4,476 research outputs found
Probing chiral interactions up to next-to-next-to-next-to-leading order in medium-mass nuclei
We study ground-state energies and charge radii of closed-shell medium-mass
nuclei based on novel chiral nucleon-nucleon (NN) and three-nucleon (3N)
interactions, with a focus on exploring the connections between finite nuclei
and nuclear matter. To this end, we perform in-medium similarity
renormalization group (IM-SRG) calculations based on chiral interactions at
next-to-leading order (NLO), NLO, and NLO, where the 3N interactions at
NLO and NLO are fit to the empirical saturation point of nuclear matter
and to the triton binding energy. Our results for energies and radii at NLO
and NLO overlap within uncertainties, and the cutoff variation of the
interactions is within the EFT uncertainty band. We find underbound
ground-state energies, as expected from the comparison to the empirical
saturation point. The radii are systematically too large, but the agreement
with experiment is better. We further explore variations of the 3N couplings to
test their sensitivity in nuclei. While nuclear matter at saturation density is
quite sensitive to the 3N couplings, we find a considerably weaker dependence
in medium-mass nuclei. In addition, we explore a consistent momentum-space SRG
evolution of these NN and 3N interactions, exhibiting improved many-body
convergence. For the SRG-evolved interactions, the sensitivity to the 3N
couplings is found to be stronger in medium-mass nuclei.Comment: 10 pages, 11 figures, published versio
Exploring sd-shell nuclei from two- and three-nucleon interactions with realistic saturation properties
We study ground- and excited-state properties of all sd-shell nuclei with
neutron and proton numbers 8 <= N,Z <= 20, based on a set of low-resolution
two- and three-nucleon interactions that predict realistic saturation
properties of nuclear matter. We focus on estimating the theoretical
uncertainties due to variation of the resolution scale, the low-energy
couplings, as well as from the many-body method. The experimental two-neutron
and two-proton separation energies are reasonably well reproduced, with an
uncertainty range of about 5 MeV. The first excited 2+ energies also show
overall agreement, with a more narrow uncertainty range of about 500 keV. In
most cases, this range is dominated by the uncertainties in the Hamiltonian.Comment: 6 pages, 4 figure
Saturation with chiral interactions and consequences for finite nuclei
We explore the impact of nuclear matter saturation on the properties and
systematics of finite nuclei across the nuclear chart. Using the ab initio
in-medium similarity renormalization group (IM-SRG), we study ground-state
energies and charge radii of closed-shell nuclei from He to Ni,
based on a set of low-resolution two- and three-nucleon interactions that
predict realistic saturation properties. We first investigate in detail the
convergence properties of these Hamiltonians with respect to model-space
truncations for both two- and three-body interactions. We find one particular
interaction that reproduces well the ground-state energies of all closed-shell
nuclei studied. As expected from their saturation points relative to this
interaction, the other Hamiltonians underbind nuclei, but lead to a remarkably
similar systematics of ground-state energies. Extending our calculations to
complete isotopic chains in the and shells with the valence-space
IM-SRG, the same interaction reproduces not only experimental ground states but
two-neutron-separation energies and first excited states. We also
calculate radii with the valence-space IM-SRG for the first time. Since this
particular interaction saturates at too high density, charge radii are still
too small compared with experiment. Except for this underprediction, the radii
systematics is, however, well reproduced. Our results highlight the importance
of nuclear matter as a theoretical benchmark for the development of
next-generation chiral interactions.Comment: 11 pages, 15 figures, 1 tabl
The potential and challenges of monitoring-supported energy efficiency improvement strategies in existing buildings
The ongoing EU-supported CAMPUS 21 explores the energy efficiency potential of integrated security, control, and building management software. The main objective of the project is to compare the energy and indoor-environmental performance of a number of existing facilities before and after real or virtual implementation of monitoring-based control improvement measures
Ground-State Electromagnetic Moments of Calcium Isotopes
High-resolution bunched-beam collinear laser spectroscopy was used to measure
the optical hyperfine spectra of the Ca isotopes. The ground state
magnetic moments of Ca and quadrupole moments of Ca were
measured for the first time, and the Ca ground state spin was
determined in a model-independent way. Our results provide a critical test of
modern nuclear theories based on shell-model calculations using
phenomenological as well as microscopic interactions. The results for the
neutron-rich isotopes are in excellent agreement with predictions using
interactions derived from chiral effective field theory including three-nucleon
forces, while lighter isotopes illustrate the presence of particle-hole
excitations of the Ca core in their ground state.Comment: Accepted as a Rapid Communication in Physical Review
Construction and Performance of a Micro-Pattern Stereo Detector with Two Gas Electron Multipliers
The construction of a micro-pattern gas detector of dimensions 40x10 cm**2 is
described. Two gas electron multiplier foils (GEM) provide the internal
amplification stages. A two-layer readout structure was used, manufactured in
the same technology as the GEM foils. The strips of each layer cross at an
effective crossing angle of 6.7 degrees and have a 406 um pitch. The
performance of the detector has been evaluated in a muon beam at CERN using a
silicon telescope as reference system. The position resolutions of two
orthogonal coordinates are measured to be 50 um and 1 mm, respectively. The
muon detection efficiency for two-dimensional space points reaches 96%.Comment: 21 pages, 17 figure
Internal Jugular Vein Geometry Under Multiple Inclination Angles with 3D Low-Field MRI in Healthy Volunteers
BACKGROUND: Cerebral venous pathways are subjected to geometrical and patency changes due to body position. The internal jugular veins (IJVs) are the main venous drainage pathway in supine position. Their patency and geometry should be evaluated under different body inclination angles over a three‐dimensional (3D) volume in the healthy situation to better understand pathological cases. PURPOSE: To investigate whether positional changes in the body can affect the geometrical properties and patency of the venous system. STUDY TYPE: Prospective. POPULATION: 15 healthy volunteers, of which seven males and median age 22 years in a range of 19–59. FIELD STRENGTH/SEQUENCE: A 0.25‐T tiltable MRI system was used to scan volunteers in 90° (sitting position), 69°, 45°, 21°, and 0° (supine position) in the transverse plane with the top at vertebra C2. A gradient echo sequence was used. ASSESSMENT: Three observers assessed IJVs on patency and created automatic centerlines from which diameter and patency were analysed perpendicular to the vessel at every 4 mm starting at the level of C2. STATISTICAL TESTS: A Student's t test was used to find statistical difference (p < 0.05) in average IJV diameters per inclination angle. RESULTS: The amount of fully collapsed IJVs increased from 33% to 93% (left IJV) and 14% to 80% (right IJV) when increasing the inclination angle from 0° to 90°. In both IJVs, the mean diameter (±SD) of the open vessels was significantly higher at 0° than 90° with 6.3 ± 0.5 mm vs. 4.4 ± 0.1 mm (left IJV) and 6.6 ± 0.6 mm vs. 4.3 ± 0.4 mm (right IJV). DATA CONCLUSION: Tiltable low‐field MRI can be used to assess IJV geometry and its associated venous pathways in 3D under multiple inclination angles. Next to a higher amount of collapsed vessels, the average diameter of noncollapsed vessels decreases with increasing inclination angles for both left and right IJVs. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY STAGE:
Image fusion of LM-MRI and MRA for endovascular interventions
Peripheral arterial occlusive disease can be treated with endovascular interventions. These interventions are currently intraoperatively guided by fluoroscopy. A possible alternative is LF-MRI, but the current image quality of low-field (LF) MRI may not be sufficient. The purpose of this study is to evaluate the possibility of image fusion of LF-MRI with preoperative MRA to improve the image quality. To test this, LF-MRI and 3T MRI images were made of a healthy test subject. These images were registrated using manual landmark detection. The result was a visually successful registration image of LF-MRI and anatomical MRI, which shows the possibility of manual image registration
Investigating the potential of low concentrations of iron-oxide contrast agents at low magnetic field strengths for the purpose of MR guided interventions
Iron-oxide contrast agents might prove valuable in endovascular interventions at low-field MRI because their relaxivities are more favorable at lower field strengths, but still maintaining and generating positive contrast. Differences between a range concentrations of a gadolinium-based and a super paramagnetic iron-oxide (SPIO) contrast agent were compared both in simulations and experimentally on 0.25T using three different MR sequences. Optimal contrast for all sequences was found around 0.15mM for the SPIO agent and for concentrations higher than 7.0mM for the gadolinium agent. The use of low concentration SPIOs therefore is more beneficial for imaging at low magnetic field strengths than gadolinium-based contrast agents
Balanced Steady-State Free Precession Techniques Improve Detection of Residual Germ Cell Tumor for Treatment Planning
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