Spectral weight function for the half-filled Hubbard model: a singular value decomposition approach

The singular value decomposition technique is used to reconstruct the electronic spectral weight function for a half-filled Hubbard model with on-site repulsion $U=4t$ from Quantum Monte Carlo data. A two-band structure for the single-particle excitation spectrum is found to persist as the lattice size exceeds the spin-spin correlation length. The observed bands are flat in the vicinity of the $(0,\pi),(\pi,0)$ points in the Brillouin zone, in accordance with experimental data for high-temperature superconducting compounds.Comment: 4 pages, Revtex

Quantum limits of super-resolution in reconstruction of optical objects

We investigate analytically and numerically the role of quantum fluctuations in reconstruction of optical objects from diffraction-limited images. Taking as example of an input object two closely spaced Gaussian peaks we demonstrate that one can improve the resolution in the reconstructed object over the classical Rayleigh limit. We show that the ultimate quantum limit of resolution in such reconstruction procedure is determined not by diffraction but by the signal-to-noise ratio in the input object. We formulate a quantitative measure of super-resolution in terms of the optical point-spread function of the system.Comment: 23 pages, 7 figures. Submitted to Physical Review A e-mail: [email protected]

Beauvericin and Enniatins: In Vitro Intestinal Effects

Food and feed contamination by emerging mycotoxins beauvericin and enniatins is a worldwide health problem and a matter of great concern nowadays, and data on their toxicological behavior are still scarce. As ingestion is the major route of exposure to mycotoxins in food and feed, the gastrointestinal tract represents the first barrier encountered by these natural contaminants and the first structure that could be affected by their potential detrimental effects. In order to perform a complete and reliable toxicological evaluation, this fundamental site cannot be disregarded. Several in vitro intestinal models able to recreate the different traits of the intestinal environment have been applied to investigate the various aspects related to the intestinal toxicity of emerging mycotoxins. This review aims to depict an overall and comprehensive representation of the in vitro intestinal effects of beauvericin and enniatins in humans from a species-specific perspective. Moreover, information on the occurrence in food and feed and notions on the regulatory aspects will be provided

Genetic structure in cultivated quinoa (Chenopodium quinoa Willd.), a reflection of landscape structure in Northwest Argentina

1027-1038Quinoa (Chenopodium quinoa Willd.), one of the main crops domesticated in the Andean highlands 1,000 of years ago, played an important role as a protein source. 35 germplasm accessions collected along the Northwest Argentina (NWA) region were studied using 22 microsatellite (SSR) markers. Results showed a great level of genetic diversity, differing from previous reports about the geographical distribution of quinoa variability. All SSR loci analysed were highly polymorphic detecting a total of 354 alleles among all populations, with an average of 16 alleles per locus. Cluster analyses grouped the accessions into four main clusters at the average genetic distance level (0.80), each of which represented a different environment of the NWA region: Puna (UHe = 0.42, ±0.07 SE), Dry Valleys (UHe = 0.27, ±0.05 SE), Eastern Humid Valleys (UHe = 0.16, ±0.04 SE) and a transition area with high altitudes between the last two environments (UHe = 0.25, ±0.03 SE). An eastward decreasing genetic diversity gradient was found. AMOVA analyses showed a strong genetic structure: a high population subdivision relative to the grouping by region (Fsr = 0.47) together with a high genetic differentiation among populations (Fst = 0.58) and a heterozygous defect (Fis = 0.63) in each of them. The variability structure, a reflection of the structure of the NWA landscapes, is discussed in connection with environmental variables

Spatially Resolved Mapping of Local Polarization Dynamics in an Ergodic Phase of Ferroelectric Relaxor

Spatial variability of polarization relaxation kinetics in relaxor ferroelectric 0.9Pb(Mg1/3Nb2/3)O3-0.1PbTiO3 is studied using time-resolved Piezoresponse Force Microscopy. Local relaxation attributed to the reorientation of polar nanoregions is shown to follow stretched exponential dependence, exp(-(t/tau)^beta), with beta~~0.4, much larger than the macroscopic value determined from dielectric spectra (beta~~0.09). The spatial inhomogeneity of relaxation time distributions with the presence of 100-200 nm "fast" and "slow" regions is observed. The results are analyzed to map the Vogel-Fulcher temperatures on the nanoscale.Comment: 23 pages, 4 figures, supplementary materials attached; to be submitted to Phys. Rev. Let