5,671 research outputs found
Analysis of Superoscillatory Wave Functions
Surprisingly, differentiable functions are able to oscillate arbitrarily
faster than their highest Fourier component would suggest. The phenomenon is
called superoscillation. Recently, a practical method for calculating
superoscillatory functions was presented and it was shown that superoscillatory
quantum mechanical wave functions should exhibit a number of counter-intuitive
physical effects. Following up on this work, we here present more general
methods which allow the calculation of superoscillatory wave functions with
custom-designed physical properties. We give concrete examples and we prove
results about the limits to superoscillatory behavior. We also give a simple
and intuitive new explanation for the exponential computational cost of
superoscillations.Comment: 20 pages, several figure
The age of the oldest Open Clusters
We determine ages of 71 old Open Clusters by a two-step method: we use
main-squence fitting to 10 selected clusters, in order to obtain their
distances, and derive their ages from comparison with our own isochrones used
before for Globular Clusters. We then calibrate the morphological age indicator
delta(V), which can be obtained for all remaining clusters, in terms of age and
metallicity. Particular care is taken to ensure consistency in the whole
procedure. The resulting Open Cluster ages connect well to our previous
Globular Cluster results. From the Open Cluster sample, as well as from the
combined sample, questions regarding the formation process of Galactic
components are addressed. The age of the oldest open clusters (NGC6791 and
Be17) is of the order of 10 Gyr. We determine a delay by 2.0+-1.5 Gyr between
the start of the halo and thin disk formation, whereas thin and thick disk
started to form approximately at the same time. We do not find any significant
age-metallicity relationship for the open cluster sample. The cumulative age
distribution of the whole open cluster sample shows a moderately significant
(~2sigma level) departure from the predictions for an exponentially declining
dissolution rate with timescale of 2.5 Gyr. The cumulative age distribution
does not show any trend with galactocentric distance, but the clusters with
larger height to the Galactic plane have an excess of objects between 2-4 and 6
Gyr with respect to their counterpart closer to the plane of the Galaxy.Comment: Astronomy & Astrophysics, in pres
Near-Field Second-Harmonic Generation Induced by Local Field Enhancement
The field near a sharp metal tip can be strongly enhanced if irradiated with an optical field polarized along the tip axis. We demonstrate that the enhanced field gives rise to local second-harmonic (SH) generation at the tip surface thereby creating a highly confined photon source. A theoretical model for the excitation and emission of SH radiation at the tip is developed and it is found that this source can be represented by a single on-axis oscillating dipole. The model is experimentally verified by imaging the spatial field distribution of strongly focused laser modes
Mitigating the effects of atmospheric distortion using DT-CWT fusion
This paper describes a new method for mitigating the effects of atmospheric distortion on observed images, particularly airborne turbulence which degrades a region of interest (ROI). In order to provide accurate detail from objects behind the dis-torting layer, a simple and efficient frame selection method is proposed to pick informative ROIs from only good-quality frames. We solve the space-variant distortion problem using region-based fusion based on the Dual Tree Complex Wavelet Transform (DT-CWT). We also propose an object alignment method for pre-processing the ROI since this can exhibit sig-nificant offsets and distortions between frames. Simple haze removal is used as the final step. The proposed method per-forms very well with atmospherically distorted videos and outperforms other existing methods. Index Terms â Image restoration, fusion, DT-CWT 1
Knowledge likely held by others affects speakersâ choices of referential expressions at different stages of discourse
Effective communication requires adjusting oneâs discourse to be understood by the addressee. While some suggest that choices of referring expressions are dependent on the addresseeâs accessibility to the referent, there is also evidence for an egocentric bias in speech production. This study relied on two new experimental tasks designed to assess whether speakers adapt their choices of referential expressions when introducing movie characters that are either likely known or likely unknown by their addressee, and when maintaining or reintroducing these characters at a later point in the discourse. Results revealed an adjustment to the addressee in the use of characterâs names (increased for likely known characters) and definite expressions (increased for likely unknown characters) observed at all the discourse stages. Use of indefinite expressions and names was affected by the participantâs own knowledge specifically when introducing the characters. These results indicate that speakers take their addresseeâs likely knowledge into account at multiple discourse stages
First experiences with HMC for dynamical overlap fermions
We describe an HMC algorithm for dynamical overlap fermions which makes use
of their good chiral properties. We test the algorithm in the Schwinger model.
Topological sectors are readily changed even in the massless case.Comment: 4 pages with 1 ps figure; crckapb.sty included; to appear in the
proceedings of the workshop "Lattice Fermions and Structure of the Vacuum",
Oct 5-9, Dubna, Russi
- âŠ