739 research outputs found
Phase-Space Volume of Regions of Trapped Motion: Multiple Ring Components and Arcs
The phase--space volume of regions of regular or trapped motion, for bounded
or scattering systems with two degrees of freedom respectively, displays
universal properties. In particular, sudden reductions in the phase-space
volume or gaps are observed at specific values of the parameter which tunes the
dynamics; these locations are approximated by the stability resonances. The
latter are defined by a resonant condition on the stability exponents of a
central linearly stable periodic orbit. We show that, for more than two degrees
of freedom, these resonances can be excited opening up gaps, which effectively
separate and reduce the regions of trapped motion in phase space. Using the
scattering approach to narrow rings and a billiard system as example, we
demonstrate that this mechanism yields rings with two or more components. Arcs
are also obtained, specifically when an additional (mean-motion) resonance
condition is met. We obtain a complete representation of the phase-space volume
occupied by the regions of trapped motion.Comment: 19 pages, 17 figure
Spectral statistics of the k-body random-interaction model
We reconsider the question of the spectral statistics of the k-body
random-interaction model, investigated recently by Benet, Rupp, and
Weidenmueller, who concluded that the spectral statistics are Poissonian. The
binary-correlation method that these authors used involves formal manipulations
of divergent series. We argue that Borel summation does not suffice to define
these divergent series without further (arbitrary) regularization, and that
this constitutes a significant gap in the demonstration of Poissonian
statistics. Our conclusion is that the spectral statistics of the k-body
random-interaction model remains an open question.Comment: 17 pages, no figure
Effect of phase relaxation on quantum superpositions in complex collisions
We study the effect of phase relaxation on coherent superpositions of
rotating clockwise and anticlockwise wave packets in the regime of strongly
overlapping resonances of the intermediate complex. Such highly excited
deformed complexes may be created in binary collisions of heavy ions, molecules
and atomic clusters. It is shown that phase relaxation leads to a reduction of
the interference fringes, thus mimicking the effect of decoherence. This
reduction is crucial for the determination of the phase--relaxation width from
the data on the excitation function oscillations in heavy--ion collisions and
bimolecular chemical reactions. The difference between the effects of phase
relaxation and decoherence is discussed.Comment: Extended revised version; 9 pages and 3 colour ps figure
Assessing the magnitude and direction of asymmetry in unilateral jump and change of direction speed tasks in youth female team-sport athletes
The direction of inter-limb asymmetries and the change of direction (COD) deficit are two aspects that have increased in recent years. The main objective of the present study was to assess the magnitude of neuromuscular asymmetries in an elite youth female team-sports sample and determine its directionality. Secondary objectives were to evaluate the relationship between COD deficit, linear speed and COD time performance. Elite female youth basketball and handball players (n = 33, age = 16 ± 1.17 y) performed the Single Leg Countermovement Jump in vertical (SLCJ-V), horizontal (SLCJ-H), and lateral (SLCJ-L) directions, the COD and the 10-m sprint. Results showed statistical differences between limbs in all the neuromuscular tests (p < 0.001). The Kappa coefficient showed poor to fair levels of agreement between tasks (K range = -0.087 to 0.233), indicating that asymmetries rarely favoured the same limb between skills. Additionally, small and non-significant correlations were found between the linear sprint capacity and the COD ability. The findings of the present study highlight the independent directionality of asymmetries across tests. The COD deficit does not appear to be much more advantageous than COD total time to measure asymmetry. Practitioners are encouraged to use a fitness testing battery to detect existing side differences and each ability should be specifically trained with functional tasks
Fluctuations of wave functions about their classical average
Quantum-classical correspondence for the average shape of eigenfunctions and
the local spectral density of states are well-known facts. In this paper, the
fluctuations that quantum mechanical wave functions present around the
classical value are discussed. A simple random matrix model leads to a Gaussian
distribution of the amplitudes. We compare this prediction with numerical
calculations in chaotic models of coupled quartic oscillators. The expectation
is broadly confirmed, but deviations due to scars are observed.Comment: 9 pages, 6 figures. Sent to J. Phys.
Level Repulsion in Constrained Gaussian Random-Matrix Ensembles
Introducing sets of constraints, we define new classes of random-matrix
ensembles, the constrained Gaussian unitary (CGUE) and the deformed Gaussian
unitary (DGUE) ensembles. The latter interpolate between the GUE and the CGUE.
We derive a sufficient condition for GUE-type level repulsion to persist in the
presence of constraints. For special classes of constraints, we extend this
approach to the orthogonal and to the symplectic ensembles. A generalized
Fourier theorem relates the spectral properties of the constraining ensembles
with those of the constrained ones. We find that in the DGUEs, level repulsion
always prevails at a sufficiently short distance and may be lifted only in the
limit of strictly enforced constraints.Comment: 20 pages, no figures. New section adde
Review of the k-Body Embedded Ensembles of Gaussian Random Matrices
The embedded ensembles were introduced by Mon and French as physically more
plausible stochastic models of many--body systems governed by one--and
two--body interactions than provided by standard random--matrix theory. We
review several approaches aimed at determining the spectral density, the
spectral fluctuation properties, and the ergodic properties of these ensembles:
moments methods, numerical simulations, the replica trick, the eigenvector
decomposition of the matrix of second moments and supersymmetry, the binary
correlation approximation, and the study of correlations between matrix
elements.Comment: Final version. 29 pages, 4 ps figures, uses iopart.st
Europe’s Culture(s): Negotiating Cultural Meanings, Values, and Identities in the European Context
The intent of this Special Issue is to be a starting point for a broadly-defined European cultural psychology. Across seven research articles, the authors of this Special Issue explore what European culture(s) and European identity entail, how acculturation within the European cultural contexts takes place and under what conditions a multicultural Europe might be possible. The special Issue also discusses what is currently missing from the research agenda. Therein, the findings of this Special Issue constitute an important starting point for future psychological research that accompanies Europe along its journey into the 21st century
Spectral fluctuation properties of constrained unitary ensembles of Gaussian-distributed random matrices
We investigate the spectral fluctuation properties of constrained ensembles
of random matrices (defined by the condition that a number N(Q) of matrix
elements vanish identically; that condition is imposed in unitarily invariant
form) in the limit of large matrix dimension. We show that as long as N(Q) is
smaller than a critical value (at which the quadratic level repulsion of the
Gaussian unitary ensemble of random matrices may be destroyed) all spectral
fluctuation measures have the same form as for the Gaussian unitary ensemble.Comment: 15 page
Simultaneous detection of the three ilarviruses affecting stone fruit trees by nonisotopic molecular hybridization and multiplex reverse-transcription polymerase chain reaction
[EN] The three most economically damaging ilarviruses affecting stone fruit trees on a worldwide scale are the related Prunus necrotic ringspot virus (PNRSV), Prune dwarf virus (PDV), and Apple mosaic virus (ApMV). Nonisotopic molecular hybridization and multiplex reverse-transcription polymerase chain reaction (RT-PCR) methodologies were developed that could detect all these viruses simultaneously. The latter technique was advantageous because it was discriminatory. For RT-PCR, a degenerate antisense primer was designed which was used in conjunction with three virus-specific sense primers. The amplification efficiencies for the detection of the three viruses in the multiplex RT-PCR reaction were identical to those obtained in the single RT-PCR reactions for individual viruses. This cocktail of primers was able to amplify sequences from all of the PNRSV, ApMV, and PDV isolates tested in five Prunus spp. hosts (almond, apricot, cherry, peach, and plum) occurring naturally in single or multiple infections. For ApMV isolates, differences in the electrophoretic mobilities of the PCR products were observed. The nucleotide sequence of the amplified products of two representative ApMV isolates was determined, and comparative analysis revealed the existence of a 28-nucleotide deletion in the sequence of isolates showing the faster electrophoretic mobility. To our knowledge, this is the first report on the simultaneous detection of three plant viruses by multiplex RT-PCR in woody hosts. This multiplex RT-PCR could be a useful time and cost saving method for indexing these three ilarviruses, which damage stone fruit tree yields, and for the analysis of mother plants in certification programs.We thank Drs. P.H. Berger and P.J. Shield for providing the ApMV clone and Dr. S. Scott for the PDV clone. We also thank P. Thomas and M.W. van der Heidjen for help with the English version of the manuscript. This work was supported by grant BIO99-0854 from the Spanish granting agency DGICYT. F.A. and J.A. S-N. were the recipients of fellowships from the Ministerio de Educacion y Cultura of Spain. M. S. was supported by the Italian Ministry of Foreign Affairs and CIHEAM/IAMB.Saade, M.; Aparicio Herrero, F.; Sánchez-Navarro, JA.; Herranz Gordo, MC.; Myrta, A.; Di Terlizzi, B.; Pallás Benet, V. (2000). Simultaneous detection of the three ilarviruses affecting stone fruit trees by nonisotopic molecular hybridization and multiplex reverse-transcription polymerase chain reaction. Phytopathology. 90(12):1330-1336. https://doi.org/10.1094/PHYTO.2000.90.12.133013301336901
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