353 research outputs found
Charge reversal and surface charge amplification in asymmetric valence restricted primitive model planar electric double layers in the modified Poisson-Boltzmann theory
The modified Poisson-Boltzmann theory of the restricted primitive model
double layer is revisited and recast in a fresh, slightly broader perspective.
Derivation of relevant equations follow the techniques utilized in the earlier
MPB4 and MPB5 formulations and clarifies the relationship between these. The
MPB4, MPB5, and a new formulation of the theory are employed in an analysis of
the structure and charge reversal phenomenon in asymmetric 2:1/1:2 valence
electrolytes. Furthermore, polarization induced surface charge amplification is
studied in 3:1/1:3 systems. The results are compared to the corresponding Monte
Carlo simulations. The theories are seen to predict the "exact" simulation data
to varying degrees of accuracy ranging from qualitative to almost quantitative.
The results from a new version of the theory are found to be of comparable
accuracy as the MPB5 results in many situations. However, in some cases
involving low electrolyte concentrations, theoretical artifacts in the form of
un-physical "shoulders" in the singlet ionic distribution functions are
observed.Comment: 15 pages, 13 figure
Electrostatic Field Classifier for Deficient Data
This paper investigates the suitability of recently developed models based on the physical
field phenomena for classification problems with incomplete datasets. An original approach
to exploiting incomplete training data with missing features and labels, involving extensive use
of electrostatic charge analogy, has been proposed. Classification of incomplete patterns has been
investigated using a local dimensionality reduction technique, which aims at exploiting all available
information rather than trying to estimate the missing values. The performance of all proposed
methods has been tested on a number of benchmark datasets for a wide range of missing data scenarios
and compared to the performance of some standard techniques. Several modifications of the
original electrostatic field classifier aiming at improving speed and robustness in higher dimensional
spaces are also discussed
Thermodynamics of primitive model electrolytes in the symmetric and modified Poisson-Boltzmann theories. A comparative study with Monte Carlo simulations
Osmotic coefficients, individual and mean activity coefficients of primitive
model electrolyte solutions are computed at different molar concentrations
using the symmetric Poisson-Boltzmann and modified Poisson-Boltzmann theories.
The theoretical results are compared with an extensive series of Monte Carlo
simulation data obtained by Abbas et al. [Fluid Phase Equilib., 2007, 260, 233;
J. Phys. Chem. B, 2009, 113, 5905]. The agreement between modified
Poisson-Boltzmann predictions with the "exact" simulation results is almost
quantitative for monovalent salts, while being semi-quantitative or better for
higher and multivalent salts. The symmetric Poisson-Boltzmann results, on the
other hand, are very good for monovalent systems but tend to deviate at higher
concentrations and/or for multi-valent systems. Some recent experimental values
for activity coefficients of HCl solution (individual and mean activities) and
NaCl solution (mean activity only) have also been compared with the symmetric
and modified Poisson-Boltzmann theories, and with the Monte Carlo simulations.Comment: 10 pages, 9 figure
How Multivalency controls Ionic Criticality
To understand how multivalency influences the reduced critical temperatures,
Tce (z), and densities, roce (z), of z : 1 ionic fluids, we study equisized
hard-sphere models with z = 1-3. Following Debye, Hueckel and Bjerrum,
association into ion clusters is treated with, also, ionic solvation and
excluded volume. In good accord with simulations but contradicting
integral-equation and field theories, Tce falls when z increases while roce
rises steeply: that 80-90% of the ions are bound in clusters near T_c serves to
explain these trends. For z \neq 1 interphase Galvani potentials arise and are
evaluated.Comment: 4 pages, 4 figure
The primitive model of ionic fluids near its critical point in the Poisson–Boltzmann and modified Poisson–Boltzmann theories
The Poisson–Boltzmann (PB) and modified Poisson–Boltzmann (MPB) theories are used to investigate the primitive model of ionic fluids in the low density–large coupling regime where the liquid–vapor transition is situated. The PB and MPB spinodal curves for the restricted primitive model are calculated from the virial route and compared with those from the mean spherical approximation (energy route) and the hybrid hypernetted‐chain/mean spherical approximation (virial route). The effect of unequal ion sizes on the critical point and spinodal curves is also considered.National Sanitation Foundation (NSF) EE.UU. CHE-8907130Fondo Institucional para la Investigación (FIPI) de la Universidad de Puerto RicoComunidad Europea (beca Marie Curie)Dirección General de Investigación Científica y Técnica (DGICYT). España PBgl / 060
Mesoscopic theory for size- and charge- asymmetric ionic systems. I. Case of extreme asymmetry
A mesoscopic theory for the primitive model of ionic systems is developed for
arbitrary size, , and charge, ,
asymmetry. Our theory is an extension of the theory we developed earlier for
the restricted primitive model. The case of extreme asymmetries
and is studied in some detail in a mean-field
approximation. The phase diagram and correlation functions are obtained in the
asymptotic regime and , and for infinite
dilution of the larger ions (volume fraction or less). We find a
coexistence between a very dilute 'gas' phase and a crystalline phase in which
the macroions form a bcc structure with the lattice constant . Such coexistence was observed experimentally in deionized aqueous
solutions of highly charged colloidal particles
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The Urgency of Critical Theory Today: Towards Optimism and Renewal in a Neoliberal World
This article takes the form of a critical conversation between three generations of critical theorists, examining the role of critical theory in the neoliberal academy: does this sort of intellectual project still have a place in an academic and educational system that tends to favour empirical research and policy-driven projects? Through a discussion of the relationship between critical theory and power, privilege, and positionality, the article addresses the ongoing urgency of such intellectual activities in the present context. The dialogue between the three participants acknowledges critical theory’s historical, and continuing, fragility within the university, while elucidating the ways that it can provide a vehicle for challenging dominant forms of power. In doing so, this cross-generational exchange demonstrates that critical theory remains a vital space of rebellion, optimism, and social change
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