A collaborative study on the determination of free amino acids in blood plasma

Collaborative work to determine the amino acid, taurine, urea and ammonia contents of a standard mixture of amino acids and of blood plasma from a preruminant and a ruminant calf was carried out at four laboratories to assess the accuracy of the ion-exchange column chromatographic technique. Samples of blood plasma were deproteinised by the organising laboratory and by the collaborating laboratories using their own methods. For the standard amino acid mixture the mean absolute deviation was 0.036 of the true concentration. This compared favourably with results from previous collaborative trials on protein hydrolysates. The mean absolute deviations were 0.192 for preruminant calf blood deproteinised by the organising laboratory and 0.159 for blood deproteinised by the collaborating laboratories. Comparable values for ruminant calf blood were 0.149 and 0.117, respectively. These results were much poorer than those obtained for protein hydrolysates and possible explanations are put forward for these different degrees of precision.     

An electron microprobe study of the influence of beam current density on the stability of detectable elements in mixed-salts (isoatomic) microdroplets

This paper shows that a means of accurately measuring beam current during microprobe analysis of inorganic fluid microdroplets is essential, since certain elements were sublimated from such specimens under easily achieved beam current densities, i.e. S at 1·8 nA/μm², K at 2·5 nA/μm², Na at 3·5 nA/μm², P at 5·3 nA/μm². In comparison, Cl was volatilized even under the mildest conditions used (0·35 nA/μm²), and Ca, Mg and Co were stable under the severest operating conditions (7·1 nA/μm²). Elements were less stable in large (3 μm diameter) droplets than in small (1 μm) droplets under identical irradiation conditions. The onset of volatilization is a direct function of the current delivered per unit area and not of the total integrated dose. The addition of 50 g/l of urea to the mixed-salts (isoatomic) solution, or (a) the mounting of the droplets so that the carbon-celloidin support film was interposed between them and the electron source, and (b) top-coating the droplets with carbon, did not, in general, raise the threshold of volatilization of a given element, but did effectively retard the rate of loss at current densities above the volatilization threshold. A literature survey confirmed that similar losses can occur from biological tissue specimens, albeit at higher beam current densities. Finally, the possibility that local specimen heating during electron/specimen interaction is a cause of element loss during microprobe analysis is discussed.     

The formation of uniformly sized drops by vibration-atomization

The effects of external vibrations on the disintegration of a liquid jet are described. Conditions for the formation of uniformly sized drops are discussed and results presented to illustrate the effect of amplitude and frequency of vibration on the drop size and break-up length of the jet. Liquids of various viscosity have been studied, 60-1400 c.p., and the results compared with existing theories. This method can be used with standard pressure nozzles and may be of use in research experiments when dispersions of uniform drops are required. It also has application in the formation of uniform prills.     

A Versatile Video-Waveform Corrector for TV Transmitter and Studio Applications

The basis of a TV system is that the video signal is assigned a specific power level (amplitude) at a specific point in time. Of prime significance, then, are the time-domain characteristics of the video signal waveform.     

Gallium concentration effects on magnetic bubble films of EuTm2(Fe,Ga)5O112 garnet grown by liquid phase epitaxy

By varying the Ga concentrations x of EuTm₂Fe_5?xGa_xO₁₂ from x = 0 to about 0.8, thin magnetic films supporting stable bubbles with diameters from 0.5 to about 8μm, respectively, are deposited epitaxially onto gadolinium gallium garnet substrates oriented (111). For low values of x, the Ga segregation coefficient is about 2 and it decreases slightly as x increases. Thus, films contain roughly twice as much Ga as the LPE fluxed melts in which they grow. Both the characteristic length and magnetic bubble stability factor (Q) increase rapidly with x and, to a lesser degree, so does the uniaxial anisotropy field H_A while both 4πM and the uniaxial anisotropy K_u decrease.     

The nucleation of aluminum grains in alloys of aluminum with titanium and boron

The microstructure of a ternary alloy, Al-5 wt pct Ti, 1 wt pct B, has been examined by optical and electron transmission microscopy, by selected area diffraction, and electron probe microscopy, by selected area diffraction, and electron probe microanalysis. Particles of Al₃Ti are found at the center of grains and there exist preferred epitaxial orientations between this compound and the surrounding aluminum. Particles containing titanium and boron occur at aluminum grain boundaries and have no preferred configurations with respect to the aluminum or to one another. It is concluded that the active heterogeneous nuclei are therefore Al₃Ti and that particles of TiB₂, AlB₂, or a ternary compound are not active in this alloy. Grain size measurements in binary Al-Ti alloys suggest that particles of a nucleating phase must be present at concentrations as low as 0.01 wt pct Ti, and it is suggested that these could be Al₃Ti if the existing binary phase diagram Al-Ti is in error.     

Properties of fused polysulphides—I. The electrical conductivity of fused sodium and potassium polysulphides

The preparation of alkali metal polysulphides is described. Conductivity measurements were made on melts in the composition ranges Na₂S₃-Na₂S₅ and K₂S₃-K₂S₆, at temperatures between 250° C and 400° C. The isothermal pressure dependence of the conductivity was measured, for melt compositions Na₂S₃, Na₂S₄ and Na₂S₅, at a number of temperatures in the above range. The conductivity of liquid sulphur saturated with Na₂S₅ was also measured.Arrhenius plots of the conductivity were non-linear for all melt compositions, but the results could be fitted to the Vogel-Tammann-Fulcher equation

The values of T₀ giving best fit were in reasonable agreement with glass transition temperatures obtained by differential thermal analysis, and with values obtained from studies of viscosity.     

Properties of fused polysulphides—V. voltammetric studies on sulphur and polysulphides in fused KSCN and LiCl-KCl eutectic

The oxidation of alkali metal polysulphides in fused KSCN and LiCl/KCl eutectic has been studied by cyclic voltammetry and potential step techniques. Sulphur was found to be the final oxidation product. For solutions in KSCN at 210°C only one oxidation peak was observed, involving a common, one-electron electrochemical process for all the polysulphides in the composition range M₂S₃-M₂S₆. It is proposed that the common electroactive species leading to the formation of the sulphur deposit is S^?₂ or S^?₃. The anodic formation of sulphur was found to be diffusion controlled, and no inhibition due to the formation of a poorly-conducting liquid phase was apparent. The cathodic dissolution of sulphur was studied in both solvents. It resembles the anodic dissolution of a metal, giving rise to characteristics stripping peaks in the cyclic voltammograms.