Simultaneous dual-wavelength-band common-path swept-source optical coherence tomography with single polygon mirror scanner

We report a novel (to the best of our knowledge) simultaneous 1310/1550 two-wavelength band swept laser source and dual-band common-path swept-source optical coherence tomography (SS-OCT). Synchronized dual-wavelength tuning is performed by using two laser cavities and narrowband wavelength filters with a single dual-window polygonal scanner. Measured average output powers of 60 and 27 mW have been achieved for the 1310 and 1550 nm bands, respectively, while the two wavelengths were swept simultaneously from 1227 to 1387 nm for the 1310 nm band and from 1519 to 1581 nm for the 1550 nm band at an A-scan rate of 65 kHz. Broadband wavelength-division multiplexing is used for coupling two wavelengths into a common-path single-mode GRIN-lensed fiber probe to form dual-band common-path SS-OCT. Simultaneous OCT imaging at 1310 and 1550 nm is achieved. This technique allows for in vivo high-speed OCT imaging with potential application in functional (spectroscopic) investigations.     

Measurement-induced decoherence in electronic interferometry at nanoscale

We introduce a theoretical formalism describing a wide class of ‘Which Path’ experiments in mesoscopic/nanoscopic transport. The physical system involves a mesoscopic interferometer (e.g. an Aharonov-Bohm ring with embedded dots or a side-coupled quantum dot) which is electrostatically coupled to a nearby quantum point constriction. Due to the charge sensing effect the latter acts as a charge detector. Therefore the interference pattern can be monitored indirectly by looking at the current characteristics of the detector as shown in the experimental work of Buks et al. [E. Buks, R. Schuster, M. Heiblum, D. Mahalu, V. Umansky, Nature (London) 391 (1998) 871]. We use the non-equilibrium Green-Keldysh formalism and a second order perturbative treatment of the Coulomb interaction in order to compute the relevant transport properties. It is shown that in the presence of the Coulomb interaction the current through the detector exhibits oscillations as a function of the magnetic field applied on a single-dot AB interferometer. We also discuss the dependence of the visibility of the Aharonov-Bohm oscillations on the gate potential applied to the dot.     

Hydrodynamic voltammetry at an interdigitated electrode array in a flow channel: Part I. Numerical simulation

This paper describes the numerical simulation of convective diffusion at an interdigitated electrode array, consisting of multiple pairs of microelectrodes held at alternating applied potentials on one wall of a flow channel. The downstream microelectrode of each pair detects species generated at the upstream microelectrode. Concentration profiles in the channel, amperometric response, and signal-to-noise ratios for the detector electrodes are calculated. The simple backward implicit finite difference (BIFD) simulation approach is applicable for a wide range of channel conditions. The upper number of electrode pairs treatable is limited only by computational time. The agreement of the simulation with previous results for a single pair of electrodes under comparable conditions is very good. Substantial improvements in signal-to-noise ratio are predicted for the multi-electrode interdigitated electrode array relative to a single generator-detector pair of equal overall area. Electrode dimensions are discussed for optimum signal/noise ratio. Relative enhancement increases significantly with the number of generator-detector pairs.     

Analysis of pyridines in mainstream cigarette smoke

A new technique has been developed for the quantitative analysis of pyridines in mainstream cigarette smoke using a GC-MS technique. For analysis, 10 cigarettes are smoked using conditions based on US Federal Trade Commission recommendations. The smoke is collected in a water trap and analyzed using a GC-MS technique. A standard or a fast GC separation can be applied for the analysis. The standard separation was followed by MS detection using selected ion monitoring (SIM) acquisition on a quadrupole instrument. The fast GC was followed by MS detection with total ion acquisition on a time-of-flight instrument. The levels of pyridine depend on the type of cigarette: for a full flavor cigarette pyridine is as high as 18.0 microg/cigarette (cig.). and for an ultra light cigarette is about 3.0 microg/cig. Substituted pyridines vary between 5.0 microg/cig. to 0.1 microg/cig. for a full flavor cigarette, and between 0.2 microg/cig. and a few ng/cig. for an ultra light cigarette. The reproducibility of the technique is very good, with less than 7-8% RSD in both separation procedures for most of the analyzed compounds.     

Quantitative determination of some food dyes using digital processing of images obtained by thin-layer chromatography

A high-performance thin-layer chromatographic method combined with image processing of scanned chromatograms was developed for the determination of some food dyes (tartrazine, azorubine and Sunset Yellow) in different products. Porous silica gel with 3-aminopropyl functional groups attached to the matrix was used as stationary phase and a mixture of isopropanol, diethyl ether and ammonia (2:2:1, v/v/v) formed the mobile phase. Quantitative evaluation was performed using special-purpose software. The linearity of the analytical procedure was sustained by the numerical parameters such as correlation coefficient (0.9952-0.9980) and standard error of determination (0.03-0.20). The limits of detection were found to be within the range of 5.21-9.34 ng/spot, and the limits of quantification between 10.21 and 18.09 ng/spot. Recovery studies performed on two levels of concentration gave values between 96.39 and 102.76%. These results show that the regression approach provides rigorous and realistic detection and quantification limits and as a consequence can be routinely applied to other analytical systems. This method does not require expensive analytical instruments compared with classical densitometry and provides a reliable quantitative evaluation with minimum of time.     

An electrochemical and structural investigation of silicon nanowires as negative electrode for Li-ion batteries

The electrochemical and structural responses of silicon nanowires deposited by chemical vapor deposition are investigated. Transmission electron microscopy and X-ray diffraction experiments show the electrochemical lithiation of SiNWs is not a quantitative process in good agreement with cycling experiments performed as a function of cycling limits. The SiNWs are not deeply lithiated as revealed by TEM micrographs. Our results suggest the existence of two well-defined lithiation steps, first at ∼0.2 V into amorphous silicon and then into crystalline silicon at ∼0.1 V. Cycling SiNWs above 100 mV avoid the lithiation of c-Si which preserves the silicon 3-D architecture and results in good cycling performances. A stable capacity value of ∼500 mAh g⁻¹ is achieved over at least 50 cycles.     

An advanced multivariate statistical approach to study coastal sediment data

The present paper deals with the application of classical and fuzzy principal components analysis to a large data set from coastal sediment analysis. Altogether 126 sampling sites from the Atlantic Coast of the USA are considered and at each site 16 chemical parameters are measured. It is found that four latent factors are responsible for the data structure (“natural”, “anthropogenic”, “bioorganic”, and “organic anthropogenic”). Additionally, estimating the scatter plots for factor scores revealed the similarity between the sampling sites. Geographical and urban factors are found to contribute to the sediment chemical composition. It is shown that the use of fuzzy PCA helps for better data interpretation especially in case of outliers.     

Ultrasound assisted reactions of steroid analogous of anticipated biological activities

A new, fast, efficient and general method for preparation of steroid analogous of anticipated biological activity under ultrasound irradiation and classical heating is reported. The reaction pathway involves two steps: quaternization of phthalazine heterocycle followed by a 3+2 dipolar cycloaddition of cycloimmonium ylides to dienophiles. Under ultrasound the reaction time decreases substantially, the yields are higher, the reaction conditions are milder. A comparative study ultrasound verses classical heating has been done.     

Solvent-reagent effect in chemical detection of energetic materials type contaminants

Present study extended the list of solvent and reagents appropriate to use for the colorimetric detection and semi quantitative analysis of various energetic compounds. The new reagents used in this study include DMSO as solvent/reagent, and tetramethylammonium hydroxide and tetrabutylammonium hydroxide for the generation of a basic medium. The advantages of these reagents vs. older procedures are discussed in this paper. Also, a standardized procedure for the analysis of several classes of energetic compounds has been developed, allowing an excellent practical application of the recommended method. The influence of different solvents on the changes in the UV/VIS spectra were evaluated and an attempt to interpret the resulting absorption UV spectra based on quantum-chemical calculations has been done. The article is published in the original.     

Dependence of the distribution constant in liquid–liquid partition equilibria on the van der Waals molecular surface area

The direct calculation of free energy of interactions between a solute j and two immiscible liquids shows a linear dependence between the (logarithm of) the distribution constant in liquid–liquid partition equilibrium log K_j and the van der Waals surface area of the solute. The study provides a thermodynamic proof for the formula log K_BA,j = c₁ log K_BC,j + c₂ that describes the linear dependence between (the logarithm of) the distribution constant for a solute j in a solvent system (B/A) and (the logarithm of) the distribution constant for the same solute in a different solvent system (B/C). This relation has been well proven by various experimental studies and it is frequently used in liquid chromatographic separations as well as in liquid–liquid extractions, but was not explained previously based on thermodynamic results. The theory was verified using the prediction of octanol/water distribution constants log K_ow for a wide range of molecules, including hydrocarbons and compounds with a variety of functional groups. The results have also been verified for the distribution constants in other solvent systems. The expression for the distribution constant obtained in this study also gives a theoretical base for the additive fragment methodology used for the prediction of log K_ow.