Fall-experiments on Merapi basaltic andesite and constraints on the generation of pyroclastic surges

International audienceWe have performed fall-experiments with basaltic andesite rock samples from Merapi volcano, using an apparatus designed to analyze samples heated up to 850°C. Relative pressure changes during impact and fragmentation of the samples were measured by a pressure transducer. From 200°C, dynamic pressure waves were formed on impact and fragmentation. Peak and duration of the pressure signal, and degree of fragmentation were found to strongly increase with increasing temperature of rock samples. The pressure waves are most likely generated by sudden heating of air forcing it to expand. We propose that the observed pressure changes are analogues to pyroclastic surges that may be generated on impact and fragmentation of large blocks during passage of a pyroclastic flow over a steep cliff. We infer that rock temperatures of ca. 400°C are sufficient for this process to occur, a temperature common in pyroclastic flows even in distal reaches

Double photo-ionization of He near a polarizable surface

We calculate the differential cross-section of the direct double photo-ionization of He physisorbed on a polarizable surface. By including the influence of the surface potential in the correlated two-electron final state wavefunction, we show that the differential cross-section carries detailed information on the electronic correlations at the surface. In particular, photo-emission along opposite directions, which is prohibited in the free space, is allowed if the surface potential is long-ranged.Comment: To appear in Phys. Rev. B - Rapid Comm. - 4 pages, 2 PostScript figures embedde

Optimal leverage from non-ergodicity

In modern portfolio theory, the balancing of expected returns on investments against uncertainties in those returns is aided by the use of utility functions. The Kelly criterion offers another approach, rooted in information theory, that always implies logarithmic utility. The two approaches seem incompatible, too loosely or too tightly constraining investors' risk preferences, from their respective perspectives. The conflict can be understood on the basis that the multiplicative models used in both approaches are non-ergodic which leads to ensemble-average returns differing from time-average returns in single realizations. The classic treatments, from the very beginning of probability theory, use ensemble-averages, whereas the Kelly-result is obtained by considering time-averages. Maximizing the time-average growth rates for an investment defines an optimal leverage, whereas growth rates derived from ensemble-average returns depend linearly on leverage. The latter measure can thus incentivize investors to maximize leverage, which is detrimental to time-average growth and overall market stability. The Sharpe ratio is insensitive to leverage. Its relation to optimal leverage is discussed. A better understanding of the significance of time-irreversibility and non-ergodicity and the resulting bounds on leverage may help policy makers in reshaping financial risk controls.Comment: 17 pages, 3 figures. Updated figures and extended discussion of ergodicit

Observation of mesoscopic crystalline structures in a two-dimensional Rydberg gas

The ability to control and tune interactions in ultracold atomic gases has paved the way towards the realization of new phases of matter. Whereas experiments have so far achieved a high degree of control over short-ranged interactions, the realization of long-range interactions would open up a whole new realm of many-body physics and has become a central focus of research. Rydberg atoms are very well-suited to achieve this goal, as the van der Waals forces between them are many orders of magnitude larger than for ground state atoms. Consequently, the mere laser excitation of ultracold gases can cause strongly correlated many-body states to emerge directly when atoms are transferred to Rydberg states. A key example are quantum crystals, composed of coherent superpositions of different spatially ordered configurations of collective excitations. Here we report on the direct measurement of strong correlations in a laser excited two-dimensional atomic Mott insulator using high-resolution, in-situ Rydberg atom imaging. The observations reveal the emergence of spatially ordered excitation patterns in the high-density components of the prepared many-body state. They have random orientation, but well defined geometry, forming mesoscopic crystals of collective excitations delocalised throughout the gas. Our experiment demonstrates the potential of Rydberg gases to realise exotic phases of matter, thereby laying the basis for quantum simulations of long-range interacting quantum magnets.Comment: 10 pages, 7 figure

The construction of marketing measures: the case of viewability

This study seeks to develop a critical understanding of marketing measures. Marketing measures inform a variety of marketing practices and have been subject to ethical, discursive and epistemological critique. Informed by a range of theoretical work, this study sheds light on the construction of a key marketing measure in digital advertising: viewability. It shows how a range of competing interests can be mobilized and aligned; how an object of interest can be stabilized; and how standards for measurement can be reconciled. Across this account, we can see how issues of accuracy, ideology and ethics are bracketed off as participants agree on which things matter and which things count

Oxygen Abundances in Nearby Stars. Clues to the formation and evolution of the Galactic disk

The abundances of iron and oxygen are homogeneously determined in a sample of 523 nearby (d<150 pc) FGK disk and halo stars with metallicities in the range -1.5<[Fe/H]<0.5. The oxygen abundances were inferred from a restricted non-LTE analysis of the 777 nm O I triplet. We use the stellar kinematics to compute the probabilities of our sample stars to be members of the thin disk, thick disk, or halo of the Galaxy. We find that the majority of the kinematically-selected thick-disk stars show larger [O/Fe] ratios compared to thin-disk stars. A close examination of this pattern for disk stars with ambiguous probabilities shows that an intermediate population with properties between those of the thin and thick disks does not exist. Excluding the stars with unusual kinematics, we find that thick-disk stars show slowly decreasing [O/Fe] ratios from about 0.5 to 0.4 in the -0.8<[Fe/H]<-0.3 range. Using a simple model for the chemical evolution of the thick disk we show that this trend results directly from the metallicity dependence of the Type II supernova yields. At [Fe/H]>-0.3, we find no obvious indication of a sudden decrease (i.e., a 'knee') in the [O/Fe] vs. [Fe/H] pattern of thick-disk stars that would connect the thick and thin disk trends at a high metallicity. We conclude that Type Ia supernovae (SN Ia) did not contribute significantly to the chemical enrichment of the thick disk. [Abridged]Comment: A&A, in pres

Text-based vs. graphical information formats in sepsis prevention and early detection: A randomized controlled trial on informed choice

Sepsis is associated with 11 million global deaths annually. Although serious consequences of sepsis can generally be avoided with prevention and early detection, research has not yet addressed the efficacy of evidence-based health information formats for different risk groups. This study examines whether two evidence-based health information formats—text based and graphical—differ in how well they foster informed choice and risk and health literacy and in how well they support different sepsis risk groups. Based on a systematic literature review, two one-page educative formats on sepsis prevention and early detection were designed—one text based and one graphical. A sample of 500 German participants was randomly shown one of the two formats; they were then assessed on whether they made informed choices and on their risk and health literacy. For both formats, >70% of participants made informed choices for sepsis prevention and >75% for early detection. Compared with the graphical format, the text-based format was associated with higher degrees of informed choice (p = 0.012, OR = 1.818) and risk and health literacy (p = 0.032, OR = 1.710). Both formats can foster informed choices and risk and health literacy on sepsis prevention and early detection, but the text-based format appears to be more effective

A review of elliptical and disc galaxy structure, and modern scaling laws

A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their models to describe the radial distribution of stars in `nebulae'. This article reviews the progress since then, providing both an historical perspective and a contemporary review of the stellar structure of bulges, discs and elliptical galaxies. The quantification of galaxy nuclei, such as central mass deficits and excess nuclear light, plus the structure of dark matter halos and cD galaxy envelopes, are discussed. Issues pertaining to spiral galaxies including dust, bulge-to-disc ratios, bulgeless galaxies, bars and the identification of pseudobulges are also reviewed. An array of modern scaling relations involving sizes, luminosities, surface brightnesses and stellar concentrations are presented, many of which are shown to be curved. These 'redshift zero' relations not only quantify the behavior and nature of galaxies in the Universe today, but are the modern benchmark for evolutionary studies of galaxies, whether based on observations, N-body-simulations or semi-analytical modelling. For example, it is shown that some of the recently discovered compact elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to appear in "Planets, Stars and Stellar Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references incl. many somewhat forgotten, pioneer papers. Original submission to Springer: 07-June-201

Historical Research Approaches to the Analysis of Internationalisation

Historical research methods and approaches can improve understanding of the most appropriate techniques to confront data and test theories in internationalisation research. A critical analysis of all “texts” (sources), time series analyses, comparative methods across time periods and space, counterfactual analysis and the examination of outliers are shown to have the potential to improve research practices. Examples and applications are shown in these key areas of research with special reference to internationalisation processes. Examination of these methods allows us to see internationalisation processes as a sequenced set of decisions in time and space, path dependent to some extent but subject to managerial discretion. Internationalisation process research can benefit from the use of historical research methods in analysis of sources, production of time-lines, using comparative evidence across time and space and in the examination of feasible alternative choices

Haloperidol differentially modulates prepulse inhibition and p50 suppression in healthy humans stratified for low and high gating levels

Schizophrenia patients exhibit deficits in sensory gating as indexed by reduced prepulse inhibition (PPI) and P50 suppression, which have been linked to psychotic symptom formation and cognitive deficits. Although recent evidence suggests that atypical antipsychotics might be superior over typical antipsychotics in reversing PPI and P50 suppression deficits not only in schizophrenia patients, but also in healthy volunteers exhibiting low levels of PPI, the impact of typical antipsychotics on these gating measures is less clear. To explore the impact of the dopamine D2-like receptor system on gating and cognition, the acute effects of haloperidol on PPI, P50 suppression, and cognition were assessed in 26 healthy male volunteers split into subgroups having low vs high PPI or P50 suppression levels using a placebo-controlled within-subject design. Haloperidol failed to increase PPI in subjects exhibiting low levels of PPI, but attenuated PPI in those subjects with high sensorimotor gating levels. Furthermore, haloperidol increased P50 suppression in subjects exhibiting low P50 gating and disrupted P50 suppression in individuals expressing high P50 gating levels. Independently of drug condition, high PPI levels were associated with superior strategy formation and execution times in a subset of cognitive tests. Moreover, haloperidol impaired spatial working memory performance and planning ability. These findings suggest that dopamine D2-like receptors are critically involved in the modulation of P50 suppression in healthy volunteers, and to a lesser extent also in PPI among subjects expressing high sensorimotor gating levels. Furthermore, the results suggest a relation between sensorimotor gating and working memory performance