Cochin University of Science and Technology

About: Cochin University of Science and Technology is a education organization based out in Kochi, Kerala, India. It is known for research contribution in the topics: Thin film & Natural rubber. The organization has 5382 authors who have published 7690 publications receiving 103827 citations. The organization is also known as: CUSAT & Cochin University.

Host Sensitized White Luminescence from ZnGa2O4 : Dy3 + Phosphor

Abstract: Dysprosium-doped zinc gallate phosphors with the nominal formulas ZnGa 2(1-x) O 4 :Dy 2x were prepared by the high-temperature conventional solid-state reaction technique, the dopant concentration being varied in the range 0 ≤ x ≤ 0.025. Zn 1-x Ga 2 O 4 :Dy x and Ga 2(1-x) O 3 :Dy 2x samples were also prepared for comparison for a dopant concentration of x = 0.02. Only the intrinsic self-activated emission of the ZnGa 2 O 4 host is observed in the photoluminescence emission spectra of Zn 0.98 Ga 2 O 4 :Dy 0.02, while both the host emission band and characteristic emission lines ( 4 F 9/2 → 6 H J ) of Dy 3+ are observed for ZnGa 2(1-x) O 4 :Dy 2x and Ga 1.98 O 3 :Dy 0.04 phosphors. The luminescent intensity differs in the phosphors due to the different energy-transfer rates from the respective hosts to the luminescent centers. Photoluminescent studies reveal the fact that Dy 3+ ions replace Ga 3+ ions in the host lattice at their octahedral sites. The source of white luminescence in the doped samples is the nonradiative resonant energy transfer via exchange interaction between the host and the activator. The CIE coordinates of the 2.5 atom % Dy 3+ -doped sample (0.32, 0.33) matches well with achromatic white (0.33, 0.33) on the chromaticity diagram.

Microstrip-Fed Pattern- and Polarization- Reconfigurable Compact Truncated Monopole Antenna

Abstract: A microstrip-fed truncated monopole antenna with radiation pattern and polarization reconfigurability is presented. The antenna fabricated on a substrate of dielectric constant 4.4 and thickness 1.6 mm is highly compact with an overall dimension of only 0.25λs × 0.25λs. The pattern of the antenna is omnidirectional and is reconfigurable with the polarization in the orthogonal planes. The proposed antenna is suitable for 2.4-GHz wireless applications with a bandwidth of 95 MHz. The measured gain of the antenna is -1.1 dBi at the resonant frequency. The simulation (Ansoft HFSS) and measurement (R&S ZVB8 Vector Network Analyzer) results are also discussed.

Delineation of Groundwater Potential Zones in River Basins Using Geospatial Tools—an Example from Southern Western Ghats, Kerala, India

Abstract: The remote sensing and geospatial tools have wide applications in water resource assessment studies. Satellite images are increasingly being used in groundwater exploration because of their utility in identifying various geomorphic features. The present study has been carried out in two important river basins—the Ithikkara and the Kallada river basins, of Southern Western Ghats, Kerala, India. The groundwater potential zones are delineated from 14 thematic layers such as drainage density, geomorphology, slope, lithology, soil, land use/land cover, lineament density, topographic wetness index, rainfall distribution, roughness, curvature, dissection index, depth to water level and topographic position index using multi-criteria evaluation method. Integration of the factors has been performed in GIS platform using weighted overlay analysis. Different classes of thematic maps have been assigned weights based on influence on groundwater hydrology (through discussions with the experts in the field), and finally, factor ranks are assigned. The final map indicates the potentiality values of groundwater occurrence in the study area, which was classified into three categories—high, moderate and low. A total of 37.2% of the study area fall in low groundwater potential zone, 42.3% in moderate potential zone and 20.5% of the area in high potential zone. The groundwater potential zones delineated using the method are validated with data of springs and dug wells from field investigations, and it was found that the overlay method using GIS and remote sensing gives 95% accuracy.

Theory of electronic relaxation in solution : exact solution for a δ-function sink in a parabolic potential

Abstract: We give a general method for finding the exact solution for the problem of a particle undergoing diffusive motion in a potential in the presence of a \ensuremath{\delta}-function sink of arbitrary position and strength. The solution requires knowledge of the Laplace transform of the Green's function for the motion in the absence of the sink. We find the exact solution for the case of the parabolic potential. This has long been an unsolved problem and is of considerable importance as a model for nonradiative electronic relaxation of a molecule in solution.