13,732 research outputs found
Development of an automated aircraft subsystem architecture generation and analysis tool
Purpose – The purpose of this paper is to present a new computational framework to address future
preliminary design needs for aircraft subsystems. The ability to investigate multiple candidate
technologies forming subsystem architectures is enabled with the provision of automated architecture
generation, analysis and optimization. Main focus lies with a demonstration of the frameworks
workings, as well as the optimizers performance with a typical form of application problem.
Design/methodology/approach – The core aspects involve a functional decomposition, coupled
with a synergistic mission performance analysis on the aircraft, architecture and component levels.
This may be followed by a complete enumeration of architectures, combined with a user defined
technology filtering and concept ranking procedure. In addition, a hybrid heuristic optimizer, based on
ant systems optimization and a genetic algorithm, is employed to produce optimal architectures in both
component composition and design parameters. The optimizer is tested on a generic architecture
design problem combined with modified Griewank and parabolic functions for the continuous space.
Findings – Insights from the generalized application problem show consistent rediscovery of the
optimal architectures with the optimizer, as compared to a full problem enumeration. In addition
multi-objective optimization reveals a Pareto front with differences in component composition as well
as continuous parameters.
Research limitations/implications – This paper demonstrates the frameworks application on a
generalized test problem only. Further publication will consider real engineering design problems.
Originality/value – The paper addresses the need for future conceptual design methods of complex
systems to consider a mixed concept space of both discrete and continuous nature via automated methods
Tarski monoids: Matui's spatial realization theorem
We introduce a class of inverse monoids, called Tarski monoids, that can be
regarded as non-commutative generalizations of the unique countable, atomless
Boolean algebra. These inverse monoids are related to a class of etale
topological groupoids under a non-commutative generalization of classical Stone
duality and, significantly, they arise naturally in the theory of dynamical
systems as developed by Matui. We are thereby able to reinterpret a theorem of
Matui on a class of \'etale groupoids as an equivalent theorem about a class of
Tarski monoids: two simple Tarski monoids are isomorphic if and only if their
groups of units are isomorphic. The inverse monoids in question may also be
viewed as countably infinite generalizations of finite symmetric inverse
monoids. Their groups of units therefore generalize the finite symmetric groups
and include amongst their number the classical Thompson groups.Comment: arXiv admin note: text overlap with arXiv:1407.147
Electron impact excitation of N IV: calculations with the DARC code and a comparison with ICFT results
There have been discussions in the recent literature regarding the accuracy
of the available electron impact excitation rates (equivalently effective
collision strengths ) for transitions in Be-like ions. In the present
paper we demonstrate, once again, that earlier results for are
indeed overestimated (by up to four orders of magnitude), for over 40\% of
transitions and over a wide range of temperatures. To do this we have performed
two sets of calculations for N~IV, with two different model sizes consisting of
166 and 238 fine-structure energy levels. As in our previous work, for the
determination of atomic structure the GRASP (General-purpose Relativistic
Atomic Structure Package) is adopted and for the scattering calculations (the
standard and parallelised versions of) the Dirac Atomic R-matrix Code ({\sc
darc}) are employed. Calculations for collision strengths and effective
collision strengths have been performed over a wide range of energy (up to
45~Ryd) and temperature (up to 2.010~K), useful for applications in
a variety of plasmas. Corresponding results for energy levels, lifetimes and
A-values for all E1, E2, M1 and M2 transitions among 238 levels of N~IV are
also reported.Comment: This paper with 5 Figs. and 8 Tables will appear in MNRAS (2016
The Genome and Methylome of a Subsocial Small Carpenter Bee, Ceratina calcarata
Understanding the evolution of animal societies, considered to be a major transition in evolution, is a key topic in evolutionary biology. Recently, new gateways for understanding social evolution have opened up due to advances in genomics, allowing for unprecedented opportunities in studying social behavior on a molecular level. In particular, highly eusocial insect species (caste-containing societies with nonreproductives that care for siblings) have taken center stage in studies of the molecular evolution of sociality. Despite advances in genomic studies of both solitary and eusocial insects, we still lack genomic resources for early insect societies. To study the genetic basis of social traits requires comparison of genomes from a diversity of organisms ranging from solitary to complex social forms. Here we present the genome of a subsocial bee, Ceratina calcarata. This study begins to address the types of genomic changes associated with the earliest origins of simple sociality using the small carpenter bee. Genes associated with lipid transport and DNA recombination have undergone positive selection in C. calcarata relative to other bee lineages. Furthermore, we provide the first methylome of a noneusocial bee. Ceratina calcarata contains the complete enzymatic toolkit for DNA methylation. As in the honey bee and many other holometabolous insects, DNA methylation is targeted to exons. The addition of this genome allows for new lines of research into the genetic and epigenetic precursors to complex social behaviors
ESR studies of the slow tumbling of vanadyl spin probes in nematic liquid crystals
ESR line shapes that are appropriate for slowly tumbling vanadyl spin probes in viscous nematic liquid crystals were calculated by the stochastic Liouville method. Because of the symmetry possessed by vanadyl, the analysis and interpretation of these line shapes was simplified considerably. Spectral line shapes agreed well with experimental spectra of VOAcAc in the nematic liquid crystal Phase V and BEPC. Deviations from Brownian rotational diffusion were noted. A slowly fluctuating torque analysis yielded good agreement with the experimental spectra
Dirac lattice
We study the emergence of Dirac fermionic field in the low energy description
of non-relativistic dynamical models on graphs admitting continuum limit. The
Dirac fermionic field appears as the effective field describing the excitations
above point-like Fermi surface. Together with the Dirac fermionic field an
effective space-time metric is also emerging. We analyze the conditions for
such Fermi points to appear in general, paying special attention to the cases
of two and three spacial dimensions.Comment: 26 pages, 4 figures; typo and grammatical corrections, new
reference(s) added, version accepted for publicatio
Bi-HKT and bi-Kaehler supersymmetric sigma models
We study CKT (or bi-HKT) N = 4 supersymmetric quantum mechanical sigma
models. They are characterized by the usual and the mirror sectors displaying
each HKT geometry. When the metric involves isometries, a Hamiltonian reduction
is possible. The most natural such reduction with respect to a half of bosonic
target space coordinates produces an N = 4 model, related to the twisted
Kaehler model due to Gates, Hull and Rocek, but including certain extra F-terms
in the superfield action.Comment: 31 pages, minor corrections in the published versio
Efficient operation of a high-power X-band gyroklystron
Experimental studies of amplification in a two-cavity X-band gyroklystron are reported. The system utilizes a thermionic magnetron injection gun at voltages up to 440 kV and currents up to 190 A in 1-μs pulses. Optimum performance is achieved by tapering the magnetic-field profile. Peak powers of 20 MW in the TE01 mode at 9.87 GHz are measured with calibrated crystals and with methanol calorimetry. Resultant efficiencies are in excess of 31% and large-signal gains surpass 26 dB. The experimental results are in good agreement with simulated results from a partially self-consistent, nonlinear, steady-state code
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