1,119 research outputs found
The Effects of Interfacial Properties on the Mechanical Behavior of Layered Aluminum Matrix Composites
Al/SiC-composites are not only ajfected by inelastic deformation processes in the metallic matrix but also by debonding occurring at the fiber-matrix-interface. Therefore a viscoplastic material law including damage evolution and growth, as well as a cohesive zone model for the interface, are integrated into a finite element technique. By this the influence of interfacial characteristics on the stress-strain behavior of a laminated Al/SiC-composite is ezramined
Effect of Uniaxial Tensile Loading on the Stiffness of Two-Dimensional Woven SiC/SiC - Modeling and Numerical Simulation
The behavior of two-dimensional woven SiC/SiC ceramic matrix composites (CMC) is studied by numerical simulations based on the finite element method (FEM). Starting point of the investigations is amicromechanical model regarding a three-dimensional unit cell. Damage as well as fracture of the singlecomponents - fiber bundles and inter yarn matrix - are regarded from a statistical point of view usingWeibull distribution. Statements of the behavior of the whole composite are possible by building up amacrostructure. The purpose of the current study is set on the stifiness reduction of the 2Dw compositesubjected to tensile loading in one of the fiber directions. Because of the strong anisotropy of the dam-age a tensor approach is used considering the terms of the elasticity matrix, which are determined forincreasing load. Regarding the elasticity matrix the behavior of the composite for any loading situationcan be predicted after an arbitrary preloading in one of the fiber direction
Stationary state volume fluctuations in a granular medium
A statistical description of static granular material requires ergodic
sampling of the phase space spanned by the different configurations of the
particles. We periodically fluidize a column of glass beads and find that the
sequence of volume fractions phi of post-fluidized states is history
independent and Gaussian distributed about a stationary state. The standard
deviation of phi exhibits, as a function of phi, a minimum corresponding to a
maximum in the number of statistically independent regions. Measurements of the
fluctuations enable us to determine the compactivity X, a temperature-like
state variable introduced in the statistical theory of Edwards and Oakeshott
[Physica A {\bf 157}, 1080 (1989)].Comment: published with minor change
Optical bistability in subwavelength apertures containing nonlinear media
We develop a self-consistent method to study the optical response of metallic
gratings with nonlinear media embedded within their subwavelength slits. An
optical Kerr nonlinearity is considered. Due to the large E-fields associated
with the excitation of the transmission resonances appearing in this type of
structures, moderate incoming fluxes result in drastic changes in the
transmission spectra. Importantly, optical bistability is obtained for certain
ranges of both flux and wavelength.Comment: 4 pages, 4 figure
Correlation between Voronoi volumes in disc packings
We measure the two-point correlation of free Voronoi volumes in binary disc
packings, where the packing fraction ranges from 0.8175 to
0.8380. We observe short-ranged correlations over the whole range of and anti-correlations for . The spatial extent of
the anti-correlation increases with while the position of the
maximum of the anti-correlation and the extent of the positive correlation
shrink with . We conjecture that the onset of anti-correlation
corresponds to dilatancy onset in this system
A Characterisation of the Weylian Structure of Space-Time by Means of Low Velocity Tests
The compatibility axiom in Ehlers, Pirani and Schild's (EPS) constructive
axiomatics of the space-time geometry that uses light rays and freely falling
particles with high velocity, is replaced by several constructions with low
velocity particles only. For that purpose we describe in a space-time with a
conformal structure and an arbitrary path structure the radial acceleration, a
Coriolis acceleration and the zig-zag construction. Each of these quantities
give effects whose requirement to vanish can be taken as alternative version of
the compatibility axiom of EPS. The procedural advantage lies in the fact, that
one can make null-experiments and that one only needs low velocity particles to
test the compatibility axiom. We show in addition that Perlick's standard clock
can exist in a Weyl space only.Comment: to appear in Gen.Rel.Gra
Explicit schemes for time propagating many-body wavefunctions
Accurate theoretical data on many time-dependent processes in atomic and
molecular physics and in chemistry require the direct numerical solution of the
time-dependent Schr\"odinger equation, thereby motivating the development of
very efficient time propagators. These usually involve the solution of very
large systems of first order differential equations that are characterized by a
high degree of stiffness. We analyze and compare the performance of the
explicit one-step algorithms of Fatunla and Arnoldi. Both algorithms have
exactly the same stability function, therefore sharing the same stability
properties that turn out to be optimum. Their respective accuracy however
differs significantly and depends on the physical situation involved. In order
to test this accuracy, we use a predictor-corrector scheme in which the
predictor is either Fatunla's or Arnoldi's algorithm and the corrector, a fully
implicit four-stage Radau IIA method of order 7. We consider two physical
processes. The first one is the ionization of an atomic system by a short and
intense electromagnetic pulse; the atomic systems include a one-dimensional
Gaussian model potential as well as atomic hydrogen and helium, both in full
dimensionality. The second process is the decoherence of two-electron quantum
states when a time independent perturbation is applied to a planar two-electron
quantum dot where both electrons are confined in an anharmonic potential. Even
though the Hamiltonian of this system is time independent the corresponding
differential equation shows a striking stiffness. For the one-dimensional
Gaussian potential we discuss in detail the possibility of monitoring the time
step for both explicit algorithms. In the other physical situations that are
much more demanding in term of computations, we show that the accuracy of both
algorithms depends strongly on the degree of stiffness of the problem.Comment: 24 pages, 14 Figure
Development and assessment of uni- and multivariable flood loss models for Emilia-Romagna (Italy)
Flood loss models are one important source of uncertainty in flood risk assessments. Many countries experience sparseness or absence of comprehensive high-quality flood loss data, which is often rooted in a lack of protocols and reference procedures for compiling loss datasets after flood events. Such data are an important reference for developing and validating flood loss models. We consider the Secchia River flood event of January 2014, when a sudden levee breach caused the inundation of nearly 52km2 in northern Italy. After this event local authorities collected a comprehensive flood loss dataset of affected private households including building footprints and structures and damages to buildings and contents. The dataset was enriched with further information compiled by us, including economic building values, maximum water depths, velocities and flood durations for each building. By analyzing this dataset we tackle the problem of flood damage estimation in Emilia-Romagna (Italy) by identifying empirical uni- and multivariable loss models for residential buildings and contents. The accuracy of the proposed models is compared with that of several flood damage models reported in the literature, providing additional insights into the transferability of the models among different contexts. Our results show that (1) even simple univariable damage models based on local data are significantly more accurate than literature models derived for different contexts; (2) multivariable models that consider several explanatory variables outperform univariable models, which use only water depth. However, multivariable models can only be effectively developed and applied if sufficient and detailed information is available
Positron spectra from internal pair conversion observed in {238}U + {181}Ta collisions
We present new results from measurements and simulations of positron spectra,
originating from 238U + 181Ta collisions at beam energies close to the Coulomb
barrier. The measurements were performed using an improved experimental setup
at the double-Orange spectrometer of GSI. Particular emphasis is put on the
signature of positrons from Internal-Pair-Conversion (IPC) processes in the
measured e+ energy spectra, following the de-excitation of electromagnetic
transitions in the moving Ta-like nucleus. It is shown by Monte Carlo
simulations that, for the chosen current sweeping procedure used in the present
experiments, positron emission from discrete IPC transitions can lead to rather
narrow line structures in the measured energy spectra. The measured positron
spectra do not show evidence for line structures within the statistical
accuracy achieved, although expected from the intensities of the observed
transitions (E keV) and theoretical conversion
coefficients. This is due to the reduced detection efficiency for IPC
positrons, caused by the limited spatial and momentum acceptance of the
spectrometer. A comparison with previous results, in which lines have been
observed, is presented and the implications are discussed.Comment: LaTeX, 20 pages including 5 EPS figures; Accepted by Eur. Phys.Jour.
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