer translocation through a nanopore under an externally applied field using the 2D fluctuating bond model with single-segment Monte Carlo moves. We concentrate on the influence of the field strength EE, length of the chain NN, and length of the pore LL on forced translocation. As our main result, we find a crossover scaling for the translocation time τ\tau with the chain length from τN2ν\tau \sim N^{2\nu} for relatively short polymers to τN1+ν\tau \sim N^{1 + \nu} for longer chains, where ν\nu is the Flory exponent. We demonstrate that this crossover is due to the change in the dependence of the translocation velocity v on the chain length. For relatively short chains vNνv \sim N^{- \nu}, which crosses over to vN1v \sim N^{- 1} for long polymers. The reason for this is that with increasing NN there is a high density of segments near the exit of the pore, which slows down the translocation process due to slow relaxation of the chain. For the case of a long nanopore for which RR_\parallel , the radius of gyration RgR_{g} along the pore, is smaller than the pore length, we find no clear scaling of the translocation time with the chain length. For large NN, however, the asymptotic scaling τN1+ν\tau \sim N^{1 + \nu} is recovered. In this regime, τ\tau is almost independent of LL. We have previously found that for a polymer, which is initially placed in the middle of the pore, there is a minimum in the escape time for RLR_\parallel \approx L. We show here that this minimum persists for a weak fields EE such that ELEL is less than some critical value, but vanishes for large values of ELEL.Comment: 25 Pages, 10 figures. Submitted to J. Chem. Phys. J. Chem. Phys. 124, in press (2006

    Understanding the Recent Growth in Consumer Loans and Credit Cards in Emerging Markets:Evidence from Turkey

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    In recent years, the surge in household indebtedness to historical heights has become a significant concern for developed economies. A similar trend has been witnessed in emerging market countries including Turkey. Our objective is to help further understand the dynamics of the recent growth in consumer loans and credit cards (CLCC) in Turkey. For this purpose, we investigate the long-term equilibrating relationships and short-term deviations from the equilibrium, and explore the determinants, directions, and strengths of causality relationships between CLCC and the selected macroeconomic variables, and analyze the dynamic interactions among the variables in the post-sample period by analyzing how CLCC responds to the shocks given to other macroeconomic variables and the contribution of each variable on the forecast variability of CLCC. We use monthly data for the period of January 2004—December 2013 of seven macroeconomic variables of money supply, interest rate, income, consumer confidence, inflation, stock market, and consumer goods imports. On empirical findings, we make suggestions about which policy tools should be used to influence, and if necessary to manage, the growth in CLCC. Copyright © Taylor & Francis Group, LLC

    On Shape Transformations and Shape Fluctuations of Cellular Compartments and Vesicles

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    We discuss the shape formation and shape transitions of simple bilayer vesicles in context with their role in biology. In the first part several classes of shape changes of vesicles of one lipid component are described and it is shown that these can be explained in terms of the bending energy concept in particular augmented by the bilayer coupling hypothesis. In the second part shape changes and vesicle fission of vesicles composed of membranes of lipid mixtures are reported. These are explained in terms of coupling between local curvature and phase separation

    A database of microRNA expression patterns in Xenopus laevis

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    MicroRNAs (miRNAs) are short, non-coding RNAs around 22 nucleotides long. They inhibit gene expression either by translational repression or by causing the degradation of the mRNAs they bind to. Many are highly conserved amongst diverse organisms and have restricted spatio-temporal expression patterns during embryonic development where they are thought to be involved in generating accuracy of developmental timing and in supporting cell fate decisions and tissue identity. We determined the expression patterns of 180 miRNAs in Xenopus laevis embryos using LNA oligonucleotides. In addition we carried out small RNA-seq on different stages of early Xenopus development, identified 44 miRNAs belonging to 29 new families and characterized the expression of 5 of these. Our analyses identified miRNA expression in many organs of the developing embryo. In particular a large number were expressed in neural tissue and in the somites. Surprisingly none of the miRNAs we have looked at show expression in the heart. Our results have been made freely available as a resource in both XenMARK and Xenbase

    Large-scale associations between the leukocyte transcriptome and BOLD responses to speech differ in autism early language outcome subtypes.

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    Heterogeneity in early language development in autism spectrum disorder (ASD) is clinically important and may reflect neurobiologically distinct subtypes. Here, we identified a large-scale association between multiple coordinated blood leukocyte gene coexpression modules and the multivariate functional neuroimaging (fMRI) response to speech. Gene coexpression modules associated with the multivariate fMRI response to speech were different for all pairwise comparisons between typically developing toddlers and toddlers with ASD and poor versus good early language outcome. Associated coexpression modules were enriched in genes that are broadly expressed in the brain and many other tissues. These coexpression modules were also enriched in ASD-associated, prenatal, human-specific, and language-relevant genes. This work highlights distinctive neurobiology in ASD subtypes with different early language outcomes that is present well before such outcomes are known. Associations between neuroimaging measures and gene expression levels in blood leukocytes may offer a unique in vivo window into identifying brain-relevant molecular mechanisms in ASD

    Understanding the influence of race/Ethnicity, gender, and class on inequalities in academic and non-academic outcomes among eighth-grade students: findings from an intersectionality approach

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    Socioeconomic, racial/ethnic, and gender inequalities in academic achievement have been widely reported in the US, but how these three axes of inequality intersect to determine academic and non-academic outcomes among school-aged children is not well understood. Using data from the US Early Childhood Longitudinal Study—Kindergarten (ECLS-K; N = 10,115), we apply an intersectionality approach to examine inequalities across eighth-grade outcomes at the intersection of six racial/ethnic and gender groups (Latino girls and boys, Black girls and boys, and White girls and boys) and four classes of socioeconomic advantage/disadvantage. Results of mixture models show large inequalities in socioemotional outcomes (internalizing behavior, locus of control, and self-concept) across classes of advantage/disadvantage. Within classes of advantage/disadvantage, racial/ethnic and gender inequalities are predominantly found in the most advantaged class, where Black boys and girls, and Latina girls, underperform White boys in academic assessments, but not in socioemotional outcomes. In these latter outcomes, Black boys and girls perform better than White boys. Latino boys show small differences as compared to White boys, mainly in science assessments. The contrasting outcomes between racial/ethnic and gender minorities in self-assessment and socioemotional outcomes, as compared to standardized assessments, highlight the detrimental effect that intersecting racial/ethnic and gender discrimination have in patterning academic outcomes that predict success in adult life. Interventions to eliminate achievement gaps cannot fully succeed as long as social stratification caused by gender and racial discrimination is not addressed

    Religion, Partisanship, and Attitudes Toward Science Policy

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    We examine issues involving science which have been contested in recent public debate. These “contested science” issues include human evolution, stem-cell research, and climate change. We find that few respondents evince consistently skeptical attitudes toward science issues, and that religious variables are generally strong predictors of attitudes toward individual issues. Furthermore, and contrary to analyses of elite discourse, partisan identification is not generally predictive of attitudes toward contested scientific issues
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