Reverse flotation of silica from Kudremukh iron ore .1. Selection of cationic reagents

Four types of cationic collectors were tested and evaluated for their performance in the reverse flotation of silica from the spiral preconcentrate of Kudremukh iron ore. A stagewise flotation was conducted by adding the reagent in three stages. Starch was used to depress hematite. Silica flotation was found to be very sensitive to the amount of cationic reagent added. The performance of the reagents was evaluated based on the percentage of silica and iron in the concentrate and percent recovery of iron obtained in the concentrate. Tests of significance, namely, t-test and F-test were performed to select the best two reagents for further investigations.

Reverse flotation of silica from Kudremukh iron ore .2. Optimization of flotation process

An experimental programme based on statistical analysis was used for optimizing the reverse Rotation of silica from non-magnetic spiral preconcentrate of Kudremukh iron ore. Flotation of silica with amine and starch as the Rotation reagents was studied to estimate the optimum reagent levels at various mesh of grind. The experiments were first carried out using a two level three factor design. Analysis of the results showed that two parameters namely, the concentration level of the amine collector and the mesh of grind, were significant. Experiments based on an orthogonal design of the hexagonal type were then carried out to determine the effects of these two variables, on recovery and grade of the concentrate. Regression equations have been developed as models. Response contours have been plotted using the 'path of steepest ascent', maximum response has been optimized at 0.27 kg/ton of amine collector, 0.5 kg/ton of starch and mesh of grind of 48.7% passing 300 mesh to give a recovery of 83.43% of Fe in the concentrate containing 66.6% Fe and 2.17% SiO2.

Studies on grinding media wear and its effect on flotation of ferrugenous phosphate ore

Marked ball grinding rests were carried out in the laboratory with a low grade phosphate ore under different experimental conditions. Two types of balls were used, namely high carbon low alloy (HCLA) cast steel and high chrome cast iron. Results of marked ball grinding tests indicated that ball wear increased with time and showed a sharp increase for wet grinding over dry grinding. Ball wear under wet grinding conditions was also influenced by the gaseous atmosphere in the mill. The grinding ball materials could be arranged in the following order with respect to their overall wear resistance: High chrome cast iron > HCLA cast steel balls Methods to minimize ball wear through control of mill atmosphere and addition of flotation reagents are discussed. Effect of grinding media and additions of flotation reagents during grinding on phosphate ore flotation are also discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.

Estimation of BT Interference in OFDM Sub Carriers with Training Signals

While wireless LAN (WLAN) is very popular now a days, its performance deteriorates in the presence of other signals like Bluetooth (BT) signal that operate in the same band as WLAN. Present interference mitigation techniques in WLAN due to BT cancel interference in WLAN sub carrier where BT has hopped but do not cancel interference in the adjacent sub carriers. In this paper BT interference signal in all the OFDM sub carriers is estimated. That is, leakage of BT in other sub carriers including the sub carriers in which it has hopped is also measured. BT signals are estimated using the training signals of OFDM system. Simulation results in AWGN noise show that proposed algorithm agrees closely with theoretical results.

Influence of two photon absorption induced free carriers on coherent polariton and phonon generation in ZnTe crystals

Combination of femtosecond Kerr, two photon absorption, and impulsive stimulated Raman scattering (ISRS) experiments have been carried out to investigate the effect of pulse energy and crystal temperature on the generation of coherent polaritons and phonons in 〈110〉 cut ZnTe single crystals of three different resistivities. We demonstrate that the effect of two photon induced free carriers on the creation of both the polaritons and phonons is largest at 4 K where the free carrier lifetime is enhanced. The temperature dependant ISRS on high and low purity ZnTe crystals allows us to unambiguously assign the phonon mode at 3.5 THz to the longitudinal acoustic mode at X-point in the Brillouin zone, LA(X).

Scattering of carriers by charged dislocations in semiconductors

The scattering of carriers by charged dislocations in semiconductors is studied within the framework of the linearized Boltzmann transport theory with an emphasis on examining consequences of the extreme anisotropy of the cylindrically symmetric scattering potential. A new closed-form approximate expression for the carrier mobility valid for all temperatures is proposed. The ratios of quantum and transport scattering times are evaluated after averaging over the anisotropy in the relaxation time. The value of the Hall scattering factor computed for charged dislocation scattering indicates that there may be a factor of two error in the experimental mobility estimates using the Hall data. An expression for the resistivity tensor when the dislocations are tilted with respect to the plane of transport is derived. Finally, an expression for the isotropic relaxation time is derived when the dislocations are located within the sample with a uniform angular distribution.

Composite cyclodextrin-calcium carbonate porous microparticles and modified multilayer capsules: novel carriers for encapsulation of hydrophobic drugs

Novel composite cyclodextrin (CD)-CaCO3 spherical porous microparticles have been synthesized through Ca2+-CD complex formation, which influences the crystal growth of CaCO3. The CDs are entrapped and distributed uniformly in the matrix of CaCO3 microparticles during crystallization. The hydrophobic fluorescent molecules coumarin and Nile red (NR) are efficiently encapsulated into these composite CD-CaCO3 porous particles through supramolecular inclusion complexation between entrapped CDs and hydrophobic molecules. Thermogravimetric (TGA) and infrared spectroscopy (IR) analysis of composite CD-CaCO3 particles reveals the presence of large CDs and their strong interaction with calcium carbonate nanoparticles. The resulting composite CD-CaCO3 microparticles are utilized as sacrificial templates for preparation of CD-modified layer-by-layer (LbL) capsules. After dissolution of the carbonate core, CDs are retained in the interior of the capsules in a network fashion and assist in the encapsulation of hydrophobic molecules. The efficient encapsulation of the hydrophobic fluorescent dye, coumarin, was successfully demonstrated using CD-modified capsules. In vitro release of the encapsulated coumarin from the CD-CaCO3 and CD-modified capsules has been demonstrated.

Developments in Biotechnology for Environmentally Benign Iron Ore Beneficiation

Biomineralization and biogenesis of iron ore deposits are illustrated in relation to indigenous microorganisms inhabiting iron ore mines. Aerobic and anaerobic microorganisms indigenous to iron oxide mineralization are analyzed. Microbially-induced flotation and flocculation of iron ore minerals such as hematite, alumina, calcite and quartz are discussed with respect to use of four types of microorganisms, namely, Paenibacillus polymyxa, Bacillus subtilis, Saccharomyces cerevisiae and Desulfovibrio desulfuricans. The role of the above organisms in the removal of silica, alumina, clays and apatite from hematite is illustrated with respect to mineral-specific bioreagents, surface chemical changes and microbe-mineral interaction mechanisms. Silica and alumina removal from real iron ores through biobeneficiation is outlined. Environmental benefits of biobeneficiation are demonstrated with respect to biodegradation of toxic reagents and environmentally-safe waste disposal and processing.

Bolaamphiphiles as carriers for siRNA delivery: From chemical syntheses to practical applications

In this study we have investigated a new class of cationic lipids - ``bolaamphiphiles'' or ``bolas'' - for their ability to efficiently deliver small interfering RNAs (siRNAs) to cancer cells. The bolas of this study consist of a hydrophobic chain with one or more positively charged head groups at each end. Recently, we reported that micelles of the bolas GLH-19 and GLH-20 (derived from vernonia oil) efficiently deliver siRNAs, while having relatively low toxicities in vitro and in vivo. Our previous studies validated that; bolaamphiphiles can be designed to vary the magnitude of siRNA shielding, its delivery, and its subsequent release. To further understand the structural features of bolas critical for siRNAs delivery, new structurally related bolas (GLH-58 and GLH-60) were designed and synthesized from jojoba oil. Both bolas have similar hydrophobic domains and contain either one, in GLH-58, or two, in GLH-60 positively charged head groups at each end of the hydrophobic core. We have computationally predicted and experimentally validated that GLH-58 formed more stable nano sized micelles than GLH-60 and performed significantly better in comparison to GLH-60 for siRNA delivery. GLH-58/siRNA complexes demonstrated better efficiency in silencing the expression of the GFP gene in human breast cancer cells at concentrations of 5 mu g/mL, well below the toxic dose. Moreover, delivery of multiple different siRNAs targeting the HIV genome demonstrated further inhibition of virus production. Published by Elsevier B.V.

Exciton-phonon scattering and nonradiative relaxation of excited carriers in hydrothermally synthesized CdTe quantum dots

Naturally formed CdTe/CdS core/shell quantum dot (QD) structures in the presence of surface stabilizing agents have been synthesized by a hydrothermal method. Size and temperature dependent photoluminescence (PL) spectra have been investigated to understand the exciton-phonon interaction, and radiative and nonradiative relaxation of carriers in these QDs. The PL of these aqueous CdTe QDs (3.0-4.8 nm) has been studied in the temperature range 15-300 K. The strength of the exciton-LO-phonon coupling, as reflected in the Huang-Rhys parameter `S' is found to increase from 1.13 to 1.51 with the QD size varying from 4.8 to 3.0 nm. The PL linewidth (FWHM) increases with increase in temperature and is found to have a maximum in the case of QDs of 3.0 nm in size, where the exciton-acoustic phonon coupling coefficient is enhanced to 51 mu eV K-1, compared to the bulk value of 0.72 mu eV K-1. To understand the nonradiative processes, which affect the relaxation of carriers, the integrated PL intensity is observed as a function of temperature. The integrated PL intensity remains constant until 50 K for relatively large QDs (3.9-4.8 nm) beyond which a thermally activated process takes over. Below 150 K, a small activation energy, 45-19 meV, is found to be responsible for the quenching of the PL. Above 150 K, the thermal escape from the dot assisted by scattering with multiple longitudinal optical (LO) phonons is the main mechanism for the fast quenching of the PL. Besides this high temperature quenching, interestingly for relatively smaller size QDs (3.4-3.0 nm), the PL intensity enhances as the temperature increases up to 90-130 K, which is attributed to the emission of carriers from interface/trap states having an activation energy in the range of 6-13 meV.

Ferromagnetism and the effect of free charge carriers on electric polarization in the double perovskite Y2NiMnO6

The double perovskite Y2NiMnO6 displays ferromagnetic transition at T-c approximate to 81 K. The ferromagnetic order at low temperature is confirmed by the saturation value of magnetization (Ms) and also validated by the refined ordered magnetic moment values extracted from neutron powder diffraction data at 10 K. This way, the dominant Mn4+ and Ni2+ cationic ordering is confirmed. The cation-ordered P2(1)/n nuclear structure is revealed by neutron powder diffraction studies at 300 and 10 K. Analysis of the frequency-dependent dielectric constant and equivalent circuit analysis of impedance data take into account the bulk contribution to the total dielectric constant. This reveals an anomaly which coincides with the ferromagnetic transition temperature (T-c). Pyrocurrent measurements register a current flow with onset near T-c and a peak at 57 K that shifts with temperature ramp rate. The extrinsic nature of the observed pyrocurrent is established by employing a special protocol measurement. It is realized that the origin is due to reorientation of electric dipoles created by the free charge carriers and not by spontaneous electric polarization at variance with recently reported magnetism-driven ferroelectricity in this material.