Broadband second-harmonic generation in a double-tapered gallium arsenide slab using total internal reflection quasiphase matching

This article analytically describes broadband second-harmonic generation in a double-tapered gallium arsenide (GaAs) slab using total internal reflection quasi-phase matching technique. This double-tapered configuration ensures a combination of increasing and then decreasing bounce lengths which provides an extremely wide 3 dB bandwidth of 573.6 nm with a conversion efficiency of 1.929%, after considering reflection and absorption losses. Effect of varying the slab dimensions, viz., length and tapering angles, as well as the operating temperature on the performance parameters has also been incorporated in the analysis.     

Langevin-Bloch equations for a spin bath

We derive the Bloch equations for a two-level system coupled to a spin bath of infinitely many two-level atoms to examine phase and energy relaxation of an optically excited system. We show that increasing temperature assists coherence. This is reflected in a number of anomalous features of relaxation of the system, e.g., decrease of integrated absorption coefficient with temperature, nonlinear variation of linewidth with incident power. We also predict that thermally induced coherence may result in anomalous narrowing of linewidth, reminiscent (but distinct) of "motional narrowing" of spectral line. The theoretical results are discussed in the light of absorption-emission experiments on single quantum dots.     

Adsorptive removal of thorium from aqueous solution using diglycolamide functionalized multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were functionalized with diglycolamide (DGA) through chemical covalent route. The adsorption behavior of the DGA-functionalized-MWCNTs (DGA-MWCNTs) towards thorium from aqueous solution was studied under varying operating conditions of pH, concentration of thorium, DGA-MWCNTs dosages, contact time, and temperature. The effective range of pH for the removal of Th(IV) is 3.0–4.0. Kinetic data followed a pseudo-second-order model. The equilibrium data were correlated with the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models. The equilibrium data are best fitted with Langmuir model. The equilibrium Th(IV) sorption capacity was estimated to be 10.58 mg g^?1 at 298 K. The standard enthalpy, entropy, and free energy of adsorption of the thorium with DGA-MWCNTs were calculated to be 8.952 kJ mol^?1, 0.093 kJ mol^?1 K^?1 and -18.521 kJ mol^?1 respectively at 298 K. The determined value of sticking probability (0.072) and observed kinetic and isotherm models reveal the chemical adsorption of thorium on DGA-MWCNTs.     

Solid-state thermal decomposition of heterobimetallic oxalate coordination compounds, zinc(II)tetraaquatris(oxalato)lanthanate(III)hexahydrate and cadmium(II)heptaaquatris(oxalato)lanthanate(III)tetrahydrate

Two heterobimetallic oxalate coordination compounds, zinc(II)tetraaquatris(oxalato)lanthanate(III)hexahydrate (ZnOLa) and cadmium(II)heptaaquatris(oxalato)lanthanate(III)tetrahydrate (CdOLa) were synthesized and characterized by elemental analysis, IR, electronic spectral and powder X-ray diffraction studies. Both the compounds were found to have monoclinic structure. Thermal decomposition studies by TG, DTG and DTA in air have proved that the aqua ligands are associated with metals in a stronger coordination mode. The temperatures for pyrolysis were adopted from the TG results chosen from the stable range of thermograms. In case of ZnOLa, it decomposes through two steps and the end product at 1000 °C was found to be consisting of mainly, La₂O_3, ZnO and La₂ZnO _x through the intermediate formation of several oxycarbonates of lanthanum at ca. 525 °C. In case of cadmium analogue, three steps decomposition were observed and the final products were confirmed as CdO₂, La₂O₃, LaCO and La₂CdO _x via the formation of several intermediates at 340 and 590 °C. The La₂C₃ and carbon are also found as part of the end product. The kinetic parameters, E ^*, lnk _o, ?H ^# and ?S ^# of all the deaquated and decomposition steps are investigated and discussed from the DSC study in nitrogen.     

A non-dominated sorting based customized random-key genetic algorithm for the bi-objective traveling thief problem

Journal of Heuristics - In this paper, we propose a method to solve a bi-objective variant of the well-studied traveling thief problem (TTP). The TTP is a multi-component problem that combines two...     

A De Novo Designed Metalloenzyme for the Hydration of CO2

Protein design will ultimately allow for the creation of artificial enzymes with novel functions and unprecedented stability. To test our current mastery of nature’s approach to catalysis, a Zn^II metalloenzyme was prepared using de novo design. α₃DH₃ folds into a stable single‐stranded three‐helix bundle and binds Zn^II with high affinity using His₃O coordination. The resulting metalloenzyme catalyzes the hydration of CO₂ better than any small molecule model of carbonic anhydrase and with an efficiency within 1400‐fold of the fastest carbonic anhydrase isoform, CAII, and 11‐fold of CAIII.     

Exploiting Supramolecular Synthons in Designing Gelators Derived from Multiple Drugs

A simple strategy for designing salt‐based supramolecular gelators comprised of various nonsteroidal anti‐inflammatory drugs (NSAIDs) and amantadine (AMN) (an antiviral drug) has been demonstrated using a supramolecular synthon approach. Single‐crystal and powder X‐ray diffraction established the existence of the well‐studied gel‐forming 1D supramolecular synthon, namely, primary ammonium monocarboxylate (PAM) synthon in all the salts. Remarkably five out of six salts were found to be capable of gelling methyl salicylate (MS)—an important ingredient in commercially available topical gels; one such selected biocompatible salt displayed an anti‐inflammatory response in prostaglandin E₂ (PGE₂) assay, thereby indicating their plausible biomedical applications.     

Improved local density functional approach for atomic systems

Through a new local density approximation to the kinetic energy density functional introduced by us recently, a simple Thomas–Fermi-like scheme for the direct calculation of electron density in atoms is proposed. The calculated density is nonsingular at the nucleus and the energy values are in very good agreement with the corresponding Hartree–Fock results for atoms. © 1994 John Wiley & Sons, Inc.     

276-nm absorption band system of m-dichlorobenzene: Rotational band contour analysis

The 276-nm absorption band system (${}^1\text{B}{}_2\text{←}{}^1\text{A}{}_1$) of m-dichlorobenzene was photographed under high resolution. The electronic origin band (0, 0) and a band at (0 + 380) cm^?1 were subjected to rotational “band contour” analysis. As a result, it is found that the origin band has a type A band contour and that at (0 + 380) cm^?1 exhibits a type B band contour. The band contour analysis also yields an accurate determination of the excited state parameters, viz., A′ = 0.0911 ± 0.0003, B′ = 0.02852 ± 0.00005, and C′ = 0.02175 ± 0.00001 cm^?1. A model geometry for the molecule m-DCB in its first excited singlet state has been proposed.     

A Heuristic Procedure for Leasing Channels in Telecommunications Networks

Rapid advances in computing and communications technology have made distributed computing an attractive alternative for geographically dispersed organizations. A telecommunication sub-network forms the backbone of these distributed systems. In general, this paper focuses on the assignment of communication channel capacities in the presence of time variant usage patterns. Specifically, we concentrate on long-range capacity planning for organizations that construct networks by leasing communication channels from telecommunication companies. We formulate the capacity assignment problem as a 0-1 integer program that seeks to minimize total leasing cost subject to communication delay restrictions. Unlike previous models that include a single-system wide-average delay constraint, our model allows the flexibility of specifying delay restrictions by communicating node pairs. We propose an efficient heuristic, and a Lagrangian relaxation based procedure to obtain performance guarantees on the solution obtained from the heuristic.