3,306 research outputs found
Infrared electron modes in light deformed clusters
Infrared quadrupole modes (IRQM) of the valence electrons in light deformed
sodium clusters are studied by means of the time-dependent local-density
approximation (TDLDA). IRQM are classified by angular momentum components
20, 21 and 22 whose branches are separated by cluster
deformation. In light clusters with a low spectral density, IRQM are
unambiguously related to specific electron-hole excitations, thus giving access
to the single-electron spectrum near the Fermi surface (HOMO-LUMO region). Most
of IRQM are determined by cluster deformation and so can serve as a sensitive
probe of the deformation effects in the mean field. The IRQM branch 21 is coupled with the magnetic scissors mode, which gives a chance to detect
the latter. We discuss two-photon processes, Raman scattering (RS), stimulated
emission pumping (SEP), and stimulated adiabatic Raman passage (STIRAP), as the
relevant tools to observe IRQM. A new method to detect the IRQM population in
clusters is proposed.Comment: 22 pages, 6 figure
Stability and Diversity in Collective Adaptation
We derive a class of macroscopic differential equations that describe
collective adaptation, starting from a discrete-time stochastic microscopic
model. The behavior of each agent is a dynamic balance between adaptation that
locally achieves the best action and memory loss that leads to randomized
behavior. We show that, although individual agents interact with their
environment and other agents in a purely self-interested way, macroscopic
behavior can be interpreted as game dynamics. Application to several familiar,
explicit game interactions shows that the adaptation dynamics exhibits a
diversity of collective behaviors. The simplicity of the assumptions underlying
the macroscopic equations suggests that these behaviors should be expected
broadly in collective adaptation. We also analyze the adaptation dynamics from
an information-theoretic viewpoint and discuss self-organization induced by
information flux between agents, giving a novel view of collective adaptation.Comment: 22 pages, 23 figures; updated references, corrected typos, changed
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Scissors modes in triaxial metal clusters
We study the scissors mode (orbital M1 excitations) in small Na clusters,
triaxial metal clusters and and the
close-to-spherical , all described in DFT with detailed ionic
background. The scissors modes built on spin-saturated ground and
spin-polarized isomeric states are analyzed in virtue of both macroscopic
collective and microscopic shell-model treatments. It is shown that the mutual
destruction of Coulomb and the exchange-correlation parts of the residual
interaction makes the collective shift small and the net effect can depend on
details of the actual excited state. The crosstalk with dipole and spin-dipole
modes is studied in detail. In particular, a strong crosstalk with spin-dipole
negative-parity mode is found in the case of spin-polarized states. Triaxiality
and ionic structure considerably complicate the scissors response, mainly at
expense of stronger fragmentation of the strength. Nevertheless, even in these
complicated cases the scissors mode is mainly determined by the global
deformation. The detailed ionic structure destroys the spherical symmetry and
can cause finite M1 response (transverse optical mode) even in clusters with
zero global deformation. But its strength turns out to be much smaller than for
the genuine scissors modes in deformed systems.Comment: 17 pages, 5 figure
Second harmonic generation in SiC polytypes
LMTO calculations are presented for the frequency dependent second harmonic
generation (SHG) in the polytypes 2H, 4H, 6H, 15R and 3C of SiC. All
independent tensor components are calculated. The spectral features and the
ratios of the 333 to 311 tensorial components are studied as a function of the
degree of hexagonality. The relationship to the linear optical response and the
underlying band structure are investigated. SHG is suggested to be a sensitive
tool for investigating the near band edge interband excitations.Comment: 12 pages, 10 figure
Development of deployable structures for large space platform systems, part 1
Eight deployable platform design objectives were established: autodeploy/retract; fully integrated utilities; configuration variability; versatile payload and subsystem interfaces; structural and packing efficiency; 1986 technology readiness; minimum EVA/RMS; and Shuttle operational compatibility
RAINIER: A Simulation Tool for Distributions of Excited Nuclear States and Cascade Fluctuations
A new code has been developed named RAINIER that simulates the -ray
decay of discrete and quasi-continuum nuclear levels for a user-specified range
of energy, angular momentum, and parity including a realistic treatment of
level spacing and transition width fluctuations. A similar program, DICEBOX,
uses the Monte Carlo method to simulate level and width fluctuations but is
restricted to -ray decay from no more than two initial states such as
de-excitation following thermal neutron capture. On the other hand, modern
reaction codes such as TALYS and EMPIRE populate a wide range of states in the
residual nucleus prior to -ray decay, but do not go beyond the use of
deterministic functions and therefore neglect cascade fluctuations. This
combination of capabilities allows RAINIER to be used to determine
quasi-continuum properties through comparison with experimental data. Several
examples are given that demonstrate how cascade fluctuations influence
experimental high-resolution -ray spectra from reactions that populate
a wide range of initial states.Comment: 14 pages, 13 figures, Nuclear Instrumentation and Methods A, 201
An introduction to quantum game theory
The application of the methods of quantum mechanics to game theory provides
us with the ability to achieve results not otherwise possible. Both linear
superpositions of actions and entanglement between the players' moves can be
exploited. We provide an introduction to quantum game theory and review the
current status of the subject.Comment: 8 pages, RevTeX; v2 minor changes to the text in light of referees
comments, references added/update
Experimental and numerical study of full-scale scissor type bridge
Mobile Bridge™ is a deployable bridge that uses a scissors mechanism to achieve its useful structural form. The bridge has a compact size in its undeployed state and can be transported easily to where it is needed. Its rapid deployment makes this type of bridge very useful in areas struck by natural disasters by enabling vehicles to cross terrain that has been made impassable. In previous research, experiments and analyses were conducted on a small-scale bridge designed for pedestrians. In order to consider a bridge of increased size, it is necessary to assess whether design and analysis techniques of the small scale bridge are applicable to the full-scale one. In this paper, we consider a full-scale deployable bridge with a lower deck and two scissor units, that allows for a light vehicle to pass across. We have carried out a light vehicle loading test in order to investigate its basic structural characteristics. Furthermore, the paper presents the theoretical design method and numerical models based on the experimental work followed by validation and comparison with the obtained experimental values
Deployable Cylindrical Vaults With Reciprocal Linkages for Emergency Buildings
Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract]
Deployable bar structures are especially useful for emergency buildings. These structures require simplicity and ease of assembly and their performance can be improve by using reciprocal linkage at their bars ends. This reciprocal configuration determines singular constructive conditions that allow all types of cylindrical vaults. This article develops this new system, from a previously theoretical analysis to a test campaign that allows verifying the validity of the proposal. Comparing these results with those resulting from construction systems with straight scissor-like elements or imposed curvature, shows the adequacy of this new proposal, verifying the advantages of the reciprocal joints in cylindrical vaults configurations.This study is part of the research project “Deployable and modular constructions for situations of humanitarian catastrophe”, funded by the Ministry of Economy and Competitiveness of the Kingdom of Spain with reference BIA2016-79459-R. Funding for open access charge: Universidade da Coruña/CISU
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