Polychromatic guide star: feasibility study

International audienceAdaptive optics at astronomical telescopes aims at correcting in real time the phase corrugations of incoming wavefronts caused by the turbulent atmosphere, as early proposed by Babcock. Measuring the phase errors requires a bright source located within the isoplanatic patch of the program source. The probability that such a reference source exists is a function of the wavelength, of the required image quality (Strehl ratio), of the turbulence optical properties, and of the direction of the observation. It turns out that the sky coverage is disastrously low in particular in the visible wavelength range where, unfortunately, the gain in spatial resolution brought by adaptive optics is the largest. Foy and Labeyrie have proposed to overcome this difficulty by creating an artificial point source in the sky in the direction of the observation relying on the backscattered light due to a laser beam. This laser guide star (hereinafter referred to as LGS) can be bright enough to allow us to accurately measure the wavefront phase errors, except for two modes which are the piston (not relevant in this case) and the tilt. Pilkington has emphasized that the round trip time of the laser beam to the mesosphere, where the LGS is most often formed, is significantly shorter than the typical tilt coherence time; then the inverse-return-of-light principle causes deflections of the outgoing and the ingoing beams to cancel. The apparent direction of the LGS is independent of the tilt. Therefore the tilt cannot be measured only from the LGS. Until now, the way to overcome this difficulty has been to use a natural guide star to sense the tilt. Although the tilt is sensed through the entire telescope pupil, one cannot use a faint source because $APEX 90% of the variance of the phase error is in the tilt. Therefore, correcting the tilt requires a higher accuracy of the measurements than for higher orders of the wavefront. Hence current adaptive optics devices coupled with a LGS face low sky coverage. Several methods have been proposed to get a partial sky coverage for the tilt. The only one providing us with a full sky coverage is the polychromatic LGS (hereafter referred to as PLGS). We present here a progress report of the R&D; program Etoile Laser Polychromatique et Optique Adaptative (ELP-OA) carried out in France to develop the PLGS concept. After a short recall of the principles of the PLGS, we will review the goal of ELP-OA and the steps to get over to bring it into play. We finally shortly described the effort in Europe to develop the LGS

Polychromatic guide star: feasibility study

International audienceAdaptive optics at astronomical telescopes aims at correcting in real time the phase corrugations of incoming wavefronts caused by the turbulent atmosphere, as early proposed by Babcock. Measuring the phase errors requires a bright source located within the isoplanatic patch of the program source. The probability that such a reference source exists is a function of the wavelength, of the required image quality (Strehl ratio), of the turbulence optical properties, and of the direction of the observation. It turns out that the sky coverage is disastrously low in particular in the visible wavelength range where, unfortunately, the gain in spatial resolution brought by adaptive optics is the largest. Foy and Labeyrie have proposed to overcome this difficulty by creating an artificial point source in the sky in the direction of the observation relying on the backscattered light due to a laser beam. This laser guide star (hereinafter referred to as LGS) can be bright enough to allow us to accurately measure the wavefront phase errors, except for two modes which are the piston (not relevant in this case) and the tilt. Pilkington has emphasized that the round trip time of the laser beam to the mesosphere, where the LGS is most often formed, is significantly shorter than the typical tilt coherence time; then the inverse-return-of-light principle causes deflections of the outgoing and the ingoing beams to cancel. The apparent direction of the LGS is independent of the tilt. Therefore the tilt cannot be measured only from the LGS. Until now, the way to overcome this difficulty has been to use a natural guide star to sense the tilt. Although the tilt is sensed through the entire telescope pupil, one cannot use a faint source because $APEX 90% of the variance of the phase error is in the tilt. Therefore, correcting the tilt requires a higher accuracy of the measurements than for higher orders of the wavefront. Hence current adaptive optics devices coupled with a LGS face low sky coverage. Several methods have been proposed to get a partial sky coverage for the tilt. The only one providing us with a full sky coverage is the polychromatic LGS (hereafter referred to as PLGS). We present here a progress report of the R&D; program Etoile Laser Polychromatique et Optique Adaptative (ELP-OA) carried out in France to develop the PLGS concept. After a short recall of the principles of the PLGS, we will review the goal of ELP-OA and the steps to get over to bring it into play. We finally shortly described the effort in Europe to develop the LGS

Venti sistema de apoio a eventos: um caso de estudo para a semana da computação

Eventos acadêmicos têm uma grande importância tanto na esfera profissional quanto acadêmica e muitos aspectos precisam ser considerados ao organizar um evento desse porte. Como base para estudo, usamos o evento da Semana da Computação da UFRJ por conta das diversas atividades que os organizadores tiveram para centralizar e organizar as informações. O objetivo deste trabalho é apresentar um sistema que auxiliará a equipe de organização de eventos nos seus processos internos, tais como inscrição em atividades, elaboração do cronograma de atividades e emissão de certificados. O sistema Venti é uma aplicação que permite que equipes e participantes interajam com o conteúdo de eventos cadastrados de acordo com seu nível de permissão

Atmospheric optical-turbulence at Roque de los Muchachos Observatory: database and recalibration of the generalized-SCIDAR data

We present the largest database so far of atmospheric optical-turbulence profiles (197035 individual CN2(h)) for an astronomical site, the Roque de los Muchachos Observatory (La Palma, Spain). This C2 (h) database was obtained through generalized-SCIDAR observations at the 1 meter Jacobus Kapteyn telescope from Febrary 2004 to August 2009, obtaining useful data for 211 nights. The overestimation of the turbulence strength induced during the generalized SCIDAR data processing has been analyzed for the different observational configurations. All the individual C2 (h) have been recalibrated to compensate the introduced errors during data treatment following (Avila & Cuevas 2009). Comparing results from profiles before and after the recalibration, we analyze its impact on the calculation of relevant parameters for adaptive optics.Comment: 8 pages, 3 figures, MNRAS accepte

Medidas de la turbulencia atmosférica en los Observatorios de Canarias: técnica SCIDAR

Ponencia presentada en: 1er Encuentro sobre Meteorología y Atmósfera de Canarias, celebrado en el Puerto de la Cruz, los días 12,13 y 14 de noviembre de 2003. El encuentro estuvo organizado por el Centro Meteorológico Territorial en Canarias Occidental, con la colaboración del Observatorio Atmosférico de Izaña y del Grupo de Física de la Atmósfera de la Facultad de Física (Universidad de La Laguna)SCIDAR es una técnica que permite medir la turbulencia atmosférica (Ci (h)) ópticamente, así como la velocidad (V(h)) de esas capas turbulentas en función de la altura. El Instituto de Astrofísica de Canarias ha comenzado un programa de caracterización de la turbulencia atmosférica en los observatorios de lzaña (Tenerife) y Roque de los Muchachos (La Palma). En esta contribución describimos la técnica SCIDAR y su aplicación a diferentes problemas científicos: óptica adaptativa y comunicaciones ópticas; y presentamos resultados estadísticos de perfiles de turbulencia atmosférica obtenidos en el observatorio de lzaña (Tenerife), así como su evolución temporal

Investigation of the Competition between Electron and Energy Transfer in the Quenching of Aromatic Ketones in the Triplet State using Picosecond Transient Grating Spectroscopy

The competition between electron transfer (ET) and triplet energy transfer (TT) in the quenching of benzophenone, xanthone, and anthraquinone in the triplet state by molecules with both a sufficiently small oxidation potential and low triplet state was investigated in the picosecond to microsecond time scales. In the longer time scale, the product distribution depends strongly on the relative exergonicity of ET and TT processes, the yield of the lower energy product being at least four times larger than that of the other product. Picosecond transient grating measurements reveal that if TT is more exergonic than ET, the TT product is predominantly formed by two sequential ET reactions, i.e., by spin-allowed back ET within the triplet geminate ion pair formed upon ET quenching. However, if ET is more exergonic than TT, no conversion from the TT product to the ET product could be detected. In this case, the product distribution in the microsecond time scale seems to reflect the competition between the two processes. When both processes are exergonic, ET appeared to be always faster than TT. This is in agreement with the severe orbital overlap requirement for TT via the Dexter exchange mechanism

Picosecond Time Resolved Dispersion Spectroscopy Using the Interference between Population and Thermal Phase Gratings

A new method is presented for measuring directly the dispersion spectrum of short‐lived transients, based on heterodyne transient grating spectroscopy. The light diffracted from a preformed thermal phase grating is used as a local oscillator, in phase with the light diffracted from the population phase grating. Time‐resolved dispersion spectra measured upon photoinduced electron transfer reaction between 9,10‐dicyano‐anthracene and anisole in acetonitrile are presented. These spectra and the corresponding absorption spectra obtained by Kramers‐Kronig transformation are compared with those deduced from the homodyne transient grating spectra. Potential applications of this technique are discussed

Picosecond transient Grating Spectroscopy: the Nature of the Diffracted Spectrum

A ps transient grating setup using white light continuum for probing is presented. Measurements on an aromatic molecule in solution have been carried out with this system. The diffracted spectrum is analyzed using Kogelnik's coupled wave theory. At short time delay after excitation, the diffracted spectrum is strongly dominated by absorption and in this case transient grating spectroscopy is equivalent but more sensitive to transient absorption spectroscopy. If some of the excitation energy is dissipated as heat, the diffracted spectrum is essentially the same as the dispersion spectrum of the transient species at time delays approaching half the acoustic period. The performances of this technique and of transient absorption spectroscopy are compared

Direct Investigation of the Dynamics of Charge Recombination Following the Fluorescence Quenching of 9,10-Dicyanoanthracene by Various Electron Donors in Acetonitrile

The dynamics of the intermediate generated upon diffusional electron transfer (ET) quenching of 9,10-dicyanoanthracene by electron donors of varying oxidation potential in acetonitrile has been investigated using several transient grating techniques. With most of the donor/acceptor pairs studied, the transient grating spectrum cannot be differentiated from those of the free ions. Exciplex fluorescence, with the same lifetime as that of the ion pair, is observed with all donors. To extract from the measured kinetics the rate constant of exciplex dissociation,, and of back ET,, within these exciplexes, three different schemes have been considered. The best agreement is obtained by assuming that charge recombination predominantly takes place within the exciplex. The obtained values are substantially different from the BET rate constants deduced indirectly from the free-ion yields and with a donor-independent rate constant of separation. For each class of donors, exhibits a logarithmic free energy dependence with a slope of about −2 eV-1. Moreover, is not constant but increases continuously with diminishing donor's oxidation potential

Avaliação do potencial embriotóxico do tacrolimus (FK506) administrado a ratas wistar

Tacrolimus is a macrolide antibiotic with immunosuppressive action, acting as a calcineurin inhibitor, that has being used as a standard drug avoiding rejection of most transplants. With the success of transplantations, which occurred mainly due to the use of immunosuppressive drugs, there was an improvement in life quality of patients. This fact, led to an increase in the number of gestations, even under continuous use of immunosuppressants. It is known that these drugs cross the placenta, leading to changes in embryo development. Body weight loss in newborns from mothers that used tacrolimus during gestation is described in literature. However, little is known about its action on blastocyst preimplantation period, being the aim of this work to assess if tacrolimus interferes with embryo development during tubaric transit and blastocyst implantation periods. Pregnant Wistar rats were randomly distributed into control C1 and C2 and treated T1, T2, T3, T4, T5 and T6. Control 1 and Treated 1, 2 and 3 received distilled water and 1, 2 and 4 mg/kg/day of tacrolimus, respectively, via oral gavage from first to fifth pregnancy day (tubaric transit period) and groups Control 2 and Treated 4, 5 and 6 received distilled water and 1, 2 and 4 mg/kg/day of tacrolimus respectively, via oral gavage from fifth to seventh day (implantation period). The clinical signs of maternal toxicity were analyzed. On 15th day, blood was collected for biochemical and hematological tests assessment, after that animals were killed. Ovaries, liver and kidneys were weighed and the corpora lutea were counted. Resorptions, live and dead fetuses were identified. Fetuses and placenta were weighed. Clinical signs of maternal toxicity were not found. During the period of tubaric transit there were no significant alteration in maternal body weight, food intake and hematological parameters. In biochemical analysis, the group treated with 4 mg/kg/day presented an increase in cholesterol, TGO and urea. In the group treated with 2 mg/kg/day there was creatinine reduction and group T1 (1mg/kg/day) showed reduction in TGO. In the period of blastocyst implantation it was not observed changes in body weight among groups. There was a decrease in food intake, during the treatment period wich was recovered after the drug administration, showing a gradative increase at food intake until the end of the experiment. An increase in food intake in the group treated with tacrolimus in the concentration of 4mg/Kg/day was shown. There were no significant alterations in hematological parameters. In biochemical analysis no alterations were found, except in the group T6 (4mg/kg/day) that presented a decrease. In the both experiments, during the period of blastocyst implantation and the tubaric transit, there were no significant alterations in maternal body, liver, kidney and ovaries weights. Were not observed significant alterations in the number of corpora lutea, live and dead fetuses, resorptions, fetuses weigh and lost in pre and pos implantation. In the groups treated with tacrolimus on the concentrations of 4mg/kg/day and 1mg/kg/day were observed a decrease of the implants number. The administration of Tacrolimus to pregnant rats during the tubal transit and implantation periods does not seem to generate any toxic effect on them.O tacrolimus é um antibiótico macrolídeo com ação imunossupressora, atuando como inibidor de calcineurina, que vem sendo utilizado como droga base na maioria dos transplantes para evitar rejeição. Com o êxito dos transplantes, decorrente principalmente do uso de imunossupressores, houve uma melhora na qualidade de vida das pacientes transplantadas. Esta melhora levou ao aumento do número de gestações, mesmo sob o uso contínuo de imunossupressores. Sabe-se que os imunossupressores atravessam a placenta podendo levar a alterações no desenvolvimento do embrião. Segundo a literatura, foram observados desvios da normalidade, como perda de peso, em recém nascidos de mães que utilizavam o tacrolimus. Entretanto, pouco se sabe sobre a sua atuação no período de préimplantação do blastocisto, sendo o objetivo deste trabalho verificar se o tacrolimus interfere no desenvolvimento do embrião de rata, durante seu trânsito tubário e na fase de implantação do blastocisto. Ratas Wistar prenhes foram distribuídas aleatoriamente nos grupos controles C1 e C2 e tratados T1, T2, T3 e T4, T5 e T6. Controle 1 e Tratados 1, 2 e 3 receberam água destilada e 1, 2 e 4 mg/kg/dia de Tacrolimus respectivamente por via intragástrica do primeiro ao quinto dia de prenhez (período de trânsito tubário) e os grupos Controle 2 e Tratados 4, 5 e 6 receberam água destilada e 1, 2 e 4 mg/kg/dia de tacrolimus , respectivamente, por via intragástrica, do quinto ao sétimo dia (período de implantação). O acompanhamento de sinais clínicos maternos possibilitou a análise de efeitos tóxicos sobre a mãe durante o período de gestação. No 150 dia, foi coletado sangue para avaliação de parâmetros bioquímicos e hematológicos, em seguida os animais foram eutanasiados. Ovários, fígado e rim foram pesados e os corpos lúteos contados. Foram identificados fetos vivos, reabsorções e fetos mortos. Fetos e placentas foram pesados. Não foram encontrados indícios clínicos de toxicidade materna. No período de trânsito tubário não foram observadas alterações significativas no peso corporal, consumo de ração e parâmetros hematológicos das mães. Na análise bioquímica, o grupo da dose de 4 mg/kg/dia apresentou aumento na concentração de colesterol, de TGO e de uréia. No grupo com dose de 2mg/kg/dia ocorreu redução de creatinina e no grupo T1 houve uma redução de TGO. No período de implantação do blastocisto, não foram observadas variações no peso corporal entre os grupos analisados. Foi observada uma diminuição no consumo de ração, durante o período de tratamento, que foi restabelecido com o término deste, apresentando um aumento gradativo do consumo até o final do experimento. O tacrolimus na concentração de 4mg/Kg/dia apresentou consumo médio superior aos demais grupos. Os parâmetros hematológicos não apresentaram alterações significativas. Os parâmetros bioquímicos não apresentaram alterações relevantes entre os grupos experimentais, exceto os referentes à TGO, que apresentou uma diminuição no grupo T6. Nos estudos realizados no período de trânsito tubário e no de implantação, observando-se o peso corporal materno corrigido, os pesos de fígado e rins maternos, peso de ovários, número de corpos lúteos, fetos vivos e mortos, reabsorções, peso de ninhada e perdas pré e pós-implantação, não foram encontradas diferenças significativas. Ocorreu aumento no peso placentário dos animais tratados com tacrolimus na concentração de 4mg/Kg/dia e no grupo tratado com a concentração de 1mg/Kg/dia, diminuição do número de implantes. Os fetos em ambos os experimentos não apresentaram malformações externas. Concluiu-se que no modelo experimental utilizado não foi evidenciado potencial embriotóxico do tacrolimus na fase de trânsito tubário e na implantação, quando administrado a ratas