Low-threshold operation of a 355-nm pumped nanosecond β-BaB2O4 optical parametric oscillator

We report the low-threshold operation of a nanosecond β-BaB₂O₄ optical parametric oscillator (OPO) pumped by the third harmonic of a Q-switched Nd:YAG laser. Using cylindrical focusing of the pump beam, a threshold pulse energy of 0.5 mJ is obtained at the signal wavelength of 560 nm, which is about sixteen times lower than that of a spherical focusing configuration. The importance of diffraction loss in the design of tightly focused OPOs is discussed in terms of a simple extension of the conventional OPO model.     

Identifying neutrino mass hierarchy at extremely small theta13 through earth matter effects in a supernova signal

Collective neutrino flavor transformations deep inside a supernova are sensitive to the neutrino mass hierarchy even at extremely small values of theta_(13). Exploiting this effect, we show that comparison of the antineutrino signals from a galactic supernova in two megaton class water Cherenkov detectors, one of which is shadowed by Earth, will enable us to distinguish between the hierarchies if sin(2)theta_(13) < or approximately 10(-5), where long baseline neutrino experiments would be ineffectual.     

Disentangling effects of nuclear structure in heavy element formation

Forming the same heavy compound nucleus with different isotopes of the projectile and target elements allows nuclear structure effects in the entrance channel (resulting in static deformation) and in the dinuclear system to be disentangled. Using three isotopes of Ti and W, forming 232Cm, with measurement spanning the capture barrier energies, alignment of the heavy prolate deformed nucleus is shown to be the main reason for the broadening of the mass distribution of the quasifission fragments as the beam energy is reduced. The complex, consistently evolving mass-angle correlations that are observed carry more information than the integrated mass or angular distributions, and should severely test models of quasifission.     

Photophysical and laser characteristics of pyrromethene 567 dye: Experimental and theoretical studies

Narrow-band laser performance of alcohol solutions of pyrromethene 567 (PM567) and rhodamine 6G (RH6G) dye was investigated using a home-made GIG-configured dye laser, excited by the second-harmonic radiation (at 532 nm) of a pulsed Nd:YAG laser. Higher laser efficiency was observed with PM567 dye (∼23% peak) in comparison to the commonly used RH6G dye (16.5%), in spite of much lower fluorescence quantum efficiency of the PM567 (0.83) vis-à-vis RH6G (0.98) dye solutions in ethanol. First principle-based electronic structure calculations were performed on PM567 dye in the ground (S ₀) and excited states (S ₁) using density functional theory to elucidate the structure and photophysical properties of the dye.     

A new method for estimating the critical current density of a superconductor from its hysteresis loop

The critical current density J_c of some of the superconducting samples, calculated on the basis of the Bean’s model, shows negative curvature for low magnetic field with a downward bending near H = 0. To avoid this problem Kim’s expression of the critical current density, J_c = k/(H₀ + H), where J_c has positive curvature for all H, has been employed by connecting the positive constants k and H₀ with the features of the hysteresis loop of a superconductor. A relation between the full penetration field H_p and the magnetic field H_min, at which the magnetization is minimum, is obtained from the Kim’s theory. Taking the value of J_c at H = H_p according to the actual loop width, as in the Bean’s theory, and at H = 0 according to an enhanced loop width due to the local internal field, values of k and H₀ are obtained in terms of the magnetization values M⁺(?H_min), M^?(H_min), M⁺(H_p) and M^?(H_p). The resulting method of estimating J_c from the hysteresis loop turns out to be as simple as the Bean’s method.     

Relating breakup and incomplete fusion of weakly bound nuclei through a classical trajectory model with stochastic breakup

A classical dynamical model that treats breakup stochastically is presented for low energy reactions of weakly bound nuclei. The three-dimensional model allows a consistent calculation of breakup, incomplete, and complete fusion cross sections. The model is assessed by comparing the breakup observables with continuum discretized coupled-channel quantum mechanical predictions, which are found to be in reasonable agreement. Through the model, it is demonstrated that the breakup probability of the projectile as a function of its distance from the target is of primary importance for understanding complete and incomplete fusion at energies near the Coulomb barrier.     

Photosensitizing potential of ciprofloxacin at ambient level of UV radiation

Ciprofloxacin is a widely used fluoroquinolone drug with broad spectrum antibacterial activities. Clinical experience has shown incidences of adverse effects related to skin, hepatic, central nervous system, gastrointestinal and phototoxicity. India is a tropical country and sunlight is abundant throughout the day. In this scenario exposure to ambient levels of ultraviolet radiation (UV-R) in sunlight may lead to harmful effects in ciprofloxacin users. Phototoxicity assessment of ciprofloxacin was studied by two mouse fibroblast cell lines L-929 and NIH-3T3. Generation of reactive oxygen species (ROS) like singlet oxygen (1O2), superoxide anion radical (O2*-) and hydroxyl radical (*OH) was studied under the exposure of ambient intensities of UV-A (1.14, 1.6 and 2.2 mW cm(-2)), UV-B (0.6, 0.9 and 1.2 mW cm(-2)) and sunlight (60 min). The drug was generating 1O2, O2*- and *OH in a concentration and dose-dependent manner. Sodium azide (NaN3) and 1,4-diazabicyclo 2-2-2-octane (DABCO) inhibited the generation of 1O2. Superoxide dismutase (SOD) inhibited 90-95% O2*- generation. The drug (5-40 microg mL(-1)) was responsible for linoleic acid peroxidation. Quenching study of linoleic acid peroxidation with SOD (25 and 50 U mL(-1)) confirms the involvement of ROS in drug-induced lipid peroxidation. The generation of *OH radical was further confirmed by using specific quenchers of *OH such as mannitol (0.5 M) and sodium benzoate (0.5 M). 2'-deoxyguanosine (2'-dGuO) assay and linoleic acid peroxidation showed that ROS were mainly responsible for ciprofloxacin-sensitized photo-degradation of guanine base. L-929 cell line showed 29%, 34% and 54% reduced cell viability at higher drug concentration (300 microg mL(-1)) under UV-A, UV-B and sunlight, respectively. 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay in NIH-3T3 cell line at higher drug concentration (300 microg mL(-1)) showed a decrease in cell viability by 54%, 56% and 59% under UV-A, UV-B and sunlight, respectively. Results of neutral red uptake assay (NRU) in L-929 cell line were in accordance with MTT assay. The NIH-3T3 cell line showed a higher photosensitizing potential than L-929. The phototoxicity end point shows a time- and concentration-dependent statistically significant (P<0.001) damage. Ciprofloxacin produced ROS by Type I and Type II photodynamic reactions, interacted with nucleic acid moiety and inhibited cell viability. Further, UV-induced photo-peroxidation of linoleic acid accorded the involvement of ROS in the manifestation of drug phototoxicity. Appearance of ciprofloxacin-induced phototoxicity at the ambient level of sunlight is a real risk for the people of India and for those of other tropical countries. We suggest that sunlight exposure should be avoided (especially peak hours) during ciprofloxacin treatment.     

High efficiency dye laser with low fluorescence yield pyrromethene dyes: experimental and theoretical studies

A combined experimental and theoretical study of the photo-physical, laser properties and molecular structures of three relatively recent Pyrromethene (PM) class dyes, PM597, PM580 and PM567, have been carried out. Laser characteristics of these three PM dyes were compared with three other widely used Rhodamine (RH) class dyes, RH6G, RHB and KRS, using a narrow-band dye laser setup, transversely pumped by the second harmonic (532 nm) of a Q-switched Nd-YAG laser. In addition to generating comparative data of these dyes for optimal use in dye lasers, we observed that unlike the RH dyes, the PM dyes show high efficiencies and wide tunability, despite the low fluorescence yield and high rate of non-radiative decay. Particularly, PM597 dye, in spite of a very low quantum yield of fluorescence (Φ=0.42), high non-radiative decay rate, and a large distortion from planarity in its excited state, when used in a laser cavity it exhibited similar laser efficiency and a beneficially wider tuning curve in comparison to other two PM dyes. Theoretical studies were carried out applying density functional theory and time-dependent density functional theory (DFT/TDDFT) to obtain new information on ground and the first excited state geometrical parameters of the PM dyes. Good correlation between calculated molecular properties and experimental results was observed for the evolution of the longest wavelength absorption maximum.     

Nickel(0)-catalyzed cyclization of N-benzoylaminals for isoindolinone synthesis

A nickel(0) catalyst effectively mediates the cyclization of N-benzoyl aminals in the presence of a stoichiometric Lewis acid. This method enables preparation of a variety of isoindolinones with substitution on the benzoyl fragment and C-3 carbon. This reaction likely proceeds via an α-amidoalkylnickel(II) intermediate, which then may cyclize via either an electrophilic aromatic substitution or an insertion pathway.