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A combined experimental-numerical study to tensile behaviour of limestone
In this paper, a combined experimental-computational study of double-edge notched stone specimen subject to cyclic tensile loading is presented. In the experimental part, the load-deformation response and the local displacement field are recorded. Both experimental results are used to validate a numerical model for the description of fracture within finite elements. The model uses displacement discontinuities to model cracks. These discontinuities are implemented using the partition of unity property of finite element shape functions. In the discontinuity, a combined damage-plasticity cohesive law is used. Numerical simulations are compared with experimental observations
A Discontinuous Model to Study Fracture of Brittle Materials
In this paper, the partition of the unity property of finite element shape functions is used to introduce displacement discontinuities into finite elements. The discontinuous character of the displacement field is captured with the Heaviside step function. Using the partition of unity concept, the governing equation of the continuum and the discontinuity are separated and are consequently described by different constitutive laws. Inside the discontinuity, a plasticity based constitutive law is used to describe the decrease of tractions in function of the crack opening while the continuum is assumed to remain elastic. The methodology will be described and validated with a comparison between numerical simulations and experimental results.This paper is dedicated to J. Sejnoha, TU Prague, with respect and admiration for his scientific achievement.
A discrete model for cyclic mode I loading
AbstractThe cyclic behaviour of a double-edge notched specimen loaded in tension is studied. Cracks in the material are modelled by displacement discontinuities that can propagate during computation. Within these discontinuities, a cohesive zone model is used. The model assumes an additive split of the inelastic jump into a recoverable and an unrecoverable part. The influence of model parameters and discretisation is studied and the results have been compared with experimental data
Towards a Microscopic Theory for Metallic Heavy-Fermion Point Contacts
The bias-dependent resistance R(V) of NS-junctions is calculated using the
Keldysh formalism in all orders of the transfer matrix element. We present a
compact and simple formula for the Andreev current, that results from the
coupling of electrons and holes on the normal side via the anomalous Green's
function on the superconducting side. Using simple BCS Nambu-Green's functions
the well known Blonder-Tinkam-Klapwijk theory can be recovered. Incorporating
the energy-dependent quasi-particle lifetime of the heavy fermions strongly
reduces the Andreev-reflection signal.Comment: 3 pages, TeX type, 1 eps figure include, SCES96 Z\"uric
Comparison of potato varieties between seasons and their potential for acrylamide formation
BACKGROUND: Acrylamide is a probable human carcinogen produced during food preparation, including frying of potato products. The aim of this study was to investigate the impact of seasonal variation on tuber composition and its acrylamide generation potential. RESULTS: The chemical composition of potato varieties used respectively for French fry (Bintje and Ramos) and crisp (Lady Rosetta and Saturna) production was studied throughout a storage period of 9 months during two growing seasons (2003 and 2004), in addition to their acrylamide generation potential during preparation of French fries. A significant impact of variable climatological conditions on the reducing sugar, dry matter, total free amino acid and free asparagine contents of tubers was observed. Exceptionally warm summers gave rise to a lower reducing sugar content (expressed on a dry matter basis) and thus a lower susceptibility to acrylamide generation during frying. CONCLUSION: It cannot be excluded that potato growers and the potato-processing industry are confronted with some harvests that are more prone to acrylamide generation than others owing to climatological variability, thus confirming the importance of a multifactorial approach to mitigate acrylamide generation in potato products.</p
Break junctions of the heavy-fermion superconductors
Mechanical-controllable break junctions of the heavy-fermion superconductors
can show Josephson-like superconducting anomalies. But a systematic study on
the contact size demonstrates that these anomalies are mainly due to Maxwell's
resistance being suppressed in the superconducting heavy-fermion phase. Up to
day, we could not find any superconducting features by vacuum-tunnelling
spectroscopy, providing further evidence for the pair-breaking effect of the
heavy-fermion interfaces.Comment: 5 pages, EPS figures included, REVTeX, to be published in Physica B
9
Point Contact Spectroscopy of Superconducting Gap Anisotropy in Nickel Borocarbide Compound LuNi2B2C
Point contacts are used to investigate the anisotropy of the superconducting
energy gap in LuNi2B2C in the ab plane and along the c axis. It is shown that
the experimental curves should be described assuming that the superconducting
gap is non-uniformly distributed over the Fermi surface. The largest and the
smallest gaps have been estimated by two-gap fitting models. It is found that
the largest contribution to the point-contact conductivity in the c direction
is made by a smaller gap and, in the ab plane by a larger gap. The deviation
from the one-gap BCS model is pronounced in the temperature dependence of the
gap in both directions. The temperature range, where the deviation occurs, is
for the c direction approximately 1.5 times more than in the ab plane. The
\Gamma parameter, allowing quantitatively estimate the gap anisotropy by
one-gap fitting, in c direction is also about 1.5 times greater than in the ab
plane. Since it is impossible to describe satisfactorily such gap distribution
either by the one- or two-gap models, a continuous, dual-maxima model of gap
distribution over the Fermi surface should be used to describe
superconductivity in this material.Comment: 10 pages, 14 Figs, accepted in PR
The puzzle of 90 degree reorientation in the vortex lattice of borocarbide superconductors
We explain 90 degree reorientation in the vortex lattice of borocarbide
superconductors on the basis of a phenomenological extension of the nonlocal
London model that takes full account of the symmetry of the system. We propose
microscopic mechanisms that could generate the correction terms and point out
the important role of the superconducting gap anisotropy.Comment: 4 pages, 2 eps figure
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