Predicting the rate of chemical transport using the flux function method

A systematic approach to the selection of independent variables for a theoretical analysis of the rate of chemical transport is discussed. The methodology is based on the use of the transport flux function, which enables optimum conditions to be found on the basis of a minimum number of the variables most likely to have the greatest effect on the transport rate. A more precise quantitative comparison between experimental and theoretical results can be made by taking into account the effects of convection, uncertainties in thermochemical data, and differences in the diffusion properties of vapour species. The latter effect can lead to a redistribution of components in the vapour, and this may have important consequences in certain CVT processes. The theoretical methodology is exemplified by consideration of transport of CoP₃ in the Co-P-Br system, FeP in the Fe-P-I system, and YIG in the Y-Fe-O-Cl and Y-Fe-O-HCl systems. The complex behaviour revealed would probably have been difficult to rationalize on the basis of experimental studies alone.     

Bistability and the phase transition in 1,3,2-dithiazolo[4,5-b]pyrazin-2-yl

The molecular radical 1,3,2-dithiazolo[4,5-b]pyrazin-2-yl (PDTA) exhibits magnetic bistability just above room temperature, undergoing a well-defined hysteretic phase change with TC downward arrow = 297(1) K and TC upward arrow = 343(1) K. The crystal structures of the two phases of PDTA have been determined by single-crystal X-ray diffraction at 323(2) K. LT-PDTA consists of diamagnetic (S = 0) nearly superimposed pi-dimer stacks, while that of HT-PDTA comprises slipped stacks of pi-radicals (S = 1/2). The structural interconversion is suggested to proceed via the cooperative breaking and making of intermolecular S- - -N interactions and an inversion symmetry-preserving "domino cascade" of the pi-stacked rings.     

Comparative study of large-mode holey and conventional fibers

Little information exists regarding how large-mode holey fibers compare, in practical terms, with their conventional counterparts. We present what is to our knowledge the first experimental study of mode area and bend loss for a range of large-mode holey and conventional fibers. It is demonstrated here that large-mode holey fibers exhibit mode areas and bending losses that are comparable to those of conventional fibers at 1.55mu . However, the novel wavelength dependence of the numerical aperture in a holey fiber offers a significant advantage for broadband and short-wavelength applications in which single-mode operation is required.     

Feasibility study of self-contained tether cable system for operating equipment on slopes of 20 to 75%

The Forest Service investigated the concept of providing support to equipment working on steep slopes through use of a self-contained tether cable system. A vehicle's downhill component of weight is reduced to near zero by the cable's tension. The vehicle can then operate on steep slopes causing only slightly more damage to terrain than when working on flat areas. Mathematical equations for the ideal tension of the cable and for both the resulting side forces and equivalent slope when operating off the fall line were developed.The methods of sensing slope, vehicle design, the winch drive system, and the controls necessary to perform with a self-contained tether cable system are all presented. Also discussed are the acceptable tolerance of the cable tension and the effect of cable tension tolerance on equivalent slope.     

The rheology of transitions

A number of transitions of state have been known for many years. Such are the sol-gel transitions and those which accompany the change of state of a vapour or a binary liquid mixture in the critical region. Others have been the subject of recent study in consequence of the industrial development of high polymers and thermo-plastics.Such are the vitreous transition of glycerine and the mesomorphic change in sulphur.The author has been studying a number of these changes, measuring (a) viscosity (b) velocity and absorption of ultrasonic waves (c) attenuation of shear waves and relating these factors to the rheological properties in the change of state.

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Zusammenfassung Eine Reihe von Zustandsumwandlungen sind seit vielen Jahren bekannt, z. B. Sol-Gel-Übergänge und Zustandsänderungen von Gasen und binären flüssigen Mischungen im kritischen Gebiet. Andere sind Untersuchungsobjekt der letzten Zeit als Folge der steigenden technischen Bedeutung der Hochpolymeren und Thermoplaste geworden: glasige Erstarrung des Glyzerins, mesomorphe Umwandlungen von Schwefel.Der Autor hat eine Anzahl dieser Umwandlungen untersucht, indem er a) die Viskosität, b) die Geschwindigkeit und Adsorption von Ultraschallwellen und c) die Dämpfung von Scherwellen gemessen und diese sämtlichen Fakten mit den rheologischen Eigenschaften während der Zustandsänderung verknüpft hat

     

Alan James Leadbetter,D.Sc., FRSC,CBE, 28th March 1934 – 11th March 2019

In cholesteric liquid crystals with a positive dielectric anisotropy, the relaxation from the electric field-aligned director configuration to the stable zero field director configuration proceeds via a metastable transient planar director configuration which has a pitch distinct from the equilibrium state. The transition from the transient planar to the equilibrium zerofield state is shown here to occur via a Helfrich-type instability which continuously leads to an in-plane helical structure. The equilibrium planar state is then seen to grow continuously from the in-plane state, leaving behind walls whose length then spontaneously shrinks.