86,551 research outputs found
Radial GRIN Lenses based on the Solution of a Regularized Ray Congruence Equation
No full textWe introduce a novel formulation for flat radial GRadient INdex (GRIN) lenses allowing for the optimal lens design through closed form expressions. The validity of the proposed formulation covers a very large range of GRIN lens design parameters (focal distance, lens thickness and maximum refractive index). The formulation is based on the derivation of a new form of non-linear integral equation representing the equalization of all the optical ray-path lengths, denoted as Regularized Ray Congruence (RRC) equation, and on its closed form solution. An analytical form of aperture efficiency is given for standard feed patterns. The application of the formulas presented here allows for an instantaneous design for medium/high gain antennas with controllable total aperture efficiency till 80%. The accuracy of the formulation is tested by a full-wave analysis and compared with other formulations available in the literature. We found that the new formulation proposed here significantly reduces the phase error in a wide range of the lens parameters, thus allowing for a more efficient, accurate and flexible design for GRIN lenses. As a proof of concept, a thin GRIN lens antenna for operation in E-band (60-90 GHz) is designed, demonstrating a high aperture efficiency (63%) across a wide frequency range
Notes on Profile Inversion and Closed Form Formulation of Compact GRIN Lenses
No full textThis note is an addendum to the paper Profile Inversion and Closed Form Formulation of Compact GRIN Lenses [1] and summarizes a few comments obtained after publication of [1]
Sei goloso o impaziente? Effetto del tipo di ricompensa in una prova di scelta intertemporale con bambini di età prescolare
No full textRay-tracing in Dielectric Inhomogeneous Metalenses
No full textA flexible and efficient algorithm, based on Geometrical Optics (GO) ray-tracing, is presented. The algorithm allows the analysis of graded index (GRIN) lenses, namely dielectric inhomogeneous lenses with radially varying refractive index. The source incident field in absence of the lens is supposed to be known by simulation or by measurements. Phase and amplitude distributions at the output interface of the lens are obtained by solving the ray-equation and the energy transport equations, respectively. Once the field distribution at the lens-antenna aperture has been achieved, the radiation pattern is derived by aperture type radiation integrals. The ray-tracing algorithm is validated by full-wave analysis, after predetermining the feed source, the lens dimensions and the refractive index profile. Moreover, beam scanning capability of GRIN lenes can be investigated with the aid of the presented algorithm. Results achieved by the raytracing algorithm and the full-wave analysis have shown to be in good agreement, demonstrating that the proposed algorithm is a valuable alternative to time-consuming full-wave simulations in the GRIN lens analysis
False belief understanding and “cool” inhibitory control in 3-and 4-years- old Italian children
No full textAre you greedy or impatient? Effect of reward type on intertemporal choice in preschool children
No full text3-D Printed All-Dielectric GRIN Lens Antenna With an Integrated Feeder
No full textIn this paper we present the design, fabrication, and experimental verification of a new type of Graded-index (GRIN) lens antenna with an integrated feeder. The continuously varying refractive index distribution is chosen appropriately to offer the rays collimation at the lens aperture. It is practically implemented by varying the material density in a host medium, thus realizing a new type of all-dielectric high gain antenna, entirely using 3D printing. This solution can find application to high gain wireless communication and measurement systems. This GRIN lens antenna is printed in one monolithic process and does not require the feeder to be placed at a focal distance, thus complying with more strict space requirements. It accepts interchangeable feeds that can cover a wide frequency range. The directivity and gain are evaluated using near-field measurements in the Ku-band. A 40% measured aperture efficiency is achieved at 14GHz. The challenges and performance limitations that come with 3D printing, as compared to the design of idealized continuous distribution GRIN lenses are discussed
Sei goloso o impaziente? Effetto del tipo di ricompensa in una prova di scelta intertemporale con bambini di età prescolare.
No full textLa capacità di inibire una risposta consolidata è una componente importante delle funzioni esecutive, coinvolte nell’ADHD (Cornoldi et al. 2010). Nella prova di scelta intertemporale, in cui il soggetto deve scegliere tra una ricompensa minore e immediata (SS) ed una maggiore e ritardata (LL) (Mazur, 1988; Moore, Barresi and Thompson, 1998; Thompson, Barresi and Moore, 1997), benché la scelta dell’opzione LL venga considerata un indice di tolleranza al ritardo, tale preferenza potrebbe essere piuttosto una risposta impulsiva verso la quantità.
Abbiamo testato 151 bambini di età prescolare in un compito di scelta intertemporale con 2 vs. 6 pezzi di cibo, low-symbolic tokens (carte raffiguranti 2 vs. 6 pallini) e high-symbolic tokens (carte raffiguranti un topolino e un elefante). I simboli migliorano la capacità inibitoria poiché permettono di distogliere l’attenzione dalle caratteristiche degli stimoli che scatenano risposte impulsive (Sigel 1970; Werner et al., 1963; Mischel et al., 1989). Due sono le ipotesi testate: (i) Tolleranza del ritardo: se la scelta di LL fosse dovuta ad autocontrollo, gli stimoli simbolici, riducendo l’attrattiva della ricompensa, dovrebbero incrementare il numero di scelte per LL, con un maggiore impatto degli high-symbolic tokens rispetto ai low-symbolic tokens (%LL: High-Symb > LowSymb > Food); (ii) Fallimento nell’inibizione: se la scelta di LL fosse dovuta all’incapacità di inibire la preferenza per la quantità, allora gli high-symbolic tokens dovrebbero ridurre la percentuale di scelte di LL, mentre i low-symbolic tokens non dovrebbero produrre alcun effetto, poiché mantengono inalterata la salienza percettiva della ricompensa (%LL: Food ~ LowSymb > HighSymb)
Numerical and Workbench Design of 2.35 T Double-Tuned (1H/23Na) Nested RF Birdcage Coils Suitable for Animal Size MRI
No full textThe birdcage Radio Frequency (RF) coil is one of the most used configurations in Magnetic Resonance Imaging (MRI) scanners for the detection of the proton (1H) signal over a large homogeneous volume. More recently, birdcage RF coils have been successfully used also in the field of X-nuclei MRI, where the signal of a second nucleus (e.g. 13C, 23Na, 31P, and many others) needs to be detected with high sensitivity and spatial homogeneity. To this purpose several technical solutions have been adopted to design Double Tuned (DT) volume RF coils, including the recent configuration of the nested birdcage RF coils. One of the main problems in the design of DT RF coils is the decoupling between the 1H and X channels, and a number of solutions have been adopted over the years. In this work, based on numerical and workbench methods, we report the decoupling optimization of DT (1H/23Na) nested RF birdcage coils suitable for 2.35 T MRI scanners encompassing an inner Low-Pass (LP) birdcage used for X-nuclei, an outer High-Pass (HP) birdcage for 1H and an external cylindrical RF shield. We show that a suitable geometrical selection of the two coaxial RF birdcage coils (relative angular orientation, diameters and lengths) and RF shield (diameter, length) allows a significant decoupling optimization. We also provide valuable information about the RF B1+ field homogeneity and efficiency. Our approach was validated both with numerical simulations and workbench testing using DT nested RF coil prototypes
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