Concentrated suspensions of Brownian beads in water: dynamic heterogeneities through a simple experimental technique

Concentrated suspensions of Brownian hard-spheres in water are an epitome for understanding the glassy dynamics of both soft materials and supercooled molecular liquids. From an experimental point of view, such systems are especially suited to perform particle tracking easily, and, therefore, are a benchmark for novel optical techniques, applicable when primary particles cannot be resolved. Differential variance analysis(DVA) is one such novel technique that simplifies significantly the characterization of structural relaxation processes of soft glassy materials, since it is directly applicable to digital image sequences of the sample. DVA succeeds in monitoring not only the average dynamics, but also its spatio-temporal fluctuations, known as dynamic heterogeneities. In this work, we study the dynamics of dense suspensions of Brownian beads in water, imaged through digital video-microscopy, by using both DVA and single-particle tracking. We focus on two commonly used signatures of dynamic heterogeneities: the dynamic susceptibility, χ_4, and the non-Gaussian parameter, α_2. By direct comparison of these two quantities,we are able to highlight similarities and differences. We do confirm that χ_4 and α_2 provide qualitatively similar information, but we find quantitative discrepancies in the scalings of characteristic time and length scale on approaching the glass transition.     

Proof of the Razumov-Stroganov conjecture

The Razumov-Stroganov conjecture relates the ground-state coefficients in the periodic even-length dense O(1) loop model to the enumeration of fully-packed loop configurations on the square, with alternating boundary conditions, refined according to the link pattern for the boundary points.Here we prove this conjecture, by means of purely combinatorial methods. The main ingredient is a generalization of the Wieland proof technique for the dihedral symmetry of these classes, based on the ‘gyration’ operation, whose full strength we will investigate in a companion paper.     

An integral form of the isoperimetric inequality

We study stability for an integral isoperimetric inequality.     

Almost everywhere well-posedness of continuity equations with measure initial data

The aim of this Note is to present some new results concerning “almost everywhere” well-posedness and stability of continuity equations with measure initial data. The proofs of all such results can be found in Ambrosio et al. [4], together with some application to the semiclassical limit of the Schrödinger equation.     

Partial differential equations of multi-quasi-elliptic type

The theory of multi-quasi-elliptic operators and associated Sobolev spaces is revised in this article and possible developments of the research are indicated concerning operators of principal type and non-linear equations. Moreover some new results concerning operators with anti-Wick symbols are presented. To the memory of Lamberto Cattabriga     

The Effect of Temperature and Magnetic Field on the Precipitation of Insoluble Salts of Alkaline Earth Metals

Journal of Solution Chemistry - A study of the effects induced by a weak magnetic field of about 0.4 T on the precipitation of insoluble alkaline earth carbonates is reported. Optical...     

Barium-Catalysed Dehydrocoupling of Hydrosilanes and Borinic Acids: A Mechanistic Insight

Two very rare cases of barium boryloxides, the homoleptic [Ba(OB{CH(SiMe₃)₂}₂)₂⋅C₇H₈] and the heteroleptic [{LO^NO4}BaOB{CH(SiMe₃)₂}₂] stabilised by the multidentate aminoetherphenolate {LO^NO4}⁻, are presented, and their structural properties are discussed. The electron-deficient [Ba(OB{CH(SiMe₃)₂}₂)₂⋅C₇H₈] shows, in particular, resilient η⁶-coordination of the toluene molecule. Together with its amido parents [Ba{N(SiMe₃)₂}₂⋅thf₂] and [Ba{N(SiMe₃)₂}₂]₂, this complex catalyses the fast and chemoselective dehydrocoupling of borinic acids R₂BOH and hydrosilanes HSiR′₃, yielding borasiloxanes R₂BOSiR′₃ in a controlled fashion. The assessment of substrate scope indicates that, for now, the reaction is limited to bulky borinic acids. Kinetic analysis shows that the rate-limiting step of the catalytic manifold traverses a dinuclear transition state. A detailed mechanistic scenario is proposed on the basis of DFT computations, the results of which are fully consistent with experimental data. It consists of a stepwise process with rate-determining nucleophilic attack of a metal-bound O-atom onto the incoming hydrosilane, involving throughout dinuclear catalytically active species.