38,532 research outputs found
Parametric Competition in non-autonomous Hamiltonian Systems
In this work we use the formalism of chord functions (\emph{i.e.}
characteristic functions) to analytically solve quadratic non-autonomous
Hamiltonians coupled to a reservoir composed by an infinity set of oscillators,
with Gaussian initial state. We analytically obtain a solution for the
characteristic function under dissipation, and therefore for the determinant of
the covariance matrix and the von Neumann entropy, where the latter is the
physical quantity of interest. We study in details two examples that are known
to show dynamical squeezing and instability effects: the inverted harmonic
oscillator and an oscillator with time dependent frequency. We show that it
will appear in both cases a clear competition between instability and
dissipation. If the dissipation is small when compared to the instability, the
squeezing generation is dominant and one can see an increasing in the von
Neumann entropy. When the dissipation is large enough, the dynamical squeezing
generation in one of the quadratures is retained, thence the growth in the von
Neumann entropy is contained
Topology and Dynamics in Complex Networks: The Role of Edge Reciprocity
A key issue in complex systems regards the relationship between topology and
dynamics. In this work, we use a recently introduced network property known as
steering coefficient as a means to approach this issue with respect to
different directed complex network systems under varying dynamics. Theoretical
and real-world networks are considered, and the influences of reciprocity and
average degree on the steering coefficient are quantified. A number of
interesting results are reported that can assist the design of complex systems
exhibiting larger or smaller relationships between topology and dynamics
Asymmetrical bloch branes and the hierarchy problem
We investigate a two scalar fields split braneworld model which leads to a
possible approach to the hierarchy problem within the thick brane scenario. The
model exhibits a resulting asymmetric warp factor suitable for this purpose.
The solution is obtained by means of the orbit equation approach for a specific
value of one of the parameters. Besides, we analyze the model qualitative
behaviour for arbitrary parameters by inspecting the underlying dynamical
system defined by the equations which give rise to the braneworld model. We
finalize commenting on the metric fluctuation and stability issues.Comment: 8 pages, 7 figure
Evidence for Lattice Effects at the Charge-Ordering Transition in (TMTTF)X
High-resolution thermal expansion measurements have been performed for
exploring the mysterious "structureless transition" in (TMTTF)X (X =
PF and AsF), where charge ordering at coincides with the
onset of ferroelectric order. Particularly distinct lattice effects are found
at in the uniaxial expansivity along the interstack
-direction. We propose a scheme involving a charge
modulation along the TMTTF stacks and its coupling to displacements of the
counteranions X. These anion shifts, which lift the inversion symmetry
enabling ferroelectric order to develop, determine the 3D charge pattern
without ambiguity. Evidence is found for another anomaly for both materials at
0.6 indicative of a phase transition
related to the charge ordering
Host reticulocytes provide metabolic reservoirs that can be exploited by malaria parasites
Human malaria parasites proliferate in different erythroid cell types during infection. Whilst Plasmodium vivax exhibits a strong preference for immature reticulocytes, the more pathogenic P. falciparum primarily infects mature erythrocytes. In order to assess if these two cell types offer different growth conditions and relate them to parasite preference, we compared the metabolomes of human and rodent reticulocytes with those of their mature erythrocyte counterparts. Reticulocytes were found to have a more complex, enriched metabolic profile than mature erythrocytes and a higher level of metabolic overlap between reticulocyte resident parasite stages and their host cell. This redundancy was assessed by generating a panel of mutants of the rodent malaria parasite P. berghei with defects in intermediary carbon metabolism (ICM) and pyrimidine biosynthesis known to be important for P. falciparum growth and survival in vitro in mature erythrocytes. P. berghei ICM mutants (pbpepc-, phosphoenolpyruvate carboxylase and pbmdh-, malate dehydrogenase) multiplied in reticulocytes and committed to sexual development like wild type parasites. However, P. berghei pyrimidine biosynthesis mutants (pboprt-, orotate phosphoribosyltransferase and pbompdc-, orotidine 5′-monophosphate decarboxylase) were restricted to growth in the youngest forms of reticulocytes and had a severe slow growth phenotype in part resulting from reduced merozoite production. The pbpepc-, pboprt- and pbompdc- mutants retained virulence in mice implying that malaria parasites can partially salvage pyrimidines but failed to complete differentiation to various stages in mosquitoes. These findings suggest that species-specific differences in Plasmodium host cell tropism result in marked differences in the necessity for parasite intrinsic metabolism. These data have implications for drug design when targeting mature erythrocyte or reticulocyte resident parasites
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