143 research outputs found
Sign problem free quantum Monte-Carlo study on thermodynamic properties and magnetic phase transitions in orbital-active itinerant ferromagnets
The microscopic mechanism of itinerant ferromagnetism is a long-standing
problem due to the lack of non-perturbative methods to handle strong magnetic
fluctuations of itinerant electrons. We have non-pertubatively studied
thermodynamic properties and magnetic phase transitions of a two-dimensional
multi-orbital Hubbard model exhibiting ferromagnetic ground states. Quantum
Monte-Carlo simulations are employed, which are proved in a wide density region
free of the sign problem usually suffered by simulations for fermions. Both
Hund's coupling and electron itinerancy are essential for establishing the
ferromagnetic coherence. No local magnetic moments exist in the system as a
priori, nevertheless, the spin channel remains incoherent showing the
Curie-Weiss type spin magnetic susceptibility down to very low temperatures at
which the charge channel is already coherent exhibiting a weakly
temperature-dependent compressibility. For the SU(2) invariant systems, the
spin susceptibility further grows exponentially as approaching zero temperature
in two dimensions. In the paramagnetic phase close to the Curie temperature,
the momentum space Fermi distributions exhibit strong resemblance to those in
the fully polarized state. The long-range ferromagnetic ordering appears when
the symmetry is reduced to the Ising class, and the Curie temperature is
accurately determined. These simulations provide helpful guidance to searching
for novel ferromagnetic materials in both strongly correlated -orbital
transition metal oxide layers and the -orbital ultra-cold atom optical
lattice systems.Comment: 17 pages, 17 figure
Butyrate induces profound changes in gene expression related to multiple signal pathways in bovine kidney epithelial cells
BACKGROUND: Global gene expression profiles of bovine kidney epithelial cells regulated by sodium butyrate were investigated with high-density oligonucleotide microarrays. The bovine microarray with 86,191 distinct 60mer oligonucleotides, each with 4 replicates, was designed and produced with Maskless Array Synthesizer technology. These oligonucleotides represent approximately 45,383 unique cattle sequences. RESULTS: 450 genes significantly regulated by butyrate with a median False Discovery Rate (FDR) = 0 % were identified. The majority of these genes were repressed by butyrate and associated with cell cycle control. The expression levels of 30 selected genes identified by the microarray were confirmed using real-time PCR. The results from real-time PCR positively correlated (R = 0.867) with the results from the microarray. CONCLUSION: This study presented the genes related to multiple signal pathways such as cell cycle control and apoptosis. The profound changes in gene expression elucidate the molecular basis for the pleiotropic effects of butyrate on biological processes. These findings enable better recognition of the full range of beneficial roles butyrate may play during cattle energy metabolism, cell growth and proliferation, and possibly in fighting gastrointestinal pathogens
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