305 research outputs found
MHD Remote Numerical Simulations: Evolution of Coronal Mass Ejections
Coronal mass ejections (CMEs) are solar eruptions into interplanetary space
of as much as a few billion tons of plasma, with embedded magnetic fields from
the Sun's corona. These perturbations play a very important role in
solar--terrestrial relations, in particular in the spaceweather. In this work
we present some preliminary results of the software development at the
Universidad Nacional Autonoma de Mexico to perform Remote MHD Numerical
Simulations. This is done to study the evolution of the CMEs in the
interplanetary medium through a Web-based interface and the results are store
into a database. The new astrophysical computational tool is called the Mexican
Virtual Solar Observatory (MVSO) and is aimed to create theoretical models that
may be helpful in the interpretation of observational solar data.Comment: 2 pages, 1 color figure. To appear in Proceedings IAU Symposium No.
259. Cosmic Magnetic Fields: From Planets, to Stars and Galaxies. In pres
Irreversible Thermodynamics in Multiscale Stochastic Dynamical Systems
This work extends the results of the recently developed theory of a rather
complete thermodynamic formalism for discrete-state, continuous-time Markov
processes with and without detailed balance. We aim at investigating the
question that whether and how the thermodynamic structure is invariant in a
multiscale stochastic system. That is, whether the relations between
thermodynamic functions of state and process variables remain unchanged when
the system is viewed at different time scales and resolutions. Our results show
that the dynamics on a fast time scale contribute an entropic term to the
"internal energy function", , for the slow dynamics. Based on the
conditional free energy , one can then treat the slow dynamics as if
the fast dynamics is nonexistent. Furthermore, we show that the free energy,
which characterizes the spontaneous organization in a system without detailed
balance, is invariant with or without the fast dynamics: The fast dynamics is
assumed to reach stationarity instantaneously on the slow time scale; they have
no effect on the system's free energy. The same can not be said for the entropy
and the internal energy, both of which contain the same contribution from the
fast dynamics. We also investigate the consequences of time-scale separation in
connection to the concepts of quasi-stationaryty and steady-adiabaticity
introduced in the phenomenological steady-state thermodynamics
Distribución del cuadrado de la máxima correlación canónica para tamaños muestrales pequeños
. Assume that the normally distributed random vector X of d components is partitioned into two subvectors X~'> and X(» of and q components ¡3 respectively. Suppose also that the two subvectors are not correlated. In this work wc study thc distribution of the largcst squared canonical correlation r12 whcn p, q and the number of observations in the sample N, are rathcr small. We give the cxplicit expressions of the cumulative distribution functions and the computed values of thc sample mean and variance of r1>. We prove that ihere cxists a stochastic order betwcen the largest squared canonical correlations obtained from two diffcrent partitions of the vector X. Morc precisely, r1> mercase stochastically when ihe diflerence between p and q decrease. Since X(1> and X~>~ are uncorrelated the largest squared canonical correlation in the population X12 is ¡ero. Therefore dic mean of r¡2 is the Ñas of r1> when r1> is used to estimate Xi>. Tbc values of the mean and the variance show that the square of thc Ñas is bigger than thc variance in ah the cases. 1
Boolean Models of Bistable Biological Systems
This paper presents an algorithm for approximating certain types of dynamical
systems given by a system of ordinary delay differential equations by a Boolean
network model. Often Boolean models are much simpler to understand than complex
differential equations models. The motivation for this work comes from
mathematical systems biology. While Boolean mechanisms do not provide
information about exact concentration rates or time scales, they are often
sufficient to capture steady states and other key dynamics. Due to their
intuitive nature, such models are very appealing to researchers in the life
sciences. This paper is focused on dynamical systems that exhibit bistability
and are desc ribedby delay equations. It is shown that if a certain motif
including a feedback loop is present in the wiring diagram of the system, the
Boolean model captures the bistability of molecular switches. The method is
appl ied to two examples from biology, the lac operon and the phage lambda
lysis/lysogeny switch
Flagellar Motility of Trypanosoma cruzi Epimastigotes
The hemoflagellate Trypanosoma cruzi is the causative agent of American trypanosomiasis. Despite the importance of motility in the parasite life cycle, little is known about T. cruzi motility, and there is no quantitative description of its flagellar beating. Using video microscopy and quantitative vectorial analysis of epimastigote trajectories, we find a forward parasite motility defined by tip-to-base symmetrical flagellar beats. This motion is occasionally interrupted by base-to-tip highly asymmetric beats, which represent the ciliary beat of trypanosomatid flagella. The switch between flagellar and ciliary beating facilitates the parasite's reorientation, which produces a large variability of movement and trajectories that results in different distance ranges traveled by the cells. An analysis of the distance, speed, and rotational angle indicates that epimastigote movement is not completely random, and the phenomenon is highly dependent on the parasite behavior and is characterized by directed and tumbling parasite motion as well as their combination, resulting in the alternation of rectilinear and intricate motility paths
A first--order irreversible thermodynamic approach to a simple energy converter
Several authors have shown that dissipative thermal cycle models based on
Finite-Time Thermodynamics exhibit loop-shaped curves of power output versus
efficiency, such as it occurs with actual dissipative thermal engines. Within
the context of First-Order Irreversible Thermodynamics (FOIT), in this work we
show that for an energy converter consisting of two coupled fluxes it is also
possible to find loop-shaped curves of both power output and the so-called
ecological function against efficiency. In a previous work Stucki [J.W. Stucki,
Eur. J. Biochem. vol. 109, 269 (1980)] used a FOIT-approach to describe the
modes of thermodynamic performance of oxidative phosphorylation involved in
ATP-synthesis within mithochondrias. In that work the author did not use the
mentioned loop-shaped curves and he proposed that oxidative phosphorylation
operates in a steady state simultaneously at minimum entropy production and
maximum efficiency, by means of a conductance matching condition between
extreme states of zero and infinite conductances respectively. In the present
work we show that all Stucki's results about the oxidative phosphorylation
energetics can be obtained without the so-called conductance matching
condition. On the other hand, we also show that the minimum entropy production
state implies both null power output and efficiency and therefore this state is
not fulfilled by the oxidative phosphorylation performance. Our results suggest
that actual efficiency values of oxidative phosphorylation performance are
better described by a mode of operation consisting in the simultaneous
maximization of the so-called ecological function and the efficiency.Comment: 20 pages, 7 figures, submitted to Phys. Rev.
Does the availability of single cigarettes promote or inhibit cigarette consumption? Perceptions, prevalence and correlates of single cigarette use among adult Mexican smokers
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