Time filter

Source Type

Dhanekar S.,Jamia Millia Islamia University | Islam S.S.,Jamia Millia Islamia University | Islam T.,Jamia Millia Islamia University | Shukla A.K.,Indian Institute of Technology Delhi | Harsh,Defense Research and Development Organisation
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2010

Porous silicon (PS) samples were prepared under different anodization conditions and correspondingly the sensor parameters were studied for organic vapours like methanol, ethanol, propanol, acetone and benzene at low ppm level using capacitive measurements. The surface morphology of the samples was characterized by scanning electron microscopy (SEM), whereas Raman spectroscopic studies were made to identify the surface species formed due to surface passivation. Selective response was observed for either methanol or ethanol depending on the combined effect of the pore morphology of PS, its surface passivation and the concentration dependent molecular kinetics in vapour phase. A probabilistic approach of the concentration dependent vapour molecular kinetics is demonstrated to explain the sensor performance and selectivity studies. © 2010 Elsevier B.V. All rights reserved.

Karamalakova Y.,Trakia University | Sharma J.,Institute of Nuclear Medicine and Allied Sciences | Nikolova G.,Trakia University | Stanev S.,Agricultural Academy | And 4 more authors.
Biotechnology and Biotechnological Equipment | Year: 2013

At present there is not enough data about different types of radiation on Bulgarian essential oils isolated from medicinal plants. Here we report for the first time our studies on the effects of UV-radiation (290 nm to 320 nm) and γ-radiation (doses of 5 Gy, 10 Gy, 20 Gy and 30 Gy) on Bulgarian lavender essential oil isolated from Lavandulla angustifolia Mill. A spectrophotometry method was used for evaluation of the changes in the reducing power of the Bulgarian lavender oil before and after radiation. The electron donation potential of non-irradiated oil was found to be lower (0.268 ± 0.0244) than those of both, UV-irradiated (0.336 ± 0.0121) and γ-irradiated, oil samples (0.427 ± 0.0251 at 5 Gy radiation, 0.341 ± 0.0371 at 10 Gy; 0.328± 0.0173 at 20 Gy). By direct electron paramagnetic resonance (EPR) spectroscopy, single almost symmetrical EPR signals with different values of the g-factor were registered in non-irradiated (g = 2.0047 ± 0.0002), UV-irradiated (g = 2.01050 ± 0.00005) and γ-irradiated oil samples (g = 2.0017 ± 0.0002), respectively. EPR spectroscopy was used for assessment of the radical scavenging capacity of the non-irradiated and UV- and γ-irradiated samples of the Bulgarian lavender oil towards the stable free radical 1,1-diphenyl- 2-picrylhydrazyl (DPPH). Excellent DPPH radical scavenging capacities were found for UV- and 30 Gy-irradiated lavender oil samples. Based on these preliminary results, we consider that, after proper UV- or γ-radiation treatment, Bulgarian lavender oil might find application as a good radioprotector and antioxidant in cosmetics and medicine.

Dhanekar S.,Jamia Millia Islamia University | Islam S.S.,Jamia Millia Islamia University | Islam T.,Jamia Millia Islamia University | Harsh,Defense Research and Development Organisation
International Journal on Smart Sensing and Intelligent Systems | Year: 2010

Porous silicon based sensors were tested in the presence of various linear aliphatic alcohols (methanol to n-hexanol) and water in the range of 10-100 ppm by photoluminescence quenching technique. An increasing trend in the degree of quenching was observed with the chain length of alcohols while minimum response was given to water. Sensitivity as high as 80-90% and nearly instant response time has proven the sensors to be highly efficient. Photoluminescence quenching phenomena is discussed on the basis of charge transfer mechanism between the host and the vapour-induced surface states, but the degree of quenching and anomalous response as a function of chain length suggests no unique quenching theory for estimating the sensitivity for the set of alcohols tested. From methanol to butanol, the sensitivity was dependent on the effective concentration of analytes in the porous silicon matrix, while for pentanol and hexanol having high boiling point, the sensitivity was linked to dielectric quenching mechanism due to the condensation of vapours inside the pores.

Dwivedi P.N.,Defense Research and Development Organisation | Bhale P.G.,Defense Research and Development Organisation | Bhattacharyya A.,Defense Research and Development Organisation | Padhi R.,Indian Institute of Science
Journal of Guidance, Control, and Dynamics | Year: 2014

An extended Kalman filter based generalized state estimation approach is presented in this paper for accurately estimating the states of incoming high-speed targets such as ballistic missiles. A key advantage of this nine-state problem formulation is that it is very much generic and can capture spiraling as well as pure ballistic motion of targets without any change of the target model and the tuning parameters.Anew nonlinear model predictive zero-effort-miss based guidance algorithm is also presented in this paper, in which both the zero-effort-miss as well as the time-to-go are predicted more accurately by first propagating the nonlinear target model (with estimated states) and zero-effort interceptor model simultaneously. This information is then used for computing the necessary lateral acceleration. Extensive six-degrees-of-freedom simulation experiments, which include noisy seeker measurements, a nonlinear dynamic inversion based autopilot for the interceptor along with appropriate actuator and sensor models and magnitude and rate saturation limits for the fin deflections, show that near-zero miss distance (i.e., hit-to-kill level performance) can be obtained when these two new techniques are applied together. Comparison studies with an augmented proportional navigation based guidance shows that the proposed model predictive guidance leads to a substantial amount of conservation in the control energy as well. © 2013 by Radhakant Padhi.Published by the American Institute of Aeronautics and Astronautics, Inc.

Jayakumari V.G.,Defense Research and Development Organisation | Shamsudeen R.K.,Defense Research and Development Organisation | Ramesh R.,Defense Research and Development Organisation | Mukundan T.,Defense Research and Development Organisation
Journal of the Acoustical Society of America | Year: 2011

The acoustic behavior of an acoustically transparent polyurethane and an interpenetrating polymer network of polyurethane with polydimethyl siloxane were studied using dynamic mechanical analysis, finite element modeling, and experimental evaluation of acoustic properties in a water-filled pulse tube setup. Dynamic mechanical measurements in the temperature range -50 C to 70 C were carried out, and the data were used for time temperature superposition to generate material behavior at high frequencies. These inputs were used for modeling the acoustic behavior of these materials using atila, which is a commercial finite element code, capable of computing transmission and reflection characteristics of materials. From this data, absorption characteristics were computed. The results were compared with the experimental results obtained using a water-filled pulse tube facility. © 2011 Acoustical Society of America.

Discover hidden collaborations