770 research outputs found
Airâsnowpack exchange of bromine, ozone and mercury in the springtime Arctic simulated by the 1-D model PHANTAS – Part 1: In-snow bromine activation and its impact on ozone
To provide a theoretical framework towards a better understanding of ozone
depletion events (ODEs) and atmospheric mercury depletion events (AMDEs) in
the polar boundary layer, we have developed a one-dimensional model that
simulates multiphase chemistry and transport of trace constituents from
porous snowpack and through the atmospheric boundary layer (ABL) as a unified
system. This paper constitutes Part 1 of the study, describing a general
configuration of the model and the results of simulations related to reactive
bromine release from the snowpack and ODEs during the Arctic spring. A common
set of aqueous-phase reactions describes chemistry both within the
liquid-like layer (LLL) on the grain surface of the snowpack and within
deliquesced "haze" aerosols mainly composed of sulfate in the atmosphere.
Gas-phase reactions are also represented by the same mechanism in the
atmosphere and in the snowpack interstitial air (SIA). Consequently, the
model attains the capacity of simulating interactions between chemistry and
mass transfer that become particularly intricate near the interface between
the atmosphere and the snowpack. In the SIA, reactive uptake on LLL-coated
snow grains and vertical mass transfer act simultaneously on gaseous HOBr, a
fraction of which enters from the atmosphere while another fraction is formed
via gas-phase chemistry in the SIA itself. A "bromine explosion", by which
HOBr formed in the ambient air is deposited and then converted
heterogeneously to Br<sub>2</sub>, is found to be a dominant process of reactive
bromine formation in the top 1 mm layer of the snowpack. Deeper in the
snowpack, HOBr formed within the SIA leads to an in-snow bromine explosion,
but a significant fraction of Br<sub>2</sub> is also produced via aqueous
radical chemistry in the LLL on the surface of the snow grains. These top-
and deeper-layer productions of Br<sub>2</sub> both contribute to the release of
Br<sub>2</sub> to the atmosphere, but the deeper-layer production is found to be
more important for the net outflux of reactive bromine. Although ozone is
removed via bromine chemistry, it is also among the key species that control
both the conventional and in-snow bromine explosions. On the other hand,
aqueous-phase radical chemistry initiated by photolytic OH formation in the
LLL is also a significant contributor to the in-snow source of Br<sub>2</sub>
and can operate without ozone, whereas the delivery of Br<sub>2</sub> to the
atmosphere becomes much smaller after ozone is depleted. Catalytic ozone loss
via bromine radical chemistry occurs more rapidly in the SIA than in the
ambient air, giving rise to apparent dry deposition velocities for ozone from
the air to the snow on the order of 10<sup>â3</sup> cm s<sup>−1</sup> during
daytime. Overall, however, the depletion of ozone in the system is caused
predominantly by ozone loss in the ambient air. Increasing depth of the
turbulent ABL under windy conditions will delay the buildup of reactive
bromine and the resultant loss of ozone, while leading to the higher column
amount of BrO in the atmosphere. During the Arctic spring, if moderately
saline and acidic snowpack is as prevalent as assumed in our model runs on
sea ice, the shallow, stable ABL under calm weather conditions may undergo
persistent ODEs without substantial contributions from blowing/drifting snow
and wind-pumping mechanisms, whereas the column densities of BrO in the ABL
will likely remain too low in the course of such events to be detected
unambiguously by satellite nadir measurements
Benchmark of quasi-linear models against gyrokinetic single scale simulations in deuterium and tritium plasmas for a JET high beta hybrid discharge
A benchmark of the reduced quasi-linear models QuaLiKiz and TGLF with GENE gyrokinetic simulations has been performed for parameters corresponding to a JET high performance hybrid pulse in deuterium. Given the importance of the study of such advanced scenarios in view of ITER and DEMO operations, the dependence of the transport on the ion isotope mass has also been assessed, by repeating the benchmark changing the ion isotope to tritium. TGLF agrees better with GENE on the linear spectra and the flux levels. However, concerning the isotope dependence, only QuaLiKiz reproduces the GENE radial trend of a basically gyro-Bohm (gB) scaling at inner radii and instead anti-gB at outer radii. The physics effects which are responsible of the antigB effect in GENE simulations have been singled out
Nanoscale piezoelectric response across a single antiparallel ferroelectric domain wall
Surprising asymmetry in the local electromechanical response across a single
antiparallel ferroelectric domain wall is reported. Piezoelectric force
microscopy is used to investigate both the in-plane and out-of- plane
electromechanical signals around domain walls in congruent and
near-stoichiometric lithium niobate. The observed asymmetry is shown to have a
strong correlation to crystal stoichiometry, suggesting defect-domain wall
interactions. A defect-dipole model is proposed. Finite element method is used
to simulate the electromechanical processes at the wall and reconstruct the
images. For the near-stoichiometric composition, good agreement is found in
both form and magnitude. Some discrepancy remains between the experimental and
modeling widths of the imaged effects across a wall. This is analyzed from the
perspective of possible electrostatic contributions to the imaging process, as
well as local changes in the material properties in the vicinity of the wall
Liquid and solid functional bio-based coatings
The development of new bio-based coating materials to be applied on cellulosic and plastic based substrates, with improved performances compared to currently available products and at the same time with improved sustainable end of life options, is a challenge of our times. Enabling cellulose or bioplastics with proper functional coatings, based on biopolymer and functional materials deriving from agro-food waste streams, will improve their performance, allowing them to effectively replace fossil products in the personal care, tableware and food packaging sectors. To achieve these challenging objectives some molecules can be used in wet or solid coating formulations, e.g., cutin as a hydrophobic water-and grease-repellent coating, polysaccharides such as chitosan-chitin as an antimicrobial coating, and proteins as a gas barrier. This review collects the available knowledge on functional coatings with a focus on the raw materials used and methods of dispersion/application. It considers, in addition, the correlation with the desired final properties of the applied coatings, thus discussing their potential
Metamorphosis of plasma turbulence-shear flow dynamics through a transcritical bifurcation
The structural properties of an economical model for a confined plasma
turbulence governor are investigated through bifurcation and stability
analyses. A close relationship is demonstrated between the underlying
bifurcation framework of the model and typical behavior associated with low- to
high-confinement transitions such as shear flow stabilization of turbulence and
oscillatory collective action. In particular, the analysis evinces two types of
discontinuous transition that are qualitatively distinct. One involves
classical hysteresis, governed by viscous dissipation. The other is
intrinsically oscillatory and non-hysteretic, and thus provides a model for the
so-called dithering transitions that are frequently observed. This
metamorphosis, or transformation, of the system dynamics is an important late
side-effect of symmetry-breaking, which manifests as an unusual non-symmetric
transcritical bifurcation induced by a significant shear flow drive.Comment: 17 pages, revtex text, 9 figures comprised of 16 postscript files.
Submitted to Phys. Rev.
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