1,951 research outputs found
Density-dependent interactions and structure of charged colloidal dispersions in the weak screening regime
We determine the structure of charge-stabilized colloidal suspensions at low
ionic strength over an extended range of particle volume fractions using a
combination of light and small angle neutron scattering experiments. The
variation of the structure factor with concentration is analyzed within a
one-component model of a colloidal suspension. We show that the observed
structural behavior corresponds to a non-monotonic density dependence of the
colloid effective charge and the mean interparticle interaction energy. Our
findings are corroborated by similar observations from primitive model computer
simulations of salt-free colloidal suspensions.Comment: Revised version, accepted to Phys. Rev. Let
Testing the relevance of effective interaction potentials between highly charged colloids in suspension
Combining cell and Jellium model mean-field approaches, Monte Carlo together
with integral equation techniques, and finally more demanding many-colloid
mean-field computations, we investigate the thermodynamic behavior, pressure
and compressibility of highly charged colloidal dispersions, and at a more
microscopic level, the force distribution acting on the colloids. The
Kirkwood-Buff identity provides a useful probe to challenge the
self-consistency of an approximate effective screened Coulomb (Yukawa)
potential between colloids. Two effective parameter models are put to the test:
cell against renormalized Jellium models
Geodesic Deviation Equation in Bianchi Cosmologies
We present the Geodesic Deviation Equation (GDE) for the
Friedmann-Robertson-Walker(FRW) universe and we compare it with the equation
for Bianchi type I model. We justify consider this cosmological model due to
the recent importance the Bianchi Models have as alternative models in
cosmology. The main property of these models, solutions of Einstein Field
Equations (EFE) is that they are homogeneous as the FRW model but they are not
isotropic. We can see this because they have a non-null Weyl tensor in the GDE.Comment: Submitted to Journal of Physics: Conference Series (JPCS), ERE200
Critical view of WKB decay widths
A detailed comparison of the expressions for the decay widths obtained within
the semiclassical WKB approximation using different approaches to the tunneling
problem is performed. The differences between the available improved formulae
for tunneling near the top and the bottom of the barrier are investigated.
Though the simple WKB method gives the right order of magnitude of the decay
widths, a small number of parameters are often fitted. The need to perform the
fitting procedure remaining consistently within the WKB framework is emphasized
in the context of the fission model based calculations. Calculations for the
decay widths of some recently found super heavy nuclei using microscopic
alpha-nucleus potentials are presented to demonstrate the importance of a
consistent WKB calculation. The half-lives are found to be sensitive to the
density dependence of the nucleon-nucleon interaction and the implementation of
the Bohr-Sommerfeld quantization condition inherent in the WKB approach.Comment: 18 pages, Late
Path Integral Approach to Strongly Nonlinear Composite
We study strongly nonlinear disordered media using a functional method. We
solve exactly the problem of a nonlinear impurity in a linear host and we
obtain a Bruggeman-like formula for the effective nonlinear susceptibility.
This formula reduces to the usual Bruggeman effective medium approximation in
the linear case and has the following features: (i) It reproduces the weak
contrast expansion to the second order and (ii) the effective medium exponent
near the percolation threshold are , , where is the
nonlinearity exponent. Finally, we give analytical expressions for previously
numerically calculated quantities.Comment: 4 pages, 1 figure, to appear in Phys. Rev.
High-order dispersion mapping of an optical fiber
We report on measurements of high-order dispersion maps of an optical fiber, showing how the ratio between the third and fourth-order dispersion (β3/β4) and the zero-dispersion wavelength (λ0) vary along the length of the fiber. Our method is based on Four-Wave Mixing between short pulses derived from an incoherent pump and a weak laser. We find that the variations in the ratio β3/β4 are correlated to those in λ0. We present also numerical calculations to illustrate the limits on the spatial resolution of the method. Due to the good accuracy in measuring λ0 and β3/β4 (10 -3% and 5% relative error, respectively), and its simplicity, the method can be used to identify fiber segments of good uniformity, suitable to build nonlinear optical devices such as parametric amplifiers and frequency comb generators28342584273FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2012/50259-8; 2015/11779-4; 2017/16151-9; 2018/08988-9; 2019/16793-6Fundação de Amparo à Pesquisa do Estado de São Paulo (2012/50259-8, 2015/11779-4,
2017/16151-9, 2018/08988-9, 2019/16793-6); Coordenação de Aperfeiçoamento de Pessoal de
Nível Superior; Departamento Administrativo de Ciencia, Tecnología e Innovación (COLCIENCIAS) (COL-10-2-05
Qualidade pós-colheita de laranja cv. salustiana sob atmosfera modificada durante o armazenamento refrigerado.
bitstream/item/30499/1/boletim-90.pd
Avaliação da qualidade de laranjas da cv. navelina em atmosfera modificada durante o armazenamento refrigerado.
bitstream/item/30435/1/boletim-74.pd
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