2,607 research outputs found
From one- to two-dimensional solitons in the Ginzburg-Landau model of lasers with frequency selective feedback
We use the cubic complex Ginzburg-Landau equation coupled to a dissipative
linear equation as a model of lasers with an external frequency-selective
feedback. It is known that the feedback can stabilize the one-dimensional (1D)
self-localized mode. We aim to extend the analysis to 2D stripe-shaped and
vortex solitons. The radius of the vortices increases linearly with their
topological charge, , therefore the flat-stripe soliton may be interpreted
as the vortex with , while vortex solitons can be realized as stripes
bent into rings. The results for the vortex solitons are applicable to a broad
class of physical systems. There is a qualitative agreement between our results
and those recently reported for models with saturable nonlinearity.Comment: Submitted to PR
Effects of a localized beam on the dynamics of excitable cavity solitons
We study the dynamical behavior of dissipative solitons in an optical cavity
filled with a Kerr medium when a localized beam is applied on top of the
homogeneous pumping. In particular, we report on the excitability regime that
cavity solitons exhibits which is emergent property since the system is not
locally excitable. The resulting scenario differs in an important way from the
case of a purely homogeneous pump and now two different excitable regimes, both
Class I, are shown. The whole scenario is presented and discussed, showing that
it is organized by three codimension-2 points. Moreover, the localized beam can
be used to control important features, such as the excitable threshold,
improving the possibilities for the experimental observation of this
phenomenon.Comment: 9 Pages, 12 figure
Spatial correlations in hexagons generated via a Kerr nonlinearity
We consider the hexagonal pattern forming in the cross-section of an optical
beam produced by a Kerr cavity, and we study the quantum correlations
characterizing this structure. By using arguments related to the symmetry
broken by the pattern formation, we identify a complete scenario of six-mode
entanglement. Five independent phase quadratures combinations, connecting the
hexagonal modes, are shown to exhibit sub-shot-noise fluctuations. By means of
a non-linear quantum calculation technique, quantum correlations among the mode
photon numbers are demonstrated and calculated.Comment: ReVTeX file, 20 pages, 7 eps figure
Frequency selection by soliton excitation in nondegenerate intracavity downconversion
We show that soliton excitation in intracavity downconversion naturally
selects a strictly defined frequency difference between the signal and idler
fields. In particular, this phenomenon implies that if the signal has smaller
losses than the idler then its frequency is pulled away from the cavity
resonance and the idler frequency is pulled towards the resonance and {\em vice
versa}. The frequency selection is shown to be closely linked with the relative
energy balance between the idler and signal fields.Comment: 5 pages, 3 figures. To appear in Phys Rev Let
A Potential of Interaction between Two- and Three-Dimensional Solitons
A general method to find an effective potential of interaction between far
separated 2D and 3D solitons is elaborated, including the case of 2D vortex
solitons. The method is based on explicit calculation of the overlapping term
in the full Hamiltonian of the system (_without_ assuming that the ``tail'' of
each soliton is not affected by its interaction with the other soliton, and, in
fact,_without_ knowing the exact form of the solution for an isolated soliton -
the latter problem is circumvented by reducing a bulk integral to a surface
one). The result is obtained in an explicit form that does not contain an
artificially introduced radius of the overlapping region. The potential applies
to spatial and spatiotemporal solitons in nonlinear optics, where it may help
to solve various dynamical problems: collisions, formation of bound states
(BS's), etc. In particular, an orbiting BS of two solitons is always unstable.
In the presence of weak dissipation and gain, the effective potential can also
be derived, giving rise to bound states similar to those recently studied in 1D
models.Comment: 29 double-spaced pages in the latex format and 1 figure in the ps
format. The paper will appear in Phys. Rev.
Variation in local population size predicts social network structure in wild songbirds
The structure of animal societies is a key determinant of many ecological and evolutionary processes. Yet, we know relatively little about the factors and mechanisms that underpin detailed social structure.
Among other factors, social structure can be influenced by habitat configuration. By shaping animal movement decisions, heterogeneity in habitat features, such as vegetation and the availability of resources, can influence the spatiotemporal distribution of individuals and subsequently key socioecological properties such as the local population size and density. Differences in local population size and density can impact opportunities for social associations and may thus drive substantial variation in local social structure.
Here, we investigated spatiotemporal variation in population size at 65 distinct locations in a small songbird, the great tit (Parus major) and its effect on social network structure. We first explored the within‐location consistency of population size from weekly samples and whether the observed variation in local population size was predicted by the underlying habitat configuration. Next, we created social networks from the birds' foraging associations at each location for each week and examined if local population size affected social structure.
We show that population size is highly repeatable within locations across weeks and years and that some of the observed variation in local population size was predicted by the underlying habitat, with locations closer to the forest edge having on average larger population sizes. Furthermore, we show that local population size affected social structure inferred by four global network metrics. Using simple simulations, we then reveal that much of the observed social structure is shaped by social processes. Across different population sizes, the birds' social structure was largely explained by their preference to forage in flocks. In addition, over and above effects of social foraging, social preferences between birds (i.e. social relationships) shaped certain network features such as the extent of realized social connections.
Our findings thus suggest that individual social decisions substantially contribute to shaping certain social network features over and above effects of population size alone
The influence of nonrandom extra-pair paternity on heritability estimates derived from wild pedigrees
Quantitative genetic analysis is often fundamental for understanding evolutionary processes in wild populations. Avian populations provide a model system due to the relative ease of inferring relatedness among individuals through observation. However, extra-pair paternity (EPP) creates erroneous links within the social pedigree. Previous work has suggested this causes minor underestimation of heritability if paternal misassignment is random and hence not influenced by the trait being studied. Nevertheless, much literature suggests numerous traits are associated with EPP and the accuracy of heritability estimates for such traits remains unexplored. We show analytically how nonrandom pedigree errors can influence heritability estimates. Then, combining empirical data from a large great tit (Parus major) pedigree with simulations, we assess how heritability estimates derived from social pedigrees change depending on the mode of the relationship between EPP and the focal trait. We show that the magnitude of the underestimation is typically small (<15%). Hence, our analyses suggest that quantitative genetic inference from pedigrees derived from observations of social relationships is relatively robust; our approach also provides a widely applicable method for assessing the consequences of nonrandom EPP
Exercise Addiction Prevalence and Correlates in the Absence of Eating Disorder Symptomology: A Systematic Review and Meta-analysis
BACKGROUND: Exercise addiction (EA) can be debilitating and can be a symptom of an eating disorder. To date, the prevalence rates of EA without indicated eating disorders in the general population and associated correlates remain unreported. METHODS: Two authors searched major databases from inception to 31/12/2018 to identify studies investigating the prevalence of EA in any population without indicated eating disorders. We conducted a random effects meta-analysis to report (i) prevalence rates of EA using the exercise addiction inventory and exercise dependence scale and compare sub-populations, (ii) compare methods of EA measurement and explore heterogeneity, and (iii) report on correlates. RESULTS: A total of 13 studies including 3635 people were included. The prevalence of EA among general exercisers was 8.1% (95% CI 1.5%-34.2%), amateur competitive athletes was 5.0% (95% CI 1.3%-17.3%), and university students was 5.5% (95% CI 1.4-19.1%%). Overall prevalence rates varied depending on the EA measurement tool. EA subjects were more likely to have lower levels of overall wellbeing (only in amateur competitive athletes), higher anxiety levels, and have greater frontal brain activity. CONCLUSIONS: EA is prevalent in the absence of indicated eating disorders across populations but varies depending on measurement tool. Further research is needed to explore EA without indicated eating disorders in different populations using homogenous measurement tools, further determine psychological correlates, and examine which measures of EA without indicated eating disorders predict poor health outcomes
Penta-Hepta Defect Motion in Hexagonal Patterns
Structure and dynamics of penta-hepta defects in hexagonal patterns is
studied in the framework of coupled amplitude equations for underlying plane
waves. Analytical solution for phase field of moving PHD is found in the far
field, which generalizes the static solution due to Pismen and Nepomnyashchy
(1993). The mobility tensor of PHD is calculated using combined analytical and
numerical approach. The results for the velocity of PHD climbing in slightly
non-optimal hexagonal patterns are compared with numerical simulations of
amplitude equations. Interaction of penta-hepta defects in optimal hexagonal
patterns is also considered.Comment: 4 pages, Postscript (submitted to PRL
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