Frequency shift in signal and idler gain peaks due to nonlinear refractive index in narrow-band optical parametric oscillators

The frequency chirp in the gain spectra for the signal and idler waves in nanosecond optical parametric oscillators (OPOs) due to the nonlinear refractive index of the gain medium at the pump wavelength is discussed. Computed results for a commonly used 355 nm pumped OPO with lithium borate and beta barium borate as a gain medium show that the frequency shift remains small compared with the gain bandwith, even for a narrow-band OPO pumped above threshold.     

Structural characteristics of titanium coating on copper substrates

The growth characteristics of titanium films deposited on glass, silicon (100) and oxygen free high purity copper substrate using magnetron sputtering have been investigated using X-ray diffraction, electron microscopy and scratch indentation techniques. The study of interface between the titanium film and the substrate was carried out to determine coating thickness, as well as intermixing of the elements at the interface. Studies revealed that the interface is free from voids and intermixing of the film and the substrate. Microstructural and diffraction analysis showed that the Ti coating was polycrystalline and exhibited columnar growth. The Ti crystallite size varied between 24 and 58 nm depending on the substrate. The thickness of the films were typically about 4 μm. Scratch test indicated that the films are adherent and the first critical load to failure was observed to be 4·5 N ± 2 N.     

Methylmercury Concentrations Found in Wild and Farm-raised Paddlefish

ABSTRACT: Paddlefish ( Polyodon spathula ) were collected from 4 sites in Kentucky: the Ohio River, Lake Cumberland, and 2 aquaculture sources (private reservoir and catfish ponds). They were tested for methylmer-cury concentrations in their flesh. Paddlefish from all sources had methylmercury levels below the 1 part per million Food and Drug Administration-mandated action limit for seafood. However, using the U.S. Environmental Protection Agency reference dose for methylmercury, only paddlefish from the Ohio River exceeded the reference dose for unrestricted consumption. Some Ohio River and Lake Cumberland paddlefish had higher-than-average methylmercury concentrations, whereas aquacultured paddlefish had low concentrations of methylm-ercury. There was a direct proportionality between fish age and methylmercury concentration; older paddlefish tended to have higher amounts of methylmercury in their meat.     

UNDERSTANDING ULTRAFILTRATION PERFORMANCE WITH MOSAMBI JUICE IN AN UNSTIRRED BATCH CELL

Ultrafiltration (UF) of sucrose and pectin solutions, their mixtures and enzymatically treated mosambi (Citrus sinensis [L.] Osbeck) juice has been performed on a batch unstirred membrane cell. Thin film composite polyamide membrane of molecular weight cut‐off 50,000 was used. The sucrose solution's permeate flux declined marginally, but for the pectin solution, it decreased rapidly over time. The sucrose–pectin mixture exhibits a flux decline similar to that of the pectin solution. The gel‐type pectin layer over the membrane's surface governs the flux decline of the sucrose–pectin mixture. The nature of the flux decline and the values of the permeated total soluble solids of enzymatically treated mosambi juice show similar behavior as compared with that of the UF of the sucrose–pectin mixture. The permeate of the enzyme‐treated mosambi juice contains almost all the soluble solids and acids (in terms of citric acid) with a remarkable improvement in juice clarity.     

Optimum lateral extent of soil domain for dynamic SSI analysis of RC framed buildings on pile foundations

This article describes a novel approach for deciding optimal horizontal extent of soil domain to be used for finite element based numerical dynamic soil structure interaction (SSI) studies. SSI model for a 12 storied building frame, supported on pile foundation-soil system, is developed in the finite element based software framework, OpenSEES. Three different structure-foundation configurations are analyzed under different ground motion characteristics. Lateral extent of soil domain, along with the soil properties, were varied exhaustively for a particular structural configuration. Based on the reduction in the variation of acceleration response at different locations in the SSI system (quantified by normalized root mean square error, NRMSE), the optimum lateral extent of the soil domain is prescribed for various structural widths, soil types and peak ground acceleration levels of ground motion. Compared to the past studies, error estimation analysis shows that the relationships prescribed in the present study are credible and more inclusive of the various factors that influence SSI. These relationships can be readily applied for deciding upon the lateral extent of the soil domain for conducting precise SSI analysis with reduced computational time.     

Life estimation model of a cantilevered beam subjected to complex random vibration

An analytic methodology was developed to predict the fatigue life of a structure experiencing stationary, Gaussian random vibration excitation. This method allows the estimation of fatigue life using a frequency domain method, where only the input power spectral density and damping factor are required. The methodology uses linear elastic fracture mechanics for fatigue crack propagation and accounts for the frequency shifting that occurs due to fatigue crack evolution. Good results have been obtained comparing the analytic model to both finite element analysis (FEA) and experimental results, for mild‐steel cantilever beams.     

Effect of capping agents on optical and antibacterial properties of cadmium selenide quantum dots

Cadmium selenide quantum dots (CdSe QDs) were synthesized in aqueous phase by the freezing temperature injection technique using different capping agents (viz. thioglycolic acid, 1-thioglycerol, L-cysteine). Absorption spectra of CdSe QDs exhibited a blue shift as compared to its bulk counterpart, which is an indication of quantum confinement effect. The photoluminescence spectra of CdSe QDs confirmed that the particles are poly-dispersed and possess enhanced luminescent property, depending upon the chemical nature of capping agents. The QDs have been characterized by Fourier-transform infrared spectroscopy, atomic absorption spectroscopy and transmission electron microscopy. Further, antimicrobial activity of as-prepared QDs has also been investigated using the disk diffusion method.