Pradeep Kumar

Variable 196Hg202Hg ratio in stone meteorites and in some of their carbon-rich residues

Abstract The 196 Hg 202 Hg ratio has been measured in Hg fractions released by stepwise heating (and in four cases in solvent extracts) from bulk samples of 17 different stone meteorites using the radiochemical neutron activation (RNA) method. Carbon-rich (CR) residues obtained from four stones (Allende, Ambapur Nagla, Plainview and Rangala) by the HF/1bHCI demineralisation process have been studied. About 50% of the Hg fractions of bulk samples (from 14 meteorites) have given both positive and negative types of anomalies (10–40%). The distillates of solvent extracts (Hg contents = 0.008–0.120 ppm) showed no clear anomaly. The residual meteoritic materials (SR-residues) after these extractions did show Hg isotopic anomalies in some distillates. In 17 out of 22 distillates from the CR-residues, large negative anomalies are noted. In some of these distillates the depletion of 196Hg was > 90. Replicate measurements did not always give consistent results, presumably due to the heterogeneous dispersion of the anomalous components. The depletion of 196Hg is more frequent in stone meteorites compared to irons, particularly in high-temperature distillates. Isotopic anomalies in Hg suggest either the presence of primitive grains with isotopic anomalies in stones or introduction of the anomalous components from other objects into the parent bodies of meteorites after their solidification.

Evolution of Quantum States in an Electro-Optic Phase Modulator

We present a quantum mechanical model to evaluate the time evolution of quantum states of light in an electro-optic phase modulator (EOPM). The phase modulator is analogous to a multilevel atomic system with equally spaced energy levels, each of which corresponds to the sidebands of the phase modulated optical field. Using perturbation theory, we solve the equations governing the interaction of the optical field with a modulating field both with and without phase velocity mismatch. A unitary operator that evolves any given quantum state allows us to evaluate the response of EOPM for single photon, coherent and squeezed states. We apply these results to the analysis of frequency coded quantum key distribution scheme.

Extraction of UO22+ into Ionic Liquid Using TTA and TBP as Extractants

Thenoyltrifluoroacetone and Tributyl-phosphate have been used for extraction of UO22+ into Ionic Liquid 1-Butyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide. Increasing acidity of uranyl solution from 0.01 to 3 mol L−1 HNO3 for TTA in IL, the distribution ratio (DU) and extraction efficiency (%E) both decreased. Further increment in acidity shows reversal of trend. Similar behavior is observed for TBP. With increasing concentration of TTA, %E increases stabilizing at 0.5 mol L−1 TTA. Adding methanol to TTA increased the DU due to active enolic formation. The developed kinetic model estimates the overall mass transfer coefficient (Ka) as 3.6 x 10−2 s−1. Synergistic effect has been observed for combination of TTA + TBP resulting in enhanced DU.

All-fibre autocorrelator for optical pulse width measurement

We report an all-fibre interferometric autocorrelation measurement of femtosecond optical pulses in the C-band. An all-fibre Mach-Zehnder interferometer with piezo-electric fiber stretcher in one arm provides the interference signal. A highly nonlinear and dispersion shifted fibre with Kerr coefficient 10.5 /W-km generates an idler by the process of degenerate four wave mixing of the pump and target pulse signals. The idler intensity is proportional to the interferometric autocorrelation of target pulse. We have measured approximately 100 fs optical pulses at 1552.52nm from an actively mode locked erbium doped fibre laser operating at 280 MHz repetition rate.

Mitigation of nonlinear effects through frequency shift free mid-span spectral inversion using counter-propagating dual pumped FWM in fiber

We propose and numerically verify a scheme of frequency-shift free mid-span spectral inversion (MSSI) for nonlinearity mitigation in an optical transmission system. Spectral inversion is accomplished by optical phase conjugation, realized by counter-propagating dual pumped four-wave mixing in a highly nonlinear fiber. We examine the performance of MSSI due to critical parameters such as nonlinear fiber length, pump and signal power. We demonstrate the near complete nonlinearity mitigation of 40 Gbps DQPSK modulated data transmitted over 1000 km standard single mode fiber using our method of MSSI. We perform simulation of bit-error rate as a function of optical signal to noise ratio to corroborate the effect of frequency-shift free MSSI.

Optical modulation schemes for frequency-coded quantum key distribution

We discuss possible modulation schemes to implement BB84 and B92 quantum key distribution protocols using frequency-coding method. We derive time evolution of quantum states of light in a Mach-Zehnder interferometer based optical intensity modulator. We then show that phase modulator-phase modulator (PM-PM) combination can be used to implement the B92 protocol and intensity modulator-intensity modulator (IM-IM) combination can be used to implement the BB84 protocol. However, the combinations-PM-IM or IM-PM-cannot be used to implement BB84 and B92 protocols using frequency-coding method. Finally, we discuss the security of frequency-coded implementation of B92 protocol.

Approximations of solutions for a nonlinear differential equation with a deviating argument

In this paper, we prove the existence and convergence of approximate solution for a class of nonlinear differential equations with a deviated argument in a Hilbert space. We establish the existence and uniqueness of a solution to every approximate integral equation using the fixed point argument. Then, we prove the convergence of a solution of the approximate integral equation to the solution of the associated integral equation. We also consider the Faedo-Galerkin approximation of a solution and prove some convergence results.

Methods for the preparation of mercury and osmium samples suitable for ion microprobe measurements

Using radiotracer solutions of Hg (203Hg) and Os (185Os), techniques have been developed for sampling these elements presumably suitable for ion probe measurements. Mercury has been electrodeposited on the cross-sectional area (∼5 mm2) of an electrochemically pure Cu wire giving a recovery ∼25 to 30% at the tip. Similar efficiency is found for Hg distillate solutions. Osmium has been collected in a Ni−NiS bead after loading its thiourea complex solution on filter paper. The recovery in the bead is 80–90%. These methods should be of help for isotopic study of these elements by ion microprobe. The suitability of these samples for measurements remains unconfirmed.

Compensation of nonlinear distortion through frequency shift free mid-span spectral inversion using counter-propagating dual pumped FWM in fiber

We propose and numerically verify a scheme of frequency-shift free mid-span spectral inversion for nonlinearity mitigation in standard single mode fiber. Spectral inversion is accomplished by optical phase conjugation, realized by counter-propagating dual pumped four-wave mixing in highly nonlinear fiber. The two pump frequencies are placed symmetrically around signal frequency to ensure that conjugate wave has the same frequency as that of signal wave. We examine the performance of mid-span spectral inversion under the effects of design parameters, nonlinear length and pump power. The bit-error rate is used to evaluate the performance of our system, carried out as a function of signal power to demonstrate near complete nonlinearity mitigation of 40 Gbps QPSK modulated data transmitted over 1000 km standard single mode fiber using our method of mid-span spectral inversion.

Approximations of Solutions of a Class of Neutral Differential Equations with a Deviated Argument

In this paper, we study the approximations of solutions to a class of nonlinear neutral differential equations with a deviated argument in a Hilbert space. We consider an associated integral equation corresponding to the given problem and a sequence of approximate integral equations. We establish the existence and uniqueness of solutions to every approximate integral equation using the fixed point theory. Then, we prove the convergence of the solutions of the approximate integral equations to the solution of the associated integral equation. Next, we consider the Faedo–Galerkin approximations of solutions and prove some convergence results.