Coulomb corrections to e+e−e^+ e^- production in ultra-relativistic nuclear collisions

The purpose of this paper is to explain the discrepancies existing in the literature relative to $e^+e^-$ pair production in peripheral heavy ion collisions at ultra-relativistic energies. A controversial issue is the possible cancellation of Coulomb corrections to the Born term in the pair production cross-section. Such a cancellation has been observed in a recent approach based on finding retarded solutions of the Dirac equation, but does not seem to hold in a perturbative approach. We show in this paper that the two approaches are in fact calculating different observables: the perturbative approach gives the exclusive cross-section of single pair production, while the other method gives the inclusive cross-section. We have also performed a thorough study of the electron propagator in the non-static background field of the two nuclei, the conclusion of which is that the retarded propagator is in the ultra-relativistic limit a much simpler object than the Feynman propagator, and can be calculated exactly.Comment: 31 pages LaTeX document, 10 postscript figures (expanded 3rd section, version to be published in Nucl. Phys. A

Influence of environmental experience on aversive conditioning in honey bees (Apis mellifera L.)

International audiencePrevious experience in a natural environment with a stimulus has lasting influences on honey bee behavior, as demonstrated in laboratory studies of appetitive conditioning. However, it is unknown whether the same holds true for studies of aversive conditioning. Aversive conditioning is important for insects such as honey bees to survive environmental risks. Previous experience in natural settings may lead to maladaptive behavioral patterns in bees exposed to new risks. This study presents the first examination of the effect of a visual stimulus presented in a naturalistic setting on aversive conditioning, using the shuttle box choice chamber paradigm. The present study examines both the effect of the visual stimuli, as well as differences present between the Apis mellifera subspecies of mellifera and ligustica. Results support the presence of behavioral biases based on the visual stimulus presented prior to the experimental sessions

Overshooting Americanisation. Accent stylisation in pop singing – acoustic properties of the bath and trap vowels in focus

The paper addresses the problem of overshoot involved in singing accent stylisation. Selected phonetic features indexed as “American” and “Cockney” are analysed in the singing and speaking styles of a British vocalist, Adele. Overshoot, understood as a greater frequency or an exaggerated quality of a given feature, is characteristic of staged performance (Bell and Gibson 2011; Coupland 2007). PRAAT is used to establish the acoustic properties (F1 and F2) of the BATH and TRAP vowels, as well as the presence or absence of the BATH-TRAP split. The results show that Americanisation regarding the BATH-TRAP split in singing is present and the Americanised vowel tokens are “overshot”, having higher F2 frequency compared with the regular British TRAP vowel

Two Planets, One Species: Does a Mission to Mars Alter the Balance in Favour of Human Enhancement?

In this chapter we examine the implications of a crewed mission to Mars, possible colonisation of the planet, and the wider implications this may have on genetic enhancement in both a terrestrial and space context. We consider the usage of both somatic and germ-line genetic engineering, and its potential impact on the evolution of Homo sapiens. We acknowledge that a mission to Mars may require the usage of such technologies if it is to be successful. Our investigation suggests that the use of such technologies might ultimately be linked with the transformation of our own species. We also consider projected timescales for the development of these genetic enhancements and the ethical questions raised by the possibility of speciation. Cooperation among spacefaring nations in this context and the development of norms for the use of such technologies is desirable

A Prospective Study of the Association of Metacognitive Beliefs and Processes with Persistent Emotional Distress After Diagnosis of Cancer

Two hundred and six patients, diagnosed with primary breast or prostate cancer completed self-report questionnaires on two occasions: before treatment (T1) and 12 months later (T2). The questionnaires included: the Hospital Anxiety and Depression Scale; Impact of Events Scale; the Metacognitions Questionnaire-30 (MCQ-30) and the Illness Perceptions Questionnaire-revised. A series of regression analyses indicated that metacognitive beliefs at T1 predicted between 14 and 19 % of the variance in symptoms of anxiety, depression and trauma at T2 after controlling for age and gender. For all three outcomes, the MCQ-30 subscale ‘negative beliefs about worry’ made the largest individual contribution with ‘cognitive confidence’ also contributing in each case. For anxiety, a third metacognitive variable, ‘positive beliefs about worry’ also predicted variance in T2 symptoms. In addition, hierarchical analyses indicated that metacognitive beliefs explained a small but significant amount of variance in T2 anxiety (2 %) and T2 depression (4 %) over and above that explained by demographic variables, T1 symptoms and T1 illness perceptions. The findings suggest that modifying metacognitive beliefs and processes has the potential to alleviate distress associated with cancer

Hierarchical spin-orbital polarisation of a giant Rashba system

The Rashba effect is one of the most striking manifestations of spin-orbit coupling in solids, and provides a cornerstone for the burgeoning field of semiconductor spintronics. It is typically assumed to manifest as a momentum-dependent splitting of a single initially spin-degenerate band into two branches with opposite spin polarisation. Here, combining polarisation-dependent and resonant angle-resolved photoemission measurements with density-functional theory calculations, we show that the two "spin-split" branches of the model giant Rashba system BiTeI additionally develop disparate orbital textures, each of which is coupled to a distinct spin configuration. This necessitates a re-interpretation of spin splitting in Rashba-like systems, and opens new possibilities for controlling spin polarisation through the orbital sector.Comment: 11 pages including supplemental figures, accepted for publication at Science Advance

The high-pressure phase of boron, {\gamma}-B28: disputes and conclusions of 5 years after discovery

{\gamma}-B28 is a recently established high-pressure phase of boron. Its structure consists of icosahedral B12 clusters and B2 dumbbells in a NaCl-type arrangement (B2){\delta}+(B12){\delta}- and displays a significant charge transfer {\delta}~0.5- 0.6. The discovery of this phase proved essential for the understanding and construction of the phase diagram of boron. {\gamma}-B28 was first experimentally obtained as a pure boron allotrope in early 2004 and its structure was discovered in 2006. This paper reviews recent results and in particular deals with the contentious issues related to the equation of state, hardness, putative isostructural phase transformation at ~40 GPa, and debates on the nature of chemical bonding in this phase. Our analysis confirms that (a) calculations based on density functional theory give an accurate description of its equation of state, (b) the reported isostructural phase transformation in {\gamma}-B28 is an artifact rather than a fact, (c) the best estimate of hardness of this phase is 50 GPa, (d) chemical bonding in this phase has a significant degree of ionicity. Apart from presenting an overview of previous results within a consistent view grounded in experiment, thermodynamics and quantum mechanics, we present new results on Bader charges in {\gamma}-B28 using different levels of quantum-mechanical theory (GGA, exact exchange, and HSE06 hybrid functional), and show that the earlier conclusion about significant degree of partial ionicity in this phase is very robust