Mode partition noise in 850 nm VCSELs

In high-speed 850 nm vertical cavity surface emitting lasers designed for 10 G Ethernet over 300 m of multimode fibre, mode partition noise (MPN) can impair the performance of the transmission link where the power budget is limited. A simple and practical method to evaluate the Ogawa k-factor from the power penalty is presented due to MPN using free space optical filters to vary the laser root mean square spectral width. k values that varied from 0.3 to 0.45 is reported. In addition, the previously reported improvement in power penalty is confirmed in the presence of polarisation mode selective filtering     

Calcination of Co-Based Fischer–Tropsch Synthesis Catalysts

The calcination of Co-based slurry-phase Fischer–Tropsch synthesis catalysts was investigated. Fischer–Tropsch synthesis is part of the gas-to-liquids (GTL) process that produces gas oil and naphtha from natural gas. For the GTL process, the preparation of highly active Co-based catalysts is of utmost importance. This paper shows that the conditions during the calcination of impregnated cobalt precursors have a significant influence on the performance of the final catalyst. The options of calcination in rotary kilns, furnaces and fluidized-bed reactors were considered. It was found that the catalyst performance is strongly dependent on the heating rate and the air-space velocity during the preferred option of fluidized bed calcination. The postulation that Co₃O₄ is not the preferred oxide phase of the calcined intermediate catalyst is supported by a temperature-programmed reduction (TPR) study.     

Ionization, partitioning, and dynamics of tryptophan octyl ester: implications for membrane-bound tryptophan residues

The presence of tryptophan residues as intrinsic fluorophores in most proteins makes them an obvious choice for fluorescence spectroscopic analyses of such proteins. Membrane proteins have been reported to have a significantly higher tryptophan content than soluble proteins. The role of tryptophan residues in the structure and function of membrane proteins has attracted a lot of attention. Tryptophan residues in membrane proteins and peptides are believed to be distributed asymmetrically toward the interfacial region. Tryptophan octyl ester (TOE) is an important model for membrane-bound tryptophan residues. We have characterized this molecule as a fluorescent membrane probe in terms of its ionization, partitioning, and motional characteristics in unilamellar vesicles of dioleoylphosphatidylcholine. The ionization property of this molecule in model membranes has been studied by utilizing its pH-dependent fluorescence characteristics. Analysis of pH-dependent fluorescence intensity and emission maximum shows that deprotonation of the alpha-amino group of TOE occurs with an apparent pKa of approximately 7.5 in the membrane. The fluorescence lifetime of membrane-bound TOE also shows pH dependence. The fluorescence lifetimes of TOE have been interpreted by using the rotamer model for the fluorescence decay of tryptophan. Membrane/water partition coefficients of TOE were measured in both its protonated and deprotonated forms. No appreciable difference was found in its partitioning behavior with ionization. Analysis of fluorescence polarization of TOE as a function of pH showed that there is a decrease in polarization with increasing pH, implying more rotational freedom on deprotonation. This is further supported by pH-dependent red edge excitation shift and the apparent rotational correlation time of membrane-bound TOE. TOE should prove useful in monitoring the organization and dynamics of tryptophan residues incorporated into membranes.     

Effect of humic acid on sorption of technetium by alumina

Sorption of technetium by alumina has been studied in absence as well as in presence of humic acid using ⁹⁵Tc^m as a tracer. Measurements were carried out at fixed ionic strength (0.1 M NaClO₄) under varying pH (3-10) as well as redox (aerobic and reducing anaerobic) conditions. Under aerobic conditions, negligible sorption of technetium was observed onto alumina both in absence and in presence of humic acid. However, under reducing conditions (simulated with [Sn(II)] = 10⁻⁶ M), presence of humic acid enhanced the sorption of technetium in the low pH region significantly and decreased at higher pH with respect to that in absence of humic acid. Linear additive as well as surface complexation modeling of Tc(IV) sorption in presence of humic acid indicated the predominant role of sorbed humic acid in deciding technetium sorption onto alumina.     

Hydromagnesite as an Efficient Recyclable Heterogeneous Solid Base Catalyst for the Synthesis of Flavanones,Flavonols and 1,4‐Dihydropyridines in Water

A form of hydromagnesite (HM) with flower‐like thin‐sheet morphology was synthesized by an environmentally benign approach using simple conventional heating at moderate temperature without using any template in water as medium. The versatility of this HM catalyst was studied in the synthesis of flavanones, flavonols and the multicomponent synthesis of 1,4‐dihydropyridines in water. The recyclability of catalyst was studied for six times and there was no appreciable loss in its catalytic activity.

     

Antioxidant potential of herbs and spices during deep frying of ghee

The present study was carried out to evaluate antioxidant potential of ashwagandha, clove, coriander, green tea, shatavari and vidarikand extracts as compared to BHA. Clove, coriander and green tea extracts showed significantly higher antioxidant activity than vidarikand, shatavari and ashwagandha extracts. Radical‐scavenging activity by DPPH model system revealed that clove and green tea extracts were superior to other extracts. All the natural antioxidants significantly reduced the formation of peroxides, FFA, thiobarbituric acid value and conjugated dienes. Ghee with added clove, green tea and coriander extracts showed higher induction period as compared to ghee containing vidarikand, ashwagandha, shatavari or BHA.     

Synthesis and characterization of low-cost ceramic membranes from fly ash and kaolin for humic acid separation

Ceramic microfiltration membranes were prepared using five different compositions formulated with different amounts of fly ash and kaolin and sintered at 900 °C. The SEM analysis evidenced a large number of small pores on the surface of kaolin-rich membranes. The M4 membrane prepared using 25% fly ash and 50% kaolin was found to be optimum as it had a good combination of pore size (0.885 μm), porosity (42.7%), mechanical strength (43.6MPa), and chemical stability (<3% weight loss in acid and 0.02% in base), and this membrane was successfully applied in separation of humic acid from water. The permeate flux data fitted very closely with cake-filtration model, indicating the formation of a cake layer on membrane surface. Membrane fouling was found to be reversible and easily negated by cleaning and backflushing. The regenerated membrane showed better rejection of humic acid than fresh membrane with a flux recovery of above 80%.