Aspect-ratio dependent oscillatory thermocapillary convection in the floating half zone

The dependency of the critical Marangoni number on the geometrical aspect ratio of the floating half zone is essential to predict the onset of oscillatory thermocapillary convection.The experimental studies in the microgravity conditions on floating half zones of several centimeters in diameter have predicted that the critical Marangoni number increases with the increasing aspect ratio,and the terrestrial experimental studies have predicted the contradictory conclusion for floating half zones of several mil...     

Non-Gravitational Effects with Density-Matching in Evaluating the Influence of Sedimentation on Colloidal Coagulation

The method of density matching between the solid and liquid phases is often adopted to effectively eliminate the effect of sedimentation of suspensions in studies on dynamic behaviour of a colloidal system. However, the associated changes in the solvent composition may bring side effects to the properties investigated and therefore might lead to a faulty conclusion if the relevant correction is not made. To illustrate the importance of this side effect, we present an example of the sedimentation influence on the coagulation rate of suspensions of 2μm （diameter） polystyrene. The liquid mixtures, in the proper proportions of water （H2O）, deuterium oxide （D2O） and methanol （MeOH） as the liquid phase, density-matched and unmatched experiments are performed. Besides the influence of viscosity, the presence of methanol in solvent media, used to enhance the sedimentation effect, causes significant changes （reduction） in rapid coagulation rates compared to that in pure water. Without the relevant corrections for those non-gravitational factors it seems that gravitational sedimentation would retard the coagulation. The magnitude of the contribution from the non-gravitational factor is quantitatively determined, making the relevant correction possible. After necessary the influence of the sedimentation on coagulation rates at corrections for all factors, our experiments show that the initial stage of the coagulation is not observable.     

Spin squeezing and quantum correlations

We discuss the notion of spin squeezing considering two mutually exclusive classes of spin-s states, namely, oriented and non-oriented states. Our analysis shows that the oriented states are not squeezed while non-oriented states exhibit squeezing. We also present a new scheme for construction of spin-s states using 2s spinors oriented along different axes. Taking the case of s=1, we show that the ‘non-oriented’ nature and hence squeezing arise from the intrinsic quantum correlations that exist among the spinors in the coupled state.     

Methane oxidation over mixed-conducting SrFe(Al)O3-delta-SrAl2O4 composite

The steady-state CH4 conversion by oxygen permeating through mixed-conducting (SrFe)0.7(SrAl2)0.3Oz composite membranes, comprising strontium-deficient SrFe(Al)O3-delta perovskite and monoclinic SrAl2O4-based phases, occurs via different mechanisms in comparison to the dry methane interaction with the lattice oxygen. The catalytic behavior of powdered (SrFe)0.7(SrAl2)0.3Oz, studied by temperature-programmed reduction in dry CH4 at 523-1073 K, is governed by the level of oxygen nonstoichiometry in the crystal lattice of the perovskite component and is qualitatively similar to that of other perovskite-related ferrites, such as Sr0.7La0.3Fe0.8Al0.2O3-delta. While extensive oxygen release from the ferrite lattice at 700-900 K leads to predominant total oxidation of methane, significant selectivity to synthesis gas formation, with H2/CO ratios close to 2, is observed above 1000 K, when a critical value of oxygen deficiency is achieved. The steady-state oxidation over dense membranes at 1123-1223 K results, however, in prevailing total combustion, particularly due to excessive oxygen chemical potential at the membrane surface. In combination with surface-limited oxygen permeability, mass transport limitations in a porous layer at the membrane permeate side prevent reduction and enable stable operation of (SrFe)0.7(SrAl2)0.3Oz membranes under air/methane gradient. Taking into account the catalytic activity of SrFeO3-delta-based phases for the partial oxidation of methane to synthesis gas and the important role of mass transport-related effects, one promising approach for membrane development is the fabrication of thick layer of porous ferrite-based catalyst at the surface of dense (SrFe)0.7(SrAl2)0.3Oz composite.