2,067 research outputs found
Computational modelling and experimental characterisation of heterogeneous materials
Heterogeneous materials can exhibit behaviour under load that cannot be described by classical continuum elasticity. Beams in bending can show a relative stiffening as the beam depth tends to zero, a size effect. Size effects are recognised in higher order continuum elastic theories such as micropolar elasticity. The drawback of higher order theories is the requirement of addition constitutive relations and associated properties that are often difficult to establish experimentally. Furthermore the finite element method, of great benefit in classical elasticity, has shown limitations when applied to micropolar elasticity. The determination of additional constitutive properties and the computational modelling of micropolar elasticity will be discussed in the context of a model heterogeneous material loaded in simple 3 point bending. The model material was created by drilling holes in aluminium bar in a regular pattern, with the hole axis normal to the plane of bending. The bending tests show that a size effect is present. These results are compared against modelling the detailed beam geometries in the finite element package ANSYS, which again shows the size effect. These two bending test are used to extract the additional micropolar elastic material properties. A comparison is then made against analytical solutions,numerical solutions using a micropolar beam finite element and a micropolar plane stress control volume method.It will be shown that the need for extensive experimental testing to determine the additional constitutive properties may not be necessary with the appropriate use of numerical methods
Scaling analysis of a divergent prefactor in the metastable lifetime of a square-lattice Ising ferromagnet at low temperatures
We examine a square-lattice nearest-neighbor Ising quantum ferromagnet
coupled to -dimensional phonon baths. Using the density-matrix equation, we
calculate the transition rates between configurations, which determines the
specific dynamic. Applying the calculated stochastic dynamic in Monte Carlo
simulations, we measure the lifetimes of the metastable state. As the magnetic
field approaches at low temperatures, the lifetime prefactor diverges
because the transition rates between certain configurations approaches zero
under these conditions. Near and zero temperature, the divergent
prefactor shows scaling behavior as a function of the field, temperature, and
the dimension of the phonon baths. With proper scaling, the simulation data at
different temperatures and for different dimensions of the baths collapse well
onto two master curves, one for and one for .Comment: published versio
Geophysical Exploration of Vesta
Dawnās year-long stay at Vesta allows
comprehensive mapping of the shape, topography,
geology, mineralogy, elemental abundances, and
gravity field using itās three instruments and highprecision
spacecraft navigation. In the current Low
Altitude Mapping Orbit (LAMO), tracking data is being
acquired to develop a gravity field expected to be
accurate to degree and order ~20 [1, 2]. Multi-angle
imaging in the Survey and High Altitude Mapping
Orbit (HAMO) has provided adequate stereo coverage
to develop a shape model accurate to ~10 m at 100 m
horizontal spatial resolution. Accurate mass determination
combined with the shape yields a more precise
value of bulk density, albeit with some uncertainty
resulting from the unmeasured seasonally-dark north
polar region. The shape and gravity of Vesta can be
used to infer the interior density structure and investigate
the nature of the crust, informing models for Vestaās
formation and evolution
Vertex Reconstruction Using a Single Layer Silicon Detector
Typical vertex finding algorithms use reconstructed tracks, registered in a
multi-layer detector, which directly point to the common point of origin. A
detector with a single layer of silicon sensors registers the passage of
primary particles only in one place. Nevertheless, the information available
from these hits can also be used to estimate the vertex position, when the
geometrical properties of silicon sensors and the measured ionization energy
losses of the particles are fully exploited. In this paper the algorithm used
for this purpose in the PHOBOS experiment is described. The vertex
reconstruction performance is studied using simulations and compared with
results obtained from real data. The very large acceptance of a single-layered
multiplicity detector permits vertex reconstruction for low multiplicity events
where other methods, using small acceptance subdetectors, fail because of
insufficient number of registered primary tracks.Comment: accepted for publication in Nucl. Instr. Meth.
Ricci-flat supertwistor spaces
We show that supertwistor spaces constructed as a Kahler quotient of a
hyperkahler cone (HKC) with equal numbers of bosonic and fermionic coordinates
are Ricci-flat, and hence, Calabi-Yau. We study deformations of the
supertwistor space induced from deformations of the HKC. We also discuss
general infinitesimal deformations that preserve Ricci-flatness.Comment: 13 pages, references and comments adde
Observability and nonlinear filtering
This paper develops a connection between the asymptotic stability of
nonlinear filters and a notion of observability. We consider a general class of
hidden Markov models in continuous time with compact signal state space, and
call such a model observable if no two initial measures of the signal process
give rise to the same law of the observation process. We demonstrate that
observability implies stability of the filter, i.e., the filtered estimates
become insensitive to the initial measure at large times. For the special case
where the signal is a finite-state Markov process and the observations are of
the white noise type, a complete (necessary and sufficient) characterization of
filter stability is obtained in terms of a slightly weaker detectability
condition. In addition to observability, the role of controllability in filter
stability is explored. Finally, the results are partially extended to
non-compact signal state spaces
Bi-Objective Community Detection (BOCD) in Networks using Genetic Algorithm
A lot of research effort has been put into community detection from all
corners of academic interest such as physics, mathematics and computer science.
In this paper I have proposed a Bi-Objective Genetic Algorithm for community
detection which maximizes modularity and community score. Then the results
obtained for both benchmark and real life data sets are compared with other
algorithms using the modularity and MNI performance metrics. The results show
that the BOCD algorithm is capable of successfully detecting community
structure in both real life and synthetic datasets, as well as improving upon
the performance of previous techniques.Comment: 11 pages, 3 Figures, 3 Tables. arXiv admin note: substantial text
overlap with arXiv:0906.061
Quantum Dynamics in Non-equilibrium Strongly Correlated Environments
We consider a quantum point contact between two Luttinger liquids coupled to
a mechanical system (oscillator). For non-vanishing bias, we find an effective
oscillator temperature that depends on the Luttinger parameter. A generalized
fluctuation-dissipation relation connects the decoherence and dissipation of
the oscillator to the current-voltage characteristics of the device. Via a
spectral representation, this result is generalized to arbitrary leads in a
weak tunneling regime.Comment: 4 pages, 1 figur
The Far-Infrared Properties of Spatially Resolved AKARI Observations
We present the spatially resolved observations of IRAS sources from the
Japanese infrared astronomy satellite AKARI All-Sky Survey during the
performance verification (PV) phase of the mission. We extracted reliable point
sources matched with IRAS point source catalogue. By comparing IRAS and AKARI
fluxes, we found that the flux measurements of some IRAS sources could have
been over or underestimated and affected by the local background rather than
the global background. We also found possible candidates for new AKARI sources
and confirmed that AKARI observations resolved IRAS sources into multiple
sources. All-Sky Survey observations are expected to verify the accuracies of
IRAS flux measurements and to find new extragalactic point sources.Comment: 11 pages, 7 figures, accepted publication in PASJ AKARI special issu
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