Group dynamics and record signals in the ant Temnothorax albipennis

Many purely physical complex systems, in which there are both stochasticity and local interactions between the components, exhibit record dynamics. The temporal statistics of record dynamics is a Poisson process operating on a logarithmic rather than a linear time scale (i.e. a log-Poisson process). Record dynamics often drive substantial changes in complex systems when new high water marks in partially stochastic processes trigger new events. Social insect colonies are exemplary complex biological systems in which many of the local interactions of the components have been moulded by natural selection for the common good. Here, we combine experimental manipulation of ant colony demography with modelling to test the hypothesis that social interactions are the mechanism underlying the record dynamics. We found that compared with the control, log-Poisson statistics were disrupted in colonies in which the pattern of interactions was modified by the removal of the brood, and disappeared completely in ‘callow’ colonies composed entirely of very young workers from the same age cohort. We conclude that a subtle interplay between the demography of the society and the pattern of the interactions between the ants is crucial for the emergence of record dynamics. This could help identify what makes an ant colony a cohesive society.     

Evolutionary events in a mathematical sciences research collaboration network

This study examines long-term trends and shifting behavior in the collaboration network of mathematics literature, using a subset of data from Mathematical Reviews spanning 1985–2009. Rather than modeling the network cumulatively, this study traces the evolution of the “here and now” using fixed-duration sliding windows. The analysis uses a suite of common network diagnostics, including the distributions of degrees, distances, and clustering, to track network structure. Several random models that call these diagnostics as parameters help tease them apart as factors from the values of others. Some behaviors are consistent over the entire interval, but most diagnostics indicate that the network’s structural evolution is dominated by occasional dramatic shifts in otherwise steady trends. These behaviors are not distributed evenly across the network; stark differences in evolution can be observed between two major subnetworks, loosely thought of as “pure” and “applied”, which approximately partition the aggregate. The paper characterizes two major events along the mathematics network trajectory and discusses possible explanatory factors.     

Traveling Reaction Zone Method for Preparation of Textured Ceramic Superconductor Thick Films

Textured thick films of superconducting YBa₂Cu₃O_7−x (YBCO) have been prepared on ceramic substrates using a traveling reaction zone method. The technique utilizes the rapid reaction between Y₂Cu₂O₅ and BaCuO₂ to form YBCO as the film passes through a steep temperature gradient furnance. The films consist of a single continuous superconducting phase with strong c -axis orientation normal to the translation direction of the film.     

Correlation-crystal-field ‘δ-function' analysis of Pr(4f) energy-level structure

Inclusion of two-electron correlation-crystal-field (CCF) contributions to the model (energy-level) Hamiltonian has been shown to resolve disparities between calculated and observed energy-level splittings within problematic multiplet manifolds of Nd³⁺ and Er³⁺ systems. Application of these CCF terms to other problematic multiplets, such as the ¹G₄ and ¹D₂ multiplets of Pr³⁺ has not been feasible, owing to the fact that the number of applicable CCF terms far exceed the number of observed levels in these multiplets. However, this problem may be obviated by use of a simplified ‘δ-function' CCF model that assumes the dominant contributions to the CCF interactions come from paired electrons within the same orbital. In the present study, we examine the 4f²(Pr³⁺) electronic energy-level structures reported for Pr³⁺:LaCl₃, Pr³⁺:GdCl₃, Pr³⁺:Cs₂NaYCl₆ and Cs₂NaPrCl₆ systems and show that inclusion of δ-function CCF interaction parameters resolves the disparities between observed and calculated energy-level splittings for the problematic ¹G₄ and ¹D₂ multiplets of these systems.     

Ear dominance and telephone sales

BACKGROUND: Lyme disease is caused by Borrelia burgdorferi which is transmitted in Europe by the tick ixodes ricinus. Erythema migrans is a skin lesion which is pathognomonic of Lyme disease. A retrospective study was carried out to determine the geographical distribution of the occurrence of tick bites and erythema migrans in the Netherlands and to identify ecological risk factors. METHODS: In April 1995, all general practitioners (GPs) in the Netherlands were asked to complete a postal questionnaire on the number of tick bites and erythema migrans case-patients seen in 1994 and the size of the practice. Reminders were sent to non-responders. Information on ecological risk factors by local government area was obtained from a geographical information system. RESULTS: The response rate was 79.9%. In 1994, GPs reported seeing approximately 33,000 patients with tick bites and 6500 with erythema migrans. The incidence rate of erythema migrans was estimated at 4.3 per 10,000 population. Ecological risk factors for both tick bites and erythema migrans were the proportion of the area covered by woods, sandy soil, dry uncultivated land, the number of tourist-nights per inhabitant and sheep population density. The cattle population density was a risk factor for erythema migrans. CONCLUSIONS: Using simple methods, a crude estimate of the incidence rate of erythema migrans was obtained rapidly, and high risk areas were identified. Lyme disease appears to be an important problem in the Netherlands.     

Determination of the sign of the electric field gradient in indium by nuclear resonance

We have studied the temperature dependence of two of the four magnetic-field perturbed NQR lines in indium. Our results indicate that the sign of the internal electric field gradient (EFG) is positive, in accord with the recent heat capacity measurements of the ISSP group and one recent theoretical prediction. We also discuss the implications of the sign of the EFG on the use of indium as an absolute thermometer below 1 mK.     

Fast subjective video quality measurement with user feedback

A new method for subjective assessment of video material is presented. The proposed method incorporates feedback from the test observer enabling a rapid choice of preferred visual quality. Comparison with an established assessment method indicates that the new method produces comparable results in a fraction of the time normally required to carry out subjective quality assessment.     

Fighting for balance

The proof of diacetylmorphine (heroin) application is based on the identification of its specific metabolite 6-monoacetylmorphine simultaneously detected with the main metabolite morphine in human urine. Codeine is another morphine derivative appearing in cases of diacetylmorphine abuse; it can be considered a metabolite of 6-acetylcodeine, a typical impurity found in raw heroin. An analytical procedure for detection of the mentioned morphine basesin urine is presented, including a screening method. A careful extraction method is required for 6-monoacetylmorphine. To classify it into the code system of the screening, its properties are expressed by a threecomponent code. Subsequent identity confirmation of the mentioned bases by means of thin layer chromatography uses mobile phases, in which optimal separation effects are achieved, even in the presence of nicotine or caffeine and its metabolites theobromine and theophylline. Circumstances of 6-monoacetylmorphine discovery in urine are discussed.     

Quantitative planar laser-induced fluorescence imaging of multi-component fuel/air mixing in a firing gasoline-direct-injection engine: Effects of residual exhaust gas on quantitative PLIF

A study of in-cylinder fuel-air mixing distributions in a firing gasoline-direct-injection engine is reported using planar laser-induced fluorescence (PLIF) imaging. A multi-component fuel synthesised from three pairs of components chosen to simulate light, medium and heavy fractions was seeded with one of three tracers, each chosen to co-evaporate with and thus follow one of the fractions, in order to account for differential volatility of such components in typical gasoline fuels. In order to make quantitative measurements of fuel-air ratio from PLIF images, initial calibration was by recording PLIF images of homogeneous fuel-air mixtures under similar conditions of in-cylinder temperature and pressure using a re-circulation loop and a motored engine. This calibration method was found to be affected by two significant factors. Firstly, calibration was affected by variation of signal collection efficiency arising from build-up of absorbing deposits on the windows during firing cycles, which are not present under motored conditions. Secondly, the effects of residual exhaust gas present in the firing engine were not accounted for using a calibration loop with a motored engine.In order to account for these factors a novel method of PLIF calibration is presented whereby ‘bookend’ calibration measurements for each tracer separately are performed under firing conditions, utilising injection into a large upstream heated plenum to promote the formation of homogeneous in-cylinder mixtures. These calibration datasets contain sufficient information to not only characterise the quantum efficiency of each tracer during a typical engine cycle, but also monitor imaging efficiency, and, importantly, account for the impact of exhaust gas residuals (EGR). By use of this method EGR is identified as a significant factor in quantitative PLIF for fuel mixing diagnostics in firing engines.The effects of cyclic variation in fuel concentration on burn rate are analysed for different fuel injection strategies. Finally, mixture distributions for late injection obtained using quantitative PLIF are compared to predictions of computational fluid dynamics calculations.