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.     

Palladium-ruthenium alloy nanoparticles dispersed on CoWO4-doped graphene for enhanced methanol electro-oxidation

Highly dispersed nanoparticles (NPs) of Pd and Pd-Ru alloys on the 10 wt% CoWO₄-doped GNS (graphene nano sheets) support have been obtained by a microwave-assisted polyol reduction and investigated for their application as efficient electrode materials for methanol oxidation reaction (MOR). Structural and electrocatalytic surface characterization of hybrid materials were carried out by XRD, TEM, XPS, cyclic voltammetry and chronoamperometry. Pure CoWO₄ and CoWO₄-doped GNS follow the monoclinic crystal structure and the Pd NPs (6–7 nm) dispersed on CoWO₄-doped GNS follow the face-centered cubic crystal structure. It is observed that with the increase of Pd loading from 5 to 20 mg on the support, the onset potential (E_op) for MOR shifts negatively and the MOR current density increases, the magnitude of shift in E_op and increase in the MOR peak current density being the greatest in the case of 15 mg Pd loading. Introduction of Ru from 0.6 to 2.0 mg into 15 mg Pd on the catalyst support, the apparent activity of the active catalyst, 15Pd/10 wt% CoWO₄-GNS improved further, the magnitude of improvement, however, being the greatest (≈50%) with 1.0 mg Ru. Thus, novel 15Pd-1.0Ru/10 wt%CoWO₄-doped GNS can be a promising electrode material for MOR in alkaline solutions.     

Nitrogen-doped graphene supported Cu-Ag2.9 nanoparticles as efficient methanol tolerant cathode for oxygen reduction

Highly dispersed nanoparticles (NPs) of Cu, Ag and their composites are obtained on nitrogen-doped graphene nanosheets (N-GNS) using a microwave-assisted polyol reduction method. Structural, electrochemical and electrocatalytic surface characterization of materials have been carried out by TEM, XRD, XPS, cyclic (CV) and linear sweep (LSV) voltammetries. The study shows that the crystallites of the Cu-Ag composite follow the face-centered cubic (fcc) crystal structure. Further, the catalytic activities of Cu/N-GNS and Ag/N-GNS towards oxygen reduction reaction (ORR) are greatly enhanced when Cu and Ag are dispersed on the N-GNS surface in 1:2.9 M ratio. The active composite material does not oxidize methanol practically and has outstanding stability under ORR condition.     

Prevalence and characterization of typical and atypical Escherichia coli from fish sold at retail in Cochin, India

Escherichia coli is a common contaminant of seafood in the tropics and is often encountered in high numbers. The count of E. coli as well as verotoxigenic E. coli O157:H7 was estimated in 414 finfish samples composed of 23 species of fresh fish from retail markets and frozen fish from cold storage outlets in and around Cochin, India. A total of 484 presumptive E. coli were isolated, and their indole-methyl red-Voges-Proskauer-citrate (IMViC) pattern was determined. These strains were also tested for labile toxin production by a reverse passive latex agglutination method and checked for E. coli serotype O157 by latex agglutination with O157-specific antisera. Certain biochemical marker tests, such as methylumbelliferyl-beta-glucuronide (MUG), sorbitol fermentation, decarboxylase reactions, and hemolysis, which are useful for screening pathogenic E. coli, were also carried out. Results showed that 81.4% of the E. coli isolates were sorbitol positive. Among this group, 82% were MUG positive, and 14.46% of the total E. coli isolates showed human blood hemolysis. None of the isolates were positive for agglutination with E. coli O157 antisera nor did any produce heat-labile enterotoxin. This study indicates that typical E. coli O157 or labile toxin-producing E. coli is absent in the fish and fishery environments of Cochin (India). However, the presence of MUG and sorbitol-negative strains that are also hemolytic indicates the existence of aberrant strains, which require further investigation.     

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.     

Antimicrobial activity of neutralized extracellular culture filtrates of lactic acid bacteria isolated from a cultured Indian milk product (‘dahi’)

Neutralized extracellular culture filtrate obtained from isolates of Lactobacillus acidophilus, Lactobacillus delbruecki ssp. bulgaricus, Lactobacillus salivarius and Lactococcus lactis ssp. lactis from ‘dahi’ showed weal to moderate inhibition of Staphylococcus aureus, Bacillus cereus, Escherichia coli, Bacillus brevis, Bacillus circulans, Bacillus coagulans, Bacillus laterosporus, Bacillus subtilis and Pseudomonas aeruginosa when tested by the diffusion agar well assay method. The effective minimum quantity of lactic culture filtrates required to obtain complete inhibition of an inoculum of 10³ cfu/ml of the bacteria tested was between 20 and 26% (vol/vol), as determined by the agar incorporation method. Neutralized extracellular culture filtrate of these lactic cultures added at a level of 10% in sterile, 10% reconstituted non-fat dry milk was able to either suppress or retard growth of selected bacterial cultures when incubated at 37°C for 24 h. This study indicated the antimicrobial activity of dahi and the potential of using neutralized extracellular culture filtrate of lactic acid bacteria in the biopreservation of foods.     

Forward and Inverse Potential Field Solutions for Cardiac Strands of Cylindrical Geometry

This paper deals with the classical forward and inverse volume conductor field problems associated with the isolated active cardiac muscle preparations of cylindrical geometry. Specifically, these are the Purkinje fiber, the atrial trabeculum, and the (idealized) single atrial cell. The electrical behavior of the multicellular preparations (Purkinje strand and atrial trabeculum) is modeled in terms of the electrical activity of an equivalent single cell, with a representative membrane that separates an anisotropic intracellular medium from an isotropic extracellular medium. The isolated single atrial fiber is considered an interesting special case anid is modeled in an idealized sense as a long cylindrical cell with an isotropic internal medium. A model based on potential theory is developed for the equivalent cardiac cell; it is based on a solution of Laplace's equation in the media of interest, subject to appropriate boundary conditions. The solution for potential at an arbitrary point in the extracellular medium is in the form of a Fourier integral; the equation is subsequently reformulated into a more convenient computational form using a discrete Fourier transform (DFT) method. Implementation of this method, using a fast Fourier transform (FFT) technique, results in a fast and efficient numerical algorithm for the calculation of volume conductor potentials. A benefit of this approach is that the classical forward and inverse problems in electrophysiology may be viewed as equivalent filtering problems.     

Smooth moving punch in an initially stressed transversely isotropic magnetoelastic medium due to shear wave

This study investigates the effect of a semi-infinite smooth moving punch due to shear wave propagation in initially stressed, magnetoelastic, transversely isotropic material. The Wiener–Hopf technique has been employed to determine the closed form expression of dynamic stress concentration due to punch with a load of constant intensity. The substantial effects of magnetoelastic coupling parameters, horizontal and vertical compressive/tensile initial stress, and anisotropy on dynamic stress concentrations has been remarkably traced out. Numerical computations and graphical illustrations, along with comparative study, have been executed for three distinct models: when the strip is comprised of Zinc, Beryl material having hexagonal symmetry, and simply isotropic material.     

Field performance of a novel passive bioaerosol sampler using polarized ferroelectric polymer films

Passive bioaerosol samplers can improve environmental and health protection by enhancing the practicality and cost-effectiveness of air sampling. Here, we present the outdoor field testing of a novel, passive bioaerosol sampler, the Rutgers Electrostatic Passive Sampler (REPS), based on the use of polarized, ferroelectric polymer film (poly(vinylidene fluoride)). Four 10-day-long field campaigns were conducted to compare total (culturable + non-culturable) and culturable bioaerosol collection efficiencies of REPS to passive samplers (PTFE settling filters and agar settling plates). These collection efficiencies were calculated relative to performance of an active, reference Button Sampler. Compared to passive PTFE filters, which exclusively rely on gravitational particle deposition, REPS collected a seven-fold higher total microorganism quantity. Relative to the Button Sampler, REPS collected 25% of the total number of bacteria and fungi and 65% of the culturable bacteria. Furthermore, REPS achieved this performance without any air movers, pumps, batteries, or external power. Since the Button Samplers operated at 4 L/min, REPS was calibrated to have equivalent sampling rates of 2.6 L/min and 1.0 L/min for culturable bacteria and total microorganisms, respectively. These results suggest that REPS can passively collect airborne microorganisms, including culturable bacteria, with high efficiency over long-term sampling durations. REPS can provide better preservation of bacterial culturability because it has no active airflow, which desiccates microbes in active samplers. Since there are limited options available for long-term, unattended bioaerosol sampling, REPS can complement currently available bioaerosol sampling technologies for numerous environmental health applications, such as exposure assessment for epidemiology and monitoring aeroallergen trends.

© 2017 American Association for Aerosol Research     

Design and development of a self-contained personal electrostatic bioaerosol sampler (PEBS) with a wire-to-wire charger

Here, we present a concept of a personal electrostatic bioaerosol sampler (PEBS), which is an open channel collector consisting of a novel wire-to-wire particle charger and a collection section housing a double-sided and removable metal collection plate and two quarter-cylinder ground electrodes. The charger consists of a tungsten wire (25.4 mm long and 0.076 mm in diameter) connected to high voltage and positioned in the center of the charging section (a cylinder 50.8 mm long and 25.4 mm in diameter); a ring of stainless steel wire 0.381 mm in diameter surrounds the hot electrode at its midpoint and is grounded. The newly designed wire-to-wire charger produces lower ozone concentrations compared to traditional wire-to-plate or wire-to-cylinder charger designs. The particles captured on the collection plate are easily eluted using water or other fluids. The sampler was iteratively optimized for optimum charging and collection voltages, and collection electrode geometry. When tested with polystyrene latex particles ranging from 0.026 µm to 3.1 µm in diameter and 10 L/min collection flow rate, the sampler's collection efficiency was approximately 70%–80% at charging and collection voltages of +5.5 kV and ?7 kV, respectively. The PEBS showed this collection efficiency at sampling times ranging from 10 min to 4 h. Preliminary tests with Bacillus atrophaeus bacterial cells and fungal spores of Penicillium chrysogenum showed similar collection efficiency. The use of a unique wire-to-wire charger resulted in ozone production below 10 ppb. Due to low ozone emissions, this sampler will allow maintaining desirable physiological characteristics of the collected bioaerosols, leading to a more accurate sample analysis.

© 2017 American Association for Aerosol Research