Reentrant transitions in colloidal or dusty plasma bilayers

The phase diagram of crystalline bilayers of particles interacting via a Yukawa potential is calculated for arbitrary screening lengths and particle densities. Staggered rectangular, square, rhombic and triangular structures are found to be stable including a first-order transition between two different rhombic structures. For varied screening length at fixed density, one of these rhombic phases exhibits both a single and even a double reentrant transition. Our predictions can be verified experimentally in strongly confined charged colloidal suspensions or dusty plasma bilayers.Comment: 4 pages, 3 eps figs - revtex4. PRL - in pres

Phonon-phonon interactions in transition metals

In this paper the phonon self energy produced by anharmonicity is calculated using second order many body perturbation theory for all bcc, fcc and hcp transition metals. The symmetry properties of the phonon interactions are used to obtain an expression for the self energy as a sum over irreducible triplets, very similar to integration in the irreducible part of the Brillouin zone for one particle properties. The results obtained for transition metals shows that the lifetime is on the order of 10^10 s. Moreover the Peierls approximation for the imaginary part of the self energy is shown to be reasonable for bcc and fcc metals. For hcp metals we show that the Raman active mode decays into a pair of acoustic phonons, their wave vector being located on a surface defined by conservation laws.Comment: 14 pages, 3 figure

Criteria for assessing grant applications: A systematic review

Criteria are an essential component of any procedure for assessing merit. Yet, little is known about the criteria peers use in assessing grant applications. In this systematic review we therefore identify and synthesize studies that examine grant peer review criteria in an empirical and inductive manner. To facilitate the synthesis, we introduce a framework that classifies what is generally referred to as 'criterion' into an evaluated entity (i.e. the object of evaluation) and an evaluation criterion (i.e. the dimension along which an entity is evaluated). In total, this synthesis includes 12 studies. Two-thirds of these studies examine criteria in the medical and health sciences, while studies in other fields are scarce. Few studies compare criteria across different fields, and none focus on criteria for interdisciplinary research. We conducted a qualitative content analysis of the 12 studies and thereby identified 15 evaluation criteria and 30 evaluated entities as well as the relations between them. Based on a network analysis, we propose a conceptualization that groups the identified evaluation criteria and evaluated entities into aims, means, and outcomes. We compare our results to criteria found in studies on research quality and guidelines of funding agencies. Since peer review is often approached from a normative perspective, we discuss our findings in relation to two normative positions, the fairness doctrine and the ideal of impartiality. Our findings suggest that future studies on criteria in grant peer review should focus on the applicant, include data from non-Western countries, and examine fields other than the medical and health sciences.Comment: Final versio

Microsoft Academic is on the verge of becoming a bibliometric superpower

Last year, the new Microsoft Academic service was launched. Sven E. Hug and Martin P. Brändle look at how it compares with more established competitors such as Google Scholar, Scopus, and Web of Science. While there are reservations about the availability of instructions for novice users, Microsoft Academic has impressive semantic search functionality, broad coverage, structured and rich metadata, and solid citation analysis features. Moreover, accessing raw data is relatively cheap. Given these benefits and its fast pace of development, Microsoft Academic is on the verge of becoming a bibliometric superpower

Comparative Study of Insertion of Light Elements N, O in Ternary Compounds Ti3AlN and Ti3Al(O)

International audienceThe region close to Ti3AlX (X= N, O) composition of the Ti-Al-O and Ti-Al-N phase diagrams has been experimentally addressed. Alloys with the compositions TiJAIN and Ti~AIO have been processed, Phase analysis and microstructural characterization have been carried out. Both alloys are found to be multi-phased. Under-stoechiornetric Ti3A10X and Ti3AlNX are found to be hexagonal and tetragonal (perovskite-like structure), respectively. Additional information concerning the crystallographic site of insertion of nitrogen and oxygen has been obtained by Electron Energy Loss Spectrometry (EELS). In the Ti-Al-N perovskite-like compound, with an average composition of Ti3AlNo,45.the tetragonal structure stems from the long range nitrogen-vacancy ordering

Pure hydrogen low-temperature plasma exposure of HOPG and graphene: Graphane formation?

Single- and multilayer graphene and highly ordered pyrolytic graphite (HOPG) were exposed to a pure hydrogen low-temperature plasma (LTP). Characterizations include various experimental techniques such as photoelectron spectroscopy, Raman spectroscopy and scanning probe microscopy. Our photoemission measurement shows that hydrogen LTP exposed HOPG has a diamond-like valence-band structure, which suggests double-sided hydrogenation. With the scanning tunneling microscopy technique, various atomic-scale charge-density patterns were observed, which may be associated with different C-H conformers. Hydrogen-LTP-exposed graphene on SiO₂ has a Raman spectrum in which the D peak to G peak ratio is over 4, associated with hydrogenation on both sides. A very low defect density was observed in the scanning probe microscopy measurements, which enables a reverse transformation to graphene. Hydrogen-LTP-exposed HOPG possesses a high thermal stability, and therefore, this transformation requires annealing at over 1000 °C