1,721,276 research outputs found
Quantum second harmonic generation in terms of elementary processes
Full text linkWe address the quantum dynamics of second harmonic generation with a
perturbative approach. By inspecting the Taylor expansion of the unitary
evolution, we identify the subsequent application of annihilation and creation
operators as elementary processes and find out how the expansion of the
second-harmonic photon-number probability distribution can be expressed in
terms of the interplay of these processes. We show that overlaps between the
output states of different elementary processes contribute to the expansion of
the probability distribution and provide a diagrammatic technique to
analytically retrieve terms of the distribution expansion at any order
Visual servoing for large camera displacements
No full textThe first aim of any visual-servoing strategy is to avoid features being lost from the field of view and that the desired location may not be reached. However, avoiding both these system failures turns out to be very difficult, especially when the initial and desired locations are distant. Moreover, the methods that succeed in presence of large camera displacements often produce a long translational trajectory that may not be allowed by the robot workspace and/or joint limits. In this paper, a new strategy for dealing with such problems is proposed, which consists of generating circular-like trajectories that may satisfy the task requirements more naturally than other solutions. Knowledge of geometrical models of the object or points depth is not required. It is shown that system failures are avoided for a calibrated camera. Moreover, necessary and sufficient conditions are provided for establishing tolerable errors on the estimates of the intrinsic and extrinsic parameters, in order to guarantee a robust field of view and robust local asymptotic stability. Several simulation results show that the translational trajectories obtained in presence of large displacements are significantly shorter than those produced by the existing methods, in cases of both correct and bad camera calibration. Very satisfactory results are achieved also in presence of small displacements. © 2004 IEEE.link_to_subscribed_fulltex
A visual servoing technique for large displacements
No full textA new visual servoing technique consisting of generating circular-like trajectories is proposed which does not require either geometrical models of the object or points depth. For calibrated camera, the object is kept in the field of view and global stability is achieved. Then, necessary and sufficient conditions are provided for establishing tolerable errors on the estimates of the intrinsic and extrinsic parameters in order to guarantee robust field of view and robust local stability. Simulation results show that the translational trajectories obtained in presence of large displacements are significantly shorter than those produced by one of the best existing methods, in both cases of correct and bad calibration. Very satisfactory results are obtained also in presence of small displacements.link_to_subscribed_fulltex
Visual servoing: Reaching the desired location following a straight line via polynomial parameterizations
No full textThe problem of establishing if it is possible to reach the desired location keeping all features in the field of view and following a straight line is considered. The proposed approach is based on the polynomial parameterization of the camera path and allows one to find the path that follows a straight line and maximizes the distance of the image trajectories from the screen boundary. © 2005 IEEE.link_to_subscribed_fulltex
Conditional measurements with silicon photomultipliers
Full text linkNonclassical states of light can be efficiently generated by performing conditional measure-ments. An experimental setup including Silicon Photomultipliers can currently be implemented for this purpose. However, these devices are affected by correlated noise, the optical cross talk in the first place. Here we explore the effects of cross talk on the conditional states by suitably expanding our existing model for conditional measurements with photon-number-resolving detectors. We assess the nonclassicality of the conditional states by evaluating the Fano factor and provide experimental evidence to support our results
Second-harmonic generation as a source of nonclassical light
No full textWe investigate the transformation of light statistics due to a second-harmonic generation process and address a quantum perturbative approach to retrieve the moments of the output light distribution for given input light states
Effects of nonideal features of silicon photomultiplier on the measurements of quantum correlations
No full textWe analyze the effects of some stochastic deviations from the ideal response in silicon photomultipliers that prove to be detrimental for the measurement of quantum properties of light. We demonstrate that an optimized operation mode can overcome some limitations of the detectors allowing the characterization of entanglement in mesoscopic twin-beam states
Effect of cross-talk on conditional measurements performed with multi-pixel photon counters
No full textWe investigate the role of the optical crosstalk in the conditional measurements performed on quantum states of light. In particular, we analyze how the statistics of the conditional states are affected by cross-talk by retrieving their first and second moments and we test the sub-Poissonianity of the state by evaluating the Fano factor
Abilità narrative nei bambini con DSL in età prescolare: un’analisi dei comportamenti linguistici e non-verbali nei compiti di retelling
No full textStructured Feedback Synthesis for Stability and Performance of Switched Systems
Full text linkThis paper addresses the synthesis of fixed-order output feedback controllers for stability and performance of continuous-time switched linear systems with dwell time constraints or arbitrary switching. Specifically, the paper starts by considering the stabilization problem, which is addressed by searching for a family of homogeneous polynomial Lyapunov functions (HPLFs) parameterized polynomially by the sought controller. In order to conduct this search, polynomials are introduced for approximating the matrix exponential and for quantifying the feasibility of the Lyapunov inequalities. It is shown that a stabilizing controller exists if and only if a condition built solving three convex optimization problems with linear matrix inequalities (LMIs) holds for polynomials of degree sufficiently large. Analogous conditions for the existence of a controller ensuring desired upper bounds on the H2 norm or on the RMS gain of the closed-loop system are derived by searching for a family of homogeneous rational Lyapunov functions (HRLFs) parameterized rationally by the sought controller.postprin
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