175 research outputs found
2s1/2 occupancies in 30Si, 31P, and 32S
Elastic electron scattering off Si-30 and P-31 was studied in an effective momentum-transfer range of 1.8-3.0 fm(-1). The form-factor data were analyzed together with existing data sets for these nuclei and for S-32 in a model-independent Fourier-Bessel expansion. For P-31 the M1 contribution was subtracted following an established parametrization. Results of Hartree-Fock (HF) calculations, performed for these three nuclei in a spherical basis and in an axially deformed basis, are compared to experiment. Occupancies have been determined which, when used in the spherical-basis HF calculations, lead to a good description of the elastic form-factor data. The deformed-basis calculations have been used to study the influence of the deformation on the calculated binding energies and ground-state charge densities. In all calculations the influence of using different effective nucleon-nucleon interactions was investigated. The resulting differences in 2s(1/2) in occupancy are combined with results from previous existing (e,e'p) experiments to yield ''absolute occupancies'' for the 2s(1/2) orbital. The deduced 2s(1/2) occupancies for Si-30 and S-32 are 0.24(4) and 1.35(19), respectively.Peer reviewe
Competing electric and magnetic excitations in backward electron scattering from heavy deformed nuclei
Important contributions to the cross sections of
low-lying orbital excitations are found in heavy deformed nuclei, arising
from the small energy separation between the two excitations with and 1, respectively. They are studied microscopically in QRPA using
DWBA. The accompanying response is negligible at small momentum transfer
but contributes substantially to the cross sections measured at for fm ( MeV)
and leads to a very good agreement with experiment. The electric response is of
longitudinal type for but becomes almost purely
transverse for larger backward angles. The transverse response
remains comparable with the response for fm
( MeV) and even dominant for MeV. This happens even at
large backward angles , where the dominance is
limited to the lower region.Comment: RevTeX, 19 pages, 8 figures included Accepted for publication in Phys
Rev
High-energy scissors mode
All the orbital M1 excitations, at both low and high energies, obtained from
a rotationally invariant QRPA, represent the fragmented scissors mode. The
high-energy M1 strength is almost purely orbital and resides in the region of
the isovector giant quadrupole resonance. In heavy deformed nuclei the
high-energy scissors mode is strongly fragmented between 17 and 25 MeV (with
uncertainties arising from the poor knowledge of the isovector potential). The
coherent scissors motion is hindered by the fragmentation and for single transitions in this region. The cross
sections for excitations above 17 MeV are one order of magnitude larger for E2
than for M1 excitations even at backward angles.Comment: 20 pages in RevTEX, 5 figures (uuencoded,put with 'figures') accepted
for publication in Phys.Rev.
Towards the Event Horizon - The Vicinity of AGN at Micro-Arcsecond Resolution
We summarize the present status of VLBI experiments at 3 mm (86 GHz), 2 mm
(129-150 GHz) and 1.3 mm (215-230 GHz). We present and discuss a new 3 mm VLBI
map of M87 (Virgo A), which has a spatial resolution of only approx. 20
Schwarzschild radii. We discuss recent VLBI results for SgrA* and argue in
favor of new observations within an extended European mm-VLBI network, in order
to search for variability. We discuss the possibilities to image the `event
horizon' of a super-massive black hole at wavelengths < 2mm, and conclude that
the addition of large and sensitive millimetre telescopes such as CARMA, the
SMA, the LMT and ALMA will be crucial for this.Comment: 4 pages, 2 figures, Proceedings of the 7th European VLBI Network
Symposium held in Toledo, Spain on October 12-15, 2004. Editors: R.
Bachiller, F. Colomer, J.-F. Desmurs, P. de Vicent
2mm Wavelength VLBI of SiO Masers and AGN
In April 2002 an array of antennas operating at 129GHz successfully detected
VLBI fringes on both continuum AGN and SiO maser sources. The 129GHz fringes on
maser sources represent the highest frequency spectral line VLBI detections to
date. The AGN 3C279 was detected on long baselines at both 129GHz (and at
147GHz, see Krichbaum et al in these proceedings) yielding fringe spacings of
50-56 micro arc seconds, an angular resolution record. The array consisted of
the University of Arizona Kittpeak 12m antenna, the Heinrich Hertz 10m
Telescope (HHT), and the IRAM 30m dish on Pico Veleta.
At 129GHz, a number of evolved stars and several young stellar objects
exhibit strong SiO maser emission in the v=1 J=3-2 transition. Preliminary
cross power spectra of SiO masers around the red hypergiant VYCMa on the
HHT-KittPeak baseline ~190km are consistent with multiple spatially separate
maser spots associated with the star. Future observations will include
continuum observations of the radio source at the Galactic Center, SgrA*, and
higher frequency maser lines including HCN and methanol.Comment: 4 pages, 3 figures, appears in: Proceedings of the 6th European VLBI
Network Symposium held on June 25th-28th in Bonn, Germany. Edited by: E. Ros,
R.W. Porcas, A.P. Lobanov, and J.A. Zensus. New version includes all editors
in paper heade
VLBI observations at 147 GHz: first detection of transatlantic fringes in bright AGN
At 147 GHz (2mm wavelength), we detected three prominent AGN (NRAO150, 3C279,
1633+382) with Very Long Baseline Interferometry (VLBI) with an angular
resolution of only 18 micro-arcseconds on the baseline between two antennas in
Arizona (10m HHT and 12m KittPeak) and the IRAM 30m antenna on Pico Veleta in
Spain. This is a new world record in radio interferometry and astronomical
imaging and opens fascinating future possibilities to directly image and study
the innermost regions in Quasars and other Active Galactic Nuclei.Comment: 4 pages, 3 figures, appears in: Proceedings of the 6th European VLBI
Network Symposium held on June 25th-28th in Bonn, Germany. Edited by: E. Ros,
R.W. Porcas, A.P. Lobanov, and J.A. Zensu
Modeling the Development of Goal-Specificity in Mirror Neurons
Neurophysiological studies have shown that parietal mirror neurons encode not only actions but also the goal of these actions. Although some mirror neurons will fire whenever a certain action is perceived (goal-independently), most will only fire if the motion is perceived as part of an action with a specific goal. This result is important for the action-understanding hypothesis as it provides a potential neurological basis for such a cognitive ability. It is also relevant for the design of artificial cognitive systems, in particular robotic systems that rely on computational models of the mirror system in their interaction with other agents. Yet, to date, no computational model has explicitly addressed the mechanisms that give rise to both goal-specific and goal-independent parietal mirror neurons. In the present paper, we present a computational model based on a self-organizing map, which receives artificial inputs representing information about both the observed or executed actions and the context in which they were executed. We show that the map develops a biologically plausible organization in which goal-specific mirror neurons emerge. We further show that the fundamental cause for both the appearance and the number of goal-specific neurons can be found in geometric relationships between the different inputs to the map. The results are important to the action-understanding hypothesis as they provide a mechanism for the emergence of goal-specific parietal mirror neurons and lead to a number of predictions: (1) Learning of new goals may mostly reassign existing goal-specific neurons rather than recruit new ones; (2) input differences between executed and observed actions can explain observed corresponding differences in the number of goal-specific neurons; and (3) the percentage of goal-specific neurons may differ between motion primitives
Early In Vitro Differentiation of Mouse Definitive Endoderm Is Not Correlated with Progressive Maturation of Nuclear DNA Methylation Patterns
The genome organization in pluripotent cells undergoing the first steps of differentiation is highly relevant to the reprogramming process in differentiation. Considering this fact, chromatin texture patterns that identify cells at the very early stage of lineage commitment could serve as valuable tools in the selection of optimal cell phenotypes for regenerative medicine applications. Here we report on the first-time use of high-resolution three-dimensional fluorescence imaging and comprehensive topological cell-by-cell analyses with a novel image-cytometrical approach towards the identification of in situ global nuclear DNA methylation patterns in early endodermal differentiation of mouse ES cells (up to day 6), and the correlations of these patterns with a set of putative markers for pluripotency and endodermal commitment, and the epithelial and mesenchymal character of cells. Utilizing this in vitro cell system as a model for assessing the relationship between differentiation and nuclear DNA methylation patterns, we found that differentiating cell populations display an increasing number of cells with a gain in DNA methylation load: first within their euchromatin, then extending into heterochromatic areas of the nucleus, which also results in significant changes of methylcytosine/global DNA codistribution patterns. We were also able to co-visualize and quantify the concomitant stochastic marker expression on a per-cell basis, for which we did not measure any correlation to methylcytosine loads or distribution patterns. We observe that the progression of global DNA methylation is not correlated with the standard transcription factors associated with endodermal development. Further studies are needed to determine whether the progression of global methylation could represent a useful signature of cellular differentiation. This concept of tracking epigenetic progression may prove useful in the selection of cell phenotypes for future regenerative medicine applications
Quaking promotes monocyte differentiation into pro-atherogenic macrophages by controlling pre-mRNA splicing and gene expression
A hallmark of inflammatory diseases is the excessive recruitment and influx of monocytes to sites of tissue damage and their ensuing differentiation into macrophages. Numerous stimuli are known to induce transcriptional changes associated with macrophage phenotype, but posttranscriptional control of human macrophage differentiation is less well understood. Here we show that expression levels of the RNA-binding protein Quaking (QKI) are low in monocytes and early human atherosclerotic lesions, but are abundant in macrophages of advanced plaques. Depletion of QKI protein impairs monocyte adhesion, migration, differentiation into macrophages and foam cell formation in vitro and in vivo. RNA-seq and microarray analysis of human monocyte and macrophage transcriptomes, including those of a unique QKI haploinsufficient patient, reveal striking changes in QKI-dependent messenger RNA levels and splicing of RNA transcripts. The biological importance of these transcripts and requirement for QKI during differentiation illustrates a central role for QKI in posttranscriptionally guiding macrophage identity and function.No sponso
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