40,437 research outputs found
Constructive Field Theory and Applications: Perspectives and Open Problems
In this paper we review many interesting open problems in mathematical
physics which may be attacked with the help of tools from constructive field
theory. They could give work for future mathematical physicists trained with
the constructive methods well within the 21st century
Limitations of B-meson mixing bounds on technicolor theories
Recent work by Burdman, Lane, and Rador has shown that B-meson mixing places
stringent lower bounds on the masses of topgluons and Z' bosons in classic
topcolor-assisted technicolor (TC2) models. This paper finds analogous limits
on the Z' bosons of flavor-universal TC2 and non-commuting extended technicolor
models, and compares the limits with those from precision electroweak
measurements. A discussion of the flavor structure of these models (contrasted
with that of classic TC2) shows that B-meson mixing is a less reliable probe of
these models than of classic TC2.Comment: 6 pages, LaTeX; added a reference; added references and discussio
The interaction of lean and building information modeling in construction
Lean construction and Building Information Modeling are quite different initiatives, but both are having profound impacts on the construction industry. A rigorous analysis of the myriad specific interactions between them indicates that a synergy exists which, if properly understood in theoretical terms, can be exploited to improve construction processes beyond the degree to which it might be improved by application of either of these paradigms independently. Using a matrix that juxtaposes BIM functionalities with prescriptive lean construction principles, fifty-six interactions have been identified, all but four of which represent constructive interaction. Although evidence for the majority of these has been found, the matrix is not considered complete, but rather a framework for research to
explore the degree of validity of the interactions. Construction executives, managers, designers and developers of IT systems for construction can also benefit from the framework as an aid to recognizing the potential synergies when planning their lean and BIM adoption strategies
Finite Boolean Algebras for Solid Geometry using Julia's Sparse Arrays
The goal of this paper is to introduce a new method in computer-aided
geometry of solid modeling. We put forth a novel algebraic technique to
evaluate any variadic expression between polyhedral d-solids (d = 2, 3) with
regularized operators of union, intersection, and difference, i.e., any CSG
tree. The result is obtained in three steps: first, by computing an independent
set of generators for the d-space partition induced by the input; then, by
reducing the solid expression to an equivalent logical formula between Boolean
terms made by zeros and ones; and, finally, by evaluating this expression using
bitwise operators. This method is implemented in Julia using sparse arrays. The
computational evaluation of every possible solid expression, usually denoted as
CSG (Constructive Solid Geometry), is reduced to an equivalent logical
expression of a finite set algebra over the cells of a space partition, and
solved by native bitwise operators.Comment: revised version submitted to Computer-Aided Geometric Desig
Dual-Context Calculi for Modal Logic
We present natural deduction systems and associated modal lambda calculi for
the necessity fragments of the normal modal logics K, T, K4, GL and S4. These
systems are in the dual-context style: they feature two distinct zones of
assumptions, one of which can be thought as modal, and the other as
intuitionistic. We show that these calculi have their roots in in sequent
calculi. We then investigate their metatheory, equip them with a confluent and
strongly normalizing notion of reduction, and show that they coincide with the
usual Hilbert systems up to provability. Finally, we investigate a categorical
semantics which interprets the modality as a product-preserving functor.Comment: Full version of article previously presented at LICS 2017 (see
arXiv:1602.04860v4 or doi: 10.1109/LICS.2017.8005089
Transport and Scaling in Quenched 2D and 3D L\'evy Quasicrystals
We consider correlated L\'evy walks on a class of two- and three-dimensional
deterministic self-similar structures, with correlation between steps induced
by the geometrical distribution of regions, featuring different diffusion
properties. We introduce a geometric parameter , playing a role
analogous to the exponent characterizing the step-length distribution in random
systems. By a {\it single-long jump} approximation, we analytically determine
the long-time asymptotic behavior of the moments of the probability
distribution, as a function of and of the dynamic exponent
associated to the scaling length of the process. We show that our scaling
analysis also applies to experimentally relevant quantities such as escape-time
and transmission probabilities.
Extensive numerical simulations corroborate our results which, in general,
are different from those pertaining to uncorrelated L\'evy-walks models.Comment: 10 pages, 11 figures; some concepts rephrased to improve on clarity;
a few references added; symbols and line styles in some figures changed to
improve on visibilit
Flat bands in fractal-like geometry
We report the presence of multiple flat bands in a class of two-dimensional
(2D) lattices formed by Sierpinski gasket (SPG) fractal geometries as the basic
unit cells. Solving the tight-binding Hamiltonian for such lattices with
different generations of a SPG network, we find multiple degenerate and
non-degenerate completely flat bands, depending on the configuration of
parameters of the Hamiltonian. Moreover, we find a generic formula to determine
the number of such bands as a function of the generation index of the
fractal geometry. We show that the flat bands and their neighboring dispersive
bands have remarkable features, the most interesting one being the spin-1
conical-type spectrum at the band center without any staggered magnetic flux,
in contrast to the Kagome lattice. We furthermore investigate the effect of the
magnetic flux in these lattice settings and show that different combinations of
fluxes through such fractal unit cells lead to richer spectrum with a single
isolated flat band or gapless electron- or hole-like flat bands. Finally, we
discuss a possible experimental setup to engineer such fractal flat band
network using single-mode laser-induced photonic waveguides.Comment: 8 pages, 9 figures, accepted versio
State of the Art in the Optimisation of Wind Turbine Performance Using CFD
Wind energy has received increasing attention in recent years due to its sustainability and geographically wide availability. The efficiency of wind energy utilisation highly depends on the performance of wind turbines, which convert the kinetic energy in wind into electrical energy. In order to optimise wind turbine performance and reduce the cost of next-generation wind turbines, it is crucial to have a view of the state of the art in the key aspects on the performance optimisation of wind turbines using Computational Fluid Dynamics (CFD), which has attracted enormous interest in the development of next-generation wind turbines in recent years. This paper presents a comprehensive review of the state-of-the-art progress on optimisation of wind turbine performance using CFD, reviewing the objective functions to judge the performance of wind turbine, CFD approaches applied in the simulation of wind turbines and optimisation algorithms for wind turbine performance. This paper has been written for both researchers new to this research area by summarising underlying theory whilst presenting a comprehensive review on the up-to-date studies, and experts in the field of study by collecting a comprehensive list of related references where the details of computational methods that have been employed lately can be obtained
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