2,832 research outputs found
Peripheral mixing of passive scalar at small Reynolds number
Mixing of a passive scalar in the peripheral region close to a wall is
investigated by means of accurate direct numerical simulations of both a
three-dimensional Couette channel flow at low Reynolds numbers and a
two-dimensional synthetic flow. In both cases, the resulting phenomenology can
be understood in terms of the theory recently developed by Lebedev and Turitsyn
[Phys. Rev. E 69, 036301, 2004]. Our results prove the robustness of the
identified mechanisms responsible for the persistency of scalar concentration
close to the wall with important consequences in completely different fields
ranging from microfluidic applications to environmental dispersion modeling.Comment: 4 pages, 5 figure
Large-scale confinement and small-scale clustering of floating particles in stratified turbulence
We study the motion of small inertial particles in stratified turbulence. We
derive a simplified model, valid within the Boussinesq approximation, for the
dynamics of small particles in presence of a mean linear density profile. By
means of extensive direct numerical simulations, we investigate the statistical
distribution of particles as a function of the two dimensionless parameters of
the problem. We find that vertical confinement of particles is mainly ruled by
the degree of stratification, with a weak dependency on the particle
properties. Conversely, small scale fractal clustering, typical of inertial
particles in turbulence, depends on the particle relaxation time and is almost
independent on the flow stratification. The implications of our findings for
the formation of thin phytoplankton layers are discussed.Comment: 5 pages, 6 figure
Of tradition and conversion : a comparative study of two Phuo griottes
La version intégrale de ce mémoire est disponible uniquement pour consultation individuelle à la Bibliothèque de musique de l’Université de Montréal (www.bib.umontreal.ca/MU).Cette recherche apporte deux contributions importantes à l’étude ethnomusicologique: l’étude de portrait ainsi que l’analyse comparative de la vie et de la musique d’une griotte traditionnelle et d’une griotte convertie au Christianisme au sein de la société Phuo au Burkina Faso. Cette étude comparative fait l’illustration de l’adaptation d’un répertoire rencontrée dans d’autres contextes musico-culturels. Cela comprend non seulement une exploration de la vie et de la musique de la tradition féminine phuo, mais aussi la compréhension du phénomène d’adaptation de la fonction de griotte, ou le rôle de Phuo ‘ƴuo,’ au milieu de l’église Chrétienne évangélique. Nous présentons aussi une brève analyse des deux répertoires ainsi qu’un regard sur les éléments esthétiques et symboliques au cœur des pratiques vocales individuelles.This research brings two important elements to the study of ethnomusicology: the study and comparative analysis between the life and music of a traditional griotte and a griotte converted to Christianity within the Phuo society of Burkina Faso. It is an illustration of the adaptation of a repertoire which can be comparatively encountered in other musico-cultural contexts. This incorporates not only an exploration into the life and the music of the feminine Phuo tradition, but also an attempt at a deeper understanding of the griotte, or ‘ƴuo,’ role and function within the evangelical Christian church. We also present a brief analysis of both repertoires, as well as look into the aesthetic and symbolic elements within their individual vocal practices
Point-particle method to compute diffusion-limited cellular uptake
We present an efficient point-particle approach to simulate
reaction-diffusion processes of spherical absorbing particles in the
diffusion-limited regime, as simple models of cellular uptake. The exact
solution for a single absorber is used to calibrate the method, linking the
numerical parameters to the physical particle radius and uptake rate. We study
configurations of multiple absorbers of increasing complexity to examine the
performance of the method, by comparing our simulations with available exact
analytical or numerical results. We demonstrate the potentiality of the method
in resolving the complex diffusive interactions, here quantified by the
Sherwood number, measuring the uptake rate in terms of that of isolated
absorbers. We implement the method in a pseudo-spectral solver that can be
generalized to include fluid motion and fluid-particle interactions. As a test
case of the presence of a flow, we consider the uptake rate by a particle in a
linear shear flow. Overall, our method represents a powerful and flexible
computational tool that can be employed to investigate many complex situations
in biology, chemistry and related sciences.Comment: 13 pages, 13 figure
Specialization of strategies and herding behavior of trading firms in a financial market
The understanding of complex social or economic systems is an important
scientific challenge. Here we present a comprehensive study of the Spanish
Stock Exchange showing that most financial firms trading in that market are
characterized by a resulting strategy and can be classified in groups of firms
with different specialization. Few large firms overally act as trending firms
whereas many heterogeneous firm act as reversing firms. The herding properties
of these two groups are markedly different and consistently observed over a
four-year period of trading.Comment: 8 pages, 5 figure
Graeber, David (2011). Debt: The First 5,000 Years
Brooklyn: Melville House, 534 pp. Traducido también al castellano. Graeber, David (2012): En Deuda. Una historia alternativa de la
economÃa. Barcelona: Ariel, 720 pp
Stock mechanics: a general theory and method of energy conservation with applications on DJIA
A new method, based on the original theory of conservation of sum of kinetic
and potential energy defined for prices is proposed and applied on Dow Jones
Industrials Average (DJIA). The general trends averaged over months or years
gave a roughly conserved total energy, with three different potential energies,
i.e. positive definite quadratic, negative definite quadratic and linear
potential energy for exponential rises (and falls), sinusoidal oscillations and
parabolic trajectories, respectively. Corresponding expressions for force
(impact) are also given. Keywords:Comment: 14 pages, 3 figures, scehudled for IJMPC 17/ issue
Statistical properties of thermodynamically predicted RNA secondary structures in viral genomes
By performing a comprehensive study on 1832 segments of 1212 complete genomes
of viruses, we show that in viral genomes the hairpin structures of
thermodynamically predicted RNA secondary structures are more abundant than
expected under a simple random null hypothesis. The detected hairpin structures
of RNA secondary structures are present both in coding and in noncoding regions
for the four groups of viruses categorized as dsDNA, dsRNA, ssDNA and ssRNA.
For all groups hairpin structures of RNA secondary structures are detected more
frequently than expected for a random null hypothesis in noncoding rather than
in coding regions. However, potential RNA secondary structures are also present
in coding regions of dsDNA group. In fact we detect evolutionary conserved RNA
secondary structures in conserved coding and noncoding regions of a large set
of complete genomes of dsDNA herpesviruses.Comment: 9 pages, 2 figure
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