One-dimensional semiconductor in a polar solvent: Solvation and low-frequency dynamics of an excess charge carrier

Due to solvation, excess charge carriers on 1d semiconductor nanostructures immersed in polar solvents undergo self-localization into polaronic states. Using a simplified theoretical model for small-diameter structures, we study low-frequency properties of resulting 1d adiabatic polarons. The combined microscopic dynamics of the electronic charge density and the solvent leads to macroscopic Langevin dynamics of a polaron and to the appearance of local dielectric relaxation modes. Polaron mobility is evaluated as a function of system parameters. Numerical estimates indicate that the solvated carriers can have mobilities orders of magnitude lower than the intrinsic values.Comment: Typo in Eq.(12) has been correcte

Homotypic and heterotypic continuity of fine-grained temperament during infancy, toddlerhood, and early childhood

Longitudinal continuity was investigated for fine-grained and factor-level aspects of temperament measured with the Infant Behaviour Questionnaire-Revised (IBQ-R), Early Childhood Behaviour Questionnaire (ECBQ), and Children\u27s Behaviour Questionnaire (CBQ). Considerable homotypic continuity was found. Convergent and discriminant validity of the measures was supported, as all fine-grained dimensions exhibited stability across adjacent measurement periods, and all scales found on both the ECBQ and CBQ were most highly correlated with their equivalent scales. At the factor level, Surgency and Negative Affect factors were stable across all time points, and Effortful Control/Regulatory Capacity was stable across adjacent time periods. High-Intensity Pleasure, Activity Level, and Impulsivity contributed strongly to continuity of Surgency, and Sadness, Frustration, and Falling Reactivity played strong roles in the continuity of Negative Affect. Heterotypic continuity was also found. High levels of Infant Surgency predicted high toddler Effortful Control, whereas high toddler Surgency predicted low Effortful Control in preschoolers. Infant Surgency dimensions especially predicted Toddler Attention Shifting and Low-Intensity Pleasure, and toddler Activity Level was most closely associated with later deficits in Effortful Control. Inverse relations were also obtained between Negative Affect and Effortful Control, with substantial negative connections between toddler Negative Affect and preschool Attention Focusing and Inhibitory Control. Copyright © 2008 John Wiley & Sons, Ltd

Comparative Genomics of Streptococcus oralis Identifies Large Scale Homologous Recombination and a Genetic Variant Associated with Infection

The viridans group streptococci (VGS) are a large consortium of commensal streptococci that colonize the human body. Many species within this group are opportunistic pathogens causing bacteremia and infective endocarditis (IE), yet little is known about why some strains cause invasive disease. Identification of virulence determinants is complicated by the difficulty of distinguishing between the closely related species of this group. Here, we analyzed genomic data from VGS that were isolated from blood cultures in patients with invasive infections and oral swabs of healthy volunteers and then determined the best-performing methods for species identification. Using whole-genome sequence data, we characterized the population structure of a diverse sample of Streptococcus oralis isolates and found evidence of frequent recombination. We used multiple genome-wide association study tools to identify candidate determinants of invasiveness. These tools gave consistent results, leading to the discovery of a single synonymous single nucleotide polymorphism (SNP) that was significantly associated with invasiveness. This SNP was within a previously undescribed gene that was conserved across the majority of VGS species. Using the growth in the presence of human serum and a simulated infective endocarditis vegetation model, we were unable to identify a phenotype for the enriched allele in laboratory assays, suggesting a phenotype may be specific to natural infection. These data highlighted the power of analyzing natural populations for gaining insight into pathogenicity, particularly for organisms with complex population structures like the VGS. IMPORTANCE The viridians group streptococci (VGS) are a large collection of closely related commensal streptococci, with many being opportunistic pathogens causing invasive diseases, such as bacteremia and infective endocarditis. Little is known about virulence determinants in these species, and there is a distinct lack of genomic information available for the VGS. In this study, we collected VGS isolates from invasive infections and healthy volunteers and performed whole-genome sequencing for a suite of downstream analyses. We focused on a diverse sample of Streptococcus oralis genomes and identified high rates of recombination in the population as well as a single genome variant highly enriched in invasive isolates. The variant lies within a previously uncharacterized gene, nrdM, which shared homology with the anaerobic ribonucleoside triphosphate reductase, nrdD, and was highly conserved among VGS. This work increased our knowledge of VGS genomics and indicated that differences in virulence potential among S. oralis isolates were, at least in part, genetically determined

Model ab initio study of charge carrier solvation and large polaron formation on conjugated carbon chains

Using long C_{N}H_{2} conjugated carbon chains with the polyynic structure as prototypical examples of one-dimensional (1D) semiconductors, we discuss self-localization of excess charge carriers into 1D large polarons in the presence of the interaction with a surrounding polar solvent. The solvation mechanism of self-trapping is different from the polaron formation due to coupling with bond-length modulations of the underlying atomic lattice well-known in conjugated polymers. Model ab initio computations employing the hybrid B3LYP density functional in conjunction with the polarizable continuum model are carried out demonstrating the formation of both electron- and hole-polarons. Polarons can emerge entirely due to solvation but even larger degrees of charge localization occur when accompanied by atomic displacements