935 research outputs found
Probing an nonequilibrium Einstein relation in an aging colloidal glass
We present a direct experimental measurement of an effective temperature in a
colloidal glass of Laponite, using a micrometric bead as a thermometer. The
nonequilibrium fluctuation-dissipation relation, in the particular form of a
modified Einstein relation, is investigated with diffusion and mobility
measurements of the bead embedded in the glass. We observe an unusual
non-monotonic behavior of the effective temperature : starting from the bath
temperature, it is found to increase up to a maximum value, and then decreases
back, as the system ages. We show that the observed deviation from the Einstein
relation is related to the relaxation times previously measured in dynamic
light scattering experiments.Comment: 4 pages, 4 figures, corrected references, published in Phys. Rev.
Lette
Empirical scaling of antisymmetric stratified wakes
Proceedings of the "Bluff Body Wakes and Vortex-Induced Vibrations - BBVIV-4"Initially turbulent wakes of a propelled cylinder at nonzero angles of yaw to the mean flow were measured in the horizontal centerplane plane up to approximately 100 buoyancy times, where vertical velocities are very small. The profiles of mean velocity were found to be antisymmetric throughout their lifetime, with both width and maximum velocity decaying at the same rate as previously studied momentum wakes. The maximum velocity of the profile is proportional to the angle of yaw, but the width is constant. Both the mean flow and fluctuating quantities show that the late wake is self-similar, with scaling laws that are consistent with previous work on propelled and drag wakes
A Superstabilizing -Approximation Algorithm for Dynamic Steiner Trees
In this paper we design and prove correct a fully dynamic distributed
algorithm for maintaining an approximate Steiner tree that connects via a
minimum-weight spanning tree a subset of nodes of a network (referred as
Steiner members or Steiner group) . Steiner trees are good candidates to
efficiently implement communication primitives such as publish/subscribe or
multicast, essential building blocks for the new emergent networks (e.g. P2P,
sensor or adhoc networks). The cost of the solution returned by our algorithm
is at most times the cost of an optimal solution, where is the
group of members. Our algorithm improves over existing solutions in several
ways. First, it tolerates the dynamism of both the group members and the
network. Next, our algorithm is self-stabilizing, that is, it copes with nodes
memory corruption. Last but not least, our algorithm is
\emph{superstabilizing}. That is, while converging to a correct configuration
(i.e., a Steiner tree) after a modification of the network, it keeps offering
the Steiner tree service during the stabilization time to all members that have
not been affected by this modification
Destabilizing Taylor-Couette flow with suction
We consider the effect of radial fluid injection and suction on
Taylor-Couette flow. Injection at the outer cylinder and suction at the inner
cylinder generally results in a linearly unstable steady spiralling flow, even
for cylindrical shears that are linearly stable in the absence of a radial
flux. We study nonlinear aspects of the unstable motions with the energy
stability method. Our results, though specialized, may have implications for
drag reduction by suction, accretion in astrophysical disks, and perhaps even
in the flow in the earth's polar vortex.Comment: 34 pages, 9 figure
The SPICE carbon isotope excursion in Siberia: a combined study of the upper Middle Cambrian-lowermost Ordovician Kulyumbe River section, northwestern Siberian Platform
An integrated, high-resolution chemostratigraphic (C, O and Sr isotopes) and
magnetostratigraphic study through the upper Middle Cambrianâlowermost Ordovician shallowmarine
carbonates of the northwestern margin of the Siberian Platform is reported. The interval was
analysed at the Kulyumbe section, which is exposed along the Kulyumbe River, an eastern tributary
of the Enisej River. It comprises the upper Ustâ-Brus, Labaz, Orakta, Kulyumbe, Ujgur and lower
Iltyk formations and includes the Steptoean positive carbon isotopic excursion (SPICE) studied here
in detail from upper Cambrian carbonates of the Siberian Platform for the first time. The peak of the
excursion, showing ÎŽ13C positive values as high as+4.6â°and least-altered 87Sr/86Sr ratios of 0.70909,
is reported herein from the Yurakhian Horizon of the Kulyumbe Formation. The stratigraphic position
of the SPICE excursion does not support traditional correlation of the boundary between theOrakta and
Labaz formations at the Kulyumbe River with its supposedly equivalent level in Australia, Laurentia,
South China and Kazakhstan, where the Glyptagnostus stolidotus and G. reticulatus biozones are
known to immediately precede the SPICE excursion and span the MiddleâUpper Cambrian boundary.
The CambrianâOrdovician boundary is probably situated in the middle Nyajan Horizon of the Iltyk
Formation, in which carbon isotope values show a local maximum below a decrease in the upper
part of the Nyajan Horizon, attributed herein to the Tremadocian Stage. A refined magnetic polarity
sequence confirms that the geomagnetic reversal frequency was very high during Middle Cambrian
times at 7â10 reversals per Ma, assuming a total duration of about 10 Ma and up to 100 magnetic
intervals in the Middle Cambrian. By contrast, the sequence attributed herein to the Upper Cambrian
on chemostratigraphic grounds contains only 10â11 magnetic intervals
History of degenerative spondylolisthesis: From anatomical description to surgical management
This review of the historical medical literature aimed at understanding the evolution of surgical management of degenerative spondylolisthesis over time. The Medic@, IndexCat and Gallica historical databases and PubMed and Embase medical databases were used, with several search-terms, exploring the years 1700-2018. Data from anatomical, biomechanical, pathophysiological and surgical studies were compiled. In total, 150 documents were obtained, dating from 1782 to 2018: 139 from PubMed, 1 from Medic@, 7 from IndexCat, and 3 from Gallica. The review thus ranges in time from (1) description of the first clinical cases by several authors in Europe (1782), (2) the identification of a distinct entity by MacNab (1963), and (3) surgical management by the emerging discipline of minimally invasive spine surgery, to its subsequent evolution up to the present day. Spondylolisthesis is a frequent condition potentially responsible for a variety of functional impairments. Understanding and surgical management have progressed since the 20th century. Historically, the first descriptions of treatments concerned only spondylolisthesis associated with spondylolysis, especially in young adults. More recently, there has been progress in the understanding of the disease in elderly people, with the recognition of degenerative spondylolisthesis. New technologies and surgical techniques, aided by advances in supportive care, now provide spine surgeons with powerful treatment tools. Better knowledge of the evolution of surgery throughout history should enable better understanding of current approaches and concepts for treating degenerative spondylolisthesis
Probing active forces via a fluctuation-dissipation relation: Application to living cells
We derive a new fluctuation-dissipation relation for non-equilibrium systems
with long-term memory. We show how this relation allows one to access new
experimental information regarding active forces in living cells that cannot
otherwise be accessed. For a silica bead attached to the wall of a living cell,
we identify a crossover time between thermally controlled fluctuations and
those produced by the active forces. We show that the probe position is
eventually slaved to the underlying random drive produced by the so-called
active forces.Comment: 5 page
Strong Equivalence Relations for Iterated Models
The Iterated Immediate Snapshot model (IIS), due to its elegant geometrical
representation, has become standard for applying topological reasoning to
distributed computing. Its modular structure makes it easier to analyze than
the more realistic (non-iterated) read-write Atomic-Snapshot memory model (AS).
It is known that AS and IIS are equivalent with respect to \emph{wait-free
task} computability: a distributed task is solvable in AS if and only if it
solvable in IIS. We observe, however, that this equivalence is not sufficient
in order to explore solvability of tasks in \emph{sub-models} of AS (i.e.
proper subsets of its runs) or computability of \emph{long-lived} objects, and
a stronger equivalence relation is needed. In this paper, we consider
\emph{adversarial} sub-models of AS and IIS specified by the sets of processes
that can be \emph{correct} in a model run. We show that AS and IIS are
equivalent in a strong way: a (possibly long-lived) object is implementable in
AS under a given adversary if and only if it is implementable in IIS under the
same adversary. %This holds whether the object is one-shot or long-lived.
Therefore, the computability of any object in shared memory under an
adversarial AS scheduler can be equivalently investigated in IIS
Facet ridge end points in crystal shapes
Equilibrium crystal shapes (ECS) near facet ridge end points (FRE) are
generically complex. We study the body-centered solid-on-solid model on a
square lattice with an enhanced uniaxial interaction range to test the
stability of the so-called stochastic FRE point where the model maps exactly
onto one dimensional Kardar-Parisi-Zhang type growth and the local ECS is
simple. The latter is unstable. The generic ECS contains first-order ridges
extending into the rounded part of the ECS, where two rough orientations
coexist and first-order faceted to rough boundaries terminating in
Pokrovsky-Talapov type end points.Comment: Contains 4 pages, 5 eps figures. Uses RevTe
Probabilistic cracking prediction via deep learned electrical tomography
In recent years, Electrical Tomography, namely Electrical Resistance Tomography (ERT), has emerged as a viable approach to detecting, localizing and reconstructing structural cracking patterns in concrete structures. High-fidelity ERT reconstructions, however, often require computationally-expensive optimization regimes and complex constraining and regularization schemes, which impedes pragmatic implementation in Structural Health Monitoring frameworks. To address this challenge, this paper proposes the use of predictive deep Neural Networks to directly and rapidly solve an analogous
ERT inverse problem. Specifically, the use of cross-entropy loss is used in optimizing networks forming a nonlinear mapping from ERT voltage measurements to binary probabilistic spatial crack distributions (cracked/not cracked). In this effort, Artificial Neural Networks and Convolutional Neural Networks are first trained using simulated electrical data. Following, the feasibility of the predictive networks is tested and affirmed using experimental and simulated data considering flexural and shear cracking patterns observed from reinforced concrete elements
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