Radiative Transfer in a Translucent Cloud Illuminated by an Extended Background Source

We discuss the radiative transfer theory for translucent clouds illuminated by an extended background source. First we derive a rigorous solution based on the assumption that multiple scattering produce an isotropic flux. Then we derive a more manageable analytic approximation showing that it nicely matches the results of the rigorous approach. To validate our model, we compare our predictions with accurate laboratory measurements for various types of well characterized grains, including purely dielectric and strongly absorbing materials representative of astronomical icy and metallic grains, respectively, finding excellent agreement without the need of adding free parameters. We use our model to explore the behavior of an astrophysical cloud illuminated by a diffuse source with dust grains having parameters typical of the classic ISM grains of Draine & Lee (1984) and protoplanetary disks, with an application to the dark silhouette disk 114-426 in Orion Nebula. We find that the scattering term modifies the transmitted radiation, both in terms of intensity (extinction) and shape (reddening) of the spectral distribution. In particular, for small optical thickness our results show that scattering makes reddening almost negligible at visible wavelengths. Once the optical thickness increases enough and the probability of scattering events become close to or larger than 1, reddening becomes present but appreciably modified with respect to the standard expression for line-of-sight absorption. Moreover, variations of the grain refractive index, in particular the amount of absorption, also play an important role changing the shape of the spectral transmission curve, with dielectric grain showing the minimum amount of reddening.Comment: 19 pages, 11 figures, accepted for publication on The Astrophysical Journa

Metodologie innovative per il supporto alla progettazione e all’analisi delle prestazioni di impianti ad energia solare a concentrazione ed eolici off-shore utilizzando immagini satellitari ottiche e SAR

In questo lavoro presentiamo delle nuove metodologie, sviluppate nell’ambito del progetto SATENERG (Servizi sATellitari per le ENergie Rinnovabili di nuova Generazione) finanziato dall’Agenzia Spaziale Italiana, sia per il supporto alla progettazione/pianificazione che per il monitoraggio quasi in tempo reale e l’analisi delle prestazioni degli impianti ad energia rinnovabile di nuova generazione (CSP, CPV ed eolici off-shore) utilizzando immagini satellitari. In particolare per quanto riguarda gli impianti solari a concentrazione (CSP e CPV), abbiamo sviluppato un metodo per ricavare l’irradianza solare incidente al suolo (in particolare la sua componente diretta normale rispetto ai raggi solari, fondamentale per questo tipo di impianti) da immagini ottiche satellitari. Ciò, unito ad un modello di funzionamento di tali impianti e degli inverter, ci ha resi in grado di poter sviluppare un servizio di supporto nella progettazione e pianificazione di nuove costruzioni di impianti CSP e CPV (analizzando serie storiche di dati satellitari) ed anche un servizio di monitoraggio e analisi delle prestazioni per quelli già esistenti (usando invece immagini satellitari quasi in tempo reale). In maniera simile, usando immagini SAR (Synthetic Aperture Radar), abbiamo sviluppato un metodo per ricavare l’intensità e la direzione del vento in aree marine da remoto che ci ha permesso, utilizzando anche un modello di impianto eolico off-shore (turbina e inverter), di sviluppare sia un servizio di supporto alla progettazione/pianificazione che un servizio di monitoraggio quasi in tempo reale della produzione di un impianto eolico off-shore. Le prime applicazioni di queste nuove metodologie hanno già portato ad avere ottimi risultati in vari casi di prova sia per quanto concerne il monitoraggio dell’irradianza diretta su piano normale, in cui l’irradianza misurata e quella ricavata da dato satellitare non si sono discostate più del 10%, sia per quanto riguarda il calcolo dell’intensità e direzione del vento da immagini SAR, in cui l’errore rispetto al dato misurato è rimasto al di sotto del 15%, fornendo quindi una buona base per il monitoraggio della energia AC prodotta dagli impianti.In this work we present new methodologies aimed to support both planning and near-real-time monitoring of new generation solar and wind energy plants (CSP, CPV and wind off-shore) using satellite imagery. Such methodologies are currently being developed in the scope of SATENERG, a project funded by ASI (Italian Space Agency). In particular, for what concerns the concentrating solar energy plants (CSP and CPV) we developed a method to calculate solar irradiance at ground (and its direct normal component, that has primary importance in this type of plants) starting from satellite optical images. Then, using also detailed opto-electronic models of the plants and inverters, we are able to calculate the producible energy, which can be used to support either the design of potential plants (using historical series of satellite images) or the monitoring and performance analysis of existing plants (using near-real- time satellite imagery). Producible energy and other interesting parameters, like production efficiency, return on investment etc., are delivered through dedicated web services. In a similar way, we developed also a method to calculate the intensity and the direction of off-shore wind from satellite SAR (Synthetic Aperture Radar) images that permitted us, together with detailed models of wind turbine and inverters, to develop a new service in support to both planning and near-real-time monitoring activities of off-shore wind plants. The first applications of these methods gave successful results in several test cases: we obtained a maximum error of 10% for satellite retrieved direct normal solar irradiance and a maximum error of 15% for wind direction and intensity calculated from SAR images (with respect to in-situ measured data)

CCD-based imaging and 3D space--time mapping of terahertz fields via Kerr frequency conversion

We investigate the spatially and temporally resolved four-wave mixing of terahertz (THz) fields and optical pulses in large-bandgap dielectrics, such as diamond. We show that it is possible to perform beam profiling and space–time resolved mapping of THz fields by encoding the spatial information into an optical signal, which can then be recorded by a standard CCD camera

Colloidal aggregation in microgravity by critical Casimir forces

By using the critical Casimir force, we study the attractive strength dependent aggregation of colloids with and without gravity by means of Near Field scattering. Significant differences were seen between microgravity and ground experiments, both in the structure of the formed fractal aggregates as well as the kinetics of growth. Ground measurements are severely affected by sedimentation resulting in reaction limited behavior. In microgravity, a purely diffusive behavior is seen reflected both in the measured fractal dimensions for the aggregates as well as the power law behavior in the rate of growth. Formed aggregates become more open as the attractive strength increases.Comment: 4 pages, 3 figure

A method for characterizing the stability of light sources

We describe a method for measuring small fluctuations in the intensity of a laser source with a resolution of 10⁻⁴. The current signal generated by a PIN diode is passed to a front-end electronics that discriminates the AC from the DC components, which are physically separated and propagated along circuit paths with different gains. The gain long the AC signal path is set one order of magnitude larger than that along the DC signal path in such a way to optimize the measurement dynamic range. We then derive the relative fluctuation signal by normalizing the input-referred AC signal component to its input-referred DC counterpart. In this way the fluctuation of the optical signal waveform relative to the mean power of the laser is obtained. A "Noise-Scattering-Pattern method" and a "Signal-Power-Spectrum method" are then used to analyze the intensity fluctuations from three different solid-state lasers. This is a powerful tool for the characterization of the intensity stability of lasers. Applications are discussed

Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV

A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7 TeV is presented. The data were collected at the LHC, with the CMS detector, and correspond to an integrated luminosity of 4.6 inverse femtobarns. No significant excess is observed above the background expectation, and upper limits are set on the Higgs boson production cross section. The presence of the standard model Higgs boson with a mass in the 270-440 GeV range is excluded at 95% confidence level.Comment: Submitted to JHE