The effect of flow oscillations on cavity drag

An experimental investigation of flow over an axisymmetric cavity shows that self-sustained, periodic oscillations of the cavity shear layer are associated with low cavity drag. In this low-drag mode the flow regulates itself to fix the mean-shear-layer stagnation point at the downstream corner. Above a critical value of the cavity width-to-depth ratio there is an abrupt and large increase of drag due to the onset of the ‘wake mode’ of instability. It is also shown by measurement of the momentum balance how the drag of the cavity is related to the state of the shear layer, as defined by the mean momentum transport $\rho\overline{u}\overline{v}$ and the Reynolds stress $\rho\overline{u^{\prime}v^{\prime}}$, and how these are related to the amplifying oscillations in the shear layer. The cavity shear layer is found to be different, in several respects, from a free shear layer

On the resonance of a pliant tube as a mechanism for valveless pumping

Valveless pumping can be achieved through the periodic compression of a pliant tube asymmetrically from its interfaces to different tubing or reservoirs. A mismatch of characteristic impedance between the flow channels is necessary for creating wave reflection sites. Previous experimental studies of the behaviour of such a pump were continued in order to demonstrate the wave mechanics necessary for the build-up of pressure and net flow. Specific measurements of the transient and resonant properties were used to relate the bulk responses to the pump mechanics. Ultrasound imaging through the tube wall allowed visualization of the wall motion concurrently with pressure and flow measurements. For analysis, a one-dimensional wave model was constructed which predicted many of the characteristics exhibited by the experiments

Turbulent vortex ring/free surface interaction

The interaction of turbulent vortex rings that approach a clean water surface under various angles is experimentally investigated. The temporal evolution of the vortex rings with an initial Reynolds number of Re_0 = 7500 is characterized by the laminar/turbulent transition and asymptotic relaminarization of the flow. Using the shadowgraph technique, two major flow cases were identified as a result of the vortex-ring/free-surface interaction: a trifurcation case that results from the interaction during the transition stage, and a bifurcation case that evolves during the fully-developed turbulent stage. In contrast to the laminar interaction, the turbulent bifurcation pattern is characterized by the reconnection and mutual interaction of many small-scale structures. Simultaneous digital particle image velocimetry (DPIV) and shadowgraph measurements reveal that the evolution of the small-scale structures at the free surface is strongly dominated by the bifurcation pattern, which in turn is a consequence of the persisting laminar sublayer in the core regions of the reconnected turbulent vortex loops

Elasto-capillary coalescence of multiple parallel sheets

We analyse two-dimensional clamped parallel elastic sheets which are partially immersed in liquid as a model for elasto-capillary coalescence. In the existing literature this problem is studied via minimal energy analysis of capillary and elastic energies of the post-coalescence state, yielding the maximal stable post-coalescence bundle size. Utilizing modal stability analysis and asymptotic analysis, we studied the stability of the configuration before the coalescence occurred. Our analysis revealed previously unreported relations between viscous forces, body forces, and the instability yielding the coalescence, thus undermining a common assumption that coalescence will occur as long as it will not create a bundle larger than the maximal stable post-coalesced size. A mathematical description of the process creating the hierarchical coalescence structure was obtained and yielded that the mean number of sheets per coalesced region is limited to the subset 2^N where N is the set of natural numbers. Our theoretical results were illustrated by experiments and good agreement with the theoretical predictions was observed

Flow measurements near a Reynolds ridge

The Reynolds ridge is a well-known phenomenon first observed in 1854 by Henry David Thoreau. It was then rediscovered by Langton in 1872, but Reynolds was the first to recognize that the surface tension difference was the physical mechanism behind its formation and saw the equality between the case of a spreading film and that of a stagnant film met by oncoming flow. However, it wasn't until McCutchen in 1970 that the prediction of a boundary layer forming beneath the film was introduced as the cause of the surface deformation rise ahead of the film due to the retardation of the flow. The first quantitative theory of the ridge was formed by Harper and Dixon (1974), who stated that the surface tension gradient balances the viscous shear stress generated in the boundary layer. Experimental studies of the ridge so far include Schlieren visualizations by Sellin (1968) as well as by Scott (1982) who measured the surface slope across the ridge and found good comparisons between the theoretical results of Harper and Dixon. Finally, it was Scott who recognized that even at very low levels of surface contamination the Reynolds ridge is found to exist

Association of systemic anaplastic large cell lymphoma and active toxoplasmosis in a child

Introduction: Anaplastic large cell lymphoma is a subset of non-Hodgkin lymphoma and an unusual disease in children. Case Presentation: Herein we have reported a 7- year- old girl with a large necrotic skin ulcer on the chest caused by systemic form of anaplastic large-cell lymphoma and simultaneous active toxoplasmosis diagnosed by PCR on lymph node specimen. There were few reports showing a role for toxoplasma infection to cause some malignancies such as lymphoma in adults. Conclusions: Based to our knowledge, this has been the first report of simultaneous systemic anaplastic large cell lymphoma and active toxoplasmosis, documented by positive PCR on tissue biopsy in a child. This case report has suggested more attention to the accompanying Toxoplasma gondii infection as a probable cause of some types of lymphomas. © 2015, Iranian Journal of Cancer Prevention

Wicking of a liquid bridge connected to a moving porous surface

We study the coupled problem of a liquid bridge connected to a porous surface and an impermeable surface, where the gap between the surfaces is an externally controlled function of time. The relative motion between the surfaces influences the pressure distribution and geometry of the liquid bridge, thus affecting the shape of liquid penetration into the porous material. Utilizing the lubrication approximation and Darcy’s phenomenological law, we obtain an implicit integral relation between the relative motion between the surfaces and the shape of liquid penetration. A method to control the shape of liquid penetration is suggested and illustrated for the case of conical penetration shapes with an arbitrary cone opening angle. We obtain explicit analytic expressions for the case of constant relative speed of the surfaces as well as for the relative motion between the surfaces required to create conical penetration shapes. Our theoretical results are compared with experiments and reasonable agreement between the analytical and experimental data is observed

Fahr’s syndrome with seizure presentation

Fahr's disease (FD) or Fahr’s syndrome is characterized by basal ganglia calcification with clinical manifestations in the form of neuropsychiatric disorders, neurological symptoms, and cognitive symptoms. FD commonly affects young to middle aged adults. The etiology of this syndrome does not identify a specific agent. Clinical manifestations of this disease incorporate a wide variety of symptoms. The diagnostic criteria of Fahr’s Syndrome consist of bilateral calcification of basal ganglia, progressive neurologic dysfunction, absence of biochemical abnormalities, infectious, traumatic, and a significant family history. Medical imaging techniques for the diagnosis consist of computed tomography (CT), magnetic resonance imaging (MRI), and plain radiography of the skull. This paper presents a case of Fahr’s syndrome in a 60-year-old married prisoner with antisocial personality and seizures. Furthermore, CT and MRI scans showed bilateral symmetric calcifications in the basal ganglia calcification (BGC) and dentate nuclei, cerebellum, and centrum semiovale