27,208 research outputs found
Scaling of the Thue-Morse diffraction measure
We revisit the well-known and much studied Riesz product representation of the Thue-Morse diffraction measure, which is also the maximal spectral measure for the corresponding dynamical spectrum in the complement of the pure point part. The known scaling relations are summarised, and some new findings are explained
Timelike self-similar spherically symmetric perfect-fluid models
Einstein's field equations for timelike self-similar spherically symmetric
perfect-fluid models are investigated. The field equations are rewritten as a
first-order system of autonomous differential equations. Dimensionless
variables are chosen in such a way that the number of equations in the coupled
system is reduced as far as possible and so that the reduced phase space
becomes compact and regular. The system is subsequently analysed qualitatively
using the theory of dynamical systems.Comment: 23 pages, 6 eps-figure
Compact high-power tunable three-level operation of double cladding Nd-doped fiber laser
We present a compact high-power continuous-wave tunable neodymium-doped double cladding fiber laser operating on three-level 4F3/2 - 4I9/2 transition with a maximum output power up to 810 mW. At 926.7 nm, it has a maximum slope efficiency of 49.3% against absorbed 808-nm pump. By compressing the fiber Bragg grating, 15-nm tuning range is achieved
The state space and physical interpretation of self-similar spherically symmetric perfect-fluid models
The purpose of this paper is to further investigate the solution space of
self-similar spherically symmetric perfect-fluid models and gain deeper
understanding of the physical aspects of these solutions. We achieve this by
combining the state space description of the homothetic approach with the use
of the physically interesting quantities arising in the comoving approach. We
focus on three types of models. First, we consider models that are natural
inhomogeneous generalizations of the Friedmann Universe; such models are
asymptotically Friedmann in their past and evolve fluctuations in the energy
density at later times. Second, we consider so-called quasi-static models. This
class includes models that undergo self-similar gravitational collapse and is
important for studying the formation of naked singularities. If naked
singularities do form, they have profound implications for the predictability
of general relativity as a theory. Third, we consider a new class of
asymptotically Minkowski self-similar spacetimes, emphasizing that some of them
are associated with the self-similar solutions associated with the critical
behaviour observed in recent gravitational collapse calculations.Comment: 24 pages, 12 figure
Faithful fermionic representations of the Kondo lattice model
We study the Kondo lattice model using a class of canonical transformations
that allow us to faithfully represent the model entirely in terms of fermions
without constraints. The transformations generate interacting theories that we
study using mean field theory. Of particular interest is a new manifestly
O(3)-symmetric representation in terms of Majorana fermions at half-filling on
bipartite lattices. This representation suggests a natural O(3)-symmetric trial
state that is investigated and characterized as a gapped spin liquid.Comment: 11 pages, 2 figures, minor update
Scheduling aircraft landings - the static case
This is the publisher version of the article, obtained from the link below.In this paper, we consider the problem of scheduling aircraft (plane) landings at an airport. This problem is one of deciding a landing time for each plane such that each plane lands within a predetermined time window and that separation criteria between the landing of a plane and the landing of all successive planes are respected. We present a mixed-integer zero–one formulation of the problem for the single runway case and extend it to the multiple runway case. We strengthen the linear programming relaxations of these formulations by introducing additional constraints. Throughout, we discuss how our formulations can be used to model a number of issues (choice of objective function, precedence restrictions, restricting the number of landings in a given time period, runway workload balancing) commonly encountered in practice. The problem is solved optimally using linear programming-based tree search. We also present an effective heuristic algorithm for the problem. Computational results for both the heuristic and the optimal algorithm are presented for a number of test problems involving up to 50 planes and four runways.J.E.Beasley. would like to acknowledge the financial support of the Commonwealth Scientific and Industrial Research Organization, Australia
X-ray fluorescence spectra of metals excited below threshold
X-ray scattering spectra of Cu and Ni metals have been measured using
monochromatic synchrotron radiation tuned from far above to more than 10 eV
below threshold. Energy conservation in the scattering process is found to be
sufficient to explain the modulation of the spectral shape, neglecting momentum
conservation and channel interference. At excitation energies close to and
above threshold, the emission spectra map the occupied local partial density of
states. For the sub-threshold excitations, the high-energy flank of the
inelastic scattering exhibits a Raman-type linear dispersion, and an asymmetric
low energy tail develops. For excitation far below threshold the emission
spectra are proportional to a convolution of the occupied and unoccuppied local
partial densities of states.Comment: 10 pages, 3 figures,
http://link.aps.org/doi/10.1103/PhysRevB.68.04511
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