92 research outputs found
Incoherent multi-gap optical solitons in nonlinear photonic lattices
We demonstrate numerically that partially incoherent light can be trapped in
the spectral band gaps of a photonic lattice, creating partially incoherent
multi-component spatial optical solitons in a self-defocusing nonlinear
periodic medium. We find numerically such incoherent multi-gap optical solitons
and discuss how to generate them in experiment by interfering incoherent light
beams at the input of a nonlinear periodic medium.Comment: 9 pages, 5 figure
Zur Entwicklung der SelbstÀndigen unter den Hochschulabsolventen. AusgewÀhlte Befunde aus der amtlichen Statistik und aus neueren Erhebungen bei erwerbstÀtigen Fachhochschul- und Hochschulabsolventen
"Zwischen 1961 und 1978 hat sich der Bestand der SelbstĂ€ndigen mit AbschluĂ einer wissenschaftlichen Hochschule um 1/4 (auf 192.000) erhöht. Seit 1976 ist ein verstĂ€rkter Zuwachs an selbstĂ€ndigen/freiberuflich TĂ€tigen mit HochschulabschluĂ zu verzeichnen. Mit vorliegendem Beitrag werden Daten aus verfĂŒgbaren Statistiken und neueren Erhebungen zusammengetragen und ForschungslĂŒcken beschrieben. Dabei wird deutlich: - Der Ăbergang in die SelbstĂ€ndigkeit vollzieht sich nur zu gewissen Anteilen an der Schwelle zwischen Studium und Beruf; gerade in "Freien Berufen" (Ărzte, AnwĂ€lte etc.) wird die selbstĂ€ndige TĂ€tigkeit vielfach erst nach einer Phase des Sammelns von Berufserfahrung aufgenommen. - Der Anteil der SelbstĂ€ndigen mit HochschulabschluĂ an allen ErwerbstĂ€tigen mit HochschulabschluĂ (= SelbstĂ€ndigenquote) ist seit 1955 - nach PrĂŒfungsjahrgĂ€ngen gegliedert - stĂ€ndig abgesunken. Leicht angestiegen ist neuerdings die Quote derer, die sich unmittelbar nach dem Studium selbstĂ€ndig machen. - Die "Selbstrekrutierung" - Ăbernahme elterlicher Praxen/Be triebe etc. - ist dabei global gesehen von geringerer Be deutung. Mehr als die HĂ€lfte derer, die nach dem AbschluĂ einer wissenschaftlichen Hochschule bzw. einer Fachhoch schule selbstĂ€ndig geworden sind, haben "ihre Stelle" neu geschaffen; nur 1/3 hat die Stelle von einem VorgĂ€nger ĂŒber nommen. - Auf ArbeitsplĂ€tze der Akademiker treffen fĂŒnf Merkmale in hohem MaĂe zu: Chancen eigene Ideen zu verwirklichen, Ge nauigkeit und QualitĂ€t der Arbeit selbst zu bestimmen, ab wechslungsreiche TĂ€tigkeit, den Arbeitsrhythmus selbst zu bestimmen und seine persönlichen FĂ€higkeiten einsetzen zu können. Der Anteil an Akademiker-ArbeitsplĂ€tzen, die diese fĂŒnf Kriterien erfĂŒllen, ist wesentlich gröĂer als die je weiligen SelbstĂ€ndigenquoten. "EigenstĂ€ndigkeit" beruflicher Arbeit reicht demnach bei Hochschulabsolventen insgesamt weit ĂŒber die Positionen der SelbstĂ€ndigen hinaus. Die statistischen Befunde bedĂŒrfen, bezogen auf "neue Formen der SelbstĂ€ndigkeit", einer Vertiefung und Absicherung durch zusĂ€tzliche Forschungsanstrengungen."Hochschulabsolventen, SelbstĂ€ndige, Fachhochschule, Hochschulabsolventen
Incoherent vector vortex-mode solitons in self-focusing nonlinear media
We suggest a novel type of composite spatial optical soliton created by a
coherent vortex beam guiding a partially incoherent light beam in a
self-focusing nonlinear medium. We show that the incoherence of the guided mode
may enhance, rather than suppress, the vortex azimuthal instability, and also
demonstrate strong destabilization of dipole-mode solitons by partially
incoherent light
Soliton transverse instabilities in anisotropic nonlocal self-focusing media
We study, both theoretically and experimentally, the transverse modulational
instability of spatial stripe solitons in anisotropic nonlocal photorefractive
media. We demonstrate that the instability scenarios depend strongly on the
stripe orientation, but the anisotropy-induced features are largely suppressed
for spatial solitons created by self-trapping of partially incoherent light.Comment: 3 pages including 4 figures (2 theoretical and 2 experimental).
submitted to Optics Letter
Counterpropagating dipole-mode vector soliton
We experimentally observe a counterpropagating dipole-mode vector soliton in
a photorefractive SBN:60Ce crystal. We investigate the transient formation
dynamics and show that the formation process differs significantly from the
copropagating geometry. The experimental results are compared with fully
anisotropic numerical simulations which show good qualitative agreement.Comment: 4 pages, 4 figure
Counterpropagating beams in biased photorefractive crystals: anisotropic theory
We formulate an anisotropic nonlocal theory of the space charge field induced by the coherent counterpropagating
beams in biased photorefractive crystals. We establish that the competition between the drift and
diffusion terms has to be taken into account when the crystal cË axis is tilted with respect to the propagation
direction of the beams. We demonstrate that this configuration combines the features of both spatial soliton
formation without energy exchange and two-wave mixing with energy exchange leading to pattern formation
Observation of multivortex solitons in photonic lattices
We report on the first observation of topologically stable spatially localized multivortex solitons generated in optically induced hexagonal photonic lattices. We demonstrate that topological stabilization of such nonlinear localized states can be achieved through self-trapping of truncated two-dimensional Bloch waves and confirm our experimental results by numerical simulations of the beam propagation in weakly deformed lattice potentials in anisotropic photorefractive media
Anomaly candidates and invariants of D=4, N=1 supergravity theories
All anomaly candidates and the form of the most general invariant local
action are given for old and new minimal supergravity, including the cases
where additional Yang--Mills and chiral matter multiplets are present.
Furthermore nonminimal supergravity is discussed. In this case local
supersymmetry itself may be anomalous and some of the corresponding anomaly
candidates are given explicitly. The results are obtained by solving the
descent equations which contain the consistency equation satisfied by
integrands of anomalies and invariant actions.Comment: 19 pages, LaTex, NIKHEF-H 93-12, ITP-UH 07/9
Generative-Adversarial-Network-Based Data Augmentation for the Classification of Craniosynostosis
Craniosynostosis is a congenital disease characterized by the premature closure of one or multiple sutures of the infantâs skull. For diagnosis, 3D photogrammetric scans are a radiation-free alternative to computed tomography. However, data is only sparsely available and the role of data augmentation for the classification of craniosynostosis has not yet been analyzed. In this work, we use a 2D distance map representation of the infantsâ heads with a convolutional-neural-network-based classifier and employ a generative adversarial network (GAN) for data augmentation. We simulate two data scarcity scenarios with 15% and 10% training data and test the influence of different degrees of added synthetic data and balancing underrepresented classes. We used total accuracy and F1-score as a metric to evaluate the final classifiers. For 15% training data, the GAN-augmented dataset showed an increased F1-score up to 0.1 and classification accuracy up to 3 %. For 10% training data, both metrics decreased. We present a deep convolutional GAN capable of creating synthetic data for the classification of craniosynostosis. Using a moderate amount of synthetic data using a GAN showed slightly better performance, but had little effect overall. The simulated scarcity scenario of 10% training data may have limited the modelâs ability to learn the underlying data distribution
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