AJP	ISSN : 0971 – 3093 Vol 24, No. 11, November 2015

 

Vol. 24, No 11 (2015) 1507-1521

A new feature of equatorial electrojet and space weather

 

R G Rastogi¹, H Chandra¹, A C Das¹, R Sridharan², B W Reinisch³, Khurshid Ahmed⁴, S L Fontes⁵, J A A Sanchez⁶

 ¹ Physical Research Laboratory, Ahmedabad-380 009,India

² Space Physics Laboratory, VSSC, Thiruvananthapuram-695 022 , India

³ University of Massachusetts, Lowell, MA 01854, USA

⁴ Indian Institute of Geomagnetism, New Panvel, Navi Mumbai 410 218, India

⁵ Observatorio Nacional Rio de Janeiro, Brazil

A new feature of the association between the equatorial electrojet and the solar wind parameters during the main phase of the magnetic storm on 24-25 September 1998 has been detected. A negative pulse in the horizontal magnetic field, H exceeding 200 nT at Trivandrum, India simultaneously with a positive pulse of more than 200 nT at Huancayo, Peru were recorded between 06-07 UT on 25 September 1998. The reversal of the sign of H pulse happened at station near the sunrise sector. The negative pulse in the Indian sector showed enhancement of the magnitude at the magnetic equator, while the positive pulse in the midnight sector was observed at all stations with similar magnitude. The ionograms at Thumba showed complete absence of equatorial sporadic-E (E_s-q) echoes during the negative H impulse. Very strong equatorial spread-F echoes were recorded in ionograms over Jicamarca during the night of 24-25 September 1998 which continued even after the sunrise at frequencies beyond f_oF₂.

The event has been shown to be associated with the sudden increase of solar wind density from 5 to 22 ions per cm³. This suggests a transient and impulsive interaction between solar wind and the magnetosphere because of an excess momentum directly. This can lead to impulsive penetration of solar wind plasma into the magnetosphere that results in a westward electric field in the ionosphere generated during the daytime and a positive electric field in the night time ionosphere. This dusk-dawn electric field imposed in the ionosphere primarily due to a large impulse in solar wind density points to a new relationship between solar wind and magnetosphere of the earth and needs further investigation.

Keywords:  Magnetic storm, Magnetic equator, Ionograms, Solar wind parameters, Magnetosphere Dusk-dawn electric field.

 Vol. 24, No 11 (2015) 1523-1539

Polymer microcantilever for bio/chemical sensing: Fabrication, characterization, instrumentation for read out, and applications

 

Sheetal Patil

Centre of Excellence in Nanoelectronics, Department of Electrical Engineering, 

Miniaturized microfabricated micro-mechanical or micro-electro-mechanical sensors (MEMS) have enabled different modes of transduction that involve nano-mechanical motion. As a result, enormous potential in chemical and biological domains have emerged. Among a variety of MEMS-based sensors, polymer microcantilevers modified with sensitive layers have attracted significant interest due to its small size, high sensitivity, and the possibility to integrate multiple sensors. Further, the microcantilever technology offers rapid, label-free, and in situ detection of specific bio/chemical analytes. In this review article, six important aspects of polymer microcantilever sensors such as: operation principles; fabrication of polymer microcantilevers; characterization; readout principles; and various bio/chemical applications have been discussed. ©Anita Publications. All rights reserved.

Keywords:Microcantilever, surface micromachining, Polymer MEMS, Optical/Electrical readout, Biosensing, Vapor-phase detection, Soil moisture.

Vol. 24, No 11 (2015) 1541-1548

SnO₂ Thin film based electronic nose: A case study

 

Niranjan S Ramgir, V Patnaik, A Patel, A K. Debnath, D K Aswal, S K Gupta

Thin Films Devices Section, Technical Physics Division,

An e-nose based on SnO₂ thin film comprising 10 sensing elements for determination of toxic gases was successfully designed and developed. An e-nose comprises of three main components namely multiple sensor arrays, data acquisition system and a pattern recognition algorithm. A multiple sensor array of dimension 1.3 cm × 2.5 cm is realized using thermally evaporated SnO₂ thin films (~900 nm thick) modified with different sensitizers. To realize 10 sensing elements, SnO₂ thin film was modified with 4 sensitizers namely Cu, Fe, Au and Ag with 10 nm thickness with selective masking. A data repository was developed by recording the response curves as a function of operating temperature, gas and its concentration. The fabricated e-nose was subjected to different gases namely NH₃, H₂S, NO, NO₂, CO, CO₂, LPG and C₂H₅OH. Of these gases the e-nose responded only towards H₂S, NO and NO_2. Measured data (SR values) was plotted on a bar plot and a unique response pattern of the sensor array was obtained for three gases namely, H₂S, NO and NO₂. This unique pattern was used for both qualitative and quantitative determination of the three gases. Thus, the developed e-nose can successfully detect three gases namely H₂S, NO, NO₂ at concentrations ranging between 1 and 10 ppm. © Anita Publications. All rights reserved.

  Vol. 24, No 11 (2015) 1551-1560

Theoretical investigation on the electronic and optical properties of Phenanthrene adsorbed on silver cluster

 

U Reeta Felscia and Beulah J M Rajkumar

The Density Functional Theory has been invoked to investigate the nonlinear optical and charge  transfer properties of Phenanthrene (Phen) on silver cluster. Theoretical computations on the shifting of frontier molecular orbitals from HOMO to LUMO, Natural population analysis  (NPA) and the orbital overlapping between silver cluster and Phen in NBO analysis have been correlated to charge transfer from silver to Phen. Significant reduction identified in the band gap of Phen after adsorption on silver coupled with a redistribution of electron density in the molecular electrostatic potential (MEP) confirms the direction of charge transfer consequently to the process of adsorption. Additionally, an enhancement in the calculated dipole moment and polarizability values are also obtained. Based on the Time-Dependent Density Functional Theory (TDDFT), surface resonance peaks in the simulated UV-Vis spectra were obtained at 404 nm with major contributions due to the charge transfers from silver cluster to Phen. Enhancement in the first order hyperpolarizability of Phen-Ag suggests its potential applications in the design of NLO devices.  ©Anita Publications. All rights reserved.

Keywords:  Phenanthrene, DFT, Hyperpolarizability, Silver nanoparticles, NBO analysis, Time-Dependent Density Functional Theory (TDDFT)

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Vol. 24, No 11 (2015)1561-1573

Crystallographic, vibrational, and DFT studies of  2,3,4-trimethoxybenzaldehyde

 

C S Chidan Kumar^a,b*, Cemal Parlak^c, Mahir Tursun^c, Hoong-Kun Fun^b,d and Siddegowda Chandraju^e

^aDepartment of Engineering Chemistry, Alva’s Institute of Engineering & Technology,

Visvesvaraya Technological University, Mijar, Moodbidri -574 225, Karnataka, India

^bX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia

^cDepartment of Physics, Dumlupinar University, Kütahya 43100, Turkey

^dDepartment of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia

Molecular structure and properties of 2,3,4-Trimethoxybenzaldehyde (TMB) were  investigated by X-ray diffraction technique and vibrational spectroscopy. The experimental results are supported with computational studies using the density functional theory (DFT), with the Becke-3-Lee-Yang-Parr (B3LYP) functional and the 6-311+G(3df,p) basis set. Potential energy distribution (PED) and potential energy surface (PES) analyses were performed to identify characteristic frequencies and reliable conformational investigation, respectively. The compound TMB (C₁₀H₁₂O₄) crystallizes in monoclinic space group P21/c with the unit cell dimensions: a = 12.1046(13) Å, b = 7.0937(12) Å, c = 11.6557(12) Å, β(°) = 109.931(3). In general, the computed parameters are in good agreement with the reported experimental data. The highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of the compound were also analyzed.  ©Anita Publications. All rights reserved.

Keywords: DFT , Vibrational spectroscopy, Potential energy distribution (PED), Potential energy surface (PES), XRD, Monoclinic space group P21/c 

Vol. 24, No 11 (2015)1575-1582

Theoretical study of zero field thermoelectric power of colossal magnetoresistive  manganites (Re_1–x A_xMnO₃): A variational treatment

 

Amit Chaudhary¹, Sunil Panwar², Vijay Kumar², Rajendra Kumar¹ and Ishwar Singh³

                ¹Department of Physics, Gurukula Kangri University, Haridwar-249 404, India

                ²Department of Applied Physics, Faculty of Engineering & Technology, Gurukula Kangri University, Haridwar-249 404, India

Using a simple variational method, we have studied the thermoelectric power Q(T) at zero magnetic field as a function of temperature of rare earth manganites doped with alkaline earths namely, Re_1-x A_xMnO₃ (where Re = La, Pr, Nd etc., and A = Ca, Sr, Ba etc.) which exhibit Colossal Magnetoresistance (CMR), metal- insulator transition and many other poorly understood phenomena. Here, we report the effects of the model parameters e.g. local Coulomb repulsion U, strong ferromagnetic Hund’s rule coupling J_H between e_g and t_2g spins, hybridization V_k between ℓ– polarons & d- electrons of same spins on Q(T). It has been found from our results that Q(T) is positive at low temperatures and shows a pronounced peak at the metal – insulator transition which gets sharpened with alkaline earth doping x and shifts towards the high temperature region. Similar effects are observed on increasing J_H also but on the contrary the magnitude of Q(T) decreases on increasing V_k and peak at low temperature becomes broader & shifts towards the high temperature region. The observed broad peak may be explained on the basis of the spin – wave theory and may be attributed to the magnon drag effect which increases with x or J_H value. Q(T) as a function of temperature computed from this method is, generally, in good agreement with the available experimental data. ©Anita Publications. All rights reserved.

Keywords: Magnetic materials, Colossal Magnetoresistive Manganites, Variational techniques,Transport properties, Thermoelectric power.

Vol. 24, No 11 (2015) 1583-1590

Development of PTh-PEO polymer composite as CO₂ gas sensor

 

P D Shirbhate¹, S P Yawale² and S V Pakade²

¹Department of Physics, Rajiv Gandhi College of Engineering And Research, Nagpur-441 110, (India)

In the present work, polythiophene-polyethylene oxide (PTh-PEO) polymer composite was synthesized by an in situ chemical oxidative polymerization method. PTh-PEO polymer composite films were characterized through scanning electron microscopy (SEM) and thermogravimetry analysis (TGA) and Differential Scanning Calorimetry (DSC). Pure PTh-PEO and doped PTh-PEO polymer composite with lithium perchlorate (LiClO₄) as  sensors were prepared by screen-printing method on cladophora substrate followed by Al₂O₃ layer. The sensors were used for CO₂ gas sensing detection at room temperature. Dynamic and static sensing response of both pure and doped sensor was studied. Sensitivity of sensors at different concentration (ppm) of CO₂ gas was measured. The variation of sensitivity with CO₂ gas concentration is found to be linear. At certain higher concentration of CO₂ gas, saturation effect was observed in both sensors. Doped PTh-PEO composite sensor shows maximum sensitivity in presence of CO₂ gas. The reproducibility and stability for both sensors were good. ©Anita Publications. All rights reserved.

Keywords: Polythiophene, Polymer Composite, Sensing response, CO₂ gas.

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Vol. 24, No 11 (2015) 1591-1600

Variation of D-region ionisation and its effects on VLF radiowave propagation

 

S C Chakravarty and Kamsali Nagaraja

The renewed interest in the study of the VLF propagation anomalies due to perturbations in the D-region electron densities under various solar/stellar and geophysical phenomena requires the availability of suitable simulation model as well as a baseline D-region electron density model for the region of interest. A Full Wave Model (FWM) for computing VLF propagation anomalies has been developed and tested by comparing results from a similar model for a given VLF path. The simulation has also been carried out under different conditions of D-region electron density profiles and the anomalies in VLF amplitude and phase for a sample propagation path determined to check the sensitivity of the model. Further work with new observations, computations of the D-region electron density profiles using measured solar radiation fluxes and simulation pertaining to different VLF networks will be required before the technique can be effectively used to identify and confirm anomalies pertaining to new applications. ©Anita Publications. All rights reserved.

Keywords:  VLF propagation, Full Wave Model (FWM), Solar radiation, Ionosphere.

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Variation of D-region ionisation and its effects on VLF radiowave propagation.pdf

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