The 85 MeV 12 C 6+ and 35 MeV 12 C 3+ ion induced forward current gain degradation on 2N 6052 transistor is investigated by I-V measurements before and after irradiation. The decrease in gain for 85 MeV C-ion irradiated transistor is drastic, indicating the device is vulnerable for higher energy irradiation. An increase in the base current leading to degradation of the current gain may be due to displacement damage dose. C-V measurements estimate the effect of irradiation on the doping concentration of the devices. A plot of (1/C 2 ) versus base-emitter voltage shows that the doping concentration increases marginally upon irradiation. DLTS measurements indicate the cluster defects are produced after irradiation to a fluence of 1 × 10 12 ions/cm 2 .

The response of liquid crystals to light is very important in applications of liquid crystals in display and memory devices. Experiments have been conducted on liquid crystals doped with photoactive azo compounds, and has been shown that under incident UV radiation such systems can lower the nematic isotropic transition temperature, T-NI. In addition, in some mixtures a photo-induced smectic phase is observed, attributable to the change from the trans (longer) isomer to the cis (shorter) isomer in the photoactive dopant. We have previously developed a molecular mean field model, on the assumption that the medium consists of interconverting anti-parallel and parallel pairs, to explain the molecular origin of 'two lengths'. The model was used to explain double re-entrance, the effect of electric field on T-NI, etc. This model has now been modified to include the change between the trans and cis isomer, which is equivalent to an increase in the fraction of parallel (shorter) pairs. The phase diagram calculated for incident UV radiation energy shows an induced smectic phase. This is in qualitative agreement with the experimental trends.

Microcontroller based thermogravimetric analyser (MTGA) is a home built technique extensively used to study the thermal decomposition of inorganic solids and preparation of nanomaterials. This paper reports the characterization of bismuth ferrite BiFeO3 (BFO) synthesized by microcontroller based thermogravimetric analyser. The synthesized nanopowder is characterized by X-ray diffraction (XRD) method for phase confirmation, crystallite size calculations and scanning electron microscope (SEM) for morphology study. The structure and thermal properties of BFO precursor are studied by using Fourier transform infrared (FTIR) spectroscopy, differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The results of nano BiFeO3 synthesized by microcontroller based TGA are in good agreement with that synthesized by other techniques.

Microcontroller based thermogravimetric analyser (MTGA) is a home built technique extensively used to study the thermal decomposition of inorganic solids and preparation of nanomaterials. This paper reports the characterization of bismuth ferrite BiFeO3 (BFO) synthesized by rnicrocontroller based thermogravimetric analyser. The synthesized nanopowder is characterized by X-ray diffraction (XRD) method for phase confirmation, crystallite size calculations and scanning electron microscope (SEM) for morphology study. The structure and thermal properties of BFO precursor are studied by using Fourier transform infrared (FTIR) spectroscopy, differential thermal analysis (DTA) and thermogravimetric analysis (TGA). The results of nano BiFeO3 synthesized by microcontroller based TGA are in good agreement with that synthesized by other techniques.

The response of liquid crystals to light is very important for applications of liquid crystals in display and memory devices. Recently experiments have been carried out on liquid crystals doped with photoactive azo compounds. It is seen that UV rays incident on such systems can lower the nematic isotropic transition temperature T-NI. Also, in some mixtures, a photo-induced smectic phase is observed. This is attributed to the change in the trans (longer) isomer to cis (shorter) isomer of the photoactive dopant. We have earlier developed a molecular mean-field model assuming the medium to consist of inter-converting anti-parallel and parallel pairs to explain the molecular origin of "two lengths". The model was used to explain double re-entrance, the effect of electric field on T-NI, etc. This model is modified to include the change of trans to cis isomer which is equivalent to an increase of fraction of parallel (shorter) pairs. The calculated phase diagram with respect to incident UV radiation energy shows an induced smectic phase. This is in qualitative agreement with experimental trends.

Thermogravimetric analyzer (TGA) is an analytical technique extensively used to study the thermal decomposition of inorganic solids, their kinetics, reaction mechanisms, chemical property, structure of intermediate and final products and synthetic conditions. This paper reports the development of microcontroller based thermogravimetric analyzer. The TGA has been setup with additional features like controlled gas delivery system suitable for the study of decomposition (gas-solid interaction) in various atmospheres like air, oxygen, hydrogen, etc. The displacement of the spring in the system due to sample weight loss or gain on heating can be measured by using Infrared (IR) grating assembly and also by using cathetometer (least count is 0.001 cm). (C) 2011 Elsevier Ltd. All rights reserved.

We investigate the root cause of Kelvin-Helmholtz instability with the aid of two simple models of energy exchange between the superposed fluids. We conclude that the density and surface tension of the fluids play a key role in determining the minimal relative speed that triggers the instability. We discuss the volume forces exerted by electric and magnetic field gradients on dielectric and ferro-fluids. We propose manipulating the field gradients to change the specific weight of fluids so that a flow of superposed fluids admits a greater relative velocity before the onset of Kelvin-Helmholtz instability. In order to include the effect of field gradients and viscosity in a closed form dispersion relation, we use the viscous potential flow approximation. It allows us to develop an analytical framework that works for dielectric fluids in presence of an electric field as well as ferro-fluid in presence of a magnetic field. The same framework is applicable to viscous as well as viscoelastic fluids described by the Oldroyd-B model. Our discussion of the Galilean transformation of the electromagnetic fields suggests ways to magnify the effects of field gradients. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3637033]

Optical response of liquid crystals is very important from the point of view of applications of liquid crystals in display and data storage devices. Experiments have shown that UV rays incident on nematic liquid crystals doped with photoactive azo compounds lower the nematic isotropic transition temperature (T(NI)). This is attributed to the transformation of photoactive trans isomer to cis isomer due to UV rays. We have earlier developed a mean field model involving molecular explanation for two lengths in which the mutual orientation of near neighbor molecules changes from an antiparallel to a parallel configuration as the temperature lowered. In this paper, this model is extended to include the length change from trans to cis isomer. The calculated values of change in T(NI) qualitatively agree with experimental trends.

Force on dielectric fluids in the presence of a nonuniform electric field is shown to reduce their specific weights. An appropriately chosen field gradient makes the specific weights of superposed fluids equal and prevents Rayleigh–Taylor instability. We derive the dispersion relation for perturbation at the interface of superposed dielectric fluids, within limits of linear theory, successively for ideal, Newtonian, and those with stratified viscosity. A dimensionless dielectric number is shown to determine the stability of the arrangement.

Hybrid recoil mass analyzer (HYRA) is a unique, dual-mode spectrometer designed to carry out nuclear reaction and structure studies in heavy and medium-mass nuclei using gas-filled and vacuum modes, respectively and has the potential to address newer domains in nuclear physics accessible using high energy, heavy-ion beams from superconducting LINAC accelerator (being commissioned) and ECR-based high current injector system (planned) at IUAC. The first stage of HYRA is operational and initial experiments have been carried out using gas-filled mode for the detection of heavy evaporation residues and heavy quasielastic recoils in the direction of primary beam. Excellent primary beam rejection and transmission efficiency (comparable with other gas-filled separators) have been achieved using a smaller focal plane detection system. There are plans to couple HYRA to other detector arrays such as Indian national gamma array (INGA) and 4 π spin spectrometer for ER tagged spectroscopic/spin distribution studies and for focal plane decay measurements.

For assessing earthquake hazard of metro cities, knowledge of soil amplification, thickness and properties of sedimentary layer are essential. In order to map the soil thickness using microtremor survey method, in Bangalore city, it is required to calibrate the relation between fundamental resonance frequency of the soil layer and its thickness for the region. For this purpose microtremor survey was carried out at 34 locations in the city where borehole log was available. The resonance frequency of the soil is evaluated from the microtremor recordings using the H/V ratio technique. A nonlinear regression relation between the thickness of sedimentary layer h (m), from the borehole logs, and the resonance frequency fr (Hz), was derived as h=(58.3±8.8)fr−(0.95)±0.1. Using the model of shear wave velocity increasing with depth at these locations, the derived average shear wave velocity and the corresponding soil thickness were used, to get an empirical relation between VS (m/s) and depth z(m), as Vs=(174±28)(1+z)0.16±0.07. This relation also compares reasonably with the fit obtained between simulated VS and depth from borehole logs for Bangalore city. The calibrated relations can be used at locations in Bangalore city where borehole logs are not available, for finding the thicknesses and shear wave velocities of the local soil layers at the survey locations.

60 MeV boron ion energy transfer in Si power BJT's for the interface charge state density is studied. LET, total ionizing dose and total displacement damage dose are correlated with the observed post-irradiated electrical characteristics.

Soil amplification and topographical effects play a major role in earthquake damage to civil structures. Study of sedimentary layer thickness and behaviour under stress cycles is crucial for earthquake hazard analysis. Borehole logs for Bangalore are used to benchmark the relation between sedimentary thickness and resonant frequency of the soil layer for this region. Microtremor measurements are carried out at the locations where borehole drilling was done and the frequencies corresponding to spectral peaks of the H/V ratio are estimated, where H and V denote the horizontal and vertical spectral component of the microtremor displacement respectively. The thicknesses of the soil layer (D), obtained from borehole logs and the soil layer resonant frequencies (f(r)) determined from the H/V spectral peaks are used to obtain a regression relation between them. The regression relation obtained is given by D = (58.29 +/- 8.8) x f(r)(-(0.95 +/- 0.1)). Using the data from the work of Divya et al., a similar regression relation is plotted. The results obtained are in agreement with the field data. This relation can be used for computing the depth to the bedrock for Bangalore using microtremor survey at a location where borehole data is not available.

The concept of non-ionizing energy loss (NIEL) has been found useful for characterizing displacement damage defects in materials and devices. When NPN power transistors (2N6688 manufactured by BEL, India) are exposed for 110 MeV Si8+ ion irradiation in the fluence range 5 x 109 to 1 x 1013 ions cm-2 at room temperature (300 K) and at liquid nitrogen temperature (77 K) cause functional failure due to surface and bulk defects. The output collector characteristics are studied as a function of total ionizing dose (TID) and total displacement damage dose (Dd) obtained using TRIM Monte Carlo code. It is observed that the shift in the output saturation voltage is considerably less for heavy ion irradiation compared to lighter ions like lithium ion irradiation. The gain of the transistor degrades with ion irradiation. Base reverse biased leakage current (BRBLC) increases with increase in ion fluence. The observed results are almost independent of the irradiation temperature. These studies help to improve the device fabrication technology to make Radiation Hard Devices for advanced applications.

Silicon NPN overlay RF power high speed commercial bipolar junction transistors (BJTs) find applications in military, space and communication equipments. Here we report the effect of 50MeV Li3+ ion irradiation in the fluence range 1×1011–1.8×1012ionscm−2 on NPN power transistor. The range (R), electronic energy loss (Se), nuclear energy loss (Sn), total ionizing dose (TID) and total displacement damage (Dd) in the silicon target are calculated from TRIM Monte Carlo Code. Output resistance is 3.568×104Ω for unirradiated device and it increases to 6×107Ω as the fluence is increased from 1×1011 to 1.8×1012ionscm−2. The capacitance of the emitter-base junction of the transistor decreases and dielectric loss of the emitter-base junction increases with increase in ion fluence. The built in voltage of the unirradiated sample is 0.5V and it shifts to 0.4V after irradiation at fluence of 1.8×1012ionscm−2 and the corresponding doping density reduced to 5.758×1016cm−3. The charge carrier removal rate varies linearly with the increase in ion fluence.

A series of Bi substituted yttrium iron garnet (Bi-YIG) nanoparticles with nominal formula of Bi x Y 3 − x Fe 5 O 12 in which x varied in steps of 0.0, 0.25 and 0.5 are prepared by conventional method. Vibration sample magnetometer (VSM) at Room temperature (RT) shows saturation magnetization decreases from 27.4 to 25.2 (emu/g) as x value increases from 0.0 to 0.5. Room temperature 57 Fe Mössbauer spectra are recorded for these series. The hyperfine field value for octahedral and tetrahedral of samples increases from 484 and 390 kOe to 491 and 397 kOe respectability, as Bi replaces Y in (Bi x Y 3 − x Fe 5 O 12 ) atom with increasing x value. The effect of Bi 3 + substitution for Y 3 + on lattice constants, morphology and magnetic properties of pure YIG has been investigated.

Magnetic and structural properties of Bi substituted YIG with nominal formula of Bi x Y3 − x Fe5O12 (x = 0.0, 0.25, 0.5, 0.75, 1.00) prepared via Mechanochemical Processing (MCP) have been studied with Mossbauer spectroscopy, X-ray diffraction (XRD). The temperature dependence of sublattice magnetic hyperfine field for samples is analyzed. The a–d intersublattice superexchange found to be antiferromagnetic and increases from − 21.97 to − 25.79 kB as Bi increases from 0.0 to 0.25. The a–a and d–d intrasublattice exchanges for sample x = 0.0 are 13.18 and 10.55 kB respectively while for sample x = 0.25 a–a and d–d intrasublattice exchanges are 7.7 and 8.9 kB respectively. The correlation of lattice constant and superexchange interaction are discussed.

Evaporation residue (ER) cross sections and gamma multiplicity distributions have been measured for 16O+184W and 19F+181Ta systems in the excitation energy range of 50–90 MeV, leading to the same compound nucleus 200Pb∗. Comparison of experimental results of both the systems shows that ER cross sections and moments of gamma multiplicity distribution of 16O+184W system are significantly higher than those of 19F+181Ta system at higher excitation energies. Present measurements directly shows the experimental signature of entrance channel effect even with the systems which are not very different with respect to their entrance channel mass asymmetry. It is further demonstrated that the reduction in the ER cross section and moments of spin distribution for 19F+181Ta system is mainly due to the suppression of fusion of higher l values.

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Space-grade Si and GaAs solar cells were irradiated with 15 and 40 MeV lithium ions. Dark-IV analysis (with and without illumination) reveals differences in the effects of such irradiation on the different cell types