1,015 research outputs found
Covalency, double-counting and the metal-insulator phase diagram in transition metal oxides
Dynamical mean field theory calculations are used to show that for late
transition-metal-oxides a critical variable for the Mott/charge-transfer
transition is the number of d-electrons, which is determined by charge transfer
from oxygen ions. Insulating behavior is found only for a narrow range of
d-occupancy, irrespective of the size of the intra-d Coulomb repulsion. The
result is useful in interpreting 'density functional +U' and 'density
functional plus dynamical mean field' methods in which additional correlations
are applied to a specific set of orbitals and an important role is played by
the 'double counting correction' which dictates the occupancy of these
correlated orbitals. General considerations are presented and are illustrated
by calculations for two representative transition metal oxide systems: layered
perovskite Cu-based "high-Tc" materials, an orbitally non-degenerate
electronically quasi-two dimensional systems, and pseudocubic rare earch
nickelates, an orbitally degenerate electronically three dimensional system.
Density functional calculations yield d-occupancies very far from the Mott
metal-insulator phase boundary in the nickelate materials, but closer to it in
the cuprates, indicating the sensitivity of theoretical models of the cuprates
to the choice of double counting correction and corroborating the critical role
of lattice distortions in attaining the experimentally observed insulating
phase in the nickelates.Comment: 10+ pages, 5 figure
Sustainable requalification of architectural and natural resources: the coastal village of Marzamemi
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Phase diagram and single-particle spectrum of CuO layers within a variational cluster approach to the 3-band Hubbard model
We carry out a detailed numerical study of the three-band Hubbard model in
the underdoped region both in the hole- as well as in the electron-doped case
by means of the variational cluster approach. Both the phase diagram and the
low-energy single-particle spectrum are very similar to recent results for the
single-band Hubbard model with next-nearest-neighbor hoppings. In particular,
we obtain a mixed antiferromagnetic+superconducting phase at low doping with a
first-order transition to a pure superconducting phase accompanied by phase
separation. In the single-particle spectrum a clear Zhang-Rice singlet band
with an incoherent and a coherent part can be seen, in which holes enter upon
doping around . The latter is very similar to the coherent
quasi-particle band crossing the Fermi surface in the single-band model. Doped
electrons go instead into the upper Hubbard band, first filling the regions of
the Brillouin zone around . This fact can be related to the enhanced
robustness of the antiferromagnetic phase as a function of electron doping
compared to hole doping.Comment: 14 pages, 15 eps figure
Salmonella enterica Control in Stick Carrots Through Incorporation of Coriander Seeds Essential Oil in Sustainable Washing Treatments
Chemical disinfectants represent one of the commonly used practice in minimally processed vegetables food-chain. However, the scarce safety and sustainability of these agents force food industry to move toward more sustainable âgreen washing solutions.â Among the latter, while the application of plant derivates for the control of several pathogens is already well-known, the potential anti-Salmonella activity of Coriandrum sativum seeds derivates is still unexplored and was therefore investigated in this study. In detail, Minimal Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) of different coriander seed derivates (i.e., essential oil, hydrosol, and ethanolic extract) were determined by broth dilution against six Salmonella enterica strains isolated from fresh and minimally processed fruits and vegetables. Only the essential oil (EO) was effective in vitro with strain-dependent results. In addition, when mixed in co-culture, the strains were more sensitive to the essential oil treatment. Chemical investigations allowed to define (s)-(+)-linalool as major compound in the essential oil, and to underline interesting phenolic content with correlated antioxidant capacity. A cocktail of three strains of different serovars was selected and employed for a preliminary in situ trial on stick carrots. The obtained results allowed to establish that the application of coriander seed EO at concentrations of 5 ÎŒL mLâ1 was able to reduce and contain the growth of the Salmonella cocktail up to 24 h at 10°C. Good sensory evaluation results were obtained by applying this EO concentration as washing treatment, especially in terms of color parameter. Further studies should be undertaken to emphasize the upstream activity, improving the formulation or exploiting a combined effect with other sanitizers or treatments (e.g., physical treatments). The present study contributes to the knowledge on coriander derivates activity against Salmonella spp. and on the potential application as sustainable washing treatment in removing this pathogen from fresh cut carrots
Is the Salmonella contamination of swine carcasses at slaughter related to the Salmonella load in caecum?
The aim of this study was to examine the relationship between the load of Salmonella spp. in caeca and the carcass contamination in an Italian slaughterhouse. The sampling scheme was designed to be representative of the pigs slaughtered in a day and to estimate a 12% prevalence of pigs highly contaminated by Salmonella spp. (HCP, cecal load â„3log). Environmental swabs were taken before slaughter. Cecal contents and carcass swabs were collected from the same pig. Salmonella MPN were estimated according to ISO6579- 2:2012/A1 and ISO7218:2007/E. The overall Salmonella prevalence were 34.64% and 7.19% for ceca and carcasses respectively, with S. Derby and S. 4,[5],12:i:- being the prevalent serotypes. The HCP prevalence was 11.44%. 7/59 environmental swabs tested positive; when the same serotype was isolated from the environment and from carcasses, the samples were excluded from further analysis. Statistical analysis was performed to investigate the relationship between Salmonella spp. loads in the cecum and contamination of the carcass of the same pig and the prevalence of HCP and the contamination of carcasses on the same day. For this purpose, the days were classified as âhigh prevalence daysâ depending on the proportion of caeca resulted positive (â„36%) and as âhigh loadâ days depending on the prevalence of HCP (â„10%). A correlation between the contamination of carcasses and the cecal Salmonella loads of the same animal was found (Spearmanâs correlation coefficient: 0.2254; p-value=0.0001). No correlation was found between the contamination of carcasses and the categorization of the day of sampling as âhigh prevalence dayâ. Conversely, a correlation was found between the contamination of carcasses and the âhigh loadâ category of the sampling day (Wilcoxon test, p=0.0011). Notably, not the prevalence of pigs carrying Salmonella spp. but the prevalence of highly contaminated pigs was shown to be related to the contamination of carcasses
Comparative gene expression profiling reveals partially overlapping but distinct genomic actions of different antiestrogens in human breast cancer cells.
Antiestrogens used for breast cancer (BC) treatment differ among each other for the ability to affect estrogen receptor (ER) activity and thereby inhibit hormone-responsive cell functions and viability. We used high-density cDNA microarrays for a comprehensive definition of the gene pathways affected by 17b-estradiol (E2), ICI 182,780 (ICI), 4OH- tamoxifen (Tamoxifen), and raloxifene (RAL) in ER-positive ZR-75.1 cells, a suitable model to investigate estrogen and antiestrogen actions in hormone-responsive BC. The expression of 601 genes was significantly affected by E2 in these cells; in silico analysis reveals that 86 among them include one or more potential ER binding site within or near the promoter and that the binding site signatures for E2F-1, NF-Y, and NRF-1 transcription factors are significantly enriched in the promoters of genes induced by estrogen treatment, while those for CAC-binding protein and LF-A1 in those repressed by the hormone, pointing to novel transcriptional effectors of secondary responses to estrogen in BC cells. Interestingly, expression of 176 E2- regulated mRNAs was unaffected by any of the antiestrogens tested, despite the fact that under the same conditions the transcriptional and cell cycle stimulatory activities of ER were inhibited. On the other hand, of 373 antiestrogen-responsive genes identified here, 52 were unresponsive to estrogen and 25% responded specifically to only one of the compounds tested, revealing non-overlapping and clearly distinguishable effects of the different antiestrogens in BC cells. As some of these differences reflect specificities of the mechanism of action of the antiestrogens tested, we propose to exploit this gene set for characterization of novel hormonal antagonists and selective estrogen receptor modulators (SERMs) and as a tool for testing new associations of antiestrogens, more effective against BC
Orbital-selective Mott transitions: Heavy fermions and beyond
Quantum phase transitions in metals are often accompanied by violations of
Fermi liquid behavior in the quantum critical regime. Particularly fascinating
are transitions beyond the Landau-Ginzburg-Wilson concept of a local order
parameter. The breakdown of the Kondo effect in heavy-fermion metals
constitutes a prime example of such a transition. Here, the strongly correlated
f electrons become localized and disappear from the Fermi surface, implying
that the transition is equivalent to an orbital-selective Mott transition, as
has been discussed for multi-band transition-metal oxides. In this article,
available theoretical descriptions for orbital-selective Mott transitions will
be reviewed, with an emphasis on conceptual aspects like the distinction
between different low-temperature phases and the structure of the global phase
diagram. Selected results for quantum critical properties will be listed as
well. Finally, a brief overview is given on experiments which have been
interpreted in terms of orbital-selective Mott physics.Comment: 29 pages, 4 figs, mini-review prepared for a special issue of JLT
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