Strain Hardening in Polymer Glasses: Limitations of Network Models

Simulations are used to examine the microscopic origins of strain hardening in polymer glasses. While traditional entropic network models can be fit to the total stress, their underlying assumptions are inconsistent with simulation results. There is a substantial energetic contribution to the stress that rises rapidly as segments between entanglements are pulled taut. The thermal component of stress is less sensitive to entanglements, mostly irreversible, and directly related to the rate of local plastic arrangements. Entangled and unentangled chains show the same strain hardening when plotted against the microscopic chain orientation rather than the macroscopic strain.Comment: 4 pages, 3 figure

IMMUNOLOGICAL MEMORY: THE ROLE OF REGULATORY CELLS (TREGS)

Memory T cells are necessary for development of the immune response and represent one of the most numerous population of human T lymphocytes. On the contrary, suppressive regulatory T cells (Tregs) may terminate the immune response and help to maintain tolerance to self-antigens. These important groups of cells are consisting of different subpopulations and retaining throughout life. However, today there is yet no clear understanding of how the relations between these two groups of cells are formed. In this work we consider possible ways of development and maintenance of CD4+ T cell memory and role of Tregs in these processes. Mechanisms of a differentiation of memory T cells, Tregs and recently described memory Tregs are discussed. The functional and genetic characteristics of these cells are compared. Division of cells according to the functional profile allows drawing parallels between memory T cells and Tregs. These two groups are consisted of central circulating populations (Tc), effector which can migrate toward specific tissues (Te) and tissue-resident cells (Tr), which are staying in peripheral tissues. The similar structural organization of Tregs and memory T cells, existence of transitional forms of tissue-resident Treg subpopulations with properties of memory cells assumes existence of close interrelation between these groups of lymphocytes. The conversion of CD4+ memory T cells into FoxP3-expressing Tregs is one of possible mechanisms of communication between these two groups. The memory Treg-cells with T cell and memory Treg-cell properties can represent a transitional stage of differentiation. On the other side, Treg cells can differentiate independently of memory T cells and accumulate during life in the form of memory Treg cells. The supressor function of Tregs is also necessary as well as function of memory T cells to develop the immune response. It is possible, that a subset of Treg cells undergoes selection in thymus and constitutively express TCR-receptors having affinity with peripheral tissues. Further, these committed cells can be settled into tissues and become tissue-resident Treg cells which maintain regional T cell memory. Tregs can represent the “mirror image” of the structural organization of memory T cells, but with the return sign – the sign of suppression. The quantitative ratio of Tregs and memory T cells (CD4+CD45RO+CD25hiFoxP3+/CD4+CD45RO+CD25-FoxP3-), perhaps, is important criterion for functional assessment of immune system. The balance between these functionally opposite cell subsets has to provide stable functioning of immune system

Analysis of complex singularities in high-Reynolds-number Navier-Stokes solutions

Numerical solutions of the laminar Prandtl boundary-layer and Navier-Stokes equations are considered for the case of the two-dimensional uniform flow past an impulsively-started circular cylinder. We show how Prandtl's solution develops a finite time separation singularity. On the other hand Navier-Stokes solution is characterized by the presence of two kinds of viscous-inviscid interactions that can be detected by the analysis of the enstrophy and of the pressure gradient on the wall. Moreover we apply the complex singularity tracking method to Prandtl and Navier-Stokes solutions and analyze the previous interactions from a different perspective

FORECAST STRUCTURE DEVELOPMENT FOR MODELLING THE SOUTHERN BRAZILIAN CONTINENTAL SHELF HYDRODYNAMIC

Global forecast models have been widely used worldwide; however, they lack ability to prescribe high quality local data. In this paper, an assembly of oceanographic (RTOFS) and atmospheric (GFS) global data base are used to set up a nested forecast system. The approach proposed relies on the  sage of python and FORTRAN scripts to download and assemble global metocean data, in addition to interpolate it towards the study area numerical grid as boundary conditions. Therefore, the TELEMAC-3D hydrodynamic model is automatically initiated in order to provide the regional forecast for the Southern Brazilian Continental Shelf. Results shows that the methodology proposed represent properly the flow dynamics inside the Patos Lagoon and also in the Tramandaí beach, with low/high frequency dynamic effects and influences being reported

Strain Hardening of Polymer Glasses: Entanglements, Energetics, and Plasticity

Simulations are used to examine the microscopic origins of strain hardening in polymer glasses. While stress-strain curves for a wide range of temperature can be fit to the functional form predicted by entropic network models, many other results are fundamentally inconsistent with the physical picture underlying these models. Stresses are too large to be entropic and have the wrong trend with temperature. The most dramatic hardening at large strains reflects increases in energy as chains are pulled taut between entanglements rather than a change in entropy. A weak entropic stress is only observed in shape recovery of deformed samples when heated above the glass transition. While short chains do not form an entangled network, they exhibit partial shape recovery, orientation, and strain hardening. Stresses for all chain lengths collapse when plotted against a microscopic measure of chain stretching rather than the macroscopic stretch. The thermal contribution to the stress is directly proportional to the rate of plasticity as measured by breaking and reforming of interchain bonds. These observations suggest that the correct microscopic theory of strain hardening should be based on glassy state physics rather than rubber elasticity.Comment: 15 pages, 12 figures: significant revision

Muon pair creation from positronium in a circularly polarized laser field

We study elementary particle reactions that result from the interaction of an atomic system with a very intense laser wave of circular polarization. As a specific example, we calculate the rate for the laser-driven reaction $e^+e^- \to \mu^+\mu^-$, where the electron and positron originate from a positronium atom or, alternatively, from a nonrelativistic $e^+e^-$ plasma. We distinguish accordingly between the coherent and incoherent channels of the process. Apart from numerical calculations, we derive by analytical means compact formulas for the corresponding reaction rates. The rate for the coherent channel in a laser field of circular polarization is shown to be damped because of the destructive interference of the partial waves that constitute the positronium ground-state wave packet. Conditions for the observation of the process via the dominant incoherent channel in a circularly polarized field are pointed out

The method of surgical access while treatment of nonclostridial anaerobic infections of soft tissues of tongue and oral cavity floor

The author analyzed the methods of operational interventions in the area of soft tissues of oral cavity floor and tongue while treatment of nonclostridial anaerobic infections. Twenty-nine of the forty-two analyzed patients were operated, using the authors’ method of T-shaped incision. The number of lethal outcomes has decreased almost twice. Treatment results allow us to recommend the proposed method for wider use in clinical practic