59 research outputs found
Fast Domain Growth through Density-Dependent Diffusion in a Driven Lattice Gas
We study electromigration in a driven diffusive lattice gas (DDLG) whose
continuous Monte Carlo dynamics generate higher particle mobility in areas with
lower particle density. At low vacancy concentrations and low temperatures,
vacancy domains tend to be faceted: the external driving force causes large
domains to move much more quickly than small ones, producing exponential domain
growth. At higher vacancy concentrations and temperatures, even small domains
have rough boundaries: velocity differences between domains are smaller, and
modest simulation times produce an average domain length scale which roughly
follows , where varies from near .55 at 50% filling
to near .75 at 70% filling. This growth is faster than the behavior
of a standard conserved order parameter Ising model. Some runs may be
approaching a scaling regime. At low fields and early times, fast growth is
delayed until the characteristic domain size reaches a crossover length which
follows . Rough numerical estimates give and simple theoretical arguments give . Our conclusion that
small driving forces can significantly enhance coarsening may be relevant to
the YBCuO electromigration experiments of Moeckly {\it et
al.}(Appl. Phys. Let., {\bf 64}, 1427 (1994)).Comment: 18 pages, RevTex3.
Aspect ratio dependence of hysteresis property of high density Co wire array buried in porous alumina template
Abstract Co wire array with 50 nm intervals was formed by electrodeposition in porous alumina template that was formed on Si substrate. Coercive field of Co wire array under perpendicular magnetic field significantly increased when aspect ratio increased from 1.5 to 2.5. This behavior was well explained by the micromagnetic simulation when magnetic anisotropy axis was assumed to be parallel to the substrate.
Use of Ionic Liquid in Fabrication, Characterization, and Processing of Anodic Porous Alumina
Two different ionic liquids have been tested in the electrochemical fabrication of anodic porous alumina in an aqueous solution of oxalic acid. It was found that during galvanostatic anodization of the aluminum at a current density of 200 mA/cm2, addition of 0.5% relative volume concentration of 1-butyl-3-methylimidazolium tetrafluoborate resulted in a three-fold increase of the growth rate, as compared to the bare acidic solution with the same acid concentration. This ionic liquid was also used successfully for an assessment of the wettability of the outer surface of the alumina, by means of liquid contact angle measurements. The results have been discussed and interpreted with the aid of atomic force microscopy. The observed wetting property allowed to use the ionic liquid for protection of the pores during a test removal of the oxide barrier layer
Directed Self-Assembly: Expectations and Achievements
Nanotechnology has been a revolutionary thrust in recent years of development of science and technology for its broad appeal for employing a novel idea for relevant technological applications in particular and for mass-scale production and marketing as common man commodity in general. An interesting aspect of this emergent technology is that it involves scientific research community and relevant industries alike. Topâdown and bottomâup approaches are two broad division of production of nanoscale materials in general. However, both the approaches have their own limits as far as large-scale production and cost involved are concerned. Therefore, novel new techniques are desired to be developed to optimize production and cost. Directed self-assembly seems to be a promising technique in this regard; which can work as a bridge between the topâdown and bottomâup approaches. This article reviews how directed self-assembly as a technique has grown up and outlines its future prospects
Estimating methane emissions using vegetation mapping in the taigaâtundra boundary of a north-eastern Siberian lowland
Taigaâtundra boundary ecosystems are affected by climate change. Methane (CH4) emissions in taigaâtundra boundary ecosystems have sparsely been evaluated from local to regional scales. We linked in situ CH4 fluxes (2009â2016) with vegetation cover, and scaled these findings to estimate CH4 emissions at a local scale (10 10 km) using high-resolution satellite images in an ecosystem on permafrost (Indigirka lowland, northeastern Siberia). We defined nine vegetation classes, containing 71 species, of which 16 were dominant. Distribution patterns were affected by microtopographic height, thaw depth and soil moisture. The Indigirka lowland was covered by willow-dominated dense shrubland and cotton-sedge-dominated wetlands with sparse larch forests. In situ CH4 emissions were high in wetlands. Lakes and rivers were CH4 sources, while forest floors were mostly neutral in terms of CH4 emission. Estimated local CH4 emissions (37mg m 2 d 1) were higher than those reported in similar studies. Our results indicate that:
(i) sedge and emergent wetland ecosystems act as hot spots for CH4 emissions, and
(ii) sparse tree coverage does not regulate local CH4 emissions and balance. Thus, larch growth and distribution, which are expected to change with climate, do not contribute to decreasing local CH4 emissions
Multi-year effect of wetting on CH<sub>4</sub> flux at taigaâtundra boundary in northeastern Siberia deduced from stable isotope ratios of CH<sub>4</sub>
The response of CH4 emission from natural wetlands due to
meteorological conditions is important because of its strong greenhouse
effect. To understand the relationship between CH4 flux and
wetting, we observed interannual variations in chamber CH4 flux, as
well as the concentration, δ13C, and δD of
dissolved CH4 during the summer from 2009 to 2013 at the
taigaâtundra boundary in the vicinity of Chokurdakh (70â37â˛ N,
147â55â˛ E), located on the lowlands of the Indigirka River in
northeastern Siberia. We also conducted soil incubation experiments to
interpret δ13C and δD of dissolved CH4
and to investigate variations in CH4 production and oxidation
processes. Methane flux showed large interannual variations in wet areas of
sphagnum mosses and sedges
(36â140 mg CH4 mâ2 dayâ1 emitted). Increased
CH4 emission was recorded in the summer of 2011 when a wetting
event with extreme precipitation occurred. Although water level decreased
from 2011 to 2013, CH4 emission remained relatively high in 2012,
and increased further in 2013. Thaw depth became deeper from 2011 to 2013,
which may partly explain the increase in CH4 emission. Moreover,
dissolved CH4 concentration rose sharply by 1 order of magnitude
from 2011 to 2012, and increased further from 2012 to 2013. Large variations
in δ13C and δD of dissolved CH4 were
observed in 2011, and smaller variations were seen in 2012 and 2013,
suggesting both enhancement of CH4 production and less significance
of CH4 oxidation relative to the larger pool of dissolved
CH4. These multi-year effects of wetting on CH4 dynamics
may have been caused by continued soil reduction across multiple years
following the wetting. Delayed activation of acetoclastic methanogenesis
following soil reduction could also have contributed to the enhancement of
CH4 production. These processes suggest that duration of water
saturation in the active layer can be important for predicting CH4
emission following a wetting event in the permafrost ecosystem.</p
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