4,053 research outputs found
Modelling and control of a high redundancy actuator
The high redundancy actuation concept is a completely new approach to fault tolerance, and it is important to appreciate that it provides a transformation of the characteristics of actuators so that the actuation performance (capability) degrades slowly rather than suddenly failing, even though individual elements themselves fail. This paper aims to demonstrate the viability of the concept by showing that a highly redundant actuator, comprising a relatively large number of actuation elements, can be controlled in such a way that faults in individual elements are inherently accommodated, although some degradation in overall performance will inevitably be found. The paper introduces the notion of fault-tolerant systems and the highly redundant actuator concept. Then a model for a two by two configuration with electro-mechanical actuation elements is derived. Two classical control approaches are then considered based on frequency domain techniques. Finally simulation results under a number of faults show the viability of the approach for fault accommodation without re-configuratio
Einstein Equations and MOND Theory from Debye Entropic Gravity
Verlinde's proposal on the entropic origin of gravity is based strongly on
the assumption that the equipartition law of energy holds on the holographic
screen induced by the mass distribution of the system. However, from the theory
of statistical mechanics we know that the equipartition law of energy does not
hold in the limit of very low temperature. Inspired by the Debye model for the
equipartition law of energy in statistical thermodynamics and adopting the
viewpoint that gravitational systems can be regarded as a thermodynamical
system, we modify Einstein field equations. We also perform the study for
Poisson equation and modified Newtonian dynamics (MOND). Interestingly enough,
we find that the origin of the MOND theory can be understood from Debye
entropic gravity perspective. Thus our study may fill in the gap existing in
the literature understanding the theoretical origin of MOND theory. In the
limit of high temperature our results reduce to their respective standard
gravitational equations.Comment: 8 pages, no figures. Accepted for publication in JCA
Asymptotic Stability of the Relativistic Boltzmann Equation for the Soft Potentials
In this paper it is shown that unique solutions to the relativistic Boltzmann
equation exist for all time and decay with any polynomial rate towards their
steady state relativistic Maxwellian provided that the initial data starts out
sufficiently close in . If the initial data are continuous then
so is the corresponding solution. We work in the case of a spatially periodic
box. Conditions on the collision kernel are generic in the sense of
(Dudy{\'n}ski and Ekiel-Je{\.z}ewska, Comm. Math. Phys., 1988); this resolves
the open question of global existence for the soft potentials.Comment: 64 page
The antiferromagnetic phi4 Model, II. The one-loop renormalization
It is shown that the four dimensional antiferromagnetic lattice phi4 model
has the usual non-asymptotically free scaling law in the UV regime around the
chiral symmetrical critical point. The theory describes a scalar and a
pseudoscalar particle. A continuum effective theory is derived for low
energies. A possibility of constructing a model with a single chiral boson is
mentioned.Comment: To appear in Phys. Rev.
Hilbert Expansion from the Boltzmann equation to relativistic Fluids
We study the local-in-time hydrodynamic limit of the relativistic Boltzmann
equation using a Hilbert expansion. More specifically, we prove the existence
of local solutions to the relativistic Boltzmann equation that are nearby the
local relativistic Maxwellian constructed from a class of solutions to the
relativistic Euler equations that includes a large subclass of near-constant,
non-vacuum fluid states. In particular, for small Knudsen number, these
solutions to the relativistic Boltzmann equation have dynamics that are
effectively captured by corresponding solutions to the relativistic Euler
equations.Comment: 50 page
Continuous Percolation Phase Transitions of Two-dimensional Lattice Networks under a Generalized Achlioptas Process
The percolation phase transitions of two-dimensional lattice networks under a
generalized Achlioptas process (GAP) are investigated. During the GAP, two
edges are chosen randomly from the lattice and the edge with minimum product of
the two connecting cluster sizes is taken as the next occupied bond with a
probability . At , the GAP becomes the random growth model and leads
to the minority product rule at . Using the finite-size scaling analysis,
we find that the percolation phase transitions of these systems with are always continuous and their critical exponents depend on .
Therefore, the universality class of the critical phenomena in two-dimensional
lattice networks under the GAP is related to the probability parameter in
addition.Comment: 7 pages, 14 figures, accepted for publication in Eur. Phys. J.
Multi-resolution texture classification based on local image orientation
The aim of this paper is to evaluate quantitatively the discriminative power of the image orientation in the texture classification process. In this regard, we have evaluated the performance of two texture classification schemes where the image orientation is extracted using the partial derivatives of the Gaussian function. Since the texture descriptors are dependent on the observation scale, in this study the main emphasis is placed on the implementation of multi-resolution texture analysis schemes. The experimental results were obtained when the analysed texture descriptors were applied to standard texture databases
Wavy stripes and squares in zero P number convection
A simple model to explain numerically observed behaviour of chaotically
varying stripes and square patterns in zero Prandtl number convection in
Boussinesq fluid is presented. The nonlinear interaction of mutually
perpendicular sets of wavy rolls, via higher mode, may lead to a competition
between the two sets of wavy rolls. The appearance of square patterns is due to
the secondary forward Hopf bifurcation of a set of wavy rolls.Comment: 8 pages and 3 figures, late
Urban climate change, livelihood vulnerability and narratives of generational responsibility in Jinja, Uganda
There is an urgent need to understand lived experiences of climate change in the context of African cities, where even small climate shocks can have significant implications for the livelihoods of the urban poor. This article examines narratives of climate and livelihood changes within Jinja Municipality, Uganda, emphasizing how Jinja's residents make sense of climate change through their own narrative frames rather than through the lens of global climate change discourses. We demonstrate how the onset of climate change in Jinja is widely attributed to perceived moral and environmental failings on the part of a present generation that is viewed as both more destructive than previous generations and unable to preserve land, trees and other resources for future generations. A focus on local ontologies of climate change highlights how the multiple, intersecting vulnerabilities of contemporary urban life in Jinja serve to obfuscate not only the conditions of possibility of an immediate future, but the longer-term horizons for future generations, as changing weather patterns exacerbate existing challenges people face in adapting to wider socio-economic changes and rising livelihood vulnerability. This form of analysis situates changing climate and environments within the context of everyday urban struggles and emphasizes the need for civic participation in developing climate change strategies that avoid the pitfalls of climate reductionism. The article draws on more than 150 qualitative interviews, generational dialogue groups, and creative methods based on research-led community theatre
Granular Solid Hydrodynamics
Granular elasticity, an elasticity theory useful for calculating static
stress distribution in granular media, is generalized to the dynamic case by
including the plastic contribution of the strain. A complete hydrodynamic
theory is derived based on the hypothesis that granular medium turns
transiently elastic when deformed. This theory includes both the true and the
granular temperatures, and employs a free energy expression that encapsulates a
full jamming phase diagram, in the space spanned by pressure, shear stress,
density and granular temperature. For the special case of stationary granular
temperatures, the derived hydrodynamic theory reduces to {\em hypoplasticity},
a state-of-the-art engineering model.Comment: 42 pages 3 fi
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