Patterns and Their Large-Scale Distortions in Marangoni Convection with Insoluble Surfactant

Nonlinear dynamics of patterns near the threshold of long-wave monotonic Marangoni instability of conductive state in a heated thin layer of liquid covered by insoluble surfactant is considered. Pattern selection between roll and square planforms is analyzed. The dependence of pattern stability on the heat transfer from the free surface of the liquid characterized by Biot number and the gravity described by Galileo number at different surfactant concentrations is studied. Using weakly nonlinear analysis, we derive a set of amplitude equations governing the large-scale roll distortions in the presence of the surface deformation and the surfactant redistribution. These equations are used for the linear analysis of modulational instability of stationary rolls.

REGULATION OF ELECTRET PROPERTIES OF POLYMER MATERIALS

A device is proposed for creating polymer electrets with an adjustable surface charge generated with distilled water, which transforms into an electrically conductive state under the action of a combined electromagnetic field.

Эффект резистивного переключения и памяти в композитных пленках на основе оксида графена в матрице металлорганических перовскитов

The effect of resistive switching in composite films based on organometallic perovskites CH3NH3PbI3 and CH3NH3PbBr3 with graphene oxide (GO) particles with a concentration of 1-3 wt% and a layer of fullerene derivative [60]PCBM is studied. It was found that the effect of resistive switching in Ag/[60]PCBM/ CH3NH3PbI3(Br3):GO/PEDOT:PSS/ITO/glass films manifests itself in a sharp change in the electrical resistance from a low-conductive to a high-conductive state when both positive and negative bias is applied on Ag and ITO electrodes (0.1-1.0 V) both in the dark and when illuminated by a simulated sunlight. It is assumed that the mechanism of resistive switching is associated with the capture and accumulation of charge carriers in GO particles due to the reduction/oxidation processes. The investigated composite films are promising for the creation of non-volatile memory cells.

High field electroformation of sodium bismuth titanate and its solid solutions with barium titanate

High electrical fields induce an acceptor doping dependent electroformation process to a highly conductive state in Na1/2Bi1/2TiO3. The mechanism involves mobile sodium and oxygen vacancies.

Resistivity-Temperature Behavior of Intrinsically Conducting Bis(3-methoxysalicylideniminato)nickel Polymer

Materials with a positive temperature coefficient have many applications, including overcharge and over-temperature protection in lithium-ion (Li-ion) batteries. The thermoresistive properties of an electrically conductive polymer, based on a Ni(salen)-type backbone, known as polyNiMeOSalen, were evaluated by means of in situ resistivity measurements. It was found that the polymer was conductive at temperatures below 220 °C; however, the polymer increased in resistivity by three orders of magnitude upon reaching 250 °C. Thermogravimetric results combined with elemental analyses revealed that the switch from the insulation stage to the conductive stage resulted from thermally dedoping the polymer. Electrochemical studies demonstrated that a polymer retains its electroactivity when it is heated and can be recovered to a conductive state through oxidation via electrochemical doping in an electrolyte solution.

Selectivity filter ion binding affinity determines inactivation in a potassium channel

Potassium channels can become nonconducting via inactivation at a gate inside the highly conserved selectivity filter (SF) region near the extracellular side of the membrane. In certain ligand-gated channels, such as BK channels and MthK, a Ca2+-activated K+channel fromMethanobacterium thermoautotrophicum, the SF has been proposed to play a role in opening and closing rather than inactivation, although the underlying conformational changes are unknown. Using X-ray crystallography, identical conductive MthK structures were obtained in wide-ranging K+concentrations (6 to 150 mM), unlike KcsA, whose SF collapses at low permeant ion concentrations. Surprisingly, three of the SF’s four binding sites remained almost fully occupied throughout this range, indicating high affinities (likely submillimolar), while only the central S2 site titrated, losing its ion at 6 mM, indicating low K+affinity (∼50 mM). Molecular simulations showed that the MthK SF can also collapse in the absence of K+, similar to KcsA, but that even a single K+binding at any of the SF sites, except S4, can rescue the conductive state. The uneven titration across binding sites differs from KcsA, where SF sites display a uniform decrease in occupancy with K+concentration, in the low millimolar range, leading to SF collapse. We found that ions were disfavored in MthK’s S2 site due to weaker coordination by carbonyl groups, arising from different interactions with the pore helix and water behind the SF. We conclude that these differences in interactions endow the seemingly identical SFs of KcsA and MthK with strikingly different inactivating phenotypes.

Conformational equilibrium shift underlies altered K+ channel gating as revealed by NMR

The potassium ion (K+) channel plays a fundamental role in controlling K+ permeation across the cell membrane and regulating cellular excitabilities. Mutations in the transmembrane pore reportedly affect the gating transitions of K+ channels, and are associated with the onset of neural disorders. However, due to the lack of structural and dynamic insights into the functions of K+ channels, the structural mechanism by which these mutations cause K+ channel dysfunctions remains elusive. Here, we used nuclear magnetic resonance spectroscopy to investigate the structural mechanism underlying the decreased K+-permeation caused by disease-related mutations, using the prokaryotic K+ channel KcsA. We demonstrated that the conformational equilibrium in the transmembrane region is shifted toward the non-conductive state with the closed intracellular K+-gate in the disease-related mutant. We also demonstrated that this equilibrium shift is attributable to the additional steric contacts in the open-conductive structure, which are evoked by the increased side-chain bulkiness of the residues lining the transmembrane helix. Our results suggest that the alteration in the conformational equilibrium of the intracellular K+-gate is one of the fundamental mechanisms underlying the dysfunctions of K+ channels caused by disease-related mutations.

The new external ion-beam station at the Demokritos Tandem 5.5 MV accelerator: A unique analytical tool in the fields of cultural heritage and environmental science

At the 5.5 MV Tandem accelerator of the Institute of Nuclear Physics of NCSR Demokritos, Athens, a new external ion-beam set-up has been recently installed. The aim of this development was to establish a complete experimental set-up integrating the analytical capabilities of the PIXE, RBS and PIGE techniques, so that a complete elemental and near surface structural characterization of samples/artifacts to be attained in an almost non-destructive way and without any limitation concerning their size or conductive state. A careful 3D mechanical drawing optimized the experimental parameters of the set-up so that the special requirements imposed for optimum performance of the aforementioned techniques to be fulfilled.The first applications were focused in the quality control of tagged materials (technologically authentic replicas of attic ceramics and in coatings used by conservators for paintings).

Dynamics of the structural transformation of crystalline hydrogen upon the transition into the conductive state under compression

The structural transformation of solid hydrogen under compression along the isotherm of 100 K in the region of transition into the conductive state was studied within the density functional theory. The pressure, the pair correlation function of protons, the density of electron states, and the electrical conductivity were calculated within a range of hydrogen densities from 1,14 to 2,11 g/cm3. The transition of the monoclinic structure of molecular solid hydrogen into the orthorhombic Cmca structure with 12 hydrogen atoms in a unit cell was revealed. In this case, the electrical conductivity was observed to grow, though hydrogen remained molecular. Hydrogen molecules decomposed under compression to the density of 1,563 g/cm3. A unit cell, the thus-formed quasi-tetrahedron, was built of five protons with a distance of 0,92 Å from the central proton to the four others.