Silver(I)-selective coated-wire electrode based on an octahydroxycalix[4]arene derivative.

The performance of octahydroxycalix[4]arene derivative used as a neutral carrier for silver polymeric membrane electrode was studied. The sensor gave a good Nernstian response of 58 +/- 1 mV per decade for silver ion in the activity range 3.3 x 10(-6) to 3.3 x 10(-2) M Ag+. The limit of detection reached 2.1 x 10(-6) M Ag+ and exhibited high selectivity for silver ion against the alkali, alkaline earth and transition metal ions. The sensor can be used in wide pH range from 1.5 to 6.5. The response time of the sensor is less than 20 s. The potentiometric sensor was used as the indicator electrode in the titration of Ag+ ions by sodium chloride solution.     

A Complete Classification of Curvature Collineations of Cylindrically Symmetric Static Metrics

Curvature collineations are symmetry directions for the Riemann tensor, as isometries are for the metric tensor and Ricci collineations are for the Ricci tensor. Complete listings of many metrics possessing some minimal symmetry have been given for a number of symmetry groups for the latter two symmetries. It is shown that a claimed complete listing of cylindrically symmetric static metrics by their curvature collineations [1] was actually incomplete and is completed here. It turns out that in this complete list, unlike the previous claim, there are curvature collineations that are distinct from the set of isometries and of Ricci collineations. The physical interpretation of some of the metrics obtained is given.     

Deactivation of vibrationally excited CD3H using laser-induced fluorescence

Infrared fluorescence observed after exciting to ν₆ (ν=1) of CD₃H with a Q-switched CO₂ laser yields the exponential deactivation rate constant of 0.84 ms^?1 torr^?1. Rate constants for deactivation of CD₃H by rare gases vary from 1.4 (for He) to 0.029 (for Xe) ms^?1 torr^?1.     

On a property of conformal spacetimes

A generalisation of Carter's Circular metrics has been used for working out N potentials. It is pointed out here that the conformal extension of these metrics has the interesting property that the conformal time-like Killing vector depends only on time.

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Zusammenfassung Bekanntlich existieren Raum-Zeit-Mannigfaltigkeiten, welche keine zeitartige Isometrie zulassen. In der vorliegenden Arbeit wird gezeigt: Falls die Metriken diese Raum-Zeit-Mannigfaltigkeiten als spezielle Verallgemeinerung der Carterschen zirkularen Metriken so gewählt werden, daß sie einen konformen zeitartigen Killing-Vektor zulassen, dann hängt dieser Vektor nur von der Zeit ab.

     

Rapid interspecies energy flow between vibrationally excited SF6 and the asymmetric stretch of N2O

Rapid, selective collision-dependent excitation of N₂O following pumping of SF₆ with a CO₂ laser is reported. The N₂O fluorescence rise depends on the pressure of each component and is dominated by the SF₆-dependent contribution of 2290 ms^?1 Torr^?1. The subsequent fall is governed by V→V processes among SF₆ vibrational modes.     

N-Iodosuccinimide (NIS) as a mild and highly chemoselective catalyst for deprotection of tert-butyldimethylsilyl ethers

A variety of alcoholic TBDMS (t-butyldimethylsilyl) ethers are easily removed in excellent yields by treatment with a catalytic amount of N-iodosuccinimide (NIS, 5 mol %) in methanol. This method is able to deprotect TBDMS ethers of alcohols in the presence of TBDMS ethers of phenols.     

Electrochemical technique for the determination of fractal dimension of dental surfaces

Fractal dimension of a carious tooth surface was determined using an electrochemical method. The method was based on time-dependent diffusion towards electrode surfaces, which is one of the most useful and reliable methods for the determination of fractal dimension of electrode surfaces. For this purpose, the tooth was covered with a gold layer, which acted as an electrode in electrochemical experiments. It is suggested that the fractal dimension can be used as a quantitative measure of the state of dental surfaces. The method presented demonstrates the power of electrochemical techniques for the determination of fractal dimension of surface of non-conducting objects.     

Removal of oxygen from silicon by electron beam melting

Small amounts of multicrystalline silicon were melted in an electron beam furnace in different experimental conditions in order to investigate the oxygen evaporation behavior during the electron beam melting (EBM) process. The oxygen content level before and after EBM was determined by secondary ion mass spectroscopy. The oxygen content was reduced from 6.177 to 1.629 ppmw when silicon was melted completely at 15 kW with removal efficiency up to 73.6 %. After that, it decreased continually to <0.0517 ppmw when the refining time exceeded 600 s with a removal efficiency of more than 99.08 %. During the melting process, the evaporation rate of silicon is 1.10 × 10^?5 kg/s. The loss of silicon could be reduced up to 1.7 % during oxygen removal process to a desirable figure, indicating EBM is an effective method to remove oxygen from silicon and decrease the loss of silicon.