Development and Research of a Theoretical Model of the Magnetic Tunnel Junction.

Spin-dependent tunneling structures are widely used in many spintronic devices and sensors. This paper describes the magnetic tunnel junction (MTJ) characteristics caused by the inhomogeneous magnetic field of ferromagnetic layers. The extremely oblate magnetic ellipsoids have been used to mimic these layers. The strong effect of an inhomogeneous magnetic field on the magnetoresistive layers' interaction was demonstrated. The magnetostatic coupling coefficient is also calculated.

Apical constriction drives tissue-scale hydrodynamic flow to mediate cell elongation.

Epithelial folding mediated by apical constriction converts flat epithelial sheets into multilayered, complex tissue structures and is used throughout development in most animals. Little is known, however, about how forces produced near the apical surface of the tissue are transmitted within individual cells to generate the global changes in cell shape that characterize tissue deformation. Here we apply particle tracking velocimetry in gastrulating Drosophila embryos to measure the movement of cytoplasm and plasma membrane during ventral furrow formation. We find that cytoplasmic redistribution during the lengthening phase of ventral furrow formation can be precisely described by viscous flows that quantitatively match the predictions of hydrodynamics. Cell membranes move with the ambient cytoplasm, with little resistance to, or driving force on, the flow. Strikingly, apical constriction produces similar flow patterns in mutant embryos that fail to form cells before gastrulation ('acellular' embryos), such that the global redistribution of cytoplasm mirrors the summed redistribution occurring in individual cells of wild-type embryos. Our results indicate that during the lengthening phase of ventral furrow formation, hydrodynamic behaviour of the cytoplasm provides the predominant mechanism transmitting apically generated forces deep into the tissue and that cell individualization is dispensable.

Measurement of cortical elasticity in Drosophila melanogaster embryos using ferrofluids.

Many models of morphogenesis are forced to assume specific mechanical properties of cells, because the actual mechanical properties of living tissues are largely unknown. Here, we measure the rheology of epithelial cells in the cellularizing Drosophila embryo by injecting magnetic particles and studying their response to external actuation. We establish that, on timescales relevant to epithelial morphogenesis, the cytoplasm is predominantly viscous, whereas the cellular cortex is elastic. The timescale of elastic stress relaxation has a lower bound of 4 min, which is comparable to the time required for internalization of the ventral furrow during gastrulation. The cytoplasm was measured to be ∼103-fold as viscous as water. We show that elasticity depends on the actin cytoskeleton and conclude by discussing how these results relate to existing mechanical models of morphogenesis.

Passive mechanical forces control cell-shape change during Drosophila ventral furrow formation.

During Drosophila gastrulation, the ventral mesodermal cells constrict their apices, undergo a series of coordinated cell-shape changes to form a ventral furrow (VF) and are subsequently internalized. Although it has been well documented that apical constriction is necessary for VF formation, the mechanism by which apical constriction transmits forces throughout the bulk tissue of the cell remains poorly understood. In this work, we develop a computational vertex model to investigate the role of the passive mechanical properties of the cellular blastoderm during gastrulation. We introduce to our knowledge novel data that confirm that the volume of apically constricting cells is conserved throughout the entire course of invagination. We show that maintenance of this constant volume is sufficient to generate invagination as a passive response to apical constriction when it is combined with region-specific elasticities in the membranes surrounding individual cells. We find that the specific sequence of cell-shape changes during VF formation is critically controlled by the stiffness of the lateral and basal membrane surfaces. In particular, our model demonstrates that a transition in basal rigidity is sufficient to drive VF formation along the same sequence of cell-shape change that we observed in the actual embryo, with no active force generation required other than apical constriction.

Tuning an Atomic Switch on a Surface with Electric and Magnetic Fields.

Controllable switching an adatom position and its magnetization could lead to a single-atom memory. Our theoretical studies show that switching adatom between different surface sites by the quantum tunneling, discovered in several experiments, can be controlled by an external electric field. Switching a single spin by magnetic fields is found to be strongly site-dependent on a surface. This could enable to control a spin-dynamics of adatom.

Electronic and magnetic properties at the edges of nanostructures in an electric field: ab initio study.

State of the art ab initio calculations of the electronic and magnetic properties at the edges of magnetic nanostructures in an external electric field are presented in this paper. Our results for the Fe stripes on Fe(0 0 1) reveal the existence of spin-polarized edge states. A spatially inhomogeneous electronic structure is found at the edge. We demonstrate that the spin-dependent screening density varies greatly at the atomic scale. Tuning of the spin-polarization by the external electric field is demonstrated.

Regional changes of brain serotonin and its metabolite 5-hydroxyindolacetic Acid and development of immunosuppression in submissive mice.

The production of submissive behavior in C57BL/6J mice during 10 or 20 days of social confrontations resulted in increases in serotonin (5-HT) content in the amygdala, hippocampus, nucleus caudatus, Al1, A10, A9, and hypothalamus. The level of 5-hydroxyindolacetic acid (5-HIAA) was higher in most structures after 20 daily encounters compared to animals tested for 10 days. The ratio 5-HIAA/5-HT was increased in the nucleus raphe, accumbens, A9, and hypothalamus in mice displaying submission during 10 and 20 confrontations. The experience of defeats during 10 days accompanied with 5-HT system activation in a number of brain structures (nucleus raphe, accumbens, and A9) produced immunosuppression. With increasing number of confrontations the ratio 5-HIAA/5-HT was decreased in the same structures and a tendency to the immune response elevation appeared.