Bejan flow visualization of free convection in a Jeffrey fluid from a semi-infinite vertical cylinder : influence of Deborah and Prandtl numbers

This article studies the pattern of heat lines in free convection non-Newtonian flow from a semi-infinite vertical cylinder via Bejan’s heat function concept. The viscoelastic Jeffrey fluid model is employed. The time-dependent, coupled, non-linear conservation equations for momentum and energy (heat) are solved computationally with the unconditionally stable finite difference Crank-Nicolson method. Extensive graphical results are presented for the influence of Deborah number (viscoelastic parameter) and Prandtl number (with ranges 0 - 0.8 and 0.68 - 7.2, respectively) on thermal and flow characteristics including time histories of overall skin friction and heat transfer rate. Lower values of Deborah number indicate that the material acts in a more fluid-like manner whereas the higher values of Deborah number correspond to the material showing characteristics more associated with a solid. The solutions indicate that the time taken for the flow-field variables to achieve the steady-state is increased with higher values of Deborah number. Boundary flow visualization is presented using heat lines, isotherms and streamlines. It is observed that as Deborah number increases the intensity of heat lines increases and they tend to deviate from the hot cylindrical wall. Furthermore, the flow field variables for the Newtonian fluid case exhibit a significantly different pattern from that of Jeffrey fluid

Finite element analysis of melting effects on MHD stagnation-point non-Newtonian flow and heat transfer from a stretching/shrinking sheet

A numerical study is presented for boundary layer flow and heat transfer of micropolar (non-Newtonian) fluid from a stretching/shrinking sheet in the presence of melting and viscous heating. In this study the velocity of ambient fluid and stretching/shrinking velocity vary linearly with the distance from the stagnation-point. A uniform magnetic field is applied normal to the sheet and moves with the free stream as encountered in certain magnetic materials processing systems. Using similarity transformations, the governing partial differential equations are transformed into a system of coupled, nonlinear ordinary differential equations. A variational finite element code is implemented to solve the resulting dimensionless boundary value problem. The influence of magnetic body force (M), stretching/shrinking (ε) and melting (Me) parameters on velocity, microrotation, temperature, surface shear stress function (skin-friction) and local Nusselt number are elaborated in detail. Velocity is decreased with a rise in melting parameter, whereas far from the wall microrotation is reduced and furthermore temperatures are depressed. The flow is accelerated, micro-rotation (angular velocity of micro-elements) increased and temperature enhanced with increasing stretching rate (ε > 0) whereas the converse behaviour is observed with increasing shrinking rate (ε < 0). Increasing magnetic parameter is found to both increase temperatures and to accelerate the flow whereas it reduces microrotation near the wall and enhances it further from the wall. Special cases of the present model (with magnetic, dissipative and melting effects negated) are benchmarked with earlier results from the literature and found to be in excellent agreement. Excellent convergence and stability is achieved with the numerical method

Transient analysis of Casson fluid thermo-convection from a vertical cylinder embedded in a porous medium : entropy generation and thermal energy transfer visualization

Thermal transport in porous media has stimulated substantial interest in engineering sciences due to increasing applications in filtration systems, porous bearings, porous layer insulation, biomechanics, geomechanics etc. Motivated by such applications, in this article a numerical investigation of entropy generation effects on the heat and momentum transfer in unsteady laminar incompressible boundary layer flow of a Casson viscoplastic fluid over a uniformly heated vertical cylinder embedded in a porous medium is presented. Darcy’s law is employed to simulate bulk drag effects at low Reynolds number for an isotropic, homogenous porous medium. Heat line visualization is also included. The mathematical model is derived and normalized using appropriate transformation variables. The resulting time-dependent non-linear coupled partial differential conservation equations with associated boundary conditions are solved with an efficient unconditionally stable implicit finite difference Crank Nicolson scheme. The time histories of average values of momentum and heat transport coefficients, entropy generation and Bejan number, as well as the steady-state flow variables are computed for several values of non-dimensional parameters arising in the flow equations. The results indicate that entropy generation parameter and Bejan number are both elevated with increasing values of Casson fluid parameter, Darcy number, group parameter and Grashof number. To analyze the heat transfer process in a two-dimensional domain, plotting heat lines provides an excellent approach in addition to streamlines and isotherms. The dimensionless heat function values are shown to correlate closely with the overall rate of heat transfer. Bejan’s heat flow visualization implies that the heat function contours are compact in the neighbourhood of the leading edge of the boundary layer on the hot cylindrical wall. It is observed that as the Darcy number increases, the deviations of heat lines from the hot wall are reduced. Furthermore the deviations of flow variables from the hot wall for a Casson fluid are significant compared with those computed for a Newtonian fluid and this has important implications in industrial thermal materials processing operations

Unsteady free convective heat transfer in third-grade fluid flow from an isothermal vertical plate : a thermodynamic analysis

The current study investigates theoretically and numerically the entropy generation in time-dependent free-convective third-grade viscoelastic fluid convection flow from a vertical plate. The non-dimensional conservation equations for mass, momentum, and energy are solved using a Crank-Nicolson finite difference method with suitable boundary conditions. Expressions for known values of flow-variables coefficients are also derived for the wall heat transfer and skin friction and numerically evaluated. The effect of Grashof number, Prandtl number, group parameter (product of dimensionless temperature difference and Brinkman number) and third-grade parameter on entropy heat generation is analyzed and shown graphically. Bejan line distributions are also presented for the influence of several control parameters. The computations reveal that with increasing third-grade parameter the entropy generation decreases and Bejan number increases. Also, the comparison graph shows that contour lines for third-grade fluid vary considerably from the Newtonian fluid. The study is relevant to non-Newtonian thermal materials processing systems

Prevalence of invasive fungal disease in hematological patients at a tertiary university hospital in Singapore

<p>Abstract</p> <p>Background</p> <p>The use of newer azoles as prophylaxis in hematological patients undergoing stem cell transplantation or immunosuppressive chemotherapy has been shown to decrease the risk of developing invasive fungal disease (IFD). However, the cost-effectiveness of such a strategy is dependent on the local epidemiology of IFD. We conducted an audit of hematological patients with IFD in our institution in order to derive the prevalence and types of IFD that occur locally.</p> <p>Findings</p> <p>We conducted a retrospective chart review of all hematological patients who developed possible, probable or definite IFD according to EORTC/MSG criteria in the period from Oct 2007 to Apr 2010. The prevalence of IFD was determined via correlation with institutional database records of all hematological patients treated at our institution over the same time period.</p> <p>There were 39 cases of IFD diagnosed during the study period, with 8 (20.5%) possible, 19 (48.7%) probable and 12 (30.8%) definite cases of IFD. <it>Aspergillus </it>spp. accounted for 83.9% of all probable and definite infections. There was 1 case each of <it>Rhinocladelia </it>spp., <it>Coprinopsis cinerea</it>, <it>Exserohilum </it>spp. sinusitis and <it>Rhizopus </it>spp. sinusitis. IFD occurred in 12 of 124 (9.7%) AML and 4 of 103 (3.9%) ALL patients treated at our institution respectively. There were 10 (16.1%) infections among 62 allogeneic HSCT recipients, six of whom were having concurrent graft-versus-host disease (GVHD). Five other cases occurred after allogeneic HSCT failure, following salvage chemotherapy for disease relapse. The prevalence of IFD during induction chemotherapy was 8.9% (11 of 124 cases) for AML and 1.0% (1 of 103 cases) for ALL. Fluconazole prophylaxis had been provided for 28 out of the 39 (71.8%) cases, while 4 (10.3%) were on itraconazole prophylaxis. The in-hospital mortality was 28.2% (11 of 39 cases), of which 5 (12.8%) deaths were attributed to IFD.</p> <p>Conclusions</p> <p>The burden of IFD is high in our institution, especially in allogeneic HSCT recipients and patients on induction chemotherapy for AML. A prophylactic strategy directed against invasive mould infections for local high-risk patients may be considered as the comparative costs of treatment, prolonged hospitalisation and subsequent delayed chemotherapy favours such an approach.</p

Transcription of toll-like receptors 2, 3, 4 and 9, FoxP3 and Th17 cytokines in a susceptible experimental model of canine Leishmania infantum infection

Canine leishmaniosis (CanL) due to Leishmania infantum is a chronic zoonotic systemic disease resulting from complex interactions between protozoa and the canine immune system. Toll-like receptors (TLRs) are essential components of the innate immune system and facilitate the early detection of many infections. However, the role of TLRs in CanL remains unknown and information describing TLR transcription during infection is extremely scarce. The aim of this research project was to investigate the impact of L. infantum infection on canine TLR transcription using a susceptible model. The objectives of this study were to evaluate transcription of TLRs 2, 3, 4 and 9 by means of quantitative reverse transcription polymerase chain reaction (qRT-PCR) in skin, spleen, lymph node and liver in the presence or absence of experimental L. infantum infection in Beagle dogs. These findings were compared with clinical and serological data, parasite densities in infected tissues and transcription of IL-17, IL-22 and FoxP3 in different tissues in non-infected dogs (n = 10), and at six months (n = 24) and 15 months (n = 7) post infection. Results revealed significant down regulation of transcription with disease progression in lymph node samples for TLR3, TLR4, TLR9, IL-17, IL-22 and FoxP3. In spleen samples, significant down regulation of transcription was seen in TLR4 and IL-22 when both infected groups were compared with controls. In liver samples, down regulation of transcription was evident with disease progression for IL-22. In the skin, upregulation was seen only for TLR9 and FoxP3 in the early stages of infection. Subtle changes or down regulation in TLR transcription, Th17 cytokines and FoxP3 are indicative of the silent establishment of infection that Leishmania is renowned for. These observations provide new insights about TLR transcription, Th17 cytokines and Foxp3 in the liver, spleen, lymph node and skin in CanL and highlight possible markers of disease susceptibility in this model

Geological-Geophysical Investigations for Hydrological Studies in a Basement Complex Terrain, Southwestern Nigeria

Geological field mapping and vertical electrical soundings (VES) were conducted in Igbo-Ora, southwestern Nigeria in order to unravel the subsurface structures, as part of the preliminary investigations for groundwater resources assessment, development and management in a crystalline basement terrain, southwestern Nigeria. The geological survey was carried out to produce a local geological map with spatial distributions of different basement rocks and their structural trends. Metamorphic and igneous rocks make up 90 and 10%, respectively, of the rocks in the study area. They include the banded gneiss, biotite granite gneiss, quartzite/quartz-schist and granitic intrusions of varying grain sizes. Twenty-five VES surveys were conducted within the biotite granite gneiss terrain of the area, using Schlumberger array, providing layering and geoelectrical parameters. Three geoelectric layers delin- eated from the VES 1D inversion models are clayey sand/sandy clay top soil (overburden), partly weathered or fractured basement and fresh basement. The corresponding inverse model resistivity values ranges are: 209.7–2298.0, 45.1–346.2 and1013.7–33,124.0Xmwithbottomdepths ranges of 0.9–2.9 and 4.6–42.0 m, respectively. The topmost clayey sand/sandy clay layer will serve as the protective layer, while the saturated portion of the partly weathered or fractured basement, at depth, favors ground- water exploration and development in the study area

The clinical features of the piriformis syndrome: a systematic review

Piriformis syndrome, sciatica caused by compression of the sciatic nerve by the piriformis muscle, has been described for over 70 years; yet, it remains controversial. The literature consists mainly of case series and narrative reviews. The objectives of the study were: first, to make the best use of existing evidence to estimate the frequencies of clinical features in patients reported to have PS; second, to identify future research questions. A systematic review was conducted of any study type that reported extractable data relevant to diagnosis. The search included all studies up to 1 March 2008 in four databases: AMED, CINAHL, Embase and Medline. Screening, data extraction and analysis were all performed independently by two reviewers. A total of 55 studies were included: 51 individual and 3 aggregated data studies, and 1 combined study. The most common features found were: buttock pain, external tenderness over the greater sciatic notch, aggravation of the pain through sitting and augmentation of the pain with manoeuvres that increase piriformis muscle tension. Future research could start with comparing the frequencies of these features in sciatica patients with and without disc herniation or spinal stenosis

Numerical study of nonlinear heat transfer from a wavy surface to a high permeability medium with pseudo-spectral and smoothed particle methods

Motivated by petro-chemical geological systems, we consider the natural convection boundary layer flow from a vertical isothermal wavy surface adjacent to a saturated non-Darcian high permeability porous medium. High permeability is considered to represent geologically sparsely packed porous media. Both Darcian drag and Forchheimer inertial drag terms are included in the velocity boundary layer equation. A high permeability medium is considered. We employ a sinusoidal relation for the wavy surface. Using a set of transformations, the momentum and heat conservation equations are converted from an (x, y) coordinate system to an (x,η) dimensionless system. The two-point boundary value problem is then solved numerically with a pseudo-spectral method based on combining the Bellman–Kalaba quasi linearization method with the Chebyschev spectral collocation technique (SQLM). The SQLM computations are demonstrated to achieve excellent correlation with smoothed particle hydrodynamic (SPH) Lagrangian solutions. We study the effect of Darcy number (Da), Forchheimer number (Fs), amplitude wavelength (A) and Prandtl number (Pr) on the velocity and temperature distributions in the regime. Local Nusselt number is also computed for selected cases. The study finds important applications in petroleum engineering and also energy systems exploiting porous media and undulating (wavy) surface geometry. The SQLM algorithm is shown to be exceptionally robust and achieves fast convergence and excellent accuracy in nonlinear heat transfer simulations