Search results for "Mathematical physics"
showing 10 items of 2687 documents
Impact of a cryogenic baffle system on the suppression of radon-induced background in the KATRIN Pre-Spectrometer
2018
The KATRIN experiment will determine the effective electron anti-neutrino mass with a sensitivity of 200 meV/c2 at 90% CL. The energy analysis of tritium β-decay electrons will be performed by a tandem setup of electrostatic retarding spectrometers which have to be operated at very low background levels of <10−2 counts per second. This benchmark rate can be exceeded by background processes resulting from the emanation of single 219,220Rn atoms from the inner spectrometer surface and an array of non-evaporable getter strips used as main vacuum pump. Here we report on the impact of a cryogenic technique to reduce this radon-induced background in electrostatic spectrometers. It is based on ins…
Die thermische Entmischung von Gasen bei hohem Druck
1950
Abstract Es wird die Druckabhängigkeit des Thermodiffusionsfaktors α einiger Gaspaare durch Untersuchung der elementaren thermischen Entmischung bestimmt. Für etwa äquimolare Mischungen steigt α bei einer mittleren Temperatur von 84° C im Bereich von 3-80 atm bei CO2/H2 von 0,32 auf 0,98, bei CO2/N2 von 0,05 auf 0,40, bei CO2/A von 0,03 auf 0,25, bei CO2/CH4 von 0,07 auf 0,37 und bei N2/H2 von 0,35 auf 0,44. Die Gaspaare N2/CH4 und N2/NH3 zeigen dagegen negative Druckabhängigkeit, die bei dem letzten schon bei 1,8 atm zu einem Vorzeichenwechsel von a führt. Die Temperatur-und Konzentrationsabhängigkeit des Thermodiffusionsfaktors von CO2/H2 besitzen bei 47 atm umgekehrtes Vorzeichen wie bei…
Durch Dehnung bewirkter Vorzeichenwechsel der Magnetostriktion
1949
Abstract Während der als Villari-Umkelir bekannte Vorzeichenwechsel der Magnetostriktion des Eisens von der Aufeinanderfolge von 90°-Wandverschiebungen und Drehprozessen bei fortschreitender Magnetisierung herrührt, findet man bei einer Heusler-Legierung und bei Fe-Ni-Legierungen eine andere Art des Vorzeichenwechsels. Sie läßt sich darauf zurückführen, daß entweder Zugspannung eine Änderung der spontanen Gitterverzerrung bewirkt oder daß durch Zug die Magnetisierungsvektoren unter Umständen trotz positiver Magnetostriktion aus der Zugrichtung herausgedreht werden können.
Ab initiocalculations of theFcenters in MgF2bulk and on the (001) surface
2012
We present and discuss the results of atomic and electronic structure calculations of the F centers in MgF2 bulk and on the (001) surface. The calculations are based on the B3PW Hartree–Fock and density functional theory hybrid exchange-correlation functional. Most of the electronic density of a missing fluorine ion is localized in the bulk vacancy and a little bit less—in a surface vacancy. It is shown that the electronic F center is a deep donor. The lattice distortion and defect formation energy on the neutral (001) surface and in the bulk are also compared.
Hydrogen adsorption on the ZnO $(1\bar{1}00)$ surface: ab initio hybrid density functional linear combination of atomic orbitals calculations
2014
Hydrogen atoms unavoidably presented in ZnO samples or thin films during their synthesis considerably affect electrical conductivity. Results of first principles hybrid functional linear combination of atomic orbitals calculations are discussed for hydrogen atoms incorporated in bulk or adsorbed upon non-polar ZnO (1¯ 100) surfaces. The energy of H incorporation, atomic relaxation, electronic density redistribution and modification of the electronic structure are compared for both surface adsorption and bulk absorption. It is shown that hydrogen forms a strong bonding with the surface O ions (Eads = 2.7eV) whereas its incorporation into bulk is energetically quite unfavorable. Hydrogen adso…
Determination of the g-Factor of Single Hydrogen-Like Ions by Mode Coupling in a Penning Trap
2004
A method has been developed and applied for the determination of the electronic g-factor of single hydrogen-like ions stored in a Penning trap. The method is based on mode coupling of the ion trapping motions and is conceptionally advantageous as compared to previously used methods. It has been applied to hydrogen-like oxygen 16O7+ and yields a value for the gJ-factor which is in agreement with previously determined values. Experimental requirements and possibilities of the new method are discussed.
Hydrogen-like bismuth
1995
Atomic physics at heavy ion storage rings allows to study matter in an extreme ionization state and at very high velocity. The concept of electron cooling yields an ion beam with epithermal temperatures, which is suited for many precision experiments. At the ESR even the heaviest elements can be stored up to the fully stripped charge state. The H-like ions with nuclear spin exhibit a groundstate hfs-splitting in the optical region. This can be used as a probe for QED at high Z and magnetization inside the nucleus. The topics related to cooling of ions and laser spectroscopy in a storage ring are reported and a first result of the 1s hfs in 209Bi82+ is discussed for the relevance in testing …
Double einzel lens extraction for the JYFL 14 GHz ECR ion source designed with IBSimu
2013
In order to improve the performance of the JYFL 14 GHz electron cyclotron resonance ion source (ECRIS) and initiate low energy beam transport (LEBT) upgrade at the University of Jyvaskyla, Department of Physics (JYFL) accelerator laboratory, a new ion beam extraction system has been designed and installed. The development of the new extraction was performed with the ion optical code IBSimu, making it the first ECRIS extraction designed with the code. The measured performance of the new extraction is in good agreement with the simulations. Compared to the old extraction the new system provides improved beam quality, i.e. lower transverse emittance values and improved structure of beam profil…
Trace detection of radiotoxic isotopes by resonance ionization mass spectrometry
1995
Resonance ionization spectroscopy combined with mass spectrometry (RIMS) has become an important technique for ultratrace environmental analysis, and is particularly well suited for the detection of long-lived radio-toxic isotopes. A variety of experimental approaches have been developed to address the specific requirements posed by individual isotopes, which have widely differing physical, chemical, and environmental properties. In this paper we discuss the principles and recent progress in the development of three different methods that are being used for the analysis of radiotoxic species. These include measurement of actinides using triple-resonance ionization and time-of-flight mass sp…
Structural factor in bending testing of fivefold twinned nanowires revealed by finite element analysis
2016
In this study, we performed finite element method simulations to investigate the effect of the structure on the elastic response of Ag and Au nanowires (NWs) with a fivefold twinned crystal structure in bending tests. Two different models of a pentagonal NW were created: a 'uniform model' having an isotropic continuous structure and a 'segmented model' consisting of five anisotropic domains. Two asymmetrical mechanical test configurations were simulated: cantilevered beam bending and 3-point bending. The dimensions of the NW, the test configurations, as well as the force and the displacement ranges were based on the previously obtained experimental data. The results of the simulations demon…