577 research outputs found
A New Metaheuristic Bat-Inspired Algorithm
Metaheuristic algorithms such as particle swarm optimization, firefly
algorithm and harmony search are now becoming powerful methods for solving many
tough optimization problems. In this paper, we propose a new metaheuristic
method, the Bat Algorithm, based on the echolocation behaviour of bats. We also
intend to combine the advantages of existing algorithms into the new bat
algorithm. After a detailed formulation and explanation of its implementation,
we will then compare the proposed algorithm with other existing algorithms,
including genetic algorithms and particle swarm optimization. Simulations show
that the proposed algorithm seems much superior to other algorithms, and
further studies are also discussed.Comment: 10 pages, 2 figure
Hydrodynamics, particle relabelling and relativity
Using the wave equation as an example, it is shown how to extend the
hydrodynamic Lagrangian-picture method of constructing field evolution using a
continuum of trajectories to second-order theories. The wave equation is
represented through Eulerian-picture models that are distinguished by their
Lorentz transformation properties. Introducing the idea of the relativity of
the particle label, it is demonstrated how the corresponding trajectory models
are compatible with the relativity principle. It is also shown how the Eulerian
variational formulation may be obtained by canonical transformation from the
Lagrangian picture, and how symmetries in the Lagrangian picture may be used to
generate Eulerian conserved charges.Comment: 21 page
"Where the mask ends and the face begins is not certain": Mediating ethnicity and cheating geography in Jonny Steinberg's Little Liberia
Mixing historical commentary, reportage, biography and personal stories, South
African writer Jonny Steinberg takes up the tale of a fractured African nation and its
diaspora in Little Liberia: An African Odyssey in New York City (2011). The "little
Liberia" founded in New York's urban jungle may have represented, for many of its
inhabitants, a way to "cheat geography" by recreating a home away from home, but
Little Liberia shows the reader it has not allowed them to cheat history. The book
deals with the lives of two inhabitants of Park Hill Avenue on Staten Island, where
nearly everyone is Liberian. Their conflict threatens to implode the community, igniting
suspicions and accusations that had been bottled up since their exile. The article
focuses on the interface of mediated ethnicity and citizenship related to the struggle
for power in the diasporic Liberian community on Staten Island. Attention is also paid
to feelings of identity of Little Liberia's author.DHE
Boson-fermion unification, superstrings, and Bohmian mechanics
Bosonic and fermionic particle currents can be introduced in a more unified
way, with the cost of introducing a preferred spacetime foliation. Such a
unified treatment of bosons and fermions naturally emerges from an analogous
superstring current, showing that the preferred spacetime foliation appears
only at the level of effective field theory, not at the fundamental superstring
level. The existence of the preferred spacetime foliation allows an objective
definition of particles associated with quantum field theory in curved
spacetime. Such an objective definition of particles makes the Bohmian
interpretation of particle quantum mechanics more appealing. The superstring
current allows a consistent Bohmian interpretation of superstrings themselves,
including a Bohmian description of string creation and destruction in terms of
string splitting. The Bohmian equations of motion and the corresponding
probabilistic predictions are fully relativistic covariant and do not depend on
the preferred foliation.Comment: 30 pages, 1 figure, revised, to appear in Found. Phy
Phenotypic Diversity for Seed Mineral Concentration in North American Dry Bean Germplasm of Middle American Ancestry
Dry bean (Phaseolus vulgaris L.) seeds are a major protein, carbohydrate, and mineral source in the human diet of peoples in multiple regions of the world. Seed mineral biofortification is an ongoing objective to improve this important food source. The objective of this research was to assess the seed mineral concentration of five macroelements and eight microelements in a large panel (n = 277) of modern race Durango and race Mesoamerica genotypes to determine if variability existed that could be exploited for targeted seed biofortification. Varieties that derive from these races are found in many diets throughout the world. The panel was grown in replicated trials under typical production conditions in the major bean growing regions of the United States, and a subset of the panel was also grown in replicated trials at three locations under control and terminal drought conditions. Except for K, seed mineral concentrations were higher for race Mesoamerica genotypes. Significantly higher seed concentrations for the majority of the minerals were observed for white-seeded genotypes and race Durango genotypes with the now preferred indeterminate, upright growth habit. Modern genotypes (since 1997) had equal or increased mineral concentrations compared with older genotypes. Drought affected mineral content differentially, having no effect on the microelement content but increased Co, Fe, and Ni concentrations. The correlation of Ca and Mn concentrations suggests that these elements may share seed deposition mechanisms. The high heritability for seed mineral concentration implies that breeding progress can be achieved by parental selection from this panel
The trade off between diversity and quality for multi-objective workforce scheduling
In this paper we investigate and compare multi-objective and
weighted single objective approaches to a real world workforce scheduling
problem. For this difficult problem we consider the trade off in solution quality
versus population diversity, for different sets of fixed objective weights. Our
real-world workforce scheduling problem consists of assigning resources with
the appropriate skills to geographically dispersed task locations while satisfying
time window constraints. The problem is NP-Hard and contains the Resource
Constrained Project Scheduling Problem (RCPSP) as a sub problem. We investigate
a genetic algorithm and serial schedule generation scheme together with
various multi-objective approaches. We show that multi-objective genetic algorithms
can create solutions whose fitness is within 2% of genetic algorithms using
weighted sum objectives even though the multi-objective approaches know
nothing of the weights. The result is highly significant for complex real-world
problems where objective weights are seldom known in advance since it suggests
that a multi-objective approach can generate a solution close to the user
preferred one without having knowledge of user preferences
Superfluid pairing in a polarized dipolar Fermi gas
We calculate the critical temperature of a superfluid phase transition in a
polarized Fermi gas of dipolar particles. In this case the order parameter is
anisotropic and has a nontrivial energy dependence. Cooper pairs do not have a
definite value of the angular momentum and are coherent superpositions of all
odd angular momenta. Our results describe prospects for achieving the
superfluid transition in single-component gases of fermionic polar molecules.Comment: 12 pages, 2 figure
Hydrodynamic excitations of trapped dipolar fermions
A single-component Fermi gas of polarized dipolar particles in a harmonic
trap can undergo a mechanical collapse due to the attractive part of the
dipole-dipole interaction. This phenomenon can be conveniently manipulated by
the shape of the external trapping potential. We investigate the signatures of
the instability by studying the spectrum of low-lying collective excitations of
the system in the hydrodynamic regime. To this end, we employ a time-dependent
variational method as well as exact numerical solutions of the hydrodynamic
equations of the system.Comment: 4 pages, 2 eps figures, final versio
Wnt/β-catenin signalling induces MLL to create epigenetic changes in salivary gland tumours
We show that activation of Wnt/{beta}-catenin and attenuation of Bmp signals, by combined gain- and loss-of-function mutations of {beta}-catenin and Bmpr1a, respectively, results in rapidly growing, aggressive squamous cell carcinomas (SCC) in the salivary glands of mice. Tumours contain transplantable and hyperproliferative tumour propagating cells, which can be enriched by fluorescence activated cell sorting (FACS). Single mutations stimulate stem cells, but tumours are not formed. We show that {beta}-catenin, CBP and Mll promote self-renewal and H3K4 tri-methylation in tumour propagating cells. Blocking {beta}-catenin-CBP interaction with the small molecule ICG-001 and small-interfering RNAs against {beta}-catenin, CBP or Mll abrogate hyperproliferation and H3K4 tri-methylation, and induce differentiation of cultured tumour propagating cells into acini-like structures. ICG-001 decreases H3K4me3 at promoters of stem cell-associated genes in vitro and reduces tumour growth in vivo. Remarkably, high Wnt/{beta}-catenin and low Bmp signalling also characterize human salivary gland SCC and head and neck SCC in general. Our work defines mechanisms by which {beta}-catenin signals remodel chromatin and control induction and maintenance of tumour propagating cells. Further, it supports new strategies for the therapy of solid tumours
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