10,862 research outputs found
Properties of holographic dark energy at the Hubble length
We consider holographic cosmological models of dark energy in which the
infrared cutoff is set by the Hubble's radius. We show that any interacting
dark energy model, regardless of its detailed form, can be recast as a non
interacting model in which the holographic parameter evolves slowly
with time. Two specific cases are analyzed. We constrain the parameters of both
models with observational data, and show that they can be told apart at the
perturbative level.Comment: 4 pages, 6 figures. Contribution to the Proceedings ERE201
Dynamics of shallow impact cratering
We present data for the time-dependence of wooden spheres penetrating into a
loose non-cohesive packing of glass beads. The stopping time is a factor of
three longer than the time needed to travel the total penetration
distance at the impact speed . The acceleration decreases
monotonically throughout the impact. These kinematics are modelled by a
position- and velocity-dependent stopping force that is constrained to
reproduce prior observations for the scaling of the penetration depth with the
total drop distance.Comment: 4 pages, experimen
Worldwide Workshop on Youth Involvement as a Strategy for Social, Economic and Democratic Development
Summarizes January 2000 discussions on building capacity in the field of youth service. Explores connections with social capital, economic productivity, adolescent development, marginalized youth, civic engagement, and policy. Includes country summaries
Block to granular-like transition in dense bubble flows
We have experimentally investigated 2-dimensional dense bubble flows
underneath inclined planes. Velocity profiles and velocity fluctuations have
been measured. A broad second-order phase transition between two dynamical
regimes is observed as a function of the tilt angle . For low
values, a block motion is observed. For high values, the velocity
profile becomes curved and a shear velocity gradient appears in the flow.Comment: Europhys. Lett. (2003) in pres
The Reawakening of Steinbeck
This analysis of the works of John Steinbeck will show that Steinbeck\u27s works have more depth and revelation that has been previously discovered. Through application of the concept of queer theory from Eve Kosofsky Sedgwick, this work will examine the relationships of John Steinbeck\u27s Lennie Small and George Milton and Danny and his friends from the classic novels Of Mice and Men and Tortilla Flat, respectively. This theory states that there is a fine line between what is considered a homosocial behavior and what is homosexual desire. Because Steinbeck\u27s novels and characters are regarded with an almost child-like innocence, many people have chosen to skim past the sexual ambiguities that adumbrate within the text and therefore he has gone mostly unread by critics in the 21st century. Close examination of the interactions between George Milton and Lennie Small and Danny and his friends will reveal the apparent sexual nature of the novels, and a queer reading of the novels Of Mice and Men and Tortilla Flat. This work will demonstrate through examples from Sedgwick\u27s theory that there is indeed a continuum between homosocial and homosexual behavior in Steinbeck\u27s the character
Exploring the movement dynamics of deception
Both the science and the everyday practice of detecting a lie rest on the same assumption: hidden cognitive states that the liar would like to remain hidden nevertheless influence observable behavior. This assumption has good evidence. The insights of professional interrogators, anecdotal evidence, and body language textbooks have all built up a sizeable catalog of non-verbal cues that have been claimed to distinguish deceptive and truthful behavior. Typically, these cues are discrete, individual behaviors—a hand touching a mouth, the rise of a brow—that distinguish lies from truths solely in terms of their frequency or duration. Research to date has failed to establish any of these non-verbal cues as a reliable marker of deception. Here we argue that perhaps this is because simple tallies of behavior can miss out on the rich but subtle organization of behavior as it unfolds over time. Research in cognitive science from a dynamical systems perspective has shown that behavior is structured across multiple timescales, with more or less regularity and structure. Using tools that are sensitive to these dynamics, we analyzed body motion data from an experiment that put participants in a realistic situation of choosing, or not, to lie to an experimenter. Our analyses indicate that when being deceptive, continuous fluctuations of movement in the upper face, and somewhat in the arms, are characterized by dynamical properties of less stability, but greater complexity. For the upper face, these distinctions are present despite no apparent differences in the overall amount of movement between deception and truth. We suggest that these unique dynamical signatures of motion are indicative of both the cognitive demands inherent to deception and the need to respond adaptively in a social context
Yield stress and shear-banding in granular suspensions
We study the emergence of a yield stress in dense suspensions of non-Brownian
particles, by combining local velocity and concentration measurements using
Magnetic Resonance Imaging with macroscopic rheometric experiments. We show
that the competition between gravity and viscous stresses is at the origin of
the development of a yield stress in these systems at relatively low volume
fractions. Moreover, it is accompanied by a shear banding phenomenon that is
the signature of this competition. However, if the system is carefully density
matched, no yield stress is encountered until a volume fraction of 62.7 0.3%
Avalanche statistics and time-resolved grain dynamics for a driven heap
We probe the dynamics of intermittent avalanches caused by steady addition of
grains to a quasi-two dimensional heap. To characterize the time-dependent
average avalanche flow speed v(t), we image the top free surface. To
characterize the grain fluctuation speed dv(t), we use Speckle-Visibility
Spectroscopy. During an avalanche, we find that the fluctuation speed is
approximately one-tenth the average flow speed, and that these speeds are
largest near the beginning of an event. We also find that the distribution of
event durations is peaked, and that event sizes are correlated with the time
interval since the end of the previous event. At high rates of grain addition,
where successive avalanches merge into smooth continuous flow, the relationship
between average and fluctuation speeds changes to dv Sqrt[v]
Speckle visibility spectroscopy and variable granular fluidization
We introduce a dynamic light scattering technique capable of resolving motion
that changes systematically, and rapidly, with time. It is based on the
visibility of a speckle pattern for a given exposure duration. Applying this to
a vibrated layer of glass beads, we measure the granular temperature and its
variation with phase in the oscillation cycle. We observe several transitions
involving jammed states, where the grains are at rest during some portion of
the cycle. We also observe a two-step decay of the temperature on approach to
jamming.Comment: 4 pages, 4 figures, experimen
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