On star formation in primordial protoglobular clouds

Using a new physical model for star formation (Padoan 1995) we have tested the possibility that globular clusters (GCs) are formed from primordial mass fluctuations, whose mass scale ($10^8$ - $10^9$ M$_{\odot}$) is selected out of a CDM spectrum by the mechanism of non-equilibrium formation of $H_2$. We show that such clouds are able to convert about 0.003 of their total mass into a bound system (GC) and about 0.02 into halo stars. The metal enriched gas is dispersed away from the GC by supernova explosions and forms the galactic disk. These mass ratios between GCs, halo and disk depend on the predicted IMF which is a consequence of the universal statistics of fluid turbulence. They also depend on the ratio of baryonic over non-baryonic mass ,$X_b$, and are comparable with the values observed in typical spiral galaxies for $X_b \approx 0.1-0.2$. The computed mass and radius for a GC ( $5\times 10^5$ M$_{\odot}$ and 30 pc) are in good agreement with the average values in the Galaxy. The model predicts an exponential cut off in the stellar IMF below 0.1 M$_{\odot}$ in GCs and 0.6 M$_{\odot}$ in the halo. The quite massive star formation in primordial clouds leads to a large number of supernovae and to a high blue luminosity during the first two Gyr of the life of every galaxy

Analysis of unidirectional non-paraxial invisibility of purely reflective PT-symmetric volume gratings

We study the diffraction produced by a slab of purely reflective PT-symmetric volume Bragg grating that combines modulations of refractive index and gain/loss of the same periodicity with a quarter-period shift between them. Such a complex grating has a directional coupling between the different diffraction orders, which allows us to find an analytic solution for the first three orders of the full Maxwell equations without resorting to the paraxial approximation. This is important, because only with the full equations can the boundary conditions, allowing for the reflections, be properly implemented. Using our solution we analyze unidirectional invisibility of such a grating in a wide variety of configurations.Comment: 17 pages, 11 figures. arXiv admin note: text overlap with arXiv:1412.050

Email Babel: Does Language Affect Criminal Activity in Compromised Webmail Accounts?

We set out to understand the effects of differing language on the ability of cybercriminals to navigate webmail accounts and locate sensitive information in them. To this end, we configured thirty Gmail honeypot accounts with English, Romanian, and Greek language settings. We populated the accounts with email messages in those languages by subscribing them to selected online newsletters. We hid email messages about fake bank accounts in fifteen of the accounts to mimic real-world webmail users that sometimes store sensitive information in their accounts. We then leaked credentials to the honey accounts via paste sites on the Surface Web and the Dark Web, and collected data for fifteen days. Our statistical analyses on the data show that cybercriminals are more likely to discover sensitive information (bank account information) in the Greek accounts than the remaining accounts, contrary to the expectation that Greek ought to constitute a barrier to the understanding of non-Greek visitors to the Greek accounts. We also extracted the important words among the emails that cybercriminals accessed (as an approximation of the keywords that they searched for within the honey accounts), and found that financial terms featured among the top words. In summary, we show that language plays a significant role in the ability of cybercriminals to access sensitive information hidden in compromised webmail accounts

Theory and applications of carbon-13 NMR spectroscopy

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Construct validity, dimensionality and factorial invariance of the Rosenberg Self Esteem Scale: A bifactor modelling approach among children of prisoners

The Rosenberg Self Esteem Scale (RSES; Rosenberg, 1989) has traditionally been conceptualised as a unidimensional measure of self-esteem but empirical evidence is equivocal, with some studies supporting a one-factor solution and others favouring multidimensional models. The aim of this study was to examine the factor structure, factorial invariance and composite reliability of the RSES within a European sample of children affected by parental imprisonment (N = 724). The study specified and tested six alternative factor models using conventional confirmatory factor analytic (CFA) techniques and a confirmatory bifactor modelling approach. The RSES was most effectively represented by a bifactor model including a general self-esteem factor comprising of all ten scale items and separate method effects for the positively and negatively phrased items. This model was found to be factorially invariant among boys and girls. Composite reliability indicated good internal consistency for the general self-esteem dimension but slightly less so for the positive and negative methods effects. Results are discussed in terms resolving the debate surrounding the appropriate factor structure and scoring of the RSES