[en] Highlights: • Simulation of Micro Turbine Generation system (MTG) to study its performance. • Analysis of MTG with Differential Evolution (DE) algorithm tuned PID controller. • Analysis of MTG with FOPID (Fractional Order PID) controller tuned by DE. • DE based FOPID controller improves both the transient and steady state responses. • Design and implementation of harmonic filter for MTG system. -- Abstract: The power system structure is complicated and the demand is increasing rapidly. In order to minimize the power losses and to reduce the power shortage, Distribution Generation (DG) is added in the power system. Microturbine Generation (MTG) is a new type of DG which has become popular source of electric power industries due to their fuel flexibility, reliability, power quality and its size. In this paper, the modelling and simulation analysis of the MTG system are carried out with Fractional Order Proportional Integral Derivative (FOPID) controller to improve the overall performance of MTG system. The performance of the MTG system is studied under various linear and non-linear load conditions. The Microturbine model and converter controller models are simulated using MATLAB Software. FOPID controller is used to maintain constant voltage for various load conditions by maintaining the torque of the Microturbine (MT) system. The power quality of MTG system is analyzed using Fast Fourier Transform (FFT) Analysis. To improve the power quality, LCL filter is added in this paper. The overall performance of MTG system is analyzed with and without FOPID controller. When the results are compared with conventional PI controller, the MTG system shows better performance in FOPID controller.

[en] Zirconium oxide (zirconia) exists in three crystalline forms of monoclinic, tetragonal and cubic structures at atmospheric pressures. The cubic form of zirconia is well known for its mechanical, electrochemical and optical applications. Fe-doped cubic zirconia (high temperature phase) compositions are synthesized by microwave combustion method. Here, we present a Moessbauer investigation of Zr_1-xFe_xO₂ composition within a range of Fe (0.03 < x < 0.09). ⁵⁷Fe Moessbauer spectra were recorded at room temperature and at low temperature (77 K) for all samples. 3% Fe-doped ZrO₂ shows doublet and the corresponding 6% and 9% Fe-doped ZrO₂ samples show superimposed sextet and doublets. The isomer shift and quadrupole moment indicate, Iron to be in III oxidation state and to occupy different octahedral sites, associated with some amount of disorder. X-ray powder diffraction pattern of Fe-doped ZrO₂ samples appear as very well crystalline. The Miller indices refer to the cubic fluorite-type ZrO₂ structure. The magnetic behavior shows increase in moment and decrease in coercivity, with increase in Fe concentration. The M vs. H plots of the as-prepared Zr_1-xFe_xO₂ essentially show typical hysteresis loops, indicating room temperature ferromagnetism. Thus, the introduced microwave combustion route is an effective process to achieve multifunctional Fe-doped Zirconia with coexistent magnetic properties.

[en] Opto-impedance characteristics of the long persistent strontium aluminate : Eu²⁺ phosphor system have been compared with fluorescent strontium chloro-apatite : Eu²⁺ phosphor. This study has shown that optical pumping on the long persistent phosphor sample leads to a type of charge build-up and subsequent dispersion through a diffusion process occurring on a slow time scale (∼s) centring on the Dy³⁺ ion in agreement with a three-level scheme based on Dy³⁺ related hole-trapping-detrapping mechanism

[en] X-ray absorption spectroscopic studies of SrRu_0.5Mn_0.5O₃ show that 2p →t_2g related peak at the Ru-L₂ edge is more intense than the Ru-L₃ edge and shift of the 2p →e_g related peak of the Ru-L_2,3 edge by ∼ 0.8 eV to higher energy than that of the Ru (IV) compound, SrRuO₃. Significant differences in the spectral change is due to the existence of the mixed valence ionic pair involving Ru⁺⁴/ Ru⁺³, rather than the crystal field splitting energy (10 Dq) effect, which is confirmed by the crystal field multiplet calculation approach. (author)

[en] Spinel type LiMn₂O₄ and inverse spinel LiNiVO₄ systems serve as standard cathode materials or potential cathode systems for application in high energy density lithium-ion batteries. Upon photo-excitation using UV radiation of energy ∼5 eV, the LiNiVO₄ system shows significant modification in the solid state impedance pattern while the LiMn₂O₄ system does not. This study has revealed a significant difference in the opto-impedance pattern for LiNiVO₄ with respect to LiMn₂O₄, which may be due to the different electronic processes involved. An attempt has been made to study this behaviour from the solid-state viewpoint

[en] Single-phase solid solution of Cd_xZn_1-yMn_yS offers possibility for tuning full color spectrum. A broad emission with FWHM of ∼155 nm leading to a broadband emission can be harvested in a nominal composition such as Cd_0.54Zn_0.43Mn_0.03S by a compounded effect of CdS, ZnS and ZnS:Mn responsible for blue, green and red emission, respectively. Contribution from (i) quantization of energy levels due to nano-dimension, (ii) emission arising from trap (mid-gap) states and (iii) Mn²⁺ spin-forbidden ⁴T₁ → ⁶A₁ transition is responsible for the mechanism of PL in these solid solutions

[en] The objective of this research work is to study the impact of graphite forms used as solid lubricant additives on brake friction materials performance. Three composites were fabricated using the conventional process and were characterised for its physical, chemical, mechanical and thermal properties conforming to industrial standards. The thermal stability of the graphite particles and developed composites was measured in an air atmosphere using the thermogravimetric analyser. The tribological performances were studied using the Chase friction test machine as per IS-2742 Part-4 standard. The results indicated that the friction composite containing expandable graphite exhibited better thermal stability with good fade and recovery performances. This led to enhance wear resistance and stable friction due to its better heat dissipation and lubricity comparing with the other two composites. An empirical relationship for the friction and wear was developed based on Chase test results. The worn surface morphologies of the Chase tested composites were analysed using scanning electron microscopy to study the sensitivity of the friction–wear mechanisms to the graphite-type effect.

[en] Microwave assisted combustion (MAC) route holds potential to achieve a substantial degree of Mg doping, >15-25% in bulk ZnO, which is evident from a blue shifted optical band edge and a shift in emission towards lower wavelength. In contrast, microwave-assisted polyol (MAP) route shows no pronounced effect on the photoluminescence features due to a segregated amorphous Mg(OH)₂ phase. Two factors underlie the substitution of Mg in Zn sites viz: (i) heats of formation of ZnO is -350.5 kJ/mol which is remarkably lower compared to MgO, -601.6 kJ/mol and (ii) the decomposition temperatures of the respective hydroxides are distinctly different, 125 and 350 deg. C, respectively. These thermodynamic requirements play an important role in the mechanism underlying the formation of Mg:ZnO solid solutions.

[en] A series of nano-crystalline Co_xAg_100-x solid solutions have been prepared by NaBH₄ reduction of the corresponding metal salts at room temperature in Ar gas flow. Alloys heat-treated at 600 deg. C in Ar/H₂ (5%) show the evolution of metastable fcc Co precipitates in Ag. Magnetic studies indicate that all the compositions are ferromagnetic with Curie temperatures >400 K. For a nominal composition of Co₆₀Ag₄₀, heat-treated at 600 deg. C, an effective negative magneto-resistance (MR) ratio of the order of ∼21% at 350 K, at 2 T is observed. This could arise from the influence of magnetic field on the electron-phonon scattering effects near to T_c and to the spin-mixing scattering by magnons

[en] The magnetoresistance (MR) of cold-pressed powder pellets of the half-metallic ferromagnet CrO₂ was measured in wide ranges of temperature T and magnetic fields H up to μ ₀ H=16 T. The MR increases from 2% at 300 K up to 64% at T=1.5 K and no saturation is observed up to 16 T. The low field resistivity depends logarithmically on temperature whereas the high-field MR shows a scaling behavior with H/T. The results favor second-order tunneling (paramagnetic assisted tunneling) at zero bias via localized magnetic moments at or within the barrier between the CrO₂ grains as the dominant resistivity mechanism for both the low- and high-field MR, respectively