5,036 research outputs found
Relation between dry granular flow regimes and morphology of deposits: formation of levees in pyroclastic deposits
Experiments on dry granular matter flowing down an inclined plane are
performed in order to study the dynamics of dense pyroclastic flows. The plane
is rough, and always wider than the flow, focusing this study on the case of
laterally unconfined (free boundary) flows.We found that several flow regimes
exist depending on the input fluxand on the inclination of the plane. Each flow
regime corresponds to a particular morphology of the associated deposit. In one
of these regimes, the flow reaches a steady state, and the deposit exhibits a
levee/channel morphology similar to those observed on small pyroclastic flow
deposits. The levees result from the combination between lateral static zones
on each border of the flow and the drainage of the central part of the flow
after the supply stops. Particle segregation featuresare created during the
flow, corresponding to those observed on the deposits of pyroclastic flows.
Moreover, the measurements of the deposit morphology (thickness of the channel,
height of the levees, width of the deposit) are quantitatively related to
parameters of the dynamics of the flow (flux, velocity, height of the flow),
leading to a way of studying the flow dynamics from only measurements of the
deposit. Some attempts to make extensions to natural cases are discussed
through experiments introducing the polydispersity of the particle sizes and
the particle segregation process
Evidence of reverse and intermediate size segregation in dry granular flows down a rough incline
In a dry granular flow, size segregation behave differently for a mixture
containing a few large beads with a size ratio (S) above 5 (Thomas, Phys.Rev.E
62,96(2000)). For moderate large S, large beads migrate to an intermediate
depth in the bed: this is called intermediate segregation. For the largest S,
large beads migrate to the bottom: this is called reverse segregation (in
contrast with surface segregation). As the reversal and intermediate depth
values depend on the bead fraction, this numerical study mainly uses a single
large tracer. Small fractions are also computed showing the link between a
tracer behavior and segregation process. For half-filled rotating drum and for
rough incline, two and three (3D) dimensional cases are studied. In the
tumbler, trajectories of a large tracer show that it reaches a constant depth
during the flow. For large S, this depth is intermediate with a progressive
sinking when S increases. Largest S correspond to tracers at the bottom of the
flow. All 3D simulation are in quantitative agreement with the experiments. In
the flow down an incline, a large tracer reaches an equilibrium depth during
flow. For large S, its depth is intermediate, inside the bed. For the largest
S, its depth is reverse, near the bottom. Results are slightly different for
thin or thick flow. For 3D thick flows, the reversal between surface and bottom
positions occurs within a short range of S: no tracer stabilizes near
mid-height and two reachable intermediate depth layers exist, below the surface
and above the bottom. For 3D thin flows, all intermediate depths are reachable,
depending on S. The numerical study of larger tracer fractions (5-10%) shows
the 3 segregation patterns (surface, intermediate, reverse) corresponding to
the 3 types of equilibrium depth. The reversal is smoother than for a single
tracer. It happens around S=4.5, in agreement with experiments.Comment: 18 pages, 27 figure
When are Stochastic Transition Systems Tameable?
A decade ago, Abdulla, Ben Henda and Mayr introduced the elegant concept of
decisiveness for denumerable Markov chains [1]. Roughly speaking, decisiveness
allows one to lift most good properties from finite Markov chains to
denumerable ones, and therefore to adapt existing verification algorithms to
infinite-state models. Decisive Markov chains however do not encompass
stochastic real-time systems, and general stochastic transition systems (STSs
for short) are needed. In this article, we provide a framework to perform both
the qualitative and the quantitative analysis of STSs. First, we define various
notions of decisiveness (inherited from [1]), notions of fairness and of
attractors for STSs, and make explicit the relationships between them. Then, we
define a notion of abstraction, together with natural concepts of soundness and
completeness, and we give general transfer properties, which will be central to
several verification algorithms on STSs. We further design a generic
construction which will be useful for the analysis of {\omega}-regular
properties, when a finite attractor exists, either in the system (if it is
denumerable), or in a sound denumerable abstraction of the system. We next
provide algorithms for qualitative model-checking, and generic approximation
procedures for quantitative model-checking. Finally, we instantiate our
framework with stochastic timed automata (STA), generalized semi-Markov
processes (GSMPs) and stochastic time Petri nets (STPNs), three models
combining dense-time and probabilities. This allows us to derive decidability
and approximability results for the verification of these models. Some of these
results were known from the literature, but our generic approach permits to
view them in a unified framework, and to obtain them with less effort. We also
derive interesting new approximability results for STA, GSMPs and STPNs.Comment: 77 page
Influence of Rough and Smooth Walls on Macroscale Flows in Tumblers
Walls in discrete element method simulations of granular flows are sometimes
modeled as a closely packed monolayer of fixed particles, resulting in a rough
wall rather than a geometrically smooth wall. An implicit assumption is that
the resulting rough wall differs from a smooth wall only locally at the
particle scale. Here we test this assumption by considering the impact of the
wall roughness at the periphery of the flowing layer on the flow of
monodisperse particles in a rotating spherical tumbler. We find that varying
the wall roughness significantly alters average particle trajectories even far
from the wall. Rough walls induce greater poleward axial drift of particles
near the flowing layer surface, but decrease the curvature of the trajectories.
Increasing the volume fill level in the tumbler has little effect on the axial
drift for rough walls, but increases the drift while reducing curvature of the
particle trajectories for smooth walls. The mechanism for these effects is
related to the degree of local slip at the bounding wall, which alters the
flowing layer thickness near the walls, affecting the particle trajectories
even far from the walls near the equator of the tumbler. Thus, the proper
choice of wall conditions is important in the accurate simulation of granular
flows, even far from the bounding wall.Comment: 32 pages, 19 figures, regular article, accepted for publication in
Physical Review E 200
Agronomists and accounting. The beginnings of capitalist rationalisation on the farm (1800-1850)
At the dawn of the nineteenth century numerous debates took place on the development of capita-list agriculture and the ways of making as much profit as possible from farm land. Until now this subject has hardly been examined and is unique in that it pertains to the economic history of agriculture, the history of agronomy and the history of managerial thinking. This article aims to highlight the usage of double-entry accounting for agronomic experiments in the first half of the nineteenth century, as well as the significance of the results and the way these were debated. Our aim is to present the authors’ reasons and the role played by bookkeeping in the construction of economically rational knowledge and reasoning. Thus we will bring to light two mechanisms which are common to this accounting quantification drive: data tabulation and the inclusion of data in balance sheets, making it possible to compare inputs and outputs in production processes
A Hybrid Approach to Privacy-Preserving Federated Learning
Federated learning facilitates the collaborative training of models without
the sharing of raw data. However, recent attacks demonstrate that simply
maintaining data locality during training processes does not provide sufficient
privacy guarantees. Rather, we need a federated learning system capable of
preventing inference over both the messages exchanged during training and the
final trained model while ensuring the resulting model also has acceptable
predictive accuracy. Existing federated learning approaches either use secure
multiparty computation (SMC) which is vulnerable to inference or differential
privacy which can lead to low accuracy given a large number of parties with
relatively small amounts of data each. In this paper, we present an alternative
approach that utilizes both differential privacy and SMC to balance these
trade-offs. Combining differential privacy with secure multiparty computation
enables us to reduce the growth of noise injection as the number of parties
increases without sacrificing privacy while maintaining a pre-defined rate of
trust. Our system is therefore a scalable approach that protects against
inference threats and produces models with high accuracy. Additionally, our
system can be used to train a variety of machine learning models, which we
validate with experimental results on 3 different machine learning algorithms.
Our experiments demonstrate that our approach out-performs state of the art
solutions
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