1,000 research outputs found
Application of the meshless procedure for the elastoplastic torsion of prismatic rods
In this paper torsion of prismatic bars considering elastic-plastic material behavior is studied. Based on the Saint-Venant displacement assumption and the Romberg-Osgood model for the stress-strain relation, the boundary value problem for stress function is formulated. In reality an area of cross section of a bar has two regions: elastic with linear governing equation and plastic with non-linear governing equation. In the solution procedure, the meshless procedure based on the Homotopy Analysis Method HAM connected with the Method of Fundamental Solutions (MFS) and Radial Basis Functions (RBF) is applied. The considered nonlinear partial differential equation (PDE) is transform into a hierarchy of linear inhomogeneous PDEs. The accuracy of the obtained approximate solution is controlled by the number of components of the calculate solution, while the convergence of the process is monitored by an additional parameter of the method. The advantage of the proposed meshless approach is that it does not require the generation of a mesh on the domain or its boundary, but only using a cloud of arbitrary located nodes
Application of the method of fundamental solutions for inverse problems related to the determination of elasto-plastic properties of prizmatic bar
The problem of determining the elastoplastic properties of a prismatic bar from the given relation from experiment between torsional moment MT and angle of twist per unit of rod’s length θ is investigated as inverse problem. Proposed method of solution of inverse problem is based on solution of some sequences of direct problem with application of the Levenberg-Marquardt iteration method. In direct problem these properties are known and torsional moment as a function of angle of twist is calculated form solution of some non-linear boundary value problem. For solution of direct problem on each iteration step the method of fundamental solutions and method of particular solutions is used for prismatic cross section of rod. The non-linear torsion problem in plastic region is solved by means of the Picard iteration
The frequency map for billiards inside ellipsoids
The billiard motion inside an ellipsoid Q \subset \Rset^{n+1} is completely
integrable. Its phase space is a symplectic manifold of dimension , which
is mostly foliated with Liouville tori of dimension . The motion on each
Liouville torus becomes just a parallel translation with some frequency
that varies with the torus. Besides, any billiard trajectory inside
is tangent to caustics , so the
caustic parameters are integrals of the
billiard map. The frequency map is a key tool to
understand the structure of periodic billiard trajectories. In principle, it is
well-defined only for nonsingular values of the caustic parameters. We present
four conjectures, fully supported by numerical experiments. The last one gives
rise to some lower bounds on the periods. These bounds only depend on the type
of the caustics. We describe the geometric meaning, domain, and range of
. The map can be continuously extended to singular values of
the caustic parameters, although it becomes "exponentially sharp" at some of
them. Finally, we study triaxial ellipsoids of \Rset^3. We compute
numerically the bifurcation curves in the parameter space on which the
Liouville tori with a fixed frequency disappear. We determine which ellipsoids
have more periodic trajectories. We check that the previous lower bounds on the
periods are optimal, by displaying periodic trajectories with periods four,
five, and six whose caustics have the right types. We also give some new
insights for ellipses of \Rset^2.Comment: 50 pages, 13 figure
Cerebrospinal fluid ferritin—Unspecific and unsuitable for disease monitoring
Background and purpose
Subarachnoid hemorrhage is sometimes difficult to diagnose radiologically. Cerebrospinal fluid (CSF) ferritin has been proposed to be highly specific and sensitive to detect hemorrhagic central nervous system (CNS) disease. We analyzed here the specificity of CSF ferritin in a large series of various CNS diseases and the influence of serum ferritin.
Materials and methods
CSF ferritin, lactate, protein and total cell count were analyzed in 141 samples: neoplastic meningitis (n=62), subarachnoid hemorrhage (n=20), pyogenic infection (n=10), viral infection (n=10), multiple sclerosis (n=10), borreliosis (n=5) and normal controls (n=24). Cerebrospinal fluid ferritin was measured with a microparticle immunoassay. In addition, serum and CSF ferritin were compared in 18 samples of bacterial and neoplastic meningitis.
Results
In CNS hemorrhage, median ferritin was 51.55ÎĽg/L (sensitivity: 90%) after the second lumbar puncture. In neoplastic meningitis, the median CSF ferritin was 16.3ÎĽg/L (sensitivity: 45%). Interestingly, ferritin was higher in solid tumors than that in hematological neoplasms. In 90% of pyogenic inflammation, ferritin was elevated with a median of 53.35ÎĽg/L, while only 50% of patients with viral infection had elevated CSF ferritin. In ventricular CSF, median ferritin was 163ÎĽg/L, but only 20.6ÎĽg/L in lumbar CSF. Ferritin was normal in multiple sclerosis and borreliosis.
Conclusions
Ferritin was elevated not only in hemorrhagic disease, but also in neoplastic and infectious meningitis. Ferritin was not a reliable marker of the course of disease. The influence of serum ferritin on CSF ferritin is negligible. We conclude that elevated CSF ferritin reliably, but unspecifically indicates severe CNS disease
Hyperbolic outer billiards : a first example
We present the first example of a hyperbolic outer billiard. More precisely
we construct a one parameter family of examples which in some sense correspond
to the Bunimovich billiards.Comment: 11 pages, 8 figures, to appear in Nonlinearit
Polya's inequalities, global uniform integrability and the size of plurisubharmonic lemniscates
First we prove a new inequality comparing uniformly the relative volume of a
Borel subset with respect to any given complex euclidean ball \B \sub \C^n
with its relative logarithmic capacity in \C^n with respect to the same ball
\B.
An analoguous comparison inequality for Borel subsets of euclidean balls of
any generic real subspace of \C^n is also proved.
Then we give several interesting applications of these inequalities.
First we obtain sharp uniform estimates on the relative size of \psh
lemniscates associated to the Lelong class of \psh functions of logarithmic
singularities at infinity on \C^n as well as the Cegrell class of
\psh functions of bounded Monge-Amp\`ere mass on a hyperconvex domain \W
\Sub \C^n.
Then we also deduce new results on the global behaviour of both the Lelong
class and the Cegrell class of \psh functions.Comment: 25 page
On the Interpretation of the Electroweak Precision Data
The recent precision electroweak data on and
are compared with the tree-level and the dominant-fermion-loop as well as the
full one-loop standard-model predictions. While the tree-level predictions are
ruled out, the dominant-fermion-loop predictions, defined by using in the tree-level formulae, as well as the full one-loop
predictions are consistent with the experimental data. Deviations from the
dominant-fermion-loop predictions are quantified in terms of an effective
Lagrangian containing three additional parameters which have a simple meaning
in terms of symmetry violation. The effective Lagrangian yields the
standard one-loop predictions for specific values of these parameters, which
are determined by and .Comment: Preprint BI-TP 93/46 (September 1993), to be published in Phys. Lett.
B, LaTeX, 10 pages, (figures are not included
The K\"ahler-Ricci flow on surfaces of positive Kodaira dimension
The existence of K\"ahler-Einstein metrics on a compact K\"ahler manifold has
been the subject of intensive study over the last few decades, following Yau's
solution to Calabi's conjecture. The Ricci flow, introduced by Richard Hamilton
has become one of the most powerful tools in geometric analysis.
We study the K\"ahler-Ricci flow on minimal surfaces of Kodaira dimension one
and show that the flow collapses and converges to a unique canonical metric on
its canonical model. Such a canonical is a generalized K\"ahler-Einstein
metric. Combining the results of Cao, Tsuji, Tian and Zhang, we give a metric
classification for K\"aher surfaces with a numerical effective canonical line
bundle by the K\"ahler-Ricci flow. In general, we propose a program of finding
canonical metrics on canonical models of projective varieties of positive
Kodaira dimension
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