Mathematical Model of the Heat and Mass Transfer Processes in a Stratified Reservoir

The box-model of the heat and mass transfer processes in the reservoir and the analysis of the model verification results on the basis of Mozhaliskoye Reservoir field observations data during 3 years are presented.     

Effects of Convective Heat and Mass Transfer in Flow of Powell-Eyring Fluid Past an Exponentially Stretching Sheet

The aim here is to investigate the effects of convective heat and mass transfer in the flow of Eyring-Powell fluid past an inclined exponential stretching surface. Mathematical formulation and analysis have been performed in the presence of Soret, Dufour and thermal radiation effects. The governing partial differential equations corresponding to the momentum, energy and concentration are reduced to a set of non-linear ordinary differential equations. Resulting nonlinear system is computed for the series solutions. Interval of convergence is determined. Physical interpretation is seen for the embedded parameters of interest. Skin friction coefficient, local Nusselt number and local Sherwood number are numerically computed and examined.     

The Combined Effects of Food and Temperature on the Life History Parameters of Brachionus patulusMULLER (Rotifera)

The combined effects of different levels of temperature (15°, 25° and 35°C) and food Chlorella (1,2 and 4 × 10⁶ cells/ml) on the life history parameters (lifespan, life expectancy, net reproductive rate, intrinsic rate of increase, developmental time, and generation time) of a laboratory population of the rotifer Brachionus patulus were investigated. Both food and temperature, independently and in interaction, significantly influenced nearly all the parameters. The reproductive performance was a direct function of the food level, but the magnitude of food effect was temperature-dependent. The observed temperature × food interaction effects are explained in terms of the energetics of resource apportionment between metabolism and reproduction.     

Conjugate Effects of Heat and Mass Transfer on MHD Free Convection Flow over an Inclined Plate Embedded in a Porous Medium

The aim of this study is to present an exact analysis of combined effects of radiation and chemical reaction on the magnetohydrodynamic (MHD) free convection flow of an electrically conducting incompressible viscous fluid over an inclined plate embedded in a porous medium. The impulsively started plate with variable temperature and mass diffusion is considered. The dimensionless momentum equation coupled with the energy and mass diffusion equations are analytically solved using the Laplace transform method. Expressions for velocity, temperature and concentration fields are obtained. They satisfy all imposed initial and boundary conditions and can be reduced, as special cases, to some known solutions from the literature. Expressions for skin friction, Nusselt number and Sherwood number are also obtained. Finally, the effects of pertinent parameters on velocity, temperature and concentration profiles are graphically displayed whereas the variations in skin friction, Nusselt number and Sherwood number are shown through tables.     

Electromagnetic Field of Microtubules: Effects on Transfer of Mass Particles and Electrons

Biological polar molecules and polymer structures with energy supply (such as microtubules in the cytoskeleton) can get excited and generate an endogenous electromagnetic field with strong electrical component in their vicinity. The endogenous electrical fields through action on charges, on dipoles and multipoles, and through polarization (causing dielectrophoretic effect) exert forces and can drive charges and particles in the cell. The transport of mass particles and electrons is analyzed as a Wiener-Lévy process with inclusion of deterministic force (validity of the Bloch theorem is assumed for transport of electrons in molecular chains too). We compare transport driven by deterministic forces (together with an inseparable thermal component) with that driven thermally and evaluate the probability to reach the target. Deterministic forces can transport particles and electrons with higher probability than forces of thermal origin only. The effect of deterministic forces on directed transport is dominant.     

Freeze-Dry Microscopy: Impact of Nucleation Temperature and Excipient Concentration on Collapse Temperature Data

The objective of this study was to investigate the impact of nucleation temperature (T _n) and excipient concentration on the collapse temperature data obtained from freeze-dry microscopy (FDM) experiments. T _n, the temperature of the onset of collapse (T _oc), and the full collapse temperature (T _fc) were determined for aqueous solutions of polyvinylpyrrolidone (PVP) 40 kDa and 2-(hydroxypropyl)-ß-cyclodextrin. Concentrations were varied from 1% to 20% (w/w) for PVP and from 1% to 30% (w/w) for the 2-(hydroxypropyl)-ß-cyclodextrin. Mutual correlation coefficients were calculated for the observed T _n, T _oc, and concentrations of the solutions. In addition, outliers were detected and eliminated by applying the leaving-one-out routine and calculating correlation coefficients without it. T _n was found to be non-correlated with concentrations and only weakly correlated with T _oc. The correlation between these two temperatures was particularly poor for the solutions of the highest and lowest concentrations. In contrast, T _oc correlated much better with the corresponding concentrations, resulting in a quadratic fit for PVP and a linear fit for 2-(hydroxypropyl)-ß-cyclodextrin.     

Liquid-to-Gas Mass Transfer in Anaerobic Processes: Inevitable Transfer Limitations of Methane and Hydrogen in the Biomethanation Process

Liquid-to-gas mass transfer in anaerobic processes was investigated theoretically and experimentally. By using the classical definition of k(L)a, the global volumetric mass transfer coefficient, theoretical development of mass balances in such processes demonstrates that the mass transfer of highly soluble gases is not limited in the usual conditions occurring in anaerobic fermentors (low-intensity mixing). Conversely, the limitation is important for poorly soluble gases, such as methane and hydrogen. The latter could be overconcentrated to as much as 80 times the value at thermodynamic equilibrium. Such overconcentrations bring into question the biological interpretations that have been deduced solely from gaseous measurements. Experimental results obtained in three different methanogenic reactors for a wide range of conditions of mixing and gas production confirmed the general existence of low mass transfer coefficients and consequently of large overconcentrations of dissolved methane and hydrogen (up to 12 and 70 times the equilibrium values, respectively). Hydrogen mass transfer coefficients were obtained from the direct measurements of dissolved and gaseous concentrations, while carbon dioxide coefficients were calculated from gas phase composition and calculation of related dissolved concentration. Methane transfer coefficients were based on calculations from the carbon dioxide coefficients. From mass balances performed on a gas bubble during its simulated growth and ascent to the surface of the liquid, the methane and carbon dioxide contents in the gas bubble appeared to be controlled by the bubble growth process, while the bubble ascent was largely responsible for a slight enrichment in hydrogen.     

Theophylline Steady-State Pharmacokinetics: Recent Concepts and Their Application in Chronotherapy of Reactive Airway Diseases

With the introduction of sustained-release theophyllíne formulations for once-daily dosing or for unequally divided twice-daily dosing, comparison with conventional equally divided twice-daily dosing has been focused on nocturnal serum theophylline concentrations (STCs), plateau properties and peak-trough fluctuation. The merits of various steady-state characteristics such as nocturnal excess, plateau time, residual concentration, peak-trough fluctuation, swing and AUC fluctuation are illustrated by 15 data sets from 7 multiple-dose studies, each including either 10–12 healthy volunteers or 12–20 COPD-patients. In all of the studies, STCs were determined at least every 2 hr over a 24-hr period in steady-state. Included in the studies were 7 sustained-release theophylline formulations which were administered either once daily (in the morning or in the evening), or twice daily (either equally divided, or unequally divided with one-third of the dose being given in the morning and two-thirds in the evening).     

Alpharadiography: A Simple Method for Determination of Mass Concentration in Cells and Tissues

A simple apparatus for the production of contact microradiographs with the help of a polonium alpha source and nuclear emulsion plates is described. This apparatus best adapted for soft tissue and low grade mineralization studies offers advantages as to resolution, geometry of specimen as well as ease of operation and cost.     

The Effect of Leaf Temperature and Photorespiratory Conditions on Export of Sugars during Steady-State Photosynthesis in Salvia splendens

Export and photosynthesis in leaves of Salvia splendens were measured concurrently during steady-state 14CO2 labeling conditions. Under ambient CO2 and O2 conditions, photosynthesis and export rates were similar at 15 and 25[deg]C, but both declined as leaf temperature was raised from 25 to 40[deg]C. Suppressing photorespiration between 15 and 40[deg]C by manipulating CO2 and O2 levels resulted in higher rates of leaf photosynthesis, total sugar synthesis, and export. There was a linear relationship between the rate of photosynthesis and the rate of export between 15 and 35[deg]C. At these temperatures, 60 to 80% of the carbon fixed was readily exported with sucrose, raffinose, and stachyose, which together constituted over 90% of phloem mobile assimilates. Above 35[deg]C, however, export during photosynthesis was inhibited both in photorespiratory conditions, which inhibited photosynthesis, and in nonphotorespiratory conditions, which did not inhibit photosynthesis. Sucrose and raffinose but not stachyose accumulated in the leaf at 40[deg]C. When leaves were preincubated at 40[deg]C and then cooled to 35[deg]C, export recovered more slowly than photosynthesis. These data are consistent with the view that impairment of export processes, rather than photosynthetic processes associated with light trapping, carbon reduction, and sucrose synthesis, accounted for the marked reduction in export between 35 and 40[deg]C. Taken together, the data indicated that temperature changes between 15 and 40[deg]C had two effects on photosynthesis and concurrent export. At all temperatures, suppressing photorespiration increased both photosynthesis and export, but above 35[deg]C, export processes were more directly inhibited independent of changes in photorespiration and photosynthesis.     

Flight Phases in the Song of Skylarks: Impact on Acoustic Parameters and Coding Strategy

Skylarks inhabit open fields and perform an aerial song display which serves as a territorial signal. The particularly long and elaborate structure of this song flight raises questions about the impact of physical and energetic constraints acting on a communication signal. Song produced during the three distinct phases of the flight - ascending, level and descending phase could be subject to different constraints, serve different functions and encode different types of information. We compared song parameters during the ascending and the level phases. We found that the structure of the song varied with the phase of the flight. In particular, song had a higher tempo when skylarks were ascending which might be related to higher oxygen and energetic demands. We also explored which phase of the song flight might encode individuality. Earlier studies reported that skylarks reduced their territorial response to established neighbours if the neighbour song was broadcasted from the correct adjacent boundary, but reacted aggressively if the neighbour songs were broadcasted from an incorrect boundary (mimicking a displaced neighbour). Such differential response provides some evidence for individual recognition. Here, we exposed subjects to playback stimuli of neighbour song in which we had replaced either the song produced during the level or the ascending phase by the relevant song of the neighbour from the incorrect border. Singing response was higher towards stimuli in which the ‘level phase song’ was replaced, indicating that skylarks could be able to recognise their neighbours based on song of this phase. Thus, individuality seems to be primarily coded in the level phase of the flight song.     

Development,Calibration and Performance of an HIV Transmission Model Incorporating Natural History and Behavioral Patterns: Application in South Africa

Understanding HIV transmission dynamics is critical to estimating the potential population-wide impact of HIV prevention and treatment interventions. We developed an individual-based simulation model of the heterosexual HIV epidemic in South Africa and linked it to the previously published Cost-Effectiveness of Preventing AIDS Complications (CEPAC) International Model, which simulates the natural history and treatment of HIV. In this new model, the CEPAC Dynamic Model (CDM), the probability of HIV transmission per sexual encounter between short-term, long-term and commercial sex worker partners depends upon the HIV RNA and disease stage of the infected partner, condom use, and the circumcision status of the uninfected male partner. We included behavioral, demographic and biological values in the CDM and calibrated to HIV prevalence in South Africa pre-antiretroviral therapy. Using a multi-step fitting procedure based on Bayesian melding methodology, we performed 264,225 simulations of the HIV epidemic in South Africa and identified 3,750 parameter sets that created an epidemic and had behavioral characteristics representative of a South African population pre-ART. Of these parameter sets, 564 contributed 90% of the likelihood weight to the fit, and closely reproduced the UNAIDS HIV prevalence curve in South Africa from 1990–2002. The calibration was sensitive to changes in the rate of formation of short-duration partnerships and to the partnership acquisition rate among high-risk individuals, both of which impacted concurrency. Runs that closely fit to historical HIV prevalence reflect diverse ranges for individual parameter values and predict a wide range of possible steady-state prevalence in the absence of interventions, illustrating the value of the calibration procedure and utility of the model for evaluating interventions. This model, which includes detailed behavioral patterns and HIV natural history, closely fits HIV prevalence estimates.     

A Two-Stage System for the Large-Scale Cultivation of Biomass: a Design and Operation Analysis Based on a Simple Steady-State Model Tuned on Laboratory Measurements

The optimal design and operation at large scale of a continuous fermentation process including a biological reactor/photobioreactor and a gravity settler with partial recycle and purge of the biomass are addressed. The proposed method is developed with reference to microalgae (Scenedesmus obliquus) cultivation, but it can be applied to any fermentation process as well as to activated sludge wastewater treatment. A procedure is developed to predict the effect of process variables, mainly the recycle ratio (R), the solid retention time (θ _c ), the reactor residence time (θ), and the ratio between feed and purge flow rates (F _I /F _W ). It includes a simple steady-state model of the two units coupled in the process and the experimental measurement of basic kinetic data, in both the bioreactor and the settler, for the tuning of model parameters. The bioreactor is assumed as perfectly mixed, and a rigorous gravity-flux approach is used for the settler. The process model is solved in terms of dimensionless variables, and plots are given to allow sensitivity analyses and optimization of operating conditions. A discussion about washout is presented, and a simple method is outlined for the calculation of the minimum values of residence time (θ _min ) and recycle ratio (R _min ) and of the maximum allowed recycle ratio (R _{max,operating} ) and biomass purge rate (F _Wmax ). In particular, it is shown that the system is sensitive to the concentration of biomass lost from the top of the settler (C _X ^S ). The proposed method can be useful for the design and analysis of large-scale processes of this type.