Half-metallic antiferromagnets in thiospinels

We have theoretically designed the half-metallic (HM) antiferromagnets (AFMs) in thiospinel systems, $\rm Mn(CrV)S_{4}$ and $\rm Fe_{0.5}Cu_{0.5}(V_{0.5}Ti_{1.5})S_{4}$, based on the electronic structure studies in the local-spin-density approximation (LSDA). We have also explored electronic and magnetic properties of parent spinel compounds of the above systems; $\rm CuV_{2}S_{4}$ and $\rm CuTi_{2}S_{4}$ are found to be HM ferromagnets in their cubic spinel structures, while $\rm MnCr_{2}S_{4}$ is a ferrimagnetic insulator. We have discussed the feasibility of material synthesis of HM-AFM thiospinel systems.Comment: 4 pages, 5 figure

Possible origins of macroscopic left-right asymmetry in organisms

I consider the microscopic mechanisms by which a particular left-right (L/R) asymmetry is generated at the organism level from the microscopic handedness of cytoskeletal molecules. In light of a fundamental symmetry principle, the typical pattern-formation mechanisms of diffusion plus regulation cannot implement the "right-hand rule"; at the microscopic level, the cell's cytoskeleton of chiral filaments seems always to be involved, usually in collective states driven by polymerization forces or molecular motors. It seems particularly easy for handedness to emerge in a shear or rotation in the background of an effectively two-dimensional system, such as the cell membrane or a layer of cells, as this requires no pre-existing axis apart from the layer normal. I detail a scenario involving actin/myosin layers in snails and in C. elegans, and also one about the microtubule layer in plant cells. I also survey the other examples that I am aware of, such as the emergence of handedness such as the emergence of handedness in neurons, in eukaryote cell motility, and in non-flagellated bacteria.Comment: 42 pages, 6 figures, resubmitted to J. Stat. Phys. special issue. Major rewrite, rearranged sections/subsections, new Fig 3 + 6, new physics in Sec 2.4 and 3.4.1, added Sec 5 and subsections of Sec

Use of biplots and Partial Least Squares regression in microarray data analysis for assessing association between genes involved in different biological pathways

Microarrays are a widespread technology mostly used to explore expression profiles for thousand of genes simultaneously. On the other hand, considerable efforts to understand inter-relationships between groups of genes were made. To this end, multivariate visualization techniques (e.g. biplots) and Partial Least Squares regression have gained relevance in the field of genomic research. Biplots provide a graphical aid to understand mutual relationships between genes and samples and among gene themselves but no dependency is implied; use of passive projection of variables, however, is helpful for understanding conditional relationships between different sets of genes. Additionally, PLS regression provides a framework for quantitatively evaluating these dependencies and for assessing which are the relevant interactions that should be deeper investigated in further studies. These techniques have been applied on a subset of a microarray study on 49 samples of malignant pleural mesothelioma. 70 genes were selected, 62 involved in cell-cell junctions disruption and 8 involved in Epithelial-Mesenchymal Transition (EMT). Since these latter are supposed to play a role in subsequent loss of apicobasal cell polarity, analysis were performed considering EMT genes as the conditioning (i.e. independent) variables and the polarity genes as conditioned (i.e. dependent) variables. PLS regression provided results consistent with those obtained from graphical visualization of EMT genes principal components and passive projections of polarity genes, and helped in detecting relevant associations between different sets of genes. These associations should be investigated in further studies for validation. Future work will address the differential pattern of expression according to histotype of subjects in the PLS framework. Moreover, PLS path modeling will be considered after the specification of a detailed dependency network