Synthesis of 2,2-dimethyl-5-hydroxy-3-(3-oxobutyl)-7-pentyl-4-chromone

Alkylation and deformylation of 2,2-dimethyl-3-hydroxymethylene-5-hydroxy-7-pentyl-4-chromone occurs in the same step to give the title compound.     

Studies on nessler's reagent and nessler's precipitate part II

The composition of the precipitate formed when the Nessler's reagent is treated with ammonia, is assumed as NH_n-1Hg₂I_n, aq. and has been studied potentiometrically from iodine-hypoiodite-system. It has been observed that the value of n depends on the concentrations of [HgI₄]^-2 and OH^- ions as well as on the amount of ammonia added and it may vary from 1 to 3. The colour of the precipitate deepens from brown to chocolate as the value of n increases.     

Label Free Colorimetric Biosensing Using Nanoparticles

In this review article, we discuss a class of biosensors that exploit the change in the colorimetric properties of noble metal nanoparticles in response to biomolecular binding at their surface. Several sensor fabrication techniques as well as sensor configurations are discussed with an emphasis on their strengths and limitations. We conclude by presenting the future prospects and challenges for the successful transition of this technology from the laboratory to a commercial product.     

Solution phase evolution of AuSe nanoalloys in Triton X-100 under UV-photoactivation

A solution phase UV-irradiation technique has been exploited to produce an AuSe nanoalloy through fusion of preformed Au (photoproduced) and Se (chemically prepared) in a micellar (TX-100) medium.     

Accelerated Bergman cyclization of porphyrinic-enediynes

The Bergman cyclization of simple diethynylporphyrinic-enediynes exhibits a double activation barrier to the formation of Bergman cyclized product. Addition of H-atom acceptor accelerates the formation of the picenoporphyrin, indicating that the second barrier is rate limiting.     

Diffusion and transport phenomena in a collisional magnetoplasma having both streaming and temperature anisotropy: Collisional kinetics

Boltzmann-transport equation is analytically solved for two-component magnetoplasma using Chapman-Enskog analysis to include collisional diffusion transport having anisotropies in both streaming velocity and temperature components. The modified collisional integrals are analytically solved with flux integrals and perturbed kinetic equation to arrive at drift diffusion velocity and resulting transport coefficients which are markedly affected by both streaming and temperature anisotropy. The early isotropic results are recovered in the limit V ₀ = 0 and T _‖ = T _⊥ which reduce to eqs (11.30) and (11.31) of [1] and eqs (2.7) and (2.13) of [2]. The electrical resistivity (η_⊥) diminishes sharply in fusion temperature limit kT _⊥ = 1 keV. The shape of the curves for both electrical resistivity and thermal conductivity is rectangular hyperbolic. However, for low thermal ratio (T _‖/T _⊥ < 1), the curves are raised up and for high thermal ratio (T _‖/T _⊥ > 1), they are lowered down the isotropic case (T _‖/T _⊥ > 1), showing comparatively diminished magnitudes of the quantities.      

Study of gain flatness for multi-channel amplification in single stage EDFA for WDM applications

In this paper, gain flatness is studied for simultaneous 16-ITU-T channel amplifications at C-band (1,532–1,558 nm) in a single stage EDFA for WDM application at different average inversion levels. The inversion levels are varied due to the change of the input signal levels from the targeted operating point and also for dropping few numbers of channels. Specially designed gain flattening filter (GFF) is used in order to get the flat gain with gain variation ±0.5 dB for −20 dBm/ch input signal power (total input signal power is −8.0 dBm) at a fixed average inversion level which is maintained by proper selection of optimum fibre length and pump power. A specific loss spectrum of GFF is obtained by writing a chirped fibre Bragg grating of length 20 mm. Gain variations are studied by changing the total input signal levels from −8.0 dBm to −20.0 dBm and maintained within 20.0 ± 0.5 dB by using automatic gain control (AGC) circuit. About 15 out of 16 channels are dropped and observed ± 0.5 dB gain-variation which is an important parameter in optical network system.     

Thin Nd:YAG slab laser pumped by lens duct coupled diode laser stacks

High power continuous wave operation of a diode face-pumped thin Nd:YAG slab laser is reported. A novel pumping geometry for a thin Nd:YAG slab using cylindrical lens duct coupled diode laser stacks is demonstrated. In a close-coupled resonator, a maximum laser output power of 260 W in multimode operation is obtained. This corresponds to a slope efficiency of 34% and an optical-to-optical efficiency of 27%, respectively. In high-brightness operation, a polarized laser output of 70 W has been obtained with a beam quality factor close to 4 in both directions. The polarization contrast ratio is >100. PACS 42.55.Xi; 42.60.Pk; 42.60.By     

Spinning cone water film power meter for high-power CO2 lasers

A laser power meter based on water as an absorbing medium has been developed to measure multi-kilowatt CO₂ laser power with high sensitivity and accuracy. Water absorbs CO₂ laser radiation readily within a very thin layer. Though water has large thermal capacity, due to short absorption length, it could vapourize at high laser powers. In order to circumvent this problem, this power meter has a centre cone and a rapidly spinning water film as the calorimetric medium. The unique feature in this development is the centre cone, which diverges the beam and reduces the power density thus reduces the possibility of vapourization. This minimizes the error in measurements. Due to the rapidly moving fluid film, it exhibits fast response at low as well as high power levels.     

Polarization switching properties of spray deposited CsNO3: PVA composite films

The ferroelectric and switching properties of spray deposited cesium nitrate: poly (vinyl alcohol) composite films at different substrate temperatures (T _s ) have been studied. The optimum value of remanent polarization was obtained in the film deposited at T _s =200°C, which may be due to larger structural distortion (c/a ratio) and less porosity as revealed by x-ray diffraction and field emission scanning electron microscope (FESEM) analysis. The switching current transients have been analyzed by nucleation limited switching model (NLS) with the Lorentzian distribution function. This model gives excellent agreement with the experimental polarization current throughout the whole time range. The switching parameters were determined in the composite films deposited at different T _s and found to be optimum at T _s =200°C. The effect of pulse amplitude on the domain switching properties has also been studied and analyzed. The peak value of polarization current exhibits an exponential dependence on the external applied field.