13,673 research outputs found
Recommended from our members
A GA-based technique for the scheduling of storage tanks
YesThis paper proposes the application of a
genetic algorithm based methodology for the scheduling
of storage tanks. The proposed approach is an
integration of GA and heuristic rule-based techniques,
which decomposes the complex mixed integer
optimisation problem into integer and real number subproblems.
The GA string considers the integer problem,
and the heuristic approach solves the real number
problems within the GA framework. The algorithm is
demonstrated for a test problem related to a water
treatment facility at a port, and has been found to give a
significantly better schedule than those generated using a
heuristic-based approach
On the use of a Modified Latin Hypercube Sampling (MLHS) approach in the estimation of a Mixed Logit model for vehicle choice
Quasi-random number sequences have been used extensively for many years in the simulation of integrals that do not have a closed-form expression, such as Mixed Logit and Multinomial Probit choice probabilities. Halton sequences are one example of such quasi-random number sequences, and various types of Halton sequences, including standard, scrambled, and shuffled versions, have been proposed and tested in the context of travel demand modeling. In this paper, we propose an alternative to Halton sequences, based on an adapted version of Latin Hypercube Sampling. These alternative sequences, like scrambled and shuffled Halton sequences, avoid the undesirable correlation patterns that arise in standard Halton sequences. However, they are easier to create than scrambled or shuffled Halton sequences. They also provide more uniform coverage in each dimension than any of the Halton sequences. A detailed analysis, using a 16-dimensional Mixed Logit model for choice between alternative-fuelled vehicles in California, was conducted to compare the performance of the different types of draws. The analysis shows that, in this application, the Modified Latin Hypercube Sampling (MLHS) outperforms each type of Halton sequence. This greater accuracy combined with the greater simplicity make the MLHS method an appealing approach for simulation of travel demand models and simulation-based models in general
Ground state properties of the bond alternating spin- anisotropic Heisenberg chain
Ground state properties, dispersion relations and scaling behaviour of spin
gap of a bond alternating spin- anisotropic Heisenberg chain have
been studied where the exchange interactions on alternate bonds are
ferromagnetic (FM) and antiferromagnetic (AFM) in two separate cases. The
resulting models separately represent nearest neighbour (NN) AFM-AFM and AFM-FM
bond alternating chains. Ground state energy has been estimated analytically by
using both bond operator and Jordan-Wigner representations and numerically by
using exact diagonalization. Dispersion relations, spin gap and several ground
state orders have been obtained. Dimer order and string orders are found to
coexist in the ground state. Spin gap is found to develop as soon as the
non-uniformity in alternating bond strength is introduced in the AFM-AFM chain
which further remains non-zero for the AFM-FM chain. This spin gap along with
the string orders attribute to the Haldane phase. The Haldane phase is found to
exist in most of the anisotropic region similar to the isotropic point.Comment: 16 pages, 6 figures, 1 tabl
Simple mechanisms that impede the Berry phase identification from magneto-oscillations
The phase of quantum magneto-oscillations is often associated with the Berry
phase and is widely used to argue in favor of topological nontriviality of the
system (Berry phase ). Nevertheless, the experimentally determined
value may deviate from arbitrarily, therefore more care should be
made analyzing the phase of magneto-oscillations to distinguish trivial systems
from nontrivial. In this paper we suggest two simple mechanisms dramatically
affecting the experimentally observed value of the phase in three-dimensional
topological insulators: (i) magnetic field dependence of the chemical
potential, and (ii) possible nonuniformity of the system. These mechanisms are
not limited to topological insulators and can be extended to other
topologically trivial and non-trivial systems.Comment: 9 pages, 4 figures, in published version the title was change
Characterizing Pixel and Point Patterns with a Hyperuniformity Disorder Length
We introduce the concept of a hyperuniformity disorder length that controls
the variance of volume fraction fluctuations for randomly placed windows of
fixed size. In particular, fluctuations are determined by the average number of
particles within a distance from the boundary of the window. We first
compute special expectations and bounds in dimensions, and then illustrate
the range of behavior of versus window size by analyzing three
different types of simulated two-dimensional pixel pattern - where particle
positions are stored as a binary digital image in which pixels have value
zero/one if empty/contain a particle. The first are random binomial patterns,
where pixels are randomly flipped from zero to one with probability equal to
area fraction. These have long-ranged density fluctuations, and simulations
confirm the exact result . Next we consider vacancy patterns, where a
fraction of particles on a lattice are randomly removed. These also display
long-range density fluctuations, but with for small . For a
hyperuniform system with no long-range density fluctuations, we consider
Einstein patterns where each particle is independently displaced from a lattice
site by a Gaussian-distributed amount. For these, at large , approaches
a constant equal to about half the root-mean-square displacement in each
dimension. Then we turn to grayscale pixel patterns that represent simulated
arrangements of polydisperse particles, where the volume of a particle is
encoded in the value of its central pixel. And we discuss the continuum limit
of point patterns, where pixel size vanishes. In general, we thus propose to
quantify particle configurations not just by the scaling of the density
fluctuation spectrum but rather by the real-space spectrum of versus
. We call this approach Hyperuniformity Disorder Length Spectroscopy
- …