Active Caustics

Heavy particles in vortical fluid flow cluster strongly, forming singular structures termed caustics for their resemblance to focal surfaces in optics. We show here that such extreme aggregation onto low-dimensional submanifolds can arise without inertia for self-propelled particles (SPPs). We establish that a singular perturbation is at the heart of caustic formation by SPPs around a single vortex, and our numerical studies of SPPs in two-dimensional Navier-Stokes turbulence shows intense caustics in the straining regions of the flow, peaking at intermediate levels of self-propulsion. Our work offers a route to singularly high local concentrations in a macroscopically dilute suspension of zero-Reynolds number swimmers, with potentially game-changing implications for communication and sexual reproduction. An intriguing open direction is whether the active turbulence of a suspension of swimming microbes could serve to generate caustics in its own concentration.Comment: 8 main pages, 11 supplementary pages, 3 main figures, 8 supplementary figures, 1 supplementary tabl

Theory of Suspension Segregation in Partially Filled Horizontal Rotating Cylinders

It is shown that a suspension of particles in a partially-filled, horizontal, rotating cylinder is linearly unstable towards axial segregation and an undulation of the free surface at large enough particle concentrations. Relying on the shear-induced diffusion of particles, concentration-dependent viscosity, and the existence of a free surface, our theory provides an explanation of the experiments of Tirumkudulu et al., Phys. Fluids 11, 507-509 (1999); ibid. 12, 1615 (2000).Comment: Accepted for publication in Phys Fluids (Lett) 10 pages, two eps figure

A Comparative Study on the Dimensional Error of 3D CAD Model and SLS RP Model for Reconstruction of Cranial Defect

Rapid Prototyping (RP) is a technology that produces models and prototype parts from 3D CAD model data, CT/MRI scan data, and model data created from 3D object digitizing systems. There are several RP process like Stereolithography (SLA), Solid Ground Curing (SGC), Selective Laser Sintering (SLS), Fused Deposition Modelling (FDM), 3D Printing (3DP) among them SLS and FDM RP processes are used to fabricate pattern of custom cranial implant. RP technology is useful in engineering and biomedical application. This is helpful in engineering for product design, tooling and manufacture etc. RP biomedical applications are design and development of medical devices, instruments, prosthetics and implantation; it is also helpful in planning complex surgical operation. The traditional approach limits the full appreciation of various bony structure movements and therefore the custom implants produced are difficult to measure the anatomy of parts and analyse the changes in facial appearances accurately. Cranioplasty surgery is a surgical correction of a defect in cranial bone by implanting a metal or plastic replacement to restore the missing part. This paper aims to do a comparative study on the dimensional error of CAD and SLS RP Models for reconstruction of cranial defect by comparing the virtual CAD with the physical RP model of a cranial defect

Oscillatory settling in wormlike-micelle solutions: bursts and a long time scale

We study the dynamics of a spherical steel ball falling freely through a solution of entangled wormlike-micelles. If the sphere diameter is larger than a threshold value, the settling velocity shows repeated short oscillatory bursts separated by long periods of relative quiescence. We propose a model incorporating the interplay of settling-induced flow, viscoelastic stress and, as in M. E. Cates, D. A. Head and A. Ajdari, Phys. Rev. E, 2002, 66, 025202(R) and A. Aradian and M. E. Cates, Phys. Rev. E, 2006, 73, 041508, a slow structural variable for which our experiments offer independent evidence.Comment: To appear in Soft Matte

Primary Amebic Meningoencephalitis Caused by Naegleria fowleri, Karachi, Pakistan

We report 13 cases of Naegleria fowleri primary amebic meningoencephalitis in persons in Karachi, Pakistan, who had no history of aquatic activities. Infection likely occurred through ablution with tap water. An increase in primary amebic meningoencephalitis cases may be attributed to rising temperatures, reduced levels of chlorine in potable water, or deteriorating water distribution systems

Acanthamoeba Encephalitis in Patient with Systemic Lupus, India

We report a fatal case of encephalitis caused by Acanthamoeba in a 24-year-old woman from India with systemic lupus erythematosus. Diagnosis was made by identification of amebas in brain sections by immunofluorescence analysis and confirmed by demonstrating Acanthamoeba mitochondrial 16S rRNA gene DNA in brain tissue sections

Mapping the nexus of transitional justice and peacebuilding

This paper explores the convergences and divergence between transitional justice and peace-building, by considering some of the recent developments in scholarship and practice. We examine the notion of ‘peace’ in transitional justice and the idea of ‘justice’ in peacebuilding. We highlight that transitional justice and peacebuilding often engage with similar or related ideas, though the scholarship on in each field has developed, largely, in parallel to each other, and of-ten without any significant engagement between the fields of inquiry. We also note that both fields share other commonalities, insofar as they often neglect questions of capital (political, social, economic) and at times, gender. We suggest that trying to locate the nexus in the first place draws attention to where peace and justice have actually got to be produced in order for there not to be conflict and violence. This in turn demonstrates that locally, ‘peace’ and ‘justice’ do not always look like the ‘peace’ and ‘justice’ drawn up by international donors and peace-builders; and, despite the ‘turn to the local’ in international relations, it is surprising just how many local and everyday dynamics are (dis)missed as sources of peace and justice, or potential avenues of addressing the past