Stokesian Dynamics simulation of Brownian suspensions

The non-equilibrium behaviour of concentrated colloidal dispersions is studied by Stokesian Dynamics, a general molecular-dynamics-like technique for simulating particles suspended in a viscous fluid. The simulations are of a suspension of monodisperse Brownian hard spheres in simple shear flow as a function of the Péclet number, Pe, which measures the relative importance of shear and Brownian forces. Three clearly defined regions of behaviour are revealed. There is first a Brownian-motion-dominated regime (Pe ≤ 1) where departures from equilibrium in structure and diffusion are small, but the suspension viscosity shear thins dramatically. When the Brownian and hydrodynamic forces balance (Pe ≈ 10), the dispersion forms a new ‘phase’ with the particles aligned in ‘strings’ along the flow direction and the strings are arranged hexagonally. This flow-induced ordering persists over a range of Pe and, while the structure and diffusivity now vary considerably, the rheology remains unchanged. Finally, there is a hydrodynamically dominated regime (Pe > 200) with a dramatic change in the long-time self-diffusivity and the rheology. Here, as the Péclet number increases the suspension shear thickens owing to the formation of large clusters. The simulation results are shown to agree well with experiment

Multidimensional Nature of Undernutrition: A Statistical Approach

The statistical assessment of undernutrition is usually restricted to a pairwise analysis of anthropometric indicators. The main objective of this study was to model the associations between underweight, stunting and wasting and to check whether multidimensionality of undernutrition can be justified from a purely statistical point of view. 3742 children aged 0 to 59 months were enrolled in a cross-sectional household survey (2004 Cameroon Demographic and Health Surveys (DHS)). The saturated loglinear model and the multiple correspondence analysis (MCA) showed no interaction and a highly significant association between underweight and stunting (P=0), underweight and wasting (P=0); but not between stunting and wasting (P=0.430). Cronbach's alpha coefficient between weight-for-age, height-for-age and weight-for-height was 0.62 (95% CI 0.59, 0.64). Thus, the study of these associations is not straightforward as it would appear in a first instance. The lack of three-factor interaction and the value of the Cronbach's alpha coefficient indicate that undernutrition is indeed (statistically) multidimensional. The three indicators are not statistically redundant; thus for the case of Cameroon the choice of a particular anthropometric indicator should depend on the goal of the policy maker, as it comes out of this study that no single indicator is to be used for all situations.Stunting; Wasting; Underweight; anthropometric measures; Z-score; Loglinear models

Using weight-for-age for predicting wasted children

Background: The equipments for taking body weights (scales) are more frequent in Cameroon health centres than measuring boards for heights. Even when the later exist there are some difficulties inherent in their qualities; thus the height measurement is not always available or accurate. Objective: To construct statistical models for predicting wasting from weight-for-age. Methods: 3742 children a ged 0 to 59 months were enrolled in a cross-sectional household survey (2004 Cameroon Demographic and Health Surveys (DHS)) covering the entire Cameroon national territory. Results: There were highly significant association between underweight and wasting. For all discriminant statistical methods used, the test error rates (using an independent testing sample) are less than 5%; the Area Under the Curve (AUC) using the Receiver Operating Characteristic (ROC) is 0.86. Conclusions: Weight-for-age can be used for accurately classifying a child whose wasting status is unknown. The result is useful in Cameroon as too often the height measurements may not be feasible, thus the need for estimating wasted children.Anthropometric measures, nutritional status, discriminant analysis, underweight, wasting

Interplane charge dynamics in a valence-bond dynamical mean-field theory of cuprate superconductors

We present calculations of the interplane charge dynamics in the normal state of cuprate superconductors within the valence-bond dynamical mean-field theory. We show that by varying the hole doping, the c-axis optical conductivity and resistivity dramatically change character, going from metallic-like at large doping to insulating-like at low-doping. We establish a clear connection between the behavior of the c-axis optical and transport properties and the destruction of coherent quasiparticles as the pseudogap opens in the antinodal region of the Brillouin zone at low doping. We show that our results are in good agreement with spectroscopic and optical experiments.Comment: 5 pages, 3 figure

Classification cards applied to team and individual learning.

Thesis (Ed.M.)--Boston Universit

Sound Velocity Anomaly at the Mott Transition: application to organic conductors and V2O3

Close to the Mott transition, lattice degrees of freedom react to the softening of electron degrees of freedom. This results in a change of lattice spacing, a diverging compressibility and a critical anomaly of the sound velocity. These effects are investigated within a simple model, in the framework of dynamical mean-field theory. The results compare favorably to recent experiments on the layered organic \kappa-(BEDT-TTF)_2Cu[N(CN)_2]Cl conductor . We predict that effects of a similar magnitude are expected for V2O3, despite the much larger value of the elastic modulus of this material.Comment: New discussion of the relation between the sound-velocity and the compressibility has been adde

Charge and spin density wave ordering transitions in strongly correlated metals

We study the quantum transition from a strongly correlated metal, with heavy fermionic quasiparticles, to a metal with commensurate charge or spin density wave order. To this end, we introduce and numerically analyze a large dimensionality model of Ising spins in a transverse field, coupled to two species of fermions; the analysis borrows heavily from recent progress in the solution of the Hubbard model in large dimensions. At low energies, the Ising order parameter fluctuations are characterized by the critical exponent $z \nu = 1$, while above an energy scale, $\Gamma$, there is a crossover to $z\nu = 1/2$ criticality. We show that $\Gamma$ is of the order of the width of the heavy quasiparticle band, and can be made arbitrarily small for a correlated metal close to a Mott-Hubbard insulator. Therefore, such a correlated metal has a significant intermediate energy range of $z\nu=1/2$ behavior, a single particle spectrum with a narrow quasiparticle band, and well-formed analogs of the lower and upper Hubbard bands; we suggest that these features are intimately related in general.Comment: 14 pages, REVTEX 3.0, 2 postscript figure

Heavy-fermion and spin-liquid behavior in a Kondo lattice with magnetic frustration

We study the competition between the Kondo effect and frustrating exchange interactions in a Kondo-lattice model within a large-${\cal N}$ dynamical mean-field theory. We find a T=0 phase transition between a heavy Fermi-liquid and a spin-liquid for a critical value of the exchange $J_c = T_{K}^0$, the single-impurity Kondo temperature. Close to the critical point, the Fermi liquid coherence scale $T^\star$ is strongly reduced and the effective mass strongly enhanced. The regime $T>T^\star$ is characterized by spin-liquid magnetic correlations and non-Fermi-liquid properties. It is suggested that magnetic frustration is a general mechanism which is essential to explain the large effective mass of some metallic compounds such as LiV$_2$O$_4$.Comment: 7 pages, 1 figure. Late

Microencapsulation of active ingredients in functional foods: From research stage to commercial food products

Background: Twelves categories of active ingredients have been recognised to enhance human health. They are to some extent susceptible to certain conditions such as heat, light and low pH. To reduce their susceptibility and achieve controlled release at the target site, various microencapsulation strategies have been introduced. Scope and approach: In this review, the chemical structures, physicochemical properties and beneficial effects of the active components are summarised. Different encapsulation techniques and tailored shell materials have been investigated to optimise the functional properties of microcapsules. Several encapsulated constituents (e.g., amino acids) have been successfully incorporated into food products while others such as lactic acid bacteria are mostly used in the free format. Encapsulating some of these active ingredients will extend their ability to withstand process conditions such as heat and shear, and prolong their shelf stability. Key findings and conclusions: The functional properties of a microcapsule are encapsulation efficiency, size, morphology, stability, and release characteristics. Several microencapsulation strategies include the use of double emulsions, hybrid wall materials and crosslinkers, increasing intermolecular attraction between shell and core, physical shielding of shell materials, and the addition of certain ions. Other approaches such as the use of hardening agents, nanoencapsulation, or secondary core materials, and the choice of shell materials possessing specific interactions with the core may be used to achieve targeted release of active ingredients. The physicochemical properties of shell materials influence where the active ingredients will be released in vivo. A suitable microencapsulation strategy of active ingredients will therefore expand their applications in the functional foods industry