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Search Results: 1 - 10 of 224303 matches for " Fredy R. Zypman "
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Nanoparticle Charge in Fluid from Atomic Force Microscopy Forces within the Nonlinear Poisson-Boltzmann Equation  [PDF]
Fredy R. Zypman
Journal of Applied Mathematics and Physics (JAMP) , 2018, DOI: 10.4236/jamp.2018.66110
Abstract: We consider the problem of measuring the electric charge of nanoparticles immersed in a fluid electrolyte. We develop a mathematical framework based on the solution of the nonlinear Poisson-Boltzmann equation to obtain interaction forces between nanoparticles immersed in a fluid electrolyte and an Atomic Force Microscopy micro spherical probe. This force-separation information is shown explicitly to depend on the charge of the nanoparticle.? This method overcomes the statistical nature of extant methods and renders a charge value for an individual single nanoparticle.
Interaction Energy between an Atomic Force Microscope Tip and a Charged Particle in Electrolyte  [PDF]
Wai-Ting Lam, Fredy R. Zypman
Journal of Applied Mathematics and Physics (JAMP) , 2016, DOI: 10.4236/jamp.2016.411199
Abstract: A variational principle to the nonlinear Poisson-Boltzmann equation (PB) in three dimensions is used to first obtain solutions to the electrostatic potential surrounding a pair of spherical colloidal particles, one of them modeling the tip of an Atomic Force Microscope. Specifically, we consider the PB action integral for the electrostatic potential produced by charged colloidal particles and propose an analytical ansatz solution. This solution introduces the density and its corresponding electrostatic potential parametrically. The PB action is then minimized with respect to the parameter. Polynomial-exponential approximations for the parameters as functions of tip-particle separation and boundary electrostatic potential are obtained. With that information, tip-particle energy-separation curves are computed as well. Finally, based on the shape of the energy-separation curves, we study the stability properties predicted by this theory.
Electromagnetic Waves Through Disordered Systems: Comparison Of Intensity, Transmission And Conductance
Gabriel A. Cwilich,Fredy R. Zypman
Physics , 2001,
Abstract: We obtain the statistics of the intensity, transmission and conductance for scalar electromagnetic waves propagating through a disordered collection of scatterers. Our results show that the probability distribution for these quantities, x, follow a universal form x^a Exp(-x^m) . This family of functions includes the Rayleigh distribution (when a=0, m=1) and the Dirac delta function (a -> Infinity), which are the expressions for intensity and transmission in the diffusive regime neglecting correlations. Finally, we find simple analytical expressions for the nth moment of the distributions and for to the ratio of the moments of the intensity and transmission, which generalizes the n! result valid in the above regime.
Transmittance quantities probability distributions of waves through disordered systems
Gabriel A. Cwilich,Fredy R. Zypman
Physics , 2001,
Abstract: Waves propagate through disordered systems in a variety of regimes. There is a threshold of disorder beyond which waves become localized and transport becomes restricted. The intensity I of the wave transmitted through a system has a dependence on the length L of the sample that is characteristic of the regime. For example, I decays as 1/L in the diffusive regime. It is of current interest to characterize the transport regime of a wave from statistical studies of the transmittance quantities through it. Studies suggest that the probability distribution of the intensity could be used to characterize the localized regime. There is an ongoing debate on what deviations from the classical Rayleigh distribution are to be expected. In this numerical work, we use scalar waves to obtain the intensity, transmission, and conductance of waves through a disordered system. We calculate the intensity, by setting an incoming plane wave towards the sample from a fixed direction. The outgoing intensity is then calculated at one point in space. This process is repeated for a collection of samples belonging to the same ensemble that characterizes the disorder, and we construct the probability distribution of the intensity. In the case of transmission, we evaluate the field arriving to a series of points distributed in the far field, and repeat the same statistical analysis. For the conductance, we calculate the field at the same series of points for incoming waves in different directions. We analyze the distribution of the transmittance quantities and their change with the degree of disorder.
Dry Friction Avalanches: Experiment and Robin Hood model
Sergey V. Buldyrev,John Ferrante,Fredy R. Zypman
Physics , 2005, DOI: 10.1103/PhysRevE.74.066110
Abstract: This paper presents experimental evidence and theoretical models supporting that dry friction stick-slip is described by self-organized criticality. We use the data, obtained with a pin-on-disc tribometer set to measure lateral force to examine the variation of the friction force as a function of time. We study nominally flat surfaces of aluminum and steel. The probability distribution of force jumps follows a power law with exponents $\mu$ in the range 2.2 -- 5.4. The frequency power spectrum follows a $1/{f^\alpha}$ pattern with $\alpha$ in the range 1 -- 2.6. In addition, we present an explanation of these power-laws observed in the dry friction experiments based on the Robin Hood model of self organized criticality. We relate the values of the exponents characterizing these power laws to the critical exponents $D$ an $\nu$ of the Robin Hood model. Furthermore, we numerically solve the equation of motion of a block pulled by a spring and show that at certain spring constant values the motion is characterized by the same power law spectrum as in experiments. We propose a physical picture relating the fluctuations of the force with the microscopic geometry of the surface.
Transitional random matrix theory nearest-neighbor spacing distributions
Fredy Zypman
Physics , 2009, DOI: 10.1088/1751-8113/43/22/225203
Abstract: This paper presents a study of the properties of a matrix model that was introduced to describe transitions between all Wigner surmises of Random Matrix theory. New results include closed-form exact analytical expressions for the transitional probability density functions, as well as suitable analytical approximations for cases not amenable to explicit representation.
Information in the Traveling Salesman Problem  [PDF]
Gilad Barach, Hugo Fort, Yoni Mehlman, Fredy Zypman
Applied Mathematics (AM) , 2012, DOI: 10.4236/am.2012.38138
Abstract: In the Simulated Annealing algorithm applied to the Traveling Salesman Problem, the total tour length decreases with temperature. Empirical observation shows that the tours become more structured as the temperature decreases. We quantify this fact by proposing the use of the Shannon information content of the probability distribution function of inter–city step lengths. We find that information increases as the Simulated Annealing temperature decreases. We also propose a practical use of this insight to improve the standard algorithm by switching, at the end of the algorithm, the cost function from the total length to information content. In this way, the final tour should not only be shorter, but also smoother.
New Supercoherent States
M. Kornbluth,F. R. Zypman
Physics , 2012,
Abstract: This study generalizes the supersymmetric coherent states introduced by Aragone and Zypman in 1986. The Hamiltonian of the supersymmetric quantum harmonic oscillator leads to the definition of the generalized supersymmetric annihilation operators as a 3-parameter family. Their eigenstates are the generalized supercoherent states, which can be calculated explicitly for three relevant regions of parameter space. The uncertainty in position and momentum is discussed, with specific concentration on where the uncertainty is saturated, where it is bounded, and where it is unbounded.
Negentropy Generation and Fractality in the Dry Friction of Polished Surfaces
Pablo Fleurquin,Hugo Fort,Mordechai Kornbluth,Roman Sandler,Mordecai Segall,Fredy Zypman
Entropy , 2010, DOI: 10.3390/e12030480
Abstract: We consider the Robin Hood model of dry friction to study entropy transfer during sliding. For the polished surface (steady state) we study the probability distribution of slips and find an exponential behavior for all the physically relevant asperity interaction-distance thresholds. In addition, we characterize the time evolution of the sample by its spatial fractal dimension and by its entropy content. Starting from an unpolished surface, the entropy decreases during the Robin Hood process, until it reaches a plateau; thereafter the system fluctuates above the critical height. This validates the notion that friction increases information in the neighborhood of the contacting surface at the expense of losing information in remote regions. We explain the practical relevance of these results for engineering surface processing such as honing.
CULTURA ORGANIZACIONAL Y POSMODERNIDAD. UNA APROXIMACIóN AL CASO VENEZUELA
Fredy R. Vallenilla Solórzano
Revista Negotium , 2006,
Abstract: The aim of this work is to approach the study of the Organizational Culture and Postmodernism. Yes, we could talk about a post Modernistic Organizational Culture, and how these concepts could be interpreted in some Venezuelan organizations. Hence, a descriptive-documental research is in course. There bibliographic sources on this subject are studied. It is clear the Organizational Culture concept, but the Postmodernism concept is not, because of the contrast between theoretical positions resulting in contradictory and excluding issues. This makes difficult the characterization of a Post modernistic-Organizational Culture. Organizations like Procter & Gamble and the Electricity de Caracas have an Organizational Culture which is characteristic of private firms, centered basically to be accordingly to new eras and changing markets. Petroleos de Venezuela, traditionally dedicated to the oil business, since 1999, due to the new politic scenery, undertakes other responsibilities aimed to enhance Venezuelan Social Indicators.
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