Neel order, ring exchange and charge fluctuations in the half-filled Hubbard model

We investigate the ground state properties of the two dimensional half-filled one band Hubbard model in the strong (large-U) to intermediate coupling limit ({\it i.e.} away from the strict Heisenberg limit) using an effective spin-only low-energy theory that includes nearest-neighbor exchange, ring exchange, and all other spin interactions to order t(t/U)^3. We show that the operator for the staggered magnetization, transformed for use in the effective theory, differs from that for the order parameter of the spin model by a renormalization factor accounting for the increased charge fluctuations as t/U is increased from the t/U -> 0 Heisenberg limit. These charge fluctuations lead to an increase of the quantum fluctuations over and above those for an S=1/2 antiferromagnet. The renormalization factor ensures that the zero temperature staggered moment for the Hubbard model is a monotonously decreasing function of t/U, despite the fact that the moment of the spin Hamiltonien, which depends on transverse spin fluctuations only, in an increasing function of t/U. We also comment on quantitative aspects of the t/U and 1/S expansions.Comment: 9 pages - 3 figures - References and details to help the reader adde

Dense colloidal suspensions under time-dependent shear

We consider the nonlinear rheology of dense colloidal suspensions under a time-dependent simple shear flow. Starting from the Smoluchowski equation for interacting Brownian particles advected by shearing (ignoring fluctuations in fluid velocity) we develop a formalism which enables the calculation of time-dependent, far-from-equilibrium averages. Taking shear-stress as an example we derive exactly a generalized Green-Kubo relation, and an equation of motion for the transient density correlator, involving a three-time memory function. Mode coupling approximations give a closed constitutive equation yielding the time-dependent stress for arbitrary shear rate history. We solve this equation numerically for the special case of a hard sphere glass subject to step-strain.Comment: 4 page

Reply to Comment on " Universal Fluctuations in Correlated Systems"

Reply to the comment, cond-mat/0209398 by by N.W. Watkins, S.C. Chapman, and G. RowlandsComment: To appear In Physical Review Letter

Quantum kagome antiferromagnet in a magnetic field: Low-lying non-magnetic excitations versus valence-bond crystal order

We study the ground state properties of a quantum antiferromagnet on the kagome lattice in the presence of a magnetic field, paying particular attention to the stability of the plateau at magnetization 1/3 of saturation and the nature of its ground state. We discuss fluctuations around classical ground states and argue that quantum and classical calculations at the harmonic level do not lead to the same result in contrast to the zero-field case. For spin S=1/2 we find a magnetic gap below which an exponential number of non-magnetic excitations are present. Moreover, such non-magnetic excitations also have a (much smaller) gap above the three-fold degenerate ground state. We provide evidence that the ground state has long-range order of valence-bond crystal type with nine spins in the unit cell.Comment: 5 pages including 4 figures, uses REVTeX4; final version with some small extensions; to appear in Phys. Rev.

Severe acute malnutrition in children aged under 5 years can be successfully managed in a non-emergency routine community healthcare setting in Ghana

This study investigated the performance of community-based management of severe acute malnutrition (CMAM) within routine healthcare services in Ghana. This was a retrospective cohort study of n = 488 children (6–59 months) who had received CMAM. Data for recovery, default, and mortality rates were obtained from enrolment cards in 56 outpatient centres in Upper East region, Ghana. Satisfactory rates of recovery of 71.8% were reported. Children who were enrolled with higher mid-upper arm circumference (MUAC) ≥11.5 cm had seven times greater chance of recovery compared with children who were enrolled with lower MUAC <11.5 cm, OR = 7.35, 95% CI [2.56, 21.15], p < .001. Children who were diagnosed without malaria at baseline were 30 times, OR = 30.39, 95% CI [10.02, 92.13], p < .001, more likely to recover compared with those with malaria (p < .001). The average weight gain was 4.7 g−1·kg−1·day−1, which was influenced by MUAC status at baseline, β = .78, 95% CI [0.46, 1.00], p < .001, presence of malaria, β = −1.25, 95% CI [−1.58, 0.92], p < .001, and length of stay, β = 0.13, 95% CI [0.08, 0.18], p < .001. The default rate (28.5%) was higher than international standards recommendations by Sphere. Mortality rate (1.6%) was lower than international standards. Our findings suggest that community-based management of SAM can achieve similar success when delivered in routine non-emergency settings. However, this success can be diluted by a high default rate, and the factors contributing to this need to be explored to improve programme effectiveness within communities

Review of food-based dietary guidelines in Africa: Opportunities to enhance the healthiness and environmental sustainability of population diets

Food-based dietary guidelines (FBDGs) are important tools for promoting healthy eating and nutrition education at the population level. Currently,&nbsp; more than 100 countries worldwide have developed FBDGs with majority of existing FBDGs in highincome countries. However, there are a few&nbsp; countries in Africa which have developed FBDGs. This review describes and compares the characteristics of existing FBDGs in Africa. Data were&nbsp; extracted from all existing FBDGs from African countries which have been archived in the Food and Agriculture Organization’s (FAO) online&nbsp; repository of FBDGs. In addition, supporting documentation from other sources linked to the identified FBDGs were also reviewed. Extracted data&nbsp; were coded and synthesized to describe the purpose of the FBDGs, the process for developing the FBDGs, and how healthy diets were expressed in&nbsp; the FBDGs. In addition, the FBDGs were examined for content on considerations for planetary health, and non-dietary recommendations. A checklist&nbsp; was used to extract the evidence in the identified documents. Of the 47 African countries in the WHO Africa region, only eight FBDGs were&nbsp; identified from seven countries. South Africa had two FBDGs (including a FBDG for young children). Multi-disciplinary technical working groups were&nbsp; convened in developing majority of the FBDGs. The working groups utilised scientific evidence on diet-related diseases and nutrient&nbsp; requirements as a basis for recommendations. All the FBDGs were intended as a tool for promoting healthy diets among the lay population. The&nbsp; FBDGs that were reviewed included between six and sixteen dietary messages. Diet diversification was promoted as the most common&nbsp; recommendation across African country FBDGs. The recommendations often promoted consumption of four to six food groups communicated&nbsp; using text as well as images (food guide). Local availability and cultural acceptability were important values promoted as part of an optimal diet in&nbsp; some of the countries. However, none of the recommendations addressed environmental sustainability. Apart from South Africa, none of the FBDGs&nbsp; had been evaluated or revised. Across Africa, there is a need for increased focus on developing new FBDGs or revising existing ones as a tool for&nbsp; meeting the dietary information needs of populations at risk of malnutrition in all its forms.&nbsp

Origin of the approximate universality of distributions in equilibrium correlated systems

We propose an interpretation of previous experimental and numerical experiments, showing that for a large class of systems, distributions of global quantities are similar to a distribution originally obtained for the magnetization in the 2D-XY model . This approach, developed for the Ising model, is based on previous numerical observations. We obtain an effective action using a perturbative method, which successfully describes the order parameter fluctuations near the phase transition. This leads to a direct link between the D-dimensional Ising model and the XY model in the same dimension, which appears to be a generic feature of many equilibrium critical systems and which is at the heart of the above observations.Comment: To appear in Europhysics Letter

A review of food-based dietary guidelines in Africa: opportunities to enhance the healthiness and environmental sustainability of population diets

Food-based dietary guidelines (FBDGs) are important tools for promoting healthy eating and nutrition education at the population level. Currently, more than 100 countries worldwide have developed FBDGs with majority of existing FBDGs in highincome countries. However, there are a few countries in Africa which have developed FBDGs. This review describes and compares the characteristics of existing FBDGs in Africa. Data were extracted from all existing FBDGs from African countries which have been archived in the Food and Agriculture Organization’s (FAO) online repository of FBDGs. In addition, supporting documentation from other sources linked to the identified FBDGs were also reviewed. Extracted data were coded and synthesized to describe the purpose of the FBDGs, the process for developing the FBDGs, and how healthy diets were expressed in the FBDGs. In addition, the FBDGs were examined for content on considerations for planetary health, and non-dietary recommendations. A checklist was used to extract the evidence in the identified documents. Of the 47 African countries in the WHO Africa region, only eight FBDGs were identified from seven countries. South Africa had two FBDGs (including a FBDG for young children). Multi-disciplinary technical working groups were convened in developing majority of the FBDGs. The working groups utilised scientific evidence on diet-related diseases and nutrient requirements as a basis for recommendations. All the FBDGs were intended as a tool for promoting healthy diets among the lay population. The FBDGs that were reviewed included between six and sixteen dietary messages. Diet diversification was promoted as the most common recommendation across African country FBDGs. The recommendations often promoted consumption of four to six food groups communicated using text as well as images (food guide). Local availability and cultural acceptability were important values promoted as part of an optimal diet in some of the countries. However, none of the recommendations addressed environmental sustainability. Apart from South Africa, none of the FBDGs had been evaluated or revised. Across Africa, there is a need for increased focus on developing new FBDGs or revising existing ones as a tool for meeting the dietary information needs of populations at risk of malnutrition in all its forms

Tensorial Constitutive Models for Disordered Foams, Dense Emulsions, and other Soft Nonergodic Materials

In recent years, the paradigm of `soft glassy matter' has been used to describe diverse nonergodic materials exhibiting strong local disorder and slow mesoscopic rearrangement. As so far formulated, however, the resulting `soft glassy rheology' (SGR) model treats the shear stress in isolation, effectively `scalarizing' the stress and strain rate tensors. Here we offer generalizations of the SGR model that combine its nontrivial aging and yield properties with a tensorial structure that can be specifically adapted, for example, to the description of fluid film assemblies or disordered foams.Comment: 18 pages, 4 figure