[en] Alumina coatings were deposited on silicon (111 orientation) substrates by reactive ac magnetron sputtering. Film deposition was done using Al targets and three O₂/Ar gas flow rate ratios at 5 kW power. X-ray diffraction studies showed that films were crystalline and contained several phases of alumina. Secondary ion mass spectroscopy analyses were used to measure O/Al atomic ratio and Ar and H concentrations in the films. Hydrogen content in the coatings depended on the O₂ partial pressure used during sputtering and also on the arrival rate of Al and O species on the substrates and seemed to influence the crystallinity of the coatings

[en] AlN films were deposited on microscopy glass slide and silicon (111 orientation) substrates by reactive ac magnetron sputtering using two nitrogen concentrations and three discharge powers of 1.5, 2.5, and 5.0 kW. X-ray diffraction studies showed that films prepared on glass and Si substrates were of hexagonal wurtizite phase. Films on Si substrates also contained small amounts of the cubic phase of AlN besides the predominantly hexagonal wurtizite phase. AlN coatings on glass substrates were textured towards the (00·2) plane; this preferred orientation of crystals was found to decrease with increase in sputtering power. Scanning electron microscopy studies showed that AlN films prepared at higher nitrogen concentration have a microstructure consisting of pebblelike crystals, some of which were hexagonal in shape. The crystal size in the coatings increased with sputtering power and was in the range of 70-230 nm

[en] We introduce a socially motivated extension of the voter model in which individual voters are also influenced by two opposing, fixed-opinion news sources. These sources forestall consensus and instead drive the population to a politically polarized state, with roughly half the population in each opinion state. Two types of social networks for the voters are studied: (a) the complete graph of N voters and, more realistically, (b) the two-clique graph with N voters in each clique. For the complete graph, many dynamical properties are soluble within an annealed-link approximation, in which a link between a news source and a voter is replaced by an average link density. In this approximation, we show that the average consensus time grows as , with . Here p is the probability that a voter consults a news source rather than a neighboring voter, and is the link density between a news source and voters, so that can be greater than 1. The polarization time, namely, the time to reach a politically polarized state from an initial strong majority state, is typically much less than the consensus time. For voters on the two-clique graph, either reducing the density of interclique links or enhancing the influence of news sources again promotes polarization. (paper: interdisciplinary statistical mechanics)

[en] Bidirectional cargo transport by molecular motors in cells is a complex phenomenon in which the cargo (usually a vesicle) alternately moves in retrograde and anterograde directions. In this case, teams of oppositely pulling motors (e.g., kinesin and dynein) bind to the cargo, simultaneously, and ‘coordinate’ their activity such that the motion consists of spells of positively and negatively directed segments, separated by pauses of varying duration. A set of recent experiments have analyzed the bidirectional motion of endosomes in the amoeba D. discoideum in detail. It was found that in between directional switches, a team of five to six dyneins stall a cargo against a stronger kinesin in a tug of war, which lasts for almost a second. As the mean detachment time of a kinesin under its stall load was also observed to be ∼1 s, we infer that the collective detachment time of the dynein assembly must also be similar. Here, we analyze this inference from a modeling perspective, using experimentally measured single-molecule parameters as inputs. We find that the commonly assumed exponential load-dependent detachment rate is inconsistent with observations, as it predicts that a five-dynein assembly will detach under its combined stall load in less than a hundredth of a second. A modified model where the load-dependent unbinding rate is assumed to saturate at stall-force level for super-stall loads gives results which are in agreement with experimental data. Our analysis suggests that the load-dependent detachment of a dynein in a team is qualitatively different at sub-stall and super-stall loads, a conclusion which is likely to have implications in other situations involving collective effects of many motors. (paper)

[en] We consider a particle in a one-dimensional box of length L, with a Maxwell bath at one end and a reflecting wall at the other end. Using a renewal approach, as well as directly solving the master equation, we show that the system exhibits a slow power law relaxation, with a logarithmic correction, towards the final equilibrium state. We extend the renewal approach to a class of confining potentials of the form $U(x)\propto <!--\; ???\; -->x^{\mathrm{\alpha <!--\; ??\; -->}}$, $x>0$, where we find that the relaxation is $\sim <!--\; ???\; -->t^{-<!--\; ???\; -->(\mathrm{\alpha <!--\; ??\; -->}+2)/(\mathrm{\alpha <!--\; ??\; -->}-<!--\; ???\; -->2)}$ for $\mathrm{\alpha <!--\; ??\; -->}>2$, with a logarithmic correction when $(\mathrm{\alpha <!--\; ??\; -->}+2)/(\mathrm{\alpha <!--\; ??\; -->}-<!--\; ???\; -->2)$ is an integer. For $\mathrm{\alpha <!--\; ??\; -->}<2$ the relaxation is exponential. Interestingly for $\mathrm{\alpha <!--\; ??\; -->}=2$ (harmonic potential) the localised bath cannot equilibrate the particle. (paper: classical statistical mechanics, equilibrium and non-equilibrium)

[en] Alumina coatings have been deposited on glass substrates by reactive ac (41 kHz) magnetron sputtering of two hollow aluminum targets in argon-oxygen plasma at 5 kW sputtering power in the poisoned mode and in the unstable region of hysteresis loop of reactive sputtering. The poisoned mode produces nanocrystalline films of γ and δ alumina at a low deposition rate of 0.06 nm•s^-1. Amorphous alumina films have been grown at a higher deposition rate of 0.2 nm•s^-1 with the aid of optical emission spectroscopy in which the feedback signal of Al emission spectral line at 396 nm monitored Al concentration in the plasma discharge and accomplished the controlled oxidation of targets during reactive sputtering. Dynamic secondary ion mass spectroscopy studies confirm that alumina films grown in the unstable region of the hysteresis loop of reactive sputtering are highly stoichiometric and of uniform composition with film thickness. Our study demonstrates the successful coupling of optical emission spectroscopy with hollow cylindrical magnetrons for deposition of alumina films. (author)

[en] CrO_x thin films were prepared on single crystal silicon (111 orientation) and glass substrates by midfrequency (41 kHz) ac sputtering technique in an Isoflux ICM-10 sputter deposition system consisting of two hollow cylindrical targets of Cr in an argon-oxygen plasma at a discharge power of 5 kW and without any deliberate substrate heating. X-ray diffraction studies showed that the coatings were of hcp rhombohedral α-phase chromium oxide. CrO_x coating samples were found to grow preferentially towards the (110) crystal orientation of α-Cr₂O₃. Texturing was found to depend on the orientation of the substrates relative to the targets and also on the nature of substrates. One coating sample grown on Si substrate was annealed in air up to 1173 K. Whereas heat treatment increased the crystallite size, CrO_x coating was thermally stable and did not show any structural transformations. Scanning electron microscopy studies showed differences in the surface morphology of the coatings grown on glass and silicon substrates. Dynamic secondary ion mass spectrometry measurements performed on one CrO_x coating deposited on silicon showed that the O/Cr ratio in the films was 1.38. Ar and H impurity concentrations were also measured in this coating as a function of film thickness. Alumina coatings were prepared on Si substrates by reactive sputtering technique using CrO_x coating as template layers. X-ray diffraction studies showed that CrO_x template layers improved the crystallinity of alumina coatings grown on top of it and also facilitated the formation of the thermodynamically stable α-alumina phase

[en] We investigate the dynamics of the voter model in which the population itself changes endogenously via the birth-death process. There are two species of voters, labeled A and B, and the population of each species can grow or shrink by the birth-death process at equal rates b. Individuals of opposite species also undergo voter model dynamics in which an AB pair can equiprobably become AA or BB with rate —neutral evolution. In the limit , the distribution of consensus times varies as t ⁻³ and the probability that the population size equals n at the moment of consensus varies as n ⁻³. As the birth/death rate b is increased, fixation occurs more more quickly; that is, population fluctuations promote consensus. (paper: biological modelling and information)