Investigations of laser pumped gas cell atomic frequency standard

The performance characteristics of a rubidium gas cell atomic frequency standard might be improved by replacing the standard rubidium discharge lamp with a single mode laser diode. Aspects of the laser pumped gas cell atomic clock studied include effects due to laser intensity, laser detuning, and the choice of the particular atomic absorption line. Results indicate that the performance of the gas cell clock may be improved by judicious choice of the operating parameters of the laser diode. The laser diode also proved to be a valuable tool in investigating the operation of the conventional gas cell clock. Results concerning linewidths, the light shift effect and the effect of isotopic spin exchange in the conventional gas cell clock are reported

Laser induced asymmetry and inhomogeneous broadening of the microwave lineshape of a gas cell atomic frequency standard

The possibility of replacing the RF discharge lamp in a rubidium gas cell clock with a single mode laser diode is addressed. Since the short term stability of the rubidium frequency standard is limited by the shot noise of the photodetector, an increased signal-to-noise ratio due to more efficient laser diode optical pumping might improve the short term performance. Because the emission wavelength of the laser diode can be tuned, improved long term performance could be gained through the control of the light shift effect. However, due to the nature of the gas cell frequency standard, various physical phenomena are strongly coupled in their effect on the frequency output, and thus careful consideration must be given to any change in one parameter because of its interrelation with other parameters. Some investigations concerning the coupled effect of the optical and microwave fields in the rubidium atomic clock are reported. It is shown that this type of coupling is an important consideration for any attempt to incorporate a laser diode into a gas cell clock

Monte Carlo simulations of precise timekeeping in the Milstar communication satellite system

The Milstar communications satellite system will provide secure antijam communication capabilities for DOD operations into the next century. In order to accomplish this task, the Milstar system will employ precise timekeeping on its satellites and at its ground control stations. The constellation will consist of four satellites in geosynchronous orbit, each carrying a set of four rubidium (Rb) atomic clocks. Several times a day, during normal operation, the Mission Control Element (MCE) will collect timing information from the constellation, and after several days use this information to update the time and frequency of the satellite clocks. The MCE will maintain precise time with a cesium (Cs) atomic clock, synchronized to UTC(USNO) via a GPS receiver. We have developed a Monte Carlo simulation of Milstar's space segment timekeeping. The simulation includes the effects of: uplink/downlink time transfer noise; satellite crosslink time transfer noise; satellite diurnal temperature variations; satellite and ground station atomic clock noise; and also quantization limits regarding satellite time and frequency corrections. The Monte Carlo simulation capability has proven to be an invaluable tool in assessing the performance characteristics of various timekeeping algorithms proposed for Milstar, and also in highlighting the timekeeping capabilities of the system. Here, we provide a brief overview of the basic Milstar timekeeping architecture as it is presently envisioned. We then describe the Monte Carlo simulation of space segment timekeeping, and provide examples of the simulation's efficacy in resolving timekeeping issues

Laser-noise-induced correlations and anti-correlations in Electromagnetically Induced Transparency

High degrees of intensity correlation between two independent lasers were observed after propagation through a rubidium vapor cell in which they generate Electromagnetically Induced Transparency (EIT). As the optical field intensities are increased, the correlation changes sign (becoming anti-correlation). The experiment was performed in a room temperature rubidium cell, using two diode lasers tuned to the $^{85}$Rb $D_2$ line ($\lambda = 780$nm). The cross-correlation spectral function for the pump and probe fields is numerically obtained by modeling the temporal dynamics of both field phases as diffusing processes. We explored the dependence of the atomic response on the atom-field Rabi frequencies, optical detuning and Doppler width. The results show that resonant phase-noise to amplitude-noise conversion is at the origin of the observed signal and the change in sign for the correlation coefficient can be explained as a consequence of the competition between EIT and Raman resonance processes.Comment: Accepted for publication in EPJ

The ac stark shift and space-borne rubidium atomic clocks

open7sìDue to its small size, low weight, and low power consumption, the Rb atomic frequency standard (RAFS) is routinely the first choice for atomic timekeeping in space. Consequently, though the device has very good frequency stability (rivaling passive hydrogen masers), there is interest in uncovering the fundamental processes limiting its long-term performance, with the goal of improving the device for future space systems and missions. The ac Stark shift (i. e., light shift) is one of the more likely processes limiting the RAFS' long-term timekeeping ability, yet its manifestation in the RAFS remains poorly understood. In part, this comes from the fact that light-shift induced frequency fluctuations must be quantified in terms of the RAFS' light-shift coefficient and the output variations in the RAFS' rf-discharge lamp, which is a nonlinear inductively-couple plasma (ICP). Here, we analyze the light-shift effect for a family of 10 on-orbit Block-IIR GPS RAFS, examining decade-long records of their on-orbit frequency and rf-discharge lamp fluctuations. We find that the ICP's light intensity variations can take several forms: deterministic aging, jumps, ramps, and non-stationary noise, each of which affects the RAFS' frequency via the light shift. Correlating these light intensity changes with RAFS frequency changes, we estimate the light-shift coefficient, K-LS, for the family of RAFS: K-LS = -(1.9 +/- 0.3) x 10(-12) /%. The 16% family-wide variation in K-LS indicates that while each RAFS may have its own individual K-LS, the variance of K-LS among similarly designed RAFS can be relatively small. Combining K-LS with our estimate of the ICP light intensity's non-stationary noise, we find evidence that random-walk frequency noise in high-quality space-borne RAFS is strongly influenced by the RAFS' rf-discharge lamp via the light shift effect. Published by AIP Publishing.openFormichella, V.; Camparo, J.; Sesia, I.; Signorile, G.; Galleani, L.; Huang, M.; Tavella, P.Formichella, V.; Camparo, J.; Sesia, Ilaria; Signorile, Giovanna; Galleani, L.; Huang, M.; Tavella, Patrizi

Palavra cantada: uma ferramenta para a inclusão educativa de crianças autistas

En el marco del trabajo de división de la infancia operado por las instituciones educativas, un grupo está sujeto a una doble exclusión: los niños autistas para quienes el acceso al lenguaje y la comunicación constituye un obstáculo para su inclusión, independientemente de su funcionamiento intelectual. Este trabajo busca contribuir a esta problemática desde una perspectiva psicoanalítica centrada en los procesos psíquicos relacionados con el lenguaje y sus manifestaciones en la lectura y la escritura. Más concretamente, se centra en el concepto de palabra cantada, a partir del estudio de su uso en una propuesta de educación terapéutica. Se presenta brevemente un estudio de caso en el contexto de un taller de música como dispositivo de tratamiento institucional. En particular, una forma de leer y escribir se ve como una metáfora de una experiencia subjetiva caracterizada por el aislamiento y la evitación de la alteridad, que guía una dirección de tratamiento. La discusión del material parte de la diferenciación entre las construcciones cognitivas subyacentes a la apropiación instrumental del lenguaje y la organización afectiva de la estructura psíquica, que posibilita la comunicación dirigida hacia otro. A continuación, ubica la palabra cantada entre los sistemas de comunicación verbal y no verbal, que terminan devolviendo huellas de musicalidad y sociabilidad al lenguaje y reforzando la incorporación de la experiencia a través de envolturas psíquicas. Se concluye que la palabra cantada es un concepto prometedor en el tratamiento del autismo y otros problemas del desarrollo, fundamentalmente por su papel en la construcción de una relación con la alteridad y el logro de la dimensión pragmática del lenguaje

Plato, the brain, and the soul: Further research into neural correlates for plato’s tripartite soul

This paper explores neuropsychological evidence for Plato’s philosophical theory of the tripartite soul as explained in Plato’s Republic. Plato contends that an express relationship of the three elements that make-up the soul (reason, appetitive, and spirit) interact to promote just behavior, and that just behavior is optimal for individual and societal well-being. Specifically, just behavior is considered to arise from reason’s oversight of the other two elements. Apparent in this theory is the proximity Plato’s analysis has with the current psychological understanding of cognitions that activate behaviors. Strack and Deutsch’s (2004) 2-system model of reflective and impulsive processing, with the addition of Wiers and Stacy’s (2006) supplementary moderators of emotion and motivation, display evidence that Plato’s theory has footing in psychological theory

Desarrollo y validación de una propuesta metodológica para el diagnóstico participativo de la vulnerabilidad a la inseguridad alimentaria a nivel local en cuatro comunidades campesinas del Valle del Cusco, Perú

107 páginas.Trabajo Fin de Máster en Agroecología: un enfoque para la sustentabilidad rural. Tutores: David Gallar Hernández ; João Carlos Canuto. La desnutrición, el hambre, la pobreza, la desigualdad y la inequidad han sido los síntomas de una sociedad que ha estructurado el concepto de progreso desde una perspectiva ajena a las condiciones sociales, culturales y ambientales de la población. La concentración global de la población vulnerable a estos problemas se ha incrementado, dificultando la viabilidad de las acciones, estrategias, programas y planes implementados por los gobiernos e instituciones encargadas de combatir sus efectos sobre la sociedad. El presente estudio, posee dos metas fundamentales. La primera consiste en desarrollar una propuesta metodológica que diagnostique la vulnerabilidad con respecto a la Inseguridad Alimentaria, para posteriormente, aplicarla en cuatro comunidades ubicadas en el Valle de Cusco, Perú -dos en la provincia de Cusco, en el distrito de San Jerónimo y dos en la provincia de Quispicanchis, en el distrito de Oropesa-, en el marco de una pasantía desarrollada en conjunto con el Centro de Educación y Comunicación Guaman Poma Ayala, y en alianza con el Programa de Cooperación Internacional llevado a cabo por la Universidad de Córdoba, institución que dio aval para estructurar la presente investigación. La segunda meta es visibilizar la contribución perceptiva del campesino, desde su quehacer local, en el proceso de fortalecimiento y promoción de la Seguridad Alimentaria. Por lo tanto, se espera que el conocimiento consignado en este documento aporte en la formulación de nuevos proyectos que permitan considerar determinantes esenciales a la hora de dinamizar procesos con este enfoque, incluyendo factores como, las relaciones de género, lo étnico, lo económico y la influencia de los contextos socio-políticos y ambientales

Phase-Control of Photoabsorption in Optically Dense Media

We present a self-consistent theory, as well as an illustrative application to a realistic system, of phase control of photoabsorption in an optically dense medium. We demonstrate that, when propagation effects are taken into consideration, the impact on phase control is significant. Independently of the value of the initial phase difference between the two fields, over a short scaled distance of propagation, the medium tends to settle the relative phase so that it cancels the atomic excitation. In addition, we find some rather unusual behavior for an optically thin layer.Comment: 5 pages, 3 figures, submitted to PR

Testis: Germ cell tumors

Review on Testis: Germ cell tumors, with data on clinics, and the genes involved