242 research outputs found
NELIOTA: The wide-field, high-cadence lunar monitoring system at the prime focus of the Kryoneri telescope
We present the technical specifications and first results of the ESA-funded,
lunar monitoring project "NELIOTA" (NEO Lunar Impacts and Optical TrAnsients)
at the National Observatory of Athens, which aims to determine the
size-frequency distribution of small Near-Earth Objects (NEOs) via detection of
impact flashes on the surface of the Moon. For the purposes of this project a
twin camera instrument was specially designed and installed at the 1.2 m
Kryoneri telescope utilizing the fast-frame capabilities of scientific
Complementary Metal-Oxide Semiconductor detectors (sCMOS). The system provides
a wide field-of-view (17.0' 14.4') and simultaneous observations in
two photometric bands (R and I), reaching limiting magnitudes of 18.7 mag in 10
sec in both bands at a 2.5 signal-to-noise level. This makes it a unique
instrument that can be used for the detection of NEO impacts on the Moon, as
well as for any astronomy projects that demand high-cadence multicolor
observations. The wide field-of-view ensures that a large portion of the Moon
is observed, while the simultaneous, high-cadence, monitoring in two
photometric bands makes possible, for the first time, the determination of the
temperatures of the impacts on the Moon's surface and the validation of the
impact flashes from a single site. Considering the varying background level on
the Moon's surface we demonstrate that the NELIOTA system can detect NEO impact
flashes at a 2.5 signal-to-noise level of ~12.4 mag in the I-band and R-band
for observations made at low lunar phases ~0.1. We report 31 NEO impact flashes
detected during the first year of the NELIOTA campaign. The faintest flash was
at 11.24 mag in the R-band (about two magnitudes fainter than ever observed
before) at lunar phase 0.32. Our observations suggest a detection rate of events .Comment: Accepted for publication in A&
On the absence of bound-state stabilization through short ultra-intense fields
We address the question of whether atomic bound states begin to stabilize in
the short ultra-intense field limit. We provide a general theory of ionization
probability and investigate its gauge invariance. For a wide range of
potentials we find an upper and lower bound by non-perturbative methods, which
clearly exclude the possibility that the ultra intense field might have a
stabilizing effect on the atom. For short pulses we find almost complete
ionization as the field strength increases.Comment: 34 pages Late
On the Influence of Pulse Shapes on Ionization Probability
We investigate analytical expressions for the upper and lower bounds for the
ionization probability through ultra-intense shortly pulsed laser radiation. We
take several different pulse shapes into account, including in particular those
with a smooth adiabatic turn-on and turn-off. For all situations for which our
bounds are applicable we do not find any evidence for bound-state
stabilization.Comment: 21 pages LateX, 10 figure
Ionization Probabilities through ultra-intense Fields in the extreme Limit
We continue our investigation concerning the question of whether atomic bound
states begin to stabilize in the ultra-intense field limit. The pulses
considered are essentially arbitrary, but we distinguish between three
situations. First the total classical momentum transfer is non-vanishing,
second not both the total classical momentum transfer and the total classical
displacement are vanishing together with the requirement that the potential has
a finite number of bound states and third both the total classical momentum
transfer and the total classical displacement are vanishing. For the first two
cases we rigorously prove, that the ionization probability tends to one when
the amplitude of the pulse tends to infinity and the pulse shape remains fixed.
In the third case the limit is strictly smaller than one. This case is also
related to the high frequency limit considered by Gavrila et al.Comment: 16 pages LateX, 2 figure
Multiphoton detachment of electrons from negative ions
A simple analytical solution for the problem of multiphoton detachment from
negative ions by a linearly polarized laser field is found. It is valid in the
wide range of intensities and frequencies of the field, from the perturbation
theory to the tunneling regime, and is applicable to the excess-photon as well
as near-threshold detachment. Practically, the formulae are valid when the
number of photons is greater than two. They produce the total detachment rates,
relative intensities of the excess-photon peaks, and photoelectron angular
distributions for the hydrogen and halogen negative ions, in agreement with
those obtained in other, more numerically involved calculations in both
perturbative and non-perturbative regimes. Our approach explains the extreme
sensitivity of the multiphoton detachment probability to the asymptotic
behaviour of the bound-state wave function. Rapid oscillations in the angular
dependence of the -photon detachment probability are shown to arise due to
interference of the two classical trajectories which lead to the same final
state after the electron emerges at the opposite sides of the atom when the
field is close to maximal.Comment: 27 pages, Latex, and PostScript figures fig1.ps, fig2.ps, fig3.ps,
accepted for publication in Phys. Rev.
Canonicalizing Knowledge Base Literals
Ontology-based knowledge bases (KBs) like DBpedia are very valuable resources, but their usefulness and usability is limited by various quality issues. One such issue is the use of string literals instead of semantically typed entities. In this paper we study the automated canonicalization of such literals, i.e., replacing the literal with an existing entity from the KB or with a new entity that is typed using classes from the KB. We propose a framework that combines both reasoning and machine learning in order to predict the relevant entities and types, and we evaluate this framework against state-of-the-art baselines for both semantic typing and entity matching
Heterogeneity of pollen food allergy syndrome in seven Southern European countries: The @IT.2020 multicenter study
Background Pollen food allergy syndrome (PFAS) is a frequently underdiagnosed disease due to diverse triggers, clinical presentations, and test results. This is especially relevant in geographic areas with a broad spectrum of pollen sensitization, such as Southern Europe. Objectives To elucidate similarities and differences of PFAS in nine Southern European centers and identify associated characteristics and unique markers of PFAS. Methods As part of the @IT.2020 Multicenter Study, 815 patients with seasonal allergic rhinitis (SAR), aged 10-60 years, were recruited in seven countries. They completed questionnaires regarding SAR, comorbidities, family history, and PFAS, and underwent skin prick testing (SPT) and serum IgE testing. Results Of the 815 patients, 167 (20.5%) reported PFAS reactions. Most commonly, eliciting foods were kiwi (58, 34.7%), peach (43, 25.7%), and melon (26, 15.6%). Reported reactions were mostly local (216/319, 67.7%), occurring within 5 min of contact with elicitors (209/319, 65.5%). Associated characteristics included positive IgE to at least one panallergen (profilin, PR-10, or nsLTP) (p = 0.007), maternal PFAS (OR: 3.716, p = 0.026), and asthma (OR: 1.752, p = 0.073). Between centers, heterogeneity in prevalence (Marseille: 7.5% vs. Rome: 41.4%, p < 0.001) and of clinical characteristics was apparent. Cypress played a limited role, with only 1/22 SPT mono-sensitized patients reporting a food reaction (p < 0.073). Conclusions PFAS is a frequent comorbidity in Southern European SAR patients. Significant heterogeneity of clinical characteristics in PFAS patients among the centers was observed and may be related to the different pollen sensitization patterns in each geographic area. IgE to panallergen(s), maternal PFAS, and asthma could be PFAS-associated characteristics
COST292 experimental framework for TRECVID 2008
In this paper, we give an overview of the four tasks submitted to TRECVID 2008 by COST292. The high-level feature extraction framework comprises four systems. The first system transforms a set of low-level descriptors into the semantic space using Latent Semantic Analysis and utilises neural networks for feature detection. The second system uses a multi-modal classifier based on SVMs and several descriptors. The third system uses three image classifiers based on ant colony optimisation, particle swarm optimisation and a multi-objective learning algorithm. The fourth system uses a Gaussian model for singing detection and a person detection algorithm. The search task is based on an interactive retrieval application combining retrieval functionalities in various modalities with a user interface supporting automatic and interactive search over all queries submitted. The rushes task submission is based on a spectral clustering approach for removing similar scenes based on eigenvalues of frame similarity matrix and and a redundancy removal strategy which depends on semantic features extraction such as camera motion and faces. Finally, the submission to the copy detection task is conducted by two different systems. The first system consists of a video module and an audio module. The second system is based on mid-level features that are related to the temporal structure of videos
Modelling Hierarchy and Specialization of a System of Cities from an Evolutionary Perspective on Firms' Interactions
Despite their great diversity, most systems of cities show remarkably similar patterns when comparing the size distribution and the economic specialization of their constitutive cities. The universality of these patterns sparked the interest of geographers, economists and physicists. However, until now, no economic model has relied on a micro-based and evolutionary approach to reproduce these regularities. In this chapter, we intend to fill this gap by proposing a model where the micro dynamics of localized firms generate the two macro regularities of size distribution and economic specialization. The model is based on boundedly rational firms’ competition and path dependent innovation. We discuss the possible emergence of macro properties from these micro behaviors of firms
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