Synthesis of luminescent yttrium silicate materials by the sol-gel method

The sol-gel method is shown to be useful for obtaining luminescent yttrium silicate-based materials with performance characteristics superior to commercial analogs. The effect of the phase composition of sol-gel luminophors on the spectral luminescence parameters is analyzed. A way to prepare materials with controlled granulometric composition is proposed.Translated from Steklo i Keramika, No. 11, pp. 23–26, November, 1996.     

Measurement of the peritectic phase composition in the Sn-Cd system through directional solidification techniques

Short Communication

Measurement of the peritectic phase composition in the Sn-Cd system through directional solidification techniques     

Fourier-transform evaluation of phase data in spatially phase-biased TV holograms

TV holograms for spatial phase stepping are formed with a small angular offset between the object and the reference beams to give a spatial frequency bias to the pattern recorded by the TV camera. It is common to set the bias so that there is a 90° or 120°phase shift between adjacent pixels and to use the irradiance of three or more adjacent pixels to evaluate the phase of the interference. We report the Fourier-transform evaluation of such recordings to obtain their phase data. We also demonstrate the direct calculation of the phase difference between successive recordings without intermediate calculation of the random phase of each hologram. This technique is proposed as an approach to pulsed TV holography.     

Method to derive ocean absorption coefficients from remote-sensing reflectance

A method to derive in-water absorption coefficients from total remote-sensing reflectance (ratio of the upwelling radiance to the downwelling irradiance above the surface) analytically is presented. For measurements made in the Gulf of Mexico and Monterey Bay, with concentrations of chlorophyll-a ranging from 0.07 to 50 mg/m(3), comparisons are made for the total absorption coefficients derived with the suggested method and those derived with diffuse attenuation coefficients. For these coastal to open-ocean waters, including regions of upwelling and the Loop Current, the results are as follows: at 440 nm the difference between the two methods is 13.0% (r(2) = 0.96) for total absorption coefficients ranging from 0.02 to 2.0 m(-1); at 488 nm the difference is 14.5% (r(2) = 0.97); and at 550 nm the difference is 13.6% (r(2) = 0.96). The results indicate that the method presented works very well for retrieval of in-water absorption coefficients exclusively from remotely measured signals, and that this method has a wide range of potential applications in oceanic remote sensing.     

Ohmic drop compensation in voltammetry: iterative correction of the applied potential

A new method of ohmic potential drop correction for use with potential step and sweep voltammetric methods is described. The method, iterative correction of the applied potential (ICAP), essentially replaces an electronic positive feedback correction with a digital positive feedback correction. This paper will present one form of the ICAP procedure, in which voltammetric current data acquired by a high-speed digital oscilloscope are used to iteratively generate a compensating potential waveform that is then synthesized by an arbitrary waveform generator. The ICAP method is advantageous for high-speed measurements, since many of the difficulties caused by electronic positive feedback compensation are eliminated.     

Detection and confirmation of N-nitrosodialkylamines using liquid chromatography-electrospray ionization coupled on-line with a photolysis reactor

Simultaneous detection and confirmation of several N-nitrosodialkylamines are accomplished by on-line coupling of a photolysis reactor with an HPLC-electrospray ionization mass spectrometer. Several parameters such as irradiation wavelength, irradiation time, mobile-phase composition, and pH, as well as different organic acid modifiers are investigated, and their impact on the detection of the N-nitrosodialkylamine-acid complex and its dissociative photolysis products is presented here. Additionally, the type of structural information obtained from the photolytic processes of N-nitrosodialkylamines is compared to that obtained by using in-source collision-induced dissociation. To demonstrate the potential of this technique, six N-nitrosodialkylamines are studied to determine the linearity of the response, the limits of detection and confirmation, and the reproducibility. The technique's versatility is also exhibited by utilizing negative-ion mode as a complementary means for analysis of the compounds. Finally, an illustrative application for N-nitrosodimethylamine analysis in beer is described.     

Microsecond pulsed glow discharge as an analytical spectroscopic source

A pulsed glow discharge, operating in the microsecond regime, has been found to be advantageous for the examination of solid samples. We have studied the spectroscopic response by atomic emission, absorption, fluorescence, and mass spectrometries. Results to date show enhanced efficiency for analytical response of the sputtered sample atoms. This type of discharge also permits acquisition of useful diagnostic information concerning glow discharge processes.     

New aspects in the microstructure of YBCO melt-textured high-Tc superconductors

The microstructure and phase constitution of bulk textured YBCO samples prepared by the modified MTG method in the longitudinal temperature gradient have been investigated. We found the existence of an unusual phase between stacked platelets. Microanalysis shows that this phase may be characterized as Y-143. This phase forms ellipsoid-like particles with a typical size about 0.05–2 which can play the role of effective pinning centers. The reason for the phase formation is discussed. We assume that this phase exists commonly in melt-textured samples prepared in the temperature field gradient.     

The axisymmetric crack problem in a non-homogeneous interfacial region between homogeneous half-spaces

In this paper, the axisymmetric crack problem in a non-homogeneous interfacial region between two homogeneous half-spaces is considered. It is assumed that the shear modulus varies continuously between that of the two half-spaces; and the shear modulus for the interface region is approximated by = ₀ e^mz. By using Hankel transform technique the problem is reduced to a pair of singular integral equations. The solutions of the problem are obtained for different material combinations and loading conditions; and modes I and II stress intensity factors, and the direction of a probable crack growth are calculated.     

Experimental and theoretical studies of the crossover behavior of the specific heat Cv,x of ethane,propane, and their mixture at critical isochores

The specific heat at constant volume, C_v, of propane, and mixture with a concentration ofx=0.0081 cool fraction of propane was measured along the critical isochores at temperatures between 290 and 400 K. The measurements were performed with a high-temperature constant-volume adiabatic calorimeter. The uncertainty of most of the measurements is estimated to be less than 1.5%. Measurements have been carried out in both the one- and two-phase regions. The results for the pure components are compared with earlier measurements. Crossover equations forC, obtained on the basis of the renormalization-group method and -expansion are applied to represent our experimental specific heat data for ethane, propane. and its mixture along the critical isochores.