Electronic structure of the Sr0.4Ca13.6Cu24O41Sr_{0.4}Ca_{13.6}Cu_{24}O_{41} incommensurate compound

We extracted, from strongly-correlated ab-initio calculations, a complete model for the chain subsystem of the $Sr_{0.4}Ca_{13.6}Cu_{24}O_{41}$ incommensurate compound. A second neighbor $t-J+V$ model has been determined as a function of the fourth crystallographic parameter $\tau$, for both low and room temperature crystallographic structures. The analysis of the obtained model shows the crucial importance of the structural modulations on the electronic structure through the on-site energies and the magnetic interactions. The structural distortions are characterized by their long range effect on the cited parameters that hinder the reliability of analyses such as BVS. One of the most striking results is the existence of antiferromagnetic nearest-neighbor interactions for metal-ligand-metal angles of $90^\circ$. A detailed analysis of the electron localization and spin arrangement is presented as a function of the chain to ladder hole transfer and of the temperature. The obtained spin arrangement is in agreement with antiferromagnetic correlations in the chain direction at low temperature

Relaxation time for a dimer covering with height representation

This paper considers the Monte Carlo dynamics of random dimer coverings of the square lattice, which can be mapped to a rough interface model. Two kinds of slow modes are identified, associated respectively with long-wavelength fluctuations of the interface height, and with slow drift (in time) of the system-wide mean height. Within a continuum theory, the longest relaxation time for either kind of mode scales as the system size N. For the real, discrete model, an exact lower bound of O(N) is placed on the relaxation time, using variational eigenfunctions corresponding to the two kinds of continuum modes.Comment: 12 pages, LaTeX; 1 figure in PostScript file; to appear, J. Stat. Phys. Sections and subsections were reshuffled to improve presentation, some text added on quantum-dimer model, fully-frustrated Ising model, and application to general class of "height" model

Sr_14Cu_24O_41Sr\_{14}Cu\_{24}O\_{41} : a complete model for the chain sub-system

A second neighbor $t-J+V$ model for the chain subsystem of the $Sr\_{14}Cu\_{24}O\_{41}$ has been extracted from ab-initio calculations. This model does not use periodic approximation but describes the entire chain through the use of the four-dimensional crystallographic description. Second neighbors interactions are found to be of same order than the first neighbors ones. The computed values of the second neighbors magnetic interaction are coherent with experimental estimations of the intra-dimer magnetic interactions, even if slightly smaller. The reasons of this underestimation are detailed. The computed model allowed us to understand the origin of the chain dimerisation and predicts correctly the relative occurrence of dimers and free spins. The orbitals respectively supporting the magnetic electrons and the holes have been found to be essentially supported by the copper 3d orbitals (spins) and the surrounding oxygen $2p$ orbitals (holes), thus giving a strong footing to the existence of Zhang-Rice singlets

NN final-state interaction in two-nucleon knockout from 16O^{16}O

The influence of the mutual interaction between the two outgoing nucleons (NN-FSI) in electro- and photoinduced two-nucleon knockout from $^{16}O$ has been investigated perturbatively. It turns out that the effect of NN-FSI depends on the kinematics and on the type of reaction considered. The effect is generally larger in pp- than in pn-knockout and in electron induced than in photoinduced reactions. In superparallel kinematics NN-FSI leads in the $(e,e'pp)$ channel to a strong increase of the cross section, that is mainly due to a strong enhancement of the $\Delta$-current contribution. In pn-emission, however, this effect is partially cancelled by a destructive interference with the seagull current. For photoreactions NN-FSI is considerably reduced in superparallel kinematics and can be practically negligible in specific kinematics.Comment: 16 pages, 9 figure

Including osteoprotegerin and collagen IV in a score-based blood test for liver fibrosis increases diagnostic accuracy

BACKGROUND: Noninvasive methods for liver fibrosis evaluation in chronic liver diseases have been recently developed, i.e. transient elastography (Fibroscan™) and blood tests (Fibrometer®, Fibrotest®, and Hepascore®). In this study, we aimed to design a new score in chronic hepatitis C (CHC) by selecting blood markers in a large panel and we compared its diagnostic performance with those of other noninvasive methods. METHODS: Sixteen blood tests were performed in 306 untreated CHC patients included in a multicenter prospective study (ANRS HC EP 23 Fibrostar) using METAVIR histological fibrosis stage as reference. The new score was constructed by non linear regression using the most accurate biomarkers. RESULTS: Five markers (alpha-2-macroglobulin, apolipoprotein-A1, AST, collagen IV and osteoprotegerin) were included in the new function called Coopscore©. Using the Obuchowski Index, Coopscore© shows higher diagnostic performances than for Fibrometer®, Fibrotest®, Hepascore® and Fibroscan™ in CHC. Association between Fibroscan™ and Coopscore© might avoid 68% of liver biopsies for the diagnosis of significant fibrosis. CONCLUSION: Coopscore© provides higher accuracy than other noninvasive methods for the diagnosis of liver fibrosis in CHC. The association of Coopscore© with Fibroscan™ increases its predictive value

Eikonal representation in the momentum-transfer space

By means of empirical fits to the differential cross section data on pp and p(bar)p elastic scattering, above 10 GeV (center-of-mass energy), we determine the eikonal in the momentum - transfer space (q^2- space). We make use of a numerical method and a novel semi-analytical method, through which the uncertainties from the fit parameters can be propagated up to the eikonal in the $q^2$- space. A systematic study of the effect of the experimental information at large values of the momentum transfer is developed and discussed in detail. We present statistical evidence that the imaginary part of the eikonal changes sign in the q^2- space and that the position of the zero decreases as the energy increases; after the position of the zero, the eikonal presents a minimum and then goes to zero through negative values. We discuss the applicability of our results in the phenomenological context, outlining some connections with nonperturbative QCD. A short review and a critical discussion on the main results concerning "model-independent" analyses are also presented.Comment: 18 pages, 17 figures, 4 tables, svjour.cls. Revised discussion on the proton's electromagnetic form factor and references added. To appear in Eur. Phys. J.

Ozone profiles in the high-latitude stratosphere and lower mesosphere measured by the Improved Limb Atmospheric Spectrometer (ILAS)-II: comparison with other satellite sensors and ozonesondes

A solar occultation sensor, the Improved Limb Atmospheric Spectrometer (ILAS)-II, measured 5890 vertical profiles of ozone concentrations in the stratosphere and lower mesosphere and of other species from January to October 2003. The measurement latitude coverage was 54–71°N and 64–88°S, which is similar to the coverage of ILAS (November 1996 to June 1997). One purpose of the ILAS-II measurements was to continue such high-latitude measurements of ozone and its related chemical species in order to help accurately determine their trends. The present paper assesses the quality of ozone data in the version 1.4 retrieval algorithm, through comparisons with results obtained from comprehensive ozonesonde measurements and four satellite-borne solar occultation sensors. In the Northern Hemisphere (NH), the ILAS-II ozone data agree with the other data within ±10% (in terms of the absolute difference divided by its mean value) at altitudes between 11 and 40 km, with the median coincident ILAS-II profiles being systematically up to 10% higher below 20 km and up to 10% lower between 21 and 40 km after screening possible suspicious retrievals. Above 41 km, the negative bias between the NH ILAS-II ozone data and the other data increases with increasing altitude and reaches 30% at 61–65 km. In the Southern Hemisphere, the ILAS-II ozone data agree with the other data within ±10% in the altitude range of 11–60 km, with the median coincident profiles being on average up to 10% higher below 20 km and up to 10% lower above 20 km. Considering the accuracy of the other data used for this comparative study, the version 1.4 ozone data are suitably used for quantitative analyses in the high-latitude stratosphere in both the Northern and Southern Hemisphere and in the lower mesosphere in the Southern Hemisphere