Two-dimensional time-dependent simulation of contaminant transport from a landfill

A numerical model to simulate solute transport in flowing groundwater is developed using finite-difference solutions to the groundwater flow equation and the solute transport equation.The use of the model is illustrated by its application to a problem of groundwater contamination in a waste-disposal area in Miami, Florida. The model integrates the effects of several factors that controlled changes in iron concentrations, and successfully reproduced the record of contamination observed during a one-year period.The model was found to be insensitive to chemical parameters, but sensitive to an aquifer dispersion coefficient and the groundwater flow velocity. This implies that there can be sites where the chemical attenuation can be approximated without a significant impact on results.     

Structure of Globularidin: An Unusual Iridoid Glucoside from Globularia alypumL.

A novel iridoid glucoside, named globularidin, lacking the typical double bond between C(3) and C(4), has been isolated from the whole plant of Globularia alypum by the combination of open column- and high-performance liquid chromatography. The structure of this compound was established by chemical transformation and spectral data.     

Inexpensive automated electropneumatic syringe dispenser

An inexpensive logic-addressable, pneumatically driven syringe dispenser utilizes two three-way valves for pneumatic control and one low-volume, inert three-way valve for liquid suction and delivery. Microliter volumes of liquid can be delivered precisely at high repetition rates (720 h^?1) against significant back-pressure.     

Laser etching of Thoria pellets for microstructural investigations

Metallographic investigation of the microstructure of sintered Thoria pellets necessitates appropriate surface preparation of these pellets. Conventional etching methods involving either chemical or thermal etching techniques being unsuitable for surface etching of irradiated Thoria fuel, laser-based surface treatment was envisaged as a potential alternative technique. Thoria pellets were subjected to laser surface treatment using a pulsed Nd:YAG laser.Our preliminary studies have successfully demonstrated laser etching of sintered Thoria pellets with good reproducibility, clearly revealing grain structures and well-defined grain boundaries. Detailed parametric investigations determining optimum laser parameters for the process, are presented. Our results on ultra-short laser-based etching of sintered Thoria pellets are also discussed.     

Investigation of the optical gain and noise figure for multi-channel amplification in EDFA under optimized pump condition

We present the results of an investigation of optical gain and noise figure for simultaneous multi-channel amplification of an erbium doped fibre amplifier (EDFA) under optimized pump condition. Different pump configurations with varying input signal levels show interesting features on gain flatness. In the experiment, population inversion along the fibre length which determines the gain-spectra and noise characteristics of the amplifier is adjusted through optimized fibre length and injected pump power in order to minimize the gain-tilt at C-band. It is observed that bi-directional pumping manifests the best combination of low noise and high gain of EDFA which are useful as in-line repeaters in WDM network. We obtain 30 ± 1.5 dB intrinsically flat small signal gain from 1538 nm to 1558 nm band of wavelength with noise figure <4 dB for 16-channel simultaneous amplification in a single stage EDFA without gain flattening filter.     

<Emphasis Type="Italic">Z</Emphasis>-scan measurement of optical nonlinearity in solid-state dye doped media

Nonlinear refraction in various polymethyl methacrylate (PMMA) solid hosts when doped with fluorescent organic dyes, commonly used as a laser active medium, has been studied. The observed thermal lensing effect arising from optical nonlinearity, results from non-radiative energy transfer from the dye molecules to the solid matrix and is, therefore, strongly dependent on the thermal properties and material parameters of the polymeric host. The non-linear index of refraction, n₂, for each sample of dye doped polymeric host, has been measured employing the standard Z-scan technique. These measured values of n₂, have been used to determine the extent of variation in the index of refraction with varying temperature, dn/dT, for the various host materials. Estimation of dn/dT is critical in determining the extent of thermal lensing in the dye doped solid-state medium, that in turn determines the spatial quality and divergence of the generated laser beam delivered by a dye doped solid-state laser system. PACS 42.55.Mv; 42.65.Jx; 42.70.Jk     

Growth mechanism of nanocrystals in solution: ZnO, a case study

We investigate the mechanism of growth of nanocrystals from solution using the case of ZnO. Spanning a wide range of values of the parameters, such as the temperature and the reactant concentration that control the growth, our results establish a qualitative departure from the widely accepted diffusion controlled coarsening (Ostwald ripening) process quantified in terms of the Lifshitz-Slyozov-Wagner theory. Further, we show that these experimental observations can be qualitatively and quantitatively understood within a growth mechanism that is intermediate between the two well-defined limits of diffusion control and kinetic control.     

Relating breakup and incomplete fusion of weakly bound nuclei through a classical trajectory model with stochastic breakup

A classical dynamical model that treats breakup stochastically is presented for low energy reactions of weakly bound nuclei. The three-dimensional model allows a consistent calculation of breakup, incomplete, and complete fusion cross sections. The model is assessed by comparing the breakup observables with continuum discretized coupled-channel quantum mechanical predictions, which are found to be in reasonable agreement. Through the model, it is demonstrated that the breakup probability of the projectile as a function of its distance from the target is of primary importance for understanding complete and incomplete fusion at energies near the Coulomb barrier.