Mathematical model of the solid-phase extrusion of polymeric composite materials

A mathematical model of the deformation of a structurally inhomogeneous material in a conical die is developed. The model accounts for the possibility of the material's compaction and loosening during extrusion. It is demonstrated that both a monotonic decrease, and extremal variation in microporosity are possible with increasing degree of drawing, depending on the character of the composite and deforming tool. Computed results are compared with experimental data obtained for superhigh-molecular polyethylene-based composites filled by polymerization. Good correspondence is established between theory and experiment.Translated from Mekhanika Kompozitnyk Materialov. Vol. 31. No. 6. pp. 834–839. November–December, 1995.     

Fountain viscous fluid flow during filling a channel when taking dissipative warming into account

Fountain viscous fluid flow arising during filling a plane channel is investigated. A finite-difference method is used to solve the problem of time-dependent nonisothermal flow taking mechanical energy dissipation, temperature dependence of the viscosity, and the presence of a free boundary into account. The results of parametric investigations of kinematic flow characteristics as functions of dimensionless constitutive criteria are given.     

Filling of channels with a non-Newtonian fluid in the gravity field

The flow of a pseudoplastic fluid with a free surface realized during the filling of a channel at a constant flow rate in the entry section is modeled. The fluid flow direction coincides with that of gravity. The mathematical problem is formulated on the basis of the complete equations of motion. A numerical technique for solving the problem in the two-dimensional formulation is developed on the basis of the SIMPLE algorithm and the method of invariants. A parametric investigation of the free surface evolution is carried out for different values of the governing criteria and rheological parameters. Three filling regimes are found to exist, namely, a complete filling regime, a transitional regime characterized by air cavity formation, and a jet regime. Criterial dependences separating these regimes are presented.     

HPTLC Determination of Polyaromatic Hydrocarbons in Smokers’ Hair

JPC – Journal of Planar Chromatography – Modern TLC - A method developed for quantitative determination of the total amount of polyaromatic hydrocarbons (PAH) in human hair has been...     

Nickel‐Catalyzed Monoarylation of Ammonia

Structurally diverse (hetero)aryl chloride, bromide, and tosylate electrophiles were employed in the Ni‐catalyzed monoarylation of ammonia, including chemoselective transformations. The employed JosiPhos/[Ni(cod)₂] catalyst system enables the use of commercially available stock solutions of ammonia, or the use of ammonia gas in these reactions, thereby demonstrating the versatility and potential scalability of the reported protocol. Proof‐of‐principle experiments established that air‐stable [(JosiPhos)NiCl₂] precatalysts can be employed successfully in such transformations.     

Very large magnetoresistance in lateral ferromagnetic (Ga,Mn)as wires with nanoconstrictions

We have fabricated (Ga,Mn)As nanostructures in which domain walls can be pinned by sub-10 nm constrictions. Controlled by shape anisotropy, we can switch the regions on either side of the constriction to either parallel or antiparallel magnetization. All samples exhibit a positive magnetoresistance, consistent with domain-wall trapping. For metallic samples, we find a magnetoresistance up to 8%, which can be understood from spin accumulation. In samples where, due to depletion at the constriction, a tunnel barrier is formed, we observe a magnetoresistance of up to 2000%.     

Kinematics of Bulkley–Herschel fluid flow with a free surface during the filling of a channel

The non-Newtonian fluid flow with a free surface occurring during the filling of a plane channel in the gravity field is modeled. The mathematical formulation of the problem using the rheological Bulkley–Herschel model is presented. A numerical finite-difference algorithm for solving this problem is developed. A parametric investigation of the main characteristics of the process as functions of the control parameters is performed. The effect of the rheological parameters of the fluid on the distribution of the quasisolid motion zones is demonstrated.     

The Shape Memory Effect in Structurally Heterogeneous Polymer Systems

The kinematics of shape recovery for the mixtures of thermodynamically incompatible polymers and polymer composites filled with thermoexpanded graphite has been investigated. It is shown that in these systems the shape recovery is accompanied by an increase in volume. The latter is attained at the expense of formation of microdiscontinuities at the interfaces (the polymer mixtures) or of recovery of filler porosity.