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171.
Rendina et al. recently proposed the original configuration of an electromagnetic power sensor for microwaves and millimeter waves that is based on an optically interrogated all-silicon chip [Electron. Lett. 35, 1748 (1999)]. Here we theoretically analyze and discuss in detail the performances of such a new class of nonperturbing and wideband probe in terms of sensitivity, resolution, intrinsic detectivity, linearity, and response time. Good agreement between theory and experiments is demonstrated. In particular, minimum resolutions of approximately 1 mW/cm2 are obtained at frequencies beyond 10 GHz. The dependence of response on the geometrical and electromagnetic parameters of the sensing element is analyzed, and on this basis the possibility of achieving optimized configurations is discussed.  相似文献   
172.
173.
Chemistry plays a fundamental role in the preservation of our heritage. Artistic and archaeological materials deteriorate over time due to their interaction with the environment, and human intervention can trigger unexpected deterioration pathways. Previous intervention can also sometimes obscure information regarding the original techniques or the materials used to execute the artwork. Our studies of past intervention and attempts to conserve the lunette of the church of Santa Maria la Vetere in Militello Val di Catania (Italy) and Donatello's carved marble panels of the pulpit of the Duomo of Prato (Italy) are discussed as two examples of how chemistry can provide guidance for conservators and fill gaps in the known life of works of art.  相似文献   
174.
We address several problems concerning the geometry of the space of Hermitian operators on a finite-dimensional Hilbert space, in particular the geometry of the space of density states and canonical group actions on it. For quantum composite systems we discuss and give examples of entanglement measures.  相似文献   
175.
176.
Carrieri AH 《Applied optics》1999,38(17):3759-3766
Artificial neural network systems were built for detecting amino acids, sugars, and other solid organic matter by pattern recognition of their polarized light scattering signatures in the form of a Mueller matrix. Backward-error propagation and adaptive gradient descent methods perform network training. The product of the training is a weight matrix that, when applied as a filter, discerns the presence of the analytes on the basis of their cued susceptive Mueller matrix difference elements. This filter function can be implemented as a software or a hardware module to a future differential absorption Mueller matrix spectrometer.  相似文献   
177.
5-O-Acyl-1,2-O-isopropylidene-D-xylofuranose and 6-O-acyl1,2∶3,4-di-O-isopropylidene-D-galactopyranose were enzymatically prepared from the corresponding monosaccharide acetals and commercial (crude) fatty acid mixtures. Subsequent acid-catalyzed hydrolysis of the isopropylidene group(s) gave monosaccharide esters with overall yields of 59–88%, where the monoester content was at least 80% (galactose oleate) and typically 90% for the other preparations. In contrast to sugar fatty acid esters prepared by conventional, high-temperature (trans)esterification, the enzymatically obtained monosaccharide esters contained no appreciable quantities of undersirable side products, and the only contaminants were monosaccharides and fatty acids.  相似文献   
178.
A pulsewidth modulation (PWM) technique is proposed, intended particularly for the reduction of the harmful effects of the harmonics in the inverter-fed drive systems. The approach is based on the minimization of the rms value of the current harmonics in the motor by a proper choice of the commutation angles. Switching patterns are calculated for a different number of commutations per period, for both single-phase and three-phase half-bridge inverters. In the case of the single-phase, an analytical procedure is developed which simplifies the computations. Comparisons are made of the results thus obtained with those given by other PWM techniques in use.  相似文献   
179.
In recent years, several publications have appeared on virtual reality (VR) therapy in the treatment of anxiety disorders. However, a limited number of these studies targeted stress management and relaxation. To evaluate the efficacy of VR as a support tool in the relaxation process, this study compared its efficacy with two other media (DVD and audiotape). The goals of the experiment were to test the efficacy of each condition in increasing relaxation and reducing anxiety, and whether the sense of presence-the feeling of being inside the media content-correlated with the efficacy of the treatment. Results suggested the importance of the sense of presence as a mediating variable between the media experience and the efficacy of the protocol. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
180.
We have investigated the influence of the growth parameters (substrate temperature and deposition rate) and the aging process on the optical properties of C70 thin films, by means of absorption and photoluminescence spectra. The Urbach energy, obtained from the absorption spectra, indicates that the substrate temperature influences the film optical properties more than the deposition rate. The luminescence spectra suggest the important role of the disorder in the radiative efficiency. The main structures of the emission spectra have been assigned to an intramolecular polaron-exciton. The analysis of the temperature dependence of the photoluminescence spectra of the as-deposited samples shows that the vibronic transitions are dominant at low temperature, whereas the singlet purely electronic recombination (due to Frenkel-type exciton) is visible at a sufficiently high temperature. On the contrary, in the aged samples this purely electronic transition is well resolved from low to high temperature. This anomalous behaviour is discussed and attributed to the disorder introduced in the film.  相似文献   
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