Effect of combining ethylene/methyl acrylate/glycidyl methacrylate terpolymer and an organoclay on the toughening of poly(lactic acid)

Blends of poly(lactic acid) (PLA) and ethylene/methyl acrylate/glycidyl methacrylate terpolymer (EMA‐GMA) with and without the addition of an organoclay were prepared by melt mixing in a twin screw extruder. Mechanical, morphological, structural, and rheological properties of the systems have been investigated as function of its compositions. The impact strength (IS) of PLA increased with the addition of EMA‐GMA. Furthermore, the addition of 2.5 wt% of organoclay to the PLA/EMA‐GMA blend promoted improvements in the mechanical properties, such as IS, tensile strength, and strain‐at‐break. Further addition of organoclay, 5 wt%, led to a formation of a double percolated network, where the clay particles form bridges across EMA‐GMA droplets and glue them together, however, without coalescence. In addition, morphological and wide‐angle X‐ray scattering analyses evidenced that the clay presents a partially exfoliated structure and that remains inside the EMA‐GMA droplets, probably as a consequence of the approach used to produce the systems. POLYM. ENG. SCI., 54:1922–1930, 2014. © 2013 Society of Plastics Engineers     

Synthesis and characterization of 15% efficient CIGSSe solar cells from nanoparticle inks

We report a total‐area power conversion efficiency of 15% for a copper indium gallium disulfoselenide (CIGSSe) solar cell fabricated from a copper indium gallium disulfide (CIGS) nanoparticle ink based process. Careful optimization of the fabrication process has resulted in a significant improvement in efficiency compared to our previously reported efficiency of 12%. This efficiency ranks among the highest reported in the literature for solution processed CIGSSe. Despite having an absorber thickness of approximately 700–800 nm, which is less than half the thickness of high efficiency devices grown by both coevaporation and solution processes in the literature, our devices show good short‐circuit current (32.1 mA/cm²). Surprisingly, the sintered film shows lateral composition fluctuations, which have not been reported for other high efficiency devices and may be responsible for the lower open circuit voltage (636 mV) observed here. This suggests an avenue for further improvement through optimization of the nanoparticle selenization process to better control composition in the sintered film. Copyright © 2015 John Wiley & Sons, Ltd.     

Fracture behavior of glass-cloth-reinforced composites

The fracture behavior of glass-cloth-reinforced composites has been studied. Fracture of these composites proceeds by tensile failure of fibers rather than by the shear failure of the matrix or the interface. Although the spread of damage in these composites is restricted to small distances away from the crack path due to the interweaving of the fibers, this distance is found to be appreciably larger for the samples with smaller initial crack lengths. Characteristic distances associated with the Whitney-Nuismer criteria are, in turn, found to be smaller for these composites than for the angle ply laminates or randomly oriented short-fiber composites reported in literature in which the spread of the damage is much greater. Analysis through the crack growth resistance also supports this correlation with the extent of damage spread and indicates that the critical crack length for these composites may be equal to the best fit value of the characteristic distance of the average stress criterion.     

Significantly high electromagnetic shielding effectiveness in polypyrrole synthesized by eco-friendly and cost-effective technique

A facile and eco-friendly synthesis of polypyrrole from monomer pyrrole using nominal amount of ferric chloride hexahydrate (FeCl₃.6H₂O) oxidant in aqueous solution by chemically oxidative polymerization method has been reported. The use of aqueous solvent and ferric chloride hexahydrate salt in polypyrrole synthesis have an eco-friendly route favorable for the production of polypyrrole in large quantities. The synthesized polypyrrole samples exhibit good electrical conductivity (2 S/cm) and yield of 80% for reaction time of 8 hr at 5°C. Quality and properties of polypyrrole samples have been thoroughly investigated with varying reaction time and temperature while other synthesis parameters like molar ratio of oxidant to monomer, oxidant concentration, and solvent were kept constant. X-ray diffraction analysis of polypyrrole with a shorter reaction time shows the presence of iron oxide (Fe₂O₃) peaks. The complete reaction may not occur at shorter reaction times due to which residual ferric ions converted into Fe₂O₃. X-ray photoelectron spectroscopy measurement of polypyrrole also confirms the formation of Fe₂O₃. Appropriate selection of reaction time and temperature produced pure phase polypyrrole with high yield and good conductivity. Synthesized polypyrrole by our eco-friendly and cost-effective technique exhibits prominent electromagnetic shielding effectiveness value of 30 dB in the X-band (8–12 GHz).     

Dynamic analysis and split range control for maximization of operating range of continuous microbial fuel cell

Human development is inherently connected with availability of water and energy. Energy production requires water, whereas water treatment needs energy. On the other hand, microbial fuel cell has capability to produce energy and water simultaneously from waste water or organic matter. In this paper, first principle-based model of variable volume microbial fuel cell is simulated. Hydraulic retention time is selected as the manipulated variable using the study of steady state and dynamic responses. Classical PI and model predictive control strategies are developed for controlling the produced power from the cell, and its performance is tested for servo problem. Settling time for positive and negative set points is found to be 126 and 889 h in case of classical PI and 120 and 750 h in case of linear MPC, respectively along with large increase (three times order of magnitude) in working volume for negative set point. These control challenges are overcome by using split range controller with variable and constant volume microbial fuel cells. The settling time for negative set point is found to be 49 and 21 h for classical PI and linear MPC schemes, respectively, which is significantly lower than using only variable volume microbial fuel cell. Also, there is no increase in the working volume of the constant volume microbial fuel cell. Hence, operating range of the microbial fuel cell is enhanced using split range controller.     

Studies of dielectric relaxation and a.c. conductivity in [(100−<Emphasis Type="Italic">x</Emphasis>)PEO + <Emphasis Type="Italic">x</Emphasis>NH<Subscript>4</Subscript>SCN]: Al-Zn ferrite nano composite polymer electrolyte

Present work deals with findings on dielectric behaviour and a.c. conduction in a ferrite doped polymer nano composite electrolyte system, namely [(100−x) PEO + xNH₄SCN]: ferrite. The formation of nano composite and structural behavior of electrolyte was studied by XRD and SEM images. The effect of salt and ferrite on conductivity behaviour of PEO based nano composite polymer electrolyte has been investigated by the impedance spectroscopy at room temperature. The variation of dielectric permittivity and dielectric loss with frequency was carried out at ambient temperature. The a.c. conductivity seems to follow the universal power law.     

Electrochromic performance of a poly(3,4-ethylenedioxythiophene)-Prussian blue device encompassing a free standing proton electrolyte film

Electrochromic devices incorporating an electropolymerized poly(3,4-ethylenedioxythiophene) (PEDOT) film and a free standing, transparent film of a proton conducting polymer electrolyte with high ambient temperature ionic conductivity of 10⁻² S cm⁻¹ have been fabricated with and without the ion storage electrodeposited Prussian blue (PB) counter electrode layer. While coloration efficiency increases as a function of applied potential in the sole PEDOT device with largest values of CE_(max,VIS) ∼ 120 cm² C⁻¹ and CE_(max,NIR) ∼ 133 cm² C⁻¹ attained at V_c = −1.9 V, the PEDOT:PB device shows a digression from this trend. Much higher coloration efficiencies in the visible (247 cm² C⁻¹ at 570 nm) and NIR (116 cm² C⁻¹ at 1100 nm) regions are achieved for the PEDOT:PB device at a relatively lower reducing voltage of −0.8 V. The PEDOT:PB device shows fast switching redox process (t_c = 2.6 s and t_b = 1.3 s for a 50% optical contrast at 632.8 nm) and a highly reversible charge density as the ratio of Q_inserted to Q_extracted was found to vary between 0.8 and 1.0. When switched between the clear and blue states for 2000 cycles, the insignificant drop in peak current density maxima observed for the PEDOT:PB device, i.e. the good cycling stability, the facile fabrication of device assembly, the ease of scaling up the electrolyte and electrochromic coatings, indicate that this method can be adapted as a simple and inexpensive alternative to conventional electrochromic windows with high cost components.     

Robust ego-motion estimation and 3-D model refinement using surface parallax.

We present an iterative algorithm for robustly estimating the ego-motion and refining and updating a coarse depth map using parametric surface parallax models and brightness derivatives extracted from an image pair. Given a coarse depth map acquired by a range-finder or extracted from a digital elevation map (DEM), ego-motion is estimated by combining a global ego-motion constraint and a local brightness constancy constraint. Using the estimated camera motion and the available depth estimate, motion of the three-dimensional (3-D) points is compensated. We utilize the fact that the resulting surface parallax field is an epipolar field, and knowing its direction from the previous motion estimates, estimate its magnitude and use it to refine the depth map estimate. The parallax magnitude is estimated using a constant parallax model (CPM) which assumes a smooth parallax field and a depth based parallax model (DBPM), which models the parallax magnitude using the given depth map. We obtain confidence measures for determining the accuracy of the estimated depth values which are used to remove regions with potentially incorrect depth estimates for robustly estimating ego-motion in subsequent iterations. Experimental results using both synthetic and real data (both indoor and outdoor sequences) illustrate the effectiveness of the proposed algorithm.     

ACAR: Adaptive Connectivity Aware Routing for Vehicular Ad Hoc Networks in City Scenarios

Multi-hop vehicle-to-vehicle communication is useful for supporting many vehicular applications that provide drivers with safety and convenience. Developing multi-hop communication in vehicular ad hoc networks (VANET) is a challenging problem due to the rapidly changing topology and frequent network disconnections, which cause failure or inefficiency in traditional ad hoc routing protocols. We propose an adaptive connectivity aware routing (ACAR) protocol that addresses these problems by adaptively selecting an optimal route with the best network transmission quality based on statistical and real-time density data that are gathered through an on-the-fly density collection process. The protocol consists of two parts: 1) select an optimal route, consisting of road segments, with the best estimated transmission quality, and 2) in each road segment of the chosen route, select the most efficient multi-hop path that will improve the delivery ratio and throughput. The optimal route is selected using our transmission quality model that takes into account vehicle densities and traffic light periods to estimate the probability of network connectivity and data delivery ratio for transmitting packets. Our simulation results show that the proposed ACAR protocol outperforms existing VANET routing protocols in terms of data delivery ratio, throughput and data packet delay. Since the proposed model is not constrained by network densities, the ACAR protocol is suitable for both daytime and nighttime city VANET scenarios.     

Self-phase modulation and spectral broadening of optical pulses insemiconductor laser amplifiers

Amplification of ultrashort optical pulses in semiconductor laser amplifiers is shown to result in considerable spectral broadening and distortion as a result of the nonlinear phenomenon of self-phase modulation (SPM). The physical mechanism behind SPM is gain saturation, which leads to intensity-dependent changes in the refractive index in response to variations in the carrier density. The effect of the shape and the initial frequency chirp of input pulses on the shape and the spectrum of amplified pulses is discussed in detail. Particular attention is paid to the case in which the input pulsewidth is comparable to the carrier lifetime so that the saturated gain has time to recover partially before the trailing edge of the pulse arrives. The experimental results, performed by using picosecond input pulses from a 1.52-μm mode-locked semiconductor laser, are in agreement with the theory. When the amplified pulse is passed through a fiber, it is initially compressed because of the frequency chirp imposed on it by the amplifier. This feature can be used to compensate for fiber dispersion in optical communication systems