398 research outputs found
Scanning the critical fluctuations: Application to the phenomenology of the two-dimensional XY model
No full textWe show how applying field conjugated to the order parameter may act as a very precise probe to explore the probability distribution function of the order parameter. Using this “magnetic-field scanning” on large-scale numerical simulations of the critical two-dimensional XY model, we are able to discard the conjectured double-exponential form of the large-magnetization asymptote.DelftChemTechApplied Science
The effect of porosity of dust particles on polarization and color with special reference to comets
No full text[EN] Cosmic dust particles are mostly responsible for polarization of the light that we observe from astrophysical objects. They also lead to color-extinction, thermal re-emission and other scattering related phenomena. Micrometric dust particles are often
made of smaller constituent (nanometric grains). They are characterized by their size (average radius), chemical composition and morphology (including porosity). In the present work, we address the question of the role of the dust particle porosity on light polarization and color, using Discrete Dipole Approximation (DDA) light scattering code. To this purpose, we develop an algorithm to generate dust particles of arbitrary values of porosity. In brief, starting from a compact spherical ensemble of dipoles,randomly the dipoles are removed one by one, such that the remaining dipoles remain connected within their neighbours. We stop the removal process when the desired porosity is obtained. Then we compute and study the optical properties of the porous dust particle.
The main objective of this paper is to develop a tool to generate dust particles with an arbitrary value of porosity and to study the effect of porosity on their light scattering properties. As a possible application, we simulate cometary polarization and color values which grossly match with the observed ones for the comet 1P/Halley, leaving scope for future work.R.B. thanks the Assam University, Silchar, for hospitality in the framework of 'Global Initiative for Academic Network' (GIAN) programme from MHRD, April 2016. The authors AKS and RV thank Erasmus Mundus - NAMASTE programme for funds to do this collaborative work. Finally, we are thankful to anonymous referees of this paper, due to whose comments we believe the quality of paper has improved.Sen, AK.; Botet, R.; Vilaplana Cerda, RI.; Choudhury, NR.; Gupta, R. (2017). The effect of porosity of dust particles on polarization and color with special reference to comets. Journal of Quantitative Spectroscopy and Radiative Transfer. 198:164-178. doi:10.1016/j.jqsrt.2017.05.009S16417819
Amélioration de la méthode T-Matrix champ moyen pour la diffusion de lumière par des agrégats fractals de sphères identiques dans des environnements astrophysiques
No full textInternational audienceAggregated particles and aerosols are common in natural or industrial environments. Analysing their scattering and absorption properties with precise methods may prove useful for gaining information about real particles, using remote sensing or in situ active optical instruments in natural environments. Many methods, with varying complexities, were developed in the past. For aggregates of spheres, the most recent version of the T-Matrix method by Mackowski and Mishchenko ( 2011) is able to treat the problem almost exactly and can yield all the details of the scattering properties. However, for computational reasons, the T-Matrix method cannot handle large particles. In order to deal with large particles, a mean-field version of the T-Matrix theory was developed by Botet et al. (1997) for aggregates of identical spheres and used in particular to analyse the case of Titan haze. This mean-field T-Matrix method is efficient to quickly calculate accurate approximations of many optical properties of aggregates of Mie spheres, but it is inherently limited by the mean field approximations. It uses crude approximation of the pair-correlation functions (Seignovert et al. ( 2017)) and leads to inaccurate estimations in the geometrical optics limit (Tazaki and Tanaka ( 2018)). In the present work, we bring improvements related to these two limitations. This significantly increases the validity range of the method and its accuracy. We display comparisons with the T-Matrix method in order to assess the performance of the new version of the mean field method (MFT-M + )
From colloidal dispersions to colloidal pastesthrough solid–liquid separation processes
No full textSolid–liquid separation is an operation that starts with a dispersion of solid particles in a liquid and removes some of the liquid from the particles, producing a concentrated solid paste and a clean liquid phase. It is similar to thermodynamic processes where pressure is applied to a system in order to reduce its volume. In dispersions, the resistance to this osmotic compression depends on interactions between the dispersed particles. The first part of this work deals with dispersions of repelling particles, which are either silica nanoparticles or synthetic clay platelets, dispersed in aqueous solutions. In these conditions, each particle is surrounded by an ionic layer, which repels other ionic layers. This results in a structure with strong short-range order. At high particle volume fractions, the overlap of ionic layers generates large osmotic pressures; these pressures may be calculated, through the cell model, as the cost of reducing the volume of each cell. The variation of osmotic pressure with volume fraction is the equation of state of the dispersion. The second part of this work deals with dispersions of aggregated particles, which are silica nanoparticles, dispersed in water and flocculated by multivalent cations. This produces large bushy aggregates, with fractal structures that are maintained through interparticle surface– surface bonds. As the paste is submitted to osmotic pressures, small relative displacements of the aggregated particles lead to structural collapse. The final structure is made of a dense skeleton immersed in a nearly homogeneous matrix of aggregated particles. The variation of osmotic resistance with volume fraction is the compression law of the paste; it may be calculated through a numerical model that takes into account the noncentral interparticle forces. According to this model, the response of aggregated pastes to applied stress may be controlled through the manipulation of interparticle adhesion
Therapeutic and other interventions to reduce the risk of mother-to-child transmission of HIV-1 in Europe. The European Collaborative Study
No full textC. Thorne, M.-L. Newell, A. Bailey, C.S. Peckham, C. Giaquinto, E. Ruga, A. De Rossi, D. Truscia, I. Grosch-Worner, A. Schafer, J. Mok, F. Johnstone, F. Omenaca, J. Jiminez, C.De Alba, M.C. Garcia-Rodriguez, I. Bates, I. De Jose, F. Hawkins, R. Martinez Zapico, F. Asensi-Botet, M.C. Otero, D. Perez-Tamarit, A. Gonzalez Molina, H. Canosa, H. Scherpbier, K. Boer, A.B. Bohlin, S. Lindgren, E. Belfrage, J. Levy, A. Alimenti, P. Barlow, A. Ferrazin, A. Dre Maria, C. Gotta, V. Maritati, A. Mur, M.T. Rovira, A. Paya, O. Coll,
C. Fortuny, J. Boguna, M. Casellas Caro, Y. Canet, G. Pardi, A.E. Semprini, M. Ravizza, C. Castagna,
S. Fiore, B. Guerra, S. Bianchi, L. Bovicelli, E. Prati, S. Zanelli, M. Duse, A. Soresina, G. Scaravelli,
M. Stegagno, M. De Santis, M.-L. Muggiasca, P. Marchisio, A. Iasci, A. Spinillo, A. Bucceri, E. Grossi,
L. Rancilio, R. Smith, A.-M. Lewi
How a colloidal paste flows – scaling behaviors in dispersions of aggregated particles under mechanical stress –
No full textWe have developed a novel computational scheme that allows direct numerical simulation of the mechanical
behavior of sticky granular matter under stress. We present here the general method, with particular emphasis on the
particle features at the nanometric scale. It is demonstrated that, although sticky granular material is quite complex and is a good example of a challenging computational problem (it is a dynamical problem, with irreversibility, self-organization
and dissipation), its main features may be reproduced on the basis of rather simple numerical model, and a small number of physical parameters. This allows precise analysis of the possible deformation processes in soft materials submitted to mechanical stress. This results in direct relationship between the macroscopic rheology of these pastes and local interactions
between the particles
Spontaneous Symmetry Breaking in Quantum Systems: Emergence or Reduction?
No full textBeginning with Anderson (1972), spontaneous symmetry breaking (SSB) in infinite quantum systems is often put forward as an example of (asymptotic) emergence in physics, since in theory no finite system should display it.
Even the correspondence between theory and reality is at stake here, since numerous real materials show SSB in their ground states (or equilibrium states at low temperature), although they are finite.
Thus against what is sometimes called `Earman's Principle',
a genuine physical effect (viz. SSB) seems theoretically recovered only in some idealization (namely the thermodynamic limit), disappearing as soon as the the idealization is removed. We review the well-known arguments that (at first sight) no finite system can exhibit SSB, using the formalism of algebraic quantum theory in order to control the thermodynamic limit and unify the description of finite- and infinite-volume systems. Using the striking mathematical analogy between the thermodynamic limit and the classical limit, we show that a similar situation obtains in quantum mechanics (which typically forbids SSB) versus classical mechanics (which allows it).
This discrepancy between formalism and reality is quite similar to the measurement problem, and hence we address it in the same way, adapting an argument of the author and Reuvers (2013) that was originally intended to explain the collapse of the wave-function within conventional quantum mechanics. Namely, exponential sensitivity to (asymmetric) perturbations of the (symmetric) dynamics as the system size increases causes symmetry breaking already in finite but very large quantum systems. This provides continuity between finite- and infinite-volume descriptions of quantum systems featuring SSB and hence restores Earman's Principle (at least in this particularly threatening case)
Probable early-onset group B streptococcal neonatal sepsis: A serious clinical condition related to intrauterine infection
No full textCarbonell-Estrany, X., Figueras-Aloy, J., Salcedo-Abizanda, S., De La Rosa-Fraile, M., Salcedo, S., López Sastre, J., Coto Cotallo, G.D., Fernández Colomer, B., González, T., Reparaz Vidal, R., Fidalgo Álvarez, I., Alvaro Iglesias, E., Aragón García, M.P., González Armengod, C., Pedraz García, C., Urbón Artero, A., Aparicio Lozano, P., Cotero Lavín, A., Paisán Grisolía, L., De Alba Romero, C., Sánchez Luna, M., Moro Serrano, M., Botet, F., Krauel Vidal, X., Iriondo Sanz, M., Porta, R., Roqués Serradilla, V., Ortiz Tardío, J., García Del Río, M., Guzmán Cabañas, J., Zamarriego, C., Rosso González, M.L., García García, M.J., Doménech Martínez, E
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