Spin effects in strong-field laser-electron interactions

The electron spin degree of freedom can play a significant role in relativistic scattering processes involving intense laser fields. In this contribution we discuss the influence of the electron spin on (i) Kapitza-Dirac scattering in an x-ray laser field of high intensity, (ii) photo-induced electron-positron pair production in a strong laser wave and (iii) multiphoton electron-positron pair production on an atomic nucleus. We show that in all cases under consideration the electron spin can have a characteristic impact on the process properties and their total probabilities. To this end, spin-resolved calculations based on the Dirac equation in the presence of an intense laser field are performed. The predictions from Dirac theory are also compared with the corresponding results from the Klein-Gordon equation.Comment: 9 pages, 6 figure

Supernova Simulations from a 3D Progenitor Model -- Impact of Perturbations and Evolution of Explosion Properties

We study the impact of large-scale perturbations from convective shell burning on the core-collapse supernova explosion mechanism using three-dimensional (3D) multi-group neutrino hydrodynamics simulations of an 18 solar mass progenitor. Seed asphericities in the O shell, obtained from a recent 3D model of O shell burning, help trigger a neutrino-driven explosion 330ms after bounce whereas the shock is not revived in a model based on a spherically symmetric progenitor for at least another 300ms. We tentatively infer a reduction of the critical luminosity for shock revival by ~20% due to pre-collapse perturbations. This indicates that convective seed perturbations play an important role in the explosion mechanism in some progenitors. We follow the evolution of the 18 solar mass model into the explosion phase for more than 2s and find that the cycle of accretion and mass ejection is still ongoing at this stage. With a preliminary value of 0.77 Bethe for the diagnostic explosion energy, a baryonic neutron star mass of 1.85 solar masses, a neutron star kick of ~600km/s and a neutron star spin period of ~20ms at the end of the simulation, the explosion and remnant properties are slightly atypical, but still lie comfortably within the observed distribution. Although more refined simulations and a larger survey of progenitors are still called for, this suggests that a solution to the problem of shock revival and explosion energies in the ballpark of observations are within reach for neutrino-driven explosions in 3D.Comment: 23 pages, 22 figures, accepted for publication in MNRA

Emission line models for the lowest-mass core collapse supernovae. I: Case study of a 9 M⊙M_\odot one-dimensional neutrino-driven explosion

A large fraction of core-collapse supernovae (CCSNe), 30-50%, are expected to originate from the low-mass end of progenitors with $M_{\rm ZAMS}~= 8-12~M_\odot$. However, degeneracy effects make stellar evolution modelling of such stars challenging, and few predictions for their supernova light curves and spectra have been presented. Here we calculate synthetic nebular spectra of a 9 $M_\odot$ Fe CCSN model exploded with the neutrino mechanism. The model predicts emission lines with FWHM$\sim$1000 km/s, including signatures from each deep layer in the metal core. We compare this model to observations of the three subluminous IIP SNe with published nebular spectra; SN 1997D, SN 2005cs, and SN 2008bk. The prediction of both line profiles and luminosities are in good agreement with SN 1997D and SN 2008bk. The close fit of a model with no tuning parameters provides strong evidence for an association of these objects with low-mass Fe CCSNe. For SN 2005cs, the interpretation is less clear, as the observational coverage ended before key diagnostic lines from the core had emerged. We perform a parameterised study of the amount of explosively made stable nickel, and find that none of these three SNe show the high $^{58}$Ni/$^{56}$Ni ratio predicted by current models of electron capture SNe (ECSNe) and ECSN-like explosions. Combined with clear detection of lines from O and He shell material, these SNe rather originate from Fe core progenitors. We argue that the outcome of self-consistent explosion simulations of low-mass stars, which gives fits to many key observables, strongly suggests that the class of subluminous Type IIP SNe is the observational counterpart of the lowest mass CCSNe.Comment: Resubmitted to MNRAS after referee comment

A simple model of price formation

A simple Ising spin model which can describe the mechanism of price formation in financial markets is proposed. In contrast to other agent-based models, the influence does not flow inward from the surrounding neighbors to the center site, but spreads outward from the center to the neighbors. The model thus describes the spread of opinions among traders. It is shown via standard Monte Carlo simulations that very simple rules lead to dynamics that duplicate those of asset prices.Comment: Version 2: 4 pages, 4 figures; added more stringent statistical analysis; to appear in Int. J. Modern Physics C, Vol. 13, No. 1 (2002

Neutrino Signal of Electron-Capture Supernovae from Core Collapse to Cooling

An 8.8 solar mass electron-capture supernova (SN) was simulated in spherical symmetry consistently from collapse through explosion to nearly complete deleptonization of the forming neutron star. The evolution time of about 9 s is short because of nucleon-nucleon correlations in the neutrino opacities. After a brief phase of accretion-enhanced luminosities (~200 ms), luminosity equipartition among all species becomes almost perfect and the spectra of electron antineutrinos and muon/tau antineutrinos very similar. We discuss consequences for the neutrino-driven wind as a nucleosynthesis site and for flavor oscillations of SN neutrinos.Comment: 4 pages, 4 eps figures; published as Physical Review Letters, vol. 104, Issue 25, id. 25110

Global Anisotropies in Supernova Explosions and Pulsar Recoil

We show by two-dimensional and first three-dimensional simulations of neutrino-driven supernova explosions that low (l=1,2) modes can dominate the flow pattern in the convective postshock region on timescales of hundreds of milliseconds after core bounce. This can lead to large global anisotropy of the supernova explosion and pulsar kicks in excess of 500 km/s.Comment: 3 pages, 2 figures, contribution to Procs. 12th Workshop on Nuclear Astrophysics, Ringberg Castle, March 22-27, 200

Overview of the 2005 cross-language image retrieval track (ImageCLEF)

The purpose of this paper is to outline efforts from the 2005 CLEF crosslanguage image retrieval campaign (ImageCLEF). The aim of this CLEF track is to explore the use of both text and content-based retrieval methods for cross-language image retrieval. Four tasks were offered in the ImageCLEF track: a ad-hoc retrieval from an historic photographic collection, ad-hoc retrieval from a medical collection, an automatic image annotation task, and a user-centered (interactive) evaluation task that is explained in the iCLEF summary. 24 research groups from a variety of backgrounds and nationalities (14 countries) participated in ImageCLEF. In this paper we describe the ImageCLEF tasks, submissions from participating groups and summarise the main fndings

Improving the accuracy of 1D SNMR surveys using the multi-central-loop configuration

Temeljna svrha i cilj ovoga rada bilo je ispitati koliko su potrošači skloni dijeljenju svojih turističkih iskustva s drugima te putem kojih medija. Osim navedenog, drugi cilj provedenog istraživanja bilo je utvrditi koliko su potrošačima važna iskustva i komentari drugih posjetitelja u procesu donošenja odluke o kupnji. Istraživanje je provedeno metodom ispitivanja, a kao instrument korišten je anketni upitnik sastavljen od 22 pitanja. Utvrđivanjem problema istraživanja, postavljene su tri hipoteze. Od tri hipoteze, u potpunosti je dokazana samo prva koja pretpostavlja da su potrošačima tuđa iskustva i komentari od velike važnosti kod planiranja i odabira putovanja. Druga hipoteza je djelomično potvrđena, tj. potvrđeno je da su potrošači skloni dijeliti svoja iskustva s drugima u situaciji kada su jako zadovoljni dok s druge strane nije potvrđeno kako su potrošači skloni dijeliti svoja iskustva u situaciji kada su nezadovoljni uslugom ili proizvodom. Na kraju, potvrđena je i treća hipoteza koja pretpostavlja kako su potrošači skloni dijeljenju vlastitog turističkog iskustva putem više društvenih medija, iako je utvrđeno kako najveći broj ispitanika ne dijeli svoja turistička iskustva. Istraživano je i mišljenje ispitanika o turističkoj destinaciji iz snova, a iznenađujuće, najveći broj ispitanika je navelo hrvatske destinacije kao svoje destinacije iz snova kao i one koje su im dosada pružile najnezaboravnije turističko iskustvo. Potrebno je provesti detaljnija istraživanja kako bi se detaljnije istražilo novije društvene medije koji su dostupni potrošačima za dijeljenje svog iskustva

Improving the accuracy of 1D SNMR surveys using the multi-central-loop configuration

A multi-central loop configuration has been studied through forward and inverse modelling of synthetics and real data. This set-up takes advantage of the multichannel features of the NMR device and consists of using several (2 to 3) additional receiver loops displayed concentrically with the main transmitter/receiver loop, which all record the NMR signal simultaneously within a single acquisition. If the loop diameters are chosen appropriately, the kernel sensitivity distributions for each receiver loop can show complementary features. Inverting simultaneously the data sets obtained through each different receiver loop can then enhance the accuracy of the final model. To do so, a 1D QT inversion scheme in the frequency domain dedicated to the inversion of multiple data sets is being used. One challenging feature is to adapt the regularization of the inverse process so as to handle correctly the noise originating from different data sets. The efficiency of this multi-central loop acquisition set-up and procedure is being assessed through the forward and inverse modelling of several scenarios implying varying aquifer characteristics. Finally a field case is being presented that was conducted on a low noise level site located in Germany, where conditions were favourable to the implementation and testing of circular multi-central loop configurations.We also introduce a new method for determining NMR parameters, named the prediction-focused-approach (PFA), that is based on statistical analysis of a large number of simple models. We observe, using synthetic examples, that the effciency of the method benefits from the use of the multi-central-loop configurations