381 research outputs found
Transform of Riccati equation of constant coefficients through fractional procedure
We use a particular fractional generalization of the ordinary differential
equations that we apply to the Riccati equation of constant coefficients. By
this means the latter is transformed into a modified Riccati equation with the
free term expressed as a power of the independent variable which is of the same
order as the order of the applied fractional derivative. We provide the
solutions of the modified equation and employ the results for the case of the
cosmological Riccati equation of FRW barotropic cosmologies that has been
recently introduced by FaraoniComment: 7 pages, 2 figure
A simple circuit realization of the tent map
We present a very simple electronic implementation of the tent map, one of
the best-known discrete dynamical systems. This is achieved by using integrated
circuits and passive elements only. The experimental behavior of the tent map
electronic circuit is compared with its numerical simulation counterpart. We
find that the electronic circuit presents fixed points, periodicity, period
doubling, chaos and intermittency that match with high accuracy the
corresponding theoretical valuesComment: 6 pages, 6 figures, 10 references, published versio
Generalized Hamiltonian structures for Ermakov systems
We construct Poisson structures for Ermakov systems, using the Ermakov
invariant as the Hamiltonian. Two classes of Poisson structures are obtained,
one of them degenerate, in which case we derive the Casimir functions. In some
situations, the existence of Casimir functions can give rise to superintegrable
Ermakov systems. Finally, we characterize the cases where linearization of the
equations of motion is possible
Economic evaluation of short treatment for multidrugresistant tuberculosis, Ethiopia and South Africa : the STREAM trial
OBJECTIVE
STREAM was a phase-III non-inferiority randomised controlled trial (RCT) to evaluate a shortened regimen for multi-drug resistant tuberculosis (MDR-TB), and included the first-ever within-trial economic evaluation of such regimens, reported here.
METHODS
We compared the costs of ‘Long’ (20-22 months) and ‘Short’ (9-11 months) regimens in Ethiopia and South Africa. Cost data were collected from trial participants, and health system costs estimated using ‘bottom-up’ and ‘top-down’ costing approaches. A cost-effectiveness analysis was conducted with the trial primary outcome as the measure of effectiveness, including a probabilistic sensitivity analysis (PSA) to illustrate decision uncertainty.
FINDINGS
The Short-regimen reduced healthcare costs per case by 21% in South Africa (US6,619 Short) and 25% in Ethiopia (US4,552 Short). The largest component of this saving was medication in South Africa (67%) and social support in Ethiopia (35%). In Ethiopia, participants on the Short-regimen reported reductions in dietary supplementation expenditure (US13 (95%CI 11-14), South Africa US19,000 (Ethiopia) or <US$14,500 (South Africa).
CONCLUSION
The Short-regimen provided substantial health system cost savings and reduced financial burden on participants. Shorter regimens are likely to be cost-effective in most settings, and an effective strategy to support the WHO goal of eliminating catastrophic costs in T
Electromagnetic modes of Maxwell fisheye lens
We provide an analysis of the radial structure of TE and TM modes of the
Maxwell fisheye lens, by means of Maxwell equations as applied to the fisheye
case. Choosing a lens of size R = 1 cm, we plot some of the modes in the
infrared range.Comment: 2+6 pages in Latex, 3 figures to be found in the published referenc
Iso-spectral potential and inflationary quantum cosmology
Using the factorization approach of quantum mechanics, we obtain a family of
isospectral scalar potentials for power law inflationary cosmology. The
construction is based on a scattering Wheeler-DeWitt solution. These
iso-spectrals have new features, they give a mechanism to end inflation, as
well as the possibility to have new inflationary epochs. The procedure can be
extended to other cosmological models.Comment: 14 pages, 5 figure
Quantum mechanical spectral engineering by scaling intertwining
Using the concept of spectral engineering we explore the possibilities of
building potentials with prescribed spectra offered by a modified intertwining
technique involving operators which are the product of a standard first-order
intertwiner and a unitary scaling. In the same context we study the iterations
of such transformations finding that the scaling intertwining provides a
different and richer mechanism in designing quantum spectra with respect to
that given by the standard intertwiningComment: 8 twocolumn pages, 5 figure
Layer Features of the Lattice Gas Model for Self-Organized Criticality
A layer-by-layer description of the asymmetric lattice gas model for
1/f-noise suggested by Jensen [Phys. Rev. Lett. 64, 3103 (1990)] is presented.
The power spectra of the lattice layers in the direction perpendicular to the
particle flux is studied in order to understand how the white noise at the
input boundary evolves, on the average, into 1/f-noise for the system. The
effects of high boundary drive and uniform driving force on the power spectrum
of the total number of diffusing particles are considered. In the case of
nearest-neighbor particle interactions, high statistics simulation results show
that the power spectra of single lattice layers are characterized by different
exponents such that as one approaches the outer
boundary.Comment: LaTeX, figures upon reques
In whose best interest? An agent-based model of high frequency trading
We study a stylized model of High Frequency Trading in which traders equipped with private values and costs operate in a Continuous Double Auction. They can revise their orders with different frequencies and, hence, (only) some agents can repeatedly revise and resubmit orders in the same session, mimicking the behavior of high frequency traders. All agents attempt to maximize profits, learning which bid and ask is to be posted in a given configuration of the book. We analyze the efficiency of the resulting market and the way the surplus from trading is apportioned among agents as a function of the number and type of high frequency traders. We find that the presence of a small proportion of high frequency traders increases the overall efficiency of the market; secondly, the ones who have the chance to frequently revise the offers learn to extract a disproportionate fraction of the profits that ordinarily would belong to slow traders
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