Textural Transitions in a Rotating Slab of 3He-A

The operation of a torsional oscillator for detection, of flow-driven textural transitions in, ³He-A is described. The detection technique, tracking the shift of the resonant frequency of the torsional oscillator, allows us to observe textural changes and the presence of vortices in zero magnetic field. It relies on. the anisotropic superfluid density of ³He-A and its change due to reorientation of the Î-texture caused by counterflow.     

Complexity classification in qualitative temporal constraint reasoning

We study the computational complexity of the qualitative algebra which is a temporal constraint formalism that combines the point algebra, the point-interval algebra and Allen's interval algebra. We identify all tractable fragments and show that every other fragment is NP-complete.     

Prediction of Undrained Sinkhole Collapse

Sinkholes are surface depressions or shafts resulting from the collapse of a submerged cavity in soil. The cavities that lead to sinkholes form as a result of underlying geology in limestone areas, or as a result of human activity such as mining or leakage from a sewer. The formation of sinkholes is often sudden and can lead to extensive damage and loss of life, especially in urban areas. Much of the literature on the subject of sinkhole formation is empirical in nature, often being associated with specific locations. This paper presents the results of a study, using numerical modeling, of the undrained stability of the submerged cavities that lead to sinkhole formation. Finite-element limit analysis techniques (using programs developed at the University of Newcastle) are used to obtain upper and lower bound values of a suitable load parameter, which bracket the exact solution. The results are compared to analytical solutions, both from literature and derived independently.     

Specific heat of amorphous3He films and confined liquid3He

We have measured the heat capacities of³He films and liquid³He in porous Vycor glass at 10 to 600 mK. With increasing the film thickness from 1 to 3 atomic layers, the specific heat evolves gradually from that typical to solid to that of liquid³He. At about 2 atomic layers, however, its low-temperature part is nearly temperature-independent; we interpret this as a result of gradual freezing of spins in an amorphous solid³He film with decreasing the temperature. The contribution of liquid³He in the center of the Vycor pores can be described as the specific heat of bulk liquid³He at corresponding pressures in the range 0 to 28 bar. The thickness of amorphous solid on the pore walls increases with external pressure roughly linearly. Preplating the walls with⁴He allows to determine the positions of³He atoms contributing to the surface specific heat at 10 to 50 mK. In addition, the contribution from the specific heat of³ He -⁴He mixing at 100 to 600 mK is discussed as a function of pressure and amount of⁴He.0n leave from ISSP Acad. Sci. of Russia, Chernogolovka, Russia     

Design of new systems for transfer hydrogenolysis of polychlorinated aromatics with 2-propanol using a Raney nickel catalyst

A multipurpose study deals with the transfer hydrogenolysis of 1,3,5-trichlorobenzene to benzene in the 2-propanol–Raney nickel system in the presence of KOH. At 70 °C, no reaction occurs without KOH or with weaker bases, e.g. amines or poorly soluble inorganic bases; however saturated KOH as well as water over 1% suppress the reaction rate, presumably due to the competitive adsorption of these species on the catalyst. The catalytic activity also drops with time because of the deposition of the solid KCl on the catalyst but can be recovered at washing the catalyst with water. The deactivation by KCl can be mitigated with the addition of promoters, e.g. quaternary ammonium salts (Aliquat 336, CTAC) or trioctylamine. Aliquat 336 also promotes hydrodechlorination in the hydrothermal system using a 10% solution of 2-propanol in water, Raney nickel and potassium carbonate as base at 150–200 °C and 10–20 bar. Under these conditions, hexachlorobenzene was also selectively dechlorinated to benzene.     

Comparative Coreflood Studies for Precipitation and Adsorption Squeeze with PPCA as the Scales Inhibitor

Comparative adsorption and precipitation squeezes carried out on field core materials demonstrate that significant lifetime enhancement is achievable for precipitation squeeze with respect to more conventional adsorption squeeze. Coreflood tests have been carried out under reservoir conditions (135°C) employing a poly-phosphinocarboxylate (PPCA) as the scales inhibitor. Field treatment simulations, carried out starting from coreflood data and considering the characteristics of a North Sea formation taken as the reference, confirmed the higher performance, in term of squeeze lifetime, of the precipitation squeeze with respect to adsorption. The results pointed out the importance of choosing the appropriate formulation once the operative conditions are known, in order to promote the inhibitor precipitation into the formation. Some implications of these results for the optimization of the precipitation squeeze technology for field applications, with particular emphasis to formation damage, are also discussed.     

Wax Diffusivity: Is It a Physical Property or a Pivotable Parameter?

In order to predict wax deposition problems the key parameter is the wax diffusion coefficient. While it is quite easy to find measured diffusivity values for well-defined compounds at quite low concentrations, very few experimental data are available for wax diffusivity in oil. Most of the literature data are estimated by interpolating experimental data obtained by loop tests and then they are affected by a noticeable uncertainty. In fact this parameter collects the whole uncertainty of the test and the paradoxical situation is that the key parameter ends to be the most error-affected or to be used as a pivotable parameter in “predictive” models. This article describes an experimental procedure to determine the overall diffusivity coefficient of waxes into the oil; the main advantage of this technique is that it allows the direct measure of diffusivity on the oil. Besides it is a very simple and straightforward technique. Results obtained were used to gain insight into the deposition process; the conclusion was that, due to the counter-intuitive diffusivity dependence on temperature, it is likely that noncompositional models available at present are structurally incorrect.     

Macroscopic model for multispecies ion-exchange kinetics

A model for multispecies ion-exchange kinetics based on the Nernst-Planck equation is suggested. It is analyzed in comparison with the “locally-determinate” model described by Hwang and Helfferich [1]. The model makes possible simple computation. The conditions for the occurrence of unusual kinetic curves with a maximum are clarified. The proposed model is developed for different types of kinetic problems and verified by the experimental investigation of a kinetics in ternary systems.     

Magnetic relaxation rates in spin-polarized hydrogen

A self-contained discussion is presented of the longitudinal (T ₁ ^–1 ) and transverse (T ₂ ^–1 ) relaxation rates in bulk and surface samples of spin-polarized atomic hydrogen (H), at sufficiently low temperatures that only the lowest two atomic hyperfine levels are thermally populated. The nonhydrodynamic contribution to the rates, due to binary collisions between hydrogen atoms, in both normal and Bose condensed samples of H are emphasized. However, the approach is general and is equally well suited for treating long-wavelength, hydrodynamic relaxation processes. Most of the discussion pertains to samples close to thermodynamic equilibrium. The calculation of the longitudinal relaxation rate for some states far from equilibrium, particularly relevant for real samples of H, is also presented. Some of the interesting results are:(1) the potentially long surface longitudinal relaxation time (T ₁) in samples with most of the available surface area oriented perpendicular to the direction of the stabilizing field; (2) the possibility of extracting the condensate fractionn _o(T)/n from aT ₁ measurement in the Bose condensed state, and finally (3) an amusingGedanken experiment that would allow us to detect the onset of Bose condensation in aT ₁ measurement in the absence of recombination.