High titers of transmissible spongiform encephalopathy infectivity associated with extremely low levels of PrP in vivo

Rona Barron - ORCID: 0000-0003-4512-9177 https://orcid.org/0000-0003-4512-9177Diagnosis of transmissible spongiform encephalopathy (TSE) disease in humans and ruminants relies on the detection in post-mortem brain tissue of the protease-resistant form of the host glycoprotein PrP. The presence of this abnormal isoform (PrPSc) in tissues is taken as indicative of the presence of TSE infectivity. Here we demonstrate conclusively that high titers of TSE infectivity can be present in brain tissue of animals that show clinical and vacuolar signs of TSE disease but contain low or undetectable levels of PrPSc. This work questions the correlation between PrPSc level and the titer of infectivity and shows that tissues containing little or no proteinase K-resistant PrP can be infectious and harbor high titers of TSE infectivity. Reliance on protease-resistant PrPSc as a sole measure of infectivity may therefore in some instances significantly underestimate biological properties of diagnostic samples, thereby undermining efforts to contain and eradicate TSEs.https://doi.org/10.1074/jbc.M704329200282pubpub4

Thermal noise properties of two aging materials

In this lecture we review several aspects of the thermal noise properties in two aging materials: a polymer and a colloidal glass. The measurements have been performed after a quench for the polymer and during the transition from a fluid-like to a solid-like state for the gel. Two kind of noise has been measured: the electrical noise and the mechanical noise. For both materials we have observed that the electric noise is characterized by a strong intermittency, which induces a large violation of the Fluctuation Dissipation Theorem (FDT) during the aging time, and may persist for several hours at low frequency. The statistics of these intermittent signals and their dependance on the quench speed for the polymer or on sample concentration for the gel are studied. The results are in a qualitative agreement with recent models of aging, that predict an intermittent dynamics. For the mechanical noise the results are unclear. In the polymer the mechanical thermal noise is still intermittent whereas for the gel the violation of FDT, if it exists, is extremely small.Comment: to be published in the Proceedings of the XIX Sitges Conference on ''Jammming, Yielding and Irreversible Deformation in Condensed Matter'', M.-C.Miguel and M. Rubi eds.,Springer Verlag, Berli

Farmers' Taxonomies as a Participatory Diagnostic Tool: Soil Fertility Management in Chihota, Zimbabwe

Soil infertility is a major constraint to food production in the communal areas of Zimbabwe. Smallholders in the region recognize the problems of low soil fertility and have devised ways of coping with them. This study describes the use of farmers� taxonomies of themselves and their soils to identify and understand the options they have, and the constraints they face in managing poor soil fertility in Chihota, a sub-humid communal area of north central Zimbabwe. It is part of an effort by a group of agricultural researchers and extensionists working on improved soil fertility technologies, to better integrate their work with farmers in order to expose the latter to promising technologies, get feedback on the technologies merits and feasibility, and help farmers experiment with them. The results show that these farmers have relatively sophisticated taxonomies, which provide a good picture of the resources, constraints, and concerns they have about soil infertility and ways to manage it. The taxonomies are an important framework for integration of technical interventions with farmers� requirements, systems, and circumstances.participatory methods, soil fertility, local taxonomies, smallholders, Zimbabwe, Farm Management, Land Economics/Use,

Simultaneous and accurate measurement of the dielectric constant at many frequencies spanning a wide range

We present an innovative technique which allows the simultaneous measurement of the dielectric constant of a material at many frequencies, spanning a four orders of magnitude range chosen between 10 --2 Hz and 10 4 Hz. The sensitivity and accuracy are comparable to those obtained using standard single frequency techniques. The technique is based on three new and simple features: a) the precise real time correction of the amplication of a current amplier; b) the specic shape of the excitation signal and its frequency spectrum; and c) the precise synchronization between the generation of the excitation signal and the acquisition of the dielectric response signal. This technique is useful in the case of relatively fast dynamical measurements when the knowledge of the time evolution of the dielectric constant is needed

Symmetrical Temperature-Chaos Effect with Positive and Negative Temperature Shifts in a Spin Glass

The aging in a Heisenberg-like spin glass Ag(11 at% Mn) is investigated by measurements of the zero field cooled magnetic relaxation at a constant temperature after small temperature shifts $|\Delta T/T_g| < 0.012$. A crossover from fully accumulative to non-accumulative aging is observed, and by converting time scales to length scales using the logarithmic growth law of the droplet model, we find a quantitative evidence that positive and negative temperature shifts cause an equivalent restart of aging (rejuvenation) in terms of dynamical length scales. This result supports the existence of a unique overlap length between a pair of equilibrium states in the spin glass system.Comment: 4 page

Combining market and nonmarket food sources provides rural households with more options to achieve better diets in Southern Benin

This study examines the relative contributions to dietary diversity of the diversity of plant and domesticated animal species which rural households produce or collect, i.e., nonmarket food sources, versus the diversity of foods purchased in markets. Although opinions differ in the literature as to their relative importance, clarifying how different sources of food contribute to the dietary diversity of rural households in the developing world is important to inform policies and interventions to improve their food security and dietary quality. This case study was carried out among a random sample of 654 rural households in southern Benin during two seasons: when food is plentiful after harvest; and when food is scarcer between harvests. We collected data on crops, wild plants, and domesticated animals utilized by households, the number of markets they visited, and the diet of a mother in the household, with a structured 24-hour food frequency questionnaire. We hypothesize that the number of markets visited is an indicator of the diversity of foods available in the markets they have access to, and thus shows the contribution of markets as food sources. Results support this hypothesis and show that households that produced more plant and domesticated animal species and those that visited more markets had more diversified diets. Obtaining diverse foods from multiple sources provides households with more options to achieve better diets. These results suggest a need for a more holistic approach that recognizes the complementarities between market and nonmarket sources of foods. This approach should build on the diversity of species rural households already utilize, and on the ways they interact with markets

Intermittent origin of the large violations of the fluctuation dissipation relations in an aging polymer glass

The fluctuation-dissipation relation (FDR) is measured on the dielectric properties of a polymer glass (polycarbonate)in the range $20mHz - 100Hz$. It is found that after a quench below the glass transition temperature the fluctuation dissipation theorem is strongly violated. The amplitude and the persistence time of this violation are decreasing functions of frequency. At frequencies larger than 1Hz it persists for about $3h$. The origin of this violation is a highly intermittent dynamics characterized by large fluctuations. The relevance of these results for recent models of aging dynamics are discussed.Comment: to be published in Europhysics Letter

Random Matrix Theory and Classical Statistical Mechanics. I. Vertex Models

A connection between integrability properties and general statistical properties of the spectra of symmetric transfer matrices of the asymmetric eight-vertex model is studied using random matrix theory (eigenvalue spacing distribution and spectral rigidity). For Yang-Baxter integrable cases, including free-fermion solutions, we have found a Poissonian behavior, whereas level repulsion close to the Wigner distribution is found for non-integrable models. For the asymmetric eight-vertex model, however, the level repulsion can also disappearand the Poisson distribution be recovered on (non Yang--Baxter integrable) algebraic varieties, the so-called disorder varieties. We also present an infinite set of algebraic varieties which are stable under the action of an infinite discrete symmetry group of the parameter space. These varieties are possible loci for free parafermions. Using our numerical criterion we have tested the generic calculability of the model on these algebraic varieties.Comment: 25 pages, 7 PostScript Figure