MORPHOLOGICAL ALTERATIONS OF THE CEPHALIC VEIN WALL AS A PAT OF A NATIVE RTERIOVENOUS FISTULA FOR CHRONIC HEMODIALYSIS

The creation of an internal arterio-venous fistula according to Brescia and Cimino (1966) changes the functional conditions of cephalic vein and radial artery. Arterial blood enters under high pressure the cephalic vein and turbulent blood flow appears. The pathomorphology of the cephalic vein incorporated in the internal native arterio-venous fistula (NAVF) for chronic hemodialysis was studied. Single portions of the vein were surgically removed from 16 patients aged from 20 to 60 years with failed NAVF and then excised because of repeated NAVF creation (group one) and from 3 patients where the vein was removed during the primary NAVF creation (group two). Light and transmission electron microscopy was used. In the first group, the intima and media of the cephalic vein was much ticker than that of the veins of the patients of the second and control group. The increased thickness of the venous intima was accompanied by an augmented number of smooth muscles cells and appearance of new layers while that of the media was followed by structural changes of its elastic network. These alterations depend on the duration of NAVF functioning

Saddle points in completely regular topological spaces

We give a characterization of completely regular topological spaces. Applying some recent results for supinf problems in completely regular topological spaces we establish a variational principle for saddle points. Well-posedness of saddle point problems is studied as well

Multi-particle Production and Thermalization in High-Energy QCD

We argue that multi-particle production in high energy hadron and nuclear collisions can be considered as proceeding through the production of gluons in the background classical field. In this approach we derive the gluon spectrum immediately after the collision and find that at high energies it is parametrically enhanced by ln(1/x) with respect to the quasi-classical result (x is the Bjorken variable). We show that the produced gluon spectrum becomes thermal (in three dimensions) with an effective temperature determined by the saturation momentum Qs, T= c Qs/2pi during the time ~1/T; we estimate c=sqrt{2pi}/2 ~ 1.2. Although this result by itself does not imply that the gluon spectrum will remain thermal at later times, it has an interesting applications to heavy ion collisions. In particular, we discuss the possibility of Bose-Einstein condensation of the produced gluon pairs and estimate the viscosity of the produced gluon system.Comment: 25 pages, 4 figures; typos fixed; discussions expanded; we added a new section IV in which we argue that at high energies the production mechanism discussed in the paper is parametrically enhanced by ln(1/x) with respect to the quasi-classical resul

Numerical investigation of high-pressure combustion in rocket engines using Flamelet/Progress-variable models

The present paper deals with the numerical study of high pressure LOx/H2 or LOx/hydrocarbon combustion for propulsion systems. The present research effort is driven by the continued interest in achieving low cost, reliable access to space and more recently, by the renewed interest in hypersonic transportation systems capable of reducing time-to-destination. Moreover, combustion at high pressure has been assumed as a key issue to achieve better propulsive performance and lower environmental impact, as long as the replacement of hydrogen with a hydrocarbon, to reduce the costs related to ground operations and increase flexibility. The current work provides a model for the numerical simulation of high- pressure turbulent combustion employing detailed chemistry description, embedded in a RANS equations solver with a Low Reynolds number k-omega turbulence model. The model used to study such a combustion phenomenon is an extension of the standard flamelet-progress-variable (FPV) turbulent combustion model combined with a Reynolds Averaged Navier-Stokes equation Solver (RANS). In the FPV model, all of the thermo-chemical quantities are evaluated by evolving the mixture fraction Z and a progress variable C. When using a turbulence model in conjunction with FPV model, a probability density function (PDF) is required to evaluate statistical averages of chemical quantities. The choice of such PDF must be a compromise between computational costs and accuracy level. State- of-the-art FPV models are built presuming the functional shape of the joint PDF of Z and C in order to evaluate Favre-averages of thermodynamic quantities. The model here proposed evaluates the most probable joint distribution of Z and C without any assumption on their behavior.Comment: presented at AIAA Scitech 201

Spline Intersection Improvement

Rendering and simulation software needs many models of reality. Every human has hair and we need to visualize realistic hair. We can model hair with many spline curves. A typical task of the ray tracing method is finding an intersection of spline curves with a ray. We try to find a fast way to calculate the point where the ray intersects the curve

Pair production by boost-invariant fields in comoving coordinates

We derive the pair-production probability in a constant electric field in Rindler coordinates in a quasi-classical approximation. Our result is different from the pair-production probability in an inertial frame (Schwinger formula). In particular, it exhibits non-trivial dependence on rapidity and deviation from Gaussian behavior at small transverse momenta. Our results can be important for analysis of particle production in heavy-ion collisions.Comment: 12 pages, 2 figures. Discussion added and typos fixe

REGULARITIES OF THE VASCULARIZATION OF HUMAN ARTERIAL VESSELS

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