11,146 research outputs found
Chaos and a Resonance Mechanism for Structure Formation in Inflationary Models
We exhibit a resonance mechanism of amplification of density perturbations in
inflationary mo-dels, using a minimal set of ingredients (an effective
cosmological constant, a scalar field minimally coupled to the gravitational
field and matter), common to most models in the literature of inflation. This
mechanism is based on the structure of homoclinic cylinders, emanating from an
unstable periodic orbit in the neighborhood of a saddle-center critical point,
present in the phase space of the model. The cylindrical structure induces
oscillatory motions of the scales of the universe whenever the orbit visits the
neighborhood of the saddle-center, before the universe enters a period of
exponential expansion. The oscillations of the scale functions produce, by a
resonance mechanism, the amplification of a selected wave number spectrum of
density perturbations, and can explain the hierarchy of scales observed in the
actual universe. The transversal crossings of the homoclinic cylinders induce
chaos in the dynamics of the model, a fact intimately connected to the
resonance mechanism occuring immediately before the exit to inflation.Comment: 4 pages. This essay received an Honorable Mention from the Gravity
Research Foundation, 1998-Ed. To appear in Mod. Phys. Lett.
The mathematical description of the electrosynthesis of composites of oxy-hydroxycompounds cobalt with polypyrrole overooxidazed
The electrosynthesis of the composite with of the overoxidized polypyrrole with cobalt oxy-hydroxide in strongly acidic media has been described mathematically, using linear stability theory and bifurcation analysis. The steadystates stability conditions and oscillatory and monotonic instability requirements have been described too. The system´s behavior was compared with behavior of other systems with overoxidation, electropolymerization of heterocyclic compounds and electrosynthesis of the cobalt oxy-hydroxides
Recent advances in magnetic electrospun nanofibers for cancer theranostics application
Funding Information: This article is a result of the project PTDC/CTM-CTM/30623/2017 supported by the Lisbon Regional Operational Program (Lisboa 2020) and Alentejo Regional Operational Program (Alentejo 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund ( ERDF ). This work is funded by National Funds through FCT - Portuguese Foundation for Science and Technology, Reference UID/CTM/50025/2019 and FCT / MCTES . P.S. also acknowledges the individual contract CEECIND.03189.2020.Cancer theranostics is a recent concept that aims to combine in the same device diagnostic and therapeutic features. Magnetic nanoparticles (mNPs) are commonly used as a critical part of these systems due to their ability to respond to an external magnetic field. Consequently, mNPs can generate heat when an alternating magnetic field is applied and enhance image contrast in magnetic resonance. However, direct administration of mNPs intravenously or directly in the tumor can lead to undesired side effects because of mNP elimination by macrophages or leakage to healthy tissues. Therefore, mNPs can be retained in a polymeric nanofibrous mesh, thus preventing misplacing or loss of mNPs. Furthermore, these magnetic nanofibers can be directly implanted in the tumor site, thus ensuring high mNPs loading and higher magnetic response. In addition, polymeric nanofibers produced by electrospinning are frequently used to maintain a sustained drug release in the tumor site. Therefore, a magnetic polymeric nanofiber produced by electrospinning is an ideal nanosystem for cancer theranostics application. This review summarizes the most recent developments of magnetic nanofibers produced by electrospinning for cancer theranostics applications.proofinpres
The low dimensional dynamical system approach in General Relativity: an example
In this paper we explore one of the most important features of the Galerkin
method, which is to achieve high accuracy with a relatively modest
computational effort, in the dynamics of Robinson-Trautman spacetimes.Comment: 7 pages, 5 figure
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