Diffusion Model

A 10-layered, finite-volume advection-dispersion model with real-time meteorological and freshwater runoff drivers investigated the interannual differences in the transport of Downs herring Clupea harengus L. larvae in the southern North Sea. Simulations were carried out for the winters of 1989 and 1996 to 2003. As they grew, the concentrations of herring larvae developed vertical behaviour. Meteorological forcing transported Downs herring larvae to the nursery grounds in the eastern North Sea with large interannual differences. Diel vertical movement was relatively unimportant in the transport of larvae in the hydrographically mixed southern North Sea. Year classes with less transport of larvae from the hatching area (which was generally warmer) were associated with greater abundances of young Downs herring in the ICES International Bottom Trawl Survey. This implies that retention, rather than dispersal or delivery of larvae to nursery grounds, is associated with the determination of year class strength in Downs herring.

Sediment-water fluxes of hydrophobic organic chemicals (HOC) may affect the quality of surface waters. Here, we present an approach to derive such fluxes from (a) in situ HOC concentration gradients measured with passive samplers and (b) mass transfer coefficients measured with a novel flux method using Empore disks. For eight undisturbed sediments, this method identified whether the sediment acted as a source or as a sink for HOCs. The analysis also identified which type of transport resistance governed sediment water exchange. For seven inland locations, exchange was limited by benthic boundary layer transport, showing no dependencies on sediment or chemical properties other than concentration. For one river mouth location, exchange was limited by slow in-bed intraparticle diffusion. A biphasic dual compartment radial diffusion model adequately described the data for this location. Fast desorption was interpreted as molecular diffusion retarded by microscale dual domain sorption to amorphous as well as black carbon (BC). Slow desorption was invariant with LogK(ow) and consistent with intraorganic matter diffusion through BC particles. Finally, it is discussed how these findings can be translated into a general framework for flux based exposure assessment.

The kinetics of water adsorption on loose grains of Fuji Davison RD silica gel was studied by a TG differential step method in the temperature range 29-64°C and in the pressure range 6.5-34 mbar. Three grain sizes were selected, 0.3-0.325, 0.355-0.425 mm and 0.8-1.0 mm. Furthermore, adsorption isobars at P H 2 O = 9, 18 and 48 mbar were measured over the temperature range of 30-150°C by a TG technique to determine pertinent equilibrium parameters which are used to calculate the coefficients of diffusion. The equilibrium uptake was described as a linear function of the Dubinin-Polanyi adsorption potential.

We present preliminary experimental data that enable us to suggest that heat transfer in cellular tissue under local strong heating is a more complex phenomenon than a simple heat diffusion. Namely, we demonstrate that under local strong heating of a muscle tissue heat transfer in it exhibits substantial anisotropy unexplained in the context of the standard diffusion model. The observed temperature dynamics is also characterized by nonlinear behavior as well as by a certain repeat reversibility. The latter means that the time variations in the temperature of a cellular tissue undergoing repeated acts of heating go in the same way at least approximately. We explain the observed anomalous properties of heat transfer by suggesting the flow of the interstitial liquid to appear due to nonuniform heating which, in turn, affects the heat transfer. A possible mechanism responsible for this effect is discussed.

The aim of this paper is to determine and forecast the timing and level of critical mass in the development of market penetration for wireless communications. We assume that critical mass is fulfilled at the point when the acceleration of the diffusion process is at its maximum. In practice, this point is determined by calculating the second derivative with respect to time of the diffusion path. Thus, the diffusion has first to be modelled in order to have a function to differentiate. The diffusion of wireless communications in 30 countries is modelled employing the Bass diffusion model. These functions' second derivatives' maximums yield the timing of critical mass, and the respective penetration levels. The penetration levels and points of time of critical masses are regressed with explanatory variables, reflecting characteristics of the countries. A regression model for critical mass timings and levels by country characteristics is used for calculating values for 72 additional countries. The findings suggest that critical mass is achieved faster and on lower penetration levels in later adopting countries.

The biosorption of Acid Red 337 and Acid Blue 324 from aqueous solution on Enteromorpha prolifera was investigated in a batch system. Optimum initial pH and temperature values for AB 324 and AR 337 dyes were found as 3.0 and 2.0, 25 and 30 • C, respectively and the optimum dye uptake amounts per unit mass were obtained at 0.5 g/l biosorbent concentration for both dyes. The Langmuir, Freundlich and Redlich-Peterson adsorption models were applied to experimental equilibrium data and the isotherm constants were calculated using Polymath 4.1 software. The monolayer covarage capacities of E. prolifera for AB 324 and AR 337 were obtained as 160.6 and 210.9 mg/g, respectively. It was observed that the biosorption data fitted well to Redlich-Peterson model than the other models. The external diffusion and intraparticle diffusion models were also applied to biosorption data of AR 337 and AB 324 and it was found that both the surface adsorption as well as intraparticle diffusion contribute to the actual adsorption process. The constants obtained from the pseudo-second order kinetic model at different temperatures were evaluated and the activation energies for the biosorption of AB 324 and AR 337 were found to be −31.5 and −19.87 kJ/mol, respectively. Thermodynamic parameters such as enthalpy, entropy and Gibb's free energy changes were also calculated and it was concluded that the biosorption of these acidic dyes on E. prolifera was exothermic in nature.

In this study, we report the effects of shear rates and polymer concentrations in the formation of asymmetric nanofiltration membrane using a simple dry/wet phase inversion technique. Employing the combination of irreversible thermodynamic model, solution-diffusion model (Spiegler-Kedem equation), steric-hindrance pore (SHP) model and Teorell-Meyers (TMS) model, the transport mechanisms and membrane structural properties were determined and have been characterized for different cases of those formation parameters. The experimental and modeling showed very promising results in terms of membrane performance with interesting structural details. The optimum shear rate (critical shear rate) was found to be at about 203.20 s −1 and the best polymer concentration toward the formation of high performance nanofiltration membrane is in the range of 19.60-23.10%. The modeling results suggested that the pore radius of the membranes produced lies within the range of pore radius of 29 commercial available membranes. This study also proposed that the electrolytes transport through nanofiltration membrane was dominated by a convection factor which accounted approximately 30% more than a diffusion factor. This study also indicated that shear rate and polymer concentration were found to affect the membrane performance and structural properties by providing, to a certain extent, an oriented membrane skin layer which in turn exhibiting an improvement in membrane separation ability.

Computational Fluid Dynamics (CFD) is used to investigate mass transfer from Taylor bubbles to the liquid phase in circular capillaries. The liquid phase volumetric mass transfer coe cient kLa was determined from CFD simulations of Taylor bubbles in up ow, using periodic boundary conditions. The separate in uences of the bubble rise velocity, unit cell length, ÿlm thickness, ÿlm length, and liquid di usivity on kLa were investigated for capillaries of 1.5, 2 and 3 mm diameter. The mass transfer from the Taylor bubble is the sum of the contributions of the two bubble caps, and the ÿlm surrounding the bubble. The Higbie penetration model is used to describe the mass transfer from the two hemispherical caps. The unsteady-state di usion model of Pigford is used to describe the mass transfer to the downward owing liquid ÿlm. The developed model for kLa is in good agreement with the CFD simulated values, and provides a practical method for estimating mass transfer coe cients in monolith reactors.

The diffusion equation (DE) is widely used for ap proximate description of non-anomalous diffusion and Brownian motion (BM). However, the DE is wrong in describing the mean-square displacement (MSD) of a particle at small values of time, where the MSD must be ballistic. We consider the equa tion of the Jeffreys type as a model equation for de scription of diffusion. We find that the MSD in the framework of this model is the same as that in the BM described by the standard Langevin equation.

In this study, intermittent drying behavior of single layer rough rice with a moisture content of between 22 and 24% on the dry basis was simulated by means of a liquid diffusion model based on a prolate spheroid geometry. For this purpose, solution of the liquid diffusion equation was fitted to the experimental data for the drying air temperature 40°C, drying velocity 1.5 ms−1 and tempering periods ranging from 0 to 1 h. In order to make a comparison, solution of the liquid diffusion equation for a finite cylindrical geometry was also fitted to the experimental data. The results show that the liquid diffusion model based on a prolate spheroid geometry explains the drying behavior of rough rice more accurately. The results also show that greater variations occur in diffusion coefficient with increasing tempering time for prolate spheroid geometry which is more realistic geometry for a rough rice grain.

This paper reports on a system dynamics simulation model which was developed to study the diffusion of medical technologies but which should be applicable to other sorts of technologies as well. The model addresses both the adoption and the changing extent of use of an evolving, product-based technology and also endogenously accounts for changes in actual and perceived performance. Two specific medical case studies provide background to the model and are used for testing the model's ability to reproduce various aspects of historical behavior. The model's relatively complex structure is presented in the form of influence diagrams showing major flows and relationships. The paper concludes with a discussion of contributions and possible future uses and modifications of the model.

In this paper, we propose a new study of a stochastic lognormal diffusion process (SLDP), with three parameters, which can be considered as an extension of the bi-parametric lognormal process with the addition of a threshold parameter. From the Kolmogorov equation, we obtain the probability density function and the moments of this process. The statistical inference of the parameter is studied by considering discrete sampling of the sample paths of the model and then using the maximum likelihood (ML) method. The estimation of the threshold parameter requires the solution of a nonlinear equation. To do so, we propose two methods: the classical Newton-Raphson (NR) method and one based on simulated annealing (SA). This methodology is applied to an example with simulated data corresponding to the process with known parameters. From this, we obtain the estimators of the parameters by both methods (NR and SA). Finally, the methodology studied is applied to a real case concerning the mean age of males in Spain at the date of their first wedding.

Leather is a unique porous material, which is composed of a three-dimensional weave of tanned collagen fibre bundles. Collagen is a fibrous protein well organized in the formation of skin as building block. This paper studies the use of ultrasound in improving the diffusion process through porous skin/leather matrix. A diffusion model for leather processing has been proposed taking into account of pore characteristics in leather. Dye diffusion experiments have been carried out with leather and powdered leather to show the influence of ultrasound under two different diffusion conditions. Apparent diffusion coefficient (D) of dye through leather matrix has been calculated from the experimental dye uptake data. The results indicate that the use of ultrasound could achieve, 16.2 and 8.56 times improvement in D value for leather at 50 • C and 30 • C, respectively as compared to 2.99 and 1.55 times for powdered leather. Scanning electron microscopy (SEM) analysis of leather has also been performed which shows that fibre structure and morphology are not affected by the use of ultrasound. This study throws some light on enhanced transport through porous materials of complex nature such as skin/leather using ultrasound.

Cleaner technologies (CT) have recently received much attention in diverse media and policy agendas. This comes out of the clear role they play in environmental protection and sustainability and the large potential to contribute to economic growth and competitiveness. The realization of both potentials depends on the level diffusion and exploitation achieved, today very low. This article presents a selective survey of papers that today represent the general wisdom concerning the factors affecting adoption as a primary condition to diffusion and exploitation of CT. The paper helps to clarify the challenges facing diffusion modelers and policy makers when dealing with policy design, assessing the levels of diffusion achieved as well as the factors affecting diffusion of a particular technology. The paper ends outlining further research need in the field.

The objectives of the present work were: (a) to establish the effect of brine concentration on porcine tissue microstructure (scanning electron microscopy) and protein denaturation (differential scanning calorimetry), (b) to examine the influence of NaCl concentration on the changes in water content, salt uptake, and protein solubilization, using mass balances, (c) to determine the effect of brine concentration on the diffusion coefficient (D m ) of NaCl in pork tissue (Longissimus dorsi) at 4°C analyzing the influence of water uptake on the results.

Experiments investigating the mass transfer of several dissolved volatile organic compounds (VOCs) across the air-water interface were conducted using a single-airchannel air-sparging system. Three different porous media were used in the study. Air velocities ranged from 0.2 cm s-• to 2.5 cm s-•. The tortuosity factor for each porous medium and the air-water mass transfer coefficients were estimated by fitting experimental data to a one-dimensional diffusion model. The estimated mass transfer coefficients K G ranged from 1.79 x 10 -3 cm min -• to 3.85 x 10 -2 cm min -•. The estimated lumped gas phase mass transfer coefficients KGa were found to be directly related to the air diffusivity of the VOC, air velocity, and particle size, and inversely related to the Henry's law constant of the VOCs. Of the four parameters investigated, the parameter that controlled or had a dominant effect on the lumped gas phase mass transfer coefficient was the air diffusivity of the VOC. Two empirical models were developed by correlating the Damkohler and the modified air phase Sherwood numbers with the air phase Peclet number, Henry's law constant, and the reduced mean particle size of porous media. The correlation developed in this study may be used to obtain better predictions of mass transfer fluxes for field conditions.

Vetiver roots have been utilized for the preparation of activated carbon (AC) by chemical activation with different impregnation ratios of phosphoric acid, X P (g H 3 PO 4 /g precursor): 0.5:1; 1:1 and 1.5:1. Textural characterization, determined by nitrogen adsorption at 77 K shows that mixed microporous and mesoporous structures activated carbons (ACs) with high surface area (>1000 m 2 /g) and high pore volume (up to 1.19 cm 3 /g) can be obtained. The surface chemical properties of these ACs were investigated by X-ray photoelectron spectroscopy (XPS) and Boehm titration. Their textural and chemical characteristics were compared to those of an AC sample obtained by steam activation of vetiver roots. Classical molecules used for characterizing liquid phase adsorption, phenol and methylene blue (MB), were used. Adsorption kinetics of MB and phenol have been studied using commonly used kinetic models, i.e., the pseudo-first-order model, the pseudo-second-order model, the intraparticle diffusion model and as well the fractal, BWS (Brouers, Weron and Sotolongo) kinetic equation. The correlation coefficients (R 2 ) and the normalized standard deviation q (%) were determined showing globally, that the recently derived fractal kinetic equation could best describe the adsorption kinetics for the adsorbates tested here, indicating a complex adsorption mechanism. The experimental adsorption isotherms of these molecules on the activated carbon were as well analysed using four isotherms: the classical Freundlich, Langmuir, Redlich-Peterson equations, but as well the newly published deformed Weibull Brouers-Sotolongo isotherm. The results obtained from the application of the equations show that the best fits were achieved with the Brouers-Sotolongo equation and with the Redlich-Peterson equation. Influence of surface functional groups towards MB adsorption is as well studied using various ACs prepared from vetiver roots and sugar cane bagasse. Opposite effects governing MB and phenol adsorption mechanism on ACs are demonstrated. The various effects involved in adsorption mechanisms of each molecule are demonstrated. (S. Gaspard).

Simultaneous membrane based solvent extraction (MBSE) and membrane based solvent stripping (MBSS) in HF contactors of a heterocyclic carboxylic acid (HCA) of industrial importance from sulphate solutions with solvent containing trioctylamine (TOA) were studied. An effective transport of HCA was achieved. The proposed reactiondiffusion model gives a much better fit to experimental values than the diffusion model. The mean values of the lumped rate constants of extraction and stripping reactions for HCA are 2.19.10" and 5.92. lo4 m.s-', respectively. The mass-transfer resistances based on reaction kinetics play a decisive role in MBSE and MBSS of HCA and participate in their overall resistances by about 65 and 40 %, respectively.

A mechanistic diffusion model for Sr in water-saturated clay (illite and kaolinite) is elaborated based on laboratory results. Both porewater and surface diffusion pathways are identified. Their relative importance is controlled by variable adsorption selectivity of Sr, associated with aqueous speciation. Conditional diffusion coefficients for Sr, obtained experimentally using three independent methods, average 1.05 Ϯ 0.12 ϫ 10 Ϫ7 cm 2 s Ϫ1 from separate determinations at 5°C. Speciation, based on analytical data and stability constants, predicts total strontium (aqueous and/or adsorbed) to comprise ϳ 90% free ion, Sr 2ϩ , in adsorption and diffusion experiments within pH ϳ 8. Total distribution coefficient doubles in the pH range ϳ 8 to ϳ 8.5, doubling again between pH ϳ 8.5 and ϳ 9.5. Minor occurrence of an aquo-carbonate species, SrCO 3 (aq), significantly increases the total adsorption affinity of Sr for the clay above pH ϳ 8.5. Adsorption is reversible with species distribution coefficient for SrCO 3 (aq) about 60 times higher than that for Sr 2ϩ . EXAFS spectroscopy indicates similar first hydration sphere coordination numbers and distances for Sr, both adsorbed to clay and as solutions of SrCl 2 and SrCO 3 . Adsorption to clay surfaces occurs as weak outer sphere bonding, including intact hydration shells. A greater mass fraction of total Sr is adsorbed, supporting any contribution of surface diffusion to net transport. Heightened adsorption affinity of Sr, due to carbonate complexation, enhances possible mass transfer by surface diffusion. Model estimates of intrinsic diffusion coefficients, independent of tortuosity, are more than one order of magnitude lower for surface compared with porewater. Invoking surface diffusion implies retardation in overall transport rate, relative to porewater diffusion alone.

A multiphysical finite element modeling of dissimilar welding via interlayer material was proposed. A 2D model including heat transfer, fluid flow and level set problems allowed to simulate the morphology and the composition of melted zone in horizontal plane. The calculated thickness of melted interlayer was used as a main criterion for the choice of optimal welding conditions, when the chemical interaction between the joined materials must be avoided. A 1D diffusion model at the limit of melted zone allowed estimating the length and the composition of diffusion layer between one of the materials and the interlayer basing on previously calculated local temperature gradient. The simulations were carried out in finite element software COMSOL Multiphysics.

Thespesia populnea is a large tree found in the tropical regions and coastal forests of India. Its pods were used as a raw material for the preparation of activated carbon. The prepared activated carbon was used for the adsorptive removal of Orange G dye from aqueous system. The effects of various parameters such as agitation time, initial dye concentration and adsorbent dosage were studied using response surface methodology (RSM). RSM results show that 0.54 g of activated carbon was required for the maximum adsorption of Orange G dye (17.6 mg L −1 ) within a time period of 4.03 h. Adsorption data were modeled using Freundlich and Langmuir adsorption isotherms. The adsorption of Orange G dye by activated carbon obeyed both Fruendlich and Langmuir isotherm. Adsorption kinetic data were tested using pseudo-zero, first, second-order and intraparticle diffusion models. Kinetic studies revealed that the adsorption followed pseudo-second-order reaction with regard to the intraparticle diffusion. FTIR spectral result indicated all the functional group except primary amines (3417 cm −1 ) and C N (1618 cm −1 ) were involved in the adsorption process. XRD data showed that Orange G dye adsorbed activated carbon might not induce the bulk phase changes. SEM results showed that the surface of the activated carbon was turned from dark to light color after dye adsorption.

This paper analyzes the diffusion of mobile telecommunications services in Vietnam and examines how telecommunications regulation and potential substitute/complement services affect the growth of the number of mobile telephone subscribers. Using a logistic diffusion model, it is found that fixed telephone services are a complement while data services have a negative relation to mobile telephone services in Vietnam. As for regulation, the policy of introducing competition has been found to be the most effective in influencing the adoption of mobile services. Another important result is that the estimated potential market is roughly 76% of the total population. The findings suggest that suitable regulation that guarantees competition in the mobile telecommunications market in a developing country such as Vietnam is one of the most important factors for a positive diffusion process.

The cementation of cadmium ions by zinc powder was studied in a batch reactor at low and high concentrations at pH 5. 2-5.4 and it is shown that the reaction is first-order. XRD and SEM analysis confirm that the deposited layer is metallic with no evidence of basic zinc sulphate or re-dissolution of cadmium. Dependence of the reaction constant on initial cadmium concentration proves the reaction mechanism. Different possible kinetic controlling models of cadmium ion (Cd 2+ ) cementation from aqueous solution by zinc powder were studied with respect to initial cadmium concentration, temperature, zinc powder size and stoichiometric ratio. The experiments demonstrate that at initial cadmium concentrations > 1000 ppm, the ash diffusion control model prevails, while at concentrations <500 ppm, the data has good agreement with the film diffusion model. For concentrations between 500 ppm and 1000 ppm, a combination of ash diffusion and film diffusion models controls the reaction rate. Based on numerical analysis, the calculated activation energies at high and low concentrations are 9.6 and 7.2 kJ/mol, respectively. Statistical data analysis was performed and different reaction rate constants were estimated from the equations for high and low initial cadmium concentrations.

Semiconductor industry is capital intensive in which capacity utilization significantly affect the capital effectiveness and profitability of semiconductor manufacturing companies. Thus, demand forecasting provides critical input to support the decisions of capacity planning and the associated capital investments for capacity expansion that require long lead-time. However, the involved uncertainty in demand and the fluctuation of semiconductor supply chains make the present problem increasingly difficult due to diversifying product lines and shortening product life cycle in the consumer electronics era. Semiconductor companies must forecast future demand to provide the basis for supply chain strategic decisions including new fab construction, technology migration, capacity transformation and expansion, tool procurement, and outsourcing. Focused on realistic needs for manufacturing intelligence, this study aims to construct a multi-generation diffusion model for semiconductor product demand forecast, namely the SMPRT model, incorporating seasonal factor (S), market growth rate (M), price (P), repeat purchases (R), technology substitution (T), in which the nonlinear least square method is employed for parameter estimation. An empirical study was conducted in a leading semiconductor foundry in Hsinchu Science Park and the results validated the practical viability of the proposed model. This study concludes with discussions of the empirical findings and future research directions.

In this study, montmorillonite clay (MC) has been utilized as the adsorbent for the removal of a cationic dye, methylene blue (MB), from aqueous solution by the batch adsorption technique under different conditions of initial dye concentration, adsorbent concentration, contact time, solution pH, and temperature. Attempts were made to fit the isothermal data using Langmuir and Freundlich equations. The experimental results have demonstrated that the equilibrium data are fitted well by a Langmuir isotherm equation. Thermodynamic parameters such as the changes in enthalpy, entropy, and Gibbs' free energy were determined, showing adsorption to be an endothermic yet spontaneous process. Pseudofirst-order, pseudo-second-order, and intraparticle diffusion models were considered to evaluate the rate parameters. The experimental data fitted the pseudo-second-order kinetic model, with an activation energy of +28.5 kJ mol −1 . The results indicate that MC adsorbs MB efficiently and could be employed as a low-cost alternative in wastewater treatment for the removal of cationic dyes.

Ion-exchange is an alternative process for uptake of heavy metals from aqueous solutions. In the present study, the sorption of nickel(II) ions from aqueous solution was investigated by using Lewatit MonoPlus SP 112 (strongly acidic, macroporous cation-exchange resin) in a batch adsorption system as a function of pH (2.0-8.0), initial nickel concentration (50-200 mg/L), resin dosage (0.5-2.0 g/L), contact time (0.5-3h), and temperatures (298-318K). The data were analyzed on the basis of Lagergren pseudo-first order, pseudo-second order (Types 1-5), Elovich and external, Weber-Morris intraparticle, pore-surface mass diffusion models. The experimental data showed that the maximum pH for efficient sorption of nickel(II) was 6.0. At the optimal conditions, nickel(II) ions sorption on the resin was decreased when the initial metal concentration increased. The results indicated that the resin dosage strongly affected the amount of nickel(II) ions removed from aqueous solution. The adsorption process was very fast due to 80% of nickel(II) sorption was occurred within 30 min and equilibrium was reached at about 90 min. Freundlich and Langmuir adsorption isotherm models were used for sorption equilibrium data and the maximum adsorption capacity (171 mg/g) of Lewatit MonoPlus SP 112 was obtained from Langmuir isotherm. The thermodynamic parameters (DeltaG degrees, free energy change; DeltaS degrees, enthalpy change; and DeltaH degrees, entropy change) for sorption of nickel(II) ions were evaluated. The rise in temperature caused a partly increase in the value of the equilibrium constant (K(c)) for the sorption of nickel(II) ions. Moreover, column flow adsorption study was also studied. Breakthrough curves were obtained from column flow studies by using both synthetic solution and rinsing bath water of filter industry. The column regeneration was carried out for two sorption-desorption cycles. The eluant used for regeneration of the cation-exchange resin was 7% (w/w) HCl. The experimental results demonstrated that Lewatit MonoPlus SP 112 cation-exchange resin could be used effectively for the removal of nickel(II) ions from aqueous medium.

Tourist taxes have become an important source of revenue for many tourist destinations. Taxes on accommodation are upheld by their proponents as a way of shifting the local tax burden on to non-residents, while the travel industry claims that these levies do significant damage to their level of competitiveness. The objective of this paper is to identify the market's sensitivity to price changes in travel-related services or groups of services, assuming that one of the main factors that influences travel decisions is the information on the destination that consumers receive. In order to include this effect, the study applies a combination of a diffusion model and a traditional economic utility theory model to tourists visiting the Balearic Islands (Spain) from the United Kingdom, Germany, France and the Netherlands. r

The authors bring together approaches from cognitive and individual differences psychology to model characteristics of reaction time distributions beyond measures of central tendency. Ex-Gaussian distributions and a diffusion model approach are used to describe individuals&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; reaction time data. The authors identified common latent factors for each of the 3 ex-Gaussian parameters and for 3 parameters central to the diffusion model using structural equation modeling for a battery of choice reaction tasks. These factors had differential relations to criterion constructs. Parameters reflecting the tail of the distribution (i.e., tau in the ex-Gaussian and drift rate in the diffusion model) were the strongest unique predictors of working memory, reasoning, and psychometric speed. Theories of controlled attention and binding are discussed as potential theoretical explanations.

Pestil, a well known fruit leather in Turkey, was prepared from boiled grape juice and starch mixture by using traditional technique. Drying of pestil was carried out by hot air drying and sun drying. The factors investigated in hot air drying were air temperature (55, 65 and 75°C), sample thickness (S 1 ¼ 0:71, S 2 ¼ 1:53, S 3 ¼ 2:20 and S 4 ¼ 2:86 mm) and air velocity (V 1 ¼ 0:86, V 2 ¼ 1:27 and V 3 ¼ 1:82 m=s). The effects of drying time, temperature and slab thickness on moisture content of pestil during drying were significant (P < 0:05) and of air velocity was not (P > 0:05). Depending on sample thickness and air temperature, the drying time ranged between 50-140 min to achieve the commercial moisture content of pestil (0:12 kg H 2 O=kg DS) in air drying. Whereas, sun drying took 180-1500 min. Almost all samples dried in the falling rate period, except S 2 , S 3 , S 4 of sun drying and S 4 at 55°C. The latter had a short (negligible) constant rate period. Effective moisture diffusivity values were estimated from Fick's diffusion model. These values were between 3:00-37:6 Â 10 À11 m 2 =s for hot air drying and 1:93-9:16 Â 10 À11 m 2 =s for sun drying. Activation energy value of water diffusion was calculated using an Arrhenius-type equation. The estimated values were 21.7, 16.5, 12.0 and 10.3 kJ/mol for S 1 , S 2 , S 3 and S 4 , respectively. Ó

Although the square-root process has long been used as an alternative to the Black-Scholes geometric Brownian motion model for option valuation, the pricing of Asian options on this diffusion model has never been studied analytically. However, the additivity property of the square-root process makes it a very suitable model for the analysis of Asian options. In this paper, we develop explicit prices for digital and regular Asian options. We also obtain distributional results concerning the square-root process and its average over time, including analytic formulae for their joint density and moments. We also show that the distribution is actually determined by those moments.

Beach nourishment provides an excellent opportunity for the study of intensified sediment transport gradients and associated morphological changes in a natural setting. The objectives of this study are to quantify and predict longshore and cross-shore transport gradients induced by 1) beach nourishment, 2) different storm wave conditions, and 3) the annual wave climate and long-term sediment supply. The details of

We consider the asymptotic behavior of posterior distributions and Bayes estimators based on observations which are required to be neither independent nor identically distributed. We give general results on the rate of convergence of the posterior measure relative to distances derived from a testing criterion. We then specialize our results to independent, nonidentically distributed observations, Markov processes, stationary Gaussian time series and the white noise model. We apply our general results to several examples of infinite-dimensional statistical models including nonparametric regression with normal errors, binary regression, Poisson regression, an interval censoring model, Whittle estimation of the spectral density of a time series and a nonlinear autoregressive model. POSTERIOR CONVERGENCE RATES 193 dressed by Amewou-Atisso, Ghosal, Ghosh and Ramamoorthi [1] and Choudhuri, Ghosal and Roy . The main purpose of the present paper is to obtain a theorem on rates of convergence of posterior distributions in a general framework not restricted to the setup of i.i.d. observations. We specialize this theorem to several classes of non-i.i.d. models including i.n.i.d. observations, Gaussian time series, Markov processes and the white noise model. The theorem applies in every situation where it is possible to test the true parameter versus balls of alternatives with exponential error probabilities and it is not restricted to any particular structure on the joint distribution. The existence of such tests has been proven in many special cases by Le Cam and Birgé , who used them to construct estimators with optimal rates of convergence, determined by the (local) metric entropy or "Le Cam dimension" of the model. Our main theorem uses the same metric entropy measure of the complexity of the model and combines this with a measure of prior concentration around the true parameter to obtain a bound on the posterior rate of convergence, generalizing the corresponding result of Ghosal, Ghosh and van der Vaart . We apply these results to obtain posterior convergence rates for linear regression, nonparametric regression, binary regression, Poisson regression, interval censoring, spectral density estimation and nonlinear autoregression. van der Meulen, van der Vaart and van Zanten have extended the approach of this paper to several types of diffusion models.

Rosemary leaves (Rosmarinus officinalis L., Lamiaceae) were dried by using sun, oven (50 °C) and microwave oven (700 W, 2450 MHz) drying methods. Microwave oven drying shortened the drying time more than 99% when compared to the sun and oven drying methods. K, Ca, Na, Mg and P were the most abundant elements in the rosemary samples. The mineral content of oven dried rosemary leaves was higher than that of the sun and microwave dried samples. The logarithmic and Midilli and Küçük models were shown to give a good fit to the sun and oven drying. The Page, Modified Page and Midilli and Küçük models have shown a better fit to the experimental microwave oven drying data of rosemary leaves. Microwave oven drying revealed optimum colour values. Oven drying resulted in a considerable decrease in the colour quality of the rosemary leaves.

Linear parabolic partial differential equations (PDE’s) and diffusion models are closely linked through the celebrated Feynman–Kac representation of solutions to PDE’s. In asset pricing theory, this leads to the representation of derivative prices as solutions to PDE’s. Very often implied derivative prices are calculated given preliminary estimates of the diffusion model for the underlying variable. We demonstrate that the implied derivative prices are consistent and derive their asymptotic distribution under general conditions. We apply this result to three leading cases of preliminary estimators: Nonparametric, semiparametric and fully parametric ones. In all three cases, the asymptotic distribution of the solution is derived. We demonstrate the use of these results in obtaining confidence bands and standard errors for implied prices of bonds, options and other derivatives. Our general results also are of interest for the estimation of diffusion models using either historical data of the underlying process or option prices; these issues are also discussed.

The views expressed in this Working Paper are those of the author(s) and do not necessarily represent those of the IMF or IMF policy. Working Papers describe research in progress by the author(s) and are published to elicit comments and to further debate.

A coupled 1-D time-dependent radiative-convective-photochemical diffusion model which extends from the surface to 60 km is used to investigate the potential impact of greenhouse trace gas emissions on long-term changes in global climate, atmospheric ozone and surface UV-B radiation, taking into accoont the influence of aerosol loading into the atmosphere from major volcanic eruptions, of thermal inertia of the upper mixed layer of the ocean and of other radiativephotochemical feedback mechanisms. Experiments are carried out under global and annual average insolation and cloudiness conditions. The transient calculations are made for three different growth scenarios for increase in trace gas concentrations. Scenario 1, which begins in 1850, uses the best estimate values for future trace gas concentrations of CO2, CH4, N2O, CFC-11, CFC-12 and tropospheric O3, based on current observational trends. Scenarios 2 and 3, which begin in 1990, assume lower and upper ranges, respectively, of observed growth rates to estimate future concentrations. The transient response of the model for Scenario 1 suggests that surface warming of the ocean mixed layer of about 1 K should have taken place between 1850 and 1990 due to a combined increase of atmospheric CO2 and other trace gases. For the three scenarios considered in this study, the cumulative surface warming induced by all major trace gases for the period 1850 to 2080 ranges from 2.7 K to 8.2 K with the best estimate value of 5 K. The results indicate that the direct and the indirect chemistry-climate interactions of non-CO2 trace gases contribute significantly to the cumulative surface warming (up to 65% by the year 2080). The thermal inertia of a mixed layer of the ocean is shown to have the effect of delaying equilibrium surface warming by almost three decades with an e-folding time of about 5 years. The volcanic aerosols which would result from major volcanic eruptions play a significant role by interrupting the long-term greenhouse surface warming trend and replacing it by a temporary cooling on a time scale of a decade or less. Furthermore, depending on the scenario used, a reduction in the net ozone column could result in an increase in the solar UV-B radiation at the surface by as much as 300% towards the end of 21st century.

In this study, efficacy of native and acidically modified Cicer arientinum pod biomass was investigated for Pb (II) removal using metal ion concentration, kinetic, sorbent dose, pH and pretreatment as operational parameters. The metal uptake of biomass increased as a result of pretreatments and maximum sorption capacity (171.28 mg/g) was shown by H 3 PO 4 modified biomass. The sorption capacity increased in the order H 3 PO 4 > H 2 SO 4 > HCl > native, with increase in metal concentration. The equilibrium data was analysed using different sorption models to know sorption mechanism and results of ANOVA showed that Dubinin-Radushkevich model is fitted well to the experimental data. Sorption rate was slow because equilibrium was attained within 7 h and rate was best described by pseudo-first-order, second-order rate equation, Bangham and intraparticle diffusion models. Sorption capacity was maximum at pH 4 and it was observed also that sorption capacity decreased but % removal increased with increase in biosorbent dose.