The African Light Source: history, context and future.

The African Light Source (AfLS) project is now almost eight years old. This article assesses the history, current context and future of the project. There is by now considerable momentum in building the user community, including deep training, facilitating access to current facilities, growing the scientific output, scientific networks and growing the local laboratory-scale research infrastructure. The Conceptual Design Report for the AfLS is in its final editing stages. This document specifies the socio-economic and scientific rationales and the technical aspects amongst others. The AfLS is supported by many national and Pan-African scientific professional bodies and voluntary associates across many scientific disciplines, and there are stakeholders throughout the continent and beyond. The current roadmap phases have expanded to include national and Pan-African level conversations with policy makers through new Strategic Task Force groups. The document summarizes this progress and discusses the future of the project.

Instability of mixing layers: Momentum and thermal transport in the continuum breakdown regime.

We examine the momentum and thermal transport in the continuum breakdown regime of a mixing layer flow, which exhibits Kelvin-Helmholtz instability under ideal continuum conditions. The Grad 13 moment model is used as it provides an adequate description of the flow physics (second-order accurate in Knudsen number) in the transition regime. Analytical solutions are developed under breakdown conditions for two-dimensional, compressible, parallel shear flows. It is shown that the deviation of viscous stress and heat flux from the Navier-Stokes-Fourier system follows two different scaling regimes depending upon the Mach number. At low Mach numbers, the departure of all stress and heat-flux components depends only upon the Knudsen number. At high Mach number, the scaling of shear stress and transverse heat flux depends on the product of the Knudsen and Mach numbers. The normal stresses depend individually on the Knudsen and Mach number. The scaling results are verified against numerical simulations of compressible mixing layers performed using the unified gas kinetic scheme for various degrees of rarefaction.

Fluoroquinolone-Induced Sweet Syndrome: A Case Report.

Sweet syndrome (SS) is a rare non-vasculitic neutrophilic dermatosis. Fever, the abrupt emergence of tender erythematous plaques and nodules, with an occasional presentation of vesicles and pustules along with dense neutrophilic infiltrates on skin biopsy are the hallmarks of the illness. Tender plaques or nodules develop along with other systemic manifestations suddenly in affected people which is considered to occur due to immune-mediated hypersensitivity. We report a case of Sweet syndrome in Pakistan presenting in a 55-year-old female. It is worth reporting due to the rarity of such cases in this region. The patient was diagnosed after profound investigations and was treated with corticosteroid therapy.

Near-wall vortical structures in domains with and without curved surfaces.

Taylor-Couette flow is a canonical flow to study Taylor-Görtler (TG) instability or centrifugal instability and the associated vortices. TG instability has been traditionally associated with flow over curved surfaces or geometries. In the computational study, we confirm the presence of TG-like near-wall vortical structures in two lid-driven flow systems, the Vogel-Escudier (VE) and the lid-driven cavity (LDC) flows. The VE flow is generated inside a circular cylinder by a rotating lid (top lid in the present study), while the LDC flow is generated inside a square or rectangular cavity by the linear movement of the lid. We look at the emergence of these vortical structures through reconstructed phase space diagrams and find that the TG-like vortices are seen in the chaotic regimes in both flows. In the VE flow, these vortices are seen when the side-wall boundary layer instability sets in at large [Formula: see text]. The VE flow is observed to go to a chaotic state in a sequence of events from a steady state at low [Formula: see text]. In contrast to VE flows, in the LDC flow with no curved boundaries, TG-like vortices are seen at the emergence of unsteadiness when the flow exhibits a limit cycle. The LDC flow is observed to have transitioned to chaos from the steady state through a periodic oscillatory state. Various aspect ratio cavities are examined in both flows for the presence of TG-like vortices. This article is part of the theme issue 'Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical transactions paper (Part 2)'.

Continuum breakdown in compressible mixing layers.

Gas-kinetic simulations of rarefied and compressible mixing layers are performed to characterize continuum breakdown and the effect on the Kelvin-Helmholtz instability. The unified gas-kinetic scheme (UGKS) is used to perform the simulations at different Mach and Knudsen numbers. The UGKS stress tensor and heat-flux vector fields are compared against those given by the Navier-Stokes-Fourier constitutive equations. The most significant difference is seen in the shear stress and transverse heat flux. The study demonstrates the existence of two distinct continuum breakdown regimes, one at low and the other at high convective Mach numbers. Overall, at low convective Mach numbers, the deviation from continuum stress and heat flux appears to scale exclusively with the micro-macro length scale ratio given by the Knudsen number. On the other hand, at high convective Mach numbers, the deviation depends on the global micro-macro timescale ratio given by the product of Mach and Knudsen numbers. We further demonstrate that, unlike shear stresses and transverse heat flux, the deviations in normal stresses and the streamwise heat flux depend separately on Knudsen and Mach numbers. A local parameter called the gradient Knudsen number is proposed to characterize the rarefaction effects on the local momentum and thermal transport. Noncontinuum aspects of gas-kinetic stress-tensor and heat-flux behavior that Grad's 13-moment equation model reasonably captures are identified.

Dynamic effects in transition from regular to Mach reflection in steady supersonic flows.

The effect of rapid wedge rotation on the transition from regular (RR) to Mach reflection (MR) is investigated. This unsteady shock reflection transition is compared with the steady-state transition. The dependence of various flow features such as the unsteady Mach stem height, position of the reflection point, and shock angle at the reflection or triple point on the wedge angle for a fixed Mach number is compared at various rotation rates. The study is further extended to compare the dynamic effects for various Mach numbers in the strong shock reflection domain at higher wedge speeds. Transition lines corresponding to different rotation speeds are obtained similar to the detachment transition line in steady cases. It is found that the pivot point has only marginal effect on the transition point, but it substantially affects the Mach stem growth and the movement of the reflection point, specifically at higher Mach numbers. The location of the transition from the inlet also depends on the pivot point and the rate of rotation.

Influence of Knudsen and Mach numbers on Kelvin-Helmholtz instability.

The combined influence of rarefaction and compressibility on classical Kelvin-Helmholtz instability is investigated with numerical simulations employing the unified gas kinetic scheme. Five different regimes in the Reynolds-Mach-Knudsen number parameter space are identified. The flow features in various Mach and Knudsen number regimes are examined. Stabilizing action of compressibility leads to suppression of perturbation kinetic energy and vorticity and/or momentum thickness. The suppression due to rarefaction exhibits a different behavior. At high enough Knudsen numbers, even as the perturbation kinetic energy is suppressed, the vorticity and/or momentum thickness grows. The flow physics underlying the contrasting mechanisms of compressibility and rarefaction is highlighted.

Texture, flavor, and sensory quality of buffalo milk Cheddar cheese as influenced by reducing sodium salt content.

The adverse health effects of dietary sodium demand the production of cheese with reduced salt content. The study was aimed to assess the effect of reducing the level of sodium chloride on the texture, flavor, and sensory qualities of Cheddar cheese. Cheddar cheese was manufactured from buffalo milk standardized at 4% fat level by adding sodium chloride at 2.5, 2.0, 1.5, 1.0, and 0.5% (wt/wt of the curd obtained). Cheese samples were ripened at 6 to 8 °C for 180 d and analyzed for chemical composition after 1 wk; for texture and proteolysis after 1, 60, 120, and 180 d; and for volatile flavor compounds and sensory quality after 180 d of ripening. Decreasing the salt level significantly reduced the salt-in-moisture and pH and increased the moisture-in-nonfat-substances and water activity. Cheese hardness, toughness, and crumbliness decreased but proteolysis increased considerably on reducing the sodium content and during cheese ripening. Lowering the salt levels appreciably enhanced the concentration of volatile compounds associated with flavor but negatively affected the sensory perception. We concluded that salt level in cheese can be successfully reduced to a great extent if proteolysis and development of off-flavors resulted by the growth of starter and nonstarter bacteria can be controlled.

Outcome of monocular surgery for horizontal strabismus in Hyderabad.

BACKGROUND AND OBJECTIVE: Squint surgery is frequently performed successfully in Hyderabad. However, no study in any detail has been performed on the outcome of monocular surgery for horizontal squint in the region. This study aims to determine the results of monocular surgery for horizontal trabismus. DESIGN: Retrospective/observational study. SUBJECTS AND METHODS: The study was conducted on patients aged under 45 years, presenting with horizontal strabismus and undergoing monocular squint surgery. Anterior segment slit lamp examination, and if possible, posterior segment examination with 90 diopter (D) and 78 D fundoscopes was performed. Angle of deviation was measured. Patients were divided into two groups (esotropia and exotropia). Investigations were performed. Surgery was done under general anesthesia. A second surgical procedure was performed after six months for any residual deviations. RESULTS: After squint surgery, patients in group 1 (79%) and in group 2 (73.3%) had residual deviation of less than 15 prism diopters (PD). The preoperative deviations of 60 PD or less illustrated excellent domino effects with residual deviation of fewer than 15 PD. Three patients with successive deviation underwent a second surgery with excellent outcomes. CONCLUSION: Few extraocular muscles can be prevented due to monocular squint surgery when multiple surgeries are needed.

Preventing transition to turbulence: a viscosity stratification does not always help.

In channel flows a step on the route to turbulence is the formation of streaks, often due to algebraic growth of disturbances. While a variation of viscosity in the gradient direction often plays a large role in laminar-turbulent transition in shear flows, we show that it has, surprisingly, little effect on the algebraic growth. Nonuniform viscosity therefore may not always work as a flow-control strategy for maintaining the flow as laminar.

Stabilization of hydrodynamic flows by small viscosity variations.

Motivated by the large effect of turbulent drag reduction by minute concentrations of polymers, we study the effects of a weakly space-dependent viscosity on the stability of hydrodynamic flows. In a recent paper [Phys. Rev. Lett. 87, 174501, (2001)], we exposed the crucial role played by a localized region where the energy of fluctuations is produced by interactions with the mean flow (the "critical layer"). We showed that a layer of a weakly space-dependent viscosity placed near the critical layer can have a very large stabilizing effect on hydrodynamic fluctuations, retarding significantly the onset of turbulence. In this paper we extend these observations in two directions: first we show that the strong stabilization of the primary instability is also obtained when the viscosity profile is realistic (inferred from simulations of turbulent flows with a small concentration of polymers). Second, we analyze the secondary instability (around the time-dependent primary instability) and find similar strong stabilization. Since the secondary instability develops around a time-dependent solution and is three dimensional, this brings us closer to the turbulent case. We reiterate that the large effect is not due to a modified dissipation (as is assumed in some theories of drag reduction), but due to reduced energy intake from the mean flow to the fluctuations. We propose that similar physics act in turbulent drag reduction.

Albendazole therapy of hydatid disease: 2-year follow-up of 40 cases.

Forty patients with 63 Echinococcus granulosus cysts affecting different sites were treated with albendazole and have been followed up for at least 24 months from completion of therapy. Twenty-one patients (53%) with 37 cysts (59%) showed evidence of healing. The criteria and pattern of healing are outlined. The most serious complication of albendazole therapy was hepatoxic jaundice, which occurred in 5% of patients. Recurrence during the observation period was encountered in 9.5% of patients with a positive response. It is suggested that patients suffering from uncomplicated hydatid disease should be given the benefit of a trial course of albendazole therapy, before surgery is undertaken.