Silane-Modified Graphene Oxide as a Compatibilizer and Reinforcing Nanoparticle for Immiscible PP/PA Blends

Graphene oxide (GO) and aminosilane (AS)-modified GO (GOAS) have been studied as possible compatibilizers for immiscible polyblends. Ideally, for localization of nanoparticles (NPs) at the interface, the thermodynamics of the constituents and mixing dynamics have to be tailored and controlled, respectively. Accordingly, a variety of oxidation levels (10%–40%) of GOs were prepared using Hummer's method and further modified by AS. Experimental results indicated that the GO goes through thermal reduction (above 200°C) during blending and reduced GO (rGO) is produced. The GOAS moderated the reduction reaction and stabilized the GO. The thermodynamic wetting coefficient of PP (polypropylene)/PA (polyamide)/rGOAS system was shown to drive the rGOAS from the PP phase to the blend's interface during time-controlled blending. The localization of the rGOAS at the interface resulted in significant enhancement of mechanical properties using only 2–3 wt% of rGOAS. Over 100% enhancement in strength, 40% enhancement in modulus, and 30% in toughness were shown, compared with neat PP/PA. Reduced GOAS and its location at the interface resulted in a third glass transition temperature (Tg), in addition to the PP and PA respective Tgs. Rheological percolation at 2–3 wt% rGOAS (20%) supports the localization of rGOAS at the interface. Storage moduli increase with interfacial tension, in accordance to the rheological models. POLYM. ENG. SCI., 60:180–191, 2020. © 2019 Society of Plastics Engineers     

Performance of solar systems with non-linear behavior calculated by the utilizability method: application to PV solar pumps

Based on the utilizability method we derived, in the first part of the paper, an analytic expression to calculate the time average of physical quantities non-linearly dependent on collected solar radiation. Results are applied to photovoltaic pumping systems (PVPS). Water flow propelled by various types of pumps, centrifugal or progressive cavity displacement, for example, can be conveniently written as a second degree polynomial of the collected solar radiation. In that case, the long-term time average of relevant physical parameters, like water flow or hydraulic power, can be calculated with a very simple expression. The procedure is validated comparing long-term averages of maximum water volume pumped by a PV system, obtained with the utilizability method, with those found by running a 10-year time series. Comparison is made for several climatic regions in Brazil. Results show very good agreement for every month of the year and all locations, with a maximum deviation of 1.7%. The method applied to calculate long-term averages, maximum water volume for example, can be useful for evaluation and design procedures of photovoltaic pumping equipment.     

Second-order statistics of maximal-ratio and equal-gain combining in Hoyt fading

Exact expressions for the level crossing rate and average fade duration of M-branch equal-gain and maximal-ratio combining systems in a Hoyt fading environment are presented. The expressions apply to unbalanced, nonidentical, independent diversity channels and have been validated by specializing the general results to some particular cases whose solutions are known and, more generally, by means of simulation.     

Optical and thermal optimization of stationary non-evacuated CPC solar concentrator with fully illuminated wedge receivers

Stationary low concentrator collectors (C < 2), of the CPC type, are of great interest for thermal energy supply of industrial processes, at temperatures below or equal to 100 °C. In particular, concentrators with fully illuminated V inverted absorbers have attractive properties for thermal energy conversion.Numerical analysis of the geometric and optical characteristics of different low concentration CPC’s (C between 1 and 2) with fully inverted wedge absorbers, shows that the cavities with the minimal relationship between the length and height of the reflector surface and the aperture, (L/A) and (H/A), and the lower average number of reflections 〈n〉 correspond to the lowest angular acceptance concentrator. If a concentration of 1.2 is desired, the smallest ratios of (L/A) and (H/A) and mean number of reflections 〈n〉 occur for C = 2 (θ_a = 30°). However, when the annual generated thermal energy is also considered (for example, for Recife, tilt equals latitude, fluid temperature equals 50 °C, East–West orientation), a very large maximum value in the concentration region between 1.4 and 1.6 (acceptance angles of 38.68° e 45.58°) occurs. The simulation results indicate, that while the operational temperature rises, the ratio between the annual generated thermal energy by the CPC and a good quality flat-plate collector becomes greater than 1: for CPC with 1.2 concentration these ratios become 1.0 at 50 °C and 1.35 at 80 °C. The improvement in the reflectivity of the reflector surface of the CPC rises significantly this relation, i.e., if the reflectivity exceeds from 0.86 to 0.96 the CPC of the concentration relation 1.2, operating at 80 °C may generate 55% more thermal energy than flat-plate collector.     

Analysis of a new relationship between monthly global irradiation and sunshine hours from a database of Brazil

Tests of the Suerhcke relationship have been made with a properly selected database of global irradiation and sunshine hours. A simple clear sky model, based on a generalisation of Beer's law using a unique dispersion parameter for the entire wavelength spectrum, has been used. It is shown that the Suerhcke relationship forecasts the solar radiation with a mean quadratic error of (7.5%), slightly better than the precision given by the Angstrom–Prescott model. Moreover, the Suerhcke model offers a great potential for improving the estimation process since, being based on the physics of the underlying fundamental phenomena, it can be used with more elaborated and/or more precise clear sky models. It should be remarked that this procedure, by converting the large database of sunshine hours, existing in the world, into global irradiation, might expand considerably the information about the earth solar resource at a negligible cost, when compared to the use of satellite-based procedures or earth-based pyranometers networks.     

Closed-form generalized power correlation coefficient of the Hoyt fading signal

Exact, closed-form and general expressions of the marginal and joint moments as well as-of the correlation coefficient of the instantaneous powers of two Hoyt (Nakagami-q) signals are derived. All provided statistics are expressed as finite sums of simple functions of the model parameters. The model allows for environments where the variances of the quadrature components of a signal are different from their counterparts of the other signal. Some numerical results illustrate the generalized power correlation coefficient provided in this work, simulations support the theoretical results, and an approximation to the envelope correlation coefficient of the Hoyt Model is proposed.     

Complete characterization of optical pulses by real-time spectral interferometry

We demonstrate a simple method for complete characterization (of amplitudes and phases) of short optical pulses, using only a dispersive delay line and an oscilloscope. The technique is based on using a dispersive delay line to stretch the pulses and recording the temporal interference of two delayed replicas of the pulse train. Then, by transforming the time domain interference measurements to spectral interferometry, the spectral intensity and phase of the input pulses are reconstructed, using a Fourier-transform algorithm. In the experimental demonstration, mode-locked fiber laser pulses with durations of approximately 1 ps were characterized with a conventional fast photodetector and an oscilloscope.     

DIAGNOSTICS OF SLIP EFFECTS IN NON-NEWTONIAN MEDIA VIA ELECTROCHEMICALLY DRIVEN TRANSIENT CONVECTIVE DIFFUSION

True velocity profiles in the close vicinity of a wall can be determined by measuring the transient limiting diffusion currents after applying a step change of electrode overpotential. Slip effects in a bento-nite slurry under viscometric flow conditions were investigated by using this novel experimental technique. Electrochemically determined apparent slip velocities were found to be in excellent agreement with the results of conventional viscometric experiments.     

Zinc oxide nanodiffusers to enhance p3ht:pcbm organic solar cells performance

Journal of Materials Science: Materials in Electronics - This work proposes a new approach on exploring Zinc Oxide (ZnO) nanodiffusers to improve organic solar cell (OSC) performance. ZnO...     

Exact crossing rates of dual diversity over unbalanced correlated Rayleigh channels

General exact expressions for the level crossing rate of dual-branch selection, equal-gain, and maximal-ratio combiners operating over unbalanced correlated Rayleigh channels are derived. Sample numerical results are presented by specializing the general expressions to a space-diversity system with horizontally spaced omnidirectional antennas at the mobile station. It is observed that, whereas power imbalance is invariably prejudicial, fading correlation may be advantageous with closely spaced antennas arranged parallel to the direction of motion.