831 research outputs found
Absolute frequency measurement of the 7s S 7s7p P transition in Ra
Transition frequencies were determined for transitions in Ra in an atomic
beam and for reference lines in Te molecules in a vapor cell. The absolute
frequencies were calibrated against a GPS stabilized Rb-clock by means of an
optical frequency comb. The 7s^2\,^1S(F = 1/2)-7s7p\,^1P(F = 3/2)
transition in Ra was determined to be MHz. The
measurements provide input for designing efficient and robust laser cooling of
Ra atoms in preparation of a search for a permanent electric dipole moment in
Ra isotopes.Comment: Accepted for publication in the rapid communication of Physical
review
Muonium-antimuonium conversion in models with heavy neutrinos
We study muonium-antimuonium conversion and mu+ e- to mu- e+ scattering
within two different lepton-flavor-violating models with heavy neutrinos: model
I is a typical seesaw that violates lepton number as well as flavor; model II
has a neutrino mass texture where lepton number is conserved. We look for the
largest possible amplitudes of these processes that are consistent with current
bounds. We find that model I has very limited chance of providing an observable
signal, except if a finely tuned condition in parameter space occurs. Model II,
on the other hand, requires no fine tuning and could cause larger effects.
However, the maximum amplitude provided by this model is still two orders of
magnitude below the sensitivity of current experiments: one predicts an
effective coupling G_MM up to 10^{-4}G_F for heavy neutrino masses near 10 TeV.
We have also clarified some discrepancies in previous literature on this
subject.Comment: 16 pages, 4 figures, reference adde
Rigorous results on spontaneous symmetry breaking in a one-dimensional driven particle system
We study spontaneous symmetry breaking in a one-dimensional driven
two-species stochastic cellular automaton with parallel sublattice update and
open boundaries. The dynamics are symmetric with respect to interchange of
particles. Starting from an empty initial lattice, the system enters a symmetry
broken state after some time T_1 through an amplification loop of initial
fluctuations. It remains in the symmetry broken state for a time T_2 through a
traffic jam effect. Applying a simple martingale argument, we obtain rigorous
asymptotic estimates for the expected times ~ L ln(L) and ln() ~ L,
where L is the system size. The actual value of T_1 depends strongly on the
initial fluctuation in the amplification loop. Numerical simulations suggest
that T_2 is exponentially distributed with a mean that grows exponentially in
system size. For the phase transition line we argue and confirm by simulations
that the flipping time between sign changes of the difference of particle
numbers approaches an algebraic distribution as the system size tends to
infinity.Comment: 23 pages, 7 figure
Simulationsbasierte Untersuchung der Einflussfaktoren auf die magnetischen Streufelder bei induktiven Ladesystemen von Elektrofahrzeugen
Alternative, elektrische Antriebskonzepte mit Batteriespeicher sind in Form von Hybridund reinen Elektrofahrzeugen Gegenstand von zukunftsorientierten Mobilitätskonzepten. Bisherige Markteintrittsbarrieren für Elektrofahrzeuge sind neben vergleichsweise hohen Anschaffungskosten und der Reichweitenproblematik auch zeitaufwendige und umständliche Ladeverfahren. Eine Möglichkeit, um das Laden von Elektrofahrzeugen anwenderfreundlicher zu machen sind induktive Ladeverfahren (engl. WPT – Wireless Power Transfer). Diese Systeme lassen sich einfach in bestehende Infrastrukturen integrieren und fügen sich unauffällig in das Stadtbild ein. Induktive Ladeverfahren werden seit einiger Zeit beispielsweise in der Medizintechnik oder in der Unterhaltungselektronik (Laden von Mobiltelefonen) eingesetzt [1]. Für das induktive Laden von Elektrofahrzeugen sind aktuell Leistungsklassen von 3,3 kW bis 7,7 kW und Übertragungsfrequenzen im Bereich mehrerer kHz angedacht. Der Wirkungsgrad dieser Systeme liegt im Bereich von 90% [2]. Bevor diese Systeme im öffentlichen Raum eingesetzt werden können, ist die Beeinflussung anderer Systeme und deren Einfluss auf den menschlichen Körper zu klären (Elektromagnetische Verträglichkeit [EMV] bzw. – Umweltverträglichkeit [EMVU]). Die ICNIRP 2010-Richtlinie definiert einen Referenzgrenzwert für Frequenzen ab 3 kHz von umgerechnet 24 dBμT. Dieser Wert sollte an keiner von Personen zugänglichen Stelle am Fahrzeug und in dessen Umgebung überschritten werden. Ziel dieser Studie ist es, mit Hilfe der EMV-Simulation Einflussfaktoren auf die magnetischen Streufelder eines modellierten induktiven Ladesystems für Elektrofahrzeuge zu identifizieren. Nachdem in Abschnitt 3 das Ladesystem und EMV-Maßnahmen betrachtet wurde, wird in Abschnitt 4 das Gesamtsystem aus Fahrzeugkarosserie und Ladesystem simuliert. Dabei werden unterschiedliche Karosseriematerialien betrachtet und die magnetische Flussdichte innerhalb und außerhalb des Fahrzeugs ermittelt
Diffusion in a generalized Rubinstein-Duke model of electrophoresis with kinematic disorder
Using a generalized Rubinstein-Duke model we prove rigorously that kinematic
disorder leaves the prediction of standard reptation theory for the scaling of
the diffusion constant in the limit for long polymer chains
unaffected. Based on an analytical calculation as well as Monte Carlo
simulations we predict kinematic disorder to affect the center of mass
diffusion constant of an entangled polymer in the limit for long chains by the
same factor as single particle diffusion in a random barrier model.Comment: 29 pages, 3 figures, submitted to PR
Spontaneous Symmetry Breaking in Two-Channel Asymmetric Exclusion Processes with Narrow Entrances
Multi-particle non-equilibrium dynamics in two-channel asymmetric exclusion
processes with narrow entrances is investigated theoretically. Particles move
on two parallel lattices in opposite directions without changing them, while
the channels are coupled only at the boundaries. A particle cannot enter the
corresponding lane if the exit site of the other lane is occupied. Stationary
phase diagrams, particle currents and densities are calculated in a mean-field
approximation. It is shown that there are four stationary phases in the system,
with two of them exhibiting spontaneous symmetry breaking phenomena. Extensive
Monte Carlo computer simulations confirm qualitatively our predictions,
although the phase boundaries and stationary properties deviate from the
mean-field results. Computer simulations indicate that several dynamic and
phase properties of the system have a strong size dependency, and one of the
stationary phases predicted by the mean-field theory disappears in the
thermodynamic limit.Comment: 13 page
Spontaneous Symmetry Breaking in a Non-Conserving Two-Species Driven Model
A two species particle model on an open chain with dynamics which is
non-conserving in the bulk is introduced. The dynamical rules which define the
model obey a symmetry between the two species. The model exhibits a rich
behavior which includes spontaneous symmetry breaking and localized shocks. The
phase diagram in several regions of parameter space is calculated within
mean-field approximation, and compared with Monte-Carlo simulations. In the
limit where fluctuations in the number of particles in the system are taken to
zero, an exact solution is obtained. We present and analyze a physical picture
which serves to explain the different phases of the model
On-line Excited-State Laser Spectroscopy of Trapped Short-Lived Ra Ions
As an important step towards an atomic parity violation experiment in one
single trapped Ra ion, laser spectroscopy experiments were performed with
on-line produced short-lived Ra ions. The isotope shift of
the 6\,^2D\,-\,7\,^2P and
6\,^2D\,-\,7\,^2P transitions and the hyperfine structure
constant of the 7\,^2S and 6\,^2D states in Ra
were measured. These values provide a benchmark for the required atomic theory.
A lower limit of ms for the lifetime of the metastable
6\,^2D state was measured by optical shelving.Comment: 4.2 pages, 6 figures, 2 tables
High accuracy theoretical investigations of CaF, SrF, and BaF and implications for laser-cooling
The NL-eEDM collaboration is building an experimental setup to search for the
permanent electric dipole moment of the electron in a slow beam of cold barium
fluoride molecules [Eur. Phys. J. D, 72, 197 (2018)]. Knowledge of molecular
properties of BaF is thus needed to plan the measurements and in particular to
determine an optimal laser-cooling scheme. Accurate and reliable theoretical
predictions of these properties require incorporation of both high-order
correlation and relativistic effects in the calculations. In this work
theoretical investigations of the ground and the lowest excited states of BaF
and its lighter homologues, CaF and SrF, are carried out in the framework of
the relativistic Fock-space coupled cluster (FSCC) and multireference
configuration interaction (MRCI) methods. Using the calculated molecular
properties, we determine the Franck-Condon factors (FCFs) for the transition, which was successfully used for
cooling CaF and SrF and is now considered for BaF. For all three species, the
FCFs are found to be highly diagonal. Calculations are also performed for the
transition recently
exploited for laser-cooling of CaF; it is shown that this transition is not
suitable for laser-cooling of BaF, due to the non-diagonal nature of the FCFs
in this system. Special attention is given to the properties of the
state, which in the case of BaF causes a leak channel, in contrast
to CaF and SrF species where this state is energetically above the excited
states used in laser-cooling. We also present the dipole moments of the ground
and the excited states of the three molecules and the transition dipole moments
(TDMs) between the different states.Comment: Minor changes; The following article has been submitted to the
Journal of Chemical Physics. After it is published, it will be found at
https://publishing.aip.org/resources/librarians/products/journals
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