312 research outputs found
A qualitative Langevin-like model for the coexistence of two distinct granular temperatures
In the present work, we study qualitatively the physics of granular
temperature coexistence, for a mixture of two different species. Our model
captures its essential aspects and this allows us to get insights on the
physical mechanisms of distinct temperature coexistence, in a way which is not
obscured by the complexities of kinetic theories or numerical simulations. Our
simple model is consistent with limit situations where we should expect
equality for the granular temperatures for the mixture.Comment: Accepted to be published on Physica
Projectile-shape dependence of impact craters in loose granular media
We report on the penetration of cylindrical projectiles dropped from rest
into a dry, noncohesive granular medium. The cylinder length, diameter,
density, and tip shape are all explicitly varied. For deep penetrations, as
compared to the cylinder diameter, the data collapse onto a single scaling law
that varies as the 1/3 power of the total drop distance, the 1/2 power of
cylinder length, and the 1/6 power of cylinder diameter. For shallow
penetrations, the projectile shape plays a crucial role with sharper objects
penetrating deeper.Comment: 3 pages, 3 figures; experimen
The effects of facial attractiveness and trustworthiness in online peer-to-peer markets
Online peer-to-peer markets, such as Airbnb, often include profile photos of sellers to reduce anonymity. Ert, Fleischer, and Magen (2016) found that more trustworthy-looking, but not more attractive-looking, Airbnb hosts from Stockholm charge higher prices for similar apartments. This suggests that people are willing to pay more for a night in an apartment if the host looks trustworthy. Here, we present a pre-registered replication testing how photo-based impressions of hostsâ attractiveness and trustworthiness influence rental prices. We extend previous investigations by (a) controlling for additional features related to price (e.g., the apartmentâs location value), (b) testing for an influence of other host features, such as race and facial expression, and (c) analyzing a substantially larger sample of apartments. An analysis of 1,020 listings in New York City showed that more attractive-looking, but not more trustworthy-looking, hosts charge higher prices for their apartments. Compared to White hosts, Black (but not Asian) hosts charge lower prices for their apartments. Hosts who smile more intensely in their profile photo charge higher prices. Our results support the general conclusion that people rely on profile photos in online markets, though we find that attractiveness is more important than trustworthiness. Keywords: first impressions, peer-to-peer markets, trustworthiness, attractivenes
Confined granular packings: structure, stress, and forces
The structure and stresses of static granular packs in cylindrical containers
are studied using large-scale discrete element molecular dynamics simulations
in three dimensions. We generate packings by both pouring and sedimentation and
examine how the final state depends on the method of construction. The vertical
stress becomes depth-independent for deep piles and we compare these stress
depth-profiles to the classical Janssen theory. The majority of the tangential
forces for particle-wall contacts are found to be close to the Coulomb failure
criterion, in agreement with the theory of Janssen, while particle-particle
contacts in the bulk are far from the Coulomb criterion. In addition, we show
that a linear hydrostatic-like region at the top of the packings unexplained by
the Janssen theory arises because most of the particle-wall tangential forces
in this region are far from the Coulomb yield criterion. The distributions of
particle-particle and particle-wall contact forces exhibit
exponential-like decay at large forces in agreement with previous studies.Comment: 11 pages, 11 figures, submitted to PRE (v2) added new references,
fixed typo
On the existence of a Bose Metal at T=0
This paper aims to justify, at a microscopic level, the existence of a
two-dimensional Bose metal, i.e. a metallic phase made out of Cooper pairs at
T=0. To this end, we consider the physics of quantum phase fluctuations in
(granular) superconductors in the absence of disorder and emphasise the role of
two order parameters in the problem, viz. phase order and charge order. We
focus on the 2-d Bose Hubbard model in the limit of very large fillings, i.e. a
2-d array of Josephson junctions. We find that the algebra of phase
fluctuations is that of the Euclidean group in this limit, and show
that the model is equivalent to two coupled XY models in (2+1)-d, one
corresponding to the phase degrees of freedom, and the other the charge degrees
of freedom. The Bose metal, then, is the phase in which both these degrees of
freedom are disordered(as a result of quantum frustration). We analyse the
model in terms of its topological excitations and suggest that there is a
strong indication that this state represents a surface of critical points, akin
to the gapless spin liquid states. We find a remarkable consistency of this
scenario with certain low-T_c thin film experiments.Comment: 16 pages, 2 figure
Slow relaxations and history dependence of the transport properties of layered superconductors
We study numerically the time evolution of the transport properties of
layered superconductors after different preparations. We show that, in
accordance with recent experiments in BSCCO performed in the second peak region
of the phase diagram (Portier et al, 2001), the relaxation strongly depends on
the initial conditions and is extremely slow. We investigate the dependence on
the pinning center density and the perturbation applied. We compare the
measurements to recent findings in tapped granular matter and we interpret our
results with a rather simple picture.Comment: 4 pages, 4 fig
Quantum entanglement with acousto-optic modulators: 2-photon beatings and Bell experiments with moving beamsplitters
We present an experiment testing quantum correlations with frequency shifted
photons. We test Bell inequality with 2-photon interferometry where we replace
the beamsplitters by acousto-optic modulators, which are equivalent to moving
beamsplitters. We measure the 2-photon beatings induced by the frequency
shifts, and we propose a cryptographic scheme in relation. Finally, setting the
experiment in a relativistic configuration, we demonstrate that the quantum
correlations are not only independent of the distance but also of the time
ordering between the two single-photon measurements.Comment: 14 pages, 16 figure
Materiality in information environments: Objects, spaces, and bodies in three outpatient hemodialysis facilities
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152032/1/asi24277.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152032/2/asi24277_am.pd
Astronomical Distance Determination in the Space Age: Secondary Distance Indicators
The formal division of the distance indicators into primary and secondary leads to difficulties in description of methods which can actually be used in two ways: with, and without the support of the other methods for scaling. Thus instead of concentrating on the scaling requirement we concentrate on all methods of distance determination to extragalactic sources which are designated, at least formally, to use for individual sources. Among those, the Supernovae Ia is clearly the leader due to its enormous success in determination of the expansion rate of the Universe. However, new methods are rapidly developing, and there is also a progress in more traditional methods. We give a general overview of the methods but we mostly concentrate on the most recent developments in each field, and future expectations. © 2018, The Author(s)
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