Formation of a bistructure of a solid in a computer experiment

Molecular-dynamics was used to investigate the structural changes occurring in a three-dimensional solid when the solid is transferred from an amorphous into a crystalline state. Crystal cells of a new type — pentadecahedrons with five square lateral faces and ten regular triangular faces at the vertices of a cell — were found for the first time in a computer experiment. It is shown that a bistructure consisting of crystal cells of different types, including cells with five-fold symmetry axes, are stable in the solid. Fiz. Tverd. Tela (St. Petersburg) 40, 1919–1924 (October 1998)     

Aqueous dispersions of single-wall and multiwall carbon nanotubes with designed amphiphilic polycations

Poor solubility of single-walled and multiwalled carbon nanotubes (NTs) in water and organic solvents presents a considerable challenge for their purification and applications. Macromolecules can be convenient solubilizing agents for NTs and a structural element of composite materials for them. Several block copolymers with different chemical functionalities of the side groups were tested for the preparation of aqueous NT dispersions. Poly(N-cetyl-4-vinylpyridinium bromide-co-N-ethyl-4-vinylpyridinium bromide-co-4-vinylpyridine) was found to form exceptionally stable NT dispersions. It is suggested that the efficiency of macromolecular dispersion agents for NT solubilization correlates with the topological and electronic similarity of polymer-NT and NT-NT interactions in the nanotube bundles. Raman spectroscopy and atomic force and transmission electron microcopies data indicate that the polycations are wrapped around NTs forming a uniform coating 1.0-1.5 nm thick. The ability to wind around the NT originates in the hydrophobic attraction of the polymer backbone to the graphene surface and topological matching. Tetraalkylammonium functional groups in the side chains of the macromolecule create a cloud of positive charge around NTs, which makes them hydrophilic. The prepared dispersions could facilitate the processing of the nanotubes into composites with high nanotube loading for electronic materials and sensing. Positive charge on their surface is particularly important for biological and biomedical applications because it strengthens interactions with negatively charged cell membranes. A high degree of spontaneous bundle separation afforded by the polymer coating can also be beneficial for NT sorting.     

Atomic structure and strength of inorganic glasses

The role of the atomic structure in the fracture processes is considered using borate, silicate, and phosphate glasses as an example. Primary attention is focused on the degree of connectivity of the atomic structure. It is shown that the degree of connectivity is a major factor responsible for the structural strength of glasses under conditions excluding the influence of both accidental surface defects and the environment. The change in the Young’s modulus as a measure of elastic deformation and the change in the hardness as a characteristic of irreversible deformation are analyzed. The ultimate elastic strain experienced by a glass at the instant of fracture is examined. It is found that the ultimate elastic strain is approximately equal to 10% for glasses with a three-dimensional atomic structure and 5% for glasses with a two-dimensional (layered) or chain structure. It is assumed that this behavior of the strength as a function of the degree of connectivity of the atomic structure is associated with the degree of uniformity of the external load distribution over atomic bonds.     

Higher order symmetrizer and application to an unusual transport equation

We study a class of stationary transport equation with nonlocal low-order tems We obtain the existence and uniqueness of a solution in sobolev spaces     

Gold nanoparticles enhance the anti-leukemia action of a 6-mercaptopurine chemotherapeutic agent

6-mercaptopurine and its riboside derivatives are some of the most widely utilized anti-leukemic and anti-inflammatory drugs. Their short biological half-life and severe side effects limit their use. A new delivery method for these drugs based on 4-5 nm gold nanoparticles can potentially resolve these issues. We have found substantial enhancement of the antiproliferative effect against K-562 leukemia cells of Au nanoparticles bearing 6-mercaptopurine-9-beta-d-ribofuranoside compared to the same drug in typically administered free form. The improvement was attributed to enhanced intracellular transport followed by the subsequent release in lysosomes. Enhanced activity and nanoparticle carriers will make possible the reduction of the overall concentration of the drug, renal clearance, and, thus, side effects. The nanoparticles with mercaptopurine also showed excellent stability over 1 year without loss of inhibitory activity.     

求解复杂湍流的非线性涡黏性系数模型和代数应力模型

非线性涡黏性系数模型和代数应力模型联系了线性涡黏性系数湍流模型和完整的微分 雷诺应力模型.随着它们受到日益关注,其形式也越来越多样化.本篇综述的目的是对这些模 型加以总结并比较它们之间的共同点及不同之处,指出它们与完整微分雷诺应力模型之间的 关系,以及相对于线性涡黏性系数模型而言它们在预报流场上所具有的优势.     

Stress relaxation in glassy polymers

Stress relaxation in amorphous linear polymers has been investigated below the glass transition point at various strain rates, temperatures, and strains. A model of a nonlinear viscoelastic body is proposed as a means of describing the effect. It is shown that stress relaxation is well described by the model considered and is correlated with the deformation characteristics of the polymers.A. F. Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 987–994, November–December, 1971.     

Computer simulation of the deformation and fracture of crystals

Methods for computer simulation of strength testing of crystals are proposed. The methods employed are similar to usual static methods, and they are used to investigate deformation and fracture of perfect fcc crystals having different orientations with respect to the tensile force. A strain-induced phase transition from the fcc to the hcp structure is detected, and the formation and displacement of crystal twins are observed. Plastoelastic deformation and fracture of crystals are investigated.