62,271 research outputs found
Mixing across fluid interfaces compressed by convective flow in porous media
We study the mixing in the presence of convective flow in a porous medium.
Convection is characterized by the formation of vortices and stagnation points,
where the fluid interface is stretched and compressed enhancing mixing. We
analyze the behavior of the mixing dynamics in different scenarios using an
interface deformation model. We show that the scalar dissipation rate, which is
related to the dissolution fluxes, is controlled by interfacial processes,
specifically the equilibrium between interface compression and diffusion, which
depends on the flow field configuration. We consider different scenarios of
increasing complexity. First, we analyze a double-gyre synthetic velocity
field. Second, a Rayleigh-B\'enard instability (the Horton-Rogers-Lapwood
problem), in which stagnation points are located at a fixed interface. This
system experiences a transition from a diffusion controlled mixing to a chaotic
convection as the Rayleigh number increases. Finally, a Rayleigh-Taylor
instability with a moving interface, in which mixing undergoes three different
regimes: diffusive, convection dominated, and convection shutdown. The
interface compression model correctly predicts the behavior of the systems. It
shows how the dependency of the compression rate on diffusion explains the
change in the scaling behavior of the scalar dissipation rate. The model
indicates that the interaction between stagnation points and the correlation
structure of the velocity field is also responsible for the transition between
regimes. We also show the difference in behavior between the dissolution fluxes
and the mixing state of the systems. We observe that while the dissolution flux
decreases with the Rayleigh number, the system becomes more homogeneous. That
is, mixing is enhanced by reducing diffusion. This observation is explained by
the effect of the instability patterns
On the stability of field-theoretical regularizations of negative tension branes
Any attempt to regularize a negative tension brane through a bulk scalar
requires that this field is a ghost. One can try to improve in this aspect in a
number of ways. For instance, it has been suggested to employ a field whose
kinetic term is not sign definite, in the hope that the background may be
overall stable. We show that this is not the case; the physical perturbations
(gravity included) of the system do not extend across the zeros of the kinetic
term; hence, all the modes are entirely localized either where the kinetic term
is positive, or where it is negative; this second type of modes are ghosts. We
show that this conclusion does not depend on the specific choice for the
kinetic and potential functions for the bulk scalar.Comment: 7 pages, 3 figure
Improved entropic uncertainty relations and information exclusion relations
The uncertainty principle can be expressed in entropic terms, also taking
into account the role of entanglement in reducing uncertainty. The information
exclusion principle bounds instead the correlations that can exist between the
outcomes of incompatible measurements on one physical system, and a second
reference system. We provide a more stringent formulation of both the
uncertainty principle and the information exclusion principle, with direct
applications for, e.g., the security analysis of quantum key distribution,
entanglement estimation, and quantum communication. We also highlight a
fundamental distinction between the complementarity of observables in terms of
uncertainty and in terms of information.Comment: 11 pages, 1 figure, v2: close to published versio
A numerical study of detonation diffraction
An investigation of detonation diffraction through an abrupt area change has been carried out via a set of two-dimensional numerical simulations parameterized by the activation energy of the reactant. Our analysis is specialized to a reactive mixture with a perfect gas equation of state and a single-step reaction in the Arrhenius form. Lagrangian particles are injected into the flow as a diagnostic tool for identifying the dominant terms in the equation that describes the temperature rate of change of a fluid element, expressed in the shock-based reference system. When simplified, this equation provides insight into the competition between the energy release rate and the expansion rate behind the diffracting front. The mechanism of spontaneous generation of transverse waves along the diffracting front is carefully analysed and related to the sensitivity of the reaction rate to temperature. We study in detail three highly resolved cases of detonation diffraction that illustrate different types of behaviour, super-, sub- and near-critical diffraction
Gravitational Rutherford scattering and Keplerian orbits for electrically charged bodies in heterotic string theory
Properties of the motion of electrically charged particles in the background
of the Gibbons-Maeda-Garfinkle-Horowitz-Strominger (GMGHS) black hole is
presented in this paper. Radial and angular motion are studied analytically for
different values of the fundamental parameter. Therefore, gravitational
Rutherford scattering and Keplerian orbits are analysed in detail. Finally,
this paper complements previous work by Fernando for null geodesics (Phys. Rev.
D 85: 024033, 2012), Olivares & Villanueva (Eur. Phys. J. C 73: 2659, 2013) and
Blaga (Automat. Comp. Appl. Math. 22, 41 (2013); Serb. Astron. J. 190, 41
(2015)) for time-like geodesics.Comment: 11 pages, 12 figure
Influence of homology and node-age on the growth of protein-protein interaction networks
Proteins participating in a protein-protein interaction network can be
grouped into homology classes following their common ancestry. Proteins added
to the network correspond to genes added to the classes, so that the dynamics
of the two objects are intrinsically linked. Here, we first introduce a
statistical model describing the joint growth of the network and the
partitioning of nodes into classes, which is studied through a combined
mean-field and simulation approach. We then employ this unified framework to
address the specific issue of the age dependence of protein interactions,
through the definition of three different node wiring/divergence schemes.
Comparison with empirical data indicates that an age-dependent divergence move
is necessary in order to reproduce the basic topological observables together
with the age correlation between interacting nodes visible in empirical data.
We also discuss the possibility of nontrivial joint partition/topology
observables.Comment: 14 pages, 7 figures [accepted for publication in PRE
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