17,775 research outputs found

    How is the Reionization Epoch Defined?

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    We study the effect of a prolonged epoch of reionization on the angular power spectrum of the Cosmic Microwave Background. Typically reionization studies assume a sudden phase transition, with the intergalactic gas moving from a fully neutral to a fully ionized state at a fixed redshift. Such models are at odds, however, with detailed investigations of reionization, which favor a more extended transition. We have modified the code CMBFAST to allow the treatment of more realistic reionization histories and applied it to data obtained from numerical simulations of reionization. We show that the prompt reionization assumed by CMBFAST in its original form heavily contaminates any constraint derived on the reionization redshift. We find, however, that prompt reionization models give a reasonable estimate of the epoch at which the mean cosmic ionization fraction was ~50%, and provide a very good measure of the overall Thomson optical depth. The overall differences in the temperature (polarization) angular power spectra between prompt and extended models with equal optical depths are less than 1% (10%).Comment: 5 pages, 3 figures; accepted on MNRA

    Breaking of the adjoint string in 2+1 dimensions

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    The roughly linear rise of the potential found between adjoint sources in SU(N) in lattice simulations is expected to saturate into a state of two `gluelumps' due to gluonic screening. We examine this in SU(2) in 2+1 dimensions. Crossover between string-like and broken states is clearly seen by the mixing-matrix technique, using different operators to probe the two states; the breaking behaviour is rather abrupt. Furthermore, we are able to show that both types of operator have a finite overlap with both states; in the case of the Wilson loops the overlap with the broken string is, as predicted, very small.Comment: LaTeX2e, 20 pages, 15 figures with epsfig; uses amstex, amssymb, a4wide; minor change to presentation (notation for operators) onl

    Internet addiction in adolescents: prevalence and risk factors

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    As new media are becoming daily fare, Internet addiction appears as a potential problem in adolescents. From the reported negative consequences, it appears that Internet addiction can have a variety of detrimental outcomes for young people that may require professional intervention. Researchers have now identified a number of activities and personality traits associated with Internet addiction. This study aimed to synthesise previous findings by (i) assessing the prevalence of potential Internet addiction in a large sample of adolescents, and (ii) investigating the interactions between personality traits and the usage of particular Internet applications as risk factors for Internet addiction. A total of 3,105 adolescents in the Netherlands filled out a self-report questionnaire including the Compulsive Internet Use Scale and the Quick Big Five Scale. Results indicate that 3.7% of the sample were classified as potentially being addicted to the Internet. The use of online gaming and social applications (online social networking sites and Twitter) increased the 2 risk for Internet addiction, whereas extraversion and conscientiousness appeared as protective factors in high frequency online gamers. The findings support the inclusion of 'Internet addiction' in the DSM-V. Vulnerability and resilience appear as significant aspects that require consideration in further studies
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