Diffusion

This paper presents a new manufacturing method to generate monodisperse microbubble contrast agents with polydispersity index (σ) values of <2% through microfluidic flow-focusing. Micronsized lipid shell-based perfluorocarbon (PFC) gas microbubbles for use as ultrasound contrast agents were produced using this method. The poly(dimethylsiloxane) (PDMS)-based devices feature expanding nozzle geometry with a 7 μm orifice width, and are robust enough for consistent production of microbubbles with runtimes lasting several hours. With high-speed imaging, we characterized relationships between channel geometry, liquid flow rate Q, and gas pressure P in controlling bubble sizes. By a simple optimization of the channel geometry and Q and P, bubbles with a mean diameter of <5 μm can be obtained, ideal for various ultrasonic imaging applications. This method demonstrates the potential of microfluidics as an efficient means for custom-designing ultrasound contrast agents with precise size distributions, different gas compositions and new shell materials for stabilization, and for future targeted imaging and therapeutic applications.

The applicability of a two-parameter Fickian diffusion model for predicting the skin steady-state permeability based on measurements of the transient transport of permeants across the skin was tested. Using five model permeants possessing different physicochemical properties and pig skin as the model membrane, the skin permeabilities predicted by the two-parameter Fickian diffusion model were compared with the measured skin permeabilities. Results show that the transient skin permeation profiles of the hydrophobic permeants, estradiol, testosterone, and dolichol, across splitthickness pig skin can be modeled adequately by the two-parameter Fickian diffusion model (with constant parameter values), and therefore, that this model can be utilized to shorten the experimental time required to determine the skin permeabilities of these compounds. However, the skin permeabilities of the highly hydrophilic permeants, mannitol and sucrose, predicted by the two-parameter Fickian diffusion model (with constant parameter values) were significantly lower than the experimentally determined values, indicating that the dominant skin pathway of polar permeants within the excised pig skin undergoes significant structural changes during the in vitro diffusion cell studies. Although the skin permeability values determined experimentally using the traditional steady-state method normally correspond to a highly hydrated skin sample, the two-parameter Fickian diffusion model enables an estimation of the skin permeability of the skin membrane at its less-hydrated state (a condition more representative of in vivo and clinical situations). Using the two-parameter Fickian diffusion model and a recently developed skin porous-pathway theory, the effects of skin hydration on the skin porous pathway within the excised pig skin were characterized. Specifically, we found that hydration leads to induction of new pores/reduction of the tortuosity of existing pores within the excised pig skin during the 48 h diffusion cell studies conducted, while the skin average pore radii remain relatively constant ($26 Å ) for up to 48 h. ß

Most industrially applied polymer resins and composites have low surface free energy and lack polar functional groups on their surface, resulting in inherently poor adhesion properties. A strong research momentum to understand polymer adhesion in the last decade has been motivated by the growing needs of the automotive and aerospace industries for better adhesion of components and surface coatings. This paper reviews the recent research efforts on polymer adhesion with a special focus on adhesion mechanisms. It starts with an introduction to adhesion with explanatory notes on adhesion phenomena. Recent research on the adhesion mechanisms of mechanical coupling, chemical bonding and thermodynamic adhesion is then discussed. The area of adhesion promoters is reviewed with the focus on plasma and chemical treatments, along with direct methods for adhesion measurement. The topics of polymer blends and reactive polymerization are considered and the interactions with adhesion mechanisms are reported. The concluding section provides recommendations regarding future research on the contentious aspects of currently accepted adhesion mechanisms and on strategies for enhancing polymer adhesion strength.

A new deterministic numerical formulation named DisPar-k based on particle displacement probability distribution for Markov processes was developed to solve advection-diffusion problems in a one-dimensional discrete spatial grid. DisPar-k is an extension of DisPar, and the major difference is the possibility of establishing a number of consecutive particle destination nodes. This was achieved by solving an algebraic linear system where the particle displacement distribution moments are known parameters taken from the Gaussian distribution. The average was evaluated by an analogy between the Fokker-Planck and the transport equations, being the variance Fickian. The particle displacement distribution is used to predict deterministic mass transfers between domain nodes. Mass conservation was guaranteed by the distribution concept. It was shown that, for linear conditions, the accuracy order is proportional to the number of particle destination nodes. DisPar-k showed to be very sensible to physical discontinuities in the transport parameters ͑water depth, dispersion, and velocity͒, showing that this type of problem can only be disguised by introducing numerical dispersion ͑i.e., changing the Fickian variance͒.

We consider a particle performing a stochastic motion on a one-dimensional lattice with jump widths distributed according to a power-law with exponent μ + 1. Assuming that the walker moves in the presence of a distribution a(x) of targets (traps) depending on the spatial coordinate x, we study the probability that the walker will eventually find any target (will eventually be trapped). We focus on the case of power-law distributions a(x) ∼ x^-α and we find that as long as μ &lt; α there is a finite probability that the walker will never be trapped, no matter how long the process is. This analytical result, valid on infinite chains, is corroborated by numerical simulations which also evidence the emergence of slow searching (trapping) times in finite-size system. The extension of this finding to higher-dimensional structures is also discussed.

We investigate the potential of fluorescence correlation spectroscopy (FCS) in screening for crystallisation conditions. Solutions that nucleate protein crystals must have different interactions than solutions that do not give rise to crystals. Due to these different interactions the average mean squared displacement of the individual proteins changes. By monitoring protein self-diffusion, we can distinguish crystallising from non-crystallising solutions. The method introduced can be applied at extremely low concentrations in femtoliter volumes as an early diagnostic for molecular association. Based on our preliminary findings FCS has the potential to become a routine screening method for crystallography.

The objective of this work was to evaluate the potential of Fourier transform infrared spectroscopy (FTIR) in the characterization and discrimination between immature and mature or ripe coffee beans. Arabica coffee beans were submitted to FTIR analysis by reflectance readings employing attenuated total reflectance (ATR) and diffuse reflectance (DR) accessories. The obtained spectra were similar, but in general higher absorbance values were observed for nondefective beans in comparison to immature ones. Multivariate statistical analysis (principal component analysis, PCA, and agglomerative hierarchical clustering, AHC) was performed in order to verify the possibility of discrimination between immature and mature coffee samples. A clear separation between immature and mature coffees was observed based on AHC and PCA analyses of the normalized spectra obtained by employing both ATR and DR accessories. Linear discriminant analysis was employed for developing classification models, with recognition and prediction abilities of 100%. Such results showed that FTIR analysis presents potential for the development of a simple routine methodology for separation of immature and mature coffee beans.

Steady-state oxygen diffusion in flesh of apples (Malus domestics Borkh. CVS. Braeburn and Cox's Orange Pippin), Asian pears (Pyrus serotina Rehder. CVS. Hosui and Kosui), and nectarines [Prunus persica (L.) Batsch. CVS. Red Gold and Sunglo] was studied using a nondestructive method at 20C. Fruit flesh was found to exert a significant resistance to O 2 diffusion resulting in measurable O 2 gradients between tissues immediately beneath the skin and those at the fruit center for all these fruits. The magnitude of these O 2 gradients varied between crops and cultivars and depended on the respiration rate and on effective O 2 diffusivity in fruit flesh (D e ). Values of D c varied with the cultivar and were broadly consistent with intercellular space volume. The range of D e values obtained suggested that 0 2 diffusion in fruit flesh takes place in a combination of series and parallel modes in the intercellular space and fluid/solid matrix of the flesh. The results imply that O 2 diffusivity in flesh tissues must be taken into consideration in the determination of critical external O 2 level in controlled/modified atmosphere (CA/MA) storage.

The OECD guideline for studies on percutaneous penetration to be used in hazard and risk evaluations prescribes experimental conditions with optimal barrier integrity of the skin, which in many occupational settings probably is not true. Thus, workers may have compromised skin due to chemical or mechanical damage, due to different medical conditions (eczema, dermatitis, skin irritation) or related to occupational scenarios involving prolonged wet work. The present study used the OECD guideline procedures to study the in vitro percutaneous penetration through human skin of a number of model substances (glyphosat, caffeine, benzoic acid, malathion) covering a range of solubilities. Further, we studied the extent to which a slightly damaged skin would change the rate, the amount absorbed during dermal exposure and the distribution of chemical deposition between epidermis and dermis. The present study demonstrates that a limited damage to the skin significantly increases the permeability coefficient (K p) as well as total percutaneous penetration of chemicals, and most significantly for those compounds that due to their physicochemical characteristics (the most hydrophilic as well as the most lipophilic) have low penetration rates through intact skin. The present experiment not only confirms the proportionality between lipophilicity and potential for percutaneous penetration, but also illustrates that at a certain degree of lipophilicity of a model compound, the different skin compartments become more attractive for temporary deposition of model compounds. Moreover, a clear change from epidermal deposition towards a dominating dermis deposition of chemicals temporarily deposited within the skin is seen following damage to the skin barrier. Thus, the distribution of chemicals within the skin compartments is affected by the physicochemical characteristics of the chemicals as well as by the integrity of the skin. This observation may have implications when evaluating the possibility of removing chemicals from the skin through different cleansing procedures following unintended dermal exposures.

Spray drying techniques have been applied to improve the solubility and dissolution rate of poorly water-soluble salicylic acid. Spray drying of the acid dispersed in acacia solutions resulted in as much as a 50% improvement in the solubility of the product. Solubility improvement was closely related not only to the concentration of acacia but also the amount of amorphous material in the spray-dried products. The heat of solution was inversely related to these parameters. The dissolution rate of spray-dried product was almost instantaneous being about 60 times faster than that of the original powder. A great improvement in the wettability of the spray-dried material seemed to be mainly responsible for the increase of dissolution rate.

The viral spread of digital misinformation has become so severe that the World Economic Forum considers it among the main threats to human society. This spread have been suggested to be related to the similarly problematized phenomenon of &quot;echo chambers&quot;, but the causal nature of this relationship has proven difficult to disentangle due to the connected nature of social media, whose causality is characterized by complexity, non-linearity and emergence. This paper uses a network simulation model to study a possible relationship between echo chambers and the viral spread of misinformation. It finds an &quot;echo chamber effect&quot;: the presence of an opinion and network polarized cluster of nodes in a network contributes to the diffusion of complex contagions, and there is a synergetic effect between opinion and network polarization on the virality of misinformation. The echo chambers effect likely comes from that they form the initial bandwagon for diffusion. These findin...

In this study an artificial neural network (ANN) model was developed to predict the oxidation behavior of magnesia graphite composites. After mechanism evaluation in different conditions, the kinetic parameters such as effective diffusion coefficient and diffusion activation energy of oxidation were calculated from ANN predicted results at different graphite content. The obtained mechanism and kinetic parameters were compared with experimental data.First of all, the reliability of the model was checked with different available data. It was found that the model results were in good agreement with experimental data prediction.The results showed that the main mechanism of oxidation was pore diffusion and effective diffusion coefficient as well as diffusion activation energy were comparable with previous works.Effective diffusion coefficient and diffusion activation energy which were calculated versus graphite content are in good agreement with experimental values.

We acknowledge financial support from the research programme ‘Environmental Policy, Economic Reform and Endogenous Technology’, funded by the Netherlands Organisation for Scientific Research (NWO). We gratefully acknowledge useful comments by Egbert Jongen, Richard Nahuis, Michiel de Nooij and Bob van der Zwaan on an earlier version of this paper. Of course, the usual disclaimer applies. Research Memorandum 0105

Fiber tracking (FT) and quantification algorithms are approximations of reality due to limited spatial resolution, model assumptions, user-defined parameter settings, and physical imaging artifacts resulting from diffusion sequences. Until now, correctness, plausibility, ...

The leaf economics spectrum (LES) represents a suite of intercorrelated leaf traits concerning construction costs per unit leaf area, nutrient concentrations, and rates of carbon fixation and tissue turnover. Although broad trade-offs among leaf structural and physiological traits have been demonstrated, we still do not have a comprehensive view of the fundamental constraints underlying the LES trade-offs. Here, we investigated physiological and structural mechanisms underpinning the LES by analysing a novel data compilation incorporating rarely considered traits such as the dry mass fraction in cell walls, nitrogen allocation, mesophyll CO2 diffusion and associated anatomical traits for hundreds of species covering major growth forms. The analysis demonstrates that cell wall constituents are major components of leaf dry mass (18-70%), especially in leaves with high leaf mass per unit area (LMA) and long lifespan. A greater fraction of leaf mass in cell walls is typically associated...

There exist structural inhomogeneities of different scales in ion-exchange membranes. We suggest a microheterogeneous model for the description of inhomogeneities on the microphase scale, and show that they are the main factor determining the concentration dependence of membrane transport properties such as electrical conductivity, diffusion permeability and transport numbers. A set of tests is proposed for determination of model structural-kinetic parameters of membranes.

Around the globe, various initiatives use the mobile phone to provide financial services to those without access to traditional banks. Yet relatively little scholarly research explores the use of these m-banking/m-payments systems. This paper calls attention to this gap in the research literature, emphasizing the need for research focusing on the context(s) of m-banking/mpayments use. Presenting illustrative data from exploratory work with small enterprises in urban India, it argues that contextual research is a critical input to effective "adoption" or "impact" research. Further, it suggests that the challenges of linking studies of use to those of adoption and impact reflect established dynamics within the Information and Communication Technologies and Development (ICTD) research community. The paper identifies three crosscutting themes from the broader literature-amplification vs. change, simultaneous causality, and a multidimensional definition of trust-each of which can offer increased theoretical clarity to future research on m-banking/m-payments systems. Notes on contributors Jonathan Donner is a researcher in the Technology for Emerging Markets Group at Microsoft Research, where he studies the social and economic impacts of mobile communication technologies in developing countries. Camilo Tellez is a doctoral student in the department of Information Systems at the London School of Economics and Political Science, where he specializes in IT for development issues. m-banking Pre-publication draft. Edits possible.

It is established for the first time that the spatial distribution of breaking waves on the ocean surface is a multifractal process. This result is based on an analysis of airborne visible and near-infrared imagery of the ocean surface under a limited range of wind speed and fetch. A detailed study of the optical spectra of the images and the cumulative probability structure of the prevalent background shows that the lower-intensity reflective areas follow a Rayleigh probability distribution. By contrast, the higher-intensity pixels associated with the scattered light from foam and breaking waves demonstrate scaling characteristics in both the optical spectra and the cumulative probability distributions. It is demonstrated that the degree to which the whitecaps are singularities on a dark background is described by a Lipschitz exponent c•, which uniquely tags each breaking wave. This identification process, called "fractal" or "singularity filtering", leads to a critical condition c• = 1 tentatively associated with the crossover from active entraining whitecaps to passively dissipating foam. The multifractal representation associated with the degree of singularity is simply a restatement that the imagery is composed of a continuum of sets, where each set consists of those breaking waves at a particular phase in their existence. The fractal spectrum of the image above a threshold is shown to be representable by a fractal generator. Physically, the fractal generator models the energy exchange in a breaking wave field as a flux of energy input from the atmosphere to the wave field cascaded over scales of the order of a kilometer to meters. If the energy flux is further parameterized in terms of the receiving area, an assumption similar to closure techniques used in classical turbulence models, the empirical results symmetrically span Phillips's basic arguments for the energy flux terms controlling a wind-driven sea. 16,179 16,180 KERMAN AND BERNIER: MULTIFRACTAL BREAKING WAVES ! . Ii . i Figure 1. (a), Field of breaking waves observed using a line scanner on board an aircraft flying at about 500 m over the Bay of Fundy. Field of view about 250m 2, resolution was about 0.5m, and optical wavelength was 0.95/•m. (b), Image thresholded to remove reflective Rayleigh component. (c), Image of asubsets (a) 1) identified with nonentraining (foam) areas. (d), Image of a subsets, a < 1, identified with entraining (breaking wave) areas. qualitative way what is observed about breaking waves, even at the risk of stating in some cases the obvious. When the field is imaged either by standard photography [Ross and Cardone, 1974; Smith, 1981; Kennedy and Snyder, 1983] or with side-scanning techniques from underneath the surface [Thorpe and Hall, 1983; Thorpe and Humphties, 1980] or from the air (Figure la) [Kerman and Szeto, 1994], several features of the spatial field of breaking waves are evident. The first feature of breaking waves is their distinct isolated nature: the fact that they are born, mature, and die almost always without affecting or being mod-16,182 K••AN AND BERNIER: MULTIFRACTAL BREAKING WAVES

This study was designed to test the hypothesis that furosemide (Fur) can be entrapped into surfactant free pegylated nanocarriers (NCs) for controlled drug release. To test this hypothesis, Fur-loaded NCs were prepared by emulsion solvent diffusion method. A 2 3 factorial design was used to optimize the effect of three formulation variables [amounts of Fur (X 1 ), poly(lactic-co-glycolic acid) (X 2 ) and poly-caprolactone-polyethylene glycol (X 3 )] on particle mean diameter (Y 1 ), polydispersity index (PDI, Y 2 ), and percent drug encapsulation efficiency (EE%, Y 3 ). The NCs were characterized for morphology, thermal behavior, optical properties, crystallinity, and drug release kinetics using electron microscopy (EM), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), and high performance liquid chromatography, respectively. The optimum formula produced with 6 mg of Fur, 7 mg of PLGA, and 1 mg of PCL-PEG corresponded to 183.26 nm, 0.26, and 88.29% as Y 1 , Y 2 and Y 3 values, respectively. DSC thermograms, FTIR spectra and PXRD diffractograms indicated that Fur was encapsulated in its polymorphic crystalline form I within the NCs polymeric matrix. This was further confirmed by a comparative study between native Fur, Fur nanocrystal and Fur loaded NCs using scanning EM, PXRD and drug release kinetics. The release kinetics of the optimized formula fit the Higuchi model indicating that the drug was released by diffusion in 12 h. These results indicate that pegylated Fur-loaded NCs could be successfully prepared with high EE% and sustained release profile intended for the inner ear drug delivery.

The nanometer-size In 2 O 3 was synthesized via a reverse microemulsion. A new catalytic combustion-type In 2 O 3 -based H 2 gas sensor was developed based on the technology for fabricating the direct-heating-type sensor and a surface-modifying process. A dense SiO 2 layer near the surface of the sensor was formed by chemical vapor deposition (CVD) of hexamethyldisiloxane (HMDS). The SiO 2 layer, which acted as a molecular sieve, reduced the penetration of large molecular, such as C 2 H 5 OH, CH 4 , i-C 4 H 10 , into the sensing layer, resulting in the improvement of selectivity to H 2 . The sensitive properties and the working mechanism of the sensor were presented. The In 2 O 3 nanoparticles prepared by microemulsion were characterized by transmission electron microscopy and X-ray diffraction.

Diffusion of mass in a solid cylinder with concentration dependent diffusivity (or temperature-dependent thermal conductivity in case of heat diffusion) does not admit of an analytical solution except in special cases. The 'shrinking core model' has been used to develop an approximate analytical solution in certain circumstances. The model, generally useful to describe heterogeneous solid-fluid reactions, is applied to theoretically analyze the adsorption-diffusion phenomena of methylene blue dye in a glass fiber in the present work. Theoretical equations have been derived for the case of diffusivity as an exponential function of concentration. The diffusivity parameters are evaluated by global minimization of the error between the experimental and the theoretical concentration history. Other forms of diffusivity, namely constant diffusivity and diffusivity varying linearly with concentration are found to involve larger errors. A parametric sensitivity analysis of the error has been done. The shrinking core model could satisfactorily interpret the experimental dye concentration profile in the substrate.

A diffusion model is presented to account for the disposition of chemicals applied to skin as transient exposures. Two conditions are considered that apply to the skin surface following the exposure period, which are applicable to chemicals exhibiting two extremes of chemical volatility. For one case, representing highly volatile compounds, the solution is generalized to apply to multiple transient exposures. For both cases, algebraic expressions are derived to calculate the total amount of chemical that penetrates the skin. The theory is applied to experimental measurements of the in vitro penetration of diethyl phthalate applied to hairless guinea pig (HGP) skin and silicone rubber membranes (SRMs) as transient exposures. The transient exposure theory ably models the experimental data, with coefficients of determination greater than 0.97 (HGP) and greater than 0.99 (SRM). The ability of parameters derived from concurrent infinite dose experiments to predict the time course of absorption from transient exposures is explored. Discrepancies were found between measured cumulative penetration of chemical from transient exposure experiments and penetration predicted from parameters derived from infinite dose experiments, particularly for HGP. Possible reasons are explored. The current model may provide a realistic framework for estimating absorption from occupational, environmental and pharmaceutical dermal exposures. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:1578–1592, 2008

The applicability of thin sol-gel films as selective interfaces in electrochemical sensors has been examined. This requires not only to create a selective interface but also to enable facile diffusion of the analytes across the films. Creation of selectivity has been aimed by molecularly imprinting an electroactive species in the course of sol-gel formation. We have focused primarily on imprinting an iron(II) complex, i.e., tris(2,2'-bipyridine)iron(II) (Fe(bpy) 2 3 , as a means of selectively determining iron(II) in aqueous solution. Hence, the effect of different parameters, such as the composition of the sol-gel film and the hydrolysis and drying time, on the diffusion of Fe(bpy) 2 3 , has been studied. We find that diffusion can be remarkably enhanced upon adding polyethylene glycol or a surfactant, such as decanoic acid. Nevertheless, so far we have not been able to develop thin films, which exhibit selectivity towards this inorganic species. The difficulties in designing such selective interfaces for heavy metals as opposed to organic species is demonstrated by successfully applying the same approach for designing a selective interface for diethyl-p-nitrophenyl phosphate (paraoxon).

The question of whether effective diffusivities in porous materials under reactive and nonreactive conditions are equal is addressed. Previous studies had considered the problem with first-order reactions. We study the issue with two nonlinear reactions-a second-order reaction and one governed by the Michaelis-Menten kinetics. Pore network and continuum models of porous media are utilized to estimate the effective diffusivities under reactive and nonreactive conditions. We show that the two effective diffusivities are significantly different. The difference is due to the heterogeneities of the porous material, and the fluctuations that they cause in the spatially varying local concentrations and diffusivities, and can be as large as a few orders of magnitude. Theoretical analysis of diffusion and reactions in porous media is also presented that supports the results of the simulations. In particular, it is shown that the results of pore network simulations cannot be fitted to the classical continuum equation of diffusion and reaction, and that a more complex continuum equation should be used for this purpose. ᭧

The structural and dynamical properties of the alkaline earth metal ions Mg 2þ , Ca 2þ , and Sr 2þ and their carbonate and bicarbonate complexes in aqueous solution are examined through first principles molecular dynamics simulations based on the density functional theory. Calculations were conducted in explicit heavy water molecules and at the average temperature of 400 K, conditions which are necessary to obtain a liquid-like water structure and diffusion time-scales when using gradient corrected density functionals. According to these simulations, the magnesium ion undergoes a significant contraction of its coordination sphere in the Mg(H)CO 3 (þ) aqueous complex, whereas calcium and strontium increase their average first shell coordination number when coordinated to HCO 3 or CO 3 2-

A conceptual framework for analysing the energetics of density-stratified Boussinesq fluid flows is discussed. The concept of gravitational available potential energy is used to formulate an energy budget in which the evolution of the background potential energy, i.e. the minimum potential energy attainable through adiabatic motions, can be explicitly examined. For closed systems, the background potential energy can change only due to diabatic processes. The rate of change of background potential energy is proportional to the molecular diffusivity. Changes in the background potential energy provide a direct measure of the potential energy changes due to irreversible diapycnal mixing. For open systems, background potential energy can also change due to boundary fluxes, which can be explicitly measured. The analysis is particularly appropriate for evaluation of diabatic mixing rates in numerical simulations of turbulent flows. The energetics of a shear driven mixing layer is used to i...

Two-photon photoluminescence (TPPL) emission spectra of DNA-gold nanoparticle (AuNP) monoconjugates and the corresponding DNA-linked AuNP dimers are obtained by photon time-of-flight spectroscopy. This technique is combined with two-photon photoluminescence fluctuation correlation spectroscopy (TPPL-FCS) to simultaneously monitor the optical and hydrodynamic behaviour of these nano-assemblies in solution, with single-particle sensitivity and microsecond temporal resolution. In this study, the AuNPs have an average core diameter of 12 nm, which renders their dark-field plasmonic light scattering too weak for single-particle imaging. Moreover, as a result of the lack of plasmonic coupling in the dimers, the optical extinction, scattering and photoluminescence spectra of the DNA-AuNP complexes are not sufficiently different to distinguish between monomers and dimers. The use of TPPL-FCS successfully addresses these bottlenecks and enables the distinction between AuNP monomers and AuNP ...

Cavitation can be effectively used for intensification of chemical processing applications and the degree of intensification depends on operating parameters. A mathematical model has been developed for prediction of cavitational intensity quantified in terms of collapse pressure and temperature. Effect of different solvents and catalyst particles, which are the key controlling parameters for hydrogenation reactions, on cavitational intensity has been investigated. The observed trends have been compared with the experimental investigations. The importance of present work lies in the fact that it provides a pathway for optimization of operating parameters and establishes guidelines for the selection of the same.

Total cyanide analysis by distillation is used most commonly to assess cyanide content of water samples. This manual method is robust but slow and provides no information about cyanide speciation, a significant limitation in that cyanide species have substantially different toxicity characteristics. Seven alternative methods for the analysis of cyanide species or groups of species were evaluated in reagent water and five different contaminated water matrices, including five species-specific methodsweak acid dissociable (WAD) cyanide, free cyanide by microdiffusion, available cyanide, automated WAD cyanide by thin film distillation, metal cyanides by ion chromatography and two automated techniques for total cyanidetotal cyanide by thin film distillation and total cyanide by lowpower UV digestion. The species-specific cyanide analytical techniques achieved low, ppb-level detection limits and exhibited satisfactory accuracy and precision for most contaminated waters. Analysis of low concentrations of cyanide species in raw wastewater was problematical for the available cyanide and ion chromatography methods, which experienced significant interference problems and/ or low recoveries. There was recovery of significant diffusible cyanide in microdiffusion tests with nickel-cyanidespiked samples, reflecting dissociation of this weak metalcyanide complex during the test and demonstrating that the test can recover some fraction of WAD cyanide in addition to free cyanide. The automated total cyanide methods, which involve UV digestion, achieved low detection limits for most waters but exhibited low recoveries for some waters.

The moisture accumulation within clothing is a serious problem for sportswear and clothing in cold climate. There are several experimental methods available to measure moisture build up in insulate materials. However, information on parameters such as temperature, relative humidity and vapor pressure can be obtained through simulation using a predictive mathematical model. The focus of this study is the development of a mathematical model to simulate heat and moisture transfer in a sample of fabric, coated to provide insulation, which is in contact with human skin on one side and with the external environment on the other. To numerically simulate the mathematical model the finite volume method is used and a computational procedure for the solution of the model is designed. The simulation results are analyzed to verify whether they are consistent with the physical reality.

The problem of steady state mass diffusion of aerosols without axial diffusion in a long cylindrical channel and for small diffusion parameter, A, is presented. Results are obtained when the laminar fluid flow is Poiseuille, plug and a combination of Poiseuille and plug, such that an allowance for slip velocity of the fluid at the wall can be taken into account. The asymptotic solution for large A, that has been obtained by several previous authors, is matched to asymptotic solutions that have been obtained in this paper for small A. A solution for the complete range of values of the parameter A is thus presented. NOMENCLATURE a,b constants c coneentration of aerosol at (r, 4~, z) Co concentration of aerosol at (r, ~p, O) mean concentration at z = L eL concentration at (r, ~b, L) D coefficient of diffusion of aerosol particles K diffusion parameter, 2A(1 + ~)/~ L length of tube Pe diffusion Peclet number, 2Uro/D q rate of formation of aerosols per unit volume r radial coordinate t similarity variable, q/(z/k) 1/2 u axial velocity of fluid U mean axial velocity of fluid v radial velocity of fluid z distance along tube slip parameter A diffusion parameter, DL/4Ur2o l-r' 0 similarity variable, q3/(zA) /~ diffusion parameters, DL/Ur 2 4~ polar angle primes denote non dimensional quantities.

The rheological and morphological properties and in vitro theophylline release of tertiary aminebased microgels were evaluated. The testing of such a formulation through in vitro diffusion experiments revealed that the release of theophylline from the microgels was pH-dependent and differs significantly with respect to a nonresponsive gel like scleroglucan (Scl). The microgels were obtained from 2-(diethyl amino) ethylmethacrylate (DEA) in the presence of a bifunctional crosslinker at pH 8-9. As the resulting microgels are pH-responsive and an increase in viscosity from high to low pH range is exhibited, the in vitro release of theophylline as model drug was studied at different pHs of both the matrix and the receptor medium. The release behaviors of PDEA-based microgels were compared to nonresponsive natural gel Scl, studied previously. For microgels, diverse release patterns were found at different acidity conditions. This observation seems to be related to complex diffusion phenomena and the different gel structure obtained for samples prepared at dissimilar pH.

ENHANCEMENT OF HEAT AND MASS TRANSFER IN MECHANICALLY-CONSTRAINED ULTRA-THIN FILMS SECTION 1.0-INTRODUCTION AND BACKGROUND Oregon State University (OSU) and the Pacific Northwest National Laboratory (PNNL) were funded by the U.S. Department of Energy to conduct research focused on resolving the key technical issues that limited the deployment of efficient and extremely compact microtechnology based heat actuated absorption heat pumps and gas absorbers. Success in demonstrating these technologies will reduce the main barriers to the deployment of a technology that can significantly reduce energy consumption in the building, automotive and industrial sectors while providing a technology that can improve our ability to sequester CO 2. The

1] A parametric study is presented on the temporal evolution of the phase space density (PSD) of the outer radiation belt energetic electrons driven by the superluminous right-hand extraordinary (R-X) mode waves at the location L = 4.5. Bounce-averaged diffusion rates in pitch angle and momentum are calculated by varying the peak wave frequency, the wave normal angle distribution, and the wave latitudinal distribution. Those diffusion rates are used as inputs to solve a 2-D momentum-pitch angle diffusion equation. In particular, three cases are considered: momentum diffusion rates alone, momentum +pitch angle diffusion rates, and momentum +pitch angle +cross diffusion rates. Numerical results show that at 24 h, electron PSDs can enhance substantially for 1 MeV energy at higher pitch angles. Momentum diffusion dominates the dynamic evolution of energetic electrons, whereas the contribution of pitch angle or cross-diffusion rates is insignificant using the specified wave model. In addition, PSD evolutions are sensitively dependent on the assumed different wave normal angle distributions and tend to be located in lower pitch angles when wave normal angles move to smaller regions. Diffusion coefficients and PSD evolution are largely determined by the wave latitudinal distributions. High-latitude R-X mode waves primarily contribute to pitch angle scattering of energetic electrons, whereas equatorial (or lower latitude) R-X mode waves yield efficient acceleration of electrons. This result supports the previous findings that superluminous R-X mode waves potentially contribute to dramatic variation in the outer radiation belt electron dynamics under appropriate conditions.

The mechanism leading to oscillations of respiration rate in Klebsiella aerogenes in continuous culture is described qualitatively. This is based on the following three conditions: (1) the respiration rate of the culture is inhibited by oxygen; (2) the respiration rate depends on the concentration of oxidizable substrate, which is lowered at high respiration rates and increased at low respiration rates; (3) the uptake of oxygen from the gas to the liquid phase is diffusion limited. These three conditions are analogous to the conditions leading to oscillations in electrochemical systems. The mathematical model for electrochemical oscillations is also applicable in the present case.

The nitric oxide (NO) donor S-nitrosoglutathione (GSNO) was incorporated in solid polymeric films of poly(vinyl alcohol) (PVA), poly(vinyl pyrrolidone) (PVP) and blended PVA/PVP. These matrices were found to provide a great stabilization effect on the thermal decomposition of GSNO, leading to 8-16-fold reduction in the first-order rate constants of NO release, compared to aqueous GSNO solutions. PVA/PVP-GSNO released 90% of the NO supply, over a time period of 24 h at 37 C. Differential scanning calorimetry has confirmed the miscibility between the two polymeric components. Stress-strain analysis has shown an improvement of the mechanical property of PVA films in the PVA/PVP blend, which leads to an increase of 25% in the stress at break. Scanning electron microscopy has shown that the PVA/PVP-GSNO blend leads to a smooth coating of metallic surfaces. These properties, allied to the already known good biocompatibility of PVA and PVP, makes GSNO-containing PVA and PVA/ PVP blend films good candidates for the local and controlled release of NO in target areas. r

The aim of this study was to evaluate the effects of preparation method and the type of surfactant on the properties of cephalexin (CPX) microspheres in order to obtain delivery systems suitable for the treatment of dairy mastitis. Microspheres were obtained using various preparation conditions and their physicochemical characteristics such as size, loading efficiency, morphology, and drug crystallinity were investigated. Antibacterial activity of microspheres from the optimum preparation condition was also studied. CPX microspheres were prepared by two different W/O/W emulsion solvent evaporation methods using PLGA as a matrix forming polymer. Several types of surfactants including nonionic, cationic, and anionic at different concentrations were used for preparation of the particles. The type and concentration of surfactant did neither affect the size nor morphology of the microspheres but showed a pronounced effect on the CPX encapsulation efficiency. It was found that Tween 80 showed the highest drug encapsulation efficiency (66.5%). Results from X-ray diffraction diffractograms and differential scanning calorimetry thermograms indicated that CPX entrapped in these microparticles was amorphous. Assessment of antibacterial activity showed that the obtained CPX microspheres exhibited good inhibition with minimum inhibitory concentration and minimum bactericidal concentration values of 128 µg/mL and 2,048 mg/mL against Staphylococcus aureus ATCC 25923, 512 µg/mL and 4,096 mg/mL against Escherichia coli ATCC 25922, respectively.

The formation and growth characteristics of Fe based aluminide diffusion layers at the Fe-Al interface have been analysed in terms of interfacial interaction potentials based on the statistico-thermodynamical theory of multicomponent alloys combined with electronic theory in the pseudopotential approximation. The pairwise interatomic interaction potentials and partial ordering energies have been calculated to predict the effect of various alloying additions on the activity coefficient of Al atoms in G(-Fe&AlI _nX,Jo.os alloys where X = Si, Ti, Ge, Sb, Mg, Cu, Ca, Ag, Cd, Cr, Co, Zn, Mn, Ni, Pb or Bi and considered up to 1 at.%. The results of calculation show that the impurity elements with regard to their effect on the activity coefficient of Al atoms may be classified into two groups; I-group impurity elements, X,=Si, Ti, Ge, Sb, Mg, Cu, Ca, Ag, Cd, and Cr which decrease the activity coefficient of Al atoms, reduce the thickness of the Fe-Al intermetallic diffusion layer and II-group impurity elements, Xu=Co, Zn, Mn, Ni, Pb and Bi, which increase the activity coefficient of Al atoms, tend to increase the thickness of diffusion layer at the Fe-Al interface. It has been established, in agreement with experimental observation, that the value of activity coefficient of Al atoms in a-Feoss(Al, _JJo.os alloys has a strong influence on the formation and growth kinetics of interfacial diffusion layers at the Fe-Al interface. The analysis of the effects of type and content of Xl and Xn impurity elements on the activity coefficients of Al atoms, Y~,/$&, in cc-Feo,9s(All _ ,,X,,),,, alloys is in good qualitative agreement with the experimental results reported in the literature. 0 1998 Acta Metallurgica Inc.

The objectives of these investigations were: (a) to make a preliminary study to assess concentration-depth profiles of mitomycin C (MMC) in the bladder wall at specified time intervals after passive diffusion (PD); and (b) to conduct a major study to compare concentration-depth profiles after PD and electromotive drug administration (EMDA) of MMC. Full thickness sections of viable human bladder wall were placed in two-chamber cells with urothelium exposed to donor compartments containing 40 mg of MMC in 100 ml of 0.96% NaCl solutions and with serosa-facing receptor compartments containing 0.9% NaCl solutions. In the preliminary study during each of nine experimental sessions, five sections of bladder wall were individually exposed to MMC for either 5, 15, 30, 45, or 60 min. In the major study, an anode and a cathode were sited in the donor and receptor compartments, and 14 paired experiments--current (20 mA)/no current--were conducted over a 30-min period. Bladder wall sections were...

Silicon carbide was joined to molybdenum by solid state bonding at temperatures ranging from 1200 "C to 1700 "C. The interfaces were characterized by scanning electron microscopy, electron probe microanalysis, and X-ray diffraction. Diffusion of Si and C into MO resulted in a reaction layer with two main phases: Mo,Si, and MO&. For temperatures higher than 1400 "C a ternary phase of composition Mo,Si,C was also formed, and at 1700 "C nucleation of MoC was observed.

In this study we investigated the impregnation of Ni-P metal into polymer substrate via catalyzation in supercritical carbon dioxide (Sc-CO 2 ) and electroless plating in Sc-CO 2 emulsion, in comparison with calculated CO 2 diffusion in polymer on the basis of Fick's law. Sc-CO 2 has two major effects, high diffusivity and good chemical affinity with polymer, on the impregnation of Ni-P metal into the polyimide substrate. Our group fabricated an Ni-P thin film in Sc-CO 2 with an electroless plating emulsion after catalyzing the Sc-CO 2 with Pd complex. According to an EDX analysis, an increase in the Sc-CO 2 catalyzation time led to increases in both the intensity and depth of the Ni-ion penetration into the polyimide. We found that the impregnation reaction of Ni by our novel method is CO 2 diffusion controlling reaction. To clarify which of the two Sc-CO 2 properties, diffusivity or chemical affinity, played a dominant role, we conducted an electroless plating reaction with emulsion using hexane as the catalyzation solvent whose diffusivity is lower than that of Sc-CO 2 . The good affinity with polyimide in the hexane catalyzation led to a film fabrication of Ni-P thin films, but numerous cracks were visible on the films under microscopic observation. According to an EDX analysis of the Ni-P catalyzed in hexane, the intensity of the penetrated Ni-ions into the polyimide was very low. The high diffusivity of the Sc-CO 2 promoted the penetration of the Pd catalyst and Ni-P electroless plating solution into the polyimide substrate.

Penicillin G acylase from Escherichia coli was immobilized on Eupergit Ò C with different enzyme loading. The activity of the immobilized preparations was assayed in the hydrolysis of penicillin G and was found to be much lower than would be expected on the basis of the residual enzyme activity in the immobilization supernatant. Active-site titration demonstrated that the immobilized enzyme molecules on average had turnover rates much lower than that of the dissolved enzyme. This was attributed to diffusion limitations of substrate and product inhibition. Indeed, when the immobilized preparations were crushed, the activity increased from 587 U g )1 to up to 974 U g )1 . The immobilized preparations exhibited up to 15% lower turnover rates than the dissolved enzyme in cephalexin synthesis from 7-ADCA and D-())-phenylglycine amide. The synthesis over hydrolysis ratios of the immobilized preparations were also much lower than that of the dissolved enzyme. This was partly due to diffusion limitations but also to an intrinsic property of the immobilized enzyme because the synthesis over hydrolysis ratio of the crushed preparations was much lower than that of the dissolved enzyme. ã

We report on a novel method of oxidase enzyme electrode response amplification, using unplasticized PVC and plasticized PVC, respectively. The anion exchanger tricaprylylmethylammonium chloride (Aliquat 336s) and hydrophobic isopropylmyristate (IPM) plasticizer have been used together to modify PVC. Resulting structures are anionic substrate selective and hydrogen peroxide impermeable and can be used as outer membranes of a classical dual membrane amperometric enzyme electrode where an oxidase is used to generate H 2 O 2 for electrochemical detection. Their effect on sensor sensitivity and linearity is considered.