Geometric partition functions of cellular systems: Explicit calculation of the entropy in two and three dimensions

A method is proposed for the characterisation of the entropy of cellular structures, based on the compactivity concept for granular packings. Hamiltonian-like volume functions are constructed both in two and in three dimensions, enabling the identification of a phase space and making it possible to take account of geometrical correlations systematically. Case studies are presented for which explicit calculations of the mean vertex density and porosity fluctuations are given as functions of compactivity. The formalism applies equally well to two- and three-dimensional granular assemblies.Comment: 14 pages, 4 figures, to appear in The European Physical Journal E - Soft Matte

From white elephant to Nobel Prize: Dennis Gabor’s wavefront reconstruction

Dennis Gabor devised a new concept for optical imaging in 1947 that went by a variety of names over the following decade: holoscopy, wavefront reconstruction, interference microscopy, diffraction microscopy and Gaboroscopy. A well-connected and creative research engineer, Gabor worked actively to publicize and exploit his concept, but the scheme failed to capture the interest of many researchers. Gabor’s theory was repeatedly deemed unintuitive and baffling; the technique was appraised by his contemporaries to be of dubious practicality and, at best, constrained to a narrow branch of science. By the late 1950s, Gabor’s subject had been assessed by its handful of practitioners to be a white elephant. Nevertheless, the concept was later rehabilitated by the research of Emmett Leith and Juris Upatnieks at the University of Michigan, and Yury Denisyuk at the Vavilov Institute in Leningrad. What had been judged a failure was recast as a success: evaluations of Gabor’s work were transformed during the 1960s, when it was represented as the foundation on which to construct the new and distinctly different subject of holography, a re-evaluation that gained the Nobel Prize for Physics for Gabor alone in 1971. This paper focuses on the difficulties experienced in constructing a meaningful subject, a practical application and a viable technical community from Gabor’s ideas during the decade 1947-1957

Loop expansion around the Bethe-Peierls approximation for lattice models

We develop an effective field theory for lattice models, in which the only non-vanishing diagrams exactly reproduce the topology of the lattice. The Bethe-Peierls approximation appears naturally as the saddle point approximation. The corrections to the saddle-point result can be obtained systematically. We calculate the lowest loop corrections for magnetisation and correlation function.Comment: 8 page

Quantifying Forest Ground Flora Biomass Using Proximal Sensing

Current focus on forest conservation and forest sustainability has increased the level of attention given to measures of ground flora in forest ecosystems. Traditionally, such data are collected via time- and resource-intensive methods of field identification, clipping, and weighing. With increased focus on community composition and structure measures of forest ground flora, the manner in which these data are collected must change. This project uses color and color infrared digital cameras to proximally sense forest ground flora and to develop regression models to predict green and dry biomass (g/m^) from the proximally sensed data. Traditional vegetative indices such as the Normalized Difference Vegetative Index (NDVI) and the Average Visible Reflectance Index (AVR) explained 35-45% of the variation in forest ground flora biomass. Adding individual color band variables, especially the red and near infrared bands, to the regression model allowed the model to explain 66% and 58% of the variation in green and dry biomass, respectively, present

Meanfield treatment of Bragg scattering from a Bose-Einstein condensate

A unified semiclassical treatment of Bragg scattering from Bose-Einstein condensates is presented. The formalism is based on the Gross-Pitaevskii equation driven by classical light fields far detuned from atomic resonance. An approximate analytic solution is obtained and provides quantitative understanding of the atomic momentum state oscillations, as well as a simple expression for the momentum linewidth of the scattering process. The validity regime of the analytic solution is derived, and tested by three dimensional cylindrically symmetric numerical simulations.Comment: 21 pages, 10 figures. Minor changes made to documen

Stable Isotope and Modelling Evidence for CO2 as a Driver of Glacial-Interglacial Vegetation Shifts in Southern Africa

Atmospheric CO2 concentration is hypothesized to influence vegetation distribution via tree-grass competition, with higher CO2 concentrations favouring trees. The stable carbon isotope (delta C-13) signature of vegetation is influenced by the relative importance of C-4 plants (including most tropical grasses) and C-3 plants (including nearly all trees), and the degree of stomatal closure - a response to aridity in C-3 plants. Compound-specific delta C-13 analyses of leaf-wax biomarkers in sediment cores of an offshore South Atlantic transect are used here as a record of vegetation changes in subequatorial Africa. These data suggest a large increase in C3 relative to C4 plant dominance after the Last Glacial Maximum. Using a process-based biogeography model that explicitly 10 simulates 13 C discrimination, we show that climate change alone cannot explain the observed shift in δ13 C values. The physiological effect of increasing CO2 concentration is decisive, altering the C3/ C4 balance and bringing the simulated and observed δ 13C values into line. It is concluded that CO2 concentration itself was a key agent of tropical vegetation 15 change during the last glacial-interglacial transition. Two additional inferences follow. First, long-term variations in terrestrial δ13 C values are not simply a proxy for regional rainfall as has sometimes been assumed. Such interpretations need to be re-examined. Second, rising CO2 concentration today is likely to be influencing tree-grass competition in a similar way, and thus contributing to the “woody thickening” observed in savannas worldwide. This second inference points to the importance of experiments to determine how vegetation composition in savannas is likely to be influenced by the continuing rise in CO2 concentratio

The Presence of Persistent Bovine Viral Diarrhea Virus Infection and a Novel Bosavirus in a Bison Herd

Objective Bovine viral diarrhea virus (BVDV) is a significant pathogen of cattle, leading to losses due to reproductive failure, respiratory disease and immune dysregulation. An investigation was conducted in an American bison (Bison bison) herd dealing with reproductive issues in 2018-2019 calving season to determine likely cause of the losses

Airfoil Boundary-Layer Development and Transition with Large Leading-Edge Roughness

An experimental study of the effects of large distributed roughness located near the leading edge of an airfoil has been performed to determine the effect on boundary-layer development and transition. Boundary-layer measurements were carried out on a two-dimensional NACA 0012 airfoil with a 53.34-cm chord through the use of hot-wire anemometry at Reynolds numbers of 0.75 £ 10 6 , 1.25 £ 10 6 , and 2.25 £ 10 6 . These measurements included mean and¯uctuating velocity, turbulence intensity,¯ow® eld intermittency, and associated integral parameters. The roughness used was of the type and density observed to occur during the initial glaze ice accretion process. Results have shown that the transitional boundary layer induced by large distributed roughness is markedly different from the smooth model Tollmein± Schlicting induced transition process. No fully developed turbulent boundary layers were observed to occur near the roughness location. Instead, the large distributed roughness was observed to trigger a transitional boundary layer at or very near the roughness location. This transitional boundary layer required a substantial chordwise extent to obtain a fully developed turbulent state. Streamwise turbulence intensity levels in the roughness induced transitional region were observed to be relatively low as compared with the smooth model transitional region. Nomenclatur

Electronic structure and optical properties of ZnX (X=O, S, Se, Te)

Electronic band structure and optical properties of zinc monochalcogenides with zinc-blende- and wurtzite-type structures were studied using the ab initio density functional method within the LDA, GGA, and LDA+U approaches. Calculations of the optical spectra have been performed for the energy range 0-20 eV, with and without including spin-orbit coupling. Reflectivity, absorption and extinction coefficients, and refractive index have been computed from the imaginary part of the dielectric function using the Kramers--Kronig transformations. A rigid shift of the calculated optical spectra is found to provide a good first approximation to reproduce experimental observations for almost all the zinc monochalcogenide phases considered. By inspection of the calculated and experimentally determined band-gap values for the zinc monochalcogenide series, the band gap of ZnO with zinc-blende structure has been estimated.Comment: 17 pages, 10 figure