5,928 research outputs found
Parallel eigenanalysis of finite element models in a completely connected architecture
A parallel algorithm is presented for the solution of the generalized eigenproblem in linear elastic finite element analysis, (K)(phi) = (M)(phi)(omega), where (K) and (M) are of order N, and (omega) is order of q. The concurrent solution of the eigenproblem is based on the multifrontal/modified subspace method and is achieved in a completely connected parallel architecture in which each processor is allowed to communicate with all other processors. The algorithm was successfully implemented on a tightly coupled multiple-instruction multiple-data parallel processing machine, Cray X-MP. A finite element model is divided into m domains each of which is assumed to process n elements. Each domain is then assigned to a processor or to a logical processor (task) if the number of domains exceeds the number of physical processors. The macrotasking library routines are used in mapping each domain to a user task. Computational speed-up and efficiency are used to determine the effectiveness of the algorithm. The effect of the number of domains, the number of degrees-of-freedom located along the global fronts and the dimension of the subspace on the performance of the algorithm are investigated. A parallel finite element dynamic analysis program, p-feda, is documented and the performance of its subroutines in parallel environment is analyzed
Gyrokinetic Large Eddy Simulations
The Large Eddy Simulation (LES) approach is adapted to the study of plasma
microturbulence in a fully three-dimensional gyrokinetic system. Ion
temperature gradient driven turbulence is studied with the {\sc GENE} code for
both a standard resolution and a reduced resolution with a model for the
sub-grid scale turbulence. A simple dissipative model for representing the
effect of the sub-grid scales on the resolved scales is proposed and tested.
Once calibrated, the model appears to be able to reproduce most of the features
of the free energy spectra for various values of the ion temperature gradient
QUANTITATION OF HUMAN RED BLOOD CELL FIXATION BY GLUTARALDEHYDE
The uptake of glutaraldehyde by human red blood cells has been measured as a function of time by a freezing point osmometer. The rate of attachment of glutaraldehyde to the cell proteins is high over the first hour, declining to zero over a period of a few days. The number of glutaraldehyde molecules cross-linking with each hemoglobin molecule is of the order of 200, in reasonable agreement with the calculated number of attachment sites. The cell membrane is immediately highly permeable to glutaraldehyde. Selective permeability to ions is lost during fixation. Ionic equilibrium is obtained only after a few hours. An optimum fixation technique for shape preservation is suggested
Three-Flavor Partially Quenched Chiral Perturbation Theory at NNLO for Meson Masses and Decay Constants
We discuss Partially Quenched Chiral Perturbation Theory (PQPT) and
possible fitting strategies to Lattice QCD data at next-to-next-to-leading
order (NNLO) in the mesonic sector. We also present a complete calculation of
the masses of the charged pseudoscalar mesons, in the supersymmetric
formulation of PQPT. Explicit analytical results are given for up to
three nondegenerate sea quark flavors, along with the previously unpublished
expression for the pseudoscalar meson decay constant for three nondegenerate
sea quark flavors. The numerical analysis in this paper demonstrates that the
corrections at NNLO are sizable, as expected from earlier work.Comment: 31 pages, numerical discussion extended including convergence NLO to
NNL
Free energy cascade in gyrokinetic turbulence
In gyrokinetic theory, the quadratic nonlinearity is known to play an
important role in the dynamics by redistributing (in a conservative fashion)
the free energy between the various active scales. In the present study, the
free energy transfer is analyzed for the case of ion temperature gradient
driven turbulence. It is shown that it shares many properties with the energy
transfer in fluid turbulence. In particular, one finds a forward (from large to
small scales), extremely local, and self-similar cascade of free energy in the
plane perpendicular to the background magnetic field. These findings shed light
on some fundamental properties of plasma turbulence, and encourage the
development of large eddy simulation techniques for gyrokinetics.Comment: 4 pages, 2 Postscript figure
B fields in OB stars (BOB): FORS2 spectropolarimetric follow-up of the two rare rigidly rotating magnetosphere stars HD23478 and HD345439
Massive B-type stars with strong magnetic fields and fast rotation are very
rare and provide a mystery for theories of both star formation and magnetic
field evolution. Only two such stars, called sigma Ori E analogs, were
previously known. Recently, a team involved in APOGEE, one of the Sloan Digital
Sky Survey III programs, announced the discovery of two additional rigidly
rotating magnetosphere stars, HD23478 and HD345439. The presence of magnetic
fields in these newly discovered sigma Ori E analogs was not investigated in
the past.
In the framework of our ESO Large Programme, and one normal ESO programme, we
carried out low-resolution FORS2 spectropolarimetric observations of HD23478
and HD345439.
From the measurements using hydrogen lines, we discover a rather strong
longitudinal magnetic field of the order of up to 1.5kG in HD23478, and up to
1.3kG using the entire spectrum. The analysis of HD345439 using four subsequent
spectropolarimetric subexposures does not reveal the presence of a magnetic
field at a significance level of 3sigma. On the other hand, the inspection of
individual subexposures indicates that HD345439 may host a strong magnetic
field, rapidly varying over 88 minutes. A hint at the fast rotation of HD345439
is also given by the behaviour of several metallic and He I lines in the
low-resolution FORS2 spectra, showing profile variations already on such a
short time scale.Comment: 5 pages, 4 figures, 1 table, accepted for publication as a letter to
A&
Size Effect in Fracture: Roughening of Crack Surfaces and Asymptotic Analysis
Recently the scaling laws describing the roughness development of fracture
surfaces was proposed to be related to the macroscopic elastic energy released
during crack propagation [Mor00]. On this basis, an energy-based asymptotic
analysis allows to extend the link to the nominal strength of structures. We
show that a Family-Vicsek scaling leads to the classical size effect of linear
elastic fracture mechanics. On the contrary, in the case of an anomalous
scaling, there is a smooth transition from the case of no size effect, for
small structure sizes, to a power law size effect which appears weaker than the
linear elastic fracture mechanics one, in the case of large sizes. This
prediction is confirmed by fracture experiments on wood.Comment: 9 pages, 6 figures, accepted for publication in Physical Review
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