arXiv subjects

Alfred Mueller

Publications and source records attributed to Alfred Mueller.

6 recordsLinked to original sources

arXiv2026

Ultra-precise TDoA-based Localization of Frequency Hopping LPWAN Transmitters

The Internet of Things (IoT) is a highly emerging market. It serves as a key enabler for a variety of applications like the digital twin or asset tracking in industrial scenarios. This often requires the provision of precise position information. However, systems like Global Navigation Satellite Systems (GNSS) are ruled out due to high energy costs and indoor applications. A variety of systems is discussed to close this gap. In order to contribute to the investigations of possible gold standards, this paper discusses the localization based on Low Power Wide Area Networks (LPWAN). Therefore, a concept is presented, based on Time Difference of Arrival (TDoA) measurements within the LPWAN standard ETSI TS 103 357. This paper addresses two major challenges. At first, TDoA measurements require highly precise temporal synchronization of the receiving base stations. Within this work, this issue is solved by exploiting Signals of Opportunity (SoO) as synchronization source, enabling sub-meter synchronization accuracy. A further issue arises from the Frequency Hopping (FH) waveform of the transmitting endpoints, resulting in a loss of phase information and thus usable localization bandwidth. A method is introduced to overcome this limitation. This paper states the system concept, proves its functionality in theoretical investigations and simulations. Finally, real-world measurements verify the functionality and show a 2D localization accuracy of below 10 m in Line of Sight (LOS) scenarios.

eess.SP↗

arXiv2017

Electron-Impact Multiple Ionization Cross Sections for Atoms and Ions of Helium through Zinc

We have compiled a set of electron-impact multiple ionization (EIMI) cross sections for astrophysically relevant ions. EIMI can have a significant effect on the ionization balance of non-equilibrium plasmas. For example, it can be important if there is a rapid change in the electron temperature or if there is a non-thermal electron energy distribution, such as a kappa distribution. Cross sections for EIMI are needed in order to account for these processes in plasma modeling and for spectroscopic interpretation. Here, we describe our comparison of proposed semiempirical formulae to the available experimental EIMI cross section data. Based on this comparison, we have interpolated and extrapolated fitting parameters to systems that have not yet been measured. A tabulation of the fit parameters is provided for 3466 EIMI cross sections. We also highlight some outstanding issues that remain to be resolved.

astro-ph.IM↗

arXiv2002

Gluon Distributions and Color Charge Correlations in a Saturated Light-cone Wavefunction

We describe the light-cone wavefunction in the saturation regime in terms of the density of gluons per unit of transverse phase space, the occupation number, and in terms of the color charge correlator. The simple McLerran- Venugopalan model gives what are claimed to be general results for the phase space gluon density, but it does not well describe the general case for the charge correlator. We derive the general momentum dependence and rapidity dependence of the color charge correlator which exhibits strong color shielding. A simplel physical picture which leads to these general results is described.

hep-ph↗

arXiv2002

Interference effects in the photorecombination of argonlike Sc3+ ions: Storage-ring experiment and theory

Absolute total electron-ion recombination rate coefficients of argonlike Sc3+(3s2 3p6) ions have been measured for relative energies between electrons and ions ranging from 0 to 45 eV. This energy range comprises all dielectronic recombination resonances attached to 3p -> 3d and 3p -> 4s excitations. A broad resonance with an experimental width of 0.89 +- 0.07 eV due to the 3p5 3d2 2F intermediate state is found at 12.31 +- 0.03 eV with a small experimental evidence for an asymmetric line shape. From R-Matrix and perturbative calculations we infer that the asymmetric line shape may not only be due to quantum mechanical interference between direct and resonant recombination channels as predicted by Gorczyca et al. [Phys. Rev. A 56, 4742 (1997)], but may partly also be due to the interaction with an adjacent overlapping DR resonance of the same symmetry. The overall agreement between theory and experiment is poor. Differences between our experimental and our theoretical resonance positions are as large as 1.4 eV. This illustrates the difficulty to accurately describe the structure of an atomic system with an open 3d-shell with state-of-the-art theoretical methods. Furthermore, we find that a relativistic theoretical treatment of the system under study is mandatory since the existence of experimentally observed strong 3p5 3d2 2D and 3p5 3d 4s 2D resonances can only be explained when calculations beyond LS-coupling are carried out.

physics.atom-ph↗

arXiv2000

Enhanced dielectronic recombination of lithium-like Ti19+ ions in external ExB fields

Dielectronic recombination(DR) of lithium-like Ti19+(1s2 2s) ions via 2s->2p core excitations has been measured at the Heidelberg heavy ion storage ring TSR. We find that not only external electric fields (0 <= Ey <= 280 V/cm) but also crossed magnetic fields (30 mT <= Bz <= 80 mT) influence the DR via high-n (2p_j nl)-Rydberg resonances. This result confirms our previous finding for isoelectronic Cl14+ ions [Bartsch T et al, PRL 82, 3779 (1999)] that experimentally established the sensitivity of DR to ExB fields. In the present investigation the larger 2p_{1/2}-2p_{3/2} fine structure splitting of Ti19+ allowed us to study separately the influence of external fields via the two series of Rydberg DR resonances attached to the 2s -> 2p_{1/2} and 2s -> 2p_{3/2} excitations of the Li-like core, extracting initial slopes and saturation fields of the enhancement. We find that for Ey > 80 V/cm the field induced enhancement is about 1.8 times stronger for the 2p_{3/2} series than for the 2p_{1/2} series.

physics.atom-ph↗

arXiv2000

Dielectronic recombination of lithium-like Ni25+ ions - high resolution rate coefficients and influence of external crossed E and B fields

Absolute dielectronic recombination (DR) rates for lithium-like Ni$^{25+}$($1s^2 2s$) ions were measured at high-energy resolution at the Heidelberg heavy-ion storage ring TSR. We studied the center-of-mass energy range 0--130 eV which covers all $Δn$=0 core excitations. The influence of external crossed electric (0--300 V/cm) and magnetic (41.8--80.1 mT) fields was investigated. For the measurement at near-zero electric field resonance energies and strengths are given for Rydberg levels up to n$=$32; also Maxwellian plasma rate coefficients for the $Δn$=0 DR at electron temperatures between 0.5 and 200 eV are provided. For increasing electric field strength we find that for both the $2p_{1/2}$ and the $2p_{3/2}$ series of Ni$^{24+}$($1s^2 2p_j n\ell$) Rydberg resonances with n>30 the DR rate coefficient increases approximately linearly by up to a factor of 1.5. The relative increase due to the applied electric field for Ni$^{25+}$ is remarkably lower than that found in previous measurements with lighter isoelectronic Si$^{11+}$, Cl$^{14+}$ and also Ti$^{19+}$ ions, [T. Bartsch et al, Phys. Rev. Lett. {\bf 79}, 2233 (1997); {\bf 82}, 3779 (1999) and to be published] and in contrast to the results for lighter ions no clear dependence of the electric field enhancement on the magnetic field strength is found. The Maxwellian plasma rate coefficients for $Δn$=0 DR of Ni$^{25+}$ are enhanced by at most 11% in the presence of the strongest experimentally applied fields.

physics.atom-ph↗