Thermogravimetric investigation on prediction of thermal behavior of petroleum distillation residues

Summary Thermogravimetry (TG) is a potential tool to evaluate petroleum distillation residues, obtained in the crude oil distillation. Analyses were done at different heating rates, mass samples and gas flow rates. No differences were observed in the yields of the products formed during the pyrolysis at different analytical conditions. Linear correlation was found between the results of the TG and the standard methods for the prediction of the light fraction rates given by the pyrolysis.     

Separation and quantification of the major casein fractions by reverse-phase high-performance liquid chromatography and urea-polyacrylamide gel electrophoresis. Detection of milk adulterations

A urea-formaldehyde resin (UF) continuous bed has been prepared through in-situ condensation polymerization in a confined tube. The monolith is an agglomerate of 2-microm irregular particles. Nitrogen adsorption shows that the monolith has a bimodal pore size distribution. It has low resistance to flow. A dyed monolith is obtained through modification of the UF monolith with Cibacron blue F3GA. Although its dye concentration and dynamic capacity are low compared to Sepharose type affinity media, the dyed monolith can separate some proteins in the affinity mode of liquid chromatography.     

Lower bounds for the surface energy of two-dimensional foams

Amongst the two-dimensional cellular patterns that fill a plane, dry foams at stable equilibrium typify a particular subset for which the total perimeter P of cell boundaries ( i.e., films between bubbles) has a local minimum. For a given set of bubble areas Ai (i=1,..., N), P can be written in the form P=R(SigmaN(i=1) square root Ai)/2, where R is topology dependent. We seek the set of areas Ai and the cluster topology that minimise R, and propose lower bounds for R that set lower bounds for the surface energy of i) individual bubbles, with circular edges meeting at 2pi/3 angles at vertices (Plateau cells), and ii) infinite periodic bubble clusters.     

Stationary vacuum fields with cylindrical symmetry

It is demonstrated that a stationary vacuum field solution with cylindrical symmetry is always reducible to a static cylindrically symmetric solution.     

On the algebraic structure of second order symmetric tensors in 5-dimensional space-times

A new approach to the algebraic classification of second order symmetric tensors in 5-dimensional space-times is presented. The possible Segre types for a symmetric two-tensor are found. A set of canonical forms for each Segre type is obtained. A theorem which collects together some basic results on the algebraic structure of the Ricci tensor in 5-dimensional space-times is also stated.     

Two canonical wedge problems for the Helmholtz equation

Boundary-transmission problems for two-dimensional Helmholtz equations in a quadrant and its complement, respectively, are considered in a Sobolev space setting. The first problem of a quadrant with Dirichlet condition on one face and transmission condition on the other is solved in closed form for the case where all the quadrants are occupied by the same medium. Unique solvability can also be shown in the case of two different media up to exceptional cases of wave numbers, while the Fredholm property holds in general. In the second problem, transmission conditions are prescribed on both faces. Similar results are obtained in the one-medium case, but the two-media case turns out to be more complicated and the equivalent system of boundary pseudodifferential equations cannot be completely analysed by this reasoning.     

p-Fractals and power series–I. Some 2 variable results

u₁,…,u_r are in kx₁,…,x_s with k and deg(u₁,…,u_r) finite. Intending applications to Hilbert–Kunz theory, we code the numbers into a function φ_u, which empirically satisfies many functional equations related to “magnification by p,” where p=chark. p-fractals, introduced here, formalize these ideas.In the first interesting case (r=3, s=2), the φ_u are p-fractals. Our proof uses functions φ_I attached to ideals I and square-free elements h of A=kx,y. The finiteness of the set of ideal classes in and the existence of “magnification maps” on this set show the φ_I to be p-fractals.We describe further functional equations coming from a theory of reflection maps on ideal classes, and the paper concludes with examples and open questions.     

Bilayer thickness in unilamellar extruded 1,2-dimyristoleoyl and 1,2-dierucoyl phosphatidylcholine vesicles: SANS contrast variation study of cholesterol effect

Small-angle neutron scattering on extruded unilamellar vesicles in water was used to study bilayer thickness when cholesterol (CHOL) was added at 44.4 mol% to 1,2-dimyristoleoylphosphatidylcholine (diC14:1PC) and 1,2-dierucoylphosphatidylcholine (diC22:1PC) bilayers. Using the (1)H(2)O/(2)H(2)O contrast variation and the small-angle form of Kratky-Porod approximation, the bilayer gyration radii at infinite contrast R(g,infinity) and the bilayer thickness parameters d(g,infinity) = 12(0.5)R(g,infinity) were obtained at 30 degrees C. Addition of cholesterol to diC14:1PC increased the d(g,infinity) from 3.72 +/- 0.02 to 4.26 +/- 0.01 nm, while in the diC22:1PC bilayers the d(g,infinity) change observed was within the experimental error: +0.23 +/- 0.23 nm.     

Brillouin scattering study of phase transitions in LiK0.80(NH4)0.20SO4 mixed crystals

Brillouin spectroscopy was used to study the phase transitions of LiK_0.80(NH₄)_0.20SO₄ mixed crystals in the temperature range 10-300 K. The relevant elastic stiffness coefficients were evaluated at room temperature. The quasi-longitudinal γ₁₆ and the quasi-transverse γ₁₇ mode frequencies were measured in the above temperature range. From their frequency vs. temperature curve, three different phase transitions were determined. Two of the four phases presented by the crystal were found to be ferroelastic. The observed phases are tentatively assigned through a comparison with the phase transitions undergone by LiKSO₄ and LiK_0.96(NH₄)_0.04SO₄ crystals. An anomalous behavior of the Brillouin linewidth near the 260 K phase transition was observed.     

The diffraction problem for a half plane with different face impedances revisited

The problem of the diffraction of an electromagnetic wave by a half plane with different face impedances is dealt with, following a rigorous approach based on the [L₂⁺( ]₂ theory of systems of Wiener-Hopf equations with piecewise continuous presymbols. The corresponding operator is defined in spaces of physically admissible solutions, the Sobolev spaces H_α⁺( )×H_α−1⁺( ) for , and its Fredholm characteristics are determined. For it is shown that the operators are invertible and their inverses are calculated. In the final section the inverse of a related operator presented by Meister and Speck is also obtained.