Home About us Contact
|
Home About us Contact | ||
|
|
||
Unit Volume (unit + volume)
Selected AbstractsLeucocyte populations in respiratory syncytial virus-induced bronchiolitisJOURNAL OF PAEDIATRICS AND CHILD HEALTH, Issue 2 2001PK Smith Objectives: To enumerate the cellular composition of the airways in infants with acute bronchiolitis. Methodology: Cells were obtained by airway lavage from the upper and lower airway and the peripheral blood of infants with respiratory syncytial virus (RSV)+ bronchiolitis, RSV, bronchiolitis and age-matched controls. Results: Neutrophils are the predominant cells present in the upper and lower airway. Neutrophils are present at a higher number/unit volume in the airway than in the peripheral blood. Conclusions: Neutrophils, being the dominant cellular infiltrate into the airway, are likely to contribute to the pathophysiology of bronchiolitis. Therapies targeted at limiting neutrophil influx or neutrophil-mediated damage in the airway may have a therapeutic role. [source] A novel self-consistent Nývlt-like equation for metastable zone width determined by the polythermal methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2009K. Sangwal Abstract Using a power-law relation between three-dimensional nucleation rate J and dimensionless supersaturation ratio S, and the theory of regular solutions to describe the temperature dependence of solubility, a novel Nývlt-like equation of metastable zone width of solution relating maximum supercooling ,Tmax with cooling rate R is proposed in the form: ln(,Tmax/T0) = , + , lnR, with intercept , = {(1,m)/m }ln(,Hs/RGTlim) + (1/m)ln(f/KT0) and slope , = 1/m. Here T0 is the initial saturation temperature of solution in a cooling experiment, ,Hs is the heat of dissolution, RG is the gas constant, Tlim is the temperature of appearance of first nuclei, m is the nucleation order, and K is a new nucleation constant connected with the factor f defined as the number of particles per unit volume. It was found that the value of the term , for a system at saturation temperature T0 is essentially determined by the constant m and the factor f. The value of the factor f for a solute,solvent system at initial saturation temperature T0 is determined by solute concentration c0. Analysis of the experiment data for four different solute-water systems according to the above equation revealed that: (1) the values of , and m for a system at a given temperature depend on the method of detection of metstable zone width, and (2) the value of slope , = 1/m for a system is practically a temperature-independent constant characteristic of the system, but the value of , increases with an increase in saturation temperature T0, following an Arrhenius-type equation with an activation energy Esat. The results showed, among others, that solubility of a solute is an important factor that determines the value of the nucleation order m and the activation energy Esat for diffusion. In general, the lower the solubility of a solute in a given solvent, the higher is the value of m and lower is the value of Esat. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nutrients, diversity, and community structure of two phytotelm systems in a lower montane forest, Puerto RicoECOLOGICAL ENTOMOLOGY, Issue 3 2000Barbara A. Richardson Summary 1. Bromeliad and heliconia phytotelmata in the same forest area were compared in terms of their animal assemblages, nutrient inputs, and plant architecture. 2. For all major elements, nutrient inputs from canopy-derived debris and rainfall in bromeliads were significantly lower than those derived from decaying flower parts and plant secretions in heliconia bracts. Bromeliads contained significantly fewer organisms per unit volume of water and unit dry weight of organic matter than did heliconia inflorescences. They also contained a significantly lower animal biomass (199 mg DW from 15 bromeliads, 527 mg DW from 15 heliconia inflorescences). 3. Species richness was independent of abundance, demonstrating that, at least for small container habitats, higher abundance does not necessarily lead to a greater species richness. Communities were remarkably similar in patterns of relative abundance and species richness (23 spp. in bromeliads, 21 spp. in heliconia), probably due to functional similarities in plant architecture, with the two most abundant species comprising 60,62% of the total community. Coefficients of similarity were low because of marked differences in species assemblages. 4. Some taxa were phytotelm generalists but most showed a preference for one particular habitat, indicating differential selection in the choice of oviposition sites and larval development within the forest ecosystem. In common with many island communities, species richness was lower than that reported for these phytotelm habitats in mainland central and south America. [source] Diffusion of strongly sorbed solutes in soil: a dual-porosity model allowing for slow access to sorption sites and time-dependent sorption reactionsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2010M. Ptashnyk We use homogenization techniques to derive a dual (or double) porosity model of solute diffusion and reaction in soil, allowing for slow access to sorption sites within micro-aggregates and time-dependent sorption reactions. We give a means for determining the conditions in which micro-scale concentration gradients affect macro-scale gradients and fluxes. We present equations for a unit volume of soil represented as a series of uniformly-spaced, porous spherical particles, containing and surrounded by solution through which solutes diffuse. The methods we use can, in principle, be applied to more complex geometries. We compare the model's predictions with those of the equivalent single porosity model for commonly used boundary conditions. We show that failure to allow for slow access to reaction sites can lead to seriously erroneous results. Slow access has the effect of decreasing the sorption of solute into soil from a source or desorption from soil to a sink. As a result of slow access, the diffusion coefficients of strongly-sorbed solutes measured at the macro-scale will be time-dependent and will depend on the method of measurement. We also show that slow access is more often likely to limit macro-scale diffusion than rates of slow chemical reactions per se. In principle, the unimportance of slow reactions except at periods longer than several weeks of diffusion simplifies modelling because, if slow access is correctly allowed for, sorption can be described with equilibrium relations with an understanding of speciation and rapid sorption-desorption reactions. [source] Interior point optimization and limit analysis: an applicationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 10 2003Joseph Pastor Abstract The well-known problem of the height limit of a Tresca or von Mises vertical slope of height h, subjected to the action of gravity stems naturally from Limit Analysis theory under the plane strain condition. Although the exact solution to this problem remains unknown, this paper aims to give new precise bounds using both the static and kinematic approaches and an Interior Point optimizer code. The constituent material is a homogeneous isotropic soil of weight per unit volume ,. It obeys the Tresca or von Mises criterion characterized by C cohesion. We show that the loading parameter to be optimized, ,h/C, is found to be between 3.767 and 3.782, and finally, using a recent result of Lyamin and Sloan (Int. J. Numer. Meth. Engng. 2002; 55: 573), between 3.772 and 3.782. The proposed methods, combined with an Interior Point optimization code, prove that linearizing the problem remains efficient, and both rigorous and global: this point is the main objective of the present paper. Copyright © 2003 John Wiley & Sons, Ltd. [source] Anode-Supported Tubular Micro-Solid Oxide Fuel CellINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2007Partho Sarkar A tubular anode-supported "micro-solid oxide fuel cell" (,SOFC) has been developed for producing high volumetric power density (VPD) SOFC systems featuring rapid turn on/off capability. An electrophoretic deposition (EPD)-based, facile manufacturing process is being refined to produce the anode support, anode functional and electrolyte layers of a single cell. ,SOFCs (diameter <5 mm) have two main potential advantages, a substantial increase in the electrolyte surface area per unit volume of a stack and also rapid start-up. As fuel cell power is directly proportional to the active electrolyte surface area, a ,SOFC stack can substantially increase the VPD of an SOFC device. A decrease in tube diameter allows for a reduction in wall thickness without any degradation of a cell's mechanical properties. Owing to its thin wall, a ,SOFC has an extremely high thermal shock resistance and low thermal mass. These two characteristics are fundamental in reducing start-up and turn-off time for the SOFC stack. Traditionally, SOFC has not been considered for portable applications due to its high thermal mass and low thermal shock resistance (start-up time in hours), but with ,SOFCs' potential for rapid start-up, new possibilities for portable and transportable applications open up. [source] Diel Changes in Phytoplankton Composition and Abundance in the Surface and Sub-Surface Strata from a Shallow Eutrophic PondINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 1 2009bieta Wilk-Wo, niak Abstract Representative phytoplankton assemblages were identified in a eutrophic pond over a 24 hour period. One assemblage characterized species in the surface (neuston) layer and another consisted of algae from 2, 5, and 20 cm sub-surface depths. The surface layer (0 cm) included a similar, but less diverse assemblage of species, and a lower abundance of cells per unit volume, than those at the lower depths. At each of the sub-surface depths (2,20 cm), the major phytoplankton components initially followed similar patterns of abundance in reference to the time and depth of sample collections then later differed in their abundance levels. The dominant algae were chlorophytes, cryptophytes, diatoms, and cyanobacteria. Mean concentrations of total phytoplankton, over the 24 hours for the surface, were 3.3 × 103 cells ml,1, compared to 36.9 × 103 cells ml,1 for depths 2,20 cm. The autotrophic picoplankton abundance was recorded separately from the phytoplankton with mean concentrations of 472.9 × 103 cells ml,1 in the surface layer and 623.0 × 103 cells ml,1 for the three sub-surface depths. Photos of representative species from these surface layers are presented. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Compressive response and energy absorption of foam EPDMJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007Biqin Wang Abstract Ethylene,propylene,diene terpolymer foam was prepared by two different processing routes. The microstructure and mechanical properties of the foams with wide relative density ranging from 0.11 to 0.62 have been studied via scanning electron microscopy and mechanical testing, respectively. Scanning electron microscopy shows that the foam with lower relative density has a unique bimodal cell size structure, which the larger cells inlay among the smaller cells, while the foam articles with higher relative density have thicker cell walls with few small cells. The compressive stress,strain curves show that the foam articles with lower relative density have three regimes: linear elastic, a wide slightly rising plateau, and densification, while the foam articles with higher relative density have only two regimes: the longer linear elastic and densification. The relative modulus increases with the increase in the relative density. The contribution of the gas trapped in the cell to the modulus could be neglected. The energy absorbed per unit volume is relationship with the permitted stress and the relative density. The efficiency and the ideality parameter were evaluated from the compressive stress,strain plots. The parameters were plotted against stress to obtain maximum efficiency and the maximum ideality region, which can be used for optimizing the choice for practical applications in cushioning and packaging. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Changes in Bone Density During Childhood and Adolescence: An Approach Based on Bone's Biological OrganizationJOURNAL OF BONE AND MINERAL RESEARCH, Issue 4 2001Frank Rauch Abstract Bone densitometry has great potential to improve our understanding of bone development. However, densitometric data in children rarely are interpreted in light of the biological processes they reflect. To strengthen the link between bone densitometry and the physiology of bone development, we review the literature on physiological mechanisms and structural changes determining bone mineral density (BMD). BMD (defined as mass of mineral per unit volume) is analyzed in three levels: in bone material (BMDmaterial), in a bone's trabecular and cortical tissue compartments (BMDcompartment), and in the entire bone (BMDtotal). BMDmaterial of the femoral midshaft cortex decreases after birth to a nadir in the first year of life and thereafter increases. In iliac trabecular bone, BMDmaterial also increases from infancy to adulthood, reflecting the decrease in bone turnover. BMDmaterial cannot be determined with current noninvasive techniques because of insufficient spatial resolution. BMDcompartment of the femoral midshaft cortex decreases in the first months after birth followed by a rapid increase during the next 2 years and slower changes thereafter, reflecting changes in both relative bone volume and BMDmaterial. Trabecular BMDcompartment increases in vertebral bodies but not at the distal radius. Quantitative computed tomography (QCT) allows for the determination of both trabecular and cortical BMDcompartment, whereas projectional techniques such as dual-energy X-ray absorptiometry (DXA) can be used only to assess cortical BMDcompartment of long bone diaphyses. BMDtotal of long bones decreases by about 30% in the first months after birth, reflecting a redistribution of bone tissue from the endocortical to the periosteal surface. In children of school age and in adolescents, changes in BMDtotal are site-specific. There is a marked rise in BMDtotal at locations where relative cortical area increases (metacarpal bones, phalanges, and forearm), but little change at the femoral neck and midshaft. BMDtotal can be measured by QCT at any site of the skeleton, regardless of bone shape. DXA allows the estimation of BMDtotal at skeletal sites, which have an approximately circular cross-section. The system presented here may help to interpret densitometric results in growing subjects on a physiological basis. [source] Fractal Dimension of Trabecular Bone Projection Texture Is Related to Three-Dimensional MicroarchitectureJOURNAL OF BONE AND MINERAL RESEARCH, Issue 4 2000L. Pothuaud Abstract The purpose of this work was to understand how fractal dimension of two-dimensional (2D) trabecular bone projection images could be related to three-dimensional (3D) trabecular bone properties such as porosity or connectivity. Two alteration processes were applied to trabecular bone images obtained by magnetic resonance imaging: a trabeculae dilation process and a trabeculae removal process. The trabeculae dilation process was applied from the 3D skeleton graph to the 3D initial structure with constant connectivity. The trabeculae removal process was applied from the initial structure to an altered structure having 99% of porosity, in which both porosity and connectivity were modified during this second process. Gray-level projection images of each of the altered structures were simply obtained by summation of voxels, and fractal dimension (Df) was calculated. Porosity (,) and connectivity per unit volume (Cv) were calculated from the 3D structure. Significant relationships were found between Df, ,, and Cv. Df values increased when porosity increased (dilation and removal processes) and when connectivity decreased (only removal process). These variations were in accordance with all previous clinical studies, suggesting that fractal evaluation of trabecular bone projection has real meaning in terms of porosity and connectivity of the 3D architecture. Furthermore, there was a statistically significant linear dependence between Df and Cv when , remained constant. Porosity is directly related to bone mineral density and fractal dimension can be easily evaluated in clinical routine. These two parameters could be associated to evaluate the connectivity of the structure. [source] Removal of cupric ions from acidic sulfate solution using reticulated vitreous carbon rotating cylinder electrodesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 9 2004Gavin W Reade Abstract The potentiostatic deposition of copper from acid sulfate solutions (0.50 mol dm,3 Na2SO4 at pH 2 and 298 K) was studied at four porosity grades (10, 30, 60 and 100 pores per linear inch, ppi) of reticulated vitreous carbon (RVC) rotating cylinder electrode (RCE). The rate of removal of cupric ions from a 200 cm3 volume of electrolyte was examined as a function of the grade of RVC foam, the electrode potential and the initial cupric ion concentration. For the 100 ppi material, the product of the mass transport coefficient and the electroactive area per unit volume of electrode (kmAe) was equal to 0.28 s,1 at a potential of ,500 mV vs SCE for an initial cupric ion concentration of 0.85 mmol dm,3 and a constant rotation speed of 1500 rev min,1. Under the experimental conditions, an initial dissolved copper concentration of 63.5 ppm could be reduced to <0.1 ppm in approximately 60 min using a 100 ppi RVC RCE. SEM studies showed some non-uniform deposition of metal due to heterogeneous nucleation of copper together with the development of rough deposits. Copyright © 2004 Society of Chemical Industry [source] Viscous co-current downward Taylor flow in a square mini-channelAICHE JOURNAL, Issue 7 2010Özge Keskin Abstract This article presents a computational study of the co-current downward Taylor flow of gas bubbles in a viscous liquid within a square channel of 1 mm hydraulic diameter. The three-dimensional numerical simulations are performed with an in-house computer code, which is based on the volume-of-fluid method with interface reconstruction. The computed (always axi-symmetric) bubble shapes are validated by experimental flow visualizations for varying capillary number. The evaluation of the numerical results for a series of simulations reveals the dependence of the bubble diameter and the interfacial area per unit volume on the capillary number. Correlations between bubble velocity and total superficial velocity are also provided. The present results are useful to estimate the values of the bubble diameter, the liquid film thickness and the interfacial area per unit volume from given values of the gas and liquid superficial velocities. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Synthesis of high-refractive index polyimide containing selenophene unitJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2009Nam-Ho You Abstract A highly refractive and transparent aromatic polyimide (PI) containing a selenophene unit has been developed. The PI was prepared by a two-step polycondensation procedure from 2,5-bis(4-aminophenylenesulfanyl)selenophene (APSP) and 4,4,-[p -thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA), and shows high thermal stabilities, such as a relatively high-glass transition temperature of 189 °C and 5% weight loss temperature (T5%) of 418 °C. The optical transmittance of the PI film at 450 nm is higher than 50%. The selenophene unit provides the PI with a refractive index of 1.7594, which is higher than corresponding PIs containing a thiophene or a phenyl unit because of the high polarizability per unit volume of the selenium atom. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4428,4434, 2009 [source] The one-commodity pickup and delivery travelling salesman problem on a path or a treeNETWORKS: AN INTERNATIONAL JOURNAL, Issue 1 2006Fan Wang Abstract Optimization algorithms for both path and tree topology classes of the one-commodity pickup and delivery travelling salesman problem (1-PDTSP) are proposed in this article, which focus on minimizing the route distance to transport products among pickup and delivery customers by a single vehicle with a limited capacity of k. Each pickup customer provides one unit volume of the product while each delivery customer requires one unit volume of the product. For the path case, we propose an O(n2/ min (k,n)) algorithm for any arbitrary k, and two O(n) algorithms for k = 1 and k = ,. For the tree case, O(n2) and O(n) algorithms are proposed for k = 1 and k = ,, respectively. Moreover, when k is arbitrary, the problem becomes NP-hard in the strong sense. © 2006 Wiley Periodicals, Inc. NETWORKS, Vol. 48(1), 24,35 2006 [source] Patch area, substrate depth, and richness affect giving-up densities: a test with mourning doves and cottontail rabbitsOIKOS, Issue 11 2009Mohammad A. Abu Baker We compared the foraging behavior of mourning doves Zenaida macroura and cottontail rabbits Sylvilagus floridanus in patches that varied in initial food abundance, surface area and substrate depth. We measured giving-up densities (GUD), food harvest and proportion of food harvested to investigate their ability to respond to characteristics of resource patches. GUDs have been analyzed in three ways: grams of per patch, grams per unit surface area (GUDAREA), and grams per unit volume of sand (GUDVOL). Mourning doves and cottontails exhibited similar responses to resource density and sand depth. Both foragers detected and responded to variation in initial food abundance. The proportion of food harvested from a patch increased from 40.7, 43.8 to 48.3% (for the doves) and 34.9, 35.8 to 38.4% (for the rabbits) in patches of low, medium and high initial food abundance, respectively. Deeper substrates reduced the foragers' encounter probability with food, decreased patch quality and resulted in higher GUDs (60% higher in the deepest relative to shallowest substrate) and lower harvests. A significant interaction between initial food abundance and substrate depth showed that both species were willing to dig deeper in patches with higher resource density. Patch size (surface area) had no effect on food harvest or the proportion of food harvested. Consequently, GUDAREA and GUDVOL increased in patches with a smaller surface area. Smaller patches appeared to hamper the dove's and cottontail's movement across the surface. Our results revealed that mourning doves and cottontails forage under imperfect information. Both species were able to respond to patch properties by biasing their feeding efforts toward rich and easy opportunities, however, mourning doves were more efficient at food harvesting. The interaction of patch area, volume and food abundance directly influenced food harvest. Such resource characters occur under natural situations where food varies in abundance, area of distribution, and accessibility. [source] Non-adiabatic small polaron hopping conduction in sodium borate tungstate glassesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2003A. Al-Shahrani Abstract The dc electrical conductivity of (100,x)Na2B4O7,xWO3 (x = 5, 15, 20 and 30 mol%) glasses is reported in the temperature range 323,473 K. The density and molar volume for these glasses are consistent with the ionic size, atomic weight and amount of different elements in the glasses. At high temperatures the Mott model of phonon-assisted small polaron hopping between nearest neighbours is consistent with conductivity data, while at intermediate temperatures the Greaves variable-range hopping model is found to be appropriate. The estimated model parameters such as number of ions per unit volume, hopping distance, polaron radius and activation energy are found to be consistent with the formation of localized states in these glasses. The electrical conduction of these glasses is confirmed to be that of non-adiabatic small polaron hopping. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Conventional and nanometric nucleating agents in poly(,-caprolactone) foaming: Crystals vs. bubbles nucleationPOLYMER ENGINEERING & SCIENCE, Issue 2 2008Carlo Marrazzo The aim of this article was to investigate the nucleating ability of different nucleating agents for the foaming of poly(,-caprolactone), a biodegradable, semicrystalline polymer. In particular, the efficiency of the nucleating agent in inducing the formation of the gaseous phase has been compared to the efficiency in inducing the formation of the crystalline phase. In effect, in foaming of semicrystalline polymers, bubble nucleation and crystal nucleation are concurrent and somehow interacting phenomena. Here, these two aspects have been evidenced and clarified. Foams were prepared by using a batch process with the pressure quench method, with nitrogen and carbon dioxide as the blowing agents. Conventional and novel nucleating agents were used: talc has been compared to several novel nanometric particles of different geometries and dimensions, such as titanium dioxide and alumina powders, exfoliated and intercalated clays, and carbon nanotubes. Foam densities and morphologies, in terms of number of cells per initial unit volume, were measured and found to depend both on crystalline phase nucleation and gaseous phase nucleation. In fact, the different nucleating agents, depending on shape, dimension, and surface functionalization, selectively nucleated the crystallites and/or the bubbles, affecting, respectively, bubble growth (and, hence, final foam density) and bubble nucleation (and, hence, cell number density,morphology). POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers [source] Industrial solidification processes in polybutene-1.POLYMER ENGINEERING & SCIENCE, Issue 1 2003Part I, quiescent melts In the first paper of this series the principles for solidification of crystallizable polymers under heat transfer conditions are discussed for the case of the absence of flow. For industrial polymers, which, in general, are forced to crystallize at large undercoolings, the pertinent kinetic data are extremely rare. In the present paper the growth speeds of spherulites and the number of nuclei per unit volume are presented as functions of temperature for two industrial polybutene-1 grades. [source] Industrial solidification processes in polybutene-1.POLYMER ENGINEERING & SCIENCE, Issue 1 2003Part II, influence of shear flow Following some early rudimentary results on shear-induced crystallization of polybutene-1 (1, 2), the present paper contains more detailed results. In the course of this work the origins of the highly oriented crystalline surface layers, as well known from injection molded samples, are more closely investigated. For the purpose, a special extrusion experiment is used, in which melts of various degrees of undercooling are moved through a duct of large aspect ratio. When, after the release of the pressure at the die entry, a quench of the duct to a temperature far below the melting point is delayed, a relaxation phenomenon is observed, in accordance with the experiences with i-PP. From these experiments one learns that the leading parameter of the process is something like the mechanical work done per unit volume, and that the relaxation time increases with decreasing temperature much faster than the viscosity of the melt. The results are qualitatively in excellent agreement with our previously obtained results for polypropylene. [source] Corrosion inhibition of carbon steel under two-phase flow (water-petroleum) simulated by turbulently agitated systemTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2008Qasim J. M. Slaiman Abstract The corrosion of carbon steel in single-phase (water with 0.1N NaCl) and two immiscible phases (kerosene-water) using turbulently agitated system was investigated. The experiments were carried out for Reynolds number (Re) range of 38 000 to 95 000 using circular disc turbine agitator at 40°C. In two-phase system, test runs were carried out in aqueous phase (water) concentrations of 1% vol, 5% vol, 8% vol, and 16.4% vol mixed with kerosene at various Re. The effect of Re, percent of dispersed phase, dispersed droplet diameter, and number of droplets per unit volume on the corrosion rate were investigated and discussed. Test runs were carried out using two types of inhibitors: sodium nitrite of concentrations 20, 40, and 60 ppm and sodium hexapolyphosphate of concentrations 485, 970, and 1940 ppm in a solution containing 8% vol aqueous phase (water) mixed with kerosene (continuous phase) at 40°C for the whole range of Re. It was found that increasing Re increased the corrosion rate and the presence of water enhanced the corrosion rate by increasing the solution electrical conductivity. For two-phase solution containing 8% vol and 16% vol of water, the corrosion rate was higher than single phase (100% vol water). The main parameters that play the major role in determining the corrosion rate in two phases were concentration of oxygen, solution electrical conductivity, and the interfacial area between the two phases (dispersed and continuous). Sodium nitrite and sodium hexapolyphosphate were found to be efficient inhibitors in two-phase solution for the investigated range of Re. On a étudié la corrosion de l'acier au carbone dans des conditions monophasiques (eau avec 0,1N de NaCl) et diphasiques immiscibles (kérosène-eau) à l'aide d'un système agité turbulent. Les expériences ont été menées pour une gamme de nombre de Reynolds (Re) de 38000 à 95000, avec un agitateur de type Rushton à 40°C. Des tests pour le système diphasique ont été effectuées dans des concentrations de phase aqueuse (eau) de 1%, 5%, 8% et 16,4% en volume, mélangée à du kérosène pour différentes valeurs de Re. L'effet du nombre de Reynolds (Re), le pourcentage de la phase dispersée, le diamètre des gouttelettes dispersées et le nombre de gouttelettes par unité de volume sur le taux de corrosion a été étudié et analysé. Les essais ont été réalisés avec deux types d'inhibiteurs: du nitrite de sodium à des concentrations de 20, 40 et 60 ppm et de l'hexapolyphosphate de sodium à des concentrations de 485, 970 et 1940 ppm dans une solution contenant 8% en volume de phase aqueuse (eau) mélangée à du kérosène (phase aqueuse) à 40°C pour la gamme complète de Re. On a trouvé que l'augmentation du Re augmentait le taux de corrosion et que la présence d'eau améliorait le taux de corrosion en augmentant la conductivité électrique des solutions. Pour la solution diphasique contenant 8% et 16% en volume d'eau, le taux de corrosion est plus grand qu'en monophasique (100% en volume d'eau). Les principaux paramètres qui jouent un rôle majeur dans la détermination du taux de corrosion dans la solution diphasique sont la concentration d'oxygène, la conductivité électrique de la solution et l'aire interfaciale entre les deux phases (dispersée et continue). On a trouvé que le nitrite de sodium et l'hexapolyphosphate étaient des inhibiteurs efficaces dans la solution diphasique pour la gamme de Re étudié. [source] A review of methods for Centropomus spp. (snooks) aquaculture and recommendations for the establishment of their culture in Latin AmericaAQUACULTURE RESEARCH, Issue 7 2008Luis Alvarez-Lajonchère Abstract The positive features of Centropomids and Latids for cultivation are analysed and highlighted. The main life cycle characteristics as well as market prices and demands are presented. Good growth, highly efficient food conversion ratios and energy utilization allow very high biomass yields per unit volume in nursery and grow-out systems. They have shown notable tolerances to main environmental conditions, as well as considerable versatility in adapting to culture systems (cages, ponds and tanks), and culture intensity (extensive, semi-intensive, intensive and superintensive), especially in estuarine and coastal sites and ponds. These positive features provide them with a high culture potential. A general summary of their culture is presented, based on the commercial cultivation of the Asian sea bass or barramundi Lates calcarifer as well as the experimental and pilot-scale results from the main American species. The importance of hatchery fry production as an essential culture pre-requisite is emphasized, in addition to an analysis of the main difficulties and constraints for future development. [source] Biosorption of heavy metal using brown seaweed in a regenerable continuous columnASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2008N. Rajamohan Abstract This paper deals with the experimental investigation on removal of cadmium [Cd(II)] ions from an aqueous solution using a marine alga, Sargassum tenerrimum, in a fixed-bed column. The effects of the inlet flow rate and the sorbent bed height on the biosorption of Cd(II) ions were studied. The dynamics of column biosorption was modeled by the bed depth service time (BDST) model and the Thomas model. The BDST model was used to study the dynamic sorption behavior at different bed heights, whereas the Thomas model was used to fit the column biosorption data at different flow rates. The uptake capacity and the breakthrough time increase with an increase in the bed height. The sorption capacities of the bed per unit volume and the rate constant Ka were found to be 3819.42 mg/l and 0.0353 mg/h respectively. In flow rate experiments, the results confirmed that the metal uptake capacity and the metal removal efficiency of S. tenerrimum decreased with increasing flow rate. The Thomas model was used to fit the column biosorption data at different flow rates and model constants were evaluated. After five sorption,desorption cycles, the selected marine alga exhibited a high cadmium uptake of 63.43 mg/g. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Variability in Transport Properties for Blackbutt Timber in New South Wales: Within and Between-Tree VariabilityASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1-2 2006S. J. Cabardo Variability is a key issue in the processing of biological materials, in this case the hying of hardwood timber. This paper reports the measurements of variability of transport properties. which are relevant to the drying of blackbutt, Eucalyptus pilularis Sm, from northern New South Wales. Specifically, within-tree and between-tree variations are reported for two blackbutt regrowth logs. An analysis of variance showed that some timber properties were affected by the board positions within-trees and between-trees. Circumferential and radial efects were significant for the within- tree variability of most transport properties. Similarly, radial and circumferential effects were signlficant for most of the transport parameters between trees, but can be tentatively stated because only two regrowth logs were assessed. Timber boards with high initial moisture contents had higher rates of diffirsion and low basic densities using principal components analysis. A possible reason is that if there is less wood material per unit volume, these vacant spaces may be occupied by water, and there is also less resistance for diffusive transport of moisture. [source] Quality of care of VLBW-neonates: relationship between unit volume and outcome is different between metropolitan and rural regionsACTA PAEDIATRICA, Issue 4 2009F Jochum No abstract is available for this article. [source] Entropy production in chiral symmetry breaking transitions,CHIRALITY, Issue 3-4 2008Dilip Kondepudi Abstract It is now well known that nonequilibrium chemical systems may reach conditions that spontaneously generate chiral asymmetry. One can find a host of model reactions that exhibit such behavior in the literature. Among these, models based on one originally devised by Frank have been studied extensively. Though the kinetic aspects of such model reactions have been discussed in great detail, the behavior of entropy in such systems is rarely discussed. In this article, the rate of entropy production per unit volume, ,, in a modified Frank model is discussed. It is shown that the slope of , changes at the point at which the asymmetric states appear, behavior similar to that observed in second-order phase transitions. Chirality, 2008. © 2007 Wiley-Liss, Inc. [source] The mean-field approximation in quantum electrodynamics: The no-photon caseCOMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 4 2007Christian Hainzl We study the mean-field approximation of quantum electrodynamics (QED) by means of a thermodynamic limit. The QED Hamiltonian is written in Coulomb gauge and does not contain any normal ordering or choice of bare electron/positron subspaces. Neglecting photons, we properly define this Hamiltonian in a finite box [,L/2; L/2)3, with periodic boundary conditions and an ultraviolet cutoff ,. We then study the limit of the ground state (i.e., the vacuum) energy and of the minimizers as L goes to infinity, in the Hartree-Fock approximation. In the case with no external field, we prove that the energy per volume converges and obtain in the limit a translation-invariant projector describing the free Hartree-Fock vacuum. We also define the energy per unit volume of translation-invariant states and prove that the free vacuum is the unique minimizer of this energy. In the presence of an external field, we prove that the difference between the minimum energy and the energy of the free vacuum converges as L goes to infinity. We obtain in the limit the so-called Bogoliubov-Dirac-Fock functional. The Hartree-Fock (polarized) vacuum is a Hilbert-Schmidt perturbation of the free vacuum and it minimizes the Bogoliubov-Dirac-Fock energy. © 2006 Wiley Periodicals, Inc. [source] | ||||||||||||||||||||||||||||