Nickel,copper and manganese hexacyanoferrate with poly(3,4-ethylenedioxythiophene) hybrid film modified electrode for selectively determination of ascorbic acid

The NiHCF-PEDOT, CuHCF-PEDOT and MnHCF-PEDOT films were prepared on glassy carbon electrode (GCE) by multiple scan cyclic voltammetry and characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM) techniques. The advantages of these films are demonstrated for selectivity detection of ascorbic acid using cyclic voltammetry and amperometric method. Interestingly, the NiHCF-PEDOT and CuHCF-PEDOT modified electrodes exhibited a wide linear response range (5 × 10⁻⁶−3 × 10⁻⁴ M, R ² = 0.9973 and 1.8 × 10⁻³−1.8 × 10⁻² M, R ² = 0.9924). The electrochemical sensors facilitated the oxidation of AA but not responded to other electroactive biomolecules such as dopamine, uric acid, H₂O₂, glucose. The difference is MnHCF-PEDOT/GCE that no response to AA. In addition, the NiHCF-PEDOT and CuHCF-PEDOT modified electrodes exhibited a distinct advantage of simple preparation, specificity, stability and reproducibility.     

Voltage-controlled optical switch in planar nematic liquid crystal film

This study presents an integrated device that consists of a directional coupler and an electro-optic switch. The device is designed to include a nematic liquid crystal cell, comprising a grating-like electrode. Applying the appropriate voltage to the cell yields a periodically distributed refractive index. An incident polarized beam will couple to an adjacent channel if it is parallel to the channel. The coupling efficiency is controlled by applied voltage. An obliquely injected polarized beam will be reflected and refracted in the channel, and propagated along a curved path. The route of the beam can be controlled by applying the voltage. A multiport routing was achieved for voltage modulation. In addition, the distribution of refractive index is also investigated by employing conoscopic technique experimentally and numerically.     

Numerical simulation of blue InGaN light-emitting diodes with polarization-matched AlGaInN electron-blocking layer and barrier layer

The effect of polarization-matched AlGaInN electron-blocking layer and barrier layer on the optical performance of blue InGaN light-emitting diodes is numerically investigated. The polarization-matched AlGaInN electron-blocking layer and barrier layer are employed in an attempt to reduce the polarization effect inside the active region of the light-emitting diodes. The simulation results show that the polarization-matched AlGaInN electron-blocking layer is beneficial for confining the electrons inside the quantum well region. With the use of both polarization-matched AlGaInN electron-blocking layer and barrier layer, the optical performance of blue InGaN light-emitting diodes is greatly improved due to the increased overlap of electron and hole wavefunctions. The method proposed in this paper can also be applied to the light-emitting diodes operating in other spectral range.     

Development of a solid-phase microextraction/reflection-absorption infrared spectroscopic method for the detection of chlorinated aromatic amines in aqueous solutions.

In this paper, the reflection-absorption infrared (IR) spectroscopic method combined with the principle of solid-phase micro-extraction (SPME) is proposed to detect chlorinated aromatic amines in aqueous solutions. This proposed method provides simplicity in both the optical system and equipment setup. Compared to the SPME/attenuated total reflection-IR method, this method reduces the cost for internal-reflection elements and optical systems. Meanwhile, it has no SPME/transmission IR method problems, which require high polymer film preparation techniques to obtain a standing film that has no physical/chemical property changes when immersed in an aqueous solution. The typical linear coefficients obtained using this method for chloroanilines in aqueous solutions are around 0.995 and the detection can be lower than 100 ppb. The thickness of the hydrophobic film is relatively important in the SPME/ATR-IR method, but the uncertainty caused by the film thickness can be partially eliminated in the proposed method. This is because the IR signals are proportional to the film thickness and can be corrected using hydrophobic film signals. The low detection limits have also indicated that this proposed method can compete with the currently existing IR methods, but allowing much simpler detection.     

Sensitivity enhancement for nitrophenols using cationic surfactant-modified activated carbon for solid-phase extraction surface-assisted laser desorption/ionization mass spectrometry

Previous work has demonstrated that a combination of solid-phase extraction with surface-assisted laser desorption/ionization (SPE-SALDI) mass spectrometry can be applied to the determination of trace nitrophenols in water. An improved method to lower the detection limit of this hyphenated technique is described in this present study. Activated carbon powder is used as both the SPE adsorbent and the SALDI solid in the analysis by SPE-SALDI. The surface of the activated carbon is modified by passing an aqueous solution of a cationic surfactant through the SPE cartridge. The results demonstrate that the sensitivity for nitrophenols in the analysis by SPE-SALDI can be improved by using cationic surfactants to modify the surface of the activated carbon. The detection limit for nitrophenols is about 25 ppt based on a signal-to-noise ratio of 3 by sampling from 100 mL of solution.     

Asymptotic theorems for estimating the distribution function under random truncation

Representation theorem and local asymptotic minimax theorem are derived for nonparametric estimators of the distribution function on the basis of randomly truncated data. The convolution-type representation theorem asserts that the limiting process of any regular estimator of the distribution function is at least as dispersed as the limiting process of the product-limit estimator. The theorems are similar to those results for the complete data case due to Beran (1977, Ann. Statist., 5, 400–404) and for the censored data case due to Wellner (1982, Ann. Statist., 10, 595–602). Both likelihood and functional approaches are considered and the proofs rely on the method of Begun et al. (1983, Ann. Statist., 11, 432–452) with slight modifications.Division of Biostatistics, School of Public Health, Columbia Univ.     

On the stereochemistry of photoaddition between α,β-unsaturated ketones and olefins. III.

The α,β-unsaturated ketone $\text{1}$ yields with allene the photocycloadduct $\text{3}$ predicted by our empirical photoaddition rule and the byproduct 7. The formation of this material may be rationalized by the sequence $\text{1}$ → $\text{4}$ → $\text{5}$ → $\text{6}$ → $\text{7}$. The isomeric ketone $\text{2}$ is unreactive under the same conditions, since α addition is prohibited by the rule and β addition is severely blocked.     

Determination of Trace Iron(II) in the Presence of Iron(III)

The determination of trace iron(II) is usually interfered by the presence of iron(III) when ortho-phenanthroline colorimetric method is used. In this report a chromogenic reagent which contains ortho-phenanthroline-EDTA mixture has been developed to decrease the interference of ferric ion after adjusting the acidity of sample at 0.1 N by adding the sulfuric acid. The procedure is also simplified by introducing sulfamate buffer solution (pH= 1.5) without adjusting the acidity of sample with sulfuric acid. If iron(III) is not present in the sample, this method is also applicable. The comparative results are exhibited for the present method and the conventional o-phenanthroline method.