Department of Physics

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IIT Jodhpur

Modified 9Cr-1Mo steels were normalized at 1050 °C/30 min and tempered over a wide range of temperatures to observe the effect of tempering temperature on the material properties. The material revealed mechanical softening when tempered at temperature less than the lower critical temperature (∼810 °C: Ac1). Beyond Ac1 temperature the materials strength increased drastically due to the formation of fresh martensite. Magnetic Hysteresis Loop (MHL) and Magnetic Barkhausen Emissions (MBE) techniques were used to evaluate the magnetic properties of the materials with tempering. Magnetic softening was observed by tempering the material below the Ac1 temperature where a decrease in coercivity and an increase in RMS voltage of the MBE were found. Tempering beyond Ac1 magnetic hardening was observed by the increase in coercivity and the decrease in RMS voltage of MBE. Such results revealed that magnetic techniques could be a better tool for the evaluation of tempering of modified 9Cr-1Mo steel. © 2009 Elsevier B.V. All rights reserved.

World University root node

Journal of Materials Processing Technology

Evaluation of tempering behaviour in modified 9Cr-1Mo steel by magnetic non-destructive techniques

The nonlinear optical properties of an unsymmetrical Zinc phthalocyanine were studied using the Z-scan technique in femtosecond and picosecond time domains. Open aperture Z-scan studies with ∼110 femtosecond pulses revealed an intriguing behavior exhibiting switching phenomena (from saturable absorption to reverse saturable absorption and back to saturable absorption) as a function of concentration and the peak intensities used. Similar behavior was observed with ∼2 picosecond pulse excitation. The observed results are qualitatively explained using an effective three-level model vis-à-vis a recent report on nonlinear absorption in a chloro-aluminum phthalocyanine where analogous performance was reported due to the solute migration. Such behavior is explicated as due to the consequence of combined effects of solvent contribution, large peak intensities, concentration, etc. The nonlinear absorption coefficients were established from the fits to the data. © 2010 Old City Publishing, Inc.

Nonlinear Optics Quantum Optics

Anomalous nonlinear absorption behavior in an unsymmetrical phthalocyanine studied near 800 nm using femtosecond and picosecond pulses

We present a simple and eco-friendly biosynthesis of silver nanoparticles using Coriandrum sativum leaf extract as reducing agent. The aqueous silver ions when exposed to leaf extract were reduced and resulted in silver nanoparticles whose average size was 26 nm. The silver nanoparticles were characterized by UV-Visible, X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FT-IR) and transmission electron microscopy (TEM) techniques. Nonlinear optical properties of silver nanoparticles were studied using Z-scan technique with 6 ns pulse duration at 532 nm. The nonlinear refractive index and third-order susceptibility |χ3| were measured to be -6.0×10-13 cm2/W and 1.38×10-9 esu, respectively. Silver nanoparticles were found to exhibit strong reverse saturable absorption (RSA). RSA was identified as the main mechanism responsible for optical limiting. © 2010 American Scientific Publishers.

Advanced Science Letters

Biosynthesis of silver Nanoparticles using Coriandrum Sativum leaf extract and their application in nonlinear optics

Nanoparticles have been attracting wide interest duetotheir potential applications in the field of nanophotonics and optoelectronics. Most of the nanoparticles exhibit interesting nonlinear optical properties and are being used for optical limiting purposes due to absorptive nonlinearities such as, two/multi-photon absorption (TPA/MPA), excited state/Free-carrier absorption (ESA/FCA) processes etc. Though the absorptive processes often provide low limiting thresholds, most of the materials have low damage threshold limiting their applications for optical limiting studies. We present our efforts on enhancing the damage threshold through nonlinear scattering so that these materials can be used efficiently even at high input fluences. Our efforts to achieve this goal have been through the preparation and nonlinear optical characterization of metal nanoclusters, semiconductor nanoparticles, and ferroelectric nanocrystals dispersed in different media. Herein nonlinear scattering results fromAg-Cu co-doped nanoclusters in Sol-Gel films, CdS nanoparticles dispersed in dimethylformamide (DMF) and BSO nanocrystals dispersed in PMMA are presented. © 2010 Old City Publishing, Inc.

Enhanced optical limiting performance through nonlinear scattering in Nanoparticles of CdS, co-doped Ag-Cu, and BSO

Modern computers operate at enormous speeds-capable of executing in excess of 10 13 instructions per secondbut their sequential approach to processing, by which logical operations are performed one after another, has remained unchanged since the 1950s. In contrast, although individual neurons of the human brain fire at around just 10 3 times per second, the simultaneous collective action of millions of neurons enables them to complete certain tasks more efficiently than even the fastest supercomputer. Here we demonstrate an assembly of molecular switches that simultaneously interact to perform a variety of computational tasks including conventional digital logic, calculating Voronoi diagrams, and simulating natural phenomena such as heat diffusion and cancer growth. As well as representing a conceptual shift from serial-processing with static architectures, our parallel, dynamically reconfigurable approach could provide a means to solve otherwise intractable computational problems.

Fulltext

Nature Physics

Massively parallel computing on an organic molecular layer

Spun films of novel substituted lead phthalocyanine derivatives between aluminum and indium tin oxide electrodes exhibit large, reproducible negative differential resistance (NDR) in their current-voltage characteristics and can be electrically switched between a high conductance on state and a low conductance off state. Space charge limited conduction mechanism was identified from temperature dependent measurements to be responsible for charge transport. The NDR effect may be due to the charge storage in the structure near the electrodes. © Springer Science+Business Media, LLC 2009.

Journal of Materials Science: Materials in Electronics

Negative differential resistance effects in spun films of substituted phthalocyanine derivatives

Molecular realizations of Cellular Automata that exhibit computational behavior have been the holy grail of nanocomputer architectures. This paper discusses a recently discovered molecular Cellular Automaton, and compares its features with those of conventional models. We find that the interaction rules in molecular Cellular Automata tend to be of a mixed variety, ranging from those with long-distance interactions to the more conventional direct-neighborhood type of rules. The probabilities according to which rules are applied in the molecular Cellular Automaton tend to be influenced by the patterns on the cellular space, resulting in much more volatile dynamics than in conventional models.

International Conference on Applied Computer Science - Proceedings

On molecular implementations of Cellular Automata

The structural, electronic and optical properties of cubic CdS1-xTex alloys, with Te-concentrations varying from 0% up to 100% are investigated. The calculations are based on the total-energy calculations using the full potential-linearized augmented plane wave (FP-LAPW) method. The exchange and correlation potential is treated by the generalized-gradient approximation (GGA) for the total-energy calculations, while for electronic properties in addition to that the Engel-Vosko (EV-GGA) formalism was also applied. The ground state properties for all Te-concentrations are presented. The optical dielectric constant is also determined for both the binary and their related ternary alloys. © 2010 Elsevier Ltd.

Solar Energy

An ab initio study of the electronic structure and optical properties of CdS1-xTex alloys

We study spinodal phase separation in unstable thin liquid films on chemically disordered substrates via simulations of the thin-film equation. The disorder is characterized by immobile patches of varying size and Hamaker constant. The effect of disorder is pronounced in the early stages (amplification of fluctuations), remains during the intermediate stages and vanishes in the late stages (domain growth). These findings are in contrast to the well-known effects of quenched disorder in usual phase-separation processes, viz. the early stages remain undisturbed and domain growth is slowed down in the asymptotic regime. We also address the inverse problem of estimating disorder by thin-film experiments. © 2010 the Owner Societies.

Physical Chemistry Chemical Physics

Spinodal phase separation in liquid films with quenched disorder

The feasibility of inferring the plasma parameters of a Penning discharge in helium, from the experimentally observed intensities of a number of spectral lines in the visible wavelength region, is explored. The collisional-radiative model of ADAS (atomic data analysis structure) code and database has been used for this analysis. The electron density, electron temperature, ground-state atom and ion densities and also the 2 3S metastable state density are the parameters thus estimated. The results are encouraging. The derived plasma parameters are then used to obtain the intensities of a few lines in the vacuum ultraviolet (VUV) region. This has been compared with the observed VUV spectral lines, recorded simultaneously with the visible lines, using a VUV spectrometer for which intensity calibration was not available, to arrive at calibration factors. It is expected that this approach might provide an alternative to the 'branching ratio' method for calibration in the VUV region once the analysis is improved and the possible re-absorption of certain lines is accounted for. © 2010 IOP Publishing Ltd.