Modelling planar polarity of epithelia: the role of signal relay in collective cell polarization

Collective cell polarization is an important characteristic of tissues. Epithelia commonly display cellular structures that are polarized within the plane of the tissue. Establishment of this planar cell polarity requires mechanisms that locally align polarized structures between neighbouring cells, as well as cues that provide global information about alignment relative to an axis of a tissue. In the Drosophila ovary, the cadherin Fat2 is required to orient actin filaments located at the basal side of follicle cells perpendicular to the long axis of the egg chamber. The mechanisms directing this orientation of actin filaments, however, remain unknown. Here we show, using genetic mosaic analysis, that fat2 is not essential for the local alignment of actin filaments between neighbouring cells. Moreover, we provide evidence that Fat2 is involved in the propagation of a cue specifying the orientation of actin filaments relative to the tissue axis. Monte Carlo simulations of actin filament orientation resemble the results of the genetic mosaic analysis, if it is assumed that a polarity signal can propagate from a signal source only through a connected chain of wild-type cells. Our results suggest that Fat2 is required for propagating global polarity information within the follicle epithelium through direct cell–cell contact. Our computational model might be more generally applicable to study collective cell polarization in tissues.     

Properties of Compliant Substrates Based on Porous Silicon Formed by Two-stage Etching

Semiconductors - Abstract—Our work reports on the influence of etching modes and their combination on the design, microstructural and optical properties of compliant substrates based on...     

On the Question of Monitoring Residual Stresses in Selectively Heat-Strengthened Rails

The question is considered of the relationship between the divergence of a longitudinal (400 mm) groove in the rail web, used as an indirect residual-stress–based rejection criterion, with internal stresses measured by acoustic strain gaging across the rail section. The internal stresses have also been evaluated in individual rail elements after cutting. A finite element simulation in the COMSOL Multiphysics software environment has been performed in order to establish connection between groove divergence and stresses. Results are presented for experimental measurements over 49 sections of different rails. The relationship is demonstrated between the stress level in rail elements and the level of stresses measured by an electromagnetic-acoustic structuroscope in an experiment on the side of the railhead. Based on the modeling and experimental results, an acoustoelastic technique is proposed for monitoring residual stresses in rails as an expert method with a rejection level of 80 MPa when sounding a rail section on the side of its head.     

Preceramic Polymer‐Derived SiAlON as Sintering Aid for Silicon Nitride

Two kinds of sintering additives based on the polysiloxanes or polysilazanes filled with nano‐sized powders as SiAlON precursors were tested for the densification of Si₃N₄‐based ceramics. The results showed that both systems can be successfully used as additives for the preparation of Si₃N₄ ceramics with favorable mechanical characteristics. The ceramics were sintered with 18 wt% of preceramic polymer‐based mixture, and good fracture resistance and high hardness values were obtained after sintering in optimized conditions (temperature, dwell time, nitrogen pressure). Higher densification temperatures and longer holding times were required for sintering of samples with polysilazane‐based precursors. The best toughness values were approximately 5 MPa·m^0.5, while the highest hardness was about 19 GPa. The differences in mechanical properties of the prepared composites can be related to the phase composition, microstructure and different chemical bonds present in the ceramic residue generated upon pyrolysis and final densification.     

Ultrasonic preparation of mesoporous silica using pyridinium ionic liquid

Mesoporous silica matrices have been prepared via classic acid catalyzed and sono-catalyzed sol-gel routes. Tetramethoxysilan (TMOS) and methyl-trimethoxysilane (MTMS) were used as silica precursors, and N-butyl-3-methylpyridinium tetrafluoroborate ([bmPy][BF₄]) was employed as co-solvent and pore template. The ionic liquid (IL) to silica mole ratio was varied between 0.007 and 0.07. Nitrogen adsorption-desorption and small-angle neutron scattering measurements were used to characterize the obtained materials. The ionic liquid played the role of catalyst that affected the formation of the primary xerogel particles, and changed the porosity of the materials. Ultrasound treatment resulted in microstructure change on the level of the colloid particle aggregates. In comparison with IL containing xerogels, the IL containing sonogels show increased pore diameter, bigger pore volumes and diminished surface areas.     

The mechanism of low temperature deposition of crystalline anatase by reactive DC magnetron sputtering

It has been reported that TiO₂ film deposition by direct current (DC) magnetron reactive sputtering can occur according to the mechanism proposed by the theory of charged clusters (TCC). In the current study, the TCC was used to explain the mechanism of low temperature TiO₂ crystalline thin film growth. Highly oriented anatase thin films were deposited on unheated substrates. The degree of crystallinity of the thin film was found to depend on the cluster size and its crystallinity as well as the charging efficiency in the reactor. Larger clusters tend to be crystalline. These produce amorphous (nanocrystalline) films. Smaller clusters tend to be amorphous and adopt the structure of clusters already deposited to produce an ordered crystalline film. Increasing the substrate-to-target distance increased the cluster size. In addition, the charge density decreased as the target to substrate distance was increased. Clusters of <2 and 3 nm in diameter were observed at a substrate-to-target distance of 50 and 250 mm, respectively, which correspondingly produced crystalline and amorphous films. The DC power level did not appear to have a large effect on the cluster size nor did it affect the degree of crystallinity of the resulting thin film. The main factors affecting whether or not a crystalline film is deposited are the cluster size and the charge density in the reactor.     

Electrical characteristics of textured polysilicon oxide preparedby a low-temperature wafer loading and N2 preannealingprocess

A low-temperature wafer loading and N₂ preannealing process was used to grow a thin textured polysilicon oxide. The polyoxide grown on the heavily doped polysilicon film exhibits less oxide tunneling leakage current and higher dielectric strength when the top electrode is positively biased