7 research outputs found
Efficient three-material PLIC interface positioning on unstructured polyhedral meshes
This paper introduces an efficient algorithm for the sequential positioning
(or nested dissection) of two planar interfaces in an arbitrary polyhedron,
such that, after each truncation, the respectively remaining polyhedron admits
a prescribed volume. This task, among others, is frequently encountered in the
numerical simulation of three-phase flows when resorting to the geometric
Volume-of-Fluid method. For two-phase flows, the recent work of Kromer & Bothe
(doi.org/10.1016/j.jcp.2021.110776) addresses the positioning of a single plane
by combining an implicit bracketing of the sought position with up to
third-order derivatives of the volume fraction. An analogous application of
their highly efficient root-finding scheme to three-material configurations
requires computing the volume of a twice truncated arbitrary polyhedron. The
present manuscript achieves this by recursive application of the Gaussian
divergence theorem in appropriate form, which allows to compute the volume as a
sum of quantities associated to the faces of the original polyhedron. With a
suitable choice of the coordinate origin, accounting for the sequential
character of the truncation, the volume parametrization becomes co-moving with
respect to the planes. This eliminates the necessity to establish topological
connectivity and tetrahedron decomposition after each truncation. After a
detailed mathematical description of the concept, we conduct a series of
carefully designed numerical experiments to assess the performance in terms of
polyhedron truncations. The high efficiency of the two-phase positioning
persists for sequential application, thereby being robust with respect to input
data and possible intersection topologies. In comparison to an existing
decomposition-based approach, the number of truncations was reduced by up to an
order of magnitude
Detection of metastable electronic states by Penning trap mass spectrometry
State-of-the-art optical clocks achieve fractional precisions of
and below using ensembles of atoms in optical lattices or individual ions in
radio-frequency traps. Promising candidates for novel clocks are highly charged
ions (HCIs) and nuclear transitions, which are largely insensitive to external
perturbations and reach wavelengths beyond the optical range, now becoming
accessible to frequency combs. However, insufficiently accurate atomic
structure calculations still hinder the identification of suitable transitions
in HCIs. Here, we report on the discovery of a long-lived metastable electronic
state in a HCI by measuring the mass difference of the ground and the excited
state in Re, the first non-destructive, direct determination of an electronic
excitation energy. This result agrees with our advanced calculations, and we
confirmed them with an Os ion with the same electronic configuration. We used
the high-precision Penning-trap mass spectrometer PENTATRAP, unique in its
synchronous use of five individual traps for simultaneous mass measurements.
The cyclotron frequency ratio of the ion in the ground state to the
metastable state could be determined to a precision of , unprecedented in the heavy atom regime. With a lifetime of about 130
days, the potential soft x-ray frequency reference at has a linewidth of only , and one of the highest electronic quality factor
() ever seen in an experiment. Our low
uncertainty enables searching for more HCI soft x-ray clock transitions, needed
for promising precision studies of fundamental physics in a thus far unexplored
frontier
Observation of a low-lying metastable electronic state in highly charged lead by Penning-trap mass spectrometry
Highly charged ions (HCIs) offer many opportunities for next-generation clock
research due to the vast landscape of available electronic transitions in
different charge states. The development of XUV frequency combs has enabled the
search for clock transitions based on shorter wavelengths in HCIs. However,
without initial knowledge of the energy of the clock states, these narrow
transitions are difficult to be probed by lasers. In this Letter, we provide
experimental observation and theoretical calculation of a long-lived electronic
state in Nb-like Pb which could be used as a clock state. With the mass
spectrometer Pentatrap, the excitation energy of this metastable state is
directly determined as a mass difference at an energy of 31.2(8) eV,
corresponding to one of the most precise relative mass determinations to date
with a fractional uncertainty of . This experimental result
agrees within 1 with two partially different \textit{ab initio}
multi-configuration Dirac-Hartree-Fock calculations of 31.68(13) eV and
31.76(35) eV, respectively. With a calculated lifetime of 26.5(5.3) days, the
transition from this metastable state to the ground state bears a quality
factor of and allows for the construction of a HCI clock
with a fractional frequency instability of
The Electron Capture in Ho Experiment - a Short Update
The definition of the absolute neutrino mass scale is one of the main goals of the Particle Physics today. The study of the end-point regions of the β- and electron capture (EC) spectrum offers a possibility to determine the effective electron (anti-)neutrino mass in a completely model independent way, as it only relies on the energy and momentum conservation.
The ECHo (Electron Capture in 163Ho) experiment has been designed in the attempt to measure the effective mass of the electron neutrino by performing high statistics and high energy resolution measurements of the 163 Ho electron capture spectrum. To achieve this goal, large arrays of low temperature metallic magnetic calorimeters (MMCs) implanted with with 163Ho are used. Here we report on the structure and the status of the experiment
High-precision mass measurement of doubly magic
The absolute atomic mass of Pb has been determined with a fractional uncertainty of by measuring the cyclotron-frequency ratio R of Pb to Xe with the high-precision Penning-trap mass spectrometer Pentatra