688 results on '"Müller, Alfred"'
Search Results
2. Coherent $\gamma^*$-nucleus scattering and coherent nuclear states
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Mueller, Alfred H.
- Subjects
High Energy Physics - Phenomenology ,Nuclear Theory - Abstract
In the context of a McLerran-Venugopalan (MV) model for a large nucleus, coherent scattering of a virtual photon on that nucleus is evaluated in the $A_-=0$ gauge, the gauge appropriate for the target nucleus. The evaluation of the scattering in $A_-=0$ gauge is very intricate compared to the usual $A_+=0$ gauge evaluation natural for the scattering process, but has the advantage of directly giving the scattering in terms of a partonic description of the nucleus. In the limit where a tagged forward jet puts the dipole-nucleus scattering in the saturation regime the coherent reactions are equal to the inelastic reactions. In terms of the nuclear wave function the coherent reactions come from color singlet and zero total transverse momentum quark-antiquark pairs in the wave function and in the saturation regime the nuclear wave function is a coherent state for these pairs. In the saturation region half of all quarks (or antiquarks) come from zero momentum and color charge pairs.
- Published
- 2024
3. Probabilistic picture for particle number densities in stretched tips of the branching Brownian motion
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Le, Anh Dung, Mueller, Alfred H., and Munier, Stéphane
- Subjects
Condensed Matter - Statistical Mechanics ,High Energy Physics - Phenomenology ,Mathematics - Probability - Abstract
In the framework of a stochastic picture for the one-dimensional branching Brownian motion, we compute the probability density of the number of particles near the rightmost one at a time $T$, that we take very large, when this extreme particle is conditioned to arrive at a predefined position $x_T$ chosen far ahead of its expected position $m_T$. We recover the previously-conjectured fact that the typical number density of particles a distance $\Delta$ to the left of the lead particle, when both $\Delta$ and $x_T-\Delta-m_T$ are large, is smaller than the mean number density by a factor proportional to $e^{-\zeta\Delta^{2/3}}$, where $\zeta$ is a constant that was so far undetermined. Our picture leads to an expression for the probability density of the particle number, from which a value for $\zeta$ may be inferred., Comment: 7 pages, 1 figure. v2: significant improvements to the text, numerous clarifications made. Approach and results unchanged. Version accepted for publications in EPL
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- 2022
- Full Text
- View/download PDF
4. $L_p$-norm spherical copulas
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Bernard, Carole, Müller, Alfred, and Oesting, Marco
- Subjects
Mathematics - Statistics Theory - Abstract
In this paper we study $L_p$-norm spherical copulas for arbitrary $p \in [1,\infty]$ and arbitrary dimensions. The study is motivated by a conjecture that these distributions lead to a sharp bound for the value of a certain generalized mean difference. We fully characterize conditions for existence and uniqueness of $L_p$-norm spherical copulas. Explicit formulas for their densities and correlation coefficients are derived and the distribution of the radial part is determined. Moreover, statistical inference and efficient simulation are considered., Comment: 17 pages, 3 figures
- Published
- 2022
5. A Model for Multiple Metal Spheres in Oscillating Magnetic Fields using Displaced Dipoles
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Bönsel, Florian, Müller, Alfred, and Psiuk, Rafael
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Physics - Classical Physics ,Physics - Applied Physics ,Physics - Computational Physics - Abstract
In this article, we derive a magnetic dipole model for two identical, electrically conducting, and permeable spheres that are exposed to an oscillating homogeneous magnetic field. Our model predicts both amplitude and phase of the induced field outside the spheres. The description is provided for parallel and transverse excitation relative to the axis through the sphere centers. This geometric decomposition allows the application of arbitrary excitation field directions. Our approach is based on one dipole per sphere. The origins of these secondary dipole fields are proposed to be found at positions slightly displaced from the sphere centers to consider the mutual interaction. This displacement and the resulting phase of the dipole moments strongly depend on the distance between the spheres as well as on complex-valued first and second order response factors, which contain material properties and the oscillation frequency. We demonstrate the usefulness of our displaced dipole model in terms of efficiency and accuracy compared to other computationally simple approaches., Comment: 11 pages, 10 figures, 30 references
- Published
- 2021
- Full Text
- View/download PDF
6. [formula omitted]-norm spherical copulas
- Author
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Bernard, Carole, Müller, Alfred, and Oesting, Marco
- Published
- 2024
- Full Text
- View/download PDF
7. Analytical asymptotics for hard diffraction
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Le, Anh Dung, Mueller, Alfred H., and Munier, Stéphane
- Subjects
High Energy Physics - Phenomenology - Abstract
We show that the cross section for diffractive dissociation of a small onium off a large nucleus at total rapidity $Y$ and requiring a minimum rapidity gap $Y_{\text{gap}}$ can be identified, in a well-defined parametric limit, with a simple classical observable on the stochastic process representing the evolution of the state of the onium, as its rapidity increases, in the form of color dipole branchings: It formally coincides with twice the probability that an even number of these dipoles effectively participate in the scattering, when viewed in a frame in which the onium is evolved to the rapidity $Y-Y_{\text{gap}}$. Consequently, finding asymptotic solutions to the Kovchegov-Levin equation, which rules the $Y$-dependence of the diffractive cross section, boils down to solving a probabilistic problem. Such a formulation authorizes the derivation of a parameter-free analytical expression for the gap distribution. Interestingly enough, events in which many dipoles interact simultaneously play an important role, since the distribution of the number $k$ of dipoles participating in the interaction turns out to be proportional to $1/[k(k-1)]$., Comment: 20 pages, 2 figures
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- 2021
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8. Nuclear scattering configurations of onia in different frames
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Le, Anh Dung, Mueller, Alfred H., and Munier, Stéphane
- Subjects
High Energy Physics - Phenomenology ,Condensed Matter - Statistical Mechanics - Abstract
In the scattering of a small onium off a large nucleus at high center-of-mass energies, when the parameters are set in such a way that the cross section at fixed impact parameter is small, events are triggered by rare partonic fluctuations of the onium, which are very deformed with respect to typical configurations. Using the color dipole picture of high-energy interactions in quantum chromodynamics, in which the quantum states of the onium are represented by sets of dipoles generated by a branching process, we describe the typical scattering configurations as seen from different reference frames, from the restframe of the nucleus to frames in which the rapidity is shared between the projectile onium and the nucleus. We show that taking advantage of the freedom to select a frame in the latter class makes possible to derive complete asymptotic expressions for some boost-invariant quantities, beyond the total cross section, from a procedure which leverages the limited available knowledge on the properties of the solutions to the Balitsky-Kovchegov equation that governs the rapidity-dependence of total cross sections. We obtain in this way an analytic expression for the rapidity-distribution of the first branching of the slowest parent dipole of the set of those which scatter. This distribution provides an estimator of the correlations of the interacting dipoles, and is also known to be related to the rapidity-gap distribution in diffractive dissociation, an observable measurable at a future electron-ion collider. Furthermore, our result may be formulated as a more general conjecture, that we expect to hold true for any one-dimensional branching random walk model, on the branching time of the most recent common ancestor of all the particles that end up to the right of a given position., Comment: 24 pages, 4 figures. v2: minor corrections, reference added
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- 2020
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9. Near L-Edge Single and Multiple Photoionization of Doubly Charged Iron Ions
- Author
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Schippers, Stefan, Beerwerth, Randolf, Bari, Sadia, Buhr, Ticia, Holste, Kristof, Kilcoyne, A. L. David, Perry-Sassmannshausen, Alexander, Phaneuf, Ronald A., Reinwardt, Simon, Savin, Daniel Wolf, Schubert, Kaja, Fritzsche, Stephan, Martins, Michael, and Müller, Alfred
- Subjects
Physics - Atomic Physics ,Astrophysics - Instrumentation and Methods for Astrophysics - Abstract
Using the photon-ion merged-beams technique at a synchrotron light source, we have measured relative cross sections for single and up to five-fold photoionization of Fe$^{2+}$ ions in the energy range 690--920 eV. This range contains thresholds and resonances associated with ionization and excitation of $2p$ and $2s$ electrons. Calculations were performed to simulate the total absorption spectra. The theoretical results show very good agreement with the experimental data, if overall energy shifts of up to 2.5 eV are applied to the calculated resonance positions and assumptions are made about the initial experimental population of the various levels of the Fe$^{2+}$([Ar]$3d^6$) ground configuration. Furthermore, we performed extensive calculations of the Auger cascades that result when an electron is removed from the $2p$ subshell of Fe$^{2+}$. These computations lead to a better agreement with the measured product-charge-state distributions as compared to earlier work. We conclude that the $L$-shell absorption features of low-charged iron ions are useful for identifying gas-phase iron in the interstellar medium and for discriminating against the various forms of condensed-phase iron bound to composite interstellar dust grains., Comment: 11 pages, 7 figures, 1 table
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- 2020
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10. Jet fragmentation function in heavy-ion collisions
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Caucal, Paul, Iancu, Edmond, Mueller, Alfred H., and Soyez, Gregory
- Subjects
High Energy Physics - Phenomenology ,Nuclear Theory - Abstract
We study the fragmentation function of jets propagating through a dense quark-gluon plasma within perturbative QCD. Our results for its nuclear modification factor are in qualitative agreement with the experimental data in Pb+Pb collisions at the LHC. In particular, we reproduce the enhancements seen in the data at both relatively soft and relatively large transverse momenta, with clear physical interpretations. The perturbative predictions however are quite sensitive to the value of the infrared cutoff mimicking the confinement scale, due to the fact that the fragmentation function is not an infrared safe quantity. To remedy this, we propose a new observable -- the (primary) subjet fragmentation function -- which is infrared safe and has features similar to the fragmentation function. We provide predictions for this observable in the vacuum and in heavy-ion collisions that could be tested against the experimental data., Comment: 4 pages, 4 figures; 10th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions
- Published
- 2020
11. Photoionization of astrophysically relevant atomic ions at PIPE
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Schippers, Stefan and Müller, Alfred
- Subjects
Physics - Atomic Physics ,Astrophysics - Astrophysics of Galaxies ,Astrophysics - Solar and Stellar Astrophysics ,Physics - Plasma Physics - Abstract
We review recent work on the photoionization of atomic ions of astrophysical interest that has been carried out at the photon-ion merged-beams setup PIPE, a permanently installed end station at the XUV beamline P04 of the PETRAIII synchrotron radiation source operated by DESY in Hamburg, Germany. Our results on single and multiple L-shell photoionization of Fe+, Fe2+, and Fe3+ ions and on single and multiple K-shell photoionization of C-, C+, C4+, Ne+, and Si2+ ions are discussed in astrophysical contexts. Moreover, these experimental results bear witness of the fact, that the implementation of the photon-ion merged-beams method at one of the world's brightest synchrotron light sources has led to a breakthrough for the experimental study of atomic inner-shell photoionization processes with ions., Comment: 18 pages, 7 figures, 1 table, 113 references
- Published
- 2020
- Full Text
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12. How to generate the tip of branching random walks evolved to large times
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Brunet, Éric, Le, Anh Dung, Mueller, Alfred H., and Munier, Stéphane
- Subjects
Condensed Matter - Statistical Mechanics - Abstract
In a branching process, the number of particles increases exponentially with time, which makes numerical simulations for large times difficult. In many applications, however, only the region close to the extremal particles is relevant (the "tip"). We present a simple algorithm which allows to simulate a branching random walk in one dimension, keeping only the particles that arrive within some distance of the rightmost particle at a predefined time $T$. The complexity of the algorithm grows linearly with $T$. We can furthermore choose to require that the realizations have their rightmost particle arbitrarily far on the right from its typical position. We illustrate our algorithm by evaluating an observable for which no other practical method is known.
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- 2020
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13. Dependence uncertainty bounds for the energy score and the multivariate Gini mean difference
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Bernard, Carole and Müller, Alfred
- Subjects
Mathematics - Statistics Theory ,Mathematics - Probability ,Statistics - Methodology ,62H05 - Abstract
The energy distance and energy scores became important tools in multivariate statistics and multivariate probabilistic forecasting in recent years. They are both based on the expected distance of two independent samples. In this paper we study dependence uncertainty bounds for these quantities under the assumption that we know the marginals but do not know the dependence structure. We find some interesting sharp analytic bounds, where one of them is obtained for an unusual spherically symmetric copula. These results should help to better understand the sensitivity of these measures to misspecifications in the copula.
- Published
- 2020
14. Monte Carlo study of the tip region of branching random walks evolved to large times
- Author
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Le, Anh Dung, Mueller, Alfred H., and Munier, Stéphane
- Subjects
Condensed Matter - Statistical Mechanics ,High Energy Physics - Phenomenology - Abstract
We implement a discretization of the one-dimensional branching Brownian motion in the form of a Monte Carlo event generator, designed to efficiently produce ensembles of realizations in which the rightmost lead particle at the final time $T$ is constrained to have a position $X$ larger than some predefined value $X_{\text{min}}$. The latter may be chosen arbitrarily far from the expectation value of $X$, and the evolution time after which observables on the particle density near the lead particle are measured may be as large as $T\sim 10^4$. We then calculate numerically the probability distribution $p_n(\Delta x)$ of the number $n$ of particles in the interval $[X-\Delta x,X]$ as a function of $\Delta x$. When $X_{\text{min}}$ is significantly smaller than the expectation value of the position of the rightmost lead particle, i.e. when $X$ is effectively unconstrained, we check that both the mean and the typical values of $n$ grow exponentially with $\Delta x$, up to a linear prefactor and to finite-$T$ corrections. When $X_{\text{min}}$ is picked far ahead of the latter but within a region extending over a size of order $\sqrt{T}$ to its right, the mean value of the particle number still grows exponentially with $\Delta x$, but its typical value is lower by a multiplicative factor consistent with $e^{-\zeta\Delta x^{2/3}}$, where $\zeta$ is a number of order unity. These numerical results bring strong support to recent analytical calculations and conjectures in the infinite-time limit., Comment: 20 pages, 10 figures. v2: discussion of the unconditioned case in Sec. 3 improved, conclusions unchanged. v3: important note added
- Published
- 2020
15. A copula-based time series model for global horizontal irradiation
- Author
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Müller, Alfred and Reuber, Matthias
- Subjects
Statistics - Applications - Abstract
The increasing importance of solar power for electricity generation leads to an increasing demand for probabilistic forecasting of local and aggregated PV yields. In this paper we use an indirect modeling approach for hourly medium to long term local PV yields based on publicly available irradiation data. We suggest a time series model for global horizontal irradiation for which it is easy to generate an arbitrary number of scenarios and thus allows for multivariate probabilistic forecasts for arbitrary time horizons. In contrast to many simplified models that have been considered in the literature so far it features several important stylized facts. Sharp time dependent lower and upper bounds of global horizontal irradiations are estimated that improve the often used physical bounds. The parameters of the beta distributed marginals of the transformed data are allowed to be time dependent. A copula-based time series model is introduced for the hourly and daily dependence structure based on a simple graphical structure known from the theory of vine copulas. Non-Gaussian copulas like Gumbel and BB1 copulas are used that allow for the important feature of so-called tail dependence. Evaluation methods like the continuous ranked probability score (CRPS), the energy score (ES) and the variogram score (VS) are used to compare the power of the model for multivariate probabilistic forecasting with other models used in the literature showing that our model outperforms other models in many respects.
- Published
- 2020
16. Near L-edge Single and Multiple Photoionization of Doubly Charged Iron Ions
- Author
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Schippers, Stefan, Beerwerth, Randolf, Bari, Sadia, Buhr, Ticia, Holste, Kristof, Kilcoyne, AL David, Perry-Sassmannshausen, Alexander, Phaneuf, Ronald A, Reinwardt, Simon, Savin, Daniel Wolf, Schubert, Kaja, Fritzsche, Stephan, Martins, Michael, and Müller, Alfred
- Subjects
Interstellar atomic gas ,Interstellar clouds ,Interstellar medium ,Interstellar absorption ,Line intensities ,Atomic spectroscopy ,Line positions ,X-ray astronomy ,Laboratory astrophysics ,Astronomical and Space Sciences ,Atomic ,Molecular ,Nuclear ,Particle and Plasma Physics ,Physical Chemistry (incl. Structural) ,Astronomy & Astrophysics - Abstract
Using the photon-ion merged-beams technique at a synchrotron light source, we have measured relative cross sections for single and up to five-fold photoionization of Fe2+ ions in the energy range of 690-920 eV. This range contains thresholds and resonances associated with ionization and excitation of 2p and 2s electrons. Calculations were performed to simulate the total absorption spectra. The theoretical results show very good agreement with the experimental data, if overall energy shifts of up to 2.5 eV are applied to the calculated resonance positions and assumptions are made about the initial experimental population of the various levels of the Fe2+([Ar]3d6) ground configuration. Furthermore, we performed extensive calculations of the Auger cascades that result when an electron is removed from the 2p subshell of Fe2+. These computations lead to a better agreement with the measured product-charge-state distributions as compared to earlier work. We conclude that the L-shell absorption features of low-charged iron ions are useful for identifying gas-phase iron in the interstellar medium and for discriminating against the various forms of condensed-phase iron bound to composite interstellar dust grains.
- Published
- 2021
17. Near L-edge photoionization of triply charged iron ions
- Author
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Beerwerth, Randolf, Buhr, Ticia, Perry-Saßmannshausen, Alexander, Stock, Sebastian O., Bari, Sadia, Holste, Kristof, Kilcoyne, A. L. David, Reinwardt, Simon, Ricz, Sandor, Savin, Daniel Wolf, Schubert, Kaja, Martins, Michael, Müller, Alfred, Fritzsche, Stephan, and Schippers, Stefan
- Subjects
Physics - Atomic Physics ,Astrophysics - Instrumentation and Methods for Astrophysics - Abstract
Relative cross sections for $m$-fold photoionization ($m=1,\ldots,5$) of Fe$^{3+}$ by single photon absorption were measured employing the photon-ion merged-beams setup PIPE at the PETRA III synchrotron light source operated at DESY in Hamburg, Germany. The photon energies used spanned the range of $680-950\,\mathrm{eV}$, covering both the photoexcitation resonances from the $2p$ and $2s$ shells as well as the direct ionization from both shells. Multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations were performed to simulate the total photoexcitation spectra. Good agreement was found with the experimental results. These computations helped to assign several strong resonance features to specific transitions. We also carried out Hartree-Fock calculations with relativistic extensions taking into account both photoexcitation and photoionization. Furthermore, we performed extensive MCDHF calculations of the Auger cascades that result when an electron is removed from the $2p$ and $2s$ shells of Fe$^{3+}$. Our theoretically predicted charge-state fractions are in good agreement with the experimental results, representing a substantial improvement over previous theoretical calculations. The main reason for the disagreement with the previous calculations is their lack of inclusion of slow Auger decays of several configurations that can only proceed when accompanied by de-excitation of two electrons. In such cases, this additional shake-down transition of a (sub-)valence electron is required to gain the necessary energy for the release of the Auger electron.
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- 2019
- Full Text
- View/download PDF
18. A copula-based time series model for global horizontal irradiation
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Müller, Alfred and Reuber, Matthias
- Published
- 2023
- Full Text
- View/download PDF
19. A new pQCD based Monte Carlo event generator for jets in the quark-gluon plasma
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Caucal, Paul, Iancu, Edmond, Mueller, Alfred H., and Soyez, Gregory
- Subjects
High Energy Physics - Phenomenology ,Nuclear Theory - Abstract
A main difficulty in understanding the dynamics of jets produced in the high-density environment of ultrarelativistic heavy ion collision, is to provide a unified description for the two sources of radiation that are a priori expected: the "vacuum-like" emissions responsible for the parton shower from large virtualities down to the hadronisation scale and the "medium-induced" emissions responsible for the energy loss by the jet. In the recent paper arXiv:1801.09703, we demonstrated that these two mechanisms can be factorized from each other within a controlled, "double-logarithmic" approximation in perturbative QCD. In this proceeding we recall the main features of the jet evolution in a dense QCD medium. We emphasize that the in-medium parton showers differ from those in the vacuum in two crucial aspects: their phase-space is reduced and the first emission outside the medium can violate angular ordering. Based on this factorized picture, which is Markovian, we have recently developed a Monte Carlo event generator which includes both vacuum-like and medium-induced emissions and goes beyond the double logarithmic approximation. We here present our first results for the fragmentation function and the energy loss by the jet., Comment: 8 pages, 6 figures, for the International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions, 30 September - 5 October 2018 in Aix-Les-Bains, Savoie, France
- Published
- 2018
20. Jet fragmentation in a dense QCD medium
- Author
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Caucal, Paul, Iancu, Edmond, Mueller, Alfred H., and Soyez, Gregory
- Subjects
High Energy Physics - Phenomenology ,Nuclear Theory - Abstract
We study the fragmentation of a jet propagating in a dense quark-gluon plasma. Using a leading, double-logarithmic approximation in perturbative QCD, we compute for the first time the effects of the medium on the vacuum-like emissions. We show that, due to the scatterings off the plasma, the in-medium parton showers differ from the vacuum ones in two crucial aspects: their phase-space is reduced and the first emission outside the medium can violate angular ordering. We compute the jet fragmentation function and find results in qualitative agreement with measurements at the LHC., Comment: 11 pages, 8 figures, XIII Quark Confinement and the Hadron Spectrum - Confinement2018. arXiv admin note: text overlap with arXiv:1807.11229
- Published
- 2018
21. Near L-edge Single and Multiple Photoionization of Triply Charged Iron Ions
- Author
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Beerwerth, Randolf, Buhr, Ticia, Perry-Sassmannshausen, Alexander, Stock, Sebastian O, Bari, Sadia, Holste, Kristof, Kilcoyne, AL David, Reinwardt, Simon, Ricz, Sandor, Savin, Daniel Wolf, Schubert, Kaja, Martins, Michael, Müller, Alfred, Fritzsche, Stephan, and Schippers, Stefan
- Subjects
Astronomical and Space Sciences ,Atomic ,Molecular ,Nuclear ,Particle and Plasma Physics ,Physical Chemistry (incl. Structural) ,Astronomy & Astrophysics - Abstract
Relative cross sections for m-fold photoionization (m = 1,., 5) of Fe3+ by single-photon absorption were measured employing the photon-ion merged-beams setup PIPE at the PETRA III synchrotron light source operated at DESY in Hamburg, Germany. The photon energies used spanned the range of 680-950 eV, covering both the photoexcitation resonances from the 2p and 2s shells, as well as the direct ionization from both shells. Multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations were performed to simulate the total photoexcitation spectra. Good agreement was found with the experimental results. These computations helped to assign several strong resonance features to specific transitions. We also carried out Hartree-Fock calculations with relativistic extensions taking into account both photoexcitation and photoionization. Furthermore, we performed extensive MCDHF calculations of the Auger cascades that result when an electron is removed from the 2p and 2s shells of Fe3+. Our theoretically predicted charge-state fractions are in good agreement with the experimental results, representing a substantial improvement over previous theoretical calculations. The main reason for the disagreement with the previous calculations is their lack of inclusion of slow Auger decays of several configurations that can only proceed when accompanied by de-excitation of two electrons. In such cases, this additional shake-down transition of a (sub)valence electron is required to gain the necessary energy for the release of the Auger electron.
- Published
- 2019
22. Roadmap on photonic, electronic and atomic collision physics: I. Light–matter interaction
- Author
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Ueda, Kiyoshi, Sokell, Emma, Schippers, Stefan, Aumayr, Friedrich, Sadeghpour, Hossein, Burgdörfer, Joachim, Lemell, Christoph, Tong, Xiao-Min, Pfeifer, Thomas, Calegari, Francesca, Palacios, Alicia, Martin, Fernando, Corkum, Paul, Sansone, Giuseppe, Gryzlova, Elena V, Grum-Grzhimailo, Alexei N, Piancastelli, Maria Novella, Weber, Peter M, Steinle, Tobias, Amini, Kasra, Biegert, Jens, Berrah, Nora, Kukk, Edwin, Santra, Robin, Müller, Alfred, Dowek, Danielle, Lucchese, Robert R, McCurdy, C William, Bolognesi, Paola, Avaldi, Lorenzo, Jahnke, Till, Schöffler, Markus S, Dörner, Reinhard, Mairesse, Yann, Nahon, Laurent, Smirnova, Olga, Schlathölter, Thomas, Campbell, Eleanor EB, Rost, Jan-Michael, Meyer, Michael, and Tanaka, Kazuo A
- Subjects
light-matter interaction ,new light sources ,synchrotron radiation sources ,femtosecond lasers ,Optics - Abstract
We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. In Roadmap I, we focus on the light-matter interaction. In this area, studies of ultrafast electronic and molecular dynamics have been rapidly growing, with the advent of new light sources such as attosecond lasers and x-ray free electron lasers. In parallel, experiments with established synchrotron radiation sources and femtosecond lasers using cutting-edge detection schemes are revealing new scientific insights that have never been exploited. Relevant theories are also being rapidly developed. Target samples for photon-impact experiments are expanding from atoms and small molecules to complex systems such as biomolecules, fullerene, clusters and solids. This Roadmap aims to look back along the road, explaining the development of these fields, and look forward, collecting contributions from twenty leading groups from the field.
- Published
- 2019
23. Ronald Phaneuf
- Author
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Crandall, David H., primary and Müller, Alfred, additional
- Published
- 2024
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24. Cost-effectiveness of a photopethysmographic procedure for screening for atrial fibrillation in 6 European countries
- Author
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Wahler, Steffen, Birkemeyer, Ralf, Alexopoulos, Dimitrios, Siudak, Zbigniew, Müller, Alfred, and von der Schulenburg, Johann-Matthias
- Published
- 2022
- Full Text
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25. Adjuvant treatment of high-risk melanoma – cost-effectiveness analysis of treatment options for BRAF 600 mutated tumors
- Author
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Wahler, Steffen, Müller, Alfred, Fuchs, Sabine, and von der Schulenburg, Johann-Matthias
- Published
- 2022
- Full Text
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26. Conformal spacelike-timelike correspondence in QCD
- Author
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Mueller, Alfred H.
- Subjects
High Energy Physics - Theory - Abstract
This paper is a study of a spacelike-timelike conformal correspondence in QCD. When the times at vertices are fixed in an A_+ = 0 gauge calculation the distribution of gluons in a highly virtual decay have an exact correspondence with the gluons in the lightcone wavefunction of a high energy dipole with the identification of angles in the timelike case and transverse coordinates in the lightcone wavefunction. Divergences show up when the time integrals are done. A procedure for dropping these divergences, analogous to the Gell-Mann Low procedure in QED, allows one to define a conformal QCD, at least through NLO. Possible uses of such a conformal QCD are discussed.
- Published
- 2018
- Full Text
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27. Near L-Edge Single and Multiple Photoionization of Singly Charged Iron Ions
- Author
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Schippers, Stefan, Martins, Michael, Beerwerth, Randolf, Bari, Sadia, Holste, Kristof, Schubert, Kaja, Viefhaus, Jens, Savin, Daniel Wolf, Fritzsche, Stephan, and Müller, Alfred
- Subjects
Astrophysics - Instrumentation and Methods for Astrophysics ,Physics - Atomic Physics - Abstract
Absolute cross sections for m-fold photoionization (m=1,...,6) of Fe+ by a single photon were measured employing the photon-ion merged-beams setup PIPE at the PETRA III synchrotron light source, operated by DESY in Hamburg, Germany. Photon energies were in the range 680-920 eV which covers the photoionization resonances associated with 2p and 2s excitation to higher atomic shells as well as the thresholds for 2p and 2s ionization. The corresponding resonance positions were measured with an uncertainty of +- 0.2 eV. The cross section for Fe+ photoabsorption is derived as the sum of the individually measured cross-sections for m-fold ionization. Calculations of the Fe+ absorption cross sections have been carried out using two different theoretical approaches, Hartree-Fock including relativistic extensions and fully relativistic Multi-Configuration Dirac Fock. Apart from overall energy shifts of up to about 3 eV, the theoretical cross sections are in good agreement with each other and with the experimental results. In addition, the complex deexcitation cascades after the creation of inner-shell holes in the Fe+ ion have been tracked on the atomic fine-structure level. The corresponding theoretical results for the product charge-state distributions are in much better agreement with the experimental data than previously published configuration-average results. The present experimental and theoretical results are valuable for opacity calculations and are expected to pave the way to a more accurate determination of the iron abundance in the interstellar medium., Comment: 18 pages, 10 figures, 4 tables, accepted for publication in The Astrophysical Journal
- Published
- 2017
- Full Text
- View/download PDF
28. Electron-Impact Multiple Ionization Cross Sections for Atoms and Ions of Helium through Zinc
- Author
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Hahn, Michael, Mueller, Alfred, and Savin, Daniel Wolf
- Subjects
Astrophysics - Instrumentation and Methods for Astrophysics ,Physics - Atomic Physics - Abstract
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., Comment: Submitted to Astrophysical Journal Supplement. The cross section database (Table 2 in the manuscript) is available upon request
- Published
- 2017
- Full Text
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29. Recombination of open-f-shell tungsten ions
- Author
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Krantz, Claude, Badnell, Nigel R., Müller, Alfred, Schippers, Stefan, and Wolf, Andreas
- Subjects
Physics - Atomic Physics - Abstract
We review experimental and theoretical efforts aimed at a detailed understanding of the recombination of electrons with highly-charged tungsten ions characterised by an open 4f sub-shell. Highly-charged tungsten occurs as a plasma contaminant in ITER-like tokamak experiments, where it acts as an unwanted cooling agent. Modelling of the charge state populations in a plasma requires reliable thermal rate coefficients for charge-changing electron collisions. The electron recombination of medium-charged tungsten species with open 4f sub-shells is especially challenging to compute reliably. Storage-ring experiments have been conducted that yielded recombination rate coefficients at high energy resolution and well-understood systematics. Significant deviations compared to simplified, but prevalent, computational models have been found. A new class of ab-initio numerical calculations has been developed that provides reliable predictions of the total plasma recombination rate coefficients for these ions., Comment: This is an author-created, un-copyedited version of an article published in Journal of Physics B: Atomic, Molecular and Optical Physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-6455/aa547d
- Published
- 2017
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30. Isomer-specific photofragmentation of C3H3+ at the carbon K-edge.
- Author
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Reinwardt, Simon, Cieslik, Patrick, Buhr, Ticia, Perry-Sassmannshausen, Alexander, Schippers, Stefan, Müller, Alfred, Trinter, Florian, and Martins, Michael
- Abstract
Individual fingerprints of different isomers of C
3 H3 + cations have been identified by studying photoionization, photoexcitation, and photofragmentation of C3 H3 + near the carbon K-edge. The experiment was performed employing the photon-ion merged-beams technique at the photon-ion spectrometer at PETRA III (PIPE). This technique is a variant of near-edge X-ray absorption fine-structure spectroscopy, which is particularly sensitive to the 1s → π* excitation. The C3 H3 + primary ions were generated by an electron cyclotron resonance ion source. C3 Hn 2+ product ions with n = 0, 1, 2, and 3 were observed for photon energies in the range of 279.0 eV to 295.2 eV. The experimental spectra are interpreted with the aid of theoretical calculations within the framework of time-dependent density functional theory. To this end, absorption spectra have been calculated for three different constitutional isomers of C3 H3 + . We find that our experimental approach offers a new possibility to study at the same time details of the electronic structure and of the geometry of molecular ions such as C3 H3 + . [ABSTRACT FROM AUTHOR]- Published
- 2024
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31. Experimental and theoretical total cross sections for single and double ionization of the open-4d-shell ions Xe12+, Xe13+, and Xe14+ by electron impact.
- Author
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Jin, Fengtao, Borovik Jr., Alexander, Döhring, B. Michel, Ebinger, Benjamin, Müller, Alfred, and Schippers, Stefan
- Subjects
ELECTRON impact ionization ,ELECTRONS ,ION energy ,IONS - Abstract
We present new experimental and theoretical cross sections for electron-impact single ionization of Xe 12 + and Xe 13 + ions, and double ionization of Xe 12 + , Xe 13 + and Xe 14 + ions for collision energies from the respective ionization thresholds up to 3500 eV. The calculations use the fully relativistic subconfiguration-averaged distorted-wave approach and, partly, the more detailed level-to-level distorted wave method. We find that, unlike in previous work, our theoretical cross sections agree with our experimental ones within the experimental uncertainties, except for the near-threshold double-ionization cross sections. We attribute this remaining discrepancy to the neglect of direct-double ionization in the present theoretical treatment. Experimental and theoretical cross sections for electron-impact single ionization of Xe 12 + . [ABSTRACT FROM AUTHOR]
- Published
- 2024
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32. Lp-norm spherical copulas
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Bernard, Carole, primary, Müller, Alfred, additional, and Oesting, Marco, additional
- Published
- 2023
- Full Text
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33. Pictures of Particle Production in Proton-Nucleus Collisions
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Mueller, Alfred H.
- Subjects
High Energy Physics - Phenomenology - Abstract
This work focuses on gluon(jet) production in dilute(proton)-dense(nucleus) collisions. Depending on the frame and gauge, gluon production can be viewed as a freeing of gluons coming from either the proton wave function or from the nucleus wave function. These (apparently) very different pictures must lead to the same result and the purpose of this paper is to see how that happens. The focus is on gluons having $k_\perp\sim Q_S$ or gluons in the scaling region $k_\perp/Q_S\gg 1$. In the McLerran-Venugopalan(MV) model with $k_\perp\sim Q_S$ we are able to derive gluon production in a way that (graphically) manifestly shows $k_\perp$-factorization in terms of the number density of gluons in the nuclear wave function. We presume that this picture, and $k_\perp$-factorization, continues to hold in the presence of small-$x$ evolution although we have not been able to explicitly verify this. Our result is in agreement with usual $k_\perp$-factorization where the gluon number density of the nucleus does not appear in an explicit way., Comment: 10 pages, 4 figures. Dedicated to Andrzej Bialas in honor of his 80th birthday
- Published
- 2016
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- View/download PDF
34. Photoionization of Ne Atoms and Ne+ Ions Near the K Edge: PrecisionSpectroscopy and Absolute Cross-sections
- Author
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Müller, Alfred, Bernhardt, Dietrich, Borovik, Alexander, Buhr, Ticia, Hellhund, Jonas, Holste, Kristof, Kilcoyne, AL David, Klumpp, Stephan, Martins, Michael, Ricz, Sandor, Seltmann, Jörn, Viefhaus, Jens, and Schippers, Stefan
- Subjects
atomic data ,atomic processes ,ISM: atoms ,line: identification ,line: profiles ,opacity ,Astronomical and Space Sciences ,Atomic ,Molecular ,Nuclear ,Particle and Plasma Physics ,Physical Chemistry (incl. Structural) ,Astronomy & Astrophysics - Abstract
Single, double, and triple photoionization of Ne+ ions by single photons have been investigated at the synchrotron radiation source PETRA III in Hamburg, Germany. Absolute cross-sections were measured by employing the photon-ion merged-beams technique. Photon energies were between about 840 and 930 eV, covering the range from the lowest-energy resonances associated with the excitation of one single K-shell electron up to double excitations involving one K- and one L-shell electron, well beyond the K-shell ionization threshold. Also, photoionization of neutral Ne was investigated just below the K edge. The chosen photon energy bandwidths were between 32 and 500 meV, facilitating the determination of natural line widths. The uncertainty of the energy scale is estimated to be 0.2 eV. For comparison with existing theoretical calculations, astrophysically relevant photoabsorption cross-sections were inferred by summing the measured partial ionization channels. Discussion of the observed resonances in the different final ionization channels reveals the presence of complex Auger-decay mechanisms. The ejection of three electrons from the lowest K-shell-excited Ne+() level, for example, requires cooperative interaction of at least four electrons.
- Published
- 2017
35. PAMOP: Petascale Atomic, Molecular and Optical Collision Calculations
- Author
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McLaughlin, Brendan M., Ballance, Connor P., Pindzola, Michael S., and Müller, Alfred
- Subjects
Physics - Atomic Physics - Abstract
Petaflop architectures are currently being utilized efficiently to perform large scale computations in Atomic, Molecular and Optical Collisions. We solve the Schr\"odinger or Dirac equation for the appropriate collision problem using the R-matrix or R-matrix with pseudo-states approach. We briefly outline the parallel methodology used and implemented for the current suite of Breit-Pauli and DARC codes. In this report, various examples are shown from our theoretical results compared with experimental results obtained from Synchrotron Radiation facilities where the Cray architecture at HLRS is playing an integral part in our computational projects., Comment: 16 pages, 6 figures, Chapter 4, in High Performance Computing in Science and Engineering 2014, edited by W. E. Nagel, D. B. Kroner, and M. Reich (Springer, New York and Berlin, 2014). http://www.springer.com/mathematics/computational+science+%26+engineering/book/978-3-319-10809-4
- Published
- 2015
36. Dependence uncertainty bounds for the energy score and the multivariate Gini mean difference
- Author
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Bernard Carole and Müller Alfred
- Subjects
dependence uncertainty bounds ,energy score ,gini mean difference ,spherically symmetric copula ,60e05 ,60e15 ,62c05 ,62e10 ,62e15 ,Science (General) ,Q1-390 ,Mathematics ,QA1-939 - Abstract
The energy distance and energy scores became important tools in multivariate statistics and multivariate probabilistic forecasting in recent years. They are both based on the expected distance of two independent samples. In this paper we study dependence uncertainty bounds for these quantities under the assumption that we know the marginals but do not know the dependence structure. We find some interesting sharp analytic bounds, where one of them is obtained for an unusual spherically symmetric copula. These results should help to better understand the sensitivity of these measures to misspecifications in the copula.
- Published
- 2020
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37. Photoionisation of ions with synchrotron radiation: from ions in space to atoms in cages
- Author
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Schippers, Stefan, Kilcoyne, AL David, Phaneuf, Ronald A, and Müller, Alfred
- Subjects
Photon-ion merged-beams technique ,synchrotron radiation ,atomic processes in plasmas ,laboratory astrophysics ,endohedral fullerenes ,Mathematical Sciences ,Physical Sciences ,Fluids & Plasmas - Abstract
The photon-ion merged-beams technique for the photoionisation of mass/charge selected ionised atoms, molecules and clusters by x-rays from synchrotron radiation sources is introduced. Examples for photoionisation of atomic ions are discussed by going from outer shell ionisation of simple few electron systems to inner shell ionisation of complex many electron ions. Fundamental ionisation mechanisms are elucidated and the importance of the results for applications in astrophysics and plasma physics is pointed out. Finally, the unique capabilities of the photon-ion merged-beams technique for the study of photoabsorption by nanoparticles are demonstrated by the example of endohedral fullerene ions.
- Published
- 2016
38. Multivariate Almost Stochastic Dominance: Transfer Characterizations and Sufficient Conditions Under Dependence Uncertainty
- Author
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Müller, Alfred, primary, Scarsini, Marco, additional, Tsetlin, Ilia, additional, and Winkler, Robert L., additional
- Published
- 2023
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- View/download PDF
39. Between First- and Second-Order Stochastic Dominance
- Author
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Müller, Alfred, Scarsini, Marco, Tsetlin, Ilia, and Winkler, Robert L.
- Published
- 2017
40. QCD in Nuclear Collisions
- Author
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Mueller, Alfred H.
- Subjects
High Energy Physics - Phenomenology - Abstract
The relationship between RHIC and HERA data is explored using the idea of saturation (color glass condensate) as a unifying framework for interpretation. A description of the early stages of a heavy ion collision is given with the RHIC results. The relevant QCD dynamics at the various stages of a heavy ion collision, from production of gluons to equilibration, is reviewed. Some comments on current phenomenology are given., Comment: 15 pages, Latex, 6 figures
- Published
- 2002
- Full Text
- View/download PDF
41. Gluon Distributions and Color Charge Correlations in a Saturated Light-cone Wavefunction
- Author
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Mueller, Alfred
- Subjects
High Energy Physics - Phenomenology - Abstract
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., Comment: 17 pages, Latex, 7 figures
- Published
- 2002
- Full Text
- View/download PDF
42. Interference effects in the photorecombination of argonlike Sc3+ ions: Storage-ring experiment and theory
- Author
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Schippers, Stefan, Kieslich, Stefan, Mueller, Alfred, Gwinner, Gerald, Schnell, Michael, Wolf, Andreas, Covington, Aaron, Bannister, Mark E., and Zhao, Li-Bo
- Subjects
Physics - Atomic Physics - Abstract
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., Comment: 11 pages, 7 figures, 3 tables, Phys. Rev. A (in print), see also: http://www.strz.uni-giessen.de/~k3
- Published
- 2002
- Full Text
- View/download PDF
43. Expectiles, Omega Ratios and Stochastic Ordering
- Author
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Bellini, Fabio, Klar, Bernhard, and Müller, Alfred
- Published
- 2018
- Full Text
- View/download PDF
44. Commissioning of a powerful electron gun for electron–ion crossed-beams experiments
- Author
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Ebinger, Benjamin, Borovik, Alexander, Jr., Molkentin, Tobias, Müller, Alfred, and Schippers, Stefan
- Published
- 2017
- Full Text
- View/download PDF
45. Enhanced dielectronic recombination of lithium-like Ti19+ ions in external ExB fields
- Author
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Bartsch, Timo, Schippers, Stefan, Beutelspacher, Michael, Boehm, Sebastian, Grieser, Manfred, Gwinner, Gerald, Saghiri, Amir A., Saathoff, Guido, Schuch, Reinhold, Schwalm, Dirk, Wolf, Andreas, and Mueller, Alfred
- Subjects
Physics - Atomic Physics ,Astrophysics - Abstract
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., Comment: 10 pages, 3 figures, to be published in Journal of Physics B, see also http://www.strz.uni-giessen.de/~k3
- Published
- 2000
- Full Text
- View/download PDF
46. Dielectronic recombination of lithium-like Ni25+ ions - high resolution rate coefficients and influence of external crossed E and B fields
- Author
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Schippers, Stefan, Bartsch, Timo, Brandau, Carsten, Mueller, Alfred, Gwinner, Gerald, Wissler, Goetz, Beutelspacher, Michael, Grieser, Manfred, Wolf, Andreas, and Phaneuf, Ronal
- Subjects
Physics - Atomic Physics ,Astrophysics ,Physics - Plasma Physics - Abstract
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 $\Delta n$=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 $\Delta n$=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 $\Delta n$=0 DR of Ni$^{25+}$ are enhanced by at most 11% in the presence of the strongest experimentally applied fields., Comment: 14 pages, 12 figures, 4 tables
- Published
- 2000
- Full Text
- View/download PDF
47. Characterizations of Classes of Lifetime Distributions Generalizing the NBUE Class
- Author
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Klar, Bernhard and Müller, Alfred
- Published
- 2003
48. Smooth Generators of Integral Stochastic Orders
- Author
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Denuit, Michel and Müller, Alfred
- Published
- 2002
49. A cost-effectiveness analysis model of Preventicus atrial fibrillation screening from the point of view of statutory health insurance in Germany
- Author
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Birkemeyer, Ralf, Müller, Alfred, Wahler, Steffen, and von der Schulenburg, Johann-Matthias
- Published
- 2020
- Full Text
- View/download PDF
50. Stochastic Comparison of Random Vectors with a Common Copula
- Author
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Müller, Alfred and Scarsini, Marco
- Published
- 2001
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