Collision between a dark soliton and a linear wave in an optical fiber.

We report an experimental observation of the collision between a linear wave propagating in the anomalous dispersion region of an optical fiber and a dark soliton located in the normal dispersion region. This interaction results in the emission of a new frequency component whose wavelength can be predicted using phase-matching arguments. The measured efficiency of this process shows a strong dependency with the soliton grayness and the linear wave wavelength, and is in a good agreement with theory and numerical simulations.

Grayness-dependent emission of dispersive waves from dark solitons in optical fibers.

We report the experimental observation of dispersive wave emission from gray solitons propagating in the normal dispersion region of an optical fiber. Besides observing for the first time, to the best of our knowledge, the emission of a dispersive wave from an isolated dark soliton, we show that the dispersive wave frequency and amplitude strongly depend on soliton grayness. This process can be explained by the higher-order dispersion contribution into the phase-matching condition and the grayness of the soliton. Numerical simulations and theoretical predictions are in good agreement with the experiments.

Spectral wings of the fiber supercontinuum and the dark-bright soliton interaction.

We present experimental and numerical data on the supercontinuum generation in an optical fiber pumped in the normal dispersion range where the seeded dark and the spontaneously generated bright solitons contribute to the spectral broadening. We report the dispersive radiation arising from the interaction of the bright and dark solitons. This radiation consists of the two weak dispersing pulses that continuously shift their frequencies and shape the short and long wavelength wings of the supercontinuum spectrum.

Emission of dispersive waves from a train of dark solitons in optical fibers.

We report the experimental observation of multiple dispersive waves (DWs) emitted in the anomalous dispersion region of an optical fiber from a train of dark solitons. Each DW can be associated to one dark soliton of the train, using phase-matching arguments involving higher-order dispersion and soliton velocity. For a large number of dark solitons (>10), we observe the formation of a continuum associated with the efficient emission of DWs.

Filamentation with nonlinear Bessel vortices.

We present a new type of ring-shaped filaments featured by stationary nonlinear high-order Bessel solutions to the laser beam propagation equation. Two different regimes are identified by direct numerical simulations of the nonlinear propagation of axicon focused Gaussian beams carrying helicity in a Kerr medium with multiphoton absorption: the stable nonlinear propagation regime corresponds to a slow beam reshaping into one of the stationary nonlinear high-order Bessel solutions, called nonlinear Bessel vortices. The region of existence of nonlinear Bessel vortices is found semi-analytically. The influence of the Kerr nonlinearity and nonlinear losses on the beam shape is presented. Direct numerical simulations highlight the role of attractors played by nonlinear Bessel vortices in the stable propagation regime. Large input powers or small cone angles lead to the unstable propagation regime where nonlinear Bessel vortices break up into an helical multiple filament pattern or a more irregular structure. Nonlinear Bessel vortices are shown to be sufficiently intense to generate a ring-shaped filamentary ionized channel in the medium which is foreseen as opening the way to novel applications in laser material processing of transparent dielectrics.

Supercontinuum optimization for dual-soliton based light sources using genetic algorithms in a grid platform.

We present a numerical strategy to design fiber based dual pulse light sources exhibiting two predefined spectral peaks in the anomalous group velocity dispersion regime. The frequency conversion is based on the soliton fission and soliton self-frequency shift occurring during supercontinuum generation. The optimization process is carried out by a genetic algorithm that provides the optimum input pulse parameters: wavelength, temporal width and peak power. This algorithm is implemented in a Grid platform in order to take advantage of distributed computing. These results are useful for optical coherence tomography applications where bell-shaped pulses located in the second near-infrared window are needed.

Estratificación del riesgo de dengue en la ciudad de Puerto Ayacucho, estado Amazonas, Venezuela: Período 1995-2010 / Dengue fever risk stratification in Puerto Ayacucho city, Amazonas State, Venezuela: 1995-2010 period

El control del Aedes aegypti (vector principal del Dengue), se dificulta por la extensión y heterogeneidad de los barrios donde se encuentran los criaderos, la carencia de acceso permanente a servicios públicos y por la ausencia de vigilancia epidemiológica estricta y constante. Se registraron 2.603 casos de dengue confirmados por IgM-dengue, durante el período 1995-2010. El estudio se realizó en Puerto Ayacucho, capital del estado Amazonas con 98.824 habitantes. Los casos confirmados se agruparon de acuerdo con la localización de su residencia. La información se representó espacialmente para analizar los patrones espacio-temporales del dengue, estableciéndose una estratificación de la ciudad. La prevalencia de dengue mostró una correlación positiva con la persistencia por barrio, lo que permitió agruparlos en dos clases: (1) alta prevalencia y persistencia, con 66% de los casos confirmados, y (2) baja prevalencia y persistencia, con 34% de los casos. Se demuestra que en Puerto Ayacucho existen “focos calientes” o de mayor transmisión y “focos fríos” o de transmisión transitoria. En conjunto, los barrios incluidos en la categoría de alta prevalencia y persistencia representan 65,1% del área urbana. Este es el espacio geográfico en el cual recomendamos concentrar los esfuerzos de control. La estratificación de la ciudad e identificación de los barrios productores de casos, mostrando las áreas donde es más probable la transmisión del virus, permitirá concentrar los esfuerzos para mitigarla. El enfoque de las actividades de control basado en una estratificación, permite dirigir los programas hacia áreas más problemáticas.

Control of Aedes aegypti is difficult to perform due to the extent and variety of neighborhoods where the breeding grounds are found, the lack of permanent access to public services, and to the absence of a strict and constant epidemiological surveillance. 2,603 confirmed dengue cases (IgM-dengue) were recorded during the 1995-2010 period. This study was carried out in Puerto Ayacucho, main city of Amazonas State, Venezuela, with 98,824 inhabitants. Confirmed cases of individuals affected were grouped according to the location of their residence. Information is spatially represented to analyze space-time patterns of dengue, establishing a stratification of the city. The prevalence of dengue showed a positive correlation with the persistence per neighborhood, allowing to group the neighborhoods into two classes: (1) High prevalence and persistence, with 66% of the confirmed cases, and (2) low prevalence and persistence, with 34% cases. The study shows there are "hot spots" or higher transmission areas, and "cold spots" or transient transmission areas in Puerto Ayacucho. All the neighborhoods included in the category of high prevalence and persistence represent 65.1% of the urban area. This is the geographical area in which we recommend to concentrate control efforts. The stratification of the city and the identification of case-producing neighborhoods, showing the areas where virus transmission is most likely, will permit concentrating efforts to mitigate it. Focus of control activities based on a stratification study allows directing programs to most problematic areas.

Multi-peak-spectra generation with Cherenkov radiation in a non-uniform single mode fiber.

We propose, by means of numerical simulations, a simple method to design a non-uniform standard single mode fiber to generate spectral broadening in the form of "ad-hoc" chosen peaks from dispersive waves. The controlled multi-peak generation is possible by an on/off switch of Cherenkov radiation, achieved by tailoring the fiber dispersion when decreasing the cladding diameter by segments. The interplay between the fiber dispersion and the soliton self-frequency shift results in discrete peaks of efficiently emitted Cherenkov radiation from low order solitons, despite the small amount of energy contained in a pulse. These spectra are useful for applications that demand low power bell-shaped pulses at specific carrier wavelengths.

Soliton families and resonant radiation in a micro-ring resonator near zero group-velocity dispersion.

We report theoretical and numerical study of the dynamical and spectral properties of the conservative and dissipative solitons in micro-ring resonators pumped in a proximity of the zero of the group velocity dispersion. We discuss frequency and velocity locking of the conservative solitons, when dissipation is accounted for. We present theory of the dispersive radiation emitted by such solitons, report their Hopf instability and radiation enhancement by multiple solitons.

Soliton-plasmon resonances as Maxwell nonlinear bound states.

We demonstrate that soliplasmons (soliton-plasmon bound states) appear naturally as eigenmodes of nonlinear Maxwell's equations for a metal/Kerr interface. Conservative stability analysis is performed by means of finite element numerical modeling of the time-independent nonlinear Maxwell equations. Dynamical features are in agreement with the presented nonlinear oscillator model.

Revisión de los casos de dengue en el estado Amazonas, Venezuela, 1995-2008 / Review of dengue cases, Amazonas State, Venezuela, 1995-2008

El dengue se ha ido incrementando significativamente en la región de las Américas e islas del Caribe en las últimas dos décadas. Venezuela ha presentado las mayores tasas de incidencia de DH y el mayor número de fallecidos. En el estado Amazonas se reportan los primeros casos de dengue en el año 1995, siendo el municipio Atures el más afectado. El presente trabajo describe el comportamiento del dengue en el estado Amazonas durante los años 1995 al 2008, mediante la revisión de los registros epidemiológicos y análisis de serotipos del virus DENV. Durante el período 1995-2008 se registró un total de 6209 casos de dengue y 27 con DH, con tres epidemias, quedando demostrada la circulación de los 4 serotipos. Durante las 3 epidemias se hospitalizaron 94 pacientes con Dengue y solo 12 con diagnóstico de DH de 33 con criterios para DH según OPS. En 1995 se registraron 546 casos de dengue, con un solo deceso reportado. La prevalencia anual del Dengue disminuyó en los años 1996-2000 de manera significativa con respecto al año de la epidemia para nuevamente ascender en el año 2001 a cifras de positividad superiores a las del año 1995. Desde el 2003 hasta la fecha el número de casos ha ido en ascenso con presencia significativa de casos de DH. Es necesario que a nivel de la Dirección Regional se estructure un Plan de Control a fin de mantener un Sistema activo de Vigilancia y se revisen periódicamente las pautas de criterios para definir DH.

Dengue fever (DF) has been significantly increasing in the Americas and the Caribbean islands over the past two decades. Venezuela has presented the highest incidence of dengue hemorrhagic fever (DHF) and the largest number of deaths. In Amazonas state the first cases of dengue were reported in 1995, being Atures the most affected municipality. This paper describes the behavior of dengue in the Ama zonas state in the years 1995 to 2008, by reviewing records and epidemiological analysis of DENV virus serotypes. In that period a total of 6209 dengue cases and 27 DHF cases was reported, with three epidemics, proving the movement of the 4 serotypes. During the epidemics 94 pa - tients with dengue were hospitalized, and only 12 were diag nosed with DHF of 33 with PAHO criteria. In 1995 there were 546 dengue cases with one death registered. The an - nual prevalence of dengue significantly declined in the years 1996-2000 compared to the year of the epidemic, but it rose again in 2001 to positive figures higher than 1995. From 2003 until today the number of cases has been increasing with a significant presence of DHF cases. Therefore, it is necessary that in the Regional Health Division a control plan be structured in order to maintain a Monitoring System and periodic reviews of guidelines defining criteria for DHF.

Unusual presentation of hepatitis B serological markers in an Amerindian community of Venezuela with a majority of occult cases.

BACKGROUND: Occult hepatitis B infection (OBI) is characterized by the presence of hepatitis B virus (HBV) DNA in the absence of HBsAg in the serum of patients. The aim of this study was to characterize HBV infection among a Piaroa community, an Amerindian group which exhibits significant evidence of exposure to HBV but relatively low presence of HBsAg, and to explore the presence of OBI in this population. RESULTS: Of 150 sera, with 17% anti-HBc and 1.3% HBsAg prevalence, 70 were tested for the presence of HBV DNA. From these, 25 (36%) were found positive for HBV DNA by PCR in the core region. Two of these 25 sera were HBsAg positive, indicating an overt infection. Of the remaining 68 sera tested, 23 exhibited OBI. Of these, 13 were HBV DNA out of 25 anti-HBc positive (52%) and 10 HBV DNA positive, out of 43 anti-HBc negative (23%), with a statistical significance of p = 0.03. Viral DNA and HBsAg were present intermittently in follow up sera of 13 individuals. Sequence analysis in the core region of the amplified DNA products showed that all the strains belonged to HBV genotype F3. The OBI isolates displayed 96-100% nucleotide identity between them. One isolate exhibited the co-circulation of a wild type variant with a variant with a premature stop codon at the core protein, and a variant exhibiting a deletion of 28 amino acids. CONCLUSIONS: The frequency of OBI found in this Amerindian group warrants further studies in other communities exhibiting different degrees of HBV exposure.

Continuum generation by dark solitons.

We demonstrate that the dark soliton trains in optical fibers with a zero of the group-velocity dispersion can generate broad spectral distribution (continuum) associated with the resonant dispersive radiation emitted by solitons. This radiation is either enhanced or suppressed by the Raman scattering depending on the sign of the third-order dispersion.