Enhanced electrooxidation of methanol,ethylene glycol,glycerol, and xylitol over a polypyrrole/manganese oxyhydroxide/palladium nanocomposite electrode

A small quantity of palladium metal (Pd, 5 wt%) nanoparticles supported by a polypyrrole/manganese oxyhydroxide (PPy/MOH) nanocomposite was developed and investigated as an electrocatalyst for the alcohol electrooxidation reaction in alkaline media. In voltammetric studies, the PPy/MOH/Pd catalyst, compared to C/Pd, exhibited improved electrocatalytic activity for methanol electrooxidation. The peak current density ratios (j ^f/j ^b) for the C/Pd and PPy/MOH/Pd nanocomposite electrodes were 0.67 and 2.43, respectively, indicating that the PPy/MOH/Pd nanocomposite electrode was much more resistant to catalytic poisoning. The electrooxidation of ethylene glycol (EG), glycerol, and xylitol was also tested using the PPy/MOH/Pd nanocomposite electrode. Among these alcohol electrooxidations, that of EG exhibited the maximum power density of 430 mA cm^?2. The intermediates formed during the electrooxidation reactions were removed by increasing the upper sweep potential from +0.2 to +1.0 V. The catalytic performance of the PPy/MOH nanocomposite is discussed in detail. The study results demonstrate that PPy/MOH acts as a superior catalytic supporting material for alcohol electrooxidation reactions in alkaline media.     

Portable, Fiber-Based, Diffuse Reflection Spectroscopy (DRS) Systems for Estimating Tissue Optical Properties

Steady-state diffuse reflection spectroscopy is a well-studied optical technique that can provide a noninvasive and quantitative method for characterizing the absorption and scattering properties of biological tissues. Here, we compare three fiber-based diffuse reflection spectroscopy systems that were assembled to create a light-weight, portable, and robust optical spectrometer that could be easily translated for repeated and reliable use in mobile settings. The three systems were built using a broadband light source and a compact, commercially available spectrograph. We tested two different light sources and two spectrographs (manufactured by two different vendors). The assembled systems were characterized by their signal-to-noise ratios, the source-intensity drifts, and detector linearity. We quantified the performance of these instruments in extracting optical properties from diffuse reflectance spectra in tissue-mimicking liquid phantoms with well-controlled optical absorption and scattering coefficients. We show that all assembled systems were able to extract the optical absorption and scattering properties with errors less than 10%, while providing greater than ten-fold decrease in footprint and cost (relative to a previously well-characterized and widely used commercial system). Finally, we demonstrate the use of these small systems to measure optical biomarkers in vivo in a small-animal model cancer therapy study. We show that optical measurements from the simple portable system provide estimates of tumor oxygen saturation similar to those detected using the commercial system in murine tumor models of head and neck cancer.     

Device scaling of pseudo-vertical diamond power Schottky barrier diodes

Device size scaling of pseudo-vertical diamond Schottky barrier diodes (SBDs) has been characterized for high-power device applications based on the control of doping concentration and thickness of the p^? CVD diamond layer. Decreasing parasitic resistance on the p⁺ layer utilising lithography and etching realises a constant specific on-resistance of less than 20 mΩ cm² with increasing device size up to 200 µm. However, the leakage current under low reverse bias conditions is increased markedly. Due to the increase in the leakage current, the reverse operation limit is decreased from 2.4 to 1.3 MV/cm when the device size is increased from 30 to 150 µm. If defects induce an increase in leakage current under the reverse conditions, the density of the defects can be estimated to be 10⁴–10⁵/cm². This value is 5–10 times larger than the density of dislocations in single crystal diamond Ib substrate.     

Monte Carlo-based inverse model for calculating tissue optical properties. Part I: Theory and validation on synthetic phantoms

A flexible and fast Monte Carlo-based model of diffuse reflectance has been developed for the extraction of the absorption and scattering properties of turbid media, such as human tissues. This method is valid for a wide range of optical properties and is easily adaptable to existing probe geometries, provided a single phantom calibration measurement is made. A condensed Monte Carlo method was used to speed up the forward simulations. This model was validated by use of two sets of liquid-tissue phantoms containing Nigrosin or hemoglobin as absorbers and polystyrene spheres as scatterers. The phantoms had a wide range of absorption (0-20 cm(-1)) and reduced scattering coefficients (7-33 cm(-1)). Mie theory and a spectrophotometer were used to determine the absorption and reduced scattering coefficients of the phantoms. The diffuse reflectance spectra of the phantoms were measured over a wavelength range of 350-850 nm. It was found that optical properties could be extracted from the experimentally measured diffuse reflectance spectra with an average error of 3% or less for phantoms containing hemoglobin and 12% or less for phantoms containing Nigrosin.     

Monte Carlo-based inverse model for calculating tissue optical properties. Part II: Application to breast cancer diagnosis

The Monte Carlo-based inverse model of diffuse reflectance described in part I of this pair of companion papers was applied to the diffuse reflectance spectra of a set of 17 malignant and 24 normal-benign ex vivo human breast tissue samples. This model allows extraction of physically meaningful tissue parameters, which include the concentration of absorbers and the size and density of scatterers present in tissue. It was assumed that intrinsic absorption could be attributed to oxygenated and deoxygenated hemoglobin and beta-carotene, that scattering could be modeled by spheres of a uniform size distribution, and that the refractive indices of the spheres and the surrounding medium are known. The tissue diffuse reflectance spectra were evaluated over a wavelength range of 400-600 nm. The extracted parameters that showed the statistically most significant differences between malignant and nonmalignant breast tissues were hemoglobin saturation and the mean reduced scattering coefficient. Malignant tissues showed decreased hemoglobin saturation and an increased mean reduced scattering coefficient compared with nonmalignant tissues. A support vector machine classification algorithm was then used to classify a sample as malignant or nonmalignant based on these two extracted parameters and produced a cross-validated sensitivity and specificity of 82% and 92%, respectively.     

Sequential estimation of optical properties of a two-layered epithelial tissue model from depth-resolved ultraviolet-visible diffuse reflectance spectra

A method for estimating the optical properties of two-layered media (such as squamous epithelial tissue) over a range of wavelengths in the ultraviolet-visible spectrum is proposed and tested with Monte Carlo modeling. The method first used a fiber-optic probe with angled illumination and the collection fibers placed at a small separation (or=1000 microm) was used to detect diffuse reflectance preferentially from the bottom layer. A second Monte Carlo-based inverse model for a two-layered medium was applied to estimate the bottom layer optical properties, as well as the top layer thickness, given that the top layer optical properties have been estimated. The results of Monte Carlo validation show that this method works well for an epithelial tissue model with a top layer thickness ranging from 200 to 500 microm. For most thicknesses within this range, the absorption coefficients were estimated to within 15% of the true values, the reduced scattering coefficients were estimated to within 20% and the top layer thicknesses were estimated to within 20%. The application of a variance reduction technique to the Monte Carlo modeling proved to be effective in improving the accuracy with which the optical properties are estimated.     

Iron(III) chloride-benzotriazole adduct for oxygen reduction reaction in alkaline medium

Transition metal-nitrogen-carbon (MNC) based non-platinum metal catalysts obtained by pyrolysis of a transition metal, carbon and nitrogen sources were viewed as an inexpensive substitute for the platinum-based electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. Due to the pyrolysis step involved in synthesizing MNC catalysts, the exact active site structure responsible for ORR was not conclusively identified thereby limiting the efforts of scientists in identifying effective synthetic routes to achieve highly active MNC catalysts with required active site structure and site density. To alleviate the lack of clarity on the active site structure of MNC catalysts, as a substitute, copper, and cobalt-based metal-organic frameworks and complexes were synthesized recently and shown to be ORR active. In this study, we have synthesized an Iron(III) chloride-benzotriazole ($\left[{\text{FeCl}}_3{\left(\text{btaH}\right)}_2\right]$) adduct and demonstrated its ORR activity in alkaline medium, which primarily reduces oxygen by 4-electron reduction pathway. Single crystal XRD characterization revealed the crystal structure of $\left[{\text{FeCl}}_3{\left(\text{btaH}\right)}_2\right]$ unambiguously. The ORR onset potential, Tafel slopes, and methanol tolerance ability of $\left[{\text{FeCl}}_3{\left(\text{btaH}\right)}_2\right]$ were compared against commercial 20 wt% Pt/C. $\left[{\text{FeCl}}_3{\left(\text{btaH}\right)}_2\right]$ adduct shows complete methanol tolerance and ORR onset potential of 0.89 V vs. RHE, which is highest among the unpyrolyzed metal-organic frameworks/complexes.     

Fast and noninvasive fluorescence imaging of biological tissues in vivo using a flying-spot scanner

We have developed a flying-spot scanner (FSS), for fluorescence imaging of tissues in vivo. The FSS is based on the principles of single-pixel illumination and detection via a raster scanning technique. The principal components of the scanner are a laser light source, a pair of horizontal and vertical scanning mirrors to deflect the laser light in these respective directions on the tissue surface, and a photo multiplier tube (PMT) detector. This paper characterizes the performance of the FSS for fluorescence imaging of tissues in vivo. First, a signal-to-noise ratio (SNR) analysis is presented. This is followed by characterization of the experimental SNR, linearity and spatial resolution of the FSS. Finally, the feasibility of tissue fluorescence imaging is demonstrated using an animal model. In summary, the performance of the FSS is comparable to that of fluorescence-imaging systems based on multipixel illumination and detection. The primary advantage of the FSS is the order-of-magnitude reduction in the cost of the light source and detector. However, the primary disadvantage of the FSS its significantly slower frame rate (1 Hz). In applications where high frame rates are not critical, the FSS will represent a low-cost alternative to multichannel fluorescence imaging-systems.     

Identification of embedded interlaminar flaw using inverse analysis

The integrity of a composite laminate can be greatly affected by an existence of embedded interlaminar flaw. In general, identification of such a flaw often requires expensive tools and tedious processes. The aim of the present work is to develop a novel method with the aid of an intelligent post-processing scheme, thereby not relying on those sophisticated experiments. Essentially the proposed procedure utilizes an inverse analysis to estimate unknown delamination parameters from limited measurements. The procedure first constructs approximate functions relating the delamination parameters to measurement parameters. Then, a multi-dimensional minimization technique is adopted to search for the best estimates of unknown parameters corresponding to the lowest value of error objective function. In the present verification and simulation analyses, surface strains at discrete locations on a composite laminate under three-point bending are selected as the input measurements. Although reasonable estimates are obtained with these measurements, to increase their accuracy, the deflection at load point is also included as measurement input. Additional improvements are observed when those measurements under multiple loading conditions are included. A detailed error sensitivity analysis is also carried out to confirm the methods robustness. These results suggest the current method to be one of the alternate identification approaches for detecting a single embedded delamination in composite laminates.     

Comparison of multiexcitation fluorescence and diffuse reflectance spectroscopy for the diagnosis of breast cancer (March 2003)

Nonmalignant (n = 36) and malignant (n = 20) tissue samples were obtained from breast cancer and breast reduction surgeries. These tissues were characterized using multiple excitation wavelength fluorescence spectroscopy and diffuse reflectance spectroscopy in the ultraviolet-visible wavelength range, immediately after excision. Spectra were then analyzed using principal component analysis (PCA) as a data reduction technique. PCA was performed on each fluorescence spectrum, as well as on the diffuse reflectance spectrum individually, to establish a set of principal components for each spectrum. A Wilcoxon rank-sum test was used to determine which principal components show statistically significant differences between malignant and nonmalignant tissues. Finally, a support vector machine (SVM) algorithm was utilized to classify the samples based on the diagnostically useful principal components. Cross-validation of this nonparametric algorithm was carried out to determine its classification accuracy in an unbiased manner. Multiexcitation fluorescence spectroscopy was successful in discriminating malignant and nonmalignant tissues, with a sensitivity and specificity of 70% and 92%, respectively. The sensitivity (30%) and specificity (78%) of diffuse reflectance spectroscopy alone was significantly lower. Combining fluorescence and diffuse reflectance spectra did not improve the classification accuracy of an algorithm based on fluorescence spectra alone. The fluorescence excitation-emission wavelengths identified as being diagnostic from the PCA-SVM algorithm suggest that the important fluorophores for breast cancer diagnosis are most likely tryptophan, NAD(P)H and flavoproteins.