Hard-Sphere Fluids in Contact with Curved Substrates

The properties of a hard-sphere fluid in contact with hard spherical and cylindrical walls are studied. Rosenfeld's density functional theory (DFT) is applied to determine the density profile and surface tension $\gamma$ for wide ranges of radii of the curved walls and densities of the hard-sphere fluid. Particular attention is paid to investigate the curvature dependence and the possible existence of a contribution to $\gamma$ that is proportional to the logarithm of the radius of curvature. Moreover, by treating the curved wall as a second component at infinite dilution we provide an analytical expression for the surface tension of a hard-sphere fluid close to arbitrary hard convex walls. The agreement between the analytical expression and DFT is good. Our results show no signs for the existence of a logarithmic term in the curvature dependence of $\gamma$.Comment: 15 pages, 6 figure

Equivalence of two approaches for the inhomogeneous density in the canonical ensemble

In this article we show that the inhomogeneous density obtained from a density-functional theory of classical fluids in the canonical ensemble (CE), recently presented by White et al [Phys. Rev. Lett. 84 (2000) 1220], is equivalent to first order to the result of the series expansion of the CE inhomogeneous density introduced by Gonzalez et al [Phys. Rev. Lett. 79 (1997) 2466].Comment: 6 pages, RevTe

Cross-National Logo Evaluation Analysis: An Individual Level Approach

The universality of design perception and response is tested using data collected from ten countries: Argentina, Australia, China, Germany, Great Britain, India, the Netherlands, Russia, Singapore, and the United States. A Bayesian, finite-mixture, structural-equation model is developed that identifies latent logo clusters while accounting for heterogeneity in evaluations. The concomitant variable approach allows cluster probabilities to be country specific. Rather than a priori defined clusters, our procedure provides a posteriori cross-national logo clusters based on consumer response similarity. To compare the a posteriori cross-national logo clusters, our approach is integrated with Steenkamp and Baumgartner’s (1998) measurement invariance methodology. Our model reduces the ten countries to three cross-national clusters that respond differently to logo design dimensions: the West, Asia, and Russia. The dimensions underlying design are found to be similar across countries, suggesting that elaborateness, naturalness, and harmony are universal design dimensions. Responses (affect, shared meaning, subjective familiarity, and true and false recognition) to logo design dimensions (elaborateness, naturalness, and harmony) and elements (repetition, proportion, and parallelism) are also relatively consistent, although we find minor differences across clusters. Our results suggest that managers can implement a global logo strategy, but they also can optimize logos for specific countries if desired.adaptation;standardization;Bayesian;international marketing;design;Gibbs sampling;concomitant variable;logos;mixture models;structural equation models

Preparation of atomically clean and flat Si(100) surfaces by low-energy ion sputtering and low-temperature annealing

Si(100) surfaces were prepared by wet-chemical etching followed by 0.3-1.5keV Ar ion sputtering, either at elevated or room temperature. After a brief anneal under ultrahigh vacuum conditions, the resulting surfaces were examined by scanning tunneling microscopy. We find that wet-chemical etching alone cannot produce a clean and flat Si(100) surface. However, subsequent 300eV Ar ion sputtering at room temperature followed by a 973K anneal yields atomically clean and flat Si(100) surfaces suitable for nanoscale device fabrication.Comment: 13 pages, 3 figures, to be published in Applied Surface Scienc

Utilization and metabolism of palmityl and oleoyl fatty acids and alcohols in caecal enterocytes of Atlantic salmon (Salmo salar L.)

The substitution of fish oil with wax ester-rich calanoid copepod-derived oil in diets for carnivorous fish, such as Atlantic salmon, has previously indicated a lower lipid digestibility. This suggests that the fatty alcohols (FAlc) present in wax esters may be a poorer substrate for intestinal enzymes than the fatty acids (FA) in triacylglycerol, the major lipid in fish oil. The hypothesis tested was that the possible lower utilization of dietary FAlc by salmon enterocytes is at the level of uptake and that subsequent intracellular metabolism was identical to that of FA. A dual-labelled FAlc-FA metabolism assay was employed to determine simultaneous FAlc and FA uptake and relative utilisation in enterocytes isolated from pyloric caeca of Atlantic salmon fed either a diet supplemented with fish oil or wax ester-rich Calanus oil. The diets were fed for 10 weeks before caecal enterocytes from each dietary group were isolated and incubated with equimolar mixtures of either [1-14C]16:0 FA and [9,10(n)-3H]16:0 FAlc, or [1-14C]18:1n-9 FA and [9,10(n)-3H]18:1n-9 FAlc. Uptake was measured after 2 h with relative utilization of labelled FAlc and FA calculated as a percentage of uptake. Differences in uptake were observed, with FA showing higher uptake than FAlc, and 18:1 chains a higher uptake than 16:0. A proportion of unesterified FAlc was possibly recovered in the cells, but the majority of FALc was recovered in lipid classes such as triacylglycerol and phospholipids indicating substantial conversion of FAlc to FA followed by esterification. However, incorporation of FA and FAlc into esterified lipids was higher when derived from FA than from FAlc. Twenty-five to fifty percentage of the absorbed 16:0 FA was recovered in TAG fraction of the enterocytes compared with fifteen to seventy-five percentage of 18:1 FA. Twenty to thirty percentage of the absorbed 16:0 FA was recovered in the PC fraction of the enterocytes compared with only five to fifteen percentage of the 18:1 FA. Less than 15% of the fatty chains taken up by the cells was used for energy production, with significantly higher oxidation of 18:1 in enterocytes from fish fed the fish oil diet compared to the Calanus oil diet. However, overall, dietary copepod oil had little effect on FAlc and FA metabolism. Metabolic modification by elongation and/or desaturation was generally low at 1-5% of uptake. We conclude that our hypothesis was generally proved in that the uptake of FAlc by salmon enterocytes was lower than the uptake of FA and that subsequent intracellular metabolism of FAlc was similar to that of FA. However, unesterified FAlc was possibly recovered in the cells suggesting that the conversion to FA may not be concomitant with uptake

Slow relaxations and history dependence of the transport properties of layered superconductors

We study numerically the time evolution of the transport properties of layered superconductors after different preparations. We show that, in accordance with recent experiments in BSCCO performed in the second peak region of the phase diagram (Portier et al, 2001), the relaxation strongly depends on the initial conditions and is extremely slow. We investigate the dependence on the pinning center density and the perturbation applied. We compare the measurements to recent findings in tapped granular matter and we interpret our results with a rather simple picture.Comment: 4 pages, 4 fig

Density functional calculations for 4He droplets

A novel density functional, which accounts correctly for the equation of state, the static response function and the phonon-roton dispersion in bulk liquid helium, is used to predict static and dynamic properties of helium droplets. The static density profile is found to exhibit significant oscillations, which are accompanied by deviations of the evaporation energy from a liquid drop behaviour in the case of small droplets. The connection between such oscillations and the structure of the static response function in the liquid is explicitly discussed. The energy and the wave function of excited states are then calculated in the framework of time dependent density functional theory. The new functional, which contains backflow-like effects, is expected to yield quantitatively correct predictions for the excitation spectrum also in the roton wave-length range.Comment: 15 pages, REVTEX, 10 figures available upon request or at http://anubis.science.unitn.it/~dalfovo/papers/papers.htm

Fatty acid metabolism in marine fish: Low activity of fatty acyl Δ5 desaturation in gilthead sea bream ( Sparus aurata ) cells

Marine fish are known to have an absolute dietary requirement for C20 and C22 highly unsaturated fatty acids. Previous studies using cultured cell lines indicated that underlying this requirement in marine fish was either a deficiency in fatty acyl Δ5 desaturase or C18-20 elongase activity. Recently, Ghioni et al. (Biochim. Biophys. Acta, 1437, 170-181, 1999) presented evidence that in turbot cells there was low activity of C18-20 elongase whereas Δ5 desaturase had high activity. In the present study, the fatty acid desaturase/elongase pathway was investigated in a cell line (SAF-1) from another carnivorous marine fish, sea bream. The metabolic conversions of a range of radiolabelled polyunsaturated fatty acids that comprised the direct substrates for Δ6 desaturase ([1-14C]18:2n-6 and [1-14C]18:3n-3), C18-20 elongase ([U-14C]18:4n-3), Δ5 desaturase ([1-14C]20:3n-6 and [U-14C]20:4n-3) and C20-22 elongase ([1-14C]20:4n-6 and [1-14C]20:5n-3) were utilized. The results showed that fatty acyl Δ6 desaturase in SAF-1 cells was highly active and there was substantial C18-20 elongase and C20-22 elongase activities. A deficiency in the desaturation/elongation pathway was clearly identified at the level of the fatty acyl Δ5 desaturase which was very low, particularly with 20:4n-3 as substrate. In comparison, the apparent activities of Δ6 desaturase, C18-20 elongase and C20-22 elongase were approximately 94-fold, 27-fold and 16-fold greater than that for Δ5 desaturase towards their respective n-3 polyunsaturated fatty acid substrates. The evidence obtained in the SAF-1 cell line is consistent with the dietary requirement for C20 and C22 highly unsaturated fatty acids in the marine fish, the sea bream, being primarily due to a deficiency in fatty acid Δ5 desaturase activity

History effects and pinning regimes in solid vortex matter

We propose a phenomenological model that accounts for the history effects observed in ac susceptibility measurements in YBa2Cu3O7 single crystals [Phys. Rev. Lett. 84, 4200 (2000) and Phys. Rev. Lett. 86, 504 (2001)]. Central to the model is the assumption that the penetrating ac magnetic field modifies the vortex lattice mobility, trapping different robust dynamical states in different regions of the sample. We discuss in detail on the response of the superconductor to an ac magnetic field when the vortex lattice mobility is not uniform inside the sample. We begin with an analytical description for a simple geometry (slab) and then we perform numerical calculations for a strip in a transverse magnetic field which include relaxation effects. In calculations, the vortex system is assumed to coexist in different pinning regimes. The vortex behavior in the regions where the induced current density j has been always below a given threshold (j_c^>) is described by an elastic Campbell-like regime (or a critical state regime with local high critical current density, j_c^>). When the VS is shaken by symmetrical (e.g. sinusoidal) ac fields, the critical current density is modified to j_c^) at regions where vortices have been forced to oscillate by a current density larger than j_c^>. Experimentally, an initial state with high critical current density (j_c^>) can be obtained by zero field cooling, field cooling (with no applied ac field) or by shaking the vortex lattice with an asymmetrical (e.g. sawtooth) field. We compare our calculations with experimental ac susceptibility results in YBa2Cu3O7 single crystals.Comment: 11 pages, 7 figures. To be published in PR

Plant invasions in South Africa: Insights from the 2017 National Status Report on Biological Invasions

The impacts of biological invasions are increasing and are felt by all sectors of society. The Department of Environmental Affairs currently invests over R1.5 billion a year on managing biological invasions, mostly on alien plant control. In this talk we discuss the key findings of the first National Status Report on Biological Invasions in South Africa (produced October 2017). In contrast to many other countries, the most diverse, widespread, and damaging invaders in South Africa are plants. They are the third-largest threat to South Africa’s terrestrial biodiversity; invasive trees and shrubs reduce surface water resources by between 3 and 5%; and they have reduced the capacity of natural rangelands to support livestock production by over 100 000 large livestock units. The size of the problem is increasing. While the risk from legally introduced alien species is being addressed, the risk due to accidental introductions is probably increasing. Data from the Southern African Plant Invaders Atlas (SAPIA) show that over the past decade, an average of ten plant species per year have naturalised, and even the most widespread invaders are still spreading. In short, South Africa has a major plant invasion debt. More taxa should be listed under national regulations, but ultimately more needs to be done to ensure that management is strategic and effective. One of the main success stories, however, is biological control. The technology has led to significant and on-going economic returns. If we are to improve policy and management decisions we need more systematic estimates of the area and abundance of plant invasions; more studies documenting the ecological and socio-economic impacts of plant invasions; better planning, including the setting of goals; and better monitoring of the effectiveness of current control operations. We welcome ideas, in particular for how SAPIA should develop in future