3,325 research outputs found
Structural accessibility and structural observability of nonlinear networked systems
The classical notions of structural controllability and structural
observability are receiving increasing attention in Network Science, since they
provide a mathematical basis to answer how the network structure of a dynamic
system affects its controllability and observability properties. However, these
two notions are formulated assuming systems with linear dynamics, which
significantly limit their applicability. To overcome this limitation, here we
introduce and fully characterize the notions "structural accessibility" and
"structural observability" for systems with nonlinear dynamics. We show how
nonlinearities make easier the problem of controlling and observing networked
systems, reducing the number of variables that are necessary to directly
control and directly measure. Our results contribute to understanding better
the role that the network structure and nonlinearities play in our ability to
control and observe complex dynamic systems
Constraining Anisotropic Baryon Oscillations
We present an analysis of anisotropic baryon acoustic oscillations and
elucidate how a mis-estimation of the cosmology, which leads to incorrect
values of the angular diameter distance, d_A, and Hubble parameter, H, manifest
themselves in changes to the monopole and quadrupole power spectrum of biased
tracers of the density field. Previous work has focused on the monopole power
spectrum, and shown that the isotropic "dilation" combination d_A^2/H is
robustly constrained by an overall shift in the scale of the baryon feature. We
extend this by demonstrating that the quadrupole power spectrum is sensitive to
an anisotropic "warping" mode d_A H, allowing one to break the degeneracy
between d_A and H. We describe a method for measuring this warping, explicitly
marginalizing over the form of redshift space distortions. We verify this
method on N-body simulations and estimate that d_A H can be measured with a
fractional accuracy of ~ 3/sqrt(V) % where the survey volume is estimated in
(Gpc/h)^3.Comment: 4 pages, 2 fig
Ultra Low-Power Analog Median Filters
The design and implementation of three analog median filter topologies, whose transistors operate in the deep weak-inversion region, is described. The first topology is a differential pairs array, in which drain currents are driven into two nodes in a differential fashion, while the second topology is based on a wide range OTA, which is used to maximize the dynamic range. Finally, the third topology uses three range-extended OTAs. The proposed weak-inversion filters were designed and fabricated in ON Semiconductor 0.5 micrometer technology through MOSIS. Experimental results of three-input fabricated prototypes for all three topologies are show, where power consumptions of 90nW in the first case, and 270nW in the other two cases can be noticed. A dual power supply +/-1.5 Volts were used
Direct measurement of the 14N(p,g)15O S-factor
We have measured the 14N(p,g)15O excitation function for energies in the
range E_p = 155--524 keV. Fits of these data using R-matrix theory yield a
value for the S-factor at zero energy of 1.64(17) keV b, which is significantly
smaller than the result of a previous direct measurement. The corresponding
reduction in the stellar reaction rate for 14N(p,g)15O has a number of
interesting consequences, including an impact on estimates for the age of the
Galaxy derived from globular clusters.Comment: 5 pages, 3 figures, submitted to Phys. Rev. Let
Comportamiento de las firmas de contadores públicos en el municipio Maracaibo
El presente artículo tiene como objetivo analizar el comportamiento de las firmas de contadores públicos del municipio Maracaibo, estado Zulia-Venezuela, con el propósito de dar aportes para mejorar la formación académica del contador público. El estudio es de tipo descriptivo, de campo, no experimental, se aplicó una encuesta a veinticuatro (24) firmas que visan sus estados financieros en el Colegio de Contadores Públicos del Estado Zulia, seleccionadas aleatoriamente. Los resultados obtenidos muestran un estancamiento en el crecimiento de las firmas de contadores públicos de la región y diversificación de los servicios ofrecidos como respuesta a las actuales exigencias del mercado. Se concluye que la contaduría se encuentra en un proceso de transformación, donde se exige mayor responsabilidad en la ejecución del trabajo, siendo necesario adaptar los programas académicos a las nuevas necesidades del ámbito laboral
World Health Organization Ranking of Antimicrobials According to Their Importance in Human Medicine: A Critical Step for Developing Risk Management Strategies for the Use of Antimicrobials in Food Production Animals
The use of antimicrobials in food animals creates an important source of antimicrobial-resistant bacteria that can spread to humans through the food supply. Improved management of the use of antimicrobials in food animals, particularly reducing the usage of those that are "critically important” for human medicine, is an important step toward preserving the benefits of antimicrobials for people. The World Health Organization has developed and applied criteria to rank antimicrobials according to their relative importance in human medicine. Clinicians, regulatory agencies, policy makers, and other stakeholders can use this ranking when developing risk management strategies for the use of antimicrobials in food production animals. The ranking allows stakeholders to focus risk management efforts on drugs used in food animals that are the most important to human medicine and, thus, need to be addressed most urgently, such as fluoroquinolones, macrolides, and third- and fourth-generation cephalosporin
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