The whistler nozzle phenomenon

The whistler nozzle is a simple device which can induce jet self-excitations of controllable amplitudes and frequencies and appears highly promising for many applications involving turbulent transport, combustion and aerodynamic noise. The characteristics of this curious phenomenon are documented for different values of the controlling parameters and attempts to explain the phenomenon. It is shown that the whistler excitation results from the coupling of two independent resonance mechanisms: shear-layer tone resulting from the impingement of the pipe-exit shear layer on the collar lip, and organ-pipe resonance of the pipe-nozzle. The crucial role of the shear-layer tone in driving the organ-pipe resonance is proven by reproducing the event in pipe-ring and pipe-hole configurations in the absence of the collar. It is also shown that this phenomenon is the strongest when the self-excitation frequency matches the preferred mode of the jet

Acoustics-turbulence interaction

An investigation of the instability frequency was undertaken. Measurements revealed that the hot wire probe induces and sustains stable upstream oscillation of the free shear layer. The characteristics of the free shear layer tone are found to be different from the slit jet wedge edgetone phenomenon. The shear tone induced by a plane wedge in a plane free shear layer was then examined in order to further document the phenomenon. The eigenvalues and eigenfunctions of the tone fundamental show agreement with the spatial stability theory. A comprehensive summary of the results is also included

Discriminative Tandem Features for HMM-based EEG Classification

Abstract—We investigate the use of discriminative feature extractors in tandem configuration with generative EEG classification system. Existing studies on dynamic EEG classification typically use hidden Markov models (HMMs) which lack discriminative capability. In this paper, a linear and a non-linear classifier are discriminatively trained to produce complementary input features to the conventional HMM system. Two sets of tandem features are derived from linear discriminant analysis (LDA) projection output and multilayer perceptron (MLP) class-posterior probability, before appended to the standard autoregressive (AR) features. Evaluation on a two-class motor-imagery classification task shows that both the proposed tandem features yield consistent gains over the AR baseline, resulting in significant relative improvement of 6.2% and 11.2 % for the LDA and MLP features respectively. We also explore portability of these features across different subjects. Index Terms- Artificial neural network-hidden Markov models, EEG classification, brain-computer-interface (BCI)

Studies on the spermatozoa of the ram with special reference to the effects of deep freezing

This thesis describes studies on the spermatozoa of the ram carried out with a view to determining the effects of deep freezing which lead to poor fertility following artificial insemination.The electro-ejaculator was employed for semen collection over 20 months and 80 samples out of 114 collections were processed.Motility of spermatozoa was assessed by scoring mass activity in raw semen samples and by estimation of the percentage of motile spermatozoa in raw and processed samples.Percentages of live spermatozoa and their general morphology were studied in eosin -nigrosin stained smears and acrosomal defects in eosin fast green FCF stained smears. Spermatozoal morphology was also studied with the electron microscope.Generally the various parameters of the raw semen were within or close to the standard ranges and they varied with season, best semen being collected in the autumn.When semen was frozen by a standard technique there was a continuous reduction in the spermatozoal viability, especially motility, associated with an increase in morphological deterioration of the spermatozoa, especially of their acrosomes, following each stage. At the same time variation in spermatozoal viability and morphology existed between different samples.Various modifications of the freezing technique were tried. On inclusion of 2 -8% glycerol or dimethyl sulphoxide (DMSO), or their combinations at different levels in an egg yolk and lactose diluent the results respectively showed that 4% glycerol, 3% DMSO and 2% glycerol with 1.5% DMSO were the optima.The effects on spermatozoa of various equilibration times (0.5 - 24.0 hours), dilution rates (1:1 - 1:10), thawing media (sodium chloride or citrate with or without lactose in solution at 37 °C or frozen pellet at -196 °C) and thawing temperatures (0 °C - 100 °C) were studied using both 4% glycerol or 3% DMSO as the cryoprotective in the diluents. The results showed that equilibration of 3.0 hours with glycerol, and of 1.5 hours with DMSO, and dilution rates of 1:4 and thawing directly in a dry test tube at 37 °C - 100 °C, irrespective of the cryoprotective, were the optima.In addition, various methods of dilution (dropping or direct at 4 °C or 20 °C or their combination) and different egg yolk levels (25 or 50%) with or without sodium citrate (3%) were used. The results indicated that equilibration at 20 °C, irrespective of method of dilution led to a high death rate of ram spermatozoa but provided surviving spermatozoa some resistance against cold shock during freezing. Direct addition of the diluent irrespective of the equilibration temperature was satisfactory, but the addition of the diluent by dropping for 0.5 hour at 20 °C followed by 1.0 hour equilibration at 4 °C was superior.Increasing the egg yolk level from 25 to 50, with or without sodium citrate in 4% glycerol containing diluent was harmful which might be the result of binding up of glycerol.Prompt dilution of the raw semen after collection and the avoidance of temperature fluctuation between stages of freezing and when sampling f,or thawing were tried and the results showed an enhanced resistance to cold shock and an improvement in spermatozoal motility when thawed after 24 hours storage at -196 °C. However, longer storage X was still deleterious, and the percentage of motile spermatozoa fell to 40/.The post -thawing life span and morphological changes of the ram spermatozoa were evaluated following thawing at 0°C - 100°C and incubation at 39°C for 0, 3.0 and 6.0 hours. The results showed that the life span of the frozen -thawed ram spermatozoa was short (around 3 hours) and their acrosomal defects increased progressively as the incubation time increased.The fertilizing efficiency of frozen semen stored for 42 - 46 days was tried on 28 ewes, but the results showed that the low post -thawing motility and short survival time which pertained were not adequate to produce pregnancy

Mapping the spin-dependent electron reflectivity of Fe and Co ferromagnetic thin films

Spin Polarized Low Energy Electron Microscopy is used as a spin dependent spectroscopic probe to study the spin dependent specular reflection of a polarized electron beam from two different magnetic thin film systems: Fe/W(110) and Co/W(110). The reflectivity and spin-dependent exchange-scattering asymmetry are studied as a function of electron kinetic energy and film thickness, as well as the time dependence. The largest value of the figure of merit for spin polarimetry is observed for a 5 monolayer thick film of Co/W(110) at an electron kinetic energy of 2eV. This value is 2 orders of magnitude higher than previously obtained with state of the art Mini-Mott polarimeter. We discuss implications of our results for the development of an electron-spin-polarimeter using the exchange-interaction at low energy.Comment: 5 pages, 4 figure

Patient and health care professional decision-making to commence and withdraw from renal dialysis: A systematic review of qualitative research

Background and objectives. To ensure decisions to start and stop dialysis in end stage kidney disease are shared, the factors that affect patients and healthcare professionals in making such decisions need to be understood. This systematic review aims to explore how and why different factors mediate the choices about dialysis treatment. Design, setting, participants, and measurements. Medline, Embase, CINAHL and PsychINFO were searched for qualitative studies of factors that affect patients’ and/or healthcare professionals’ decisions to commence or withdraw from dialysis. A thematic synthesis was conducted. Results. Of 494 articles screened, 12 studies (conducted: 1985-2014) were included. These involved 206 predominantly haemodialysis patients and 64 healthcare professionals (age range: patients 26-93; professionals 26-61 years). (i) Commencing dialysis: patients based their choice on ‘gut-instinct’ as well as deliberating the impact of treatment on quality-of-life and survival. How individuals coped with decision-making was influential, some tried to take control of the problem of progressive renal failure, whilst others focussed on controlling their emotions. Healthcare professionals weighed-up biomedical factors and were led by an instinct to prolong life. Both patients and healthcare professionals described feeling powerless. (ii) Dialysis withdrawal: Only after prolonged periods of time on dialysis, were the realities of life on dialysis fully appreciated and past choice questioned. By this stage however patients were physically treatment dependent. Similar to commencing dialysis, individuals coped with treatment withdrawal in a problem or emotion-controlling way. Families struggled to differentiate choosing versus allowing death. Healthcare teams avoided and queried discussions regarding dialysis withdrawal. Patients however missed the dialogue they experienced during pre-dialysis education. Conclusions. Decision-making in end stage kidney disease is complex, dynamic, and evolves over time and towards death. The factors at work are multi-faceted and operate differently for patients and health professionals. More training and research on open-communication and shared decision-making is needed

Waterlogging and salinity management in the Sindh Province. Volume 1 - The irrigated landscape: resource availability across the hydrological divides

Irrigation management / River basins / Irrigated farming / Climate / Irrigation systems / Irrigation canals / Discharges / Water balance / Waterlogging / Salinity / Groundwater development / Tube wells / Water table / Drainage / Public sector / Land reclamation / Pakistan / Sindh Province / Indus Basin / Rohri / Larkana / Shikarpur / Hairdin / North Dadu / Ghotki / East Khairpur / Sukkur Barrage

On the cytotoxicity of carbon nanotubes

The cytotoxicity of carbon nanotubes (CNTs) is a major concern today well before its unusual physicochemical, mechanical, and electrical properties are fully exploited for commercial interests and subsequent mass production leading to greater possibilities for its exposure to humans and the environment. Contradictory reports on cytotoxicity of CNTs often appear in the literature and a mechanistic explanation of the reported toxicity remains obscure. We review here the conflicting results to focus categorically on an array of issues in CNT cytotoxicity. They include dispersion, aggregation status, coating or functionalization and immobilization, cellular uptake or internalization, purity in terms of metal catalyst contaminants, size and size distribution, surface area, surface chemistry and surface reactivity, cell types selected for experimentation as well as bioassay of nanotoxicity itself attesting as an issue in cytotoxicity. Recently a general agreement has emerged towards the potential toxicity of CNTs, although various paradigms explaining the mechanisms of CNT cytotoxicity continue to be elusive in the literature. A lack of synergy among various issues while studying cytotoxicity and most developed paradigms for the mechanism of CNT toxicity is highlighted