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Alberto Vailati

Other affiliations: University of Cagliari
Bio: Alberto Vailati is an academic researcher from University of Milan. The author has contributed to research in topics: Scattering & Diffusion (business). The author has an hindex of 24, co-authored 84 publications receiving 1661 citations. Previous affiliations of Alberto Vailati include University of Cagliari.


Papers
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Journal ArticleDOI
01 Nov 1997-Nature
TL;DR: In this paper, the authors show that large spatial fluctuations in concentration can occur during a free diffusion process, and that these pronounced inhomogeneities are due to a coupling between velocity and concentration fluctuations in the non-equilibrium state.
Abstract: Macroscopic concentration gradients in physical systems relax towards equilibrium by diffusion1,2,3, in the absence of bulk motion. This is normally regarded as a spatially homogeneous mixing process. Here, however, we show that unexpectedly large spatial fluctuations in concentration can occur during a free diffusion process. We set up an initially sharp interface between two miscible fluids by letting a mixture phase-separate below the critical consolution temperature and then raising the temperature quickly to the single-phase region. Shadowgraph images and low-angle light scattering show evidence for large fluctuations in composition, orders of magnitude larger in amplitude than those seen in the equilibrium state. We show that these pronounced inhomogeneities are due to a coupling between velocity and concentration fluctuations in the non-equilibrium state4,5,6. Gravity cuts off the fluctuations above a certain wavelength, and the amplitude of the fluctuations at longer wavelengths does not depend on any relevant thermodynamic property of the fluid. As a consequence, these giant fluctuations should be observable in any mixture undergoing mixing by diffusion.

121 citations

Journal ArticleDOI
TL;DR: Experimental results obtained in microgravity during the flight of the FOTON M3 satellite find that during a diffusion process a dilute polymer solution exhibits scale-invariant concentration fluctuations with sizes ranging up to millimetres, and relaxation times as large as 1,000 s.
Abstract: Spatial scale invariance represents a remarkable feature of natural phenomena. A ubiquitous example is represented by miscible liquid phases undergoing diffusion. Theory and simulations predict that in the absence of gravity diffusion is characterized by long-ranged algebraic correlations. Experimental evidence of scale invariance generated by diffusion has been limited, because on Earth the development of long-range correlations is suppressed by gravity. Here we report experimental results obtained in microgravity during the flight of the FOTON M3 satellite. We find that during a diffusion process a dilute polymer solution exhibits scale-invariant concentration fluctuations with sizes ranging up to millimetres, and relaxation times as large as 1,000 s. The scale invariance is limited only by the finite size of the sample, in agreement with recent theoretical predictions. The presence of such fluctuations could possibly impact the growth of materials in microgravity.

105 citations

Journal ArticleDOI
TL;DR: The two point intensity correlation in the near field of the scattered light is directly related to the two point density correlation g(r) and a discussion on the desirability of the technique as a simple and powerful alternative to low angle scattering is presented.
Abstract: We show that the two point intensity correlation in the near field of the scattered light is directly related to the two point density correlation g(r). Preliminary measurements on two sets of calibrated random pinholes of 140 and 300 mm diameters, and on aqueous solutions of latex spheres of 5, 10, and 40 mm are reported. A discussion on the desirability of the technique as a simple and powerful alternative to low angle scattering will be presented.

99 citations

Journal ArticleDOI
TL;DR: It is shown that heat convection in water can be suppressed by adding a small amount of highly thermophilic nanoparticles, but such suppression is not effective when a suspension with uniform concentration of nanoparticles is suddenly heated from below.
Abstract: Heat convection in water can be suppressed by adding a small amount of highly thermophilic nanoparticles. We show that such suppression is not effective when a suspension with uniform concentration of nanoparticles is suddenly heated from below. At Rayleigh numbers smaller than a sample dependent threshold Ra;{*} we observe transient oscillatory convection. Unexpectedly, the duration of convection diverges at Ra;{*}. Above Ra;{*} oscillatory convection becomes permanent and the heat transferred exhibits bistability. Our results are explained only partially and qualitatively by existing theories.

89 citations

Journal ArticleDOI
TL;DR: In this article, a fluctuating hydrodynamics approach is presented for the calculation of the structure factor for imedependentnonequilibrium diffusive processes in binary liquid mixtures, where the hydrodynamic equations are linearized around the time-dependent macroscopic state given by the usual phenomenological diffusion equation.
Abstract: A fluctuating hydrodynamics approach is presented for the calculation of the structure factor for imedependentnonequilibrium diffusive processes in binary liquid mixtures. The hydrodynamic equations are linearized around the time-dependent macroscopic state given by the usual phenomenological diffusion equation. The cases of free diffusion, thermal diffusion, and barodiffusion are considered in detail. The results are used to describe the low-angle scattered intensity distributions from the time-dependent concentration profiles during the approach to steady state. The theoretical predictions are found to be in agreement with experimental data from thermal diffusion and free diffusion experiments. It is shown that in general the presence of nonequilibrium concentration fluctuations yields a substantial increase in the static structure factor over the equilibrium value, at least for the cases of free diffusion and thermal diffusion. As in the case of nonequilibrium fluctuations at steady state, the static structure factor displays a fast k divergence at larger wave vectors k, and saturation to a constant value for k smaller than a critical wave vector kRO. It is also shown that the static structure factor from a sedimenting mixture is actually temporarily lowered below the equilibrium value for k smaller thankRO. As the steady state is approached, the structure factor loses any k dependence and it attains the equilibrium value.@S1063-651X~98!14910-3#

82 citations


Cited by
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TL;DR: In this article, the authors summarized the recent progress on the study of nanofluids, such as the preparation methods, the evaluation methods for the stability of nanometrics, and the ways to enhance the stability for nanofl fluids, and presented the broad range of current and future applications in various fields including energy and mechanical and biomedical fields.
Abstract: Nanofluids, the fluid suspensions of nanomaterials, have shown many interesting properties, and the distinctive features offer unprecedented potential for many applications. This paper summarizes the recent progress on the study of nanofluids, such as the preparation methods, the evaluation methods for the stability of nanofluids, and the ways to enhance the stability for nanofluids, the stability mechanisms of nanofluids, and presents the broad range of current and future applications in various fields including energy and mechanical and biomedical fields. At last, the paper identifies the opportunities for future research.

1,320 citations

Journal ArticleDOI
TL;DR: In this article, the authors describe suspensions of nanoparticles in fluids that show significant enhancement of their properties at modest nanoparticle concentrations, i.e., at nanoparticles' concentrations.
Abstract: Nanofluids are suspensions of nanoparticles in fluids that show significant enhancement of their properties at modest nanoparticle concentrations. Many of the publications on nanofluids are about u...

882 citations

Journal Article
TL;DR: The International Nanofluid Property Benchmark Exercise (INPBE) as discussed by the authors was held in 1998, where the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or "nanofluids" was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady state methods, and optical methods.
Abstract: This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

881 citations

Journal ArticleDOI
TL;DR: There has been a lot of experimental and theoretical work on the nature of critical phenomena in the neighbourhood of second order phase transitions as discussed by the authors, but it has not been easy to get a good overall view of this work without digging through the rather complex original literature, although there are some good review articles covering particular aspects of the work.
Abstract: H E Stanley Oxford: University Press 1971 pp xx + 308 price ?5 In the past fifteen years or so there has been a lot of experimental and theoretical work on the nature of critical phenomena in the neighbourhood of second order phase transitions. It has not been easy to get a good overall view of this work without digging through the rather complex original literature, although there are some good review articles covering particular aspects of the work.

481 citations