Use of modelling to inform public health policy: a case study on the blood-borne transmission of variant-CJD

Since the identification of variant Creutzfeldt–Jacob Disease in the late 1980s, the possibility that this disease might be passed on via blood transfusion has presented challenging policy questions for Government and blood services in the UK. This paper discusses the use of mathematical modelling to inform policy in this area of health protection. We focus on the use of a relatively simple analytical model to explore how many such infections might eventually be expected to result in clinical cases under a range of alternative scenarios of interest to policy, and on the potential impact of possible additional counter measures. We comment on the value of triangulating between findings generated using distinct modelling approaches and observational data

Landau Theory of Domain Wall Magnetoelectricity

We calculate the exact analytical solution to the domain wall properties in a multiferroic system with two order parameters that are coupled bi-quadratically. This is then adapted to the case of a magnetoelectric multiferroic material such as BiFeO3, with a view to examine critically whether the domain walls can account for the enhancement of magnetization reported for thin films fo this material, in view of the correlation between increasing magnetization and increasing volume fraction of domain walls as films become thinner. The present analysis can be generalized to describe a class of magnetoelectric devices based upon domain walls rather than bulk properties.Comment: 9 pages, 4 figure

Enhanced electric conductivity at ferroelectric vortex cores in BiFeO3

In many large ensembles, the property of the system as a whole cannot be understood from studying the individual entities alone ¿ these ensembles can be made up by neurons in the brain, transport users in traffic networks or data packages in the Internet. The past decade has seen important progress in our fundamental understanding of what such seemingly disparate 'complex systems' have in common; some of these advances are surveyed here

Landau Theory of Ferroelectric Domain Walls in Magnetoelectrics

V. Janovec and J. Privratska developed [Ferroelectrics 204, 321 (1997)] a group theoretical model for the existence of pyromagnetism (or pyroelectricity) within the domain walls of an antiferromagnet (or antiferroelectric). However, their approach did not permit any estimate of magnitudes, or even whether it would be observable. In the present work we extend the Janovec-Privratska theory to an analytic model of magnitudes (local magnetization and polarization) within the domain-walls and discuss the wall thickness and domain widths as a function of those magnitudes. Specifically, it is shown that both the wall thickness and the domain width of magnetoelectric multiferroics are bigger than for pure ferroelectrics and smaller than for pure ferromagnets. It is also shown how ferroelectric domain walls in magnetoelectric materials may have net magnetization even when the domains themselves are still paramagnetic. Possible implications for magnetoelectric BiFeO3 are indicated

How do the grains slide in fine-grained zirconia polycrystals at high temperature?

International audienceDegradation of mechanical properties of zirconia polycrystals is hardly discussed in terms of solution-precipitation grain-boundary sliding due to experimental controversies over imaging of intergranular amorphous phases at high and room temperatures. Here, the authors applied the techniques of mechanical spectroscopy and transmission electron microscopy (TEM) to shed light on the amorphization of grain interfaces at high temperature where the interface reaction determines the behavior of fine-grained zirconia polycrystals. They present mechanical spectroscopy results, which yield evidences of an intergranular amorphous phase in silica doped and in high-purity zirconia. Quenching of zirconia polycrystals reveals an intergranular amorphous phase on TEM images at room temperatur

Ultrathin organic transistors on oxide surfaces

We have built a model organic field-effect transistor that is basically composed of a single layer of pentacene crystal in interaction with an oxide surface. Drain and source contacts are ohmic so that the pentacene layer can carry a current density as high as 3000 A cm-2 at a gate voltage of -60 V. Four-probe and two-probe transport measurements as a function of temperature and fields are presented in relation with structural near-field observations. The experimental results suggest a simple two-dimensional model where the equilibrium between free and trapped carriers at the oxide interface determines the OFET characteristics and performanceLOMM860924

Memory effect of a mechanical anomaly related to ferroelastic domain switching in rhombohedral lead zirconate titanate ceramics

Can Wang, Simon A. T. Redfern, Maren Daraktchiev, and Richard J. Harrison Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ United Kingdom An anomaly in the temperature dependent mechanical properties of a lead zirconate titanate ferroelectric ceramic has been observed by dynamic mechanical analysis. The anomaly, seen as a rise in modulus, accompanied by a decrease in internal friction, occurs in the low-temperature phase below TC. The temperature of the anomalies varies systematically with the applied forces and the anomaly does exhibit a memory effect. The corresponding static bending deformation, mainly from remnant strain by ferroelastic domain switching, is analyzed, and a critical remnant strain value for triggering the anomaly is obtained. The anomaly is thought to be induced by pinning and depinning of domain walls. The results confirm that the memory effect and the occurrence of the anomaly are controlled by ferroelastic domain switchin

Effects of carbon nanotubes on grain boundary sliding in zirconia polycrystals

Mechanical properties of zirconia polycrystals decrease drastically at high temperature due to thermally activated grain boundary (GB) sliding, leading to plastic or even super-plastic deformation. As GB sliding is a source of energy dissipation in the material, mechanical loss measurements are well suited to study such a mechanism. They reveal, in general, a mechanical loss peak, which evolves into an exponential increase at higher temperature. When intergranular glassy films or/and amorphous pockets are presented in polycrystalline ceramics, the mechanical loss is globally higher and so is the creep rate. Here we show that introducing carbon nanotubes in zirconia, in particular, reduces drastically GB sliding and consequently the mechanical loss at high temperature. The nanotubes were observed at the grain boundaries by high-resolution transmission electron microscopy and were related to the reduction of superplasic flow through the boundaries, which should improve the material creep resistance

Effect of transformation twins on the anelastic behavior of polycrystalline Ca1-xSrxTiO3 and SrxBa1-xSnO3 perovskite in relation to the seismic properties of Earths mantle perovskite

The mechanical loss of Ca1−xSrxTiO3 as a function of temperature has been studied up to 1000 ◦C using dynamical mechanical analysis. The loss spectrum reveals a relaxation peak in the tetragonal phase and negligible mechanical loss in the cubic and orthorhombic phases. The peak is accompanied by a softening of the storage modulus, caused by the formation of mobile transformation twin domain walls. The small value of internal friction in the orthorhombic phase is associated with a negative volume strain, resulting in domain walls that are strongly pinned by lattice defects. The volume changes and mechanical loss in Ca1−xSrxTiO3 are compared with those in SrxBa1−xSnO3, a system which shows a positive volume strain. In contrast to Ca1−xSrxTiO3, SrxBa1−xSnO3 displays a thermally activated peak in the orthorhombic phase. A frequency-independent peak attributed to the tetragonal–orthorhombic transition is also seen. The positive volume strain in SrxBa1−xSnO3 results in domain wall structures that are less strongly pinned by lattice defects