1,072 research outputs found
Shear band formation in granular media as a variational problem
Strain in sheared dense granular material is often localized in a narrow
region called shear band. Recent experiments in a modified Couette cell
provided localized shear flow in the bulk away from the confining walls. The
non-trivial shape of the shear band was measured as the function of the cell
geometry. First we present a geometric argument for narrow shear bands which
connects the function of their surface position with the shape in the bulk.
Assuming a simple dissipation mechanism we show that the principle of minimum
dissipation of energy provides a good description of the shape function.
Furthermore, we discuss the possibility and behavior of shear bands which are
detached from the free surface and are entirely covered in the bulk.Comment: 4 pages, 5 figures; minor changes, typos and journal-ref adde
The origin of net electric currents in solar active regions
There is a recurring question in solar physics about whether or not electric
currents are neutralized in active regions (ARs). This question was recently
revisited using three-dimensional (3D) magnetohydrodynamic (MHD) numerical
simulations of magnetic flux emergence into the solar atmosphere. Such
simulations showed that flux emergence can generate a substantial net current
in ARs. Another source of AR currents are photospheric horizontal flows. Our
aim is to determine the conditions for the occurrence of net vs. neutralized
currents with this second mechanism. Using 3D MHD simulations, we
systematically impose line-tied, quasi-static, photospheric twisting and
shearing motions to a bipolar potential magnetic field. We find that such
flows: (1) produce both {\it direct} and {\it return} currents, (2) induce very
weak compression currents - not observed in 2.5D - in the ambient field present
in the close vicinity of the current-carrying field, and (3) can generate
force-free magnetic fields with a net current. We demonstrate that neutralized
currents are in general produced only in the absence of magnetic shear at the
photospheric polarity inversion line - a special condition rarely observed. We
conclude that, as magnetic flux emergence, photospheric flows can build up net
currents in the solar atmosphere, in agreement with recent observations. These
results thus provide support for eruption models based on pre-eruption magnetic
fields possessing a net coronal current.Comment: 14 pages and 11 figures (Accepted in The Astrophysical Journal
Anti-Saccharomyces cerevisiae antibodies in patients with inflammatory bowel disease and their first-degree relatives: Potential clinical value
Anti-Saccharomyces cerevisiae antibodies (ASCA) have been described as specific markers in Crohn's disease and their healthy first-degree relatives. 171 patients with Crohn's disease, their 105 first-degree relatives, 145 patients with ulcerative colitis and 101 first-degree relatives of patients with ulcerative colitis, 50 patients with infectious enterocolitis and 100 healthy controls were tested for ASCA employing the ELISA technique. When compared with the healthy controls (p < 0.0001) and patients with infectious enterocolitis (p < 0.0001) the prevalence of ASCA was significantly increased in patients with Crohn's disease and their first-degree relatives (p < 0.01). Further significant differences concerning the frequency of ASCA within the different groups of our study population were not observed. In particular, ASCA were not found in increased prevalence in infectious enterocolitis. These observations are compatible with a role of ASCA as a marker of genetic predisposition to Crohn's disease. Copyright (C) 2002 S. Karger AG, Basel
Static pair free energy and screening masses from correlators of Polyakov loops: continuum extrapolated lattice results at the QCD physical point
We study the correlators of Polyakov loops, and the corresponding gauge
invariant free energy of a static quark-antiquark pair in 2+1 flavor QCD at
finite temperature. Our simulations were carried out on = 6, 8, 10, 12,
16 lattices using Symanzik improved gauge action and a stout improved staggered
action with physical quark masses. The free energies calculated from the
Polyakov loop correlators are extrapolated to the continuum limit. For the free
energies we use a two step renormalization procedure that only uses data at
finite temperature. We also measure correlators with definite Euclidean time
reversal and charge conjugation symmetry to extract two different screening
masses, one in the magnetic, and one in the electric sector, to distinguish two
different correlation lengths in the full Polyakov loop correlator
SzubmikromĂ©teres lĂ©ptĂ©kƱ megfigyelĂ©sek az Ăbrennbergi CsillĂĄmpalĂĄban â HĂĄrom tektonikai ciklus elkĂŒlönĂtĂ©se
Study of fluid rock interactions in mafic granulite xenoliths from the Bakony-Balaton Highland volcanic field, Hungary
Rhönite in silicate melt inclusions of olivine phenocrysts from the alkali basalt of HegyestƱ, Balaton Highlands, Hungary
Evaluation of the efficiency of consolidants on Hungarian porous limestone by non-destructive test methods
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