The vortex depinning transition in untwinned YBaCuO using complex impedance measurements

We present surface impedance measurement of the vortex linear response in a large untwinned YBCO crystal. The depinning spectra obtained over a broad frequency range (100 Hz- 30 MHz) are those of a surface pinned vortex lattice with a free flux flow resistivity (two modes response). The critical current in the "Campbell" like regime and the flux flow resistivity in the dissipative regime are extracted. Those two parameters are affected by the first order transition, showing that this transition may be related to the electronic state of vortices.Comment: to be published in the proceedings of M2S RI

Physicochemical changes in maize plant (Zea mays) grown on contaminated soil exposed to sawdust treatment

The potential effects of sawdust for bioremediation of growing maize grown on crude oil contaminated soil was evaluated in this study. The experiment was divided into 3 groups control (soil without crude oil), polluted (soil with varying concentrations of crude oil), and sawdust treated (polluted soil with 50g sawdusts). The polluted and sawdust treated regime received four levels of treatments with crude oil (25g, 50g, 75g and 100g). Viable seeds of maize were grown on the soil beds for 35 days to assess the % germination, % survival, stem height, chlorophyll a and b, oxidative stress indicators and selected macronutrients using standard methods. Data obtained shows that the growth performance of the sawdust treated samples containing low concentration of crude oil was better in comparison to polluted groups but less than that of control. Sawdust remediation helped in overcoming the growth inhibition due to pollution to some extent. Significant increase (p<0.001) in the activity of antioxidant enzymes (superoxide dismutase, catalase and peroxidase) were observed in the sawdust treated regime when compared with the polluted and control groups. The result also showed a significant decrease (p<0.001) in Malondialdehyde levels and a non- significant increase (p>0.05) in macronutrients assessed in the remediated regime when compared with the polluted regime. Remediation of the polluted soil with sawdust relieved the inhibitory effect of crude oil on the plant growth particularly in groups containing lower concentrations of crude oil.Keywords: crude oil, sawdust, antioxidants, oxidative stres

Prevalence of glycosuria and diabetes among Indians and Bantu

No Abstract

A novel method for the analysis of particle coating behaviour via contact spreading in a tumbling drum: Effect of coating liquid viscosity

Spray coating is a common method of distributing liquids over powders, especially in the pharmaceutical, detergent and food industries. During this process, liquid drops are deposited on the surface of particles. Liquid is then transferred between particles via particle collisions, in a process called liquid contact spreading. This contact spreading process facilitates inter-particle coating, in which wetting, de-wetting, mixing and drying are occurring simultaneously. This work presents the first experimental study of the mechanism of liquid contact spreading. In this work, a novel experimental method has been developed to investigate the mechanism of contact spreading, incorporating a newly developed image analysis technique, based on colourimetric measurements, to quantitatively determine coating behaviour via contact spreading. Here, experiments designed to isolate the contact spreading coating mechanism were performed in a tumbling drum using a model material system; alumina particles and dyed polyethylene glycol solutions of varying viscosities. The coating uniformity was quantified by the variation in inter-particle coating; the coefficient of variation (CoV). For all systems, the uniformity of the coating increased with time until the CoV decreased to an asymptotic value. The rate of the decrease in the CoV was successfully fitted using an exponential decay function. The viscosity of the coating solution had a significant effect on the rate of liquid transfer; the lower the viscosity the faster the contact spreading process. This effect is attributed to differences in the formation and stability of liquid bridges between the particles, influencing the extent of liquid transfer. The results also show that in most cases examined here, viscous forces play a main role in the contact spreading process, and the contribution of capillary forces are minimal. This understanding could assist the design and scale up for the wet coating processes

Instabilities in the Flux Line Lattice of Anisotropic Superconductors

The stability of the flux line lattice has been investigated within anisotropic London theory. This is the first full-scale investigation of instabilities in the `chain' state. It has been found that the lattice is stable at large fields, but that instabilities occur as the field is reduced. The field at which these instabilities first arise, $b^*(\epsilon,\theta)$, depends on the anisotropy $\epsilon$ and the angle $\theta$ at which the lattice is tilted away from the $c$-axis. These instabilities initially occur at wavevector $k^*(\epsilon,\theta)$, and the component of $k^*$ along the average direction of the flux lines, $k_z$, is always finite. As the instability occurs at finite $k_z$ the dependence of the cutoff on $k_z$ is important, and we have used a cutoff suggested by Sudb\ospace and Brandt. The instabilities only occur for values of the anisotropy $\epsilon$ appropriate to a material like BSCCO, and not for anisotropies more appropriate to YBCO. The lower critical field $H_{c_1}(\phi)$ is calculated as a function of the angle $\phi$ at which the applied field is tilted away from the crystal axis. The presence of kinks in $H_{c_1}(\phi)$ is seen to be related to instabilities in the equilibrium flux line structure.Comment: Extensively revised paper, with modified analysis of elastic instabilities. Calculation of the lower critical field is included, and the presence of kinks in $H_{c_1}$ is seen to be related to the elastic instabilities. 29 pages including 16 figures, LaTeX with epsf styl

Rotating ellipsoidal catalytic micro-swimmers via glancing angle evaporation

The ability to generate rotation in ellipsoidal catalytic micro swimming devices by catalyst deposition at glancing angles allows reliable access to circling trajectories. This behaviour could enable propulsive ellipsoids to gather cargo and enhance mixing at small scales. Catalytically propelled colloidal rotation has been previously achieved in spherical swimming devices by means of neighbour shadowing during catalyst deposition leading to non-symmetrical coatings. However in this work shadowing effects arise due to the ellipsoid's inherent anisotropy, removing the requirement for a closely packed colloidal crystal monolayer. We use geometric analysis of the catalyst deposition process, and mechanistic understanding to propose a link between the observed trajectories and the catalyst distribution and suggest further routes to improve control of rotation rates

Effects of unidirectional flow shear stresses on the formation, fractal microstructure and rigidity of incipient whole blood clots and fibrin gels

Incipient clot formation in whole blood and fibrin gels was studied by the rheometric techniques of controlled stress parallel superposition (CSPS) and small amplitude oscillatory shear (SAOS). The effects of unidirectional shear stress on incipient clot microstructure, formation kinetics and elasticity are reported in terms of the fractal dimension (df ) of the fibrin network, the gel network formation time (TGP ) and the shear elastic modulus, respectively. The results of this first haemorheological application of CSPS reveal the marked sensitivity of incipient clot microstructure to physiologically relevant levels of shear stress, these being an order of magnitude lower than have previously been studied by SAOS. CSPS tests revealed that exposure of forming clots to increasing levels of shear stress produces a corresponding elevation in df , consistent with the formation of tighter, more compact clot microstructures under unidirectional flow. A corresponding increase in shear elasticity was recorded. The scaling relationship established between shear elasticity and df for fibrin clots and whole blood confirms the fibrin network as the dominant microstructural component of the incipient clot in terms of its response to imposed stress. Supplementary studies of fibrin clot formation by rheometry and microscopy revealed the substantial additional network mass required to increase df and provide evidence to support the hypothesis that microstructural changes in blood clotted under unidirectional shear may be attributed to flow enhanced thrombin generation and activation. CSPS also identified a threshold value of unidirectional shear stress above which no incipient clot formation could be detected. CSPS was shown to be a valuable haemorheological tool for the study of the effects of physiological and pathological levels of shear on clot properties

Universality of Frequency and Field Scaling of the Conductivity Measured by Ac-Susceptibility of a Ybco-Film

Utilizing a novel and exact inversion scheme, we determine the complex linear conductivity $\sigma (\omega )$ from the linear magnetic ac-susceptibility which has been measured from 3\,mHz to 50\,MHz in fields between 0.4\,T and 4\,T applied parallel to the c-axis of a 250\,nm thin disk. The frequency derivative of the phase $\sigma ''/\sigma '$ and the dynamical scaling of $\sigma (\omega)$ above and below $T_g(B)$ provide clear evidence for a continuous phase transition at $T_g$ to a generic superconducting state. Based on the vortex-glass scaling model, the resulting critical exponents $\nu$ and $z$ are close to those frequently obtained on films by other means and associated with an 'isotropic' vortex glass. The field effect on $\sigma(\omega)$ can be related to the increase of the glass coherence length, $\xi_g\sim B$.Comment: 8 pages (5 figures upon request), revtex 3.0, APK.94.01.0

Elasticity-driven interaction between vortices in type-II superconductors

The contribution to the vortex lattice energy which is due to the vortex-induced strains is calculated covering all the magnetic field range which defines the vortex state. This contribution is compared with previously reported ones what shows that, in the most part of the vortex state, it has been notably underestimated until now. The reason of such underestimation is the assumption that only the vortex cores induce strains. In contrast to what is generally assumed, both core and non-core regions are important sources of strains in high-$\kappa$ superconductors.Comment: 10 pages, 1 figure, revtex

Phase Transitions in Isolated Vortex Chains

In very anisotropic layered superconductors (e.g. Bi$_2$Sr$_2$CaCu$_2$O$_x$) a tilted magnetic field can penetrate as two co-existing lattices of vortices parallel and perpendicular to the layers. At low out-of-plane fields the perpendicular vortices form a set of isolated vortex chains, which have recently been observed in detail with scanning Hall-probe measurements. We present calculations that show a very delicate stability of this isolated-chain state. As the vortex density increases along the chain there is a first-order transition to a buckled chain, and then the chain will expel vortices in a continuous transition to a composite-chain state. At low densities there is an instability towards clustering, due to a long-range attraction between the vortices on the chain, and at very low densities it becomes energetically favorable to form a tilted chain, which may explain the sudden disappearance of vortices along the chains seen in recent experiments.Comment: 9 pages, 10 figure