56 research outputs found
Dynamical constants for electromagnetic fields with elliptic-cylindrical symmetry
Taking into account the characteristics of a free scalar field in elliptic
coordinates, a new dynamical variable is found for the free electromagnetic
field. The conservation law associated to this variable cannot be obtained by
direct application of standard Noether theorem since the symmetry generator is
of second order. Consequences on the expected mechanical behavior of an atomic
system interacting with electromagnetic waves exhibiting such a symmetry are
also discussed.Comment: 17 pages, 5 figures, revised version, animated graphs provided at
http://www.fisica.unam.mx/research/movie
Frank-Condon principle and adjustment of optical waveguides with nonhomogeneous refractive indices
The adjustment of two different selfocs is considered using both exact
formulas for the mode-connection coefficients expressed in terms of Hermite
polynomials of several variables and a qualitative approach based on the
Frank-Condon principle. Several examples of the refractive-index dependence are
studied and illustrative plots for these examples are presented. The connection
with the tomographic approach to quantum states of a two-dimensional oscillator
and the Frank-Condon factors is established.Comment: 8 pages, 4 figures, published version (layout of figures changed,
typos corrected, references added
Consenso Mexicano de Hepatitis AlcohĂłlica
La hepatitis alcohĂłlica es una condiciĂłn frecuente en la poblaciĂłn mexicana, se
caracteriza por insuficiencia hepática aguda sobre crónica, importante reacción inflamatoria
sistémica y fallo multiorgánico, que en la variante grave de la enfermedad implica una elevada
mortalidad. Por lo anterior, la AsociaciĂłn Mexicana de GastroenterologĂa y la AsociaciĂłn Mexicana
de HepatologĂa conjuntaron un equipo multidisciplinario de profesionales de la salud para
elaborar el primer consenso mexicano de hepatitis alcohĂłlica. El consenso fue elaborado con la
metodologĂa Delphi, emitiendo 37 recomendaciones. La enfermedad hepática relacionada con
el consumo de alcohol comprende un amplio espectro, que incluye esteatosis, esteatohepatitis,
fibrosis en diferentes grados, cirrosis y sus complicaciones. La hepatitis alcohĂłlica grave se
define por una funciĂłn modificada de Maddrey
≥
32 o por un puntaje de MELD (Model for End-
Stage Liver Disease) igual o mayor a 21. Actualmente no existe un biomarcador especĂfico para el diagnĂłstico. La presencia de leucocitosis con neutrofilia, hiperbilirrubinemia (> 3 mg/dL),AST > 50 U/L ( 1.5-2 pueden orientar al diagnĂłstico. La piedraangular del tratamiento es la abstiencia junto con el soporte nutricional. Los esteroides estanindicados en la forma grave, en donde han resultado efectivos para reducir la mortalidad a28 dĂas. El trasplante hepático es en la actualidad la Ăşnica opciĂłn con que se cuenta parasalvar la vida de pacientes que no responden a los esteroides. Ciertos fármacos, como la N-acetilcisteĂna, el factor estimulante de colonias de granulocitos y la metadoxina, pueden seruna terapia adyuvante que puede mejorar la supervivencia de los pacientes
The Mexican consensus on alcoholic hepatitis
Alcoholic hepatitis is a frequent condition in the Mexican population. It is characterized
by acute-on-chronic liver failure, important systemic inflammatory response, and
multiple organ failure. The severe variant of the disease implies elevated mortality. Therefore,
the AsociaciĂłn Mexicana de GastroenterologĂa and the AsociaciĂłn Mexicana de HepatologĂa
brought together a multidisciplinary team of health professionals to formulate the first Mexican consensus on alcoholic hepatitis, carried out utilizing the Delphi method and resultingin 37 recommendations. Alcohol-related liver disease covers a broad spectrum of patholo-gies that includes steatosis, steatohepatitis, different grades of fibrosis, and cirrhosis and itscomplications. Severe alcoholic hepatitis is defined by a modified Maddrey’s discriminant func-tion score ≥ 32 or by a Model for End-Stage Liver Disease (MELD) score equal to or above 21.There is currently no specific biomarker for its diagnosis. Leukocytosis with neutrophilia, hyper-bilirubinemia (>3 mg/dl), AST > 50 U/l ( 1.5-2 can guide thediagnosis. Abstinence from alcohol, together with nutritional support, is the cornerstone oftreatment. Steroids are indicated for severe disease and have been effective in reducing the28-day mortality rate. At present, liver transplantation is the only life-saving option for patientsthat are nonresponders to steroids. Certain drugs, such as N-acetylcysteine, granulocyte-colonystimulating factor, and metadoxine, can be adjuvant therapies with a positive impact on patientsurvival
Nondiffracting beams: travelling, standing, rotating and spiral waves
A reformulation of nondiffracting beams, based on more general (travelling wave) solutions of the nonparaxial wave equation, is presented. Zero order nondiffracting beams are found to be radial standing waves arising from counterpropagating zero order Hankel waves of the first and second kind, while higher order nondiffracting beams are formed from counter-rotating spiral waves which are described by Hankel functions of the corresponding order. The resulting physical picture is more general than the well-known integral representation of Bessel functions and we expect it to have implications for studies of the applications of nondiffracting beams. Generic descriptions of the transverse profiles of the electric field, applicable to experimental configurations for realising nondiffracting beams, follow directly from this formulation. Finally, the existence of classes of periodically nondiffracting beams, possessing finite angular momentum and having the characteristics of rotating and spiral waves, is predicted
3-D Optical forces and transfer of orbital angular momentum from multi-ringed light beams to spherical microparticles
Experimental evidence of transfer of orbital angular momentum of multiringed beams to dielectric particles has been reported recently [e.g., J. Opt. B 4, S82 (2002); Phys. Rev. Lett. 91, 093602 (2003)]. Here we present a detailed theoretical examination of the forces involved in trapping and transferring orbital angular momentum to microparticles due to a multiringed light beam, particularly a Bessel beam. Our investigation gathers, in a more general way, the trapping forces for high-index and low-index dielectric transparent particles, as well as for reflective metallic particles, as a function of particle size and position relative to the dimensions of the rings of the beam. We find that particles can be trapped in different regions of the beam intensity profile according to their size and that an azimuthal force component opposite to the beam helicity may appear under certain circumstances, depending on the relative size and radial equilibrium position with respect to the beam for high-index spheres. (C) 2004 Optical Society of America.</p
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