Plasma dynamics and determination of ablation parameters using the near-target magnified imaging during pulsed laser ablation

A comparative study of the ultrafast dynamics on ZnO thin films deposited on flat Si substrates and on Si micro-cones following ultrashort laser excitation has been carried out using time-resolved optical spectroscopy. By monitoring the transient band gap renormalization induced by nonlinearly excited carriers it is found that fast electron scattering and trapping occurs more efficiently in the micro-cones as compared to the flat films. This enhanced trapping efficiency is attributed to the defects and imperfections that are introduced by the increased surface roughness due to the conical shape.     

L p Wiener–Tauberian theorems for M(2)

We prove two sided and one sided analogues of the Wiener-Tauberian theorem for the Euclidean motion group, M(2).     

Pulsed ion beam-assisted carburizing of titanium in methane discharge

The carburizing of titanium (Ti) is accomplished by utilizing energetic ion pulses of a 1.5 kJ Mather type dense plasma focus (DPF) device operated in methane discharge. X-ray diffraction (XRD) analysis confirms the deposition of polycrystalline titanium carbide (TiC). The samples carburized at lower axial and angular positions show an improved texture for a typical (200)TiC plane. The Williamson-Hall method is employed to estimate average crystallite size and microstrains in the carburized Ti surface. Crystallite size is found to vary from ～ 50 to 100 nm, depending on the deposition parameters. Microstrains vary with the sample position and hence ion flux, and are converted from tensile to compressive by increasing the flux. The carburizing of Ti is confirmed by two major doublets extending from 300 to 390 cm-1 and from 560 to 620 cm-1 corresponding to acoustic and optical active modes in Raman spectra, respectively. Analyses by scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS) have provided qualitative and quantitative profiles of the carburized surface. The Vickers microhardness of Ti is significantly improved after carburizing.     

Laser frequency stabilization using a balanced bi-polarimeter

We report on a Doppler-free polarization spectroscopy based technique of laser frequency stabilization using a balanced bi-polarimeter set-up. Two linearly polarized weak laser beams are used to probe birefringence induced by two oppositely circularly polarized strong pump beams in a vapour cell. Subtraction of balanced polarimeter signals obtained from the two probe beams results in a background-free dispersion-like reference signal without frequency modulation. The dispersion-like signal corresponding to the closed transition 5 ² S _1/2 (F=2) →5 ² P _3/2 (F^′=3) of ⁸⁷Rb was used for frequency locking of a diode laser. The frequency fluctuations and the drift were measured to be less than 0.25 MHz and 0.02 MHz, respectively, for an observation period of more than 10 hours. PACS 42.62.Fi; 42.55.Px; 32.30.-r     

Feasibility of in-house sterilization of laboratory plastic consumables using 2 MeV electron beam facility

In-house sterilization by electron beam (EB) radiation of various plastic consumables (plastic petridishes, micro centrifugal tubes and screw-capped vials) used routinely in the lab was studied by use of three microbiological cultures (S. aureus, Bacillus subtilis and Candida albicans). Current international standards (ISO 11137-Part 2 -ISO, 2011) recommend an irradiation dose of 25 kGy as a reference dose for terminal sterilization. All containers were exposed in an ILU-6, 2 MeV, 20 kW, Pulse EB accelerator located in our complex. Sterility test (S.T.) was performed and results revealed that 10⁶ and 10⁷ population of all strains passed whereas 10⁸ population failed S.T. for all micro-organisms indicating the potential of 2 MeV EB for commercial sterilization of plastic lab consumables for up to 10⁷ population of these micro-organisms.     

Chemical Analysis of the Luminous Slime Secreted by the Marine Worm Chaetopterus (Annelida,Polychaeta)

The marine annelid Chaetopterus variopedatus produces bioluminescence by an unknown and potentially novel mechanism. We have advanced the study of this fascinating phenomenon, which has not been investigated for nearly 60 years after initial studies were first reported for this species. Here, we show that the luminous slime produced by the worm exhibits blue fluorescence that matches the bioluminescence emission. This result suggests that the oxyluciferin emitter is present. However, while the blue fluorescence decays over time green fluorescence is increasingly revealed that is likely associated with products of the luminescence reaction. LC/MS and fluorescence analysis of harvested luminescent material revealed riboflavin as the major green fluorescent component. Riboflavin is usually associated with the mechanism of light production in bacteria, yet luminous bacteria were not found in the worm mucus, and accordingly were not reported to be directly responsible for the light emission, which is under nervous control in the worm. We therefore propose a hypothesis in which riboflavin or a structurally related derivative serves as the emitter in the worm's light producing reaction.     

Simultaneous Determination of Bergenin and Gallic Acid in Different Bergenia Species

JPC – Journal of Planar Chromatography – Modern TLC - A simple, highly precise method has been established for the simultaneous determination of the bioactive molecules bergenin and...     

A Validated HPLC Method for Quantification and Optimization of Furocoumarins in Different Extracts of Fruits of Heracleum candicans

Heracleum candicans Wall. ex DC (Apiaceae) finds use as an aphrodisiac, nerve tonic and also in the treatment of skin diseases in the Indian system of medicines and is reported to be rich in furocoumarins which are extensively used in pharmaceutical industry for their photosensitizing activity on human skin. Thus a HPLC–PDA method has been developed for the selection of suitable solvent for extraction and quantitative estimation of these furocoumarins viz. heraclenol, heraclenin, bergapten and psoralen in fruits of H. candicans. The results indicate that heraclenol is found to be maximum in 30% aqueous methanolic extract (0.108%) while the maximum concentration of heraclenin (anti-inflammatory principle) and bergapten (melanogenesis stimulation activity) was found in the pure methanolic extract (0.386 and 0.281%, respectively). However psoralen (anti-psoriatric principle) was found in very low concentration in all the extracts. Further validation of the method was done in view to demonstrate its selectivity, linearity, precision, accuracy and robustness. The method thus developed can be applied in quality evaluation of H. candicans.     

Liquid-liquid equilibrium in the toluene-methyl ethyl ketone-water system

For the toluene-methyl ethyl ketone-water system the liquid-liquid equilibrium tie-line data have been determined at 40 and 0°C and the binodal curve for this system has been determined at 40, 0 and −10°C. The tie-line data at 40 and 0°C could be correlated with good accuracy using NRTL and UNIQUAC model equations.     

Synthesis, characterization and fluorescence studies of 3,5-diaryl substituted 2-pyrazolines

A series of 2-pyrazolines have been synthesized from α, β unsaturated ketones and hydrazine hydrate with acetic/formic acid in ethanol/DMSO. The structures of 2-pyrazolines have been established by spectroscopic techniques i.e. UV, IR, (1)H NMR, (13)C NMR and micro element analysis. Fluorescence spectra were recorded in the solution at fixed concentration and same excitation wavelength at 290 nm. The absorption band positions of all the compounds broadly lie between 280 and 336 nm and fluorescence band positions in the range between 300 and 370 nm, the near ultraviolet region.