Comparative study of the electronic structure of natural and synthetic rubies using XAFS and EDAX analyses

We have studied the Cr-K-edge XANES and EXAFS in natural Indian rubies from two sources and a synthetic ruby at ESRF. Weight % of various constituents in them is determined using EDAX measurements. Taking the results from the three techniques together we are able to demonstrate their feasibility in quantitative study of precious stones.     

Si-implantation into GaAs grown on Si

200 keV Si implantations were performed in the dose range of 5 × 10¹² − 1 × 10¹⁴ cm⁻² in GaAs grown on Si. For comparison implants were also performed in GaAs layers grown on GaAs substrates. Implanted layers were annealed by both furnace and halogen lamp rapid thermal anneals. Significantly lower donor activations were observed in GaAs layers grown on Si substrates than in the layers grown on GaAs substrates. Extremely low dopant activations were obtained for Be implants in GaAs grown on Si. Photoluminescence and photoreflectance measurements were also performed on the implanted material.     

Peroxidase-mediated oxidative coupling of 1-naphthol: characterization of polymerization products

The oxidative polymerization of 1-naphthol was investigated in the presence of horseradish peroxidase (HRP). Naphthol polymerization products (NPP) were characterized for their relative polarity using octanol--water partitioning experiments and reverse-phase high pressure liquid chromatography, for structure using size exclusion chromatography and liquid chromatography-mass spectrometry (LC/MS), and for ecotoxicity using inhibition of bacterial bioluminescence. Peroxidase addition resulted in the production of soluble and insoluble NPP. Soluble NPP was predominantly more polar than the parent naphthol and comprised of trimers and tetramers. Insoluble NPP oligomers included dimers, trimers and tetramers. The net aqueous-phase toxicity was significantly reduced due to polymer formation and subsequent precipitation. A reaction model deduced from the LC/MS fragmentation patterns of trimeric naphthol was proposed for NPP formation. Results from this study suggest that HRP-mediated treatment of naphthol contaminated soils can achieve risk reduction through (i) the formation of large hydrophobic oligomers that are immobilized on the soil matrix; and (ii) reduction in aqueous-phase toxicity due to polymer precipitation.     

Electrical characterization of coupled and uncoupled MEMS ultrasonic transducers

We report electrical characterization of micromachined polysilicon capacitive diaphragms for use as ultrasonic transducers. Admittance measurements yield insight into the resonant behavior and also the damping resulting from ultrasonic radiation and frictional forces caused by the etch release holes. Unbonded transducers exhibit sharp resonances with Q values that increase with decreasing air pressure. We also report for the first time direct bonding of these transducers to solid surfaces. Transducers survive the bonding process and show distinctly different displacement in response to applied dc bias. Finally, a single-degree-of-freedom model is used to obtain insight into the various contributions to damping.     

Functional reconstitution of protein ion channels into planar polymerizable phospholipid membranes

We demonstrate that polymerizable planar membranes permit reconstitution of protein ion channels formed by the bacterial toxins Staphylococcus aureus alpha-hemolysin (alphaHL) and Bacillus anthracis protective antigen 63. The alphaHL channel remained functional even after membrane polymerization. Surface pressure measurements suggest that the ease of forming membranes depends on membrane surface elasticity estimated from Langmuir-Blodgett monolayer pressure-area isotherms. The ability to stabilize nanoscale pores in robust ultrathin films may prove useful in single molecule sensing applications.     

Field Applicability of the SCS-CN-Based Mishra–Singh General Model and its Variants

The general soil conservation service curve number (SCS-CN)-based Mishra and Singh (Mishra and Singh, 1999, J. Hydrologic. Eng. ASCE, 4(3), 257–264) model and its eight variants were investigated for their field applicability using a large set of rainfall-runoff events, derived from a number of U.S. watersheds varying in size from 0.3 to 30351.5 ha, grouped into five classes based on the rainfall magnitude. The analysis based on the goodness of fit criteria of root mean square error (RMSE) and error in computed and observed mean runoff revealed that the performance of the existing version of the SCS-CN method was significantly poorer than that of all the model variants on all the five data sets with rainfall 38.1 mm. The existing version showed a consistently improved performance on the data with increasing rainfall amount, but greater than 38.1 mm. The one-parameter modified SCS-CN method (a = 0.5 and = a median value) performed significantly better than the existing one on all the data sets, but far better on rainfall data less than 2 inches. Finally, the former with = 0 was recommended for routine field applications to any data set.     

Large-scale evaluation of multimodal biometric authentication using state-of-the-art systems

We examine the performance of multimodal biometric authentication systems using state-of-the-art commercial off-the-shelf (COTS) fingerprint and face biometric systems on a population approaching 1,000 individuals. The majority of prior studies of multimodal biometrics have been limited to relatively low accuracy non-COTS systems and populations of a few hundred users. Our work is the first to demonstrate that multimodal fingerprint and face biometric systems can achieve significant accuracy gains over either biometric alone, even when using highly accurate COTS systems on a relatively large-scale population. In addition to examining well-known multimodal methods, we introduce new methods of normalization and fusion that further improve the accuracy.     

Analysis of heat transfer augmentation and flow characteristics due to rib roughness over absorber plate of a solar air heater

A computational analysis of heat transfer augmentation and flow characteristics due to artificial roughness in the form of ribs on a broad, heated wall of a rectangular duct for turbulent flow (Reynolds number range 3000–20,000, which is relevant in solar air heater) has been carried out. Shear stress transport k−ω turbulence model is selected by comparing the predictions of different turbulence models with experimental results available in the literature. A detailed analysis of heat transfer variation within inter rib region is done by using the selected turbulence model. The analysis shows that peak in local heat transfer coefficient occurs at the point of reattachment of the separated flow as observed experimentally. The results predict a significant enhancement of heat transfer in comparison to that for a smooth surface. There is a good matching between the predictions by SST k−ω and experimental results. In this work, nine different shapes of rib are examined using SST k−ω model and compared on the basis of heat transfer enhancement, friction characteristics and performance index considering heat transfer enhancement with the same pumping power.     

Effect of injection efficiency and dimensions on the performance of a forward biased P+−I alloyed junction

P⁺?I junction has a high carrier injection, when forward biased. The bias voltage is dropped across the junction and the intrinsic region. The injection efficiency γ at the junction has been found to depend upon the voltage drop V_J across the barrier and the thickness of the intrinsic layer expressed as $\text{d}\text{L}$ where d is the thickness of the intrinsic layer and L is a measure of the diffusion length of the carriers in the intrinsic region. As V_J is varied the injection efficiency remains close to unity for low values of V_J but decreases for larger values of V_J, the decrease being more for larger values of $\text{d}\text{L}$. The ratio of the voltage drop across the intrinsic layer V_I to the voltage drop V_J across the junction depends upon the injection efficiency at the junction γ and the ratio $\text{d}\text{L}$. As γ decreases $\text{V}{}_{\mathrm{I}}\text{V}{}_{\mathrm{J}}$ increases, the increase being more for larger values of $\text{d}\text{L}$. The forward J?V characteristic is found to depend upon $\text{d}\text{L}$. As $\text{d}\text{L}$ decreases a lower resistance is offered by the diode. Modifications arising out of carrier-carrier scattering have also been considered. For a given V_J and $\text{d}\text{L}$, carrier-carrier scattering reduces γ. A reduced value of γ increases $\text{V}{}_{\mathrm{I}}\text{V}{}_{\mathrm{J}}$ and makes J?V curve less steep. The analysis has been carried out for $\text{V}{}_{\mathrm{J}}\text{?}\text{4kT}\text{e}$.     

Second-harmonic generation of several argon-ion laser lines

Second-harmonic generation of the 496.5-nm, 501.7-nm, and 514.5-nm lines of the argon laser has been achieved. This was done by 90° phase matching in an ADP crystal at temperatures of -93.2°C, -68.4°C, and -10.2°C, respectively.