2,087 research outputs found
Finding weakly reversible realizations of chemical reaction networks using optimization
An algorithm is given in this paper for the computation of dynamically
equivalent weakly reversible realizations with the maximal number of reactions,
for chemical reaction networks (CRNs) with mass action kinetics. The original
problem statement can be traced back at least 30 years ago. The algorithm uses
standard linear and mixed integer linear programming, and it is based on
elementary graph theory and important former results on the dense realizations
of CRNs. The proposed method is also capable of determining if no dynamically
equivalent weakly reversible structure exists for a given reaction network with
a previously fixed complex set.Comment: 18 pages, 9 figure
Conformational mechanism for the stability of microtubule-kinetochore attachments
Regulating the stability of microtubule(MT)-kinetochore attachments is
fundamental to avoiding mitotic errors and ensure proper chromosome segregation
during cell division. While biochemical factors involved in this process have
been identified, its mechanics still needs to be better understood. Here we
introduce and simulate a mechanical model of MT-kinetochore interactions in
which the stability of the attachment is ruled by the geometrical conformations
of curling MT-protofilaments entangled in kinetochore fibrils. The model allows
us to reproduce with good accuracy in vitro experimental measurements of the
detachment times of yeast kinetochores from MTs under external pulling forces.
Numerical simulations suggest that geometrical features of MT-protofilaments
may play an important role in the switch between stable and unstable
attachments
A critical look at the role of the bare parameters in the renormalization of Phi-derivable approximations
We revisit the renormalization of Phi-derivable approximations from a
slightly different point of view than the one which is usually followed in
previous works. We pay particular attention to the question of the existence of
a solution to the self-consistent equation that defines the two-point function
in the Cornwall-Jackiw-Tomboulis formalism and to the fact that some of the
ultraviolet divergences which appear if one formally expands the solution in
powers of the bare coupling do not always appear as divergences at the level of
the solution itself. We discuss these issues using a particular truncation of
the Phi functional, namely the simplest truncation which brings non-trivial
momentum and field dependence to the two-point function.Comment: 30 pages, 12 figure
Geometrodynamics in a spherically symmetric, static crossflow of null dust
The spherically symmetric, static spacetime generated by a crossflow of
non-interacting radiation streams, treated in the geometrical optics limit
(null dust) is equivalent to an anisotropic fluid forming a radiation
atmosphere of a star. This reference fluid provides a preferred / internal
time, which is employed as a canonical coordinate. Among the advantages we
encounter a new Hamiltonian constraint, which becomes linear in the momentum
conjugate to the internal time (therefore yielding a functional Schr\"{o}dinger
equation after quantization), and a strongly commuting algebra of the new
constraints.Comment: Section on boundary behavior and fall-off conditions of canonical
variables added. New references, 1 new figure, 12 pages. Version accepted in
Phys.Rev.
Estimations of orbital parameters of exoplanets from transit photometry by using dynamical constraints
The probability of the detection of Earth-like exoplanets may increase in the
near future after the launch of the space missions using the transit photometry
as observation method. By using this technique only the semi-major axis of the
detected planet can be determined, and there will be no information on the
upper limit of its orbital eccentricity. However, the orbital eccentricity is a
very important parameter, not only from a dynamical point of view, since it
gives also information on the climate and the habitability of the Earth-like
planets. In this paper a possible procedure is suggested for confining the
eccentricity of an exoplanet discovered by transit photometry if an already
known giant planet orbits also in the system.Comment: 16 pages, 10 figures, accepted for Cel. Mech. Dyn. Astro
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