89 research outputs found
Analysis of Chiral Mean-Field Models for Nuclei
An analysis of nuclear properties based on a relativistic energy functional
containing Dirac nucleons and classical scalar and vector meson fields is
discussed. Density functional theory implies that this energy functional can
include many-body effects that go beyond the simple Hartree approximation.
Using basic ideas from effective field theory, a systematic truncation scheme
is developed for the energy functional, which is based on an expansion in
powers of the meson fields and their gradients.
Chiral models are analyzed by considering specific lagrangians that realize
the spontaneously broken chiral symmetry of QCD in different ways and by
studying them at the Hartree level. Models that include a light scalar meson
playing a dual role as the chiral partner of the pion and the mediator of the
intermediate-range nucleon-nucleon interaction, and which include a
"Mexican-hat" potential, fail to reproduce basic ground-state properties of
nuclei. In contrast, chiral models with a nonlinear realization of the symmetry
are shown to contain the full flexibility inherent in the general energy
functional and can therefore successfully describe nuclei.Comment: 47 pages, REVTeX 3.0 with epsf.sty, plus 12 figures in separate
uuencoded compressed postscript fil
Electrode Polarization Effects in Broadband Dielectric Spectroscopy
In the present work, we provide broadband dielectric spectra showing strong
electrode polarization effects for various materials, belonging to very
different material classes. This includes both ionic and electronic conductors
as, e.g., salt solutions, ionic liquids, human blood, and
colossal-dielectric-constant materials. These data are intended to provide a
broad data base enabling a critical test of the validity of phenomenological
and microscopic models for electrode polarization. In the present work, the
results are analyzed using a simple phenomenological equivalent-circuit
description, involving a distributed parallel RC circuit element for the
modeling of the weakly conducting regions close to the electrodes. Excellent
fits of the experimental data are achieved in this way, demonstrating the
universal applicability of this approach. In the investigated ionically
conducting materials, we find the universal appearance of a second dispersion
region due to electrode polarization, which is only revealed if measuring down
to sufficiently low frequencies. This indicates the presence of a second
charge-transport process in ionic conductors with blocking electrodes.Comment: 9 pages, 6 figures, experimental data are provided in electronic form
(see "Data Conservancy"
Colossal dielectric constants in transition-metal oxides
Many transition-metal oxides show very large ("colossal") magnitudes of the
dielectric constant and thus have immense potential for applications in modern
microelectronics and for the development of new capacitance-based
energy-storage devices. In the present work, we thoroughly discuss the
mechanisms that can lead to colossal values of the dielectric constant,
especially emphasising effects generated by external and internal interfaces,
including electronic phase separation. In addition, we provide a detailed
overview and discussion of the dielectric properties of CaCu3Ti4O12 and related
systems, which is today's most investigated material with colossal dielectric
constant. Also a variety of further transition-metal oxides with large
dielectric constants are treated in detail, among them the system La2-xSrxNiO4
where electronic phase separation may play a role in the generation of a
colossal dielectric constant.Comment: 31 pages, 18 figures, submitted to Eur. Phys. J. for publication in
the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator
Transitions and Ordering of Microscopic Degrees of Freedom
ENIGMA-anxiety working group : Rationale for and organization of large-scale neuroimaging studies of anxiety disorders
Altres ajuts: Anxiety Disorders Research Network European College of Neuropsychopharmacology; Claude Leon Postdoctoral Fellowship; Deutsche Forschungsgemeinschaft (DFG, German Research Foundation, 44541416-TRR58); EU7th Frame Work Marie Curie Actions International Staff Exchange Scheme grant 'European and South African Research Network in Anxiety Disorders' (EUSARNAD); Geestkracht programme of the Netherlands Organization for Health Research and Development (ZonMw, 10-000-1002); Intramural Research Training Award (IRTA) program within the National Institute of Mental Health under the Intramural Research Program (NIMH-IRP, MH002781); National Institute of Mental Health under the Intramural Research Program (NIMH-IRP, ZIA-MH-002782); SA Medical Research Council; U.S. National Institutes of Health grants (P01 AG026572, P01 AG055367, P41 EB015922, R01 AG060610, R56 AG058854, RF1 AG051710, U54 EB020403).Anxiety disorders are highly prevalent and disabling but seem particularly tractable to investigation with translational neuroscience methodologies. Neuroimaging has informed our understanding of the neurobiology of anxiety disorders, but research has been limited by small sample sizes and low statistical power, as well as heterogenous imaging methodology. The ENIGMA-Anxiety Working Group has brought together researchers from around the world, in a harmonized and coordinated effort to address these challenges and generate more robust and reproducible findings. This paper elaborates on the concepts and methods informing the work of the working group to date, and describes the initial approach of the four subgroups studying generalized anxiety disorder, panic disorder, social anxiety disorder, and specific phobia. At present, the ENIGMA-Anxiety database contains information about more than 100 unique samples, from 16 countries and 59 institutes. Future directions include examining additional imaging modalities, integrating imaging and genetic data, and collaborating with other ENIGMA working groups. The ENIGMA consortium creates synergy at the intersection of global mental health and clinical neuroscience, and the ENIGMA-Anxiety Working Group extends the promise of this approach to neuroimaging research on anxiety disorders
Cellular Therapy for Cardiovascular Disease Part 2—Delivery of Cells and Clinical Experience
A new interpretation of flow-stress measurements of high-purity NaAl below room temperature
Assessment of terrestrial laser scanning technology for obtaining high-resolution DEMs of soils
Terrestrial Laser Scanners (TLS) provide a non-contact method to measure soil microtopography of relatively large surface areas. The appropriateness of the technology in relatation to the derived Digital Elevation Models (DEM) however has not been reported. The suitability of TLS for soil microtopography measurements was tested on-field for three large soil surface areas in agricultural fields. The acquired point clouds were filtered with a custom cloud import algorithm, and converted into digital elevation models (DEM) of different resolutions. To assess DEM quality, point clouds measured from different viewpoints were statistically compared. The statistical fit between point clouds from different viewpoints depends on spatial resolution of the DEM. The best results were obtained at the higher resolutions (0.02 to 0.04¿cm), where less than 5 % of the grid cells showed significant differences between one viewpoint and the next (p
Test Measurements On A Resonance Filter Spectrometer Using Electronvolt Neutrons
Inelastic neutron scattering measurements carried out on a prototype spectrometer at the WNR pulsed neutron facility are presented. Energy transfers are determined by differencing time-of-flight spectra taken with and without absorbing foils containing sharp nuclear resonances which define the scattered neutron energy. The quality of the spectra are enhanced by i) applying a double difference technique to improve line shape and ii) using fixed incident and scattered beam filters which discriminate in favour of the inelastic difference signal
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