Diffusion Process (diffusion + process)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Neutron Reflectometry: A Tool to Investigate Diffusion Processes in Solids on the Nanometer Scale,

ADVANCED ENGINEERING MATERIALS, Issue 6 2009
Harald Schmidt
Abstract The investigation of self-diffusion for the characterization of kinetic process in solids is one of the most fundamental tasks in materials science. We present the method of neutron reflectometry (NR), which allows the detection of extremely short diffusion lengths in the order of 1,nm and below at corresponding low self-diffusivities between 10,25 and 10,20,m2 s,1. Such a combination of values cannot be achieved by conventional methods of diffusivity determination, like the radiotracer method, secondary ion mass spectrometry, quasielastic neutron scattering, or nuclear magnetic resonance. Using our method, the extensive characterization of materials which are in a non-equilibrium state, like amorphous or nanocrystalline solids becomes possible. Due to the small experimentally accessible diffusion length microstructural changes (grain growth and crystallization) taking place simultaneously during the actual diffusion experiment can be avoided. For diffusion experiments with NR isotope multilayers are necessary, which are chemical homogeneous but isotope modulated films. We illustrate the basic aspects and potential of this technique using model systems of different classes of materials: single crystalline germanium, amorphous silicon nitride, and nanocrystalline iron. [source]


Who Learns from What in Policy Diffusion Processes?

AMERICAN JOURNAL OF POLITICAL SCIENCE, Issue 3 2010
Fabrizio Gilardi
The idea that policy makers in different states or countries may learn from one another has fascinated scholars for a long time, but little systematic evidence has been produced so far. This article improves our understanding of this elusive argument by distinguishing between the,policy,and,political,consequences of reforms and by emphasizing the conditional nature of learning processes. Using a directed dyadic approach and multilevel methods, the analysis of unemployment benefits retrenchment in OECD countries demonstrates that policy makers learn selectively from the experience of others. Right governments tend to be more sensitive to information on the electoral consequences of reforms, while left governments are more likely to be influenced by their policy effects. [source]


Characterization of Diffusion Processes of Pharmacologically Relevant Molecules through Polydimethylsiloxane Membranes by Confocal Micro-resonance Raman Spectroscopy

CHEMPHYSCHEM, Issue 3 2003
Michael Schmitt
Focus on diffusion. Confocal micro resonance Raman spectroscopy (see picture) was applied to investigate the kinetics of diffusion processes of , -carotene dissolved in DMSO through polydimethylsiloxane membranes. By using this technique the dynamics of the diffusion process at well-defined points inside the membrane and the formation of a concentration gradient before reaching steady-state conditions at specific points inside the membrane can be observed. [source]


STRUCTURAL COVARIATES OF U.S. COUNTY HOMICIDE RATES: INCORPORATING SPATIAL EFFECTS,

CRIMINOLOGY, Issue 3 2001
ROBERT D. BALLER
Spatial analysis is statistically and substantively important for macrolevel criminological inquiry. Using county-level data for the decennial years in the 1960 to 1990 time period, we reexamine the impact of conventional structural covariates on homicide rates and explicitly model spatial effects. Important findings are: (1) homicide is strongly clustered in space; (2) this clustering cannot be completely explained by common measures of the structural similarity of neighboring counties; (3) noteworthy regional differences are observed in the effects of structural covariates on homicide rates; and (4) evidence consistent with a diffusion process for homicide is observed in the South throughout the 1960,1990 period. [source]


Emissions of greenhouse gases attributable to the activities of the land transport: modelling and analysis using I-CIR stochastic diffusion,the case of Spain

ENVIRONMETRICS, Issue 2 2008
R. Gutiérrez
Abstract In this study, carried out on the basis of the conclusions and methodological recommendations of the Fourth Assessment Report (2007) of the International Panel on Climate Change (IPCC), we consider the emissions of greenhouse gases (GHG), and particularly those of CO2, attributable to the activities of land transport, for all sectors of the economy, as these constitute a significant proportion of total GHG emissions. In particular, the case of Spain is an example of a worrying situation in this respect, both in itself and in the context of the European Union. To analyse the evolution, in this case, of such emissions, to enable medium-term forecasts to be made and to obtain a model that will enable us to analyse the effects of possible corrector mechanisms, we have statistically fitted a inverse Cox-Ingersoll-Ross (I-CIR) type nonlinear stochastic diffusion process, on the basis of the real data measured for the period 1990,2004, during which the Kyoto protocol has been applicable. We have studied the evolution of the trend of these emissions using estimated trend functions, for which purpose probabilistic complements such as trend functions and stationary distribution are incorporated, and a statistical methodology (estimation and asymptotic inference) for this diffusion, these tools being necessary for the application of the analytical methodology proposed. Copyright © 2007 John Wiley & Sons, Ltd. [source]


NMR Studies of Proton Transport in Anhydrous Polymer Electrolytes for High Temperature Fuel Cells,

FUEL CELLS, Issue 3-4 2008
H. A. Every
Abstract This paper presents an NMR study of the dynamic processes related to proton transport in a new polymer consisting of two blocks , poly(2,6-diphenylphenol) (P3O) and an imidazole functionalised poly(2,6-dimethylphenol) (imi-PPE) , and subsequently doped with polyphosphoric acid (PPA). From 1H and 31P NMR relaxation and diffusion measurements of the individual homopolymers and block copolymer, it was observed that addition of PPA significantly enhanced the mobility of imi-PPE and the imi-block copolymer, but not of P3O. The similarity in 1H T2 values between imi-PPE and the imi-block copolymer suggests that the relaxation behaviour in the block copolymer is dominated by the imi-PPE phase. 1H diffusion in P3O and the imi-block copolymer were comparable to pure PPA, suggesting that the proton diffusion is similar in each case. For imi-PPE, the diffusion coefficients were several orders of magnitude lower, reflecting a restricted diffusion process that is not indicative of the proton mobility. For all three polymers, the 31P T2 relaxation behaviour and inability to measure 31P diffusion coefficients imply hindered translational motion of the phosphonate groups. From these results, it can be concluded that hydrogen bonds between the phosphoric acid and the polymer form a network that facilitates proton transport via a hopping mechanism. [source]


The effect of water content on proton transport in polymer electrolyte membranes

FUEL CELLS, Issue 3-4 2002
P. Commer
Abstract We investigate proton transport in a polymer electrolyte membrane using continuum theory and molecular dynamics (MD) computer simulations. Specifically our goal is to understand the possible molecular origin of the effect of water content on the activation energy (AE) and pre-exponential factor of proton conductivity, in comparison with experimental observations reported for Nafion, where a decrease of AE with increasing water content has been observed. We study proton diffusion in a single pore, using a slab-like model. We find that although the average proton diffusion coefficient is several times smaller in a narrow pore than in a wide water-rich pore, its AE is almost unaffected by the pore width. This contradicts an earlier proposed conjecture that the sizable Coulomb potential energy barriers near the lattice of immobile point-like SO3, groups increase the AE in a narrow pore. Here we show that these barriers become smeared out by thermal motion of SO3, groups and by the spatial charge distribution over their atoms. This effect strongly diminishes the variation of the AE with pore width, which is also found in MD simulations. The pre-exponential factor for the diffusion process, however, decreases, indicating a limited number of pathways for proton transfer and the freezing out of degrees of freedom that contribute to the effective frequency of transfer. Decreasing the pore size diminishes bulk-like water regions in the pore, with only less mobile surface water molecules remaining. This hampers proton transfer. The increase of AE takes place only if the thermal motion of the SO3, head groups freezes out simultaneously with decreasing water content, but the effect is not profound. The stronger effect observed experimentally may thus be associated with some other rate-determining consecutive process, concerned with polymer dynamics, such as opening and closing of connections (bridges) between aqueous domains in the membrane under low water content. [source]


The maximum principle violations of the mixed-hybrid finite-element method applied to diffusion equations

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2002
H. Hoteit
Abstract The abundant literature of finite-element methods applied to linear parabolic problems, generally, produces numerical procedures with satisfactory properties. However, some initial,boundary value problems may cause large gradients at some points and consequently jumps in the solution that usually needs a certain period of time to become more and more smooth. This intuitive fact of the diffusion process necessitates, when applying numerical methods, varying the mesh size (in time and space) according to the smoothness of the solution. In this work, the numerical behaviour of the time-dependent solutions for such problems during small time duration obtained by using a non-conforming mixed-hybrid finite-element method (MHFEM) is investigated. Numerical comparisons with the standard Galerkin finite element (FE) as well as the finite-difference (FD) methods are checked. Owing to the fact that the mixed methods violate the discrete maximum principle, some numerical experiments showed that the MHFEM leads sometimes to non-physical peaks in the solution. A diffusivity criterion relating the mesh steps for an artificial initial,boundary value problem will be presented. One of the propositions given to avoid any non-physical oscillations is to use the mass-lumping techniques. Copyright © 2002 John Wiley & Sons, Ltd. [source]


Awakening dynamics via passive coupling and synchronization mechanism in oscillatory cellular neural/nonlinear networks

INTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 5-6 2008
István Szatmári
Abstract We have studied synchronization mechanism in locally coupled nonlinear oscillators. Here, synchronization takes place by passive coupling based on a reaction,diffusion process. We will compare this mechanism with basic synchronization techniques, showing their similarities and specific properties. In addition to synchronization, passive and local coupling can also ,awaken' non-oscillating cell circuits and trigger oscillation, provided that cells are locally active. This result resembles Turing's and Smale's works showing that locally communicating simple elements can produce very different patterns even if separate elements do not show any activity. This property will be demonstrated for two second-order cells and also for a large ensemble of oscillatory cells. In latter case, the network of oscillatory cells exhibits very sophisticated spatio-temporal waves, e.g. spiral waves. Copyright © 2008 John Wiley & Sons, Ltd. [source]


An analysis of water vapour diffusion in whey protein films

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 5 2003
Cristiana M. P. Yoshida
Summary The macroscopic aspects of moisture transmission in whey protein films were determined by measuring water vapour adsorption. A theoretical model was constructed in which two kinds of water vapour fluxes were considered: one originating from diffusion, whilst the other was a flux due to the gravitation drift of moisture. The comparison of theoretical and experimental results showed that only the diffusion process was present. [source]


Distribution in TLM models for diffusion (Part II: multi-dimensional treatment)

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 6 2003
P. Chardaire
Abstract The signals obtained at each time step of a transmission line matrix (TLM) simulation of Gaussian diffusion are analysed for two- and three-dimensional cases. A combinatorial formula is derived to provide the signal magnitude at any spatial position and any time step after a single-shot excitation in the two-dimensional link-line model. Formulae for the expectation and variance of the axial positions of a particle are determined for two- and three-dimensional link-line and link-resistor models. A generalization of these formulae is proposed for higher dimensions, and an entirely numerical proving scheme is devised. Finally, we briefly compare the resulting variances and that of the underlying diffusion process. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Influence of the carrier diffusion process on the transient response of vertical-cavity surface-emitting lasers

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 1 2003
M. S. Torre
Abstract We investigate the transverse mode dynamics of weakly index-guided vertical-cavity surface-emitting lasers (VCSEL). The turn-on time of transverse modes are calculated by implementing a model for the VCSEL dynamics including diffusion and transport/capture phenomena. It takes into account the spatial dependence of the two carrier density profiles associated with the confined carriers in the quantum wells, and with the unconfined carriers in the barrier region. Devices of different aperture diameter under different excitation conditions are also studied. The model displays the correct turn-on time dependence on the injection current density when compared with the experimental data available. We show that the turn-on time of the modes increases when capture time increases and escape time decreases and also when diffusion increases. Copyright © 2002 John Wiley & Sons, Ltd. [source]


Time-steppers and ,coarse' control of distributed microscopic processes

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 2 2004
Antonios Armaou
Abstract We present an equation-free multiscale computational framework for the design of ,coarse' controllers for complex spatially distributed processes described by microscopic/mesoscopic evolution rules. We illustrate this framework by designing discrete-time, coarse linear controllers for a Lattice,Boltzmann (LB) scheme modelling a reaction,diffusion process (a kinetic-theory based realization of the FitzHugh,Nagumo equation dynamics in one spatial dimension). Short ,bursts' of appropriately initialized simulation of the LB model are used to extract the stationary states (stable and unstable) and to estimate the information required to design the coarse controller (e.g. the action of the coarse slow Jacobian of the process). Copyright © 2004 John Wiley & Sons, Ltd. [source]


Generalized Diffusion Tensor Imaging (GDTI): A Method for Characterizing and Imaging Diffusion Anisotropy Caused by Non-Gaussian Diffusion

ISRAEL JOURNAL OF CHEMISTRY, Issue 1-2 2003
Chunlei Liu
For non-Gaussian distributed random displacement, which is common in restricted diffusion, a second-order diffusion tensor is incapable of fully characterizing the diffusion process. The insufficiency of a second-order tensor is evident in the limited capability of diffusion tensor imaging (DTI) in resolving multiple fiber orientations within one voxel of human white matter. A generalized diffusion tensor imaging (GDTI) method was recently proposed to solve this problem by generalizing Fick's law to a higher-order partial differential equation (PDE). The relationship between the higher-order tensor coefficients of the PDE and the higher-order cumulants of the random displacement can be derived. The statistical property of the diffusion process was fully characterized via the higher-order tensor coefficients by reconstructing the probability density function (PDF) of the molecular random displacement. Those higher-order tensor coefficients can be measured using conventional diffusion-weighted imaging or spectroscopy techniques. Simulations demonstrated that this method was capable of quantitatively characterizing non-Gaussian diffusion and accurately resolving multiple fiber orientations. It can be shown that this method is consistent with the q-space approach. The second-order approximation of GDTI was shown to be DTI. [source]


Small-angle X-ray scattering study of the smart thermo-optical behavior of zirconyl aqueous colloids

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000
L.A. Chiavacci
The smart thermo-optical systems studied here are based on the unusual thermoreversible sol-gel transition of zirconyl chloride aqueous solution modified by sulfuric acid in the molar ratio Zr/SO4:3/1. The transparency to the visible light changes during heating due to light scattering. This feature is related to the aggregates growth that occurs during gelation. These reversible changes can be controlled by the amount of chloride ions in solution. The thermoreversible sol-gel transition temperature increases from 323 to 343 K by decreasing the molar ratio Cl/Zr from 7.0 to 1.3. In this work the effect of the concentration of chloride ions on the structural characteristics of the system has been analyzed by in situ SAXS measurements during the sol-gel transition carried out at 323 and 333 K. The experimental SAXS curves of sols exhibit three regions at small, medium and high scattering vectors characteristics of Guinier, fractal and Porod regimes, respectively. The radius of primary particles, obtained from the crossover between the fractal and Porod regimes, remains almost invariable with the chloride concentration, and the value (4 Ĺ) is consistent with the size of the molecular precursor. During the sol-gel transition the aggregates grow with a fractal structure and the fractal dimensionality decreases from 2.4 to 1.8. This last value is characteristic of a cluster-cluster aggregation controlled by a diffusion process. Furthermore, the time exponent of aggregate growth presents values of 0.33 and 1, typical of diffusional and hydrodynamic motions. A crossover between these two regimes is observed. [source]


Aqueous chloramine diffusion into elastomers

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010
Raja M. Nagisetty
Abstract Aqueous chloramine diffusion into styrene butadiene rubber (SBR) and natural rubber was analyzed using approximate analytical and numerical solutions of Fick's second law of diffusion to develop long-term mass intake prediction curves. Diffusion coefficients were calculated for 1 mg/L chloramine concentration at three temperatures (23, 45, and 70°C) and also for 23°C at three chloramine concentrations (1, 30, and 60 mg/L). The reasonableness of using increased temperature and/or chloramine concentration to accelerate the diffusion process to obtain long-term information was discussed. For 1 mg/L chloramine concentration, the activation energy for the diffusion of chloramines into SBR and natural rubber were computed to be 51.13 and 77.29 kJ/mol, respectively. Also, concentration profiles were developed to understand the extent of penetration through the elastomer thickness over time and temperature. Considering the reports of elastomeric compound failure in chloramine disinfectant water distribution systems because of swelling, this study will be helpful in understanding the performance of the elastomeric compounds in the system. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]


Dye,fiber interactions in PET fibers: Hydrogen bonding studied by IR-spectroscopy

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007
Karen De Clerck
Abstract Dye,fiber interactions are studied in poly (ethylene terephthalate) fibers by FT-IR spectroscopy. It is shown for the first time that DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) serves as an easy applicable and accurate technique for the study of fibrous structures. This article focuses on the possible hydrogen bond interactions in the dye,fiber system, where the PET fibers are dyed with anthraquinone-based disperse dyes. The dyes and related anthraquinone structures are studied in both the dilute solution state, the solid state, and as present in the PET fibers. It is proven that 1-amino anthraquinones show strong "chelate-type" intramolecular hydrogen bonding in all three states. In the fibers an important supplementary intermolecular hydrogen bonding with the CO groups in the PET fiber is observed. The extend of hydrogen bonding seems to be prone to dye concentration variations. Further analysis by modulated differential scanning calorimetry links the hydrogen bonding to an intrinsic plasticizing effect of the dyes affecting the dye diffusion process. This thus offers a tool for the fundamental understanding of the dyeing process and possible observed differences in dyeing behavior in dye,fiber systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source]


Sorption and permeation behavior for CO2 in NH3 -plasma-treated and untreated polystyrene membranes

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2007
Y.-S. Yang
Abstract In our preceding work, the simultaneous deviation from the conventional dual-mode sorption and mobility model was observed in a case of CO2 in polystyrene (PS) membrane (glass transition temperature of pure polymer = 95°C) at 60 and 70°C. The plasticization effect of sorbed CO2 on both the sorption and diffusion processes tends to be brought about in glassy polymer membranes near the glass transition temperature. The behavior was simulated based on the concept that only one population of sorbed gas molecules of plasticizing ability to the polymer should exist. In the present work, the sorption and permeation behavior for CO2 in NH3 -plasma-treated and untreated PS membranes at 40°C was investigated, where NH3 -plasma treatment was executed at plasma discharge powers of 40, 80, 120, and 160 W for an exposure time of 2 min. The sorption isotherm could be described by the sorption theory of Mi et al. (Macromolecules 1991, 24, 2361), where the glass transition temperature is depressed by a concentration of sorbed CO2 of plasticizing ability. NH3 -plasma treatment on PS membrane had little influence on the sorption behavior of CO2 at plasma discharge powers up to 160 W. The mean permeability coefficients were somewhat increased only at a discharge power of 160 W. At CO2 pressures below 0.9 MPa, the pressure dependencies of mean permeability coefficients for CO2 in both NH3 -plasma-treated and untreated PS membranes at 40°C could also be simulated on the basis of the concept that only one population of sorbed gas molecules of plasticizing ability should exist. At CO2 pressures above 0.9 MPa, however, a plasticization action of sorbed CO2 had much more influence on the diffusion process rather than on the sorption one, and such a combined concept underestimated the mean permeability coefficient. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1798,1805, 2007 [source]


Gender, social capital and information exchange in rural Uganda

JOURNAL OF INTERNATIONAL DEVELOPMENT, Issue 1 2008
Enid Katungi
Abstract Changing agricultural research and extension systems mean that informal mechanisms of information diffusion are often the primary source of information about improved seed and practices for farmers in sub-Saharan Africa. This paper investigates the interactions between gender, social capital and information exchange in rural Uganda. Within the framework of farmer-to-farmer models, we conceptualise the informal information diffusion process to comprise social capital accumulation and information exchange. We assume that each agent participates in information exchange with a fixed (predetermined) level of social capital and examine how endowments of social capital influence information exchange, paying close attention to gender differences. A multinomial logit model is used to analyse multiple participation choices of information exchange facing the farmer. Findings demonstrate that social capital is an important factor in information exchange, with men generally having better access to social capital than women. We also find strong evidence in support of group-based technology dissemination systems. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Fluoride ion diffusion from a glass,ionomer cement

JOURNAL OF ORAL REHABILITATION, Issue 7 2000
S.-Y. Lee
The aims of this study were to observe the release of fluoride ions (F,) from GC-Fuji Lining-LC® glass,ionomer cement, to assess the diffusion process, and to measure fluoride diffusivity (D) in the set cement. Specimens of various dimensions and shapes, ranging from discs to cylindrical rods, were fabricated for both open and embedded modes of testing. In the open mode studies, specimens with different surface to volume ratios were selected and immersed in 37 °C distilled water. In the embedded mode studies, only one diametral surface of the rod-shaped specimens of different lengths and diameters was exposed. F, concentration was measured using a fluoride electrode. The storage solution was analysed at predetermined intervals hourly, daily, and weekly (up to 10 weeks). Immediately after each sampling, the old storage solution was discarded and replaced with new distilled water. F, release from the set cements was detectable (0·4,3·8 ppm, varied with sample geometry), even after a 10-week sampling interval. F, release was greater in ground set cements (0.37 ppm/mg powder) than in control samples of unmixed powder (0.01 ppm/mg powder) immersed for 1 h. Two mechanisms for F, release were proposed. One was short-term and involved rapid dissolution from the cement surface. The other was more gradual and resulted in the sustained diffusion of ions through the bulk cement, which can be modelled by applying a mathematical technique known as separation of variables to Fick's Second Law of Diffusion. The mean D of F, in embedded set cements of glass,ionomer was (1·4±0·5)×10,11 cm2/s, with higher apparent D observed in open mode samples [(7·6±1·4)×10,11 cm2/s]. [source]


An investigation into the influence of counterion on the RS -propranolol and S -propranolol skin permeability

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2010
Francesco Cilurzo
Abstract The effects of two contra-ions, namely benzoate (Bz) and oleate (Ol), on the in vitro human skin permeability of propranolol racemate (RS -PR) or S -enantiomer (S -PR) were studied. Saline solution (SS) or mineral oil (MO) were selected as vehicles. The MO increased the permeability coefficient (Kp) of PR-Bz (pKp,,,4) of about four times with respect to SS (pKp,,,8) probably due to the ion pair formation. The steady-state flux of S -enantiomers resulted about twofold higher than that of racemates according to their lower melting temperatures with the exception of (S)-PR-Ol and (RS)-PR-Ol vehicled in SS which not resulted statistically different. This anomalous result could be explained considering the behavior of (RS)-PR-Ol or (S)-PR-Ol in aqueous solutions: these salts formed ion pairs which associated to form aggregates up to a concentration of 20,µg/mL as verified by light scattering. Therefore, their effective concentrations in SS resulted similar and justified the overlapped skin permeation profiles. All three considered variables, namely counterion, vehicle, and chirality, resulted mutually interfering on and deeply influenced the passive diffusion process of PR. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1217,1224, 2010 [source]


Applicability of laser-induced Raman microscopy for in situ monitoring of imine formation in a glass microfluidic chip

JOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2003
Moonkwon Lee
Abstract Laser-induced Raman microscopy has been used to illustrate its applicability for the in situ monitoring of imine formation reaction in a glass microfluidic chip. In order to monitor the diffusion process in a micro channel, the Raman spectra were measured at various points along the channel with a constant flow rate of 2.7 µl min,1. Time-dependent Raman spectra were also measured without flow in order to monitor the variation of Raman peaks to a complete conversion. The disappearance of the CO stretching peak at 1700 cm,1 of the reactant, benzaldehyde, and the appearance of the Raman peak for the product, an imine, at 1628 cm,1 were successfully monitored. In addition, the intensity increases of three phenyl stretching modes in the 1550,1630 cm,1 region were also observed. The increase in Raman intensity for this vibrational mode is caused by an effective ,-electron conjugation between two phenyl rings through the ,CN,bridging group of the product. Laser-induced Raman microscopy enables us to monitor in situ product formation and to obtain detailed structural information in a glass microfluidic chip. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Formation of a Nanocrystalline Layer on the Surface of Stone Wool Fibers

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2009
Yuanzheng Yue
In the present paper, we report a simple approach for creating a nanocrystalline layer on the surface of stone wool fibers (SWFs) with a basalt-like composition. The approach is based on a preoxidation process of the SWFs in atmospheric air at a temperature around the glass transition temperature (Tg) for various durations. During preoxidation, the network-modifying ions diffuse from the interior toward the surface of SWFs and react with oxygen on the surface to form oxides. This diffusion process is accompanied by an inward diffusion of electron holes via the oxidation process of Fe2+ to Fe3+. It is found that the diffusion of Mg2+ is dominant in the overall diffusion process. The main phase of the nanocrystalline layer is identified to be periclase (MgO) crystals. The thickness of the nanocrystalline layer can be varied by adjusting the temperature and the duration of preoxidation. The nanocrystalline layer plays a significant role in enhancing the high-temperature stability of the SWFs. [source]


Loading and Release of Ibuprofen in Multi- and Monofilament Surgical Sutures

MACROMOLECULAR BIOSCIENCE, Issue 9 2006
Raül Zurita
Abstract Summary: The preparation of mono- and multifilament sutures incorporating ibuprofen as an anti-inflammatory agent is considered. Poly(p -dioxanone) monofilament samples can be loaded by a molecular diffusion process using a swelling agent such as dichloromethane. The mechanical properties have been measured and have not shown a significant change for the ibuprofen loaded samples in knot tensile assays. The kinetics of both the loading process and the release in a Sörensen's medium at 37,°C have been investigated. Diffusion coefficients have also been estimated from film and slab poly(p -dioxanone) samples containing ibuprofen and their release behavior compared to that shown by monofilaments. Release from a coating copolymer based on lactide, , -caprolactone and trimethylene carbonate (PLA/PCA/PTMC 10/60/30) has also been studied. This coating solubilizes ibuprofen molecules well and can be used for braided sutures or when a rapid dose of ibuprofen is preferred. [source]


Peculiar manifestation of the dipole,dipole interaction between non-Kramers paramagnetic centers as studied by tunable high-frequency EPR spectroscopy,

MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2005
K. M. Salikhov
Abstract EPR spectral shape of non-Kramers paramagnetic centers (PCs) is theoretically analyzed under conditions of saturation. The analysis is performed in a model that includes the spectral diffusion process induced by a random modulation of the dipole,dipole interaction of the paramagnetic centers, by reorientations of magnetic moments. It is shown that around zero magnetic field, a ,hole' might appear in the EPR spectrum. We have also studied experimentally the saturation behavior of the EPR spectrum in Cr2+ : Mg2SiO4. The experimental results are interpreted in the framework of the model considered. By comparing simulated and experimental spectra, the paramagnetic relaxation times and the characteristic rate of the spectral diffusion are estimated. Copyright © 2005 John Wiley & Sons, Ltd. [source]


PRICING EQUITY DERIVATIVES SUBJECT TO BANKRUPTCY

MATHEMATICAL FINANCE, Issue 2 2006
Vadim Linetsky
We solve in closed form a parsimonious extension of the Black,Scholes,Merton model with bankruptcy where the hazard rate of bankruptcy is a negative power of the stock price. Combining a scale change and a measure change, the model dynamics is reduced to a linear stochastic differential equation whose solution is a diffusion process that plays a central role in the pricing of Asian options. The solution is in the form of a spectral expansion associated with the diffusion infinitesimal generator. The latter is closely related to the Schrödinger operator with Morse potential. Pricing formulas for both corporate bonds and stock options are obtained in closed form. Term credit spreads on corporate bonds and implied volatility skews of stock options are closely linked in this model, with parameters of the hazard rate specification controlling both the shape of the term structure of credit spreads and the slope of the implied volatility skew. Our analytical formulas are easy to implement and should prove useful to researchers and practitioners in corporate debt and equity derivatives markets. [source]


PRICING IN AN INCOMPLETE MARKET WITH AN AFFINE TERM STRUCTURE

MATHEMATICAL FINANCE, Issue 3 2004
Virginia R. Young
We apply the principle of equivalent utility to calculate the indifference price of the writer of a contingent claim in an incomplete market. To recognize the long-term nature of many such claims, we allow the short rate to be random in such a way that the term structure is affine. We also consider a general diffusion process for the risky stock (index) in our market. In a complete market setting, the resulting indifference price is the same as the one obtained by no-arbitrage arguments. We also show how to compute indifference prices for two types of contingent claims in an incomplete market, in the case for which the utility function is exponential. The first is a catastrophe risk bond that pays a fixed amount at a given time if a catastrophe does not occur before that time. The second is equity-indexed term life insurance which pays a death benefit that is a function of the short rate and stock price at the random time of the death of the insured. Because we assume that the occurrence of the catastrophe or the death of the insured is independent of the financial market, the markets for the catastrophe risk bond and the equity-indexed life insurance are incomplete. [source]


First-Order Schemes in the Numerical Quantization Method

MATHEMATICAL FINANCE, Issue 1 2003
V. Bally
The numerical quantization method is a grid method that relies on the approximation of the solution to a nonlinear problem by piecewise constant functions. Its purpose is to compute a large number of conditional expectations along the path of the associated diffusion process. We give here an improvement of this method by describing a first-order scheme based on piecewise linear approximations. Main ingredients are correction terms in the transition probability weights. We emphasize the fact that in the case of optimal quantization, many of these correcting terms vanish. We think that this is a strong argument to use it. The problem of pricing and hedging American options is investigated and a priori estimates of the errors are proposed. [source]


Diffusion characteristics of a joint-proton source for the wet etch of LiNbO3

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2008
Tien-Lun Ting
Abstract Diffusion characteristics of a joint-proton source for proton exchange in LiNbO3 are presented. With a concentration-dependent diffusivity derived from experimental results, the diffusion process is simulated to estimate the proton-exchanged wet-etched depth. Good agreement between simulated and measured depth is obtained. In addition, an S-shaped ridge waveguide is fabricated to demonstrate the improvement in power transmission efficiency. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2736,2738, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23752 [source]


Application of a computer model to evaluate the ability of plastics to act as functional barriers

PACKAGING TECHNOLOGY AND SCIENCE, Issue 3 2003
Jong-Koo Han
Abstract A simulation model computer program, which accounts for not only the diffusion process inside the polymer but also partitioning of the contaminant between the polymer and the contacting phase, was developed based on a numerical treatment, the finite element method, to quantify migration through multilayer structures. The accuracy of the model in predicting migration was demonstrated successfully by comparing simulated results to experimental data. For this study, three-layer co-extruded high density polyethylene (HDPE) film samples, having a symmetrical structure with a contaminated core layer and virgin outer layers as the functional barriers, were fabricated with varying thickness of the outer layers and with a known amount of selected contaminant simulant, 3,5-di-t-butyl-4-hydroxytoluene (BHT), in the core layer. Migration of the contaminant simulant from the core layer to the liquid food simulants was determined experimentally as a function of the thickness of the outer layer at different temperatures. The computer program, developed as a total solution package for migration problems, can be applied not only to multilayer structures made with the same type of plastics but also to structures with different plastics, e.g. PP/PE/PP. This work might provide the potential for wider use of recycled plastic, especially polyolefins, which have lower barrier properties, in food packaging, and simplification of the task of convincing the FDA that adequate safety guarantees have been provided. Copyright © 2003 John Wiley & Sons, Ltd. [source]