Dynamic radiation force of acoustic waves on solid elastic spheres

The present study concerns the dynamic radiation force on solid elastic spheres exerted by a plane wave with two frequencies (bichromatic wave) considering the nonlinearity of the fluid. Our approach is based on solving the wave scattering for the sphere in the quasilinear approximation within the preshock wave range. The dynamic radiation force is then obtained by integrating the component of the momentum flux tensor at the difference of the primary frequencies over the boundary of the sphere. Results reveal that effects of the nonlinearity of the fluid plays a major role in dynamic radiation force leading it to a parametric amplification regime. The developed theory is used to calculate the dynamic radiation force on three different solid spheres (aluminium, silver, and tungsten). Resonances are observed in the spectrum of the force on the spheres. They have larger amplitude and better shape than resonances present in static radiation force.Comment: 9 pages, 4 figures, to appear in Physical Review

A method of column chromatographic isolation of major phospholipid components on Escherichia coli

For the column chromatographic isolation of individual phospholipids from the total phospholipid mixture, silicic acid, DEAE cellulose, alumina and others, have been used as adsorbent. However, it must be emphasized that silicic acid (1, 2, 3, 4) is the most useful adsorbent for the separation of the total phospholipid mixture from each other in reasonable purity. VAN DEENEN reported that pure phosphatidyl glycerol was obtained from the lipid fraction of spinach leaves after repeated chromatography on silicic acid column (5). The phospholipid extracted from Escherichia coli B consists of abundant phosphatidyl ethanolamine (70-80 %), cardiolipin, phosphatidyl glycerol and other minor components as described in the previous paper (6). The high percentage content of phosphatidyl ethanolamine renders it difficult to separate the phospholipids by the column chromatography. Therefore, repeated chromatographies on the silicic acid column treated with sodium bicarbonate (7) and normal silicic acid column were employed for the isolation of the major components from the total phospholipid of E. coli B. Stepwise elution (4) was carried out with chloroform containing increasing proportions of methanol, and the eluent was divided into several fractions according to experience with thin-layer chromatography.</p

Theory of pressure acoustics with boundary layers and streaming in curved elastic cavities

The acoustic fields and streaming in a confined fluid depend strongly on the acoustic boundary layer forming near the wall. The width of this layer is typically much smaller than the bulk length scale set by the geometry or the acoustic wavelength, which makes direct numerical simulations challenging. Based on this separation in length scales, we extend the classical theory of pressure acoustics by deriving a boundary condition for the acoustic pressure that takes boundary-layer effects fully into account. Using the same length-scale separation for the steady second-order streaming, and combining it with time-averaged short-range products of first-order fields, we replace the usual limiting-velocity theory with an analytical slip-velocity condition on the long-range streaming field at the wall. The derived boundary conditions are valid for oscillating cavities of arbitrary shape and wall motion as long as the wall curvature and displacement amplitude are both sufficiently small. Finally, we validate our theory by comparison with direct numerical simulation in two examples of two-dimensional water-filled cavities: The well-studied rectangular cavity with prescribed wall actuation, and the more generic elliptical cavity embedded in an externally actuated rectangular elastic glass block.Comment: 18 pages, 5 figures, pdfLatex, RevTe

Acoustic radiation- and streaming-induced microparticle velocities determined by micro-PIV in an ultrasound symmetry plane

We present micro-PIV measurements of suspended microparticles of diameters from 0.6 um to 10 um undergoing acoustophoresis in an ultrasound symmetry plane in a microchannel. The motion of the smallest particles are dominated by the Stokes drag from the induced acoustic streaming flow, while the motion of the largest particles are dominated by the acoustic radiation force. For all particle sizes we predict theoretically how much of the particle velocity is due to radiation and streaming, respectively. These predictions include corrections for particle-wall interactions and ultrasonic thermoviscous effects, and they match our measurements within the experimental uncertainty. Finally, we predict theoretically and confirm experimentally that the ratio between the acoustic radiation- and streaming-induced particle velocities is proportional to the square of the particle size, the actuation frequency and the acoustic contrast factor, while it is inversely proportional to the kinematic viscosity.Comment: 11 pages, 9 figures, RevTex 4-

Integrated acoustic and magnetic separation in microfluidic channels

With a growing number of cell-based biotechnological applications, there is a need for particle separation systems capable of multiparameter separations at high purity and throughput, beyond what is presently offered by traditional methods including fluorescence activated cell sorting and column-based magnetic separation. Toward this aim, we report on the integration of microfluidic acoustic and magnetic separation in a monolithic device for multiparameter particle separation. Using our device, we demonstrate high-purity separation of a multicomponent particle mixture at a throughput of up to 10(8) particles/hr. (C) 2009 American Institute of Physics. [doi:10.1063/1.3275577

Particle separation by phase modulated surface acoustic waves

High efficiency isolation of cells or particles from a heterogeneous mixture is a critical processing step in lab-on-a-chip devices. Acoustic techniques offer contactless and label-free manipulation, preserve viability of biological cells, and provide versatility as the applied electrical signal can be adapted to various scenarios. Conventional acoustic separation methods use time-of-flight and achieve separation up to distances of quarter wavelength with limited separation power due to slow gradients in the force. The method proposed here allows separation by half of the wavelength and can be extended by repeating the modulation pattern and can ensure maximum force acting on the particles. In this work, we propose an optimised phase modulation scheme for particle separation in a surface acoustic wave microfluidic device. An expression for the acoustic radiation force arising from the interaction between acoustic waves in the fluid was derived. We demonstrated, for the first time, that the expression of the acoustic radiation force differs in surface acoustic wave and bulk devices, due to the presence of a geometric scaling factor. Two phase modulation schemes are investigated theoretically and experimentally. Theoretical findings were experimentally validated for different mixtures of polystyrene particles confirming that the method offers high selectivity. A Monte-Carlo simulation enabled us to assess performance in real situations, including the effects of particle size variation and non-uniform acoustic field on sorting efficiency and purity, validating the ability to separate particles with high purity and high resolution

Valoración de Volcan Compañía Minera S.A.A.

El presente trabajo de investigación tiene como objetivo determinar el valor fundamental de Volcan Compañía Minera S.A.A. Para calcularlo, se ha empleado el método de flujos de caja descontados, al costo promedio ponderado de capital (WACC, por sus siglas en inglés). Se efectuó una proyección de los estados financieros de la empresa por un horizonte de cuarenta años (2020 a 2059), para lo cual se utilizaron distintos supuestos respecto a producción, precios, inversiones, costos operativos y fuentes de financiamiento, entre otros aspectos. A través de esta metodología, se estimó un valor del patrimonio de $745.0 millones y un valor de S/ 0.44 por acción tipo B, lo cual representa un downside del 7.8 % respecto a la cotización al 30 de septiembre de 2019 de S/ 0.48. Asimismo, se estimó un valor de S/ 0.89 por acción de tipo A, con base en un valor del voto estimado de 2.03x. Luego de realizar el respectivo análisis de riesgos se encontró que la volatilidad del valor intrínseco de la acción es alta, principalmente debido a la alta sensibilidad del valor de la compañía a los precios del zinc y la plata