Modification of the optical and structural properties of ZnO nanowires by low-energy Ar+ ion sputtering

The effects of low-energy (≤2 kV) Ar⁺ irradiation on the optical and structural properties of zinc oxide (ZnO) nanowires (NWs) grown by a simple and cost-effective low-temperature technique were investigated. Both photoluminescence spectra from ZnO NW-coated films and cathodoluminescence analysis of individual ZnO NWs demonstrated obvious evidences of ultraviolet/visible luminescent enhancement with respect to irradiation fluence. Annihilation of the thinner ZnO NWs after the ion bombardment was appreciated by means of high-resolution scanning electron microscopy and transmission electron microscopy (TEM), which results in an increasing NW mean diameter for increasing irradiation fluences. Corresponding structural analysis by TEM pointed out not only significant changes in the morphology but also in the microstructure of these NWs, revealing certain radiation-sensitive behavior. The possible mechanisms accounting for the decrease of the deep-level emissions in the NWs with the increasing irradiation fluences are discussed according to their structural modifications.     

Two- and three-dimensional optical carrier generation determination in crystalline silicon solar cells

Two- and three-dimensional analyses of the distribution of optically generated charge carriers in textured crystalline silicon solar cells of arbitrary geometry have been performed. The simulation algorithm, developed for that purpose, is based on geometrical optics and ray tracing. It determines the dominant contributions to the optical generation within textured silicon exactly. The contribution of weakly absorbed long-wavelength photons is calculated using a Monte-Carlo simulation. The presented algorithm is fast and accurate and can also be used to calculate reflectance and transmittance spectra in excellent agreement with measurements. Two- and three-dimensional generation profiles in single- and double-sided textured solar cells are presented and discussed in detail. Examples for applications are given. Finally, the presented algorithm is compared with a pure Monte-Carlo algorithm.     

Technical assessment of solar thermal energy storage technologies

Solar energy is recognized as one of the most promising alternative energy options. On sunny days, solar energy systems generally collect more energy than necessary for direct use. Therefore, the design and development of solar energy storage systems, is of vital importance and nowadays one of the greatest efforts in solar research. These systems, being part of a complete solar installation, provide an optimum tuning between heat demand and heat supply. This paper reviews the basic concepts, systems design, and the latest developments in (sensible and latent heat) thermal energy storage. Parameters influencing the storage system selection, the advantages and disadvantages of each system, and the problems encountered during the systems operation are highlighted.     

Solar distillation under climatic conditions of Egypt

Solar distillation in a single basin was studied theoretically under the climatic conditions of Alexandria, Egypt. The unsteady energy equations for the glass cover, water and basin were simultaneously solved. The effects of saline water depth, insulation thickness and wind speed on the still productivity were evaluated. A year-round study showed that the productivity of the still strongly depends on the solar radiation and ambient temperature. The daily still productivity varies from 1.1 to 5.2 kg/m² of basin area with an annual average of 3.16 kg/m². The solar still efficiency variesfrom 0.34 to 0.49 with an annual average of 0.42. The daily total still production increased with decreasing the water depth and increasing the insulation thickness. Increasing the wind speed resulted in a relatively small reduction in still productivity. The maximum production rate occurred after the peak in solar radiation and the time lag increases with the increase in water depth.     

Ellagic acid promoted biomimetic synthesis of shape-controlled silver nanochains

In this work, ellagic acid (EA), a naturally occurring plant polyphenol, was utilized for the biomimetic synthesis of silver (Ag) nanoparticles, which over a period of time formed extended branched nanochains of hexagonal-shaped silver nanoparticles. It was found that EA not only has the capability of reducing silver ions, resulting in the formation of Ag nanoparticles, due to its extended polyphenolic system, but also appears to recognize and affect the Ag nanocrystal growth on the (111) face, leading to the formation of hexagon-shaped Ag nanocrystals. Initially, various Ag nanocrystal shapes were observed; however, over a longer period of time, a majority of hexagonal-shaped nanocrystals were formed. Although the exact mechanism of formation of the nanocrystals is not known, it appears that EA attaches to the silver nuclei, leading to lower surface energy of the (111) face. Further, the nanocrystals fuse together, forming interfaces among the aggregates, and, with time, those interfaces become lesser, and the nanoparticles merge together and share the same single crystallographic orientation, which leads to the formation of long elongated chains of hexagonal nanoparticles. This biomimetic approach may be developed as a green synthetic method to prepare building blocks with tunable properties for the development of nanodevices. Further, we explored the antibacterial properties and found that the tandem of EA-Ag nanochains substantially enhanced the antibacterial properties of both gram-positive and gram-negative bacteria compared to silver nanoparticles or EA alone. Additionally, the materials were also utilized for imaging of mammalian NRK (normal rat kidney) cells.     

Characterization of a calmodulin-binding transporter from the plasma membrane of barley aleurone

We have used Arabidopsis calmodulin (CaM) covalently coupled to horseradish peroxidase to screen a barley aleurone cDNA expression library for CaM binding proteins. The deduced amino acid sequence of one cDNA obtained by this screen was shown to be a unique protein of 702 amino acids with CaM and cyclic nucleotide binding domains at the carboxyl terminus and high similarity to olfactory and K+ channels. This cDNA was designated HvCBT1 (Hordeum vulgare CaM binding transporter). Hydropathy plots of HvCBT1 showed the presence of six putative transmembrane domains, but sequence alignment indicated a pore domain that was unlike the consensus domains in K+ and olfactory channels. Expression of a subclone of amino acids 482-702 in Escherichia coli generated a peptide that bound CaM. When a fusion protein of HvCBT1 and green fluorescent protein was expressed in barley aleurone protoplasts, fluorescence accumulated in the plasma membrane. Expression of HvCBT1 in the K+ transport deficient Saccharomyces cerevisiae mutant CY162 showed no rescue of the mutant phenotype. However, growth of CY162 expressing HvCBT1 with its pore mutated to GYGD, the consensus sequence of K+ channels, was compromised. We interpret these data as indicating that HvCBT1 acts to interfere with ion transport.     

Thin film silicon solar cells on upgraded metallurgical silicon substrates prepared by liquid phase epitaxy

Thin layers of about 30 μm thickness were grown on upgraded metallurgical (UMG) silicon substrates by liquid phase epitaxy (LPE) from an indium solvent. Instead of adding electronic grade silicon to the solution, a melt back step was carried out before each growth process to supply silicon to the melt from the UMG-Si wafers. We present an LPE technology which is capable to be directly scaled up to a few hundred layers per run. Solar cells have been fabricated based on phosphorous paste diffusion with efficiencies up to η=10.0%.     

Computational aspects of the linear optimal regulator problem

This paper considers computational problems arising in the solution of the linear optimal regulator problem. The proposed solution for the constant feedback gain matrix is an adaption of the eigenvector solution proposed by many authors. Techniques are given which are numerically stable and do not require complex arithmetic. These techniques offer considerable savings in computation time and eliminate many of the problems that plague more conventional methods.     

Overexpression of Tropomyosin Isoform Tpm3.1 Does Not Alter Synaptic Function in Hippocampal Neurons

Tropomyosin (Tpm) has been regarded as the master regulator of actin dynamics. Tpms regulate the binding of the various proteins involved in restructuring actin. The actin cytoskeleton is the predominant cytoskeletal structure in dendritic spines. Its regulation is critical for spine formation and long-term activity-dependent changes in synaptic strength. The Tpm isoform Tpm3.1 is enriched in dendritic spines, but its role in regulating the synapse structure and function is not known. To determine the role of Tpm3.1, we studied the synapse structure and function of cultured hippocampal neurons from transgenic mice overexpressing Tpm3.1. We recorded hippocampal field excitatory postsynaptic potentials (fEPSPs) from brain slices to examine if Tpm3.1 overexpression alters long-term synaptic plasticity. Tpm3.1-overexpressing cultured neurons did not show a significantly altered dendritic spine morphology or synaptic activity. Similarly, we did not observe altered synaptic transmission or plasticity in brain slices. Furthermore, expression of Tpm3.1 at the postsynaptic compartment does not increase the local F-actin levels. The results suggest that although Tpm3.1 localises to dendritic spines in cultured hippocampal neurons, it does not have any apparent impact on dendritic spine morphology or function. This is contrary to the functional role of Tpm3.1 previously observed at the tip of growing neurites, where it increases the F-actin levels and impacts growth cone dynamics.     

Path following algorithm for skid-steering mobile robot based on adaptive discontinuous posture control

The kinematic model of a skid-steering mobile robot (SSMR) is manipulated using signed polar transformation which represents a discontinuous state transformation. The influence of relative position between the instantaneous center of rotation (ICR) and SSMR center of mass is considered. Then, adaptive state feedback controller is designed and stability regions are studied. Subsequently, a point-to-point tracking algorithm is introduced to track a trajectory that is defined by a set of way-points, which is the more realistic case of dangerous exploration or landmine detection purposes. The closed-loop system is simulated using MATLAB environment and experimentally validated using a modified TURTLEBOT3 Burger. Results show that the proposed controller reaches almost zero steady state error with smooth paths for point stabilization, moreover, good tracking capabilities are demonstrated. The proposed control system integrates both posture and tracking algorithm, thus achieve trajectory tacking which is defined by a set of way-points.