Preparation, characterization, and electrochemical performances of carbon-coated TiO2 anatase

Several carbon-coated anatase TiO₂ samples have been prepared by impregnation with lactose as carbon precursor and annealed at different temperatures (650 and 700 °C). X-ray diffraction was carried out to study the anatase to rutile phase transition and to evaluate the crystallite size. Scanning electron microscopy was utilized to evaluate the morphology, and transmission electron microscopy was used to show the distribution and nature of the carbon coating. The galvanostatic measurements and cyclic voltammetry revealed better kinetics, cycling stability, and high rate capacity for the carbon-coated materials when compared with the noncoated ones.     

Optimization of smoothing process-the method to improve calibration in voltammetry Part I. Simulated voltammograms

The problem of the optimal choice of algorithmic filter and the evaluation of smoothing effects in voltammetry is studied. The basic idea of the optimization is an investigation of the improvement of the calibration and the recovery functions parameters during denoising process. The evaluation routine yields the answer in numerical form and may be used for the best filter selection. In order to show how the proposed criterion operates, it was applied to the simulated curves which were peak shaped and distorted by noise of different type and amplitude. Results were compared to the other method based on difference between true and denoised signal. The described tool may be applied for the automatic signal processing.     

The Cyclic Renewable Mercury Film Silver Based Electrode for Determination of Uranium(VI) Traces Using Adsorptive Stripping Voltammetry

The new cyclic renewable mercury film silver based electrode (Hg(Ag)FE), applied for the determination of uranium(VI) traces using differential pulse adsorptive cathodic stripping voltammetry (DP AdCSV) is presented. The Hg(Ag)FE electrode with a surface area adjustable from 1.1 to 12 mm² is characterized by very good surface reproducibility (≤2%) and long‐term stability (more than 2 thousand measurement cycles). The mechanical refreshing of mercury film is realized in the simple constructed device, in a time shorter than 1–2 seconds. The effects of various factors such as: preconcentration potential and time, pulse height, step potential and supporting electrolyte composition are optimized. The calibration graph is linear from 0.4 nM (95 ng L^?1) to 250 nM (60 μg L^?1) for an accumulation time of t_acc=20 s, with correlation coefficient of 0.9996. For a Hg(Ag)FE with a surface area of 2.7 mm² the detection limit for an accumulation time of 120 s is as low as 12 ng L^?1. The repeatability of the method at a concentration level of the analyte as low as 2.4 μg L^?1, expressed as RSD is 2.5% (n=7). The proposed method was successfully applied and validated by studying the recovery of U(VI) from spiked river water and sediment samples.     

Yeast-based carbon paste bioelectrode for ethanol

An amperometric bioelectrode for primary alcohols based on the incorporation of yeasts into the carbon paste matrix is reported. The response is based on the activity of alcohol dehydrogenase in yeasts. The intimate contact between the biocatalytic and sensing sites results in short response times. The addition of a redox-mediating hexacyanoferrate (III) ion greatly facilitates the detection of the enzymatically produced NADH. The effects of operating potential, carbon paste composition, concentration of coenzyme or redox mediator and other parameters are explored for optimum analytical performance. The dynamic properties of this electrode are exploited for detection in flow-injection systems, with a detection limit of 2 × 10^?6 M (9 ng) of ethanol. The relative standard deviation for repetitive injections of a 1× 10^?3 M ethanol solution over a 100-min period is 2.8%. Applicability to alcoholic beverages is illustrated. The trend in sensitivity toward different alcohols is in agreement with the known biospecificity of yeast alcohol dehydrogenase.     

The sequential injection system with adsorptive stripping voltammetric detection

Two sequential injection systems have been developed for adsorptive stripping voltammetric measurement. One is for substances adsorbing at mercury, e.g. riboflavin. In this case, a simple arrangement with only sample aspiration is needed. Reproducibility was 3% and detection limit 0.07 μM. The measuring system was applied to determination of riboflavin in vitamin pills and to study the photodegradation process of riboflavin in aqueous solutions. In the second case, metal ions were determined. They have to be complexed before deposition on the mercury surface. Thus, both the sample and the ligand have to be aspirated in the system. In this case, the reproducibility was ≈6% and the detection limit <0.1 ppm for cadmium, lead and copper when complexation with oxine was used. Dimethylglyoxime was used in determination of nickel and cobalt and nioxime complexes were used in determination of nickel and copper. With these complexing agents, the reproducibility was the same as with oxine, but the metals could be determined at concentrations lower than 0.01 ppm. Application of two ligands in a SIA system with AdSV detection was also studied. Simultaneous determination of copper, lead, cadmium and cobalt was possible by using oxine and dimethylglyoxime. Copper and nickel were simultaneously determined by using dimethylglyoxime and nioxime.     

Intervalence involvement of bridging ligand vibrations in hexaruthenium mixed-valence clusters probed by resonance Raman spectroscopy

Resonance Raman spectroscopy, performed using spectroelectrochemistry and with excitation in the intervalence bands of three pyrazine-bridged, mixed-valence dimers of trinuclear ruthenium clusters, shows resonant enhancement of symmetric bridging ligand modes. The resonant enhancements and frequency shifts of these bridging ligand modes are observed as a function of varying electronic communication between charge sites, and they show that a three-state vibronic model which explicitly includes the participation of the bridging ligand is needed to explain the spectroscopic behavior of these near-delocalized complexes.     

Coevaporation phosphorus doping in Si grown by molecular beam epitaxy

Phosphorus-doped Si epilayers with bulk-like mobilities were grown by molecular beam epitaxy (Si-MBE) by coevaporation of phosphorus from a tin phosphide source. The behaviour of P doping as a function of growth parameters and of potential enhanced doping indicates a non-unity, almost growth-temperature independent incorporation efficiency with negligible surface segregation -a unique combination among coevaporated dopants in Si-MBE.     

Scheduling unit — time tasks on flow — shops under resource constraints

We consider the problem of scheduling tasks on flow shops when each task may also require the use of additional resources. It is assumed that all operations have unit lengths, the resource requirements are of 0–1 type and there is one type of the additional resource in the system. It is proved that when the number of machines is arbitrary, the problem of minimizing schedule length is NP-hard, even when only one unit of the additional resource is available in the system. On the other hand, when the number of machines is fixed, then the problem is solvable in polynomial time, even for an arbitrary number of resource units available. For the two machine case anO(n log ₂ ² n) algorithm minimizing maximum lateness is also given. The presented results are also of importance in some message transmission systems.