Strength estimation of unisothermally cured concretes with matrices

A new matrix method was developed for estimating the strength of in situ concrete exposed to unisothermal curing conditions. The model considers effect of various curing temperatures occurred at different ages of concrete on strength development of concrete. The cross-over effects on later age concrete strength due to hot or cold weather conditions in early-ages of concrete were also considered. The model ensures precise strength estimations with error percentages below 7%. The time required for form removal of concrete can be determined by the method.     

Configuration of segmented leg for the enhanced performance of segmented thermoelectric generator

Thermal analysis of a segmented thermoelectric generator is performed, and the segmented leg configurations maximizing the efficiency and the output power are formulated. The effect of operating conditions such as external load resistance, the temperatures of hot and cold junctions, on the device performance is studied. The segmented thermoelectric generator has the leg configuration consisting of the combination of modified lead telluride and modified bismuth telluride. The segmented thermoelectric generator performance, such as device efficiency and output power, is compared with those corresponding to a single material leg configuration (modified lead telluride or modified bismuth telluride) for various operating conditions. It is found that a unique value of the segmented leg combination maximizes the efficiency and the output power for each operating condition. The variation in the operating conditions changed the locus points of the maximum efficiency and the maximum output power. The segmented thermoelectric generator gives rise to the higher device efficiency and the output power than those of the single material leg configuration, especially for the low external load resistance. Copyright © 2016 John Wiley & Sons, Ltd.     

Domain-Size-Dependent Residual Stress Governs the Phase-Transition and Photoluminescence Behavior of Methylammonium Lead Iodide

Methylammonium lead iodide (MAPbI₃) perovskite has garnered significant interest as a versatile material for optoelectronic applications. The temperature-dependent photoluminescence (TDPL) and phase-transition behaviors revealed in previous studies have become standard indicators of defects, stability, charge carrier dynamics, and device performance. However, published reports abound with examples of irregular photoluminescence and phase-transition phenomena that are difficult to reconcile, posing major challenges in the correlation of those properties with the actual material state or with the subsequent device performance. In this paper, a unifying explanation for the seemingly inconsistent TDPL and phase-transition (orthorhombic-to-tetragonal) characteristics observed for MAPbI₃ is presented. By investigating MAPbI₃ perovskites with varying crystalline states, ranging from polycrystal to highly oriented crystal as well as single-crystals, key features in the TDPL and phase-transition behaviors are identified that are related to the extent of crystal domain-size-dependent residual stress and stem from the considerable volume difference (ΔV ≈ 4.5%) between the primitive unit cells of the orthorhombic (at 80 K) and tetragonal phases (at 300 K) of MAPbI₃. This fundamental connection is essential for understanding the photophysics and material processing of soft perovskites.     

Influence of substrate temperature on structural and optical properties of RF sputtered ZnMnO thin films

The ZnMnO thin films were deposited on glass substrates by radio frequency magnetron sputtering method. The properties of ZnMnO thin films were investigated by high-resolution x-ray diffractometer (HRXRD),atomic force microscopy (AFM), UV-Vis spectrometer and room temperature photoluminescence (PL), under the influence of substrate temperature. The substrate temperature was varied from 300, 400 and 500°C. With increasing the substrate temperature, the structure of the films changed from cubic to hexagonal. The cubic ZnMnO thin films grown along [210] direction, while the hexagonal ones grown along [002] direction. The changes in surface morphology provided a proof on the structural transition. Also, decrease and increase of optical band gap is associated with cubic or hexagonal structure of the films.

     

Exergoeconomic analysis of a vehicular PEM fuel cell system

In this study, we deal with the exergoeconomic analysis of a proton exchange membrane (PEM) fuel cell power system for transportation applications. The PEM fuel cell performance model, that is the polarization curve, is previously developed by one of the authors by using the some derived and developed equations in literature. The exergoeconomic analysis includes the PEM fuel cell stack and system components as compressor, humidifiers, pressure regulator and the cooling system. A parametric study is also conducted to investigate the system performance and cost behaviour of the components, depending on the operating temperature, operating pressure, membrane thickness, anode stoichiometry and cathode stoichiometry. For the system performance, energy and exergy efficiencies and power output are investigated in detail. It is found that with an increase of temperature and pressure and a decrease of membrane thickness the system efficiency increases which leads to a decrease in the overall production cost. The minimization of the production costs is very crucial in commercialization of the fuel cells in transportation sector.     

Liquid Phase Exfoliated Indium Selenide Based Highly Sensitive Photodetectors

Layered semiconductors of the IIIA–VIA group have attracted considerable attention in (opto)electronic applications thanks to their atomically thin structures and their thickness‐dependent optical and electronic properties, which promise ultrafast response and high sensitivity. In particular, 2D indium selenide (InSe) has emerged as a promising candidate for the realization of thin‐film field effect transistors and phototransistors due to its high intrinsic mobility (>10² cm² V^?1 s^?1) and the direct optical transitions in an energy range suitable for visible and near‐infrared light detection. A key requirement for the exploitation of large‐scale (opto)electronic applications relies on the development of low‐cost and industrially relevant 2D material production processes, such as liquid phase exfoliation, combined with the availability of high‐throughput device fabrication methods. Here, a β polymorph of indium selenide (β‐InSe) is exfoliated in isopropanol and spray‐coated InSe‐based photodetectors are demonstrated, exhibiting high responsivity to visible light (maximum value of 274 A W^?1 under blue excitation 455 nm) and fast response time (15 ms). The devices show a gate‐dependent conduction with an n‐channel transistor behavior. Overall, this study establishes that liquid phase exfoliated β‐InSe is a valid candidate for printed high‐performance photodetectors, which is critical for the development of industrial‐scale 2D material‐based optoelectronic devices.     

Integration of a speech activated control system and a wireless interworking unit for a CAN-based distributed application

Ever increasing number of mobile devices in automation systems have revealed the requirement of utilizing wireless communication systems enabling interoperability between existing wired and wireless systems. Therefore, a wireless interworking unit (WIU) is usually employed to provide required interworking functionality. This work briefly exploits a controller area network (CAN)/IEEE 802.11b WIU and a speech activated control application to be used in a CAN-based industrial networking environment and presents its prototype. The WIU employed provides communication skills with the speech activated control system including a speech recognition process and CAN-based distributed control application over the wireless medium.     

Solar Cells with Enhanced Photocurrent Efficiencies Using Oligoaniline‐Crosslinked Au/CdS Nanoparticles Arrays on Electrodes

Different configurations of CdS nanoparticles (NPs) are linked to Au electrodes by electropolymerization of thioaniline‐functionalized CdS NPs onto thioaniline‐functionalized Au‐electrodes. In one configuration, thioaniline‐functionalized CdS NPs are electropolymerized in the presence of thioanline‐modified Au NPs to yield an oligoaniline‐crosslinked CdS/Au NPs array. The NP‐functionalized electrode generates a photocurrent with a quantum yield that corresponds to ca. 9%. The photocurrent intensities are controlled by the potential applied on the electrode, and the redox‐state of the oligoaniline bridge. In the oxidized quinoide state of the oligoaniline units, the bridges act as electron acceptors that trap the conduction‐band electrons that are transported to the electrode and lead to high quantum yield photocurrents. The reduced π‐donor oligoaniline bridges act as π‐donor sites that associate N,N′‐dimethyl‐4,4′‐bipyridinium, MV²⁺, by donor/acceptor interactions, K_a = 5270 M^?1. The associated MV²⁺ acts as an effective trap of the conduction‐band electrons, and in the presence of triethanolamine (TEOA) as an electron donor, high photocurrent values are measured (ca. 12% quantum yield). The electropolymerization of thioaniline‐functionalized Au NPs and thioaniline‐modified CdS NPs in the presence of MV²⁺ yields a MV²⁺‐imprinted NP array. The imprinted array exhibits enhanced affinities toward the association of MV²⁺ to the oligoaniline π‐donor sites, K_a = 2.29 × 10⁴ M^?1. This results in the effective trapping of the conduction‐band electrons and an enhanced quantum yield of the photocurrent, ca. 34%. The sacrificial electron donor, TEOA, was substituted with the reversible donor I₃^?. A solar cell consisting of the imprinted CdS/Au NPs array, with MV²⁺ and I₃^?, was constructed. The cell generated a photocurrent with a quantum yield of 4.7%.     

The Annealing Effects in the Iron-Based Superconductor FeTe0.8Se0.2 Prepared by the Self-Flux Method

FeTe_0.8Se_0.2 single crystals as-cast and post-annealed were prepared by the self-flux method. We have investigated the structural properties of samples by using the XRD, scanning electron microscope (SEM), energy dispersive X-ray (EDX), and magnetic techniques. The SEM results clearly demonstrate that Te ions are quite well substituted for Se ions in the FeSe lattice for the samples. From the XRD and EDX spectra of the both samples, it has been concluded that the post-annealing causes no change in the tetragonal structure of FeTe_0.8Se_0.2. According to M–H measurements, the perfect diamagnetism has been observed only in low field at 5 and 10 K temperatures. The trend of the magnetization versus temperature curves, measured under a magnetic field of 10 Oe, also support our conclusion about diamagnetic contribution in FeTe_0.8Se_0.2 single crystal explored in this study. The as-cast and post-annealed samples show the onset of diamagnetism at temperatures, \(T_{\mathrm {c.on}}^{\text {mag}}\) , 12.45 and 13.27 K, respectively. In addition, those curves indicate that the high field value and some impurities reveal ferromagnetic interactions.     

A spin wave resonance study on reentrant Au77Fe23 films

Thin films prepared by both flash and slow evaporation of the bulk Au₇₇Fe₂₃ alloy have been studied by electron spin resonance (ESR) technique at the temperature range between 77–300 K. A series of spin wave resonance (SWR) peaks were observed at all temperatures when the external de magnetic field is applied along the directions lying in a small angular interval with respect to the film normal. The classical spin wave model has been used to analyze the experimental data. The magnetic parameters, such as exchange stiffness constant, the effective bulk and the surface anisotropy energy parameters of the system have been derived as a function of temperature. While the easy plane surface anisotropy almost remains constant, considerable increments were found in the exchange parameter, the magnetization and the linewidth with decreasing temperature. The SWR linewidths for the films obtained by slow evaporation at higher substrate temperatures are noticeably smaller compared to those of the film prepared by flash evaporation technique.