462 research outputs found
Air–snowpack 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>−3</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
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
The Effect of Hybrid Photovoltaic Thermal Device Operating Conditions on Intrinsic Layer Thickness Optimization of Hydrogenated Amorphous Silicon Solar Cells
Historically, the design of hybrid solar photovoltaic thermal (PVT) systems
has focused on cooling crystalline silicon (c-Si)-based photovoltaic (PV)
devices to avoid temperature-related losses. This approach neglects the
associated performance losses in the thermal system and leads to a decrease in
the overall exergy of the system. Consequently, this paper explores the use of
hydrogenated amorphous silicon (a-Si:H) as an absorber material for PVT in an
effort to maintain higher and more favourable operating temperatures for the
thermal system. Amorphous silicon not only has a smaller temperature
coefficient than c-Si, but also can display improved PV performance over
extended periods of higher temperatures by annealing out defect states from the
Staebler-Wronski effect. In order to determine the potential improvements in
a-Si:H PV performance associated with increased thicknesses of the i-layers
made possible by higher operating temperatures, a-Si:H PV cells were tested
under 1 sun illumination (AM1.5) at temperatures of 25oC (STC), 50oC
(representative PV operating conditions), and 90 oC (representative PVT
operating conditions). PV cells with an i-layer thicknesses of 420, 630 and 840
nm were evaluated at each temperature. Results show that operating a-Si:H-based
PV at 90 oC, with thicker i-layers than the cells currently used in commercial
production, provided a greater power output compared to the thinner cells
operating at either PV or PVT operating temperatures. These results indicate
that incorporating a-Si:H as the absorber material in a PVT system can improve
the thermal performance, while simultaneously improving the electrical
performance of a-Si:H-based PV
A fully autonomous ozone, aerosol and nighttime water vapor lidar: a synergistic approach to profiling the atmosphere in the Canadian oil sands region
Lidar technology has been rapidly advancing over the past several decades. It
can be used to measure a variety of atmospheric constituents at very high
temporal and spatial resolutions. While the number of lidars continues to
increase worldwide, there is generally a dependency on an operator,
particularly for high-powered lidar systems. Environment and Climate Change
Canada (ECCC) has recently developed a fully autonomous, mobile lidar system
called AMOLITE (Autonomous Mobile Ozone Lidar Instrument for Tropospheric
Experiments) to simultaneously measure the vertical profile of tropospheric
ozone, aerosol and water vapor (nighttime only) from near the ground to
altitudes reaching 10 to 15 km. This current system uses a dual-laser,
dual-lidar design housed in a single climate-controlled trailer. Ozone
profiles are measured by the differential absorption lidar (DIAL) technique
using a single 1 m Raman cell filled with CO2. The DIAL
wavelengths of 287 and 299 nm are generated as the second and third Stokes
lines resulting from stimulated Raman scattering of the cell pumped using the
fourth harmonic of a Nd:YAG laser (266 nm). The aerosol lidar transmits
three wavelengths simultaneously (355, 532 and 1064 nm) employing a detector
designed to measure the three backscatter channels, two nitrogen Raman
channels (387 and 607 nm) and one cross-polarization channel at 355 nm. In
addition, we added a water vapor channel arising from the Raman-shifted
355 nm output (407 nm) to provide nighttime water vapor profiles. AMOLITE
participated in a validation experiment alongside four other ozone DIAL
systems before being deployed to the ECCC Oski-ôtin ground site in the
Alberta oil sands region in November 2016. Ozone was found to increase
throughout the troposphere by as much as a factor of 2 from stratospheric
intrusions. The dry stratospheric air within the intrusion was measured to be
less than 0.2 g kg−1. A biomass burning event that impacted the region
over an 8-day period produced lidar ratios of 35 to 65 sr at 355 nm and 40
to 100 sr at 532. Over the same period the Ångström exponent
decreased from 1.56±0.2 to 1.35±0.2 in the 2–4 km smoke region.</p
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.
Aerodynamic investigations of ventilated brake discs.
The heat dissipation and performance of a ventilated brake disc strongly depends
on the aerodynamic characteristics of the flow through the rotor passages. The
aim of this investigation was to provide an improved understanding of ventilated
brake rotor flow phenomena, with a view to improving heat dissipation, as well
as providing a measurement data set for validation of computational fluid
dynamics methods. The flow fields at the exit of four different brake rotor
geometries, rotated in free air, were measured using a five-hole pressure probe
and a hot-wire anemometry system. The principal measurements were taken using
two-component hot-wire techniques and were used to determine mean and unsteady
flow characteristics at the exit of the brake rotors. Using phase-locked data
processing, it was possible to reveal the spatial and temporal flow variation
within individual rotor passages. The effects of disc geometry and rotational
speed on the mean flow, passage turbulence intensity, and mass flow were
determined. The rotor exit jet and wake flow were clearly observed as
characterized by the passage geometry as well as definite regions of high and
low turbulence. The aerodynamic flow characteristics were found to be reasonably
independent of rotational speed but highly dependent upon rotor geometry
Transport and turbulence studies in the linear ohmic confinement regime in Alcator C-Mod
Transport in ohmically heated plasmas in Alcator C-Mod was studied in both the linear (LOC) and saturated (SOC) ohmic L-mode confinement regimes and the importance of turbulent transport in the region r/a = 0.5–0.8 was established. After an extensive analysis with TGLF and GYRO, it is found that using an effective impurity ion species with Z[subscript i] = 8, and moderately high Z[subscript eff] (2.0–5.6), in the LOC regime electron transport becomes dominant due to TEM turbulence. The key ingredient in the present results is the observation that dilution of the main ion species (deuterium) by impurity species of moderate charge state reduces dominant ITG turbulence, in contrast to the SOC regime with little, if any dilution. The turbulent spectrum measured with the phase contrast imaging (PCI) diagnostic is in qualitative agreement with predictions of a synthetic PCI diagnostic adopted to Global GYRO. The toroidal rotation in the low-density LOC regime is in the co-current direction but as the density is raised in the SOC regime the rotation reverses to the counter current drive direction. The impurity content of the plasma was measured recently and an effective Z[subscript i] of 9 was deduced.United States. Dept. of Energy (Grant DE-FC02-99ER54512-CMOD
The link between rejection sensitivity and borderline personality disorder:A systematic review and meta-analysis
OBJECTIVE: People with Borderline Personality Disorder (BPD) may experience heightened rejection sensitivity (RS), a disposition developing from repeated childhood rejecting experiences. It is not known whether the full RS model accounts for the cognitive-affective experiences common in BPD. This systematic review extends upon previous reviews, firstly by assessing the link between childhood rejecting experiences and adult RS, and secondly by considering the link between BPD and RS in both non-clinical and clinical samples.METHOD: Two research questions were devised, and searches based on predetermined criteria were conducted using PsycNET, PubMed, SCOPUS, and Web of Science. Data were extracted by one researcher and 20% was inter-rated, with high levels of agreement. Forty-three papers were systematically reviewed, and 31 included in meta-analysis and meta-regression.RESULTS: Studies assessing the link between childhood rejection and RS are limited; however, emotional abuse and neglect appears linked with RS. Pooled effect sizes suggest RS is linked with BPD (r = .326), with strong effect sizes when comparing clinical and control samples (r = .655). Qualitative synthesis suggests this may be mediated by executive control, although further research is required. The small number of studies considering the full RS model with regard to BPD suggests the interaction between emotional abuse and neglect affects rejection sensitivity; however, outcomes are inconsistent.CONCLUSIONS: Childhood rejection, particularly emotional abuse and neglect, appears to be linked to rejection sensitivity, and rejection sensitivity is linked to BPD. However, this may not be linear. Implications for clinical practice and research are discussed.PRACTITIONER POINTS: Rejection sensitivity is consistently linked with BPD, in clinical and non-clinical samples. Supporting mentalization or improved theory of mind may offer a therapeutic target for this disposition. Considering the causes and effects of rejection sensitivity may offer a non-blaming explanation of interpersonal difficulties in BPD and could be utilized as part of formulation and the therapeutic relationship. However, the possible interaction between emotional abuse and neglect and rejection sensitivity suggests rejection sensitivity is not always apparent for people with BPD. Idiosyncratic formulation should consider this. The literature included in the review is limited to Western populations with a high proportion of females, which may limit generalizability. Measures of rejection sensitivity included in the review were restricted to self-report, which may be subject to bias. Furthermore, measures of childhood rejection were retrospective in nature due to the exclusion of child samples. Further research should consider longitudinal and observational study designs.</p
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