arXiv subjects

A. Fischer

Publications and source records attributed to A. Fischer.

12 recordsLinked to original sources

arXiv2020

Pretrained Transformers for Simple Question Answering over Knowledge Graphs

Answering simple questions over knowledge graphs is a well-studied problem in question answering. Previous approaches for this task built on recurrent and convolutional neural network based architectures that use pretrained word embeddings. It was recently shown that finetuning pretrained transformer networks (e.g. BERT) can outperform previous approaches on various natural language processing tasks. In this work, we investigate how well BERT performs on SimpleQuestions and provide an evaluation of both BERT and BiLSTM-based models in datasparse scenarios.

cs.CL↗

arXiv2017

Effect of PYTHIA8 tunes on event shapes and top-quark reconstruction in $e^+e^-$ annihilation at CLIC

This paper describes the effect of PYTHIA8 tunes on event simulation of $e^+e^-$ collisions with center-of-mass (CM) energies of 380 GeV and 3 TeV at the proposed CLIC collider. Event shapes, such as thrust, thrust major, thrust minor, oblateness, as well as particle multiplicities have been analyzed and relative differences with respect to the default PYTHIA8 tune were determined. The effect of tunes on top-mass reconstruction in the resolved and boosted regimes was analyzed. No statistically significant variation for reconstructed top masses using invariant masses of three jets was found for events with a CM energy of 380 GeV. For the fully boosted top reconstruction at a CM energy of 3 TeV, a significant shift in reconstructed top mass of about 700 MeV for the "Montull" tune was observed. This shift correlates with an increase in particle multiplicity compared to all other PYTHIA8 tunes.

hep-ph↗

arXiv2017

Observation and Control of Laser-Enabled Auger Decay

Single photon laser enabled Auger decay (spLEAD) has been redicted theoretically [Phys. Rev. Lett. 111, 083004 (2013)] and here we report its first experimental observation in neon. Using coherent, bichromatic free-electron laser pulses, we have detected the process and coherently controlled the angular distribution of the emitted electrons by varying the phase difference between the two laser fields. Since spLEAD is highly sensitive to electron correlation, this is a promising method for probing both correlation and ultrafast hole migration in more complex systems.

physics.atom-ph↗

arXiv2017

Coherent control with a short-wavelength Free Electron Laser

XUV and X-ray Free Electron Lasers (FELs) produce short wavelength pulses with high intensity, ultrashort duration, well-defined polarization and transverse coherence, and have been utilised for many experiments previously possible at long wavelengths only: multiphoton ionization, pumping an atomic laser, and four-wave mixing spectroscopy. However one important optical technique, coherent control, has not yet been demonstrated, because Self- Amplified Spontaneous Emission FELs have limited longitudinal coherence. Single-colour pulses from the FERMI seeded FEL are longitudinally coherent, and two-colour emission is predicted to be coherent. Here we demonstrate the phase correlation of two colours, and manipulate it to control an experiment. Light of wavelengths 63.0 and 31.5 nm ionized neon, and the asymmetry of the photoelectron angular distribution was controlled by adjusting the phase, with temporal resolution 3 attoseconds. This opens the door to new shortwavelength coherent control experiments with ultrahigh time resolution and chemical sensitivity.

physics.optics↗

arXiv2012

A retrospective of the GREGOR solar telescope in scientific literature

In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post-focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i.e., the final stages of commissioning and science verification. Taking stock of the various publications in peer-reviewed journals and conference proceedings also provides the "historical" context for the reference articles in this special issue of Astronomische Nachrichten/Astronomical Notes.

astro-ph.IM↗

arXiv2012

Induced surface enhancement in coral Pt island films attached to nanostructured Ag electrodes

Coral Pt islands films are deposited via electrochemical reduction on silica coated nanostructured Ag electrodes. From these devices surface enhanced (resonance) Raman [SE(R)R] signals of molecules exclusively attached to Pt are obtained with intensities up to 50% of the value determined for Ag. SE(R)R spectroscopic investigations are carried out with different probe molecules, silica coating thicknesses and excitation lines. Additionally, field enhancement calculations on Ag-SiO2-Pt support geometries are performed to elucidate the influence of the Pt island film nanostructure on the observed Raman intensities. It is concluded that the non perfect coating of the Pt island film promotes the efficiency of the induced Pt SER activity. Comparison with similar measurements on Ag-SiO2-Au electrodes further suggests that the chemical nature of the deposited metal island film plays a minor role for the SE(R)R intensity.

cond-mat.mes-hall↗

arXiv2010

The Filter Imager SuFI and the Image Stabilization and Light Distribution System ISLiD of the Sunrise Balloon-Borne Observatory: Instrument Description

We describe the design of the Sunrise Filter Imager (SuFI) and the Image Stabilization and Light Distribution (ISLiD) unit onboard the Sunrise balloon borne solar observatory. This contribution provides the necessary information which is relevant to understand the instruments working principles, the relevant technical data, and the necessary information about calibration issues directly related to the science data.

astro-ph.IM↗

arXiv2010

Relative luminosity measurement of the LHC with the ATLAS forward calorimeter

In this paper it is shown that a measurement of the relative luminosity changes at the LHC may be obtained by analysing the currents drawn from the high voltage power supplies of the electromagnetic section of the forward calorimeter of the ATLAS detector. The method was verified with a reproduction of a small section of the ATLAS forward calorimeter using proton beams of known beam energies and variable intensities at the U-70 accelerator at IHEP in Protvino, Russia. The experimental setup and the data taking during a test beam run in April 2008 are described in detail. A comparison of the measured high voltage currents with reference measurements from beam intensity monitors shows a linear dependence on the beam intensity. The non-linearities are measured to be less than 0.5 % combining statistical and systematic uncertainties.

physics.ins-det↗

arXiv2008

Formation Of A Cold Antihydrogen Beam in AEGIS For Gravity Measurements

The formation of the antihydrogen beam in the AEGIS experiment through the use of inhomogeneous electric fields is discussed and simulation results including the geometry of the apparatus and realistic hypothesis about the antihydrogen initial conditions are shown. The resulting velocity distribution matches the requirements of the gravity experiment. In particular it is shown that the inhomogeneous electric fields provide radial cooling of the beam during the acceleration.

physics.atom-ph↗

arXiv2004

Hadronic Calibration of the ATLAS Liquid Argon End-Cap Calorimeter in the Pseudorapidity Region 1.6 < |eta| < 1.8 in Beam Tests

A full azimuthal phi-wedge of the ATLAS liquid argon end-cap calorimeter has been exposed to beams of electrons, muons and pions in the energy range 6 GeV <= E <= 200 GeV at the CERN SPS. The angular region studied corresponds to the ATLAS impact position around the pseudorapidity interval 1.6 < |eta| < 1.8. The beam test set-up is described. A detailed study of the performance is given as well as the related intercalibration constants obtained. Following the ATLAS hadronic calibration proposal, a first study of the hadron calibration using a weighting ansatz is presented. The results are compared to predictions from Monte Carlo simulations, based on GEANT 3 and GEANT 4 models.

physics.ins-det↗

arXiv2001

Accretion physics of AM Herculis binaries, I. Results from one-dimensional stationary radiation hydrodynamics

We have solved the one-dimensional stationary two-fluid hydrodynamic equations for post-shock flows on accreting magnetic white dwarfs simultaneous with the fully frequency and angle-dependent radiative transfer for cyclotron radiation and bremsstrahlung. Magnetic field strengths B = 10 to 100 MG are considered. At given B, this theory relates the properties of the emission region to a single physical parameter, the mass flow density (or accretion rate per unit area). We present the normalized temperature profiles and fit formulae for the peak electron temperature, the geometrical shock height, and the column density of the post-shock flow. The results apply to pillbox-shaped emission regions. With a first-order temperature correction they can also be used for narrower columns provided they are not too tall.

astro-ph↗

arXiv2001

A model for the optical high state light curve of AM Herculis

We present a simple quantitative model that can describe the photometric B and V band light curves of AM Herculis obtained during a high state. The double-humped shape of the V band light curve is dominated by cyclotron emission from a region at the main accreting pole with an area of ~5x10e16 cm^2 and sustaining an inflow of ~0.06 g/cm^2/s. The almost unmodulated B band is dominated by emission from the accretion stream. The contribution of the heated white dwarf to the optical emission is small in the B band, but comparable to that of the accretion stream in the V band. The emission of the secondary star is negligible both in B and in V.

astro-ph↗