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Chandra B.P.,Ashoka Institute of Technology and Management | Tiwari C.S.,Government Postgaduate College | Sharma R.,Arts and Commerce Girls College
Luminescence | Year: 2013

When an γ-irradiated Dy-, Tm-, Sm- or Mn-doped CaSO4 crystal is impulsively deformed, two peaks appear in the ML intensity versus time curve, whereby the first ML peak is found in the deformation region and the second in the post-deformation region of the crystals. In this study, intensities Im1 and Im2 corresponding to first and second ML peaks, respectively, increased linearly with an impact velocity v0 of the piston used to deform the crystals, and times tm1 and t m2 corresponding to the first and second ML peaks, respectively, decreased with impact velocity. Total ML intensity initially increased with impact velocity and then reached a saturation value for higher values of impact velocity. ML intensity increased with increasing γ-doses and size of crystals. Results showed that the electric field produced as a result of charging of newly-created surfaces caused tunneling of electrons to the valence band of the hole-trapping centres. The free holes generated moved in the valence band and their subsequent recombination with electron trapping centres released energy, thereby resulting in excitation of luminescent centres. Copyright © 2012 John Wiley & Sons, Ltd. Source


Chandra B.P.,Disha Institute of Management and Technology | Chandra B.P.,Ashoka Institute of Technology and Management | Chandra V.K.,Chhatrapati Shivaji Institute of Technology | Mahobia S.K.,Rani Durgavati University | And 3 more authors.
Sensors and Actuators, A: Physical | Year: 2012

The present paper reports the real-time sensing of the amplitude and duration of impact stress using mechanoluminescence (ML) of the films such as ZnS:Mn and SrAl 2O 4:Eu. After the impact of a small ball from a low height onto the film, initially the elastico mechanoluminescence (EML) intensity increases with time, attains a peak value and then it decreases with time, initially at a fast rate and later on at a slow rate. The fast decay time of the EML intensity is related to the rate constant for the rise of impact stress and the slow decay time of EML is equal to the lifetime of electrons in the shallow traps lying in the normal piezoelectric region of the crystals, which get filled during the detrapping of thermally stable traps at the time of the increase of pressure. Both the peaks of EML intensity and total EML intensity increase linearly with the height through which the ball is dropped onto the films. The EML spectra are similar to the corresponding photoluminescence and electroluminescence spectra. On the basis of the localized piezoelectrically induced electron detrapping model, expressions are derived for different parameters of the impact stress-induced EML of the films, whereby a good agreement is found between the experimental and theoretical results. As the EML intensity depends on the impact stress, the impact stress can be sensed by measuring the EML intensity. Furthermore, the duration of stress is related to the time t m corresponding to the peak of the EML intensity versus time curve; hence, the pulse duration of the impact stress can be monitored by measuring the value of time t m. © 2011 Elsevier B.V. All rights reserved. Source


Singh D.,Ashoka Institute of Technology and Management | Singh B.,Indian Institute of Technology BHU Varanasi | Singh N.,Motilal Nehru National Institute of Technology
International Journal of Power Electronics and Drive Systems | Year: 2014

This paper presents a framework to carry out a simulation to tune the speed controller gains for known input of DC drive system. The objective is to find the optimal controller gains (proportional and integral) in a closed loop system. Various performance indices have been considered as optimal criterion in this work. The optimal gain values have been obtained by conventional and Genetic Algorithm (GA) based optimization methods. The study has been conducted on a simulink model of three phase converter controlled direct current (DC) drive with current and speed control strategy. The results show that the GA based tunning provided better solutions as compared to conventional optimization methods based tunning. © 2014 Institute of Advanced Engineering and Science. All rights reserved. Source


Chandra V.K.,Chhatrapati Shivaji Institute of Technology | Chandra B.P.,Disha Institute of Management and Technology | Chandra B.P.,Ashoka Institute of Technology and Management
Organic Electronics: physics, materials, applications | Year: 2012

In phosphorescent organic light-emitting diodes (PHOLEDs), both the rise time and decay time decrease with increasing amplitude of the applied voltage pulse. The rise time τ r of the transient electroluminescence (TEL) increases linearly with increasing value of the ratio of voltage V to the current j, that is, with V/j. Using the equations for the dynamics of charge carriers an expression is derived for the rise time τ r of the TEL in OLEDs. It is shown that τ r should increase with increasing values of the ratio (V/j), dielectric constant , and area of cross-section of the emission layer, however, it should decrease with the thickness of emission layer. For higher values of the applied voltage nonlinearity occurs in the τ r versus V/j plot because the increase in mobility of carriers at high electric field causes increase in the current flowing through the OLEDs. In fact, the rise time of TEL is related to the product of capacitance and effective resistance of the OLED. Considering the rate of generation and decay of radiative triplet excitons in the emission layer, an expression is derived for the decay time of TEL in PHOLEDs and it is shown that, for higher values of the time-constant of OLED, the decay time should be equal to the time-constant, however, for lower values of the time-constant, the decay time should be equal to the lifetime of radiative triplet excitons in the emission layer. A good agreement is found between the theoretical and experimental results. © 2011 Elsevier B.V. All rights reserved. Source


Pervez Y.,Chhatrapati Shivaji Institute of Technology | Janghel E.K.,Ashoka Institute of Technology and Management | Sar S.K.,Bhilai Institute of Technology
Asian Journal of Chemistry | Year: 2016

Flow injection spectrophotometric method is developed for the determination of cypermethrin insecticide. The method is based on alkaline hydrolysis of cypermethrin is converted into 2-diphenyl ether cyano ethane and hydrolyzed with HCl and resulting product was diazotized with nitrate and coupled with aniline. The absorption maxima of the azo dye formed is measured at 535 nm in acidic medium. Beer's law is obeyed over the concentration range of 5.5 to 36 μg/25 mL. The molar absorptivity and Sandell's sensitivity were found to be 5.3 × 104 L mol-1 cm-1 and 0.066 μg cm-2, respectively. The standard deviation and relative standard deviation were found to be ± 0.003 and 0.56 %, respectively. The % recovery for the determination of cypermethrin was found to be 92 %. The sampling frequency was 80 samples per hour for flow injection analysis. The method is simple sensitive and free from interferences of other pesticides and diverse ions. Other pyrethroid insecticides do not interfere in the proposed method. The method is simple, fast and has been satisfactorily applied to the determination of cypermethrin in commercial formation, food and environmental sample. Source

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