Frustration Effects in Antiferromagnetic FCC Heisenberg Films

We study the effects of frustration in an antiferromagnetic film of FCC lattice with Heisenberg spin model including an Ising-like anisotropy. Monte Carlo (MC) simulations have been used to study thermodynamic properties of the film. We show that the presence of the surface reduces the ground state (GS) degeneracy found in the bulk. The GS is shown to depend on the surface in-plane interaction $J_s$ with a critical value at which ordering of type I coexists with ordering of type II. Near this value a reentrant phase is found. Various physical quantities such as layer magnetizations and layer susceptibilities are shown and discussed. The nature of the phase transition is also studied by histogram technique. We have also used the Green's function (GF) method for the quantum counterpart model. The results at low-$T$ show interesting effects of quantum fluctuations. Results obtained by the GF method at high $T$ are compared to those of MC simulations. A good agreement is observed.Comment: 11 pages, 19 figures, submitted to J. Phys.: Condensed Matte

FRUSTRATION - EXACTLY SOLVED FRUSTRATED MODELS

After a short introduction on frustrated spin systems, we study in this chapter several two-dimensional frustrated Ising spin systems which can be exactly solved by using vertex models. We show that these systems contain most of the spectacular effects due to the frustration: high ground-state degeneracy, existence of several phases in the ground-state phase diagram, multiple phase transitions with increasing temperature, reentrance, disorder lines, partial disorder at equilibrium. Evidences of such effects in non solvable models are also shown and discussed. http://www.worldscibooks.com/phy_etextbook/5697/5697_chap1.pd

Metagenomic analysis of the microbial community in fermented grape marc reveals that Lactobacillus fabifermentans is one of the dominant species: insights into its genome structure

Grape marc used for the production of distilled beverages undergoes prolonged storage which allows alcoholic fermentation to occur. Harsh conditions including low pH, limited oxygen and nutrients, temperature fluctuations, and high ethanol concentrations imposed by that environment create a strong selective pressure on microorganisms. A detailed characterization of the bacterial community during two time points of the fermentation process was performed using high-throughput sequencing of the V3-V6 16S rDNA hypervariable regions. The results revealed a marked reduction in the number of bacterial species after 30 days of incubation and made it possible to identify those species that are able to grow in that extreme environment. The genome sequence of Lactobacillus fabifermentans, one of the dominant species identified, was then analyzed using shotgun sequencing and comparative genomics. The results revealed that it is one of the largest genomes among the Lactobacillus sequenced and is characterized by a large number of genes involved in carbohydrate utilization and in the regulation of gene expression. The genome was shaped through a large number of gene duplication events, while lateral gene transfer contributed to a lesser extent with respect to other Lactobacillus species. According to genomic analysis, its carbohydrate utilization pattern and ability to form biofilm are the main genetic traits linked to the adaptation the species underwent permitting it to grow in fermenting grape marc