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Viscous
Terms modified by Viscous Selected AbstractsWater-Miscible Liquid Multiwalled Carbon NanotubesADVANCED MATERIALS, Issue 17 2009Maurizio Fagnoni Viscous, water-miscible, liquid multiwalled carbon nanotubes with an extraordinarily high degree of functionalization (hf-MWCNTs) have been obtained by means of a deep-sidewall modification process. The hf-MWCNTs behave as an ionic liquid, with a conductivity of 1,mS,cm,1 at 100,°C. The unique properties of this material render it suitable in a wide spectrum of applications, ranging from nanomedicine to energetics. [source] Gelifluction: viscous flow or plastic creep?EARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2003Charles Harris Abstract This paper reports results from two scaled centrifuge modelling experiments, designed to simulate thaw-related geli,uction. A planar 12° prototype slope was modelled in each experiment, using the same natural ,ne sandy silt soil. However two different scales were used. In Experiment 1, the model scale was 1/10, tested in the centrifuge at 10 gravities (g) and in Experiment 2, the scale was 1/30, tested at 30 g. Centrifuge scaling laws indicate that the time scaling factor for thaw consolidation between model and prototype is N2, where N is the number of gravities under which the model was tested. However, the equivalent time scaling for viscous ,ow is 1/1. If geli,uction is a viscosity-controlled ,ow process, scaling con,icts will therefore arise during centrifuge modelling of thawing slopes, and rates of displacement will not scale accurately to the prototype. If, however, no such scaling con,icts are observed, we may conclude that geli,uction is not controlled by viscosity, but rather by elasto-plastic soil deformation in which frictional shear strength depends on effective stress, itself a function of the thaw consolidation process. Models were saturated, consolidated and frozen from the surface downwards on the laboratory ,oor. The frozen models were then placed in the geotechnical centrifuge and thawed from the surface down. Each model was subjected to four freeze,thaw cycles. Soil temperatures and pore water pressures were monitored, and frost heave, thaw settlement and downslope displacements measured. Pore water pressures, displacement rates and displacement pro,les re,ecting accumulated shear strain, were all similar at the two model scales and volumetric soil transport per freeze,thaw cycle, when scaled to prototype, were virtually identical. Displacement rates and pro,les were also similar to those observed in earlier full-scale laboratory ,oor experiments. It is concluded therefore that the modelled geli,uction was not a time-dependent viscosity-controlled ,ow phenomenon, but rather elasto-plastic in nature. A ,rst approximation ,,ow' law is proposed, based on the ,Cam Clay' constitutive model for soils. Copyright © 2003 John Wiley & Sons, Ltd. [source] Self-centering structural systems with combination of hysteretic and viscous energy dissipationsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2010Weng Yuen Kam Abstract This paper presents an innovative set of high-seismic-resistant structural systems termed Advanced Flag-Shaped (AFS) systems, where self-centering elements are used with combinations of various alternative energy dissipation elements (hysteretic, viscous or visco-elasto-plastic) in series and/or in parallel. AFS systems is developed using the rationale of combining velocity-dependent with displacement-dependent energy dissipation for self-centering systems, particularly to counteract near-fault earthquakes. Non-linear time-history analyses (NLTHA) on a set of four single-degree-of-freedom (SDOF) systems under a suite of 20 far-field and 20 near-fault ground motions are used to compare the seismic performance of AFS systems with the conventional systems. It is shown that AFS systems with a combination in parallel of hysteretic and viscous energy dissipations achieved greater performance in terms of the three performance indices. Furthermore, the use of friction slip in series of viscous energy dissipation is shown to limit the peak response acceleration and induced base-shear. An extensive parametric analysis is carried out to investigate the influence of two design parameters, ,1 and ,2 on the response of SDOF AFS systems with initial periods ranging from 0.2 to 3.0,s and with various strength levels when subjected to far-field and near-fault earthquakes. For the design of self-centering systems with combined hysteretic and viscous energy dissipation (AFS) systems, ,1 is recommended to be in the range of 0.8,1.6 while ,2 to be between 0.25 and 0.75 to ensure sufficient self-centering and energy dissipation capacities, respectively. Copyright © 2010 John Wiley & Sons, Ltd. [source] Asymmetric one-storey elastic systems with non-linear viscous and viscoelastic dampers: Earthquake responseEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2003Wen-Hsiung Lin Abstract Investigated are earthquake responses of one-way symmetric-plan, one-storey systems with non-linear fluid viscous dampers (FVDs) attached in series to a linear brace (i.e. Chevron or inverted V-shape braces).Thus, the non-linear damper is viscous when the brace is considered rigid or viscoelastic (VE) when the brace is flexible. The energy dissipation capacity of a non-linear FVD is characterized by an amplitude-dependent damping ratio for an energy-equivalent linear FVD, which is determined assuming the damper undergoes harmonic motion. Although this formulation is shown to be advantageous for single-degree-of-freedom (SDF) systems, it is difficult to extend its application to multi-degree-of-freedom (MDF) systems for two reasons: (1) the assumption that dampers undergo harmonic motion in parameterizing the non-linear damper is not valid for its earthquake-induced motion of an MDF system; and (2) ensuring simultaneous convergence of all unknown amplitudes of dampers is difficult in an iterative solution of the non-linear system. To date, these limitations have precluded the parametric study of the dynamics of MDF systems with non-linear viscous or VE dampers. However, they are overcome in this investigation using concepts of modal analysis because the system is weakly non-linear due to supplemental damping. It is found that structural response is only weakly affected by damper non-linearity and is increased by a small amount due to bracing flexibility. Thus, the effectiveness of supplemental damping in reducing structural responses and its dependence on the planwise distribution of non-linear VE dampers were found to be similar to that of linear FVDs documented elsewhere. As expected, non-linear viscous and VE dampers achieve essentially the same reduction in response but with much smaller damper force compared to linear dampers. Finally, the findings in this investigation indicate that the earthquake response of the asymmetric systems with non-linear viscous or VE dampers can be estimated with sufficient accuracy for design applications by analysing the same asymmetric systems with all non-linear dampers replaced by energy-equivalent linear viscous dampers. Copyright © 2003 John Wiley & Sons, Ltd. [source] The pseudo-viscous frictional energy dissipator: a new device for mitigating seismic effectsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2003Bin Wu Abstract Viscous energy dissipators (EDORs) have good suppressing effects on acceleration or base shear and they do not add axial pressure to the column when peak moment in the column occurs at peak displacement. Pall frictional EDORs can dissipate energy even when the compression brace buckles due to a special frictional damping mechanism. Retaining the advantages of viscous and Pall EDORs and overcoming their disadvantages, a pseudo-viscous frictional energy dissipator (PVEDOR) is developed. PVEDORs use the frictional damping mechanism of Pall EDORs, but the slip force of PVEDORs is made variable so that the slip force reduces with increasing displacement. Behaviour testing of PVEDORs shows that they possess the important hysteretic feature of viscous EDORs, i.e. the restoring force of PVEDORs are out-of-phase with displacement. Earthquake simulation tests of a 16-storey frame structure incorporating PVEDORs and ordinary steel braces and bare frame are carried out. The test results show that PVEDORs have good vibration-suppressing effects. An analytical hysteretic model of PVEDORs basically agrees with the behaviour testing results. Finally, the parameter influence of PVEDORs on suppressive effectiveness of structural vibration under earthquake conditions is studied. Numerical analyses show that PVEDORs have good control effects on both seismic displacement and acceleration, and that control effects of PVEDORs on base shear are much better than Coulomb-type frictional EDORs or metallic EDORs. Copyright © 2002 John Wiley & Sons, Ltd. [source] THE FEMINIZATION OF TEACHING AND THE PRACTICE OF TEACHING: THREAT OR OPPORTUNITY?EDUCATIONAL THEORY, Issue 4 2006Morwenna Griffiths She outlines a feminist theory of practice that draws critically on theories of embodiment, diversity, and structures of power to show that any practice is properly seen as fluid, leaky, and viscous. Examining different and competing understandings of "feminization", referring either to the numbers of women in teaching or to a culture associated with women , Griffith argues that concerns about increasing number of women teachers are misplaced. She complicates the cultural question, observing that masculine practices have a hegemonic form while feminized practices have developed in resistance to these, and she ultimately argues that hegemonic masculinity, not feminization, is the problem because it drives out diversity. Griffiths concludes that the leaky, viscous practices of teaching would benefit from the increased diversity and decreased social stratification feminization brings to the profession. [source] Biofilm formation and cellulose expression among diverse environmental Pseudomonas isolatesENVIRONMENTAL MICROBIOLOGY, Issue 11 2006Susanne Ude Summary The ability to form biofilms is seen as an increasingly important colonization strategy among both pathogenic and environmental bacteria. A survey of 185 plant-associated, phytopathogenic, soil and river Pseudomonas isolates resulted in 76% producing biofilms at the air,liquid (A,L) interface after selection in static microcosms. Considerable variation in biofilm phenotype was observed, including waxy aggregations, viscous and floccular masses, and physically cohesive biofilms with continuously varying strengths over 1500-fold. Calcofluor epifluorescent microscopy identified cellulose as the matrix component in biofilms produced by Pseudomonas asplenii, Pseudomonas corrugata, Pseudomonas fluorescens, Pseudomonas marginalis, Pseudomonas putida, Pseudomonas savastanoi and Pseudomonas syringae isolates. Cellulose expression and biofilm formation could be induced by the constitutively active WspR19 mutant of the cyclic-di-GMP-associated, GGDEF domain-containing response regulator involved in the P. fluorescens SBW25 wrinkly spreader phenotype and cellular aggregation in Pseudomonas aeruginosa PA01. WspR19 could also induce P. putida KT2440, which otherwise did not produce a biofilm or express cellulose, as well as Escherichia coli K12 and Salmonella typhimurium LT2, both of which express cellulose yet lack WspR homologues. Statistical analysis of biofilm parameters suggest that biofilm development is a more complex process than that simply described by the production of attachment and matrix components and bacterial growth. This complexity was also seen in multivariate analysis as a species-ecological habitat effect, underscoring the fact that in vitro biofilms are abstractions of those surface and volume colonization processes used by bacteria in their natural environments. [source] Magnetic polarity stratigraphy of Siwalik Group sediments of Karnali River section in western NepalGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2000Pitambar Gautam The remanent magnetization of siltstones and sandstones sampled at 476 levels/sites throughout a 3560 m thick molasse sequence belonging to the Siwalik Group (0,2015 m: Lower; 2015,3560 m: Middle) has been studied by stepwise thermal demagnetization. This section is exposed along the Karnali River in Nepal. The natural remanent magnetization (NRM) usually consists of two components: a viscous or thermoviscous component of recent field origin, and an ancient characteristic component (ChRM). The former component is of normal polarity and resides either in goethite (unblocking temperature < 150 °C; resistant to AFD up to 150 mT) or in maghemite (unblocking temperature 150,400 °C). Goethite contributes up to 90 per cent of the total intensity in the finer variegated muddy samples belonging to the lower half of the section. Maghemite content is significant in the grey mud-free lithologies from the upper half of the section. The main component, unblocked in the high-temperature range (commonly 610,680 °C) and believed to reside in haematite, presumably of mostly detrital origin, represents a characteristic remanence (ChRM). The tilt-corrected ChRM directions at individual sites show antipodal clusters (ratio of normal- to reverse-polarity sites: 0.62), and yield mean inclinations recording significant inclination shallowing,a feature well recorded in the Siwaliks. This ChRM is interpreted to represent a largely primary detrital remanence. The ChRM data from 430 sites yield the Karnali River magnetic polarity sequence, whose correlation with the geomagnetic polarity timescale (Cande & Kent 1995) suggests a depositional age of 16 Ma (younger than chron C5Cn.1n) to 5.2 Ma (around the top of chron C3r) for the 3560 m section sampled. Hence, the Karnali River exposes the oldest part of the Siwalik Group in Nepal. Estimates of the sediment accumulation rate (SAR) average to 32.9 cm kyr,1 for the 10.8 Myr time span of deposition. [source] Numerical modelling of fluid flow in microscopic images of granular materialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2002E. Masad Abstract A program for the simulation of two-dimensional (2-D) fluid flow at the microstructural level of a saturated anisotropic granular medium is presented. The program provides a numerical solution to the complete set of Navier,Stokes equations without a priori assumptions on the viscous or convection components. This is especially suited for the simulation of the flow of fluids with different density and viscosity values and for a wide range of granular material porosity. The analytical solution for fluid flow in a simple microstructure of porous medium is used to verify the computer program. Subsequently, the flow field is computed within microscopic images of granular material that differ in porosity, particle size and particle shape. The computed flow fields are shown to follow certain paths depending on air void size and connectivity. The permeability tensor coefficients are derived from the flow fields, and their values are shown to compare well with laboratory experimental data on glass beads, Ottawa sand and silica sands. The directional distribution of permeability is expressed in a functional form and its anisotropy is quantified. Permeability anisotropy is found to be more pronounced in the silica sand medium that consists of elongated particles. Copyright © 2001 John Wiley & Sons, Ltd. [source] Effects of chemical reaction, heat and mass transfer on non-linear MHD flow over an accelerating surface with heat source and thermal stratification in the presence of suction or injectionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 7 2003S. P. Anjali Devi Abstract An approximate numerical solution for the steady MHD laminar boundary-layer flow over an accelerating vertical surface with suction or injection in the presence of species concentration and mass diffusion has been obtained by solving the governing equations using R.K. Gill method. The fluid is assumed to be viscous, incompressible and electrically conducting with a magnetic field applied transversely to the direction of the flow. It has been observed that in the presence of mass diffusion: (i) in the case of suction, the velocity decreases and the temperature distribution and concentration of the fluid increase and for injection, the velocity increases and the temperature distribution and concentration of the fluid decrease with increase of thermal stratification parameter, (ii) in the presence of thermal stratification parameter in both the cases of suction and injection, the skin friction and rate of mass transfer decrease and the rate of heat transfer of the fluid increases with increase of chemical reaction effects, (iii) in the cases of suction and injection, an increase in the strength of magnetic field leads to fall in the velocity and rise in the temperature and concentration of the fluid along the surface. Copyright © 2003 John Wiley & Sons, Ltd. [source] Interface tracking finite volume method for complex solid,fluid interactions on fixed meshesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 2 2002H. S. Udaykumar Abstract We present a numerical technique for computing flowfields around moving solid boundaries immersed in fixed meshes. The mixed Eulerian,Lagrangian framework treats the immersed boundaries as sharp solid,fluid interfaces and a conservative finite volume formulation allows boundary conditions at the moving surfaces to be exactly applied. A semi-implicit second-order accurate spatial and temporal discretization is employed with a fractional-step scheme for solving the flow equations. A multigrid accelerator for the pressure Poisson equations has been developed to apply in the presence of multiple embedded solid regions on the mesh. We present applications of the method to two types of problems: (a) solidification in the presence of flows and particles, (b) fluid,structure interactions in flow control. In both these problems, the sharp interface method presents advantages by being able to track arbitrary interface motions, while capturing the full viscous, unsteady dynamics. Copyright © 2001 John Wiley & Sons, Ltd. [source] Adaptive embedded unstructured grid methodsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2004Rainald Löhner Abstract A simple embedded domain method for node-based unstructured grid solvers is presented. The key modification of the original, edge-based solver is to remove all geometry-parameters (essentially the normals) belonging to edges cut by embedded surface faces. Several techniques to improve the treatment of boundary points close to the immersed surfaces are explored. Alternatively, higher-order boundary conditions are achieved by duplicating crossed edges and their endpoints. Adaptive mesh refinement based on proximity to or the curvature of the embedded CSD surfaces is used to enhance the accuracy of the solution. User-defined or automatic deactivation for the regions inside immersed solid bodies is employed to avoid unnecessary work. Several examples are included that show the viability of this approach for inviscid and viscous, compressible and incompressible, steady and unsteady flows, as well as coupled fluid,structure problems. Copyright © 2004 John Wiley & Sons, Ltd. [source] Effect of magnetic Reynolds number on the two-dimensional hydromagnetic flow around a cylinderINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2009T. V. S. Sekhar Abstract Numerical experiments have been conducted to study the effect of magnetic Reynolds number on the steady, two-dimensional, viscous, incompressible and electrically conducting flow around a circular cylinder. Besides usual Reynolds number Re, the flow is governed by the magnetic Reynolds number Rm and Alfvén number ,. The flow and magnetic field are uniform and parallel at large distances from the cylinder. The pressure Poisson equation is solved to find the pressure fields in the entire flow region. The effects of the magnetic field and electrical conductivity on the recirculation bubble, drag coefficient, standing vortex and pressure are presented and discussed. For low interaction parameter (N<1), the suppression of the flow-separation is nearly independent of the conductivity of the fluid, whereas for large interaction parameters, the conductivity of the fluid strongly influences the control of flow-separation. Copyright © 2008 John Wiley & Sons, Ltd. [source] CFD-based optimization of aerofoils using radial basis functions for domain element parameterization and mesh deformationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2008A. M. Morris Abstract A novel domain element shape parameterization method is presented for computational fluid dynamics-based shape optimization. The method is to achieve two aims: (1) provide a generic ,wrap-around' optimization tool that is independent of both flow solver and grid generation package and (2) provide a method that allows high-fidelity aerodynamic optimization of two- and three-dimensional bodies with a low number of design variables. The parameterization technique uses radial basis functions to transfer domain element movements into deformations of the design surface and corresponding aerodynamic mesh, thus allowing total independence from the grid generation package (structured or unstructured). Independence from the flow solver (either inviscid, viscous, aeroelastic) is achieved by obtaining sensitivity information for an advanced gradient-based optimizer (feasible sequential quadratic programming) by finite-differences. Results are presented for two-dimensional aerofoil inverse design and drag optimization problems. Inverse design results demonstrate that a large proportion of the design space is feasible with a relatively low number of design variables using the domain element parameterization. Heavily constrained (in lift, volume, and moment) two-dimensional aerofoil drag optimization has shown that significant improvements over existing designs can be achieved using this method, through the use of various objective functions. Copyright © 2008 John Wiley & Sons, Ltd. [source] Numerical simulations of viscous flows using a meshless methodINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2008Changfu You Abstract This paper uses the element-free Galerkin (EFG) method to simulate 2D, viscous, incompressible flows. The control equations are discretized with the standard Galerkin method in space and a fractional step finite element scheme in time. Regular background cells are used for the quadrature. Several classical fluid mechanics problems were analyzed including flow in a pipe, flow past a step and flow in a driven cavity. The flow field computed with the EFG method compared well with those calculated using the finite element method (FEM) and finite difference method. The simulations show that although EFG is more expensive computationally than FEM, it is capable of dealing with cases where the nodes are poorly distributed or even overlap with each other; hence, it may be used to resolve remeshing problems in direct numerical simulations. Flows around a cylinder for different Reynolds numbers are also simulated to study the flow patterns for various conditions and the drag and lift forces exerted by the fluid on the cylinder. These forces are calculated by integrating the pressure and shear forces over the cylinder surface. The results show how the drag and lift forces oscillate for high Reynolds numbers. The calculated Strouhal number agrees well with previous results. Copyright © 2008 John Wiley & Sons, Ltd. [source] Acoustic upwinding for sub- and super-sonic turbulent channel flow at low Reynolds numberINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2007H. C. de LangeArticle first published online: 13 FEB 200 Abstract A recently developed asymmetric implicit fifth-order scheme with acoustic upwinding for the spatial discretization for the characteristic waves is applied to the fully compressible, viscous and non-stationary Navier,Stokes equations for sub- and super-sonic, mildly turbulent, channel flow (Re,=360). For a Mach number of 0.1, results are presented for uniform (323, 643 and 1283) and non-uniform (expanding wall-normal, 323 and 643) grids and compared to the (incompressible) reference solution found in (J. Fluid. Mech. 1987; 177:133,166). The results for uniform grids on 1283 and 643 nodes show high resemblance with the reference solution. Expanding grids are applied on 643 - and 323 -node grids. The capability of the proposed technique to solve compressible flow is first demonstrated by increasing the Mach number to 0.3, 0.6 and 0.9 for isentropic flow on the uniform 643 -grid. Next, the flow speed is increased to Ma=2. The results for the isothermal-wall supersonic flows give very good agreement with known literature results. The velocity field, the temperature and their fluctuations are well resolved. This means that in all presented (sub- and super-sonic) cases, the combination of acoustic upwinding and the asymmetric high-order scheme provides sufficient high wave-number damping and low wave-number accuracy to give numerically stable and accurate results. Copyright © 2007 John Wiley & Sons, Ltd. [source] Numerical simulation of flapping-wing insect hovering flight at unsteady flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2007Decan Zuo Abstract A computational fluid dynamics (CFD) analysis was conducted to study the unsteady aerodynamics of a virtual flying bumblebee during hovering flight. The integrated geometry of bumblebee was established to define the shape of a three-dimensional virtual bumblebee model with beating its wings, accurately mimicking the three-dimensional movements of wings during hovering flight. The kinematics data of wings documented from the measurement to the bumblebee in normal hovering flight aided by the high-speed video. The Navier,Stokes equations are solved numerically. The solution provides the flow and pressure fields, from which the aerodynamic forces and vorticity wake structure are obtained. Insights into the unsteady aerodynamic force generation process are gained from the force and flow-structure information. The CFD analysis has established an overall understanding of the viscous and unsteady flow around the virtual flying bumblebee and of the time course of instantaneous force production, which reveals that hovering flight is dominated by the unsteady aerodynamics of both the instantaneous dynamics and also the past history of the wing. A coherent leading-edge vortex with axial flow and the attached wingtip vortex and trailing edge vortex were detected. The leading edge vortex, wing tip vortex and trailing edge vortex, which caused by the pressure difference between the upper and the lower surface of wings. The axial flow, which include the spanwise flow and chordwise flow, is derived from the spanwise pressure gradient and chordwise pressure gradient, will stabilize the vortex and gives it a characteristic spiral conical shape. Copyright © 2006 John Wiley & Sons, Ltd. [source] The emulsifying properties of a polysaccharide isolated from the fruit of Cordia abyssinicaINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 5 2004Mudadi Albert Nhamoiesu Benhura Summary Polysaccharide was isolated from Cordia abyssinica and its effect, at differing concentrations, on its emulsifying ability was determined. Emulsions of vegetable oil containing up to 1% of the polysaccharide in phosphate pH 7.4 buffer, were prepared by using a hand piston homogenizer. Emulsification was assessed by diluting samples of the emulsions in sodium dodecyl sulphate and measuring absorbance at 500 nm. Addition of increasing concentrations of the polysaccharide up to 1% enhanced emulsification and emulsion stability. Above 1% concentration the polysaccharide solutions were too viscous for making emulsions conveniently. At a constant concentration of the polysaccharide, addition of up to a 1% concentration of salt enhanced emulsion formation. Further addition of salt above 1% resulted in no further changes in emulsifying ability, but the stability of the emulsions formed decreased on increasing the concentration of salt above 1%. The effect of pH on emulsifying ability was investigated by preparing emulsions using buffers of different pH, from pH 3 to pH 13. The polysaccharide had poor emulsifying ability below pH 7. Emulsifying ability increased with pH between pH 7 and 11. At pH above 11 there was a decrease in emulsifying ability. [source] Reactive mold filling in resin transfer molding processes with edge effectsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2009Yanyu Ding Abstract Reactive mold filling is one of the important stages in resin transfer molding processes, in which resin curing and edge effects are important characteristics. On the basis of previous work, volume-averaging momentum equations involving viscous and inertia terms were adopted to describe the resin flow in fiber preform, and modified governing equations derived from the Navier,Stokes equations are introduced to describe the resin flow in the edge channel. A dual-Arrhenius viscosity model is newly introduced to describe the chemorheological behavior of a modified bismaleimide resin. The influence of the curing reaction and processing parameters on the resin flow patterns was investigated. The results indicate that, under constant-flow velocity conditions, the curing reaction caused an obvious increase in the injection pressure and its influencing degree was greater with increasing resin temperature or preform permeability. Both a small change in the resin viscosity and the alteration of the injection flow velocity hardly affected the resin flow front. However, the variation of the preform permeability caused an obvious shape change in the resin flow front. The simulated results were in agreement with the experimental results. This study was helpful for optimizing the reactive mold-filling conditions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Effect of floc concentration on the rheology of a ferric flocJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2004Wendy AM McMinn Abstract The primary interest of this work is to determine the effect of floc concentration on ferric floc particle interactions and hence, rheology. In accordance with established theory, ferric floc viscosity exhibits a non-linear increase with solids content, with the viscosity increasing sharply above a concentration of 12 000 ppm. Shear effectively breaks down floc structure, and thus reduces viscosity, the extent of which is independent of solids content. The effect of shear is also observed to diminish over time and can be adequately characterised by a power law model. Addition of aluminium nitrate to ferric floc increases the quantity of water bound within the floc, and thus produces suspensions which are more viscous in nature. Copyright © 2003 Society of Chemical Industry [source] Gonadal maturation in the blackspot seabream Pagellus bogaraveo: a comparison between a farmed and a wild broodstockJOURNAL OF FISH BIOLOGY, Issue 2004V. Micale The blackspot seabream Pagellus bogaraveo(Brünnich, 1768) has been regarded as a possible alternative to traditionally cultured Mediterranean species such as seabream and seabass, due to its high market value and good adaptation to captivity. Broodstock establishment and management represent the first step towards reliable production of eggs and fry, which is required to develop aquaculture of this new species. Two different broodstocks were tested for gonadal maturation and spawning, one constituting of wild fish caught as juveniles and reared in tanks until sexual maturity (4 years), and one assembled from wild adult fish caught during or just before the reproductive season. All fish were maintained under the same rearing conditions and fed the same diet. Gonadal stripping and biopsies were performed weekly to monitor maturation in both males and females. Ovarian samples were staged for maturity on the basis of follicular diameter and migration of germinal vesicle. Sperm samples were tested for density (number of spermatozoa ml,1) and motility. The fish reared in captivity reached ovarian maturity during the breeding season of the wild stock. Eggs were obtained by stripping from both farmed and wild specimens, but appeared degenerated as a result of being retained too long in the ovarian cavity due to the absence of spontaneous spawning. Spermiation was prolonged in the farmed fish, but appeared to be blocked in the wild breeders after first sampling. However, the sperm was very viscous and the motile spermatozoa did not exceed 10%. [source] The ovarian morphology of Scorpaena notata shows a specialized mode of oviparityJOURNAL OF FISH BIOLOGY, Issue 4 2002M. Muñoz Scorpaena notata is an oviparous species with external fertilization that deposits its eggs in a gelatinous matrix. The internal epithelium of the ovarian wall is chiefly responsible for the production of this matrix, which is particularly abundant and viscous during the spawning period. The oocytes lack lipid droplets, so flotation and transport of the eggs is probably accomplished by means of the matrix that surrounds them. The ovarian stroma is situated along the centre of the gonad and the developing oocytes are connected to it by peduncles. The paucity and small size of the cortical alveoli of the oocytes are notable, as is the thinness of the zona radiata. These are characteristics that would be typical of viviparous species. The histological and ultrastructural observations lead to the conclusion that this species presents a type of oviparity more highly specialized than that of the majority of teleosts. [source] EFFECT OF COMPOSITION OF GLUTHNIN SUBFRACTIONS ON RHEOLOGICAL PROPERTIES OF WHEATJOURNAL OF FOOD BIOCHEMISTRY, Issue 4 2000S. JOOD ABSTRACT Gluten extracted from defatted flours of cv. Aubaine (extra-strong), Hereward (strong) and Riband (weak) was separated into five different fractions (R2 to R6) by sequential centrifugation and addition of sodium chloride. A seven-minute mixing time was used to carry out fractionation on the basis of depolymerization of glutenin macropolymers (GMP). Depolymerization of GMP occurred at much higher rates in dough of the weak cultivar compared to the strong and extra-strong cultivars. Polypeptide compositions of different ghttenin fractions were determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis under reduced and non-reduced conditions, followed by densitometric scanning of stained patterns. The amount of HMW-glutenin subunits decreased and LMW-glutenin subunits increased correspondingly in each cultivar with the fractionation from R2 to R6. The rheological behavior of the fractions was analyzed by small deformation rheological tests (strain sweep and frequency tests). The high molecular weight fraction (R2) from extra-strong wheat had a higher vahte of G' and a lower tan , value as compared to strong and weak bread-making wheats. The moduli of HMW glutenin fractions (R2 and R3) were frequency independent and promoted the network properties, whereas moduli of LMW glutenin fractions were frequency dependent and gave rise to a plasticizing effect. Therefore, it was concluded from the present studies that HMW-glutenin subunits are not the only factors governing good bread-making quality but their proportions in relation to low molecular weight glutenin subunits is equally important in sinking a balance between viscous and elastic properties essential for bread making performance. [source] VISCOSITY AND QUALITY OF TOMATO JUICE AS AFFECTED BY PROCESSING METHODSJOURNAL OF FOOD QUALITY, Issue 6 2007CHARANJIT KAUR ABSTRACT Quality and viscosity of tomato juice is strongly governed by mechanical and thermal abuse during processing. The effect of processing and storage duration on the viscosity and quality parameters of tomato juice was evaluated in the present work. Tomato juice was obtained by two different methods, normal method (NM) and variable method (VM), and was heated by both conventional and microwave hot break treatments. Tomato juice was evaluated for various quality characteristics including precipitate weight ratio, degree of serum separation (DOSS), Brookfield viscosity, lycopene levels, vitamin C, phenols and antioxidant activity. Changes observed in several quality parameters during storage were statistically insignificant. The methods and processing had the greatest contribution toward viscosity, whereas storage duration had no significant effects. Viscosity parameters viz precipitate weight, DOSS and Bostwick consistency revealed that juice processed by VM was more viscous than that of NM, irrespective of the hot break processing used. Ascorbic acid and lycopene content varied significantly with mechanical methods and processing conditions. However, phenolic content and antioxidant activity remained stable. The variable process represents an improvement over the conventional by enabling tomato processors to improve the consistency of the tomato product. PRACTICAL APPLICATIONS Quartering or slicing tomatoes followed by hot break processing techniques can significantly improve the quality of tomato juice in terms of reduced degree of serum separation and precipitate weight ratio. The modified technology could be considered as a viable and economical method for small- and medium-scale tomato processors with limited resources and facilities at their disposal. [source] Perceived Creaminess and Viscosity of Aggregated Particles of Casein Micelles and ,-CarrageenanJOURNAL OF FOOD SCIENCE, Issue 5 2010Kelly L. Flett Abstract:, Creaminess, in terms of sensory science, is a very complex and multifaceted term. It is a descriptor often reserved for fat-containing dairy emulsions, however, has also been used to describe nondairy food emulsions. In the food industry, it is a great challenge to decrease fat content while maintaining the original quality and sensory characteristics of a food product. An aggregated particle consisting of casein micelles and ,-carrageenan has the potential to enhance the perceived creaminess of a low-fat food product, due to its colloidal size. In this study, these aggregates were incorporated into nonfat dairy beverages and subjected to sensory studies. In the 1st sensory study, the aggregates, either as a powdered ingredient or a fresh ingredient, were added to thickened dairy beverages and compared to similar beverages containing skim milk powder and either no fat or 2% dairy fat. The panelists found the aggregate-containing beverages to be creamier and more viscous in comparison to the control beverages. In the 2nd sensory study, fresh and powdered aggregates, at 2 concentrations, were added to a sweetened nonfat dairy beverage and compared to a similar beverage containing 2% dairy fat. The results of this panel showed that aggregates, especially at increased concentrations, were perceived as more creamy than the fat-containing beverage. Panelists described the creaminess of the aggregates as more thick and viscous while the dairy fat was described more in terms of mouth-coating. Thus, we have developed a nonfat milk ingredient that can contribute creaminess to a food product. Practical Application:, This study shows potential applications of aggregates of casein micelles and ,-carrageenan as a fat-mimetic or creaminess-enhancing ingredient. These particles may be produced as either fresh aggregates directly formed in a dairy product or as powdered aggregates added to dairy or nondairy products. [source] Characterization of ultrasound extrudated and cut citric acid/paracetamol blendsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 6 2009P. Hoppu Abstract The purpose of the present work was to study the effect of ultrasound extrusion and cutting on the physical stability of a viscous and sticky supercooled melt containing (50/50, w/w, %) citric acid anhydrate and paracetamol. Samples were extrudated at temperatures of 50, 60, and 70°C using power levels of 0, 50, 100, and 150 W. Similarly, extrudates prepared at 60°C were cut at temperatures ranging from 25,60°C with an ultrasound knife in the range 0, 50, and 100 W. The characterization methods used were: high performance liquid chromatography, differential scanning calorimetry, Karl Fischer titration, X-ray powder diffraction, Fourier transform infrared microscopy, optical- and stereomicroscopy. There was no physical difference in extrudates or cut surfaces whether processed with or without ultrasound. During 1-year aging time in dry conditions, all the samples were observed to crystallize slowly and ultrasound processing did not enhance the crystallization. Ultrasound thus holds some promise for processing of viscous and sticky pharmaceuticals, provided the material is physically stable enough to withstand mechanical and thermal stress. Processing of sticky and viscous material would be difficult without ultrasound with the methods currently used in pharmaceutical industry. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2140,2148, 2009 [source] Coalescence of deformable granules in wet granulation processesAICHE JOURNAL, Issue 3 2000L. X. Liu In this work, the coalescence of deformable granules in wet granulation processes is modelled. The model accounts for both the mechanical properties of the granules and the effect of the liquid layer at the granule surface. It is an extension to the model of Ennis et al. (1991) to include the possibility of granule plastic deformation during collisions. The model is written in dimensionless groups such as viscous and deformation Stokes numbers and the ratio of granule dynamic yield strength to granule Young's modulus (Yd/E*). These variables are bulk parameters of the powder-binder mixture and also functions of the process intensity. The model gives the conditions for two types of coalescence,type I and type II. Type I coalescence occurs when granules coalesce by viscous dissipation in the surface liquid layer before their surfaces touch. Type II coalescence occurs when granules are slowed to a halt during rebound, after their surfaces have made contact. The model explains some of the trends observed in the literature, are preliminary validation of the coalescence criterion with drum granulation data is encouraging. An extension is also made to the case of surface dry granules, where liquid is squeezed to the surface during granule deformation. [source] Carrier proteins determine local pharmacokinetics and arterial distribution of paclitaxelJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2001Mark A. Lovich Abstract The growing use of local drug delivery to vascular tissues has increased interest in hydrophobic compounds. The binding of these drugs to serum proteins raises their levels in solution, but hinders their distribution through tissues. Inside the arterial interstitium, viscous and steric forces and binding interactions impede drug motion. As such, this might be the ideal scenario for increasing the amount of drug delivered to, and residence time within, arterial tissues. We quantified carrier-mediated transport for paclitaxel, a model hydrophobic agent with potential use in proliferative vascular diseases, by determining, in the presence or absence of carrier proteins, the maximum concentration of drug in aqueous solution, the diffusivity in free solution, and the diffusivity in arterial tissues. Whereas solubility of paclitaxel was raised 8.1-, 21-, and 57-fold by physiologic levels of ,1 -acid glycoproteins, bovine serum albumin, and calf serum over that in protein-free solution, diffusivity of paclitaxel in free solution was reduced by 41, 49, and 74%, respectively. When paclitaxel mixed in these solutions was applied to arteries both in vitro and in vivo, drug was more abundant at the tissue interface, but protein carriers tended to retain drug in the lumen. Once within the tissue, these proteins did not affect the rate at which drug traverses the tissue because this hydrophobic drug interacted with the abundant fixed proteins and binding sites. The protein binding properties of hydrophobic compounds allow for beneficial effects on transvascular transport, deposition, and distribution, and may enable prolonged effect and rationally guide local and systemic strategies for their administration. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1324,1335, 2001 [source] Solid acid clay mediated copolymerization of methyl acrylate and 1-octene: 2D NMR substantiation of predominant alternating comonomer sequenceJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2009Sukhdeep Kaur Abstract Montmorillionite K10 powder presence during radically initiated copolymerization of methyl acrylate (M) and 1-octene (O) gave copolymers with higher incorporation of alkene unit. Highly viscous and transparent copolymers showed alternation irrespective of the copolymer composition. Increasing the amount of K10 powder increased the total percentage conversion, as well as 1-octene incorporation. The monomodal curves obtained in gel permeation chromatography (GPC) substantiated that true copolymers were formed. The alternation in the copolymers was authenticated through Heteronuclear Multiple Quantum Correlation (HMQC) experiments in conjugation with Total Correlated Spectroscopy (TOCSY). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2156,2162, 2009 [source] EFFECTS OF DELIVERY METHOD ON THE SENSORY PERCEPTION OF SEMISOLID DAIRY DESSERTSJOURNAL OF SENSORY STUDIES, Issue 5 2004L. ENGELEN ABSTRACT This study tests the possibility that sensory attributes are affected by the method by which a food is transferred to the mouth. For example, hot liquids appear to be considerably hotter when taken through a straw than when taken using a cup. Pre-weighed samples of two vanilla flavoured dairy custards were presented, in random order, to 16 trained panellists using a spoon, an 11-mm diameter straw or a modified straw that had a 4-mm diameter constriction within it. Panellists rated products using a subset of attributes generated by a quantitative descriptive analysis panel. The amount ingested was measured by re-weighing each sample after assessment. Each experiment was repeated three times. There were significant differences in the amount ingested for the two products. The delivery method had no effect on the sensory attributes of the products other than for thickness and melting, where products taken with the spoon were rated as less viscous than when taken through a straw. The constriction in the straw had no effect on either the amount ingested or on any of the sensory attributes. This study demonstrates that resistance to sucking does not affect perception of thickness. [source] | ||||||||||||||||||||||||||||