Enhanced photoluminescence of Gd 2O 3:Eu 3+ nanophosphors with alkali (M = Li +, Na +, K +) metal ion co-doping

Gd 1.95Eu 0.04M 0.01O 3 (M = Li +, Na +, K +) nanophosphors have been synthesized by a low temperature solution combustion (LSC) method. Powder X-ray diffraction pattern (PXRD), scanning electron microscopy (SEM), UV-vis and photoluminescence (PL) measurements were carried out to characterize their structural and luminescent properties. The excitation and emission spectra indicated that the phosphor could be well excited by UV light (243 nm) and emit red light about 612 nm. The effect of alkali co-dopant on PL properties has been examined. The results showed that incorporation of Li +, Na + and K + in to Gd 2O 3:Eu 3+ phosphor would lead to a remarkable increase of photoluminescence. The PL intensity of Gd 2O 3:Eu 3+ phosphor was improved evidently by co-doping with Li + ions whose radius is less than that of Gd 3+ and hardly with Na +, K + whose radius is larger than that of Gd 3+. The effect of co-dopants on enhanced luminescence was mainly regarded as the result of a suitable local distortion of crystal field surrounding the Eu 3+ activator. These results will play an important role in seeking some more effective co-dopants. © 2011 Elsevier B.V. All rights reserved

Cadmium silicate nanopowders for radiation dosimetry application: Luminescence and dielectric studies

AbstractPure cadmium silicate (CdSiO3) nanophosphor was prepared by a low temperature solution combustion technique. In this technique, meso-structured silica was used as silica source. The prepared compounds were well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy, high resolution transmission electron microscopy, Fourier transform infrared and UV–vis spectroscopic techniques. The PXRD peaks of as-formed sample are broad and amorphous in nature. The compound calcined at 800°C shows pure monoclinic phase, which is the lowest temperature reported so far to obtain in this phase. The average crystallite size for phase pure compound was found to be ∼31nm. The optical energy band gap of ∼5.6eV was observed for the compound. Raman spectrum of the sample showed the all possible states of vibrational motions of the prepared samples. The UV irradiated samples with different dose and time with constant heating rate exhibit the thermoluminescence (TL) with a well resolved glow peak at ∼160°C. The variation of TL intensity with dosage time results that the material was found to be quite useful in radiation dosimetry. The frequency dependent dielectric constant of the prepared sample exhibits high value at low frequency and vice versa

Diffraction of light by ultrasonic waves

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Item analysis of multiple choice questions of undergraduate pharmacology examinations in a medical college in Belagavi, Karnataka, India

Background: Multiple choice questions (MCQs) are a common method of assessment of medical students. The quality of MCQs is determined by three parameters such as difficulty index (DIF I), discrimination index (DI), and Distractor efficiency (DE). Item analysis is a valuable yet relatively simple procedure, performed after the examination that provides information regarding the reliability and validity of a test item. The objective of this study was to perform an item analysis of MCQs for testing their validity parameters.Methods: 50 items consisting of 150 distractors were selected from the formative exams. A correct response to an item was awarded one mark with no negative marking for incorrect response. Each item was analysed for three parameters such as DIF I, DI, and DE.Results: A total of 50 items consisting of 150 Distractor s were analysed. DIF I of 31 (62%) items were in the acceptable range (DIF I= 30-70%) and 30 had ‘good to excellent’ (DI >0.25). 10 (20%) items were too easy and 9 (18%) items were too difficult (DIF I <30%). There were 4 items with 6 non-functional Distractor s (NFDs), while the rest 46 items did not have any NFDs.Conclusions: Item analysis is a valuable tool as it helps us to retain the valuable MCQs and discard or modify the items which are not useful. It also helps in increasing our skills in test construction and identifies the specific areas of course content which need greater emphasis or clarity

A New Approach to Automatic Generation of all Quadrilateral Finite Element Mesh for Planar Multiply Connected Regions

A new approach for the automatic generation and refinement of finite element meshes over multiply connected planar regions has been developed. This paper represents continuation of authors research activities in that area. An algorithm for producing a triangular mesh in a convex polygon is presented in authors recent work. It is used for the finite element triangulation of a complex polygonal region of the plane decomposed into convex polygons. We decompose the convex polygonal regions into simple sub regions in the shape of triangles. These simple regions are then triangulated to generate a fine mesh of triangular elements. We then propose an automatic triangular to quadrilateral conversion scheme.In this scheme, each isolated triangle is split into three quadrilaterals according to the usual scheme, adding three vertices in the middle of the edges and a vertex a the barycentre of the element. To preserve the mesh conformity, a similar procedure is also applied to every triangle of the domain to fully discretize the given complex polygonal domain into all quadrilaterals, thus propagating uniform refinement. This simple method generates a mesh whose elements confirm well to the requested shape by refining the problem domain. We have modified these algorithms and demonstrated their use by generating high quality meshes for some typical multiply connected regions: square domains with regular polygonal holes inside and vice versa. We have also made improvements and modifications to to the above triangulation algorithm of the triangle which can now triangulate a trapezium cut out of a triangle. This new algorithm on the triangulation of a trapezium cut out of a triangle is applied to quadrangulate the planar regions in the shape of a circular annulus and square domain with a square hole inside. We have appended MATLAB programs which incorporate the mesh generation schemes developed in this paper. These programs provide valuable output on the nodal coordinates, element connectivity and graphic display of the all quadrilateral mesh for application to finite element analysi

A CONTROL SCHEME USING A STATCOM FOR A GRID CONNECTED OWF AND MCF TO IMPROVE THE DYNAMIC STABILITY OF THE SYSTEM

This paper presents a Novel control scheme is based on the STATCOM for the grid connected integrated system which has 80-MW offshore wind farm (OWF) and 40-MW marine current farm (MCF) to achieve the both voltage control and damping enhancement. The PID damping controller is designed for the STATCOM to contribute effective damping characteristics to the studied system under different operating conditions such as noise wind speed disturbances and marine current speed disturbances. A frequency-domain approach based on a linearized system model using Eigen value techniques and a time-domain scheme based on a nonlinear system model subject to various disturbances are employed to simulate the effectiveness of the proposed control scheme. It can be concluded from the simulated results that the proposed STATCOM joined with the designed PID damping controller is very effective to stabilize the studied system under disturbance conditions. The voltage fluctuations of the AC bus subject to the active-power variations of the studied system can also be effectively controlled by the proposed control scheme. The system performance is also improved

A NOVEL DESIGN OF DUAL BAND MICROSTRIP ANTENNA FOR WIRELESS APPLICATIONS

A simple and compact inset fed dual band microstrip antenna is presented. The proposed antenna has a low profile and can easily be fed by using a 50 ohms microstripline. The proposed antenna covers all the 2.4/4.2 GHz WLAN/ RADIO ALTIMETERS operating bands, IEEE WLAN protocol 802.11 b/g employs 2.4 GHz. The antenna is simulated using An soft’s HFSSv11. Which shows good agreement with simulated results, Measured Return loss and Radiation patterns are observed to be nearly omnidirectional, moderate gain and wide frequcency band suitable for wireless applications. The antenna has an overall dimension of only 29.5mm x 38 mm x1.6mm, when printed on a FR4 substrate of dielectric constant 4.4

In-orbit Performance of UVIT on ASTROSAT

We present the in-orbit performance and the first results from the ultra-violet Imaging telescope (UVIT) on ASTROSAT. UVIT consists of two identical 38cm coaligned telescopes, one for the FUV channel (130-180nm) and the other for the NUV (200-300nm) and VIS (320-550nm) channels, with a field of view of 28 $arcmin$. The FUV and the NUV detectors are operated in the high gain photon counting mode whereas the VIS detector is operated in the low gain integration mode. The FUV and NUV channels have filters and gratings, whereas the VIS channel has filters. The ASTROSAT was launched on 28th September 2015. The performance verification of UVIT was carried out after the opening of the UVIT doors on 30th November 2015, till the end of March 2016 within the allotted time of 50 days for calibration. All the on-board systems were found to be working satisfactorily. During the PV phase, the UVIT observed several calibration sources to characterise the instrument and a few objects to demonstrate the capability of the UVIT. The resolution of the UVIT was found to be about 1.4 - 1.7 $arcsec$ in the FUV and NUV. The sensitivity in various filters were calibrated using standard stars (white dwarfs), to estimate the zero-point magnitudes as well as the flux conversion factor. The gratings were also calibrated to estimate their resolution as well as effective area. The sensitivity of the filters were found to be reduced up to 15\% with respect to the ground calibrations. The sensitivity variation is monitored on a monthly basis. UVIT is all set to roll out science results with its imaging capability with good resolution and large field of view, capability to sample the UV spectral region using different filters and capability to perform variability studies in the UV.Comment: 10 pages, To appear in SPIE conference proceedings, SPIE conference paper, 201

Synthesis, Characterization of Nano MnO2 and its Adsorption Characteristics Over an Azo Dye

ABSTRACT Nano MnO2 powder was synthesized by low temperature solution combustion method using oxalyl dihydrazide (ODH) fuel. The final product was well characterized by Powder X-ray diffraction (PXRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning electron microscopy (SEM) for crystallographic purity, phase formation and surface morphology respectively. PXRD results show that pure MnO2 was synthesized at 300 0 C with no other impurities. SEM micrograph shows the product has highly porous structure with large voids, typical of combustion derived material. An adsorption characteristic of the porous MnO2 was studied over direct green dye (DG). The optimum dose of MnO2 for removal of 10 ppm DG azo dye was found to be 0.4 g L -1