690 research outputs found
Pairing correlations beyond the mean field
We discuss dynamical pairing correlations in the context of configuration
mixing of projected self-consistent mean-field states, and the origin of a
divergence that might appear when such calculations are done using an energy
functional in the spirit of a naive generalized density functional theory.Comment: Proceedings of the XIII Nuclear Physics Workshop ``Maria and Pierre
Curie'' on ``Pairing and beyond - 50 years of the BCS model'', held at
Kazimierz Dolny, Poland, September 27 - October 1, 2006. Int. J. Mod. Phys.
E, in prin
On the decay of deformed actinide nuclei
decay through a deformed potential barrier produces significant
mixing of angular momenta when mapped from the nuclear interior to the outside.
Using experimental branching ratios and either semi-classical or
coupled-channels transmission matrices, we have found that there is a set of
internal amplitudes which are essentially constant for all even--even actinide
nuclei. These same amplitudes also give good results for the known anisotropic
particle emission of the favored decays of odd nuclei in the same mass
region.
PACS numbers: 23.60.+e, 24.10.Eq, 27.90.+bComment: 5 pages, latex (revtex style), 2 embedded postscript figures
uuencoded gz-compressed .tar file To appear in Physical Review Letter
The second ESGAR consensus statement on CT colonography
To update quality standards for CT colonography based on consensus among opinion leaders within the European Society of Gastrointestinal and Abdominal Radiology (ESGAR).
A multinational European panel of nine members of the ESGAR CT colonography Working Group (representing six EU countries) used a modified Delphi process to rate their level of agreement on a variety of statements pertaining to the acquisition, interpretation and implementation of CT colonography. Four Delphi rounds were conducted, each at 2 months interval.
The panel elaborated 86 statements.
In the final round the panelists achieved complete consensus in 71 of 86 statements (82 %). Categories including the highest proportion of statements with excellent Cronbach's internal reliability were colon distension, scan parameters, use of intravenous contrast agents, general guidelines on patient preparation, role of CAD and lesion measurement.
Lower internal reliability was achieved for the use of a rectal tube, spasmolytics, decubitus positioning and number of CT data acquisitions, faecal tagging, 2D vs. 3D reading, and reporting.
The recommendations of the consensus should be useful for both the radiologist who is starting a CTC service and for those who have already implemented the technique but whose practice may need updating
Phase Decomposition and Chemical Inhomogeneity in Nd2-xCexCuO4
Extensive X-ray and neutron scattering experiments and additional
transmission electron microscopy results reveal the partial decomposition of
Nd2-xCexCuO4 (NCCO) in a low-oxygen-fugacity environment such as that typically
realized during the annealing process required to create a superconducting
state. Unlike a typical situation in which a disordered secondary phase results
in diffuse powder scattering, a serendipitous match between the in-plane
lattice constant of NCCO and the lattice constant of one of the decomposition
products, (Nd,Ce)2O3, causes the secondary phase to form an oriented,
quasi-two-dimensional epitaxial structure. Consequently, diffraction peaks from
the secondary phase appear at rational positions (H,K,0) in the reciprocal
space of NCCO. Additionally, because of neodymium paramagnetism, the
application of a magnetic field increases the low-temperature intensity
observed at these positions via neutron scattering. Such effects may mimic the
formation of a structural superlattice or the strengthening of
antiferromagnetic order of NCCO, but the intrinsic mechanism may be identified
through careful and systematic experimentation. For typical reduction
conditions, the (Nd,Ce)2O3 volume fraction is ~1%, and the secondary-phase
layers exhibit long-range order parallel to the NCCO CuO2 sheets and are 50-100
angstromsthick. The presence of the secondary phase should also be taken into
account in the analysis of other experiments on NCCO, such as transport
measurements.Comment: 15 pages, 17 figures, submitted to Phys. Rev.
Subthreshold K+ production in deuteron and alpha induced nuclear reactions
Double differential cross sections have been measured for pi+ and K+ emitted
around midraidity in d+A and He+A collisions at a beam kinetic energy of 1.15
GeV/nucleon. The total pi+ yield increases by a factor of about 2 when using an
alpha projectile instead of a deuteron whereas the K+ yield increases by a
factor of about 4. According to transport calculations, the K+ enhancement
depends both on the number of hadron-hadron collisions and on the energy
available in those collisions: their center-of-mass energy increases with
increasing number of projectile nucleons
Rsp5/​Nedd4 is the main ubiquitin ligase that targets cytosolic misfolded proteins following heat stress
The heat-shock response is a complex cellular program that induces major changes in protein translation, folding and degradation to alleviate toxicity caused by protein misfolding. Although heat shock has been widely used to study proteostasis, it remained unclear how misfolded proteins are targeted for proteolysis in these conditions. We found that ​Rsp5 and its mammalian homologue ​Nedd4 are important E3 ligases responsible for the increased ubiquitylation induced by heat stress. We determined that ​Rsp5 ubiquitylates mainly cytosolic misfolded proteins upon heat shock for proteasome degradation. We found that ubiquitylation of heat-induced substrates requires the Hsp40 co-chaperone ​Ydj1 that is further associated with ​Rsp5 upon heat shock. In addition, ubiquitylation is also promoted by PY ​Rsp5-binding motifs found primarily in the structured regions of stress-induced substrates, which can act as heat-induced degrons. Our results support a bipartite recognition mechanism combining direct and chaperone-dependent ubiquitylation of misfolded cytosolic proteins by ​Rsp5
Strength of Correlations in electron and hole doped cuprates
High temperature superconductivity was achieved by introducing holes in a
parent compound consisting of copper oxide layers separated by spacer layers.
It is possible to dope some of the parent compounds with electrons, and their
physical properties are bearing some similarities but also significant
differences from the hole doped counterparts. Here, we use a recently developed
first principles method, to study the electron doped cuprates and elucidate the
deep physical reasons why their behavior is so different than the hole doped
materials. We find that electron doped compounds are Slater insulators, e.g. a
material where the insulating behavior is the result of the presence of
magnetic long range order. This is in sharp contrast with the hole doped
materials, where the parent compound is a Mott charge transfer insulator,
namely a material which is insulating due to the strong electronic correlations
but not due to the magnetic order.Comment: submitted to Nature Physic
The second ESGAR consensus statement on CT colonography
Objective: To update quality standards for CT colonography based on consensus among opinion leaders within the European Society of Gastrointestinal and Abdominal Radiology (ESGAR). Material and methods: A multinational European panel of nine members of the ESGAR CT colonography Working Group (representing six EU countries) used a modified Delphi process to rate their level of agreement on a variety of statements pertaining to the acquisition, interpretation and implementation of CT colonography. Four Delphi rounds were conducted, each at 2 months interval. Results: The panel elaborated 86 statements. In the final round the panelists achieved complete consensus in 71 of 86 statements (82 %). Categories including the highest proportion of statements with excellent Cronbach's internal reliability were colon distension, scan parameters, use of intravenous contrast agents, general guidelines on patient preparation, role of CAD and lesion measurement. Lower internal reliability was achieved for the use of a rectal tube, spasmolytics, decubitus positioning and number of CT data acquisitions, faecal tagging, 2D vs. 3D reading, and reporting. Conclusion: The recommendations of the consensus should be useful for both the radiologist who is starting a CTC service and for those who have already implemented the technique but whose practice may need updating. Key Points: • Computed tomographic colonography is the optimal radiological method of assessing the colon • This article reviews ESGAR quality standards for CT colonography • This article is aimed to provide CT-colonography guidelines for practising radiologists • The recommendations should help radiologists who are starting/updating their CTC services © 2012 The Author(s)
Many-body approach to proton emission and the role of spectroscopic factors
The process of proton emission from nuclei is studied by utilizing the
two-potential approach of Gurvitz and Kalbermann in the context of the full
many-body problem. A time-dependent approach is used for calculating the decay
width. Starting from an initial many-body quasi-stationary state, we employ the
Feshbach projection operator approach and reduce the formalism to an effective
one-body problem. We show that the decay width can be expressed in terms of a
one-body matrix element multiplied by a normalization factor. We demonstrate
that the traditional interpretation of this normalization as the square root of
a spectroscopic factor is only valid for one particular choice of projection
operator. This causes no problem for the calculation of the decay width in a
consistent microscopic approach, but it leads to ambiguities in the
interpretation of experimental results. In particular, spectroscopic factors
extracted from a comparison of the measured decay width with a calculated
single-particle width may be affected.Comment: 17 pages, Revte
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The evolution of microstructural changes in pressed HMX explosives
Recently developed techniques for investigating the microstructure of plastic-bonded explosives have been applied to HMX explosives pressed to various levels of porosity. Microstructural changes in PBX 9501 area followed from the early stages of prill consolidation through typical density to very low porosity (0.6%). As porosity is reduced, the following sequence is observed. Large inter- and intra-prill voids are eliminated with first damage to HMX crystals occurring at prill boundaries. This is followed by increased incidence of crystal twinning and cracking. At the lowest porosities, spall pullout artifacts are observed, cracks associated with particle contact points are more obvious, and the results of intercrystalline indentation or intergrowth migration processes are apparent. A comparison is made, at lowest porosities achieved, with PX 9404 and X-0242 (a formulation like PBX 9501 with higher binder volume). Possible implications on porosity trends in shock sensitivity data are discussed
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