Generation and Quenching of Intensity Pulsations in Semiconductor Lasers Coupled to External Cavities

The behavior of self-pulsing and nonpulsing lasers coupled to external cavities is investigated experimentally and theoretically. We investigate the dependence of the pulsation characteristics on the external cavity length using a saturable absorber model for self-pulsing lasers. It was found that quenching of self-pulsation occurs only for a certain limited range of external cavity length, and the frequencies of external-cavity induced pulsations lies within a certain range determined by the coupling coefficient. Small-signal analysis allows these ranges to be derived analytically. Hitherto, complex pulsation phenomena can be explained very intuitively by interpreting the combined laser-external cavity system as a microwave oscillator with a limited gain band and discrete mode structure

A geometric construction of the exceptional Lie algebras F4 and E8

We present a geometric construction of the exceptional Lie algebras F4 and E8 starting from the round 8- and 15-spheres, respectively, inspired by the construction of the Killing superalgebra of a supersymmetric supergravity background. (There is no supergravity in the paper.)Comment: 12 page

Studies of (GaAI)As injection lasers operating with an optical fiber resonator

The characteristics of an optical fiber external resonator in conjunction with (GaAl)As stripe geometry lasers are described. We have observed a 6–10% reduction in the threshold current and have obtained 150 ps pulses at gigahertz repetition rates. The fiber resonator has also been used to quench self‐pulsations in a (GaAl)As injection laser. In order to explain many of our results we have used a model that uses the conventional semiconductor rate equations modified by the addition of saturable electron traps and the effects of the external cavity. Our results predict many of the self‐locking effects observed in injection lasers operating in an external cavity. Furthermore, the degree of self‐locking will be a strong function of the external cavity length and the density of saturable absorbers

Supersymmetry and homogeneity of M-theory backgrounds

We describe the construction of a Lie superalgebra associated to an arbitrary supersymmetric M-theory background, and discuss some examples. We prove that for backgrounds with more than 24 supercharges, the bosonic subalgebra acts locally transitively. In particular, we prove that backgrounds with more than 24 supersymmetries are necessarily (locally) homogeneous.Comment: 19 pages (Erroneous Section 6.3 removed from the paper.

Quantum memory for squeezed light

We produce a 600-ns pulse of 1.86-dB squeezed vacuum at 795 nm in an optical parametric amplifier and store it in a rubidium vapor cell for 1 us using electromagnetically induced transparency. The recovered pulse, analyzed using time-domain homodyne tomography, exhibits up to 0.21+-0.04 dB of squeezing. We identify the factors leading to the degradation of squeezing and investigate the phase evolution of the atomic coherence during the storage interval.Comment: To appear in PRL. Changes to version 3: we present a larger data set featuring somewhat less squeezing, but also better statistics and a lower margin of error. Some additional revisions are made in response to the referees' comment

Estrategias de Comunicación Participativa, Saneamiento Básico y la Salud Pública de los Pobladores de Paucartambo-Cusco: Participatory Communication Strategies, Basic Sanitation and Public Health of the People of Paucartambo-Cusco

Objectives: To analyze the influence that the application of participatory communication strategies has on the adequate use of basic sanitation services and its impact on the public health of the residents of communities in Paucartambo. Explore the political and cultural dimensions immersed in the communication processes between populations and health promoters of the study communities. Analyze the intervention processes in the field of health communication. Methods: The type of research is qualitative and observational, with a cross-sectional design based on unstructured interviews and in-depth interviews. Data from the National Population and Housing Censuses 2017, 2007 - National Institute of Statistics and Informatics were used. (INEI) - PERU. Results: In-depth interviews, as well as direct observation, result in the fact that although efforts have been made to improve the situation of basic sanitation through the installation of a public sewage network, and other forms such as latrines and septic tanks In addition to being insufficient, they were not used properly, because participatory communication strategies were not applied from the diagnostic stage to the final evaluation, even more so due to the permanent lack of monitoring and surveillance activities, which have a very decisive role in the quality of life and therefore in public health Conclusion: The communication strategies most used by institutions that have the role of promoting the adequate use of basic sanitation services such as public sewage networks have been of a vertical nature such as those talks, radio, the use of pictures, precisely for this reason, adequate knowledge, attitudes and practices were not generated s for their use and conservation, a situation that had negative impacts on public and environmental health.Objetivos: Analizar la influencia que tiene la aplicación de estrategias de comunicación participativa en el uso adecuado de servicios de saneamiento básico y su incidencia en la salud pública de los pobladores de comunidades de Paucartambo. Explorar las dimensiones políticas y culturales inmersas en los procesos de comunicación entre poblaciones y promotores de salud de las comunidades de estudio Analizar los procesos de intervención en el campo de la comunicación en salud. Métodos: El tipo de investigación es cualitativo y observacional, con un diseño de tipo transversal en base a entrevistas no estructuradas y entrevistas en profundidad, Se utilizó los datos de los Censos Nacionales de Población y Vivienda 2017, 2007- Instituto Nacional de Estadística e Informática (INEI) - PERÚ. Resultados: Las entrevistas a profundidad, así como la observación directa, dan como resultado que si bien se han realizado esfuerzos por mejorar la situación del saneamiento básico a través de la instalación de red pública de desagüe, y otras formas como las letrinas y pozos sépticos, además de ser insuficientes, no fueron utilizados adecuadamente, porque no se aplicaron estrategias de comunicación participativa desde la etapa de diagnóstico, hasta la evaluación final, más aun por la falta permanente de actividades de monitoreo y vigilancia, que tienen un rol muy decisivo en la calidad de vida y por tanto en la salud pública Conclusión: Las estrategias de comunicación más utilizadas por las instituciones que tienen el rol de promover el uso adecuado de los servicios de saneamiento básico como las redes públicas de desagüe han sido de carácter vertical como las charlas, la radio, el uso de láminas, precisamente por esta razón no se generaron conocimientos, actitudes y prácticas adecuadas  para el uso y la conservación de los mismos, situación que tuvo impactos negativos sobre la salud pública y también ambiental

A One-Parameter Family of Hamiltonian Structures for the KP Hierarchy and a Continuous Deformation of the Nonlinear \W_{\rm KP} Algebra

The KP hierarchy is hamiltonian relative to a one-parameter family of Poisson structures obtained from a generalized Adler map in the space of formal pseudodifferential symbols with noninteger powers. The resulting \W-algebra is a one-parameter deformation of \W_{\rm KP} admitting a central extension for generic values of the parameter, reducing naturally to \W_n for special values of the parameter, and contracting to the centrally extended \W_{1+\infty}, \W_\infty and further truncations. In the classical limit, all algebras in the one-parameter family are equivalent and isomorphic to \w_{\rm KP}. The reduction induced by setting the spin-one field to zero yields a one-parameter deformation of \widehat{\W}_\infty which contracts to a new nonlinear algebra of the \W_\infty-type.Comment: 31 pages, compressed uuencoded .dvi file, BONN-HE-92/20, US-FT-7/92, KUL-TF-92/20. [version just replaced was truncated by some mailer

New AdS3AdS_3 Branes and Boundary States

We examine D-branes on $AdS_3$, and find a three-brane wrapping the entire $AdS_3$, in addition to 1-branes and instantonic 2-branes previously discussed in the literature. The three-brane is found using a construction of Maldacena, Moore, and Seiberg. We show that all these branes satisfy Cardy's condition and extract the open string spectrum on them.Comment: 18 pages, late