Gaining Insight into Determinants of Physical Activity using Bayesian Network Learning

Contains fulltext : 228326pre.pdf (preprint version ) (Open Access) Contains fulltext : 228326pub.pdf (publisher's version ) (Open Access)BNAIC/BeneLearn 202

Study of solid 4He in two dimensions. The issue of zero-point defects and study of confined crystal

Defects are believed to play a fundamental role in the supersolid state of 4He. We report on studies by exact Quantum Monte Carlo (QMC) simulations at zero temperature of the properties of solid 4He in presence of many vacancies, up to 30 in two dimensions (2D). In all studied cases the crystalline order is stable at least as long as the concentration of vacancies is below 2.5%. In the 2D system for a small number, n_v, of vacancies such defects can be identified in the crystalline lattice and are strongly correlated with an attractive interaction. On the contrary when n_v~10 vacancies in the relaxed system disappear and in their place one finds dislocations and a revival of the Bose-Einstein condensation. Thus, should zero-point motion defects be present in solid 4He, such defects would be dislocations and not vacancies, at least in 2D. In order to avoid using periodic boundary conditions we have studied the exact ground state of solid 4He confined in a circular region by an external potential. We find that defects tend to be localized in an interfacial region of width of about 15 A. Our computation allows to put as upper bound limit to zero--point defects the concentration 0.003 in the 2D system close to melting density.Comment: 17 pages, accepted for publication in J. Low Temp. Phys., Special Issue on Supersolid

Weber and church governance: religious practice and economic activity

The debate about the relationship between religion and economic activity in the wake of Weber has been cast largely in terms of belief and values. This article suggests an alternative focus on practice. It argues that taken for granted practices of church governance formed to-hand resources for the organization of economic activity. The argument is developed through an examination of the historical development of church governance practices in the Presbyterian Church of Scotland, with particular emphasis on the way in which theological belief gave rise to practices of accountability and record keeping. In turn such practices contributed to a ‘culture of organization’ which had implications for economic activity. A focus on governance practices can help to illuminate enduring patterns of difference in the organization of economic activity

The instrument suite of the European Spallation Source

An overview is provided of the 15 neutron beam instruments making up the initial instrument suite of the European Spallation Source (ESS), and being made available to the neutron user community. The ESS neutron source consists of a high-power accelerator and target station, providing a unique long-pulse time structure of slow neutrons. The design considerations behind the time structure, moderator geometry and instrument layout are presented. The 15-instrument suite consists of two small-angle instruments, two reflectometers, an imaging beamline, two single-crystal diffractometers; one for macromolecular crystallography and one for magnetism, two powder diffractometers, and an engineering diffractometer, as well as an array of five inelastic instruments comprising two chopper spectrometers, an inverse-geometry single-crystal excitations spectrometer, an instrument for vibrational spectroscopy and a high-resolution backscattering spectrometer. The conceptual design, performance and scientific drivers of each of these instruments are described. All of the instruments are designed to provide breakthrough new scientific capability, not currently available at existing facilities, building on the inherent strengths of the ESS long-pulse neutron source of high flux, flexible resolution and large bandwidth. Each of them is predicted to provide world-leading performance at an accelerator power of 2 MW. This technical capability translates into a very broad range of scientific capabilities. The composition of the instrument suite has been chosen to maximise the breadth and depth of the scientific impact o

Neutron scattering study of methyl group rotation in solid para-azoxyanisole (PAA)

Using incoherent neutron scattering, we show that the methyl groups in solid PAA undergo random rotational motion around their three-fold axis, and that rotations about other molecular axes on the same time scale can be excluded. A model for uniaxial rotational jumps between three equidistant sites on a circle of radius a = 1.032 Å is fitted to the quasielastic spectra. The mean jump time τ between two consecutive jumps is determined and found to vary from 2.93 x 10-11 to 0.95 x 10-11 s between 17 and 117 °C, yielding an activation energy of Ea = 2.54 ± 0.13 kcal/mole. The intense peak observed in the inelastic region at 31 meV energy transfer is assigned to the ν = 1 → ν = 0 torsional frequency of the methyl group in a three-fold potential. For a cosine potential one obtains a barrier V3 = 4.21 ± 0.37 kcal/mole. Attempts to relate Ea and V3 values lead to the conclusion that the potential shape differs appreciably from the cosine form. Our results are then compared with other experimental data. In particular, it seems that the barrier to rotation of the methyl groups arises mainly from intramolecular interactions.On montre, par diffusion incohérente de neutrons, que dans le PAA solide les groupes méthyle sont animés d'un mouvement de rotation aléatoire autour de leur axe ternaire, et que des rotations, sur la même échelle de temps, autour d'autres axes moléculaires peuvent être exclues. On interprète les spectres quasi-élastiques par un modèle rotationnel figurant des sauts entre trois points équidistants situés sur un cercle de rayon a = 1,032 Å. On trouve que le temps moyen entre deux sauts consécutifs varie de 2,93 x 10-11 à 0,95 × 10-11 s entre 17 et 117 °C, ce qui conduit à une énergie d'activation de Ea = 2,54 ± 0,13 kcal/mole. Le pic intense observe dans le spectre inélastique autour de 31 meV est assigné à la transition v = 1 → v = 0 d'un groupe methyle se mouvant dans un potentiel sinusoidal à trois puits. On obtient ainsi une barrière V3 = 4,21 ± 0,37 kcal/ mole. Les deux résultats mènent à la conclusion que la forme du potentiel s'écarte notablement de la sinusoide. On compare ensuite ces conclusions à d'autres résultats expérimentaux. On en déduit, en particulier, que la barrière agissant sur les groupes méthyle provient presque exclusivement de forces intramoléculaires

MICROSCOPIC DYNAMICS.END CHAIN MOTION IN THE SOLID PHASE OF TBBA

On rapporte des expériences de diffusion quasi élastique de neutrons, à haute résolution, dans la phase solide du terephtal-bis-butyl aniline (TBBA). Celles-ci révèlent que les extrémités des chaînes butyle se réorientent rapidement. Les meilleurs résultats sont obtenus en supposant une rotation des derniers groupes méthylène et méthyle des chaînes. Les valeurs des temps de corrélation et de l'énergie d'activation sont compatibles avec celles, obtenues par RMN dans des substances solides contenant des chaînes aliphatiques.High resolution quasielastic neutron scattering experiments on the crystalline phase of terephtal-bis-butyl aniline (TBBA) are reported. The data are discussed in terms of rotational motion of the butyl chain extremities. Best agreement with the experiment is obtained assuming that the last methylene and methyl groups are rotating. Both correlation times and activation energy are consistent with previous NMR work on solid substances containing alkyl chains

Uniaxial rotational diffusion in the smectic B phase of TBBA observed by quasi-elastic neutron scattering

High resolution quasi-elastic neutron time-of-flight experiments performed at 119 °C on smectic B TBBA and on a partially-deuterated derivative have revealed that the molecules perform a random rotational motion about their long axis. The corresponding rotational correlation time is about 1.8 x 10-11 s. Furthermore, the results suggest a much faster random motion of the aliphatic end chains superimposed on the rotation of the body. Large proton « Debye-Waller factors » e-Q2u2 related to motions other than cylindrical rotation were found. For the body protons u2 ~ 0.26 Å2, for the tail protons u2 ~ 0.61 Å2. Preliminary results are also given for the solid (104 °C) and for the smectic C phase.On a effectué des expériences de diffusion quasi-élastique de neutrons, avec un appareil à temps de vol, haute résolution, sur la phase smectique B du TBBA et de l'un de ses dérivés partiellement deutérié. Celles-ci ont révélé que les molécules sont animées d'un mouvement de diffusion rotationnelle autour de leur axe principal, avec un temps de corrélation d'environ 1,8 x 10-11 s. Les résultats suggèrent en outre l'existence d'un mouvement beaucoup plus rapide des chaînes aliphatiques terminales, qui se superpose à la rotation de l'ensemble de la molécule. On a trouvé des facteurs de Debye-Waller e- Q2u2 relativement importants, liés à des mouvements autres que la rotation cylindrique. Pour les protons du corps u2 ~ 0,26 Å2 et pour les protons des chaînes u2 ~ 0,61 Å2. On donne aussi quelques résultats préliminaires sur la phase solide (104 °C) et sur la phase smectique C

Gaining Insight into Determinants of Physical Activity using Bayesian Network Learning

Contains fulltext : 228326pre.pdf (preprint version ) (Open Access) Contains fulltext : 228326pub.pdf (publisher's version ) (Open Access)BNAIC/BeneLearn 202