Nanolayered lightweight flexible shields with multidirectional optical transparency

New nanolayered coatings are designed and deposited on flexible plastic substrate having the thickness of 100 /spl mu/m, in order to realize lightweight ultrathin transparent shielding foils. The structure of the coating is optimized considering three figures of merit: the average transmittance in the visible range for normal incidence, the normalized average transmittance for oblique incidence at 550 nm, and the transmittance quality factor. The nanotechnology exploited for the deposition of the transparent metals is the dual ion beam sputtering. Tests of durability, optical transmission, and shielding effectiveness demonstrate that the film has a high adhesion under mechanical solicitation, high resistance against aging, peak transmittance in the visible range higher than 70%, omnidirectional properties in the range 0/spl deg/-60/spl deg/, and shielding effectiveness of 40 dB up to 6 GHz.     

Enzymatic hydrolysis of cotton wastes. Effect of γ-ray pretreatments

Textile cotton wastes were irradiated with γ-rays at different doses and solubilized with 10% NaOH solutions. The regenerated products underwent enzymatic hydrolysis and their degradation pattern was compared with that of the cotton celluloses untreated or treated only with γ-rays. The different samples were characterized by measurements of X-ray diffraction, degree of polymerization, moisture regain and water retention. The structural and morphological modifications induced by the pretreatments were correlated with the variations of kinetic parameters, particularly the V_max/K_m ratio, defined as specificity constant. Only the combination of irradiation with dissolution pretreatments gave a considerable increase of hydrolysis reaction effectiveness.     

Photorefractive processing for large adaptive phased arrays

An adaptive null-steering phased-array optical processor that utilizes a photorefractive crystal to time integrate the adaptive weights and null out correlated jammers is described. This is a beam-steering processor in which the temporal waveform of the desired signal is known but the look direction is not. The processor computes the angle(s) of arrival of the desired signal and steers the array to look in that direction while rotating the nulls of the antenna pattern toward any narrow-band jammers that may be present. We have experimentally demonstrated a simplified version of this adaptive phased-array-radar processor that nulls out the narrow-band jammers by using feedback-correlation detection. In this processor it is assumed that we know a priori only that the signal is broadband and the jammers are narrow band. These are examples of a class of optical processors that use the angular selectivity of volume holograms to form the nulls and look directions in an adaptive phased-array-radar pattern and thereby to harness the computational abilities of three-dimensional parallelism in the volume of photorefractive crystals. The development of this processing in volume holographic system has led to a new algorithm for phased-array-radar processing that uses fewer tapped-delay lines than does the classic time-domain beam former. The optical implementation of the new algorithm has the further advantage of utilization of a single photorefractive crystal to implement as many as a million adaptive weights, allowing the radar system to scale to large size with no increase in processing hardware.     

Influence of counterface roughness on friction properties of engineering plastics for bearing applications

The study investigates the effects of the roughness of the metal counterface (mirror finished or polished) on the coefficient of dry friction for some of the most common engineering plastics used in current bearing technology. The results show that an optimal roughness for minimum friction is likely to exist for any polymer, and it depends on the bulk properties of the polymer itself. “Soft” plastics characterized by a low modulus of elasticity exhibit better sliding behaviour on very smooth, mirror finished surfaces, whereas for high-modulus plastics lower friction is measured in combination with rougher, polished counterfaces. The influence of the contact pressure and sliding velocity are also investigated and found to depend on the layout of the tribological system.     

Spatio-temporal operator formalism for holographic recording and diffraction in a photorefractive-based true-time-delay phased-array processor

We present a spatio-temporal operator formalism and beam propagation simulations that describe the broadband efficient adaptive method for a true-time-delay array processing (BEAMTAP) algorithm for an optical beamformer by use of a photorefractive crystal. The optical system consists of a tapped-delay line implemented with an acoustooptic Bragg cell, an accumulating scrolling time-delay detector achieved with a traveling-fringes detector, and a photorefractive crystal to store the adaptive spatio-temporal weights as volume holographic gratings. In this analysis, linear shift-invariant integral operators are used to describe the propagation, interference, grating accumulation, and volume holographic diffraction of the spatio-temporally modulated optical fields in the system to compute the adaptive array processing operation. In addition, it is shown that the random fluctuation in time and phase delays of the optically modulated and transmitted array signals produced by fiber perturbations (temperature fluctuations, vibrations, or bending) are dynamically compensated for through the process of holographic wavefront reconstruction as a byproduct of the adaptive beam-forming and jammer-excision operation. The complexity of the cascaded spatial-temporal integrals describing the holographic formation, and subsequent readout processes, is shown to collapse to a simple imaging condition through standard operator manipulation. We also present spatio-temporal beam propagation simulation results as an illustrative demonstration of our analysis and the operation of a BEAMTAP beamformer.     

Innovative absorbing-boundary conditions for the efficient FDTDanalysis of lightning-interaction problems

Absorbing boundary conditions are developed for the efficient truncation of three-dimensional finite-difference time-domain (3-D FDTD) meshes, used for the analysis of low-frequency transient problems, such as the lightning interaction with an aircraft. The proposed boundary conditions are combined with an innovative time-marching scheme in order to assure numerical stability of the FDTD procedure for millions of time-iterations. The main advantage of the developed approach consists in the great computer saving allowed in the analysis of FDTD problems in which the space discretization step is several thousands of times smaller than the minimum wavelength excited by the transient source. Numerical applications are included in order to demonstrate the accuracy and efficiency of the proposed method     

Digital transmission performance of carrier channels ondistribution power line networks

The analysis of the transmitting features of wire-to-ground and wire-to-wire carrier channels on power distribution networks is performed both in the frequency- and in the time-domain. A new formulation of the lossy ground return parameters is considered, which applies in a wide frequency-range and in case of poorly conductive soil. The sensitivity of the frequency-spectra and longitudinal profiles of the transmitted voltages to the distribution system configuration, load termination and ground resistivity is investigated. The eye-diagram approach is used in order to ascertain the transmission quality of carrier channels on tree- and mesh-type networks, in case of high capacity digital signals     

Blue sensitizers for solar cells: Natural dyes from Calafate and Jaboticaba

Blue-violet anthocyanins from Jaboticaba (Myrtus cauliflora Mart) and Calafate (Berberies buxifolia Lam) were employed as TiO₂ dye-sensitizers. Solar cells sensitized by Jaboticaba extracts achieved up to J_sc=9.0 mA cm⁻², V_oc=0.59 V, P_max=1.9 mW cm⁻² and ff=0.54, while for Calafate sensitized cells the values determined were up to J_sc=6.2 mA cm⁻², V_oc=0.47 V, P_max=1.1 mW cm⁻² and ff=0.36. Other natural dyes were evaluated without significant photocurrent, demonstrating that only selected extracts are capable of converting sunlight in electricity. The results obtained with extracts of Jaboticaba and Calafate show a successful conversion of visible light into electricity by using natural dyes as wide band-gap semiconductor sensitizers in dye-sensitized solar cells. It also represents an environmentally friendly alternative for dye-sensitized solar cells with low cost production and an excellent system for educational purposes.     

200-MHz superscalar RISC microprocessor

Design and implementation details of the MIPS R10000, 200-MHz, 64-b superscalar dynamic issue RISC microprocessor is presented. It fetches and decodes four instructions per cycle and dynamically issues them to five fully pipelined, low latency execution units, Its hierarchical nonblocking memory system helps hide memory latency with two levels of set-associative, write-back caches. The processor has over 6.8 M transistors and is built in 3.3-V, 0.30 μm, four-layer metal CMOS technology with under 30 W of power consumption. The processor delivers peak performance of Spec95int of 9 and Spec95fp of 19 operating at 200 MHz. Clock and power distribution as well as circuit design techniques of several blocks are addressed