Spectroscopic test of Bose-Einstein statistics for photons

Using Bose-Einstein-statistics-forbidden two-photon excitation in atomic barium, we have limited the rate of statistics-violating transitions, as a fraction $\nu$ of an equivalent statistics-allowed transition rate, to $\nu<4.0\times10^{-11}$ at the 90% confidence level. This is an improvement of more than three orders of magnitude over the best previous result. Additionally, hyperfine-interaction enabling of the forbidden transition has been observed, to our knowledge, for the first time

Investigation into the limits of perturbation theory at low Q^2 using HERA deep inelastic scattering data

A phenomenological study of the final combined HERA data on inclusive deep inelastic scattering (DIS) has been performed. The data are presented and investigated for a kinematic range extending from values of the four-momentum transfer, $Q^2$, above 10$^4$ GeV$^2$ down to the lowest values observable at HERA of $Q^2$ = 0.045 GeV$^2$ and Bjorken $x$, $x_{\rm Bj}$ = 6 $\cdot$ 10$^{-7}$. The data are well described by fits based on perturbative quantum chromodynamics (QCD) using collinear factorisation and evolution of the parton densities encompassed in the DGLAP formalism from the highest $Q^2$ down to $Q^2$ of a few GeV$^2$. The Regge formalism can describe the data up to $Q^2 \approx$ 0.65 GeV$^2$. The complete data set can be described by a new fit using the ALLM parameterisation. The region between the Regge and the perturbative QCD regimes is of particular interest.Comment: 38 pages, 13 figure

Comorbidity of respiratory and cardiovascular diseases among the elderly residing close to mine dumps in South Africa: A cross-sectional study

Background. Pollution arising from mine dumps in South Africa (SA) has been a source of concern to nearby communities.Objective. To investigate whether comorbidity of respiratory and cardiovascular diseases among elderly persons (≥55 years) was associated with proximity to mine dumps.Methods. Elderly persons in communities 1 - 2 km (exposed) and ≥5 km (unexposed) from five preselected mine dumps in Gauteng and North West provinces in SA were included in a cross-sectional study.Results. Exposed elderly persons had a significantly higher prevalence of cardiovascular and respiratory diseases than those who were unexposed. Multiple logistic regression analysis indicated that living close to mine dumps was significantly associated with asthma + hypertension (odds ratio (OR) 1.67; 95% confidence interval (CI) 1.22 - 2.28), asthma + pneumonia (OR 1.86; 95% CI 1.14 - 3.04), emphysema + arrhythmia (OR 1.38; 95% CI 1.07 - 1.77), emphysema + myocardial infarction (OR 2.01; 95% CI 1.73 - 2.54), emphysema + pneumonia (OR 3.36; 95% CI 1.41 - 7.98), hypertension + myocardial infarction (OR 1.60; 95% CI 1.04 - 2.44) and hypertension + pneumonia (OR 1.34; 95% CI 1.05 - 1.93).Conclusion. Detrimental associations between comorbidity of the health outcomes and proximity to mine dumps were observed among the elderly in SA

On the interaction of a single-photon wave packet with an excited atom

The interaction of a single-photon wave packet with an initially excited two-level atom in free space is studied in semiclassical and quantum approaches. It is shown that the final state of the field does not contain doubly occupied modes. The process of the atom's transition to the ground state may be accelerated, decelerated or even reversed by the incoming photon, depending on parameters. The spectrum of emitted radiation is close to the sum of the spectrum of the incoming single-photon wave packet and the natural line shape, with small and complicated deviations.Comment: 17 pages, 5 figure

Modeling two-language competition dynamics

During the last decade, much attention has been paid to language competition in the complex systems community, that is, how the fractions of speakers of several competing languages evolve in time. In this paper we review recent advances in this direction and focus on three aspects. First we consider the shift from two-state models to three state models that include the possibility of bilingual individuals. The understanding of the role played by bilingualism is essential in sociolinguistics. In particular, the question addressed is whether bilingualism facilitates the coexistence of languages. Second, we will analyze the effect of social interaction networks and physical barriers. Finally, we will show how to analyze the issue of bilingualism from a game theoretical perspective.Comment: 15 pages, 5 figures; published in the Special Issue of Advances in Complex Systems "Language Dynamics

Universals versus historical contingencies in lexical evolution

© 2014 The Author(s) Published by the Royal Society. All rights reserved. The frequency with which we use different words changes all the time, and every so often, a new lexical item is invented or another one ceases to be used. Beyond a small sample of lexical items whose properties are well studied, little is known about the dynamics of lexical evolution. How do the lexical inventories of languages, viewed as entire systems, evolve? Is the rate of evolution of the lexicon contingent upon historical factors or is it driven by regularities, perhaps to do with universals of cognition and social interaction?We address these questions using the Google Books N-Gram Corpus as a source of data and relative entropy as a measure of changes in the frequency distributions of words. It turns out that there are both universals and historical contingencies at work. Across several languages, we observe similar rates of change, but only at timescales of at least around five decades. At shorter timescales, the rate of change is highly variable and differs between languages. Major societal transformations as well as catastrophic events such as wars lead to increased change in frequency distributions, whereas stability in society has a dampening effect on lexical evolution

``Superfast'' Reaction in Turbulent Flow with Potential Disorder

We explore the regime of ``superfast'' reactivity that has been predicted to occur in turbulent flow in the presence of potential disorder. Computer simulation studies confirm qualitative features of the previous renormalization group predictions, which were based on a static model of turbulence. New renormalization group calculations for a more realistic, dynamic model of turbulence show that the superfast regime persists. This regime, with concentration decay exponents greater than that for a well-mixed reaction, appears to be a general result of the interplay among non-linear reaction kinetics, turbulent transport, and local trapping by potential disorder.Comment: 14 pages. 4 figures. Uses IOP styles. To appear in J. Phys. A: Math. Ge

Using WALS and Jazyki mira

The article's primary concern is to address the usage of The world atlas of language structures through comparing it with another typological database of similar scope, Jazyki mira. Such a comparison is carried out based on a set of criteria. First, the scope of the databases is compared, as well as their differences and similarities in structure, in the number of errors, and in the existing user interfaces. Then calculations of typological similarity and temporal stability of language features based on the data provided by both databases are compared. Finally, conclusions are drawn as to the relative efficiency and usefulness of these databases for different aims of research or educational goals. © Walter de Gruyter

Comorbidity of respiratory and cardiovascular diseases among the elderly residing close to mine dumps in South Africa: A cross-sectional study.

Background. Pollution arising from mine dumps in South Africa (SA) has been a source of concern to nearby communities.Objectives. To investigate whether comorbidity of respiratory and cardiovascular diseases among elderly persons (≥55 years) was associated with proximity to mine dumps.Methods. Elderly persons in communities 1 - 2 km (exposed) and ≥5 km (unexposed) from five preselected mine dumps in Gauteng and North West provinces in SA were included in a cross-sectional study.Results. Exposed elderly persons had a significantly higher prevalence of cardiovascular and respiratory diseases than those who were unexposed. Multiple logistic regression analysis indicated that living close to mine dumps was significantly associated with asthma + hyper- tension (odds ratio (OR) 1.67; 95% confidence interval (CI) 1.22 - 2.28), asthma + pneumonia (OR 1.86; 95% CI 1.14 - 3.04), emphysema + arrhythmia (OR 1.38; 95% CI 1.07 - 1.77), emphysema + myocardial infarction (OR 2.01; 95% CI 1.73 - 2.54), emphysema + pneumonia (OR 3.36; 95% CI 1.41 - 7.98), hypertension + myocardial infarction (OR 1.60; 95% CI 1.04 - 2.44) and hypertension + pneumonia (OR 1.34; 95% CI 1.05 - 1.93).Conclusion. Detrimental associations between comorbidity of the health outcomes and proximity to mine dumps were observed among the elderly in SA.