257 research outputs found
Rocking and rolling: a can that appears to rock might actually roll
A beer bottle or soda can on a table, when slightly tipped and released,
falls to an upright position and then rocks up to a somewhat opposite tilt.
Superficially this rocking motion involves a collision when the flat circular
base of the container slaps the table before rocking up to the opposite tilt. A
keen eye notices that the after-slap rising tilt is not generally just
diametrically opposite the initial tilt but is veered to one side or the other.
Cushman and Duistermaat (2006) recently noticed such veering when a flat disk
with rolling boundary conditions is dropped nearly flat. Here, we generalize
these rolling disk results to arbitrary axi-symmetric bodies and to
frictionless sliding. More specifically, we study motions that almost but do
not quite involve a face-down collision of the round container's bottom with
the table-top. These motions involve a sudden rapid motion of the contact point
around the circular base. Surprisingly, like for the rolling disk, the net
angle of motion of this contact point is nearly independent of initial
conditions. This angle of turn depends simply on the geometry and mass
distribution but not on the moment of inertia about the symmetry axis. We
derive simple asymptotic formulas for this "angle of turn" of the contact point
and check the result with numerics and with simple experiments. For tall
containers (height much bigger than radius) the angle of turn is just over
and the sudden rolling motion superficially appears as a nearly symmetric
collision leading to leaning on an almost diametrically opposite point on the
bottom rim.Comment: 10 pages, 5 figure
Unified Description of Aging and Rate Effects in Yield of Glassy Solids
The competing effects of slow structural relaxations (aging) and deformation
at constant strain rate on the shear yield stress of simple model
glasses are examined using molecular simulations. At long times, aging leads to
a logarithmic increase in density and . The yield stress also rises
logarithmically with rate, but shows a sharp transition in slope at a rate that
decreases with increasing age. We present a simple phenomenological model that
includes both intrinsic rate dependence and the change in properties with the
total age of the system at yield. As predicted by the model, all data for each
temperature collapse onto a universal curve.Comment: 4 pages, 3 figure
Rate- and State-Dependent Friction Law and Statistical Properties of Earthquakes
In order to clarify how the statistical properties of earthquakes depend on
the constitutive law characterizing the stick-slip dynamics, we make an
extensive numerical simulation of the one-dimensional spring-block model with
the rate- and state-dependent friction law. Both the magnitude distribution and
the recurrence-time distribution are studied with varying the constitutive
parameters characterizing the model. While a continuous spectrum of seismic
events from smaller to larger magnitudes is obtained, earthquakes described by
this model turn out to possess pronounced ``characteristic'' features.Comment: Minor revisions are made in the text and in the figures. Accepted for
publication in Europhys. Letter
Memory in Self Organized Criticality
Many natural phenomena exhibit power law behaviour in the distribution of
event size. This scaling is successfully reproduced by Self Organized
Criticality (SOC). On the other hand, temporal occurrence in SOC models has a
Poisson-like statistics, i.e. exponential behaviour in the inter-event time
distribution, in contrast with experimental observations. We present a SOC
model with memory: events are nucleated not only as a consequence of the
instantaneous value of the local field with respect to the firing threshold,
but on the basis of the whole history of the system. The model is able to
reproduce the complex behaviour of inter-event time distribution, in excellent
agreement with experimental seismic data
The Work of Seduction : Intimacy and Subjectivity in the London 'Seduction Community'
This paper explores negotiations of intimate and sexual subjectivity among men involved in the London 'seduction community', a central locus within what is more properly regarded as a community-industry. Herein, heterosexual men undertake various forms of skills training and personal development in order to gain greater choice and control in their relationships with women. As an entry point to this discussion I consider the international media event that enveloped American 'pickup artist' Julien Blanc in November 2014. Shifting focus away from the cultural figure of the 'pickup artist' and onto socially located men, I attempt to complicate a dominant narrative that characterises men who participate in this community-industry as pathetic, pathological or perverse. This analysis makes use of extensive ethnographic research undertaken within the London seduction community, and examines how men who participate in this setting engage a mode of intimate and sexual subjectivity ordered by themes of management and enterprise. Ultimately I argue that the central logics of the seduction community are not dissonant from but are in fact consistent with broader reconfigurations of intimacy and sexuality taking place in the contemporary UK context
Towards Landslide Predictions: Two Case Studies
In a previous work [Helmstetter, 2003], we have proposed a simple physical
model to explain the accelerating displacements preceding some catastrophic
landslides, based on a slider-block model with a state and velocity dependent
friction law. This model predicts two regimes of sliding, stable and unstable
leading to a critical finite-time singularity. This model was calibrated
quantitatively to the displacement and velocity data preceding two landslides,
Vaiont (Italian Alps) and La Clapi\`ere (French Alps), showing that the former
(resp. later) landslide is in the unstable (resp. stable) sliding regime. Here,
we test the predictive skills of the state-and-velocity-dependent model on
these two landslides, using a variety of techniques. For the Vaiont landslide,
our model provides good predictions of the critical time of failure up to 20
days before the collapse. Tests are also presented on the predictability of the
time of the change of regime for la Clapi\`ere landslide.Comment: 30 pages with 12 eps figure
Logarithmic rate dependence in deforming granular materials
Rate-independence for stresses within a granular material is a basic tenet of
many models for slow dense granular flows. By contrast, logarithmic rate
dependence of stresses is found in solid-on-solid friction, in geological
settings, and elsewhere. In this work, we show that logarithmic rate-dependence
occurs in granular materials for plastic (irreversible) deformations that occur
during shearing but not for elastic (reversible) deformations, such as those
that occur under moderate repetitive compression. Increasing the shearing rate,
\Omega, leads to an increase in the stress and the stress fluctuations that at
least qualitatively resemble what occurs due to an increase in the density.
Increases in \Omega also lead to qualitative changes in the distributions of
stress build-up and relaxation events. If shearing is stopped at t=0, stress
relaxations occur with \sigma(t)/ \sigma(t=0) \simeq A \log(t/t_0). This
collective relaxation of the stress network over logarithmically long times
provides a mechanism for rate-dependent strengthening.Comment: 4 pages, 5 figures. RevTeX
Evidence for Anthropogenic Surface Loading as Trigger Mechanism of the 2008 Wenchuan Earthquake
Two and a half years prior to China's M7.9 Wenchuan earthquake of May 2008,
at least 300 million metric tons of water accumulated with additional seasonal
water level changes in the Minjiang River Valley at the eastern margin of the
Longmen Shan. This article shows that static surface loading in the Zipingpu
water reservoir induced Coulomb failure stresses on the nearby Beichuan thrust
fault system at <17km depth. Triggering stresses exceeded levels of daily lunar
and solar tides and perturbed a fault area measuring 416+/-96km^2. These stress
perturbations, in turn, likely advanced the clock of the mainshock and directed
the initial rupture propagation upward towards the reservoir on the
"Coulomb-like" Beichuan fault with rate-and-state dependent frictional
behavior. Static triggering perturbations produced up to 60 years (0.6%) of
equivalent tectonic loading, and show strong correlations to the coseismic
slip. Moreover, correlations between clock advancement and coseismic slip,
observed during the mainshock beneath the reservoir, are strongest for a longer
seismic cycle (10kyr) of M>7 earthquakes. Finally, the daily event rate of the
micro-seismicity (M>0.5) correlates well with the static stress perturbations,
indicating destabilization.Comment: 22 pages, 4 figures, 3 table
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