Grain size dependent magnetization, electrical resistivity and magnetoresistance in mechanically milled La0.67Sr0.33MnO3

We have studied magnetization, ac susceptibility, resistivity and magnetoresistance in mechanically milled La_0.67Sr_0.33MnO₃. The material with grain size micron to nanometer scale has stabilized in rhombohedral crystal structure with space group R3C. We have found various grain size effects, e.g., decrease of ferromagnetic moment, increase of surface spin disorder, and appearance of insulator/semiconductor type resistivity. In addition to these conventional features, we have identified a magnetic anomaly at 45 K in bulk sample. Ferromagnetic to paramagnetic transition temperature (T_C) is above room temperature for all samples. The samples are typical soft ferromagnet that transformed from multi-domain state to single domain state in nanocrystalline samples. The remarkable observation is that low temperature freezing of ferromagnetic domains/clusters does not follow the conventional spin glass features. Experimental results clearly showed the enhancement of high field magnetoresistance in nanocrystalline samples below 200 K, whereas low field magnetoresistance gradually decreases above 200 K and almost absent at 300 K. We have discussed few more magnetic and electrical changes, highly relevant to the progress of nanomaterial research in ferromagnetic manganites.     

Performance prediction of 60 kWp PV power plant in an educational institute

Due to government initiatives, many solar photovoltaic (PV) power plants of different sizes will be set up in India in the near future. In this context, the performance of a 60?kW_p PV power plant is discussed in this paper which is installed at National Institute of Technology (a centrally funded institute of Government of India), Agartala, located in a small state (Tripura) of North East India where supply of grid electricity is a critical issue. This article examines the various parameters for performance prediction of this solar power plant.     

Structural and Optical Characterizations of Electrochemically Grown Connected and Free-Standing TiO2 Nanotube Array

A TiO₂ nanotube array was grown electrochemically by using single and mixed electrolyte/s with 20 V constant potential at room temperature. Anodization was carried out for 120 min using five different electrolytes, e.g., H₃PO₄, NH₄F, HF, NH₄F with H₃PO₄ and HF with H₃PO₄. Structural characterizations of the grown titania nanotubes were conducted by using x-ray diffraction and field emission scanning electron microscopy. Optical properties of the grown nanotubes were investigated through photoluminescence (PL) spectroscopy. In the case of the 4 M H₃PO₄ electrolyte, no perceptible growth of nanotubes was observed. The individual electrolytes of 0.3 M NH₄F and 1 M HF resulted into the formation of the wall-connected nanotubes. In contrast, the mixed electrolytes comprising the strong (NH₄F, HF) and weak (H₃PO₄) electrolytes have been found to be efficient for the growth of wall-separated titania nanotubes. The results of the PL spectroscopy have demonstrated that the free-standing nanotubes offer low PL intensity compared to its connected counterpart owing to the lower carrier recombination rate of free-standing nanotubes.     

Voltage sag ride-through for adjustable-speed drives with activerectifiers

Adjustable-speed drives (ASDs) trip due to voltage sags, interfering with production and resulting in financial losses. In this paper, a methodology for incorporating voltage sag ride-through in the design of ASDs with active rectifiers is presented. The magnitude of the voltage sag for which ride-through can be provided is determined by the current rating of the active rectifier and load condition of the ASD, but a sag of any duration can be compensated for     

Heat loss factor of evacuated tubular receivers

Tubular receivers with an evacuated space between the absorber and concentric glass cover to suppress convection heat loss are employed as absorbers of linear concentrators in the intermediate temperature range. A knowledge of their heat loss factor is important for a study of the thermal performance of such solar concentrating systems. The heat loss factor of a collector can be calculated by solving the governing heat transfer equations or estimated from an empirical equation, if available. The governing equations must be solved simultaneously by iterations, but this is tedious and cumbersome. Although several correlations exist for determining the heat loss factor for flat-plate collectors and non-evacuated tubular absorbers of linear solar collectors, there is no available correlation for predicting the heat loss factor of evacuated receivers.

A correlation to calculate the heat loss factor (U_L) of evacuated tubular receivers as a function of variables involved (absorber temperature, emittance, diameter and wind loss coefficient) has been obtained. The correlation developed by a least square regression analysis predicts the heat loss factor to within ±1.5% of the value obtained by exact solution of the simultaneous equations in the following range of variables: wind loss coefficient, 10–60 W/m²°C; emittance, 0.1–0.95; and absorber temperature, 50–200°C.     

Photoelectrochemical cells consisting of phenosafranin-EDTA and different redox couples with illuminated semiconductor electrode

A photoelectrochemical cell, semiconductor (In₂O₃)/dye-EDTA//redox couple/Pt, has been developed using phenosafranin dye and EDTA aqueous solution in one compartment and Cu⁺/Cu²⁺, Fe(CN)₆⁴⁻/Fe(CN)₆³⁻, I⁻/I₂, and Fe²⁺/Fe³⁺ in the other compartment of an H-shaped cell separated by a glass membrane. All the cell characteristics such as open-circuit voltage, short-circuit current, fill factor, power efficiency, and solar energy efficiency have been determined. There is 2-3-fold increase of efficiency of the cell compared to the same cell with illuminated Pt electrode.     

Quasi‐static and dynamic nanoindentation and scratch behavior of multifunctional titania/poly(methyl methacrylate) composite

Nanoindentation (NI) and nanoscratch testing was used to determine the dynamic viscoelastic properties of titania reinforced poly(methyl methacrylate) nanocomposites. It was observed that the dynamic NI have a significant effect on the measured indentation modulus and nano‐hardness of the polymer‐based composite. Agreement was found between quasi‐static and dynamic NI result of the nanocomposites. The sinus‐nanoindentation had a limited effect on the measured viscoelastic properties of the composite. However, tribological properties and scratch hardness confirmed that the titania nanofillers act as the friction coefficient modifier in polymer matrix. POLYM. COMPOS., 35:1372–1376, 2014. © 2013 Society of Plastics Engineers     

An Improved PSOGSA for Clustering and Routing in WSNs

Wireless Personal Communications - Wireless sensor network (WSN) is an integration of sensing, communicating, computing in a board range environment. Efficient energy consumption becomes the most...     

High-performance nanoadhesive bonding of titanium for aerospace and space applications

In this investigation, attempts are made to prepare high-performance nanoadhesive bonding of titanium for its essential applications to aviation and space. The high-performance nanoadhesive is prepared by dispersing silicate nanoparticles into the ultra-high-temperature-resistant epoxy adhesive at 10 wt% ratio with the matrix adhesive followed by modification of the nanoadhesive after curing under high-energy radiation for 6 h in the pool of SLOWPOKE-2 nuclear reactor with a dose rate of 37 kGy/h to promote crosslink into the adhesive. Prior to bonding, the surfaces of the titanium sheets are mechanically polished by wire brushing, ultrasonically cleaned by acetone and thereafter the titanium sheets are modified by plasma ion implantation using plasma nitriding. The titanium surface is characterized by X-ray photoelectron spectroscopy (XPS). The thermal characteristics of the epoxy adhesive and the high-performance nanoadhesive are carried out by thermal gravimetric analysis (TGA). The TGA studies clearly shows that for the basic adhesive there is a weight loss of the adhesive, however, in the case of epoxy–silicate nanoadhesive, there is almost 100% retention of weight of the adhesive, when the adhesive is heated up to 350 °C. Lap shear tensile strength of the joint increases considerably, when the titanium surface is modified by plasma-nitriding implantation. There is a further massive increase in joint strength, when the plasma-nitriding implanted titanium joint is prepared by nanosilicate–epoxy adhesive and further modification of the adhesive joint under high-energy radiation results a further significant increase in joint strength. In order to simulate with aviation and space climatic conditions, the joints are separately exposed to cryogenic (?196 °C) and elevated temperature (+300 °C) for 100 h and thermal fatigue tests of the joints are carried out under 10 cycles by exposing the joint for 2 h under the above temperatures. When the joint completely kept at ambient condition and the joint strength compared with those joints exposed to aviation and space climatic conditions, it is observed that the joint could retain 95% of the joint strength. Finally, to understand the behavior of the high-performance silicate–epoxy nanoadhesive bonding of titanium, the fractured surfaces of the joints are examined by scanning electron microscope.