Cationic Substitution Sites in Mn2+-doped ZnS Nanoparticles

Mn²⁺-doped ZnS nanoparticles of average size 2.5±0.3 nm have been studied and characterized in the dopant concentration range 0.1–0.3% using XRD, EPR, XPS and photoluminescence methods. The experimental results obtained from these studies indicate that the doping of Mn²⁺ occurs primarily at the T _d sites at low dopant concentration, causing the⁴T₁(G) → ⁶A₁(S) transition to take place in the host lattice; the observed decrease in the intensity of photoluminescence at high dopant concentration is due to the setting in of the strong Mn²⁺–Mn²⁺ interaction arising from cluster formation at the highly distorted sites near the particle surface.An erratum to this article can be found at     

Determination of diffusion length of minority carriers in epitaxial layers by photocurrent spectroscopy

We have determined the minority carrier diffusion length in n-type and p-type GaAs epitaxial layers grown on GaAs substrates as well as on intentionally misoriented Si substrates by photocurrent spectroscopy. It is found that for heteroepitaxial GaAs-on-Si, the minority carrier diffusion length is limited by the amount of dislocation density irrespective of the doping level. The value of dislocation density obtained from diffusion length measurements agrees well with that obtained from the double-crystal x-ray diffraction measurements.     

The crystal structure of bis-(L-threonine) copper(II).H2O

The crystal structure of bis-(L-threonine) copper (II).H₂O, Cu (C₄H₈NO₃)₂.H₂O has been determined by heavy atom and Fourier methods and refined by least-squares using visually estimated three-dimensional x-ray data of 893 reflections. The blue crystals are monoclinic, space groupP2₁ withα=11·02,b=4·90,c=11·16Å andβ=93·5°,Z=2. The finalR is 0·10. Coordination of copper is distorted square pyramidal with ligands intrans configuration. The conformation of one of the aminoacid ligand is identical with L_s-Threonine while the other has a conformation with torsional angleχ ^{1, 2}=?74(1)°.     

Numerical simulation of vortex induced vibrations and its control by suction and blowing

The vortex formation and shedding behind bluff structures is influenced by fluid flow parameters such as, Reynolds number, surface roughness, turbulence level, etc. and structural parameters such as, mass ratio, frequency ratio, damping ratio, etc. When a structure is flexibly mounted, the Kármán vortex street formed behind the structure gives rise to vortex induced oscillations. The control of these flow induced vibrations is of paramount practical importance for a wide range of designs. An analysis of flow patterns behind these structures would enable better understanding of wake properties and their control. In the present study, flow past a smooth circular cylinder is numerically simulated by coupling the mass, momentum conservation equations along with a dynamical evolution equation for the structure. An active flow control strategy based on zero net mass injection is designed and implemented to assess its efficacy. A three actuator system in the form of suction and blowing slots are positioned on the cylinder surface. A single blowing slot is located on the leeward side of the cylinder, while two suction slots are positioned at an angle α = 100°. This system is found to effectively annihilate the vortex induced oscillations, when the quantum of actuations is about three times the free stream velocity. The dynamic adaptability of the proposed control strategy and its ability to suppress vortex induced oscillations is verified. The exact quantum of actuation involved in wake control is achieved by integrating a control equation to decide the actuator response in the form of a closed loop feed back system. Simulations are extended to high Reynolds number flows by employing eddy viscosity based turbulence models. The three actuator system is found to effectively suppress vortex induced oscillations.     

Metastable zonewidth, induction period and interfacial energy of zinc tris(thiourea) sulfate

Metastable zonewidth and induction period measurements on ZTS and ZTSP crystals are presented. The effect of pH on the solubility, metastable zonewidth and induction period has been studied. The effect of substitution of phosphate on the nucleation parameters has been presented. The interfacial energy for pure and phosphate mixed ZTS solutions at 30°C has also been estimated. There is a significant variation in the induction period and interfacial energy due to decrease in solution pH and phosphate substitution.     

Modeling the coupling of reaction kinetics and hydrodynamics in a collapsing cavity

We introduce a model of cavitation based on the multiphase Lattice Boltzmann method (LBM) that allows for coupling between the hydrodynamics of a collapsing cavity and supported solute chemical species. We demonstrate that this model can also be coupled to deterministic or stochastic chemical reactions. In a two-species model of chemical reactions (with a major and a minor species), the major difference observed between the deterministic and stochastic reactions takes the form of random fluctuations in concentration of the minor species. We demonstrate that advection associated with the hydrodynamics of a collapsing cavity leads to highly inhomogeneous concentration of solutes. In turn these inhomogeneities in concentration may lead to significant increase in concentration-dependent reaction rates and can result in a local enhancement in the production of minor species.     

Domain-specific incorporation of noninvasive optical probes into recombinant proteins

An integrated approach is described that allows the domain-specific incorporation of optical probes into large recombinant proteins. The strategy is the combination of two existing techniques, expressed protein ligation (EPL) and in vivo amino acid replacement of tryptophans with tryptophan (Trp) analogues. The Src homology 3 (SH3) domain from the c-Crk-I adaptor protein has been labeled with a Trp analogue, 7-azatryptophan (7AW), using Escherichia coli Trp auxotrophs. Structural, biochemical, and thermodynamic studies show that incorporation of 7AW does not significantly perturb the structure or function of the isolated domain. Ligation of the 7AW-labeled SH3 domain to the c-Crk-I Src homology 2 (SH2) domain, via EPL, generated the multidomain protein, c-Crk-I, with a domain-specific label. Studies of this labeled protein show that the biochemical and thermodynamic properties of the SH3 domain do not change within the context of a larger multidomain protein. The technology described here is likely to be a useful tool in enhancing our understanding of the behavior of modular domains in their natural context, within multidomain proteins.     

Bioenergetics and bioremediation of contaminated soil

The microbial biodegradation of xenobiotic compounds in soil and ground water is constrained by the laws of thermodynamics. Bioremediation is being investigated in a rhizosphere environment in which higher plants provide carbon and energy to sustain the microbial population. Toluene, phenol, trichloroethylene and trichloroethane have been fed in separate experiments to a pilot scale system with alfalfa growing in sandy soil containing less than 10% of silt. It is well known that microbial populations are numerous in the root zone of healthy vegetation. Root exudates can stimulate aerobic microbial biodegradation of compounds which by themselves support growth poorly or not at all. Polynuclear aromatic compounds such as phenanthrene, anthracene, and pyrene, which are not very soluble in water, and chlorinated aliphatic hydrocarbons such as trichloroethylene are examples of compounds that can be biodegraded in the rhizosphere when root exudates are present to enhance and sustain microbial activity. Solar driven transport processes such as water and solute movements due to evapotranspiration increase the likelihood that the contaminants will come into contact with the microorganisms and be degraded. The thermodynamic and bioenergetic aspects of transport and biodegradation in the rhizosphere are examined through a review of the literature and the analysis of experimental data collected in the pilot scale system.     

Nanostructured NiO based all solid state electrochromic device

A nickel oxide film with a thickness of 445 nm was deposited from nickel acetate precursor using the sol–gel dip coating method. The NiO films exhibit optical transmission of 84% at 550 nm and direct energy gap (E _gd) value is 3.64 eV. The FTIR spectrum of the films confirms the formation of Ni–O bond. XRD spectrum reveals the formation of nano crystallites along (111) and (200) planes with a particle size of 17 nm. The electrochromic properties have been studied using cyclic voltammetric (CV) technique. The optical transmission of a glass/FTO/NiO/ZrO₂/FTO/glass EC device is reported.