Complementary Speckle Patterns : deterministic interchange of intrinsic vortices and maxima through Scattering Media

Intensity minima and maxima of speckle patterns obtained behind a diffuser are experimentally interchanged by applying a spiral phase delay of charge $\pm 1$ to the impinging coherent beam. This transform arises from the intuitive expectation that a tightly focused beam is so-changed into a vortex beam and vice-versa. The statistics of extrema locations and the intensity distribution of the so-generated "complementary" patterns are characterized by numerical simulations. It is demonstrated experimentally that the incoherent superposition of the three "complementary speckle patterns" yield a synthetic speckle grain size enlarged by a factor $\sqrt{3}$. A cyclic permutation of optical vortices and maxima is unexpectedly observed and discussed.Comment: 9 pages, 9 figure

Solvent free method for intense vaporization of solid molecular and inorganic compounds

New tools have been developed for vaporization of solid precursors to meet the demands of high feed rate for CVD, ALD and other deposition processes

Non Data Aided Parameter Estimation for Multi-User ARGOS Receivers

In this paper, parameter estimators are analyzed in the context of Successive Interference Cancelation (SIC) receivers for the ARGOS system. A Non Data Aided (NDA) feed forward estimator is proposed for the amplitude and the carrier phase parameters. Time delays are assumed to be known. A Window Accumulator (WA) is used to reduce the influence of the additive noise. In the presence of frequency offset, the window length L cannot be chosen arbitrarily large but an optimal length Lopt can be determined. However, because the estimator induces a different optimal length for each parameter, a trade-off must be made. We show that a window length of around 35 samples induces mean square errors (MSEs) lower than 0.012 for both parameters. The MSE of the proposed estimator is also compared to the Modified Cram´er Rao Bound (MCRB)

Multiuser Detection For Asynchronous ARGOS Signals

In this paper, we investigate the application of multiuser detection techniques to a Low Polar Orbit (LPO) mobile satellite used in the ARGOS system. These techniques are used to mitigate the multiple access interference in the uplink transmission of the system. Unlike CDMA, due to the Doppler Effect, each signal has a different received carrier frequency and a different propagation delay. Multiuser detection techniques are proposed for asynchronous transmission in ARGOS system: the maximum likelihood detector, the conventional detector, and the sequential interference cancellation detector, as solutions to tackle the interference effects. Bit Error Rate performance graphs are shown for these techniques

Impact of Imperfect Parameter Estimation on the Performance of Multi-User ARGOS Receivers

In this paper, we analyze the performance of Successive Interference Cancelation (SIC) receivers in the context of the ARGOS satellite system. Multi-user SIC receivers are studied in presence of imperfect estimates of signal parameters. We derive performance graphs that show the parameter ranges over which a successful demodulation of all users is possible. First, the graphs are derived in the context of perfect parameter estimation. Then, imperfect parameter estimation is considered. Erroneous estimations affect both the amplitude and the time delay of the received signal. Carrier frequencies are assumed to be accurately measured by the receiver. ARGOS SIC receivers are shown to be both robust to imperfect amplitude estimation and sensitive to imperfect time delay estimation

Multiuser detection for time synchronous ARGOS signals

Multiuser detection has recently been a big challenge in the increase of the performance for a satellite communication system. In the previous studies on systems such as CDMA, researchers have derived general mathematical expressions to describe the system model. However, when it comes to specific system such as ARGOS system, solutions based on general expressions may no longer be valid and thus new mathematical derivations could be formulated. In this paper, we propose a new mathematical model for synchronous multiuser communication in ARGOS system and we analyse the performance of the optimum multiuser detector and some sub optimum techniques such as conventional, decorrelator, Minimum Mean Square Error, and successive interference cancellation detectors

Communication, Localization and Synchronization of Spacecraft for Swarm Missions

Swarm missions are based on the use of several spacecraft working together to pursue a specific task for a specific mission. To allow these elements to work together, it is necessary for them to be able to communicate with each other and to synchronize themselves within the swarm. Moreover, the mission may likely require knowing the relative or absolute positions of the spacecraft in the swarm. In order to collect simultaneous measurements allowing computing localization and synchronization in the swarm, a full duplex CDMA communication method is studied by CNES. An Inter Satellite Link (ISL) transmitter prototype is currently under development and first performance evaluation is conducted. CNES is also working on measurement signal processing. Based on signal exchange between satellites, one can estimate jointly the distance and clock offset between a pair of satellites. In parallel, CNES is developing a swarm simulator implying both dynamics and functional behavior of each spacecraft in the swarm. First, this simulator will be software only but its architecture will allow integration of hardware equipment in a future version. This simulator will be used for the validation of the services provided by the link at a system level

The use of an artificial wetland by Shoveler Anas clypeata in western France: the role of food resources

Sewage works are known to be attractive to waterbirds, especially during the breeding season. The sewage works of Rochefort (Western France) regularly hosts internationally important numbers of wintering Shovelers (> 400 individuals). During the present study the number of Shovelers present over the winter period was related to zooplankton density. Since zooplankton density differed between the eight ponds of the station, we tested if the birds' spatial distribution reflected food abundance. Pond size and zooplankton abundance were negatively correlated. Ducks concentrated on ponds of intermediate invertebrate richness and intermediate size, suggesting that pond size as weil as food abundance affected their distribution. The relative avoidance of large ponds could be due to low resource availability and the avoidance of small ponds with restricted visibility may be related to minimizing the risk of predation. We propose an experimental test of the second hypothesis. If our interpretation is confirmed, then these results have implications for the planning of future sewage treatment works: where use by Shoveler is an objective, ponds should be large (> 5 ha) in order to allow birds to distribute in an optimal manner and thus to use the site to its full potentialLes stations d'épuration sont des zones favorables aux oiseaux d'eau, particulièrement en période de reproduction. La station d'épuration de Rochefort, dans l'ouest de la France, revêt une importance internationale pour le Canard souchet en hivernage (> 400 individus). Durant cette étude, le nombre de Souchets hivernants était lié à la densité de zooplankton. La densité de zooplankton étant différente dans les huit bassins de la station, nous avons testé la relation entre distribution spatiale des oiseaux sur le site et distribution des proies. La taille des bassins et leur densité de zooplancton étaient inversement corrélées. Les canards utilisaient principalement les bassins de taille et de densité de plancton intermédiaires, suggérant que les deux facteurs déterminaient leur distribution. L'évitement des grands bassins semble lié à la faible disponibilité de ressources, alors que les bassins petits pourraient avoir été peu utilisés afin d'éviter un risque de prédation potentiel. Nous proposons un test expérimental de cette dernière hypothèse. Si cette interprétation était vérifiée, les résultats de ce travail pourraient permettre de concevoir les futures stations d'épuration de manière à les rendre pleinement utilisables par les Souchets, en augmentant la taille des bassins (> 5 ha) afin d'assurer une distribution optimale des oiseaux