9,088 research outputs found
Creep-rupture reliability analysis
A probabilistic approach to the correlation and extrapolation of creep-rupture data is presented. Time temperature parameters (TTP) are used to correlate the data, and an analytical expression for the master curve is developed. The expression provides a simple model for the statistical distribution of strength and fits neatly into a probabilistic design format. The analysis focuses on the Larson-Miller and on the Manson-Haferd parameters, but it can be applied to any of the TTP's. A method is developed for evaluating material dependent constants for TTP's. It is shown that optimized constants can provide a significant improvement in the correlation of the data, thereby reducing modelling error. Attempts were made to quantify the performance of the proposed method in predicting long term behavior. Uncertainty in predicting long term behavior from short term tests was derived for several sets of data. Examples are presented which illustrate the theory and demonstrate the application of state of the art reliability methods to the design of components under creep
Compaction dynamics in ductile granular media
Ductile compaction is common in many natural systems, but the temporal
evolution of such systems is rarely studied. We observe surprising oscillations
in the weight measured at the bottom of a self-compacting ensemble of ductile
grains. The oscillations develop during the first ten hours of the experiment,
and usually persist through the length of an experiment (one week). The weight
oscillations are connected to the grain--wall contacts, and are directly
correlated with the observed strain evolution and the dynamics of grain--wall
contacts during the compaction. Here, we present the experimental results and
characteristic time constants of the system, and discuss possible reasons for
the measured weight oscillations.Comment: 11 pages, 14 figure
The revival of the Feldstein-Horioka Puzzle and moderation of capital flows after the Global Financial Crisis (2008/09)
This study investigates the recent trend of the Feldstein-Horioka puzzle and the underlying reasons for moderation in capital flows. This issue is analysed quite inadequately for the period after the Global Financial Crisis, which represents a crucial turning point for economic climate and policies. The Feldstein-Horioka Puzzle is estimated using the World’s 13 largest economies, with panel GMM regression, between 1996 and 2016. We uncover that the Global Financial Crisis had a persistent detrimental effect on capital liberalization, after which the Feldstein-Horioka puzzle has revived and capital mobility has decreased. We suggest two possible explanations for such moderation in capital flows: the increasing risk perception and risk aversion behaviour of fund supplying countries, which increases the home bias, and capital controls against free flow of capital that have been applied after the Global Financial Crisis of 2008/2009.info:eu-repo/semantics/acceptedVersio
Size segregation and convection
The size segregation of granular materials in a vibrating container is
investigated using Molecular Dynamics. We find that the rising of larger
particles is accompanied by the existence of convection cells even in the case
of the lowest possible frequencies. The convection can, however, also be
triggered by the larger particle itself. The possibility of rising through this
mechanism strongly depends on the depth of the larger particle.Comment: 7 pages, 4 figure
Ripple and kink dynamics
We propose a relevant modification of the Nishimori-Ouchi model [{\em Phys.
Rev. Lett.} {\bf 71}, 197 (1993)] for granular landscape erosion. We explicitly
introduce a new parameter: the angle of repose , and a new process:
avalanches. We show that the parameter leads to an asymmetry of the
ripples, as observed in natural patterns. The temporal evolution of the maximum
ripple height is limited and not linear, according to recent
observations. The ripple symmetry and the kink dynamics are studied and
discussed.Comment: 7 pages, 10 figure, RevTe
Penetration depth for shallow impact cratering
We present data for the penetration of a variety of spheres, dropped from
rest, into a level non-cohesive granular medium. We improve upon our earlier
work [Uehara {\it et al.} Phys. Rev. Lett. {\bf 90}, 194301 (2003)] in three
regards. First, we explore the behavior vs sphere diameter and density more
systematically, by holding one of these parameters constant while varying the
other. Second, we prepare the granular medium more reproducibly and, third, we
measure the penetration depth more accurately. The new data support our
previous conclusion that the penetration depth is proportional to the 1/2 power
of sphere density, the 2/3 power of sphere diameter, and the 1/3 power of total
drop distance
Wall effects on granular heap stability
We investigate the effects of lateral walls on the angle of movement and on
the angle of repose of a granular pile. Our experimental results for beads
immersed in water are similar to previous results obtained in air and to recent
numerical simulations. All of these results, showing an increase of pile angles
with a decreasing gap width, are explained by a model based on the redirection
of stresses through the granular media. Two regimes are observed depending on
the bead diameter. For large beads, the range of wall effects corresponds to a
constant number of beads whereas it corresponds to a constant characteristic
length for small beads as they aggregate via van der Waals forces
The Dendritic magnetic avalanches in carbon-free MgB thin films with and without a deposited Au layer
From the magneto optics images (MOI), the dendritic magnetic avalanche is
known to appear dominantly for thin films of the newly discovered MgB. To
clarify the origin of this phenomenon, we studied in detail the MOI of
carbon-free MgB thin films with and without a deposited gold layer. The MOI
indicated carbon contamination was not the main source of the avalanche. The
MOI clearly showed that the deposition of metallic gold deposition on top of a
MgB thin film improved its thermal stability and suppressed the sudden
appearance of the dendritic flux avalanche. This is consistent with the
previous observation of flux noise in the magnetization.Comment: 9 pages, 4 figeure
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