In this paper we examine the foundations of the Cahn-Hilliard-Cook (CHC) theory of phase separation, which has been used routinely in recent years to interpret dynamic scattering experiments on binary polymer blends, and discuss its... more
In this paper we examine the foundations of the Cahn-Hilliard-Cook (CHC) theory of phase separation, which has been used routinely in recent years to interpret dynamic scattering experiments on binary polymer blends, and discuss its extension to multi-component mixtures. The CHC-theory is based on the following nonlinear Langevin equation:where Φ(q,t) is the Fourier transform of the local volume fraction Φr,t) of one of the components of the binary mixture which is assumed to be incompressible; λ(q) is the q-dependent onsager coefficient; μ(q,t) is the Fourier transform of the local chemical potential difference μ(r,t); and η(q,t) is the random force which is added to account for the thermal fluctuations. The latter is assumed to be a stationary white noise process with zero mean and an autocovariance (η(q,t) q(-q,t′)) = λ(q) q2 δ(t - t′), which is determined from fluctuation-dissipation theorem. The use of the Langevin equation method to describe fluctuations in nonlinear macroscopic systems, in the way done in the CHC theory, was questioned by van Kampen, for reasons which we discuss in this paper. The proper way of using the Langevin equation method in nonlinear systems was provided by Akcasu in 1977 through van Kampen's system size expansion, which we sketch next.
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En este artículo se analiza un problema que resulta crucial para el desarrollo económicode México: el bajo crecimiento económico y la consecuente imposibilidad para generarlos empleos necesarios. Se supone, en base a la teoría del... more
En este artículo se analiza un problema que resulta crucial para el desarrollo económicode México: el bajo crecimiento económico y la consecuente imposibilidad para generarlos empleos necesarios. Se supone, en base a la teoría del crecimiento kaldoriana, que dicha problemática es resultado de errores de política económica, básicamente el abandono de la política industrial activa orientada al cambio estructural y desarrollo económico. Se proporciona evidencia que da cuenta de la alta correlación entre el bajo crecimiento económico y el bajo crecimiento del producto manufacturero, resultado que es compatible con los hallazgos de otros investigadores. De haberse implementado una política industrial activa, la tasa de crecimiento del sector manufacturero sería mayora la observada y ello contribuiría a un mejor desempeño económico global. Por su importancia, el artículo expone las razones por las cuales se abandonó esta clase de políticaindustrial y sugiere retomarla.
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Abstract The excluded volume of several polymers in the dilute solution regime is calculated using the Monte Carlo integration. The calculated scaling exponent, λ , for the excluded volume for a polymer chain with another chain of the... more
Abstract The excluded volume of several polymers in the dilute solution regime is calculated using the Monte Carlo integration. The calculated scaling exponent, λ , for the excluded volume for a polymer chain with another chain of the same length is 1.74±0.02. This exponent is consistent with the idea that the interaction of chains with one another in a good solvent is similiar to the interaction of two hard spheres. The effective radius of the hard sphere is proportional to the radius of gyration which has a scaling exponent of ν =0.595±0.005. This result is close to the theoretical value of 0.589. This study establishes the relationship λ =3 ν .
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Page 1. Ann. Rev. Mater. Sci. 1983. 13: 387-412 BULK AND INTERFACE THERMODYNAMICS OF POLYMER ALLOYS Isaac C. Sanchezt Center for Materials Science, National Bureau of Standards, Washington, DC 20234 INTRODUCTION ...
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Partial expansion of a collapsed Lennard-Jones chain in SPC/E water with decreasing temperature is seen by Monte Carlo simulation. This unexpected behavior is related to the development of large cavities at low temperatures. Cavity size... more
Partial expansion of a collapsed Lennard-Jones chain in SPC/E water with decreasing temperature is seen by Monte Carlo simulation. This unexpected behavior is related to the development of large cavities at low temperatures. Cavity size distributions of water and the Lennard- Jones fluid are determined by simulation and contrasted. Water differs from the Lennard-Jones fluid in its increasing average cavity size upon cooling.
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Configurational Properties of Some Simple Fluids and Water I. C. SANCHEZ and T. TRUSKETT University of Texas at Austin In a Monte Carlo or molecular dynamics simulation of a model molecular fluid, the configurational contribution to the... more
Configurational Properties of Some Simple Fluids and Water I. C. SANCHEZ and T. TRUSKETT University of Texas at Austin In a Monte Carlo or molecular dynamics simulation of a model molecular fluid, the configurational contribution to the chemical potential can be determined. Other configurational properties, such as the configurational energy and entropy, can also be calculated. To effect a comparison of model properties with those of a real fluid, it is necessary to calculate the corresponding configurational properties of the real fluid. Heretofore, it is not been clear how this would be accomplished. In this paper, we determine recipes for calculating configurational properties of real fluids from experimental vapor pressure and PVT data. Of special interest is an explicit equation for the configurational entropy of a fluid or solid. With the help of statistical mechanics, configurational properties can also be given a microscopic interpretation. Configurational properties of water are calculated and compared with those of 5 simple fluids.
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The addition of charges, either free in solution or on the polymer chain itself, significantly alters the lower critical solution temperature (LCST) transition that drives the behavior of many stimuli responsive polymers (SRPs). Various... more
The addition of charges, either free in solution or on the polymer chain itself, significantly alters the lower critical solution temperature (LCST) transition that drives the behavior of many stimuli responsive polymers (SRPs). Various proposed mechanisms rely upon binary hydration interactions, ternary or higher order hydration interactions, or hydrophobic interactions in explaining this behavior. In order to elucidate the role of these mechanisms and guide targeted design of SRPs, an analytical model is thus developed that yields the LCST of lightly charged polyelectrolyte solutions as a function of ionic strength, counterion concentration, and polymer backbone charge fraction. It incorporates the above physics through a hybrid approach: a lattice fluid model addresses excluded volume and dispersion interactions; the Debye-Huckel model is employed for long range electrostatic interactions; and an extension of the combinatorial approach of Veytsman is applied to hydrogen bonding, ion-dipole interactions, and ionic bonding. In addition to treating the LCST of polyelectrolytes, in a simplified form the model is employed to treat the lyotropic series of salts and investigate its physical origins. The model demonstrates qualitative or semiquantitative agreement with experimental LCST measurements for various charge-containing polymer systems.
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Solubilities of chain in water as measured by Henry's Law constant is controlled by the availability of sufficiently large cavities to accommodate the solute (entropy term) and the interaction of solute with the solvent molecules... more
Solubilities of chain in water as measured by Henry's Law constant is controlled by the availability of sufficiently large cavities to accommodate the solute (entropy term) and the interaction of solute with the solvent molecules (energy term). In this study, different configurational factors such as bond length, bond angle, torsional energy have been applied to a Lennard-Jones chain model, and their effects on the solubilities are assessed.
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Este proyecto desarrolla la construccion de un paso elevado sobre la linea ferroviaria en el municipio de Coslada, situado en la zona Este de la comunidad de Madrid. Dicha poblacion se encuentra dividida por la linea de ferrocarril que... more
Este proyecto desarrolla la construccion de un paso elevado sobre la linea ferroviaria en el municipio de Coslada, situado en la zona Este de la comunidad de Madrid. Dicha poblacion se encuentra dividida por la linea de ferrocarril que conecta Madrid con Guadalajara y por la que circulan los trenes de cercanias de la linea C-2 y C-7. Esta linea ferroviaria supone una barrera en la correcta movilidad urbana, impidiendo el acceso entre los diferentes barrios del municipio. Los principales objetivos del proyecto son mejorar la movilidad en el area central del municipio, permitiendo el transito peatonal mediante la realizacion de un paso superior sobre las vias del tren que divide el termino municipal y dotar a la nueva unidad de ejecucion definida en el Plan Parcial de Reforma Interior de un paso peatonal que permita conectar las nuevas viviendas con el barrio de “El casco”.
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A new Monte Carlo algorithm has been developed to characterize the cavity size distribution in disordered materials. The computational method is based on energetic rather than geometric considerations. It is easy to implement and is... more
A new Monte Carlo algorithm has been developed to characterize the cavity size distribution in disordered materials. The computational method is based on energetic rather than geometric considerations. It is easy to implement and is applicable to any liquid or glass structure that can be generated by molecular dynamic or Monte Carlo methods. To illustrate its utility, it has been applied to a variety of model liquids and glasses that include water and dense polymeric glasses. For the latter, it will be shown that the cavity size distribution can be correlated with experimentally observed gas permeability and diffusion. Its relevance to dual mode sorption of gases will also be discussed.
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The single-chain polymer coil-globule transition (CGT) is of great interest due to its applicability both in biological macromolecules and in synthetic stimuli responsive polymers. The present authors have published a lattice-fluid model... more
The single-chain polymer coil-globule transition (CGT) is of great interest due to its applicability both in biological macromolecules and in synthetic stimuli responsive polymers. The present authors have published a lattice-fluid model for the lower critical solution temperature (LCST)-related CGT and for a theoretical high temperature upper critical solution temperature (UCST)-related CGT. However, more recently an updated model for these transitions has been developed based on a scaled particle theory approach. This model, without the use of adjustable solution parameters, provides a semi-quantitative match with extant experimental measures of CGT behavior. The predicted CGT also reproduces important aspects of a recently proposed qualitative master curve for the phase behavior of polymer solutions. In particular, the model predicts an LCST-related CGT temperature which increases with pressure until it merges at a pressure Pmax with a UCST-related CGT
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ABSTRACT The aim of this study is to develop and evaluate a new set of color features and their performance on the classification of skin lesions. The proposed system introduces new features based on 2-dimensional color histograms, an... more
ABSTRACT The aim of this study is to develop and evaluate a new set of color features and their performance on the classification of skin lesions. The proposed system introduces new features based on 2-dimensional color histograms, an automated segmentation method using a fusion of thresholding methods, classification procedures and is designed to be used by dermatologists as a complete integrated dermatological analysis tool to improve the rate of correct diagnosis above 90%. Simulations are implemented to show the measured features as well as classification results. The outcomes showed that the CAD model discussed in this paper has an improved classification performance and is an objective diagnostic tool that can be used in medical practice.
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Structure-controlled synthesis of gold nanostructures (AuNSs) induced by temperature in a nonaqueous urea–choline chloride deep eutectic solvent (DES) is reported.
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Page 1. J . MACROMOL . SCI.-REVS. MACROMOL . CHEM., ClO(1). 113-148 (1974) Modern Theories of Polymer Crystallization ISAAC C . SANCHEZ Polymer Science and Engineering University of Massachusetts Amherst. Massachusetts 01 002 ...
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Molecular dynamic simulations of hard sphere tracer diffusion in hard sphere chain solvents is investigated for chains up to size 16. At a given occupied volume fraction, diffusion coefficients of small tracer molecules are independent of... more
Molecular dynamic simulations of hard sphere tracer diffusion in hard sphere chain solvents is investigated for chains up to size 16. At a given occupied volume fraction, diffusion coefficients of small tracer molecules are independent of chain length. Diffusion coefficients of larger tracer molecules decrease slowly with increasing chain length. Although the viscosity of chain fluids increases dramatically with chain
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Prostate cancer automatic grading has attracted a lot of attention during the last years [1]. Many research efforts have been fixated on the development of computerized recognition and classification systems to automatically grade Gleason... more
Prostate cancer automatic grading has attracted a lot of attention during the last years [1]. Many research efforts have been fixated on the development of computerized recognition and classification systems to automatically grade Gleason patterns. Automatic computerized Gleason grading methods can be classified into two basic classes: image textural-based class and tissue structural-based (nuclear architecture, gland morphology) class. To the best of our knowledge, tissue structural classification based on three-class classification results including Gleason grade 3, 4 and 5 carcinoma were not reported. The goal of this article is to: (1) develop computerized assessment support systems to automatically grade Gleason patterns 3, 4 and 5 by integrating gland morphology and architectural features; (2) improve classification accuracy especially between intermediate Gleason grades 3 and 4. Computer simulations show an average correct classification accuracy of 97.63%, 96.57% and 87.30% when distinguishing Gleason 3 vs. Gleason 4, Gleason 3 vs. Gleason 5, and Gleason 4 vs. Gleason 5 respectively. These results lead the way towards providing an effective and promising software tool in automatic prostate cancer histological Gleason grading.
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ABSTRACT We report the preparation of Ni nanowire colloidal suspension that exhibits large light scattering changes when a magnetic field is applied. These changes occur during the application of alternating transversal magnetic fields.... more
ABSTRACT We report the preparation of Ni nanowire colloidal suspension that exhibits large light scattering changes when a magnetic field is applied. These changes occur during the application of alternating transversal magnetic fields. The intensity variation can easily be detected and measured since the light signal produced is very large with ratios much larger compared with signals obtained from light transmission through the nanowire colloidal suspension. Ni nanowires used for the experiments are about 1.2 μm long and 50 nm in diameter; suspensions of 44 μg/ml of these nanowires yield a scattering light variation ratio up to 35% when subjected to transversal alternating magnetic fields of 10 G. The methodology proposed could be implemented to detect and characterize magnetic nanowires even at concentrations as low as 4.4 μg/ml. Using finite element modeling, we observe that nanowires in a suspension scatter light depending strongly on the incidence angle of the applied light. From the finite element simulations, we also observe that nanowires may present plasmonic-antenna absorption effects that can be useful to indirectly measure nanowire properties, such as length and composition.
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A self-consistent field (SCF) is constructed for a polymer chain with excluded volume modeled as a self-avoiding random walk (SAW) of N steps (N →∞). The SCF requires the introduction of a second exponent \(\bar \theta \) in addition to... more
A self-consistent field (SCF) is constructed for a polymer chain with excluded volume modeled as a self-avoiding random walk (SAW) of N steps (N →∞). The SCF requires the introduction of a second exponent \(\bar \theta \) in addition to the usual ν exponent that characterizes the size of a SAW. The SCF equals N times the probability \({\bar P_N}\) of an interaction of the chain end with a distant part of the chain. In d-dimensional space \({\bar P_N}\) scales as \({N^{ - \gamma \left( {d + \bar \theta } \right)}} \left( {d \leqslant 4} \right);\); self-consistency of the field yields the relations θ = (4 - d)/3 and \(\upsilon \left( {d + \bar \theta } \right) = 2.\). It is shown that \({\theta _0} 1 is the exponent associated with the probability of a SAW forming a large loop with a long tail. A SCF ( Φ ) is also determined for a semidilute solution of polymer volume fraction φ. The number of binary interactions scales as Φ φ ∼ φ9/4
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The aim of this study is to develop a method of lesion extraction from a large image of a skin surface and evaluate a new set of color features and their ability to classify the extracted skin lesions. It is beneficial for a dermatologist... more
The aim of this study is to develop a method of lesion extraction from a large image of a skin surface and evaluate a new set of color features and their ability to classify the extracted skin lesions. It is beneficial for a dermatologist to be able to take a snapshot of a large skin surface and have an automated system locate and diagnose atypical lesions. The proposed system accomplishes this task and is designed to be used by dermatologists as a completely integrated analytical tool to improve the rate of correct diagnosis well above 90%. Simulations are implemented to show extraction of skin lesions and how their features are measured as well as classification results. The outcomes showed that the computer aided diagnosis model discussed in this paper has an improved classification performance and is an objective diagnostic tool that can be used in medical practice.
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Page 1. J. Phys. Chem. 1989, 93, 6983-6991 6983 was not very sensitive to any of these model variables. The exponent, a, was fixed at 0.8; the fit for eq 5 was not sensitive to the value of a. The uncertainty in the viscosity was ...
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This paper discusses four general problem areas and their associated theories: the relationship between crystal growth and nucleation; the concentration dependence of crystal growth rates; the crystallization of random copolymers, and the... more
This paper discusses four general problem areas and their associated theories: the relationship between crystal growth and nucleation; the concentration dependence of crystal growth rates; the crystallization of random copolymers, and the annealing (thickening) behavior of polymer crystals.
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Publisher Summary This chapter presents an overview of the development, comparison, and application of Flory and lattice fluid theories. The Flory and lattice fluid theories represent promising alternatives to the solubility parameter... more
Publisher Summary This chapter presents an overview of the development, comparison, and application of Flory and lattice fluid theories. The Flory and lattice fluid theories represent promising alternatives to the solubility parameter approach for predicting polymer compatibility, which means thermodynamic miscibility. The Flory theory demonstrates that mixture thermodynamic properties depend on the thermodynamic properties of the pure components. In particular, lower critical solution temperatures (LCST) behavior can be understood in terms of the dissimilarity of the equation of state properties of polymer and solvent. In the Flory theory, each pure component is characterized by three equations of state parameters: (1) a characteristic temperature T*, (2) a characteristic pressure p*, and (3) a characteristic specific volume vsp*. The lattice fluid theory does not require separation of internal and external degrees of freedom as does the Flory theory and Prigogine corresponding state theories. Both the Flory and lattice fluid theories require three equations of state parameters for each pure component. For mixtures, both the theories reduce to the Flory–Huggins theory at very low temperatures. According to the lattice fluid theory, a fluid is completely characterized by three molecular parameters: (1) ɛ*, (2) ν*, and (3) r or equivalently, the three equation of state parameters T*, p*, and ρ*. The chapter presents the complete thermodynamic description of the model fluid. In both the theories, for the sake of clarity, only the results for binary mixtures are presented.