Terms Of Effective Diffusivity Research Articles

MODELING OPEN AIR AND SHADE DRYING OF CORYMBIA CITRIODORA LEAVES FOR THE ESSENTIAL OIL PRODUCTION

In the literature, the drying mechanism were generally analyzed in terms of effective diffusivity through the pseudo first order diffusion model. This process was revisited through the modified Peleg model, assuming the drying as a moisture desorption versus drying time. The leaves of Corymbia citriodora acclimatized in the Congo Brazzaville “Plateau des Cataractes” were dried in open air and under shade thanks to a domestic scale of essential oil production. One obtains following model parameters: kinetic constant k1: 0.8555 - 2.1355 d.(g/g)-1, extraction capacity constant K2: 1.5255 - 1.8733 (g/g)-1; end equilibrium moisture X∞ = 0.53 - 0.66 g/g. and first order drying kinetic constant k = K2/k1: 1.71 - 1.78 d-1. Pseudo first order diffusion model fits experimental data with k = 0.368 - 0.587 d-1 and t1/2 = 1,18 - 1,88 d.. These results needed for the optimization of proccess and sizing equipments came from a fast graphic data processing, with low computer inputs.

Relationship of Different Properties from Non-Destructive Testing of Heavy Concrete from Magnetite and Serpentinite.

Radiation-shielding concrete has been analyzed by several methods of destructive and non-destructive testing (NDT). Concretes made of crushed basalt, magnetite, serpentinite, and two different types of cement (Portland cement CEM I and slag cement CEM III/A) were studied. In this study, we analyzed concrete columns with a height of 1200 mm and a cross-section of 200 × 200 mm2. The top and bottom of the column were analyzed using data from compressive strength, dynamic modulus of elasticity, water penetration, and diffusion coefficients derived from the electrical resistivity test. This article presents the properties of fresh concrete and concrete after two years of setting. It was determined how the different ratios of basalt, magnetite, and serpentinite affect the individual measured parameters. Furthermore, correlation relations between individual resulting values were analyzed. It was observed that compressive strength generally does not correlate with other results. The diffusion coefficient correlated well with density and water penetration. Little or no correlation was observed in the diffusion coefficient with compressive strength and modulus of elasticity. The results of the study make it possible to refine the testing of heavy concretes in terms of electrical resistivity, and point to the possible use of NDT methods. The results also show which composition of heavy concrete is better in terms of effective diffusivity.

Water diffusion measurements in cement paste, mortar and concrete using a fast NMR based technique

With a NMR based fast diffusion measurement technique we performed a comprehensive experimental program on 30 samples to measure the pore diffusion coefficient in two series of cement pastes, mortar and concrete made with an ordinary Portland cement (CEM I) and a composite cement (CEM V). In addition, measurements were also possible in the presence of fibers and their effect could be evaluated. The principle is to monitor a deuterium-water exchange in a well-defined cylindrical geometry. The NMR technique allows the measurement of 1H concentration inside the sample as a function of time, while ignoring 1H outside the sample. Using well known analytical formulations, the diffusion curve can be fitted to obtain the pore diffusion coefficient of the material.The results are first presented in terms of the measured pore diffusion coefficients at 30 °C characterizing the porous network independently of porosity. For CEM I based materials, the measured values are Dp = 7.6 ± 1.4x10−12 m2/s for pastes, 40 ± 20x10−12 m2/s for pastes with fibers, 9.5 ± 0.6x10−12 m2/s for mortars, 4.4 ± 0.2x10−12 m2/s for concretes and 28 ± 7x10−12 m2/s for concretes with fibers. For CEM V based materials, the measured values are Dp = 1.1 ± 0.4x10−12 m2/s for pastes, 9.3 ± 2.7x10−12 m2/s for pastes with fibers, 0.8 ± 0.1x10−12 m2/s for mortars, 5.9 ± 2.2x10−12 m2/s for concretes and 5.3 ± 0.8x10−12 m2/s for concretes with fibers. In all cases, the fibers produce an increase of Dp together with a sample dependent result within a set of 3. When expressed in terms of effective diffusion by taking into account the porosity that can be exchanged by D2O estimated during the diffusion experiments, the results were found in agreement with a few existing values measured with HTO through diffusion techniques (Dp = 2.1 ± 0.4×10−12 m2/s for the CEMI paste, 1.1 ± 0.06×10−12 m2/s for the CEMI mortar, 0.12 ± 0.02×10−12 m2/s for the CEMV concrete with fibers).

Quantifying Tortuosity of Porous Li-Ion Battery Electrodes: Comparing Polarization-Interrupt and Blocking-Electrolyte Methods

Ionic mass transport including electrolyte diffusivity and conductivity depends on the geometric tortuosity of the electrode. This paper compares two experimental methods that determine tortuosity based on diffusivity or conductivity. The polarization-interrupt method previously developed by our group determines tortuosity in terms of effective diffusivity. The blocking-electrolyte method proposed by Gasteiger and coworkers determines tortuosity in terms of effective ionic conductivity and is analyzed using a generalized transmission-line model to account for multiple sources of impedance. Tortuosity of several commercial-quality electrodes was measured using both methods, producing reasonable agreement between the two methods in most cases. The advantages and disadvantages of each method and variables that can affect the accuracy of the measurement, such as electrode wetting and model fitting, are discussed. For particular electrodes, one method may be advantageous or more conveniently applied than the other.

Stable dissipative optical vortex clusters by inhomogeneous effective diffusion.

We numerically show the generation of robust vortex clusters embedded in a two-dimensional beam propagating in a dissipative medium described by the generic cubic-quintic complex Ginzburg-Landau equation with an inhomogeneous effective diffusion term, which is asymmetrical in the two transverse directions and periodically modulated in the longitudinal direction. We show the generation of stable optical vortex clusters for different values of the winding number (topological charge) of the input optical beam. We have found that the number of individual vortex solitons that form the robust vortex cluster is equal to the winding number of the input beam. We have obtained the relationships between the amplitudes and oscillation periods of the inhomogeneous effective diffusion and the cubic gain and diffusion (viscosity) parameters, which depict the regions of existence and stability of vortex clusters. The obtained results offer a method to form robust vortex clusters embedded in two-dimensional optical beams, and we envisage potential applications in the area of structured light.

Modeling and Simulation of Cu Diffusion in Porous Low-k Dielectrics

Integrating nanometer sized pores into low-k ILD films is one of the approaches to lower the RC signal delay and thus help sustain the continued scaling of micro-electronic devices. While increasing porosity of porous dielectrics achieves the desirable lowering of the dielectric constant (k), it also creates a myriad of reliability and implementation issues. One of the problems is the little understood metal diffusion in porous media. Here, we present a rigorous simulation method of Cu diffusion based on master equation with elementary jump probabilities within the contiguous dielectric film, along the pore boundary, from the dielectric matrix to the pore boundary, and from the pore boundary to the matrix material. In view of the diffusional jump distance being as large as 2 nm, the nano-pores being on a similar length scale, and the film thickness being only a few tens of nanometers, the conventional diffusion equation in differential equation form is grossly inadequate and elementary jump frequencies are required for a proper description of the Cu diffusion in porous dielectric. The present atomistic approach allows a consistent implementation of Cu ion drift in electric field by lowering and raising of the diffusion barriers along the field direction. Two numerical methods are being used to evaluate the atomistic Cu transport: 1) Diffusion tensor theory (4th rank tensor in 2D, 9th rank in 3D), 2) Sequential lattice point evaluation of elementary diffusion jumps. The 2nd method is very efficient in 3D, where the simulation time increases only linearly with the dimension of the matrix, while the 1st method allows an easy implementation of jump frequencies at the boundaries of the film and pore boundaries.

Effect of flow and peristaltic mixing on bacterial growth in a gut-like channel

The ecology of microbes in the gut has been shown to play important roles in the health of the host. To better understand microbial growth and population dynamics in the proximal colon, the primary region of bacterial growth in the gut, we built and applied a fluidic channel that we call the "minigut." This is a channel with an array of membrane valves along its length, which allows mimicking active contractions of the colonic wall. Repeated contraction is shown to be crucial in maintaining a steady-state bacterial population in the device despite strong flow along the channel that would otherwise cause bacterial washout. Depending on the flow rate and the frequency of contractions, the bacterial density profile exhibits varying spatial dependencies. For a synthetic cross-feeding community, the species abundance ratio is also strongly affected by mixing and flow along the length of the device. Complex mixing dynamics due to contractions is described well by an effective diffusion term. Bacterial dynamics is captured by a simple reaction-diffusion model without adjustable parameters. Our results suggest that flow and mixing play a major role in shaping the microbiota of the colon.

Evaluation of Leakage Through Graphite-Based Compression Packing Rings

The prediction of leakage is one of the most challenging tasks when designing bolted flanged connections and industrial valves. Failure of these pressure vessel components can cause shutdowns but also accidents, loss of revenue, and environmental damages. With the strict regulations on fugitive emissions and environmental protection laws new tightness-based standards and design methods are being adopted to improve the sealing performance of bolted joints and valves. In addition, there is a practical interest in using a reliable correlation that could predict leak rates of one fluid on the basis of tests carried out with another on compressed packings. The paper presents an innovative approach to accurately predict and correlate leak rates in porous braided packing rings. The approach is based on Darcy–Klinkenberg to which a modified effective diffusion term is added to the equation. Experimentally measured gas flow rates were performed on a set of graphite-based compression packing rings with a large range of leak rates under isothermal steady conditions. Leakage from three different gases namely helium, nitrogen, and argon were used to validate the developed correlation. In the presence of the statistical properties of porous packings, the leak rates for different gases can be predicted with reasonable accuracy.

Hot and Crowded: New Insights into the Dynamics of Thermophilic Enzymes from Multiscale Modeling

Understanding how the amino acid sequence of a protein determines its three-dimensional structure, dynamics, and, ultimately, its biological function remains one of the most fundamental biophysical problems. Although this problem is unlikely to be solved in a single step, one way of breaking it down is offered to us by nature's diversity itself. Adaptation to extreme environmental conditions, e.g., high temperatures, led to the evolution of thermophilic enzymes that are not only stable at temperatures beyond 60°C, but also exhibit their maximum activity at elevated temperatures. Remarkably, these thermophilic enzymes still maintain a significant degree of homology to their mesophilic counterparts, enzymes that catalyze the same reactions in species that thrive at moderate temperatures. Studying mesophilic/thermophilic enzyme homologs from different species side-by-side enables an assessment of how moderate changes in sequence and structure alter the enzyme's properties toward higher thermostability and high activity at elevated temperatures. Such a comparison also provides additional insights into structure-function relationships in general. The requirements for thermostability and enzyme activity at elevated temperatures are still under debate. Thermophilic enzymes with an increased rigidity compared to their mesophilic counterparts are reported in the literature, although there are also reported examples of thermophilic enzymes with an increased flexibility. Recently, increased resilience, manifested as a weak temperature dependence of protein flexibility measured by elastic incoherent neutron scattering (EINS), has been proposed (1) as an additional characteristic of thermophilic adaptation. EINS is a versatile tool that allows quantification of the flexibility of a protein via mean-squared fluctuations of nonexchangeable hydrogen atoms on picosecond-nanosecond timescales. In powder samples in which translational and rotational diffusion of the molecule as a whole are suppressed, EINS probes internal motions, and hence protein flexibility, directly. However, accurate extraction of internal motions from EINS data on proteins in solution requires deconvolution of the contributions of internal dynamics and translational and rotational diffusion to the observed atomic motion. These problems have been addressed, e.g., via an effective diffusion term after comparison to measurements on hydrated protein powders (2) and by molecular dynamics (MD) simulation (3). When comparing the dynamics between proteins of similar mass, shape, and size, such as thermophilic/mesophilic pairs of enzymes, it is reasonable to assume very similar diffusive dynamics. Under such an assumption, differences in the overall dynamics can be assigned to differences in the internal motions/structural flexibility. However, under crowding conditions, e.g., at the high protein concentrations used in solution EINS experiments, as well as under physiological conditions in the cell, this assumption may break down due to specific or nonspecific interactions, which may have distinct effects on the diffusive motion of the compared proteins. Marcos et al. (4) push our understanding of this matter to a new level by combining Brownian dynamics of the crowded protein solution with atomistic MD simulations of the isolated protein. With this multiscale approach, they are able to cleanly separate the contributions to the scattering function and extracted mean-squared fluctuations from internal dynamics from the rotational and diffusive motion of the molecule as a whole. Marcos et al. (4) consider a pair of homologous thermophilic and mesophilic enzymes, malate dehydrogenase from Methanococcus jannaschii and lactate dehydrogenase from Oryctolagus cunniculus, which were studied previously using EINS experiments (1). Marcos et al. not only confirm the previously observed increased flexibility of the thermophilic protein compared to the mesophilic one, but they also find that distinct diffusional motion of the two proteins under crowding conditions contributes significantly to the experimentally observed differences in overall dynamics and their temperature dependence. Moreover, their simulations reveal that the greater number of charged residues on the surface of the thermophilic enzyme results in significant attractive interactions in the crowded solution, which effectively reduces the diffusional mobility. The lower dielectric constant of water at increasing temperature further increases the strength of these electrostatic interactions, and compensates the increase in diffusive motion with increasing temperature. The slower diffusive motion, in turn, compensates the increased internal motion in the thermophilic versus the mesophilic enzyme, and this translates into the higher resilience, namely the weaker increase in overall dynamics with increasing temperature, observed via the fluctuations of scattering hydrogen atoms for the thermophilic enzyme. The article by Marcos et al. (4) exposes a new fundamental difference between thermophilic enzymes and their mesophilic counterparts, which typically carry a less amount of charged residues on their solvent exposed surface (5). The authors speculate that the increased electrostatic interactions for thermophilic enzymes may actually result in diffusion properties at the enzymes' optimum temperature that are comparable to those of mesophilic enzymes at moderate temperatures. Since diffusion plays a crucial role in enzymatic catalysis, the tuning of diffusive motion to challenging environmental conditions might be a key aspect of the adaptation of extremophilic enzymes for optimal activity.

Stable topological modes in two-dimensional Ginzburg-Landau models with trapping potentials

Complex Ginzburg-Landau (CGL) models of laser media (with cubic-quintic nonlinearity) do not contain an effective diffusion term, which makes all vortex solitons unstable in these models. Recently, it has been demonstrated that the addition of a two-dimensional periodic potential, which may be induced by a transverse grating in the laser cavity, to the CGL equation stabilizes compound (four-peak) vortices, but the most fundamental ``crater-shaped'' vortices (CSVs), alias vortex rings, which are essentially squeezed into a single cell of the potential, have not been found before in a stable form. In this work we report on families of stable compact CSVs with vorticity $S=1$ in the CGL model with the external potential of two different types: an axisymmetric parabolic trap and the periodic potential. In both cases, we identify a stability region for the CSVs and for the fundamental solitons ($S=0$). Those CSVs which are unstable in the axisymmetric potential break up into robust dipoles. All the vortices with $S=2$ are unstable, splitting into tripoles. Stability regions for the dipoles and tripoles are identified, too. The periodic potential cannot stabilize CSVs with $S\ensuremath{\geqslant}2$ either; instead, families of stable compact square-shaped quadrupoles are found.

Infrared-Convective Drying of Organic Pigments

The drying of organic pigments is a challenging assignment due to the complex relationship between heat and mass transfer and the quality attributes such as color, shade, and strength. There is an urgent need to address the drying technology-related issues of this industrially important class of specialty chemicals. The widely used tray dryers and band dryers need further attention due to abysmally low energy efficiency. One of the ways to overcome the longer drying time is to make use of infrared source in addition to convective air drying. The present article discusses the effect of combinatorial IR-convective drying on the quality aspect of organic pigments. The heat and mass transfer rates were analyzed in terms of Biot number to ascertain the role of infrared in bringing down the drying time without compromising the pigment qualities. The mathematical analysis of drying of preformed pellet of pigments was carried out in terms of effective diffusivity, which was obtained in the range of 10−9 to 10−10 m2/s.

Turbulent transport in the TCV SOL

From probe measurements in the far SOL of TCV it is demonstrated that while the particle density profile becomes increasingly broader with increasing line averaged density, the radial variation of the fluctuation statistics remains the same. Excellent agreement is found between the experimental measurements and an interchange turbulence simulation, revealing intermittent plasma transport dominated by radial motion of plasma filaments. On the basis of this favourable code–experiment agreement, it is concluded that no reliable parameterization exists for the turbulent particle flux in terms of effective diffusion and convection coefficients.

Equilibrium and kinetics for temperature swing adsorption of a target metal on molecular imprinted thermosensitive gel adsorbents

A novel thermosensitive gel adsorbent, which adsorbs and/or desorbs a specific heavy metal, as a function of gel shrinking/swelling by temperature swing was developed. The gel, a copolymer of N-isopropylacrylamide as a thermosensitive component, 4-(vinylbenzyl)ethylenediamine (VBEDA) as a chelating agent, and cross-linker, was prepared by copolymerization by means of a molecular imprinting technique using Cu(II) ion as a template. Equilibria and kinetics for the adsorption/desorption for a temperature swing of 307/283 K were investigated. Adsorption equilibria, expressed as the Langmuir isotherms, indicated that one Cu molecule is strongly coordinated to two VBEDA groups at 307 K and weakly coordinated to one VBEDA group at 283 K. The rates of adsorption and desorption were dominantly expressed with the diffusion equation within the gel and were evaluated in terms of effective diffusivity. The equilibria and kinetics data shows the thermosensitive reconstruction/destruction of an adsorption site composed of two VBEDA groups.

Electrochemical identity of copper hexacyanoferrate in the solid-state: evidence for the presence and redox activity of both iron and copper ionic sites

We describe the electrochemical behavior of solid copper hexacyanoferrate (powder) investigated in the absence of contact with a liquid external supporting electrolyte. In addition to a typical hexacyanoferrate(III,II) redox transition, the system is characterized by a second electrode process which appears at more negative potentials. Diagnostic experiments, which include spectrochemical and solid-state voltammetric characterization, support our view that the latter redox reaction most likely originates from reduction of the system's lattice copper(II) ions. The overall dynamics of charge transport in the material, when discussed in terms of effective diffusion, is moderately high (on the level of 10 −8 cm 2 s −1). Comparison has been also made to the electrochemical behavior of solid Prussian blue and to the voltammetric characteristics of conventional electrodes modified with thin films of copper hexacyanoferrate.

Drying of pear d’Anjou with and without osmotic dehydration

This work compares the drying behavior exhibited by in natura and by osmotic dehydrated pears. The dryer was a convective vertical tray dryer. The drying was analyzed in terms of effective diffusivity and drying rates. The effective diffusivity varied from 1.59×10 −10 to 7.64×10 −10 m 2/s for in natura pear and from 1.87×10 −10 to 8.12×10 −10 m 2/s for the pears after osmotic dehydration. In the case of moisture content below 1.0 kg w/kg dm, the drying rates only depends on temperature, as internal resistance to moisture transfer prevails.