Diffusion

We consider a two dimensional Turing like system with two diffusing species which interact with each other. Considering the species to be charged, we include the effect of an electric field along a given direction which can lead to a drift induced instability found by A.B.Rovinsky and M.Menzinger[9]. This allows one to study the competition between diffusion and drift as was done numerically by Riaz et al. We show here that an analytic formula can be found on the basis of a linear stability analysis that incorporates all the effects that are known for the system and also allows for some detailed predictions.

Both resins and activated carbons are commonly used as adsorbents in water and wastewater treatment. In general, intraparticle diffusion mechanisms within macro reticular resin particles (such as XAD-2000) are different from those in activated carbon particles. Currently, completely mixed batch reactor (CMBR) technique can be used to determine the intraparticle diffusivity for phenolic compounds adsorbed onto activated carbon systems. However, the technology cannot determine the intraparticle diffusivity accurately if the fluid-film resistance is significant, such as synthetic macro-reticular resins. Therefore, this study develops a technique to determine the intraparticle diffusivities of XAD-2000 resin. This paper characterized the concentration decay curves of para-nitrophenol in CMBR to determine effective pore diffusivity (D P) of the resin. The obtained mean and standard deviation of D P are about 1.1 Â 10 À5 and 3.2 Â 10 À6 (cm 2 s À1), respectively. The technology developed in this study has the advantages of significant chemical saving and easy operation.

A simple analytical solution is proposed to predict the minimumbed length, Zmin, necessary to make two adsorption zones in bi-component fixed-bed adsorption separate from each other, by use of the so-called constant pattern concept and the linear driving force approximation. Values of Zminobtained from the analytical solution werecomparedwith those fromnumerical breakthroughcurves based on a rather rigorous massbalance as well as diffusion equations. The solution was found to be accurate enough. Experiments were performed for two monohydric alcohols-activated carbon and two monocarboxylic acids-activated carbon systems, respectively. Comparison of the predicted Zmin based on the proposed equation gave larger values than the experimental values.

In general, the adsorption uptake curve (AUC) can be easily determined in either intraparticle diffusion or liquid film mass transfer dominating systems. However, for both intraparticle diffusion and liquid film mass transfer controlling systems, the characterization of AUC is much more complicated, for example, when relatively small adsorbent particles are employed. In addition, there is no analytical solution available for both intraparticle diffusion and liquid film mass transfer controlling systems. Therefore, this paper is trying to characterize AUC for both intraparticle diffusion and liquid film mass transfer controlling adsorption systems using the shallow bed reactor technique. Typical parameters influencing AUC include liquid film mass transfer coefficient (k F), effective intraparticle diffusivity (D S), influent concentration (c 0) and equilibrium parameters (such as Freundlich isotherm constants k and 1/n). These parameters were investigated in this research and the simulated results indicated that the ratio of k F /D S and Freundlich constant 1/n had impact on AUC. Biot number (Bi) was used to replace the ratio of k F /D S in this study. Bi represents the ratio of the rate of transport across the liquid layer to the rate of intraparticle diffusion. Furthermore, Bi is much more significant than that of 1/n for AUC. Therefore, AUC can be characterized by Bi. In addition, the obtained Bi could be used to determine D S and k F simultaneously. Both parameters (D S and k F) are important for designing and operating fixed bed reactors.

For the design of a fixed-bed reactor, intraparticle diffusivity of adsorbents is one of the most important parameters. However, determining this diffusivity is difficult as measuring the effects of fluid film resistance of adsorbents. Shallow-bed (differential reactor) technique is commonly used to determine intraparticle diffusivity. The conventional shallow-bed technique is based on the assumption that fluid film resistance is negligible because of high fluid velocity; hence, the fluid film mass transfer is not calculated. For an activated carbon-phenolic compound system, both intraparticle diffusivity and fluid film mass transfer coefficient were determined using a shallowbed reactor. However, no one has confirmed the accuracy of the conventional assumption for a synthetic resin adsorbent-phenolic compound system. In general, synthetic resin adsorbents have a larger fluid film resistance than activated carbon. Therefore, this study focused on the effect of fluid film resistance based on the conventional assumption. The conventional analysis method (intraparticle diffusion controlling model) and the new analysis method (both intraparticle diffusion and fluid film mass transfer controlling model) were compared, and the results indicated that the conventional assumption, which neglects the elimination of fluid film resistance, had no effect on intraparticle diffusivity. Therefore, the conventional analysis method is useful for determining intraparticle diffusivity for a resin adsorbent-phenolic compound system.

To make clear the mechanismof intraparticle diffusion at relatively high concentration ranges, the values of intraparticle diffusivity, Diq, of tetrahydrofuran (THF) within activated carbon pellets were measured at 308 K by use of two methods, i.e. the steady-state diffusion method and the flow method for fixed-bed adsorption. The two values of Diq obtained agreed with each other fairly well. Surface and pore diffusivities were calculated from Diq based on a concept of simultaneous occurrence of transfer through pore spacings and through surfaces. The value of surface diffusivity, Ds, thus calculated was almost equal to those reported for solvent vapor-activated carbon systems in lower concentration ranges. The value of pore diffusivity, Dp, calculated was close to that evaluated from molecular diffusion theory combined with Knudsen diffusion. It became clear that breakthrough curves numerically estimated using the values of D, r variable with the change in amount adsorbed, fitted the experimental breakthrough curves more closely than those estimated by use of the values of diffusivity assumed to be constant irrespective of amountadsorbed for specific experimental runs.

A novel, simple numerical method to determine the pore and surface diffusivities in adsorbents from a single experimental concentration decay curve obtained using the batch adsorption technique was investigated in this study. The pore and surface diffusion coefficients were determined based on the conventional parallel diffusion model in its dimensionless form using a theoretical model correlation. The model assumed that the film mass transfer resistance was negligible, i.e., the condition with a large Biot number, from the single concentration decay curve. The procedure for determining the kinetic parameters was investigated, and the effectiveness of the proposed simple method was validated by comparing the parameters with those reported previously. The single decay curve of p-nitrophenol, obtained by the batch adsorption system using granular activated carbon as an adsorbent, was used for validation. The diffusivities determined by the simple method corresponded fairly well with t...

Both resins and activated carbons are commonly used as adsorbents in water and wastewater treatment. In general, intraparticle diffusion mechanisms within macro reticular resin particles (such as XAD-2000) are different from those in activated carbon particles. Currently, completely mixed batch reactor (CMBR) technique can be used to determine the intraparticle diffusivity for phenolic compounds adsorbed onto activated carbon systems. However, the technology cannot determine the intraparticle diffusivity accurately if the fluid-film resistance is significant, such as synthetic macro-reticular resins. Therefore, this study develops a technique to determine the intraparticle diffusivities of XAD-2000 resin. This paper characterized the concentration decay curves of para-nitrophenol in CMBR to determine effective pore diffusivity (D P) of the resin. The obtained mean and standard deviation of D P are about 1.1 Â 10 À5 and 3.2 Â 10 À6 (cm 2 s À1), respectively. The technology developed in this study has the advantages of significant chemical saving and easy operation.

A simple analytical solution is proposed to predict the minimumbed length, Zmin, necessary to make two adsorption zones in bi-component fixed-bed adsorption separate from each other, by use of the so-called constant pattern concept and the linear driving force approximation. Values of Zminobtained from the analytical solution werecomparedwith those fromnumerical breakthroughcurves based on a rather rigorous massbalance as well as diffusion equations. The solution was found to be accurate enough. Experiments were performed for two monohydric alcohols-activated carbon and two monocarboxylic acids-activated carbon systems, respectively. Comparison of the predicted Zmin based on the proposed equation gave larger values than the experimental values.

In order to design and operate a fixed-bed reactor, accurate modeling is important. For a single component system, the determination of intraparticle diffusivity is rather easy. However, the calculations of multi-component systems are normally complicated and very time-consuming. Therefore, an alternative simple determination procedure using the shallow bed technique is proposed in this research to determine the intraparticle diffusivities for multi-component systems. Ternary component systems of phenol (PH), benzoic acid (BA), and p-nitro-phenol (PNP) were investigated as model components. This study illustrated that adsorption uptake curves of different components in ternary systems can be converted into one typical characteristic curve (theoretical uptake curve, TUC) by using a set of dimensionless groups. By matching the dimensionless experimental uptake curve (DEUC) with TUC, diffusivities of PH, BA and PNP were determined as 8.00 × 10 −8 , 5.92 × 10 −8 and 5.05 × 10 −8 cm 2 s −1 , respectively. These values are in good agreement with simulated experimental values. This study demonstrated that the shallow bed technique can be used to simultaneous determination of intraparticle diffusivities from multi-component systems.

Primary intraocular lymphoma (PIOL) is an uncommon but clinically and pathologically distinct form of non-Hodgkin's lymphoma. It provides a therapeutic challenge because of its diverse clinical presentations and variable clinical course. Currently available treatments for PIOL include intravenous multiple drug chemotherapy, external beam radiation therapy, and intravitreal methotrexate (MTX) injection. Each intravitreal injection of MTX is associated with potentially toxic peaks and subtherapeutic troughs of intraocular MTX concentration. Repetitive injections are required to maintain therapeutic levels of MTX in the eye. A sustained release drug delivery system is desired for optimized therapeutic release (0.2–2.0 μg/day) of MTX for over a period of 1 month to achieve effective treatment of PIOL. This study reports development of a unique intravitreal micro-implant, which administers therapeutic release of MTX over a period of 1 month. Chitosan (CS) and polylactic acid (PLA) ba...

The early stages of Cu electrodeposition onto Pt(poly) have been investigated in 0.5 M H 2 SO 4 + 0.01 M CuSO 4 solution without or with H 2 SeO 3 when a molar concentration ratio [Cu(II)]/ [Se(IV)] ‡ 2•10 2 using electrochemical and ex situ AFM techniques. The overpotential deposition of Cu has been performed onto a Pt surface precovered independently with Cu in amount close to an equivalent monolayer. Chronoamperometric results have been shown to follow an instantaneous 3D nucleation and diffusion-controlled growth model. The values of diffusion coefficient D for Cu 2+ , number of nuclei N and average nuclei radius r av have been calculated. In the local regions of the surface, the separate large agglomerates composed of the different diameter clusters have been revealed in both cases, but, in the presence of the H 2 SeO 3 , they attained a distinct chain-like configuration. Some morphological characteristics have been reported.

The early stages of Cu electrodeposition onto Pt(poly) have been investigated in 0.5 M H 2 SO 4 + 0.01 M CuSO 4 solution without or with H 2 SeO 3 when a molar concentration ratio [Cu(II)]/ [Se(IV)] ‡ 2•10 2 using electrochemical and ex situ AFM techniques. The overpotential deposition of Cu has been performed onto a Pt surface precovered independently with Cu in amount close to an equivalent monolayer. Chronoamperometric results have been shown to follow an instantaneous 3D nucleation and diffusion-controlled growth model. The values of diffusion coefficient D for Cu 2+ , number of nuclei N and average nuclei radius r av have been calculated. In the local regions of the surface, the separate large agglomerates composed of the different diameter clusters have been revealed in both cases, but, in the presence of the H 2 SeO 3 , they attained a distinct chain-like configuration. Some morphological characteristics have been reported.

The poly(amic ethyl esters) (PAEs) of pyromellitic dianhydride/4,4'-oxydianiline (PMDA/ODA) were prepared in three isomeric forms, with meta-linkages, para-linkages and randomly alternating meta-and para-linkages (referred to as mixed PAEs). In addition to the normal PAEs (which contained only hydrogen and which were cast as base layers for diffusion studies), each of these isomeric PAE was synthesized in two other forms: (1) labelled with deuterium on the ODA segments, and (2) labelled with deuterium on the ethyl ester moiety to allow determination of the imide fraction, f. Forward recoil spectrometry (FRES) was utilized to provide information about the polyimide-polyimide interface by measuring the depth profile of hydrogen and deuterium for bilayer samples consisting of a thick non-deuterated base layer, and a thin deuterated tracer layer. FRES measurements indicated that the interdiffusion distance, w, decreased markedly with increasing imidization temperature, Ti. For base layers prepared from N-methylpyrrolidone, w for the para-and mixed PAE base layers decreased more rapidly with T i than with w for the meta-PAE base layers. However, these differences were found to result from the differences in imidization kinetics of the various isomers with f increasing more rapidly with Ti for para-and mixed PAE than for the meta-PAE. Nevertheless, when w was plotted as a function of f, all of the isomers exhibited similar behaviour, i.e. w decreased steadily as the imide fraction f approached 1. Base layers cast from dimethyl sulfoxide did not show differences in either f or w after imidization at a given Ti.

The supercritical fluid (SFC) extraction efficiency of phenanthrene from clayey soils was modeled. The model accounts for effective diffusion of the phenanthrene in the solid pores, axial dispersion in the fluid phase, and external mass transfer to the fluid phase from the particle surface. This model, involving partial differential equations, was solved using the finite difference. The model showed the relationship between diffusivity, mass transfer coefficient, and properties of porous media (clay texture). The porous media analysis was performed with a microscope and by an image analysis. The proposed model compared well with the experimental data available in the literature.

Drying is one of the primary methods of food preservation. Determining coefficients used in drying models is essential to predict the drying behaviour. The present study was conducted to compute effective moisture diffusivity and activation energy of samples of apple slices. The thin-layer drying experiments were carried out under five air temperatures of 40, 50, 60, 70 and 80ºC, three air velocities of 0.5, 1.0 and 2.0 m/s and three apple slice thicknesses of 2, 4 and 6 mm and constant air humidity of 21%. Results indicated that drying took place in the falling rate period. Moisture transfer from apple slices was described by applying the Fick's diffusion model. The effective diffusivity values for all conditions changed from 1.50×10-8 to 1.71×10-7 m²/s. An Arrhenius relation with an activation energy value of 22664.1 to 30919.0 J/mol and the diffusivity constant value of 1.16×10-4 to 6.34×10-3 m²/s were obtained which shows the effect of drying air temperature, air velocity and slice thickness on the diffusivity.

Thin-layer drying kinetics of bell pepper was experimentally investigated in a laboratory scale convective dryer. Experiments were performed at air temperatures of 40, 50, 60, 70, and 80ºC and constant air velocity of 2 m/s. In order to select a suitable form of the drying curve, 12 different thin layer drying models were fitted to experimental data. The high values of coefficient of determination and the low values of reduced chi-square and root mean square error indicated that the Logarithmic model could satisfactorily illustrate the drying curve of bell pepper. The Logarithmic model had the highest value of R 2 (0.9929), the lowest 2 χ (0.00003497) and RMSE (0.00481743). The Logarithmic model was found to satisfactorily describe the drying behavior of bell pepper. Fick's second law was used to calculate the Effective moisture diffusivity. The moisture diffusion coefficient varied between 1.7 × 10-9 and 11.9 × 10-9 m 2 /s for the given temperature range and corresponding activation energy was 44.49 kJ/mol.

The presence of cadmium (Cd) in the marine environment is a serious pollution problem. The ability of activated carbon (AC) as an adsorbent for Cd removal from Cdcontaminated simulated seawater was studied. Experiments were carried out as function of the effect of adsorbent dose, contact time, stirring speed, initial Cd concentration and temperature. The pH was kept constant for all the experiment. The study has shown that AC is capable of removing Cd from contaminated seawater. The equilibrium and kinetic data agreed very well with the Freundlich isotherm and pseudo second-order kinetic models, respectively. Cd adsorption was endothermic. o S  and o H  was 73.43 JK-1 mol-1 and 6.63 KJmol-1 , respectively. The maximum percentage removal of Cd achieved was 99.85 % and the Freundlich adsorption equilibrium constant was 5.52 x 10 6 (mg/g (L/mg) 1/n).

Ž Ž. . Ž Ž. y. Dissolved boron in seawater occurs mainly in the form of boric acid B OH and borate B OH. While the 3 4 3 4 required to establish the boric acid-borate equilibrium in seawater is calculated to be ; 95ms at temperature T s 258C and salinity S s 35. Considering stable boron isotopes 11 B and 10 B, the isotopic equilibration time is ; 125 ms. As a result, kinetic isotope effects during coprecipitation of boron in calcium carbonate are unlikely and therefore do not affect the use of stable boron isotopes as a paleo-pH recorder.

Conductivity isotherms of (CdTe)x(AgI)0.5-x/2(As2Te3)0.5-x/2 glasses (0.0 ≤ x ≤ 0.15) reveal a non-monotonic behavior with increasing CdTe content reminiscent of mixed cation effect in oxide and chalcogenide glasses. Nevertheless, the apparent similarity appears to be partly incorrect. Using 110m Ag tracer diffusion measurements, we show that semiconducting CdTe additions produce a dual effect: (i) decreasing the Ag + ion transport by a factor of ≈200 with a simultaneous increase of the diffusion activation energy, and (ii) increasing the electronic conductivity by 1.5 orders of magnitude. Consequently, the conductivity minimum at x = 0.05 reflects an ionic-to-electronic transport crossover; the silver ion transport number decreases by three orders of magnitude with increasing x.

The present study aimed at identifying potential correlations between rheological and optical properties of artery rings before and after cryopreservation, at different deformations, using experimental and simulation results. For experiments, an artery ring uniaxial mechanical test bench was coupled to fibered optical spectroscopes measuring 410 nm-excited autofluorescence and 650-850 nm elastically back-scattered intensity spectra. Furthermore, we developed a statistical simulation program of light transport and fluorescence adapted to our specific experimental configuration. Both spectroscopies gave intensity spectra with higher amplitude for the cryopreserved samples. These observations are to be related to histological modifications affecting the arterial wall of post-cryopreserved samples. We also observed significative spectral amplitude variations (increasing autofluorescence intensity and decreasing diffuse reflectance) as a function of the circumferential strains (0-60%).Using the simulation, we identified values of absorption, diffusion and anisotropy coefficients and their variations as a function of state (fresh-cryopreserved), strains (0, 30%, 60%) and wavelengths (700, 740, 780 nm). The media and the adventice are respectively less and more absorbing for post-cryopreserved rings and it is the opposite for the fresh ones at higher wavelengths. Absorption and diffusion coefficients are slightly higher, whatever the wavelengths and strains, for the fresh than for the cryopreserved samples.

The present experiments focused on the response of burning gaseous fuel jets to prescribed transverse acoustic excitation as a means of exploring the coupling of reactive, acoustic, and flow processes relevant to combustion instabilities. Single reactive methane microjets were exposed to transverse resonant standing wave disturbances within an acoustic waveguide for which a range of amplitudes of excitation were applied. Temporal flame response to acoustic excitation was studied via simultaneous phase-locked OH* chemiluminescence and visible imaging, and additionally via high speed, temporally resolved visible imaging. Quantification of flame dynamics was achieved for phase-locked data via the Rayleigh and temporal flame distortion measurements, and for time-resolved data via proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD). Characteristic signatures associated with various types of flame response were identified, including weakly oscillatory combustion, full-scale flame coupling and lock-in to excitation, and multi-mode flame dynamics preceding flame extinction. It was found that modal decomposition of flame dynamics via POD and DMD analysis revealed important additional dynamical features and signatures in metrics characteristic of transitions in the flame-acoustic coupling.

Flame structure and ignition and extinction processes associated with a strained fuel strip are explored numerically using detailed transport and complex kinetics for a propaneair reaction. Ignition modes are identified that are similar to those predicted by one-step activation energy asymptotics, i.e., modes in which diffusion flames can ignite as independent or dependent interfaces, and modes in which single premixed or partially premixed flames ignite. These ignition modes are found to be dependent on critical combinations of strain rate, fuel strip thickness, and initial reactant temperatures. Extinction in this configuration is seen to occur due to fuel consumption bv adjacent flames, although viscosity is seen to have the effect of delaying extinction by reducing the effective strain rate and velocity field experienced by the flames.

This study examines the factors influencing students' enrollment decisions at the National University of Battambang (NUBB), Cambodia. Specifically, it aims to (1) identify the key factors shaping students' enrollment decisions, (2) analyze students' perceptions of these factors, and (3) explore gender-based differences in enrollment decisions. A quantitative research approach was adopted, surveying 350 first-year students using a structured questionnaire comprising 33 items across seven categories. The analysis highlights four significant factors influencing enrollment decisions: parental influence, prospective career opportunities, family support, and personal characteristics. Conversely, the university's reputation and multidisciplinary aspects did not show statistically significant effects. Gender analysis revealed a significant difference in family influence, with females reporting more potent effects than males. These findings underscore the need for higher education institutions to prioritize personalized support systems, career development initiatives, and strategies to address gender-specific needs to enhance student enrollment. Recommendations include strengthening family engagement strategies and refining university offerings to align with students' career aspirations and personal goals.

T he effec t o f e ig ht o rga ni c co unter-io ns (a li phati c. both mo no and dica rboxy lates) on the s urface and mice ll ar behaviou r o f decy l and dodecy l ammo nium carboxy lates in aqu eous soluti on has been exa min ed by d iffe re nt physicochem ica l tec hn iques suc h as surface te nsio n, dye solubi lza tion, cond uc tance viscosit y a nd nu clea r magnetic reso nance. T he e ffec t of th ese cou nter-io ns as obse rved fro m surface ac ti vit y, a nd c riti ca l mi ce ll e co nce ntrati o n (CMC) is explain ed in term s of th eir conde nsati o n /pe ne trati o n o nto/int o th e m ice ll es. T he dec rease in C MC a nd in crease in cou nte r-io n bind in g of cati o nic surfac ta nts is attri buted to the inc reased hydrophobic ity in alky l c hain of co unte r-io ns. In th e case of mo nocarboxy late co unte r-io ns, CMC dec reases sig nifica ntl y in the ord er: II-butyrate < propi o nate < ace tate <fo rma te. w hile for dicarboxy lates decrease in CMC wi th in crease in nu mbe r o f ca rbon ato ms in the co unter-io n is less substant ial. Compa red to mo nocarboxy lates, di carboxy late counte r-io ns co nd e nse stro ng ly o nto the mi ce ll e su rface a nd thus are capab le of be in g easi ly incorpo rated into the mi celles and co nsequentl y show g rea te r sur face ac ti vity, and lower CMC o f cati o nic surfac tant. The effect o f te mperature o n surface activ ity and mi cell ar behav io ur of dec y l ammo niu m succ in ate is also re po rted.

Purpose-Through the reconstruction of the events of some foreign entrepreneurs who worked in the territory of the Italian city of Bari in the first half of the 19th century, this paper aims to analyze the role of entrepreneurial migration in the economic development of Apulia land in this period. Design/methodology/approach-This study adopts a theoretical framework that combines the concept of mixed embeddedness in a multifocal perspective, with the model of the diffusion of innovation focusing on the role of the so-called agency of actors, and of the network, in the dissemination of innovation. The theoretical framework is applied to multiple case studies to compare the evidence that emerged from the simultaneous analysis of several situations. Findings-By analyzing how innovations have spread within the network of entrepreneurs of that time, it is possible to identify some relevant aspects related to the mechanisms of dissemination of innovations in the context of entrepreneurial migration. Specifically, the opportunity structure is intended in an even broader sense than indicated in the classic approach to mixed embeddedness: it is considered as the result of the joint interaction of the political, institutional and economic context of several places, and the behavioral dynamics of several groups. Research limitations/implications-Due to the specific method chosen, the outcomes of the research might apply to a narrow context. Therefore, the results need to be tested and confirmed in further empirical studies, and by applying multiple research methods. Practical implications-Findings are useful and significant in the analysis of the link that exists between the diffusion of innovations and migrant entrepreneurship, and then the conclusions can be applied and extended to the current phenomenon of migration-related innovations, with specific reference to developing countries. Social implications-Findings can be applied and extended to the current phenomenon of migrationrelated innovations and highly skilled migration, with specific reference to developing countries.

Reaction dynamics involving subdiffusive species is an interesting topic with only few known results, especially when the motion of different species is characterized by different anomalous diffusion exponents. Here we study the reaction dynamics of a (sub)diffusive particle surrounded by a sea of (sub)diffusive traps in one dimension. Under some reasonable assumptions we find rigorous results for the asymptotic survival probability of the particle in most cases, but have not succeeded in doing so for a particle that diffuses normally while the anomalous diffusion exponent of the traps is smaller than 2/3.

A number of results for reactions involving subdiffusive species all with the same anomalous exponent γ have recently appeared in the literature and can often be understood in terms of a subordination principle whereby time t in ordinary diffusion is replaced by t γ. However, very few results are known for reactions involving different species characterized by different anomalous diffusion exponents. Here we study the reaction dynamics of a (sub)diffusive particle surrounded by a sea of (sub)diffusive traps in one dimension. We find rigorous results for the asymptotic survival probability of the particle in most cases, with the exception of the case of a particle that diffuses normally while the anomalous diffusion exponent of the traps is smaller than 2/3.

While there are many well-known and extensively tested results involving diffusion-limited binary reactions, reactions involving subdiffusive reactant species are far less understood. Subdiffusive motion is characterized by a mean square displacement x 2 ∼ t γ with 0 < γ < 1. Recently we calculated the asymptotic survival probability P (t) of a (sub)diffusive particle (γ ′) surrounded by (sub)diffusive traps (γ) in one dimension. These are among the few known results for reactions involving species characterized by different anomalous exponents. Our results were obtained by bounding, above and below, the exact survival probability by two other probabilities that are asymptotically identical (except when γ ′ = 1 and 0 < γ < 2/3). Using this approach, we were not able to estimate the time of validity of the asymptotic result, nor the way in which the survival probability approaches this regime. Toward this goal, here we present a detailed comparison of the asymptotic results with numerical simulations. In some parameter ranges the asymptotic theory describes the simulation results very well even for relatively short times. However, in other regimes more time is required for the simulation results to approach asymptotic behavior, and we arrive at situations where we are not able to reach asymptotia within our computational means. This is regrettably the case for γ ′ = 1 and 0 < γ < 2/3, where we are therefore not able to prove or disprove even conjectures about the asymptotic survival probability of the particle.

This paper investigates the diffusion and institutionalization of change in formal organization structure, using data on the adoption of civil service reform by cities. It is shown that when civil service procedures are required by the state, they diffuse rapidly and directly from the state to each city. When the procedures are not so legitimated, they diffuse gradually and the underlying sources of adoption change overtime. In the latter case, early adoption of civil service by cities is related to internal organizational requirements, with city characteristics predicting adoption, while late adoption is related to institutional definitions of legitimate structural form, so that city characteristics no longer predict the adoption decision. Overall, the findings provide strong support for the argument that the adoption of a policy or program by an organization is importantly determined by the extent to which the measure is institutionalizedwhether by law or by gradual legitimation.*

Abbreviations used: CRP, cysteine and glycine-rich protein; LIM, speci®c double zinc ®nger domain; LIM1, aminoterminal LIM domain of CRP protein; LIM2, carboxyl-terminal LIM domain of CRP protein; CSRP, gene encoding CRP protein; CRIP, cysteine-rich intestinal protein; PCR, polymerase chain reaction; NOE, nuclear Overhauser effect; HSQC, heteronuclear single-quantum correlation spectroscopy; T 1 , longitudinal relaxation time; T 2 , transverse relaxation time.

We present a fluorescence fluctuation image correlation analysis method that can rapidly and simultaneously measure the diffusion coefficient, photoblinking rates, and fraction of diffusing particles of fluorescent molecules in cells. Unlike other image correlation techniques, we demonstrated that our method could be applied irrespective of a non-uniformly distributed, immobile blinking fluorophore population. This allows us to measure blinking and transport dynamics in complex cell morphologies, a benefit for a range of super-resolution fluorescence imaging approaches that rely on probe emission blinking. Furthermore, we showed that our technique could be applied without directly accounting for photobleaching. We successfully employed our technique on several simulations with realistic EMCCD noise and photobleaching models, as well as on Dronpa-C12 labeled beta-actin in living NIH/3T3 and HeLa cells. We found that the diffusion coefficients measured using our method were consistent with previous literature values. We further found that photoblinking rates measured in the live HeLa cells varied as expected with changing excitation power.

Income convergence across countries turns on whether technological knowledge spillovers are global or local. I estimate the amount of spillovers from R&D expenditures on a geographic basis, using a new data set which encompasses most of the world&#39;s innovative activity between 1970 and 1995. I find that technology is to a substantial degree local, not global, as the benefits from spillovers are declining with distance. The distance at which the amount of spillovers is halved is about 1,200 kilometers. I also find that over time, technological knowledge has become considerably more global. Moreover, language skills are important for spillover diffusion.

A new cellular-automaton model for fluid dynamics is introduced in this paper, that focus on discrete models based on point particles moving on a lattice in order to mimic a fully molecular dynamics. The CA model uses an easily implementable, deterministic pair of interaction rules. Therefore, we combine the advantage of the low computational cost of CA and its ability to mimic the realistic fluid dynamics to develop a new animating framework for computer graphics applications. 2000 Mathematics Subject Classification. Primary 68Q80; Secondary 37B15.

We study a class of statistical systems which simulate 3D gonihedric system on euclidean lattice. We have found the exact partition function of the 3D-model and the corresponding critical indices analysing the transfer matrix K(P i , P f) which describes the propagation of loops on a lattice. The connection between 3D gonihedric system and 2D-Ising model is clearly seen.

We study a class of statistical systems which simulate 3D gonihedric system on euclidean lattice. We have found the exact partition function of the 3D-model and the corresponding critical indices analysing the transfer matrix K(P i , P f) which describes the propagation of loops on a lattice. The connection between 3D gonihedric system and 2D-Ising model is clearly seen.

Proton diffusion in the co-PNIS85/15 membrane was investigated in the temperature range from 200 to 363 K at different water contents (4 ≤ λ ≤ 21) using 1H SFG NMR diffusometry. At high hydration values, above the threshold value λ0 = 10.5, the ln(DNMR(1/T)) dependences show two different activation modes, separated by a crossover point Tcr ≈ 250–260 K. At temperatures above Tcr, the activation energy is Ea ~ 0.20 eV, which is close to the value for bulk water (Ea ~ 0.17 eV). At temperatures below the crossover point, the ln(DNMR(1/T)) dependences for different water contents merge together into one straight line characterized by a much higher Ea = 0.46 eV. At low hydration values λ &lt; λ0, the activation energies for the high-temperature and low-temperature modes converge, so that at λ = 4, the dependence ln(DNMR(1/T)) is described by one straight line throughout the studied temperature range with Ea = 0.38 eV. A model is proposed that phenomenologically describes the diffusion in...

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

This study examined the effects of traversing cracks of concrete on chloride diffusion. Three different concretes were tested: one ordinary concrete (OC) and two high performance concretes with two different mix designs (HPC and HPCSF, with silica fume) to show the influence of the water/cement ratio and silica fume addition. Cracks with average widths ranging from 30 to 250 μm, were induced using a splitting tensile test. Chloride diffusion coefficients of concrete were evaluated using a steady-state migration test. The results showed that the diffusion coefficient of uncracked HPCSF was less than HPC and OC, but the cracking changed the material behavior in terms of chloride diffusion. The diffusion coefficient increased with the increasing crack width, and this trend was present for all three concretes. The diffusion coefficient through the crack D cr was not dependent of material parameters and becomes constant when the crack width is higher than ∼80 μm, where the value obtained was the diffusion coefficient in free solution.

A method to simultaneously measure the moisture diffusion coefficient, D θ , of unsaturated concrete, and the saturated concrete hydraulic conductivity, K l , was developed for cylindrical specimens placed on a container filled with water that could be maintained at a given hydraulic pressure. Ordinary Portland cement Concrete (OPC) with a moderate and High Performance Concrete (HPC) with a low water to cement ratio were tested. The time dependent distribution of water content in the specimens was measured using a non-intrusive method based on gamma-ray attenuation. The measurements were conducted with varying hydraulic head (positive or null). Boltzmann's transformation was used to analyze the experimental results obtained at different hydraulic pressures and the difference between the null (or atmospheric) and positive pressure results is used to accurately determine K l and also D θ. This paper will present the results obtained using this original method, possible interpretations and future research.

Measurement of exhaled breath temperature(EBT) has been increasingly used as asimple and reproducible marker of airwayinflammation [1,2]. Temperature of deep structures of lungs is mainly determined by amount of blood flowing along rich vascular bed of alveoli which transfers its energy to alveolar gas. Inflammation or remodeling of airway walls which could modify blood flow might be reflected in the temperature of outgoing air or EBT [3]. Paredi, et al. [2,4] have reported faster rise of EBT in asthma patients and its significant correlation with exhaled nitric oxide and slower rise of EBT in chronic obstructive pulmonary disease patients. As cystic fibrosis (CF) is characterized by airway inflammation [5] and remodeling [6], we hypothesized that an altered bronchial blood flow will affect EBT in these patients. This study was thus designed and conducted to measure EBT in children with CF and compare it with healthy controls.

The mechanisms of moisture diffusion in wood are not yet fully understood, due to the complex and hierarchical structure of the wood cell wall constituents. To investigate the diffusion mechanism in such hierarchical structure, fractal geometry analysis was used as proper tool. The objective of this study is to develop a theoretical fractal moisture diffusion model for wood cell wall by taking into consideration its structural geometry and to upscale that model to gross wood by employing electrical resistance modeling and validation. The proposed fractal diffusion model is a function of fractal dimensions, porosity, and pore size distribution of the wood cell wall as well as ambient conditions such as moisture content, temperature, and inverse slope of the sorption isotherm. The water vapor sorption data that was used to drive the experimental diffusion coefficient of various wood types were studied using the dynamic sorption method. Mercury intrusion porosimetry was used to explore the detailed structural parameters of pore size distributions and calculate the pore fractal dimension. The derived fractal diffusion model was validated using experimental and data calculated by a past published model. The trends for diffusion coefficients predicted by the fractal model were similar to the experimental and published data. The developed model was successfully predicted the diffusion coefficients at low moisture contents. Pore fractal dimension, tortuous fractal dimension, and pore size ratio were negatively correlated to fractal diffusivity, while the porosity was positively correlated. The findings are expected to predict the moisture transport and the wood cell wall geometric properties through the fractal dimensions of the structure.