Conductivity measurements on liquid sulphur

The electrical conductivity of liquid sulphur has been measured from the melting point to 900° C, evaporation of the sulphur being prevented by use of an atmosphere of argon at elevated pressure. With rise in temperature, the conductivity increases except at the polymerization maximum near 170° C where a minimum in the conductivity is confirmed. Above 400° C the plot of log versus 1/T is linear, and on the assumption that the conductivity at these temperatures is intrinsic, a value of 3.1 eV is obtained for the energy gap. Although the rise in conductivity above 400° C is accompanied by a decrease in mean chain length in the liquid, there is no simple relationship between the two properties. The behaviour of sulphur is compared with that of liquid selenium.     

Pore segmentation of cement-based materials from backscattered electron images

A technique to segment pores from a normal backscattered electron (BSE) image of cement-based materials is presented. The upper threshold grey level for porosity is determined from the inflection point of the cumulative brightness histogram of the BSE image. This represents a critical point where a small incremental grey value will cause a sudden increase in thresholded area, a condition termed as overflow. The proposed technique was found to be more consistent and reliable than existing methods. Significantly fewer images are required to achieve a satisfactory level of statistical confidence for quantifying porosity.     

On the machining of glass

A study to examine the feasibility of cutting glass in the same manner as ductile metals was carried out on three types of glass (soda-lime microscope slides, carefully polished specimens of lead-doped flint and fused silica). No success was obtained with fused silica while soda-lime glass showed clear evidence of cutting in a manner similar to ductile metals, but provided variable results with different specimens. The most encouraging results were obtained with the lead-doped flint glass. Using a diamond tool with a semicircular face at a rake angle of –34°, crackfree cuts were produced with widths and depths up to about 100 and 1.6 m, respectively. The chips produced during this machining are tightly curled with a serrated concave side. The results of this preliminary investigation suggest many aspects for further study. However, the essential conclusion is that certain glasses may be machined in a manner similar to ductile metals if the size of the cut is small enough.     

Preparation of octacalcium phosphate by the hydrolysis of α-tricalcium phosphate

A new simple method of preparation for the thermodynamically unstable octacalcium phosphate [Ca₈H₂(PO₄)₆·5H₂O; OCP] has been developed using the hydrolysis of -Ca₃(PO₄)₂ instead of the conventional hydrolysis of CaHPO₄·2H₂O. The hydrolysis experiments were carried out by treating an -Ca₃(PO₄)₂(1 g)-H₂O(50 m) suspension for 3 h at temperatures in the range 40 to 80° C and at pHs in the range 3 to 7.5. The formation of OCR was limited to within a narrow region between formation regions of other phosphates. Favourable conditions for OCP preparation were, for example, 70° C, pH4.5 to 5.0 and 60° C, pH5.0. Particles of OCP were composed of tight aggregates of strip-like microcrystals growing probably along the [0 0 1] and (1 0 0) plane of the OCP structure. Nearly stoichiometric OCP was obtained under the most suitable conditions with good reproducibility. Pyrolytic processes of OCP were approximately consistent with the data published so far. However, the temperatures of the appearance and disappearance of pyrolytic crystalline phases and ionic species deviated slightly from the published data. Thermal dehydration up to 150° C without destruction of OCP and decomposition reactions above 300° C resulted in changes in surface area and average pore radius of OCP.     

MVA-vaccine in primovaccination against smallpox after the age of three (author's transl)

These are the results of 417 primary vaccinations against smallpox with MVA, an attenuated vaccine. All of the patients were over three years old. In Europe, this group has an increased risk of postvaccinal encephalitis. The intracutaneous inoculation produced a light local infiltration and only 11.7% showed a light generalized reaction. In order to attain a reliable immunity, a second inoculation was performed one week later, epicutaneously with Elstree-vaccine. The local reaction was in general that of a normal revaccination, and 79.4% of our patients had neither fever nor general symptoms. Among the others no one became seriously ill. We did not observe any complications specific for a smallpox vaccination. In comparison to the other vaccination methods currently used, the MVA "Two-step"-vaccination is probably the safest. Its risk of a postvaccinal encephalitis is supposed to be lower according to animal experiments and theoretical considerations. This hypothesis has been confirmed meanwhile by the results of several thousand vaccinations in the already mentioned age-group.     

Unsteady mixed convection from an isothermal circular cylinder

Summary Combined unsteady convection from an isothermal horizontal cylinder in a stream flowing vertically upwards has been investigated. Numerical solutions of the unsteady boundary-layer equations have been obtained at any station along the cylinder using the series truncation method. Solutions which are valid near the front and near stagnation points have been obtained using standard finite-difference methods. A series solution in powers of time has been obtained with which the numerical solutions has been checked.

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Unstetige, gemischte Konvektion um einen isothermen Kreiszylinder

Zusammenfassung Es wird eine kombinierte, unstetige Konvektion eines isothermen, horizontalen Zylinders in einer vertikal nach oben gerichteten Strömung untersucht. Numerische Lösungen der unstetigen Grenzschichtgleichungen werden an jeder Stelle längs des Zylinders durch die Verwendung der Reihenabbruchsmethode erhalten.Nahe der Vorderseite und nahe bei den Staupunkten gültige Lösungen werden durch Verwendung üblicher Methoden der finiten Differenzen erhalten. Mit Hilfe einer Reihenlösung in Potenzen der Zeit wird das numerische Ergebnis überprüft.

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Notation a radius of the cylinder - g acceleration of gravity - G _r Grashof number =g|T|a ³/v ² - Q heat transfer - R _e Reynolds number =U ₀ a/v - T temperature of fluid in the boundary layer - T ₀ temperature of the ambient fluid - T ₁ temperature of the cylinder - T temperature difference=T ₁–T ₀ - t time - U ₀ free stream - x co-ordinate measuring distance round the cylinder - y co-ordinate measuring distance normal to the cylinder - G _r /R _e ² - coefficient of expansion - coefficient of kinematic viscosity - _w skin friction With 7 Figures     

Thermopower ofAg_{2 + \delta } S across theα-β transitionacross theα-β transition

Thermopower data of S in both of itsα- andβ-phases are reported and the results are compared with the data on Se. Communication No. 129 from the Solid State and Structural Chemistry Unit.     

Transport properties of nonelectrolyte liquid mixtures—IV. Viscosity coefficients for benzene,perdeuterobenzene, hexafluorobenzene,and an equimolar mixture of benzene + hexafluorobenzene from 25 to 100°c at pressures up to the freezing pressure

Viscosity coefficient measurements made with an estimated accuracy of ±2% using a self-centering falling body viscometer are reported for benzene, perdeuterobenzene, hexafluorobenzene and an equimolar mixture of benzene + hexafluorobenzene at 25, 50, 75 and 100°C at pressures up to the freezing pressure. The data for each liquid at different temperatures and pressures are correlated very satisfactorily by a graphical method based on plots of 9.118×10⁷ V ^2/3/(MRT)^1/2 versus logV, and are reproduced to within the experimental uncertainty by a free-volume form of equation. Application of the empirical Grunberg and Nissan equation to the mixture viscosity coefficient data shows that the characteristic constant G is practically temperature- and pressure-independent for this system.