70 research outputs found
Enhanced Electrocatalytic Oxygen Reduction Performance of Differently Optimized S,N Heteroatom Dual-Doped Carbon-Encapsulated Iron Carbide–Carbon (Fe<sub>3</sub>C@C-SN) Nanostructures
In this study, we present a pyrolytically derived iron-based
nonprecious
metal catalyst (NPMC), Fe3C embedded in heteroatom (S,N)-codoped
carbon matrix, and explored it as a potential NPMC for oxygen reduction
in alkaline media. The as-prepared catalysts are well characterized
for their structure, crystallite size, morphology, different bonding
states of the dopants, and defect levels in the carbon matrix. The
optimization is performed for ideal reaction temperature and dopant
amounts in Fe3C@C nanostructures. From the electrochemical
study, it is found that among the different variants, the sample prepared
at a temperature of 800 °C with 20 wt % dopant, i.e., Fe3C@C-SN/25-800, shows a more positive onset potential (Eonset) of 0.844 V (vs reversible hydrogen electrode
(RHE)) and a low half-wave potential (E1/2) value of 0.670 V. It also shows good long-term oxygen reduction
reaction (ORR) stability and methanol tolerance in a 0.1 M KOH aqueous
electrolyte. The measurement of intrinsic parameters, double-layer
capacitance (Cdl), and charge transfer
resistance (RCT) values validate the current–voltage
profile of the samples. The major active sites are identified as Fe–Nx and Nx–C
in the nanostructures. Fe3C@C-SN/25-800 also exhibits considerable
oxygen evolution reaction (OER) activity among its variants and requires
a potential difference (ΔE = E1/2(ORR) – EJ=10 mA cm–2 (OER)) of
0.980 V for overall oxygen electrochemistry. The best electrocatalytic
activity can be attributed to the combination of several factors,
namely, chosen reaction temperature, dopant concentration, better
graphitization, and the presence of a high amount of heteroatoms suitably
aligned in the carbon matrix (pyridinic-N, thiophenic-S, etc.) that
synergistically enhance the overall performance
SSmsy and ESmsy for 13 species in Mille Lacs Lake with and without the temperature forcing function.
<p>SSmsy and ESmsy for 13 species in Mille Lacs Lake with and without the temperature forcing function.</p
Vertical Phase Segregation Induced by Dipolar Interactions in Planar Polymer Brushes
We present a generalized theory for
studying structural properties
of a planar dipolar polymer brush immersed in a polar solvent. We
show that an explicit treatment of the dipolar interactions yields
a macroscopic concentration dependent effective “chi”
(the Flory–Huggins-like interaction) parameter. Furthermore,
it is shown that the concentration dependent chi parameter promotes
phase segregation in polymer solutions and brushes so that the polymer-poor
phase consists of a finite/nonzero polymer concentration. Such a destabilization
of the homogeneous phase by the dipolar interactions appears as vertical
phase segregation in a planar polymer brush. In a vertically phase
segregated polymer brush, the polymer-rich phase near the grafting
surface coexists with the polymer-poor phase at the other end. Predictions
of the theory are directly compared with prior reported experimental
results for dipolar polymers in polar solvents. Excellent agreements
with the experimental results are found, hinting that the dipolar
interactions play a significant role in vertical phase segregation
of planar polymer brushes. We also compare our field theoretical approach
with the two-state and other models invoking <i>ad hoc</i> concentration dependence of the chi parameter. Interplay between
the short-ranged excluded volume interactions and long-ranged dipolar
interactions is shown to play an important role in affecting the vertical
phase separation. Effects of mismatch between the dipole moments of
the polymer segments and the solvent molecules are investigated in
detail
Temperature-influenced ecosystem MSY (ESmsyT) for walleye in Mille Lacs Lake.
<p>The black line (solid) shows predicted catch, and grey line (solid) shows predicted biomass. The black and grey dashed lines show the interquartile range for catch and biomass respectively.</p
Mille Lacs Lake, Minnesota, USA.
<p>The map was generated using R package: “ggmap” [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0185575#pone.0185575.ref019" target="_blank">19</a>].</p
Change in P/B as temperature deviates from the optimum.
<p>The slope of the decline of P/B value depends on the difference between the optimum and the critical temperature: for a species with small tolerance range, the P/B decreases sharply compared to a species with wide tolerance rage. Also, EwE allows the user to parameterise the temperature tolerance below optimum (blue) and above optimum (red) separately (i.e. there is no restriction that the tolerance map should be symmetric around the mean).</p
Temperature-influenced ecosystem MSY (ESmsyT) for key recreational species in Mille Lacs Lake.
<p>The black line (solid) shows predicted catch, and grey line (solid) shows predicted biomass. The black and grey dashed lines show the interquartile range for catch and biomass respectively. Species included are northern pike, yellow perch, cisco, smallmouth bass, burbot, white sucker, rock bass, black crappie, largemouth bass, carp, bowfin, and bullhead.</p
Ecosystem approach to fisheries: Exploring environmental and trophic effects on Maximum Sustainable Yield (MSY) reference point estimates
<div><p>We present a comprehensive analysis of estimation of fisheries Maximum Sustainable Yield (MSY) reference points using an ecosystem model built for Mille Lacs Lake, the second largest lake within Minnesota, USA. Data from single-species modelling output, extensive annual sampling for species abundances, annual catch-survey, stomach-content analysis for predatory-prey interactions, and expert opinions were brought together within the framework of an Ecopath with Ecosim (EwE) ecosystem model. An increase in the lake water temperature was observed in the last few decades; therefore, we also incorporated a temperature forcing function in the EwE model to capture the influences of changing temperature on the species composition and food web. The EwE model was fitted to abundance and catch time-series for the period 1985 to 2006. Using the ecosystem model, we estimated reference points for most of the fished species in the lake at single-species as well as ecosystem levels with and without considering the influence of temperature change; therefore, our analysis investigated the trophic and temperature effects on the reference points. The paper concludes that reference points such as MSY are not stationary, but change when (1) environmental conditions alter species productivity and (2) fishing on predators alters the compensatory response of their prey. Thus, it is necessary for the management to re-estimate or re-evaluate the reference points when changes in environmental conditions and/or major shifts in species abundance or community structure are observed.</p></div
Maximum and average air temperature in July-Aug recorded at Isle station, near Mille Lacs Lake.
<p>Panel A shows maximum temperatures. Panel B shows average temperatures. In panel B the dashed grey lines show the average temperature for the corresponding time-frame (1990–1999, 2000–2005, and 2006–2013, and the blue dotted line is the trend line through the data.</p
Disturbed State Concept-Based Model Incorporating Strain-Softening Behavior for Gas Hydrate Sediments
Gas extraction from methane hydrate
reservoirs results
in significant
changes to pore pressure, causing soil deformation and progressive
failure. Current advanced constitutive models, which are capable of
capturing this deformation process, are often complex, computationally
expensive, and challenging to implement in numerical solvers. Hence,
simpler models are generally preferred; however, these models fail
to predict critical geomechanical aspects such as strain softening
and dilation. To address this limitation, the present study proposes
a unified constitutive model based on the disturb state concept (DSC),
considering the state variables such as hydrate saturation, temperature,
and effective confining pressure for gas hydrate sediments. The stress–strain
relationship is derived by combining two distinct responses: a hyperbolic
hardening response that extends the stress–strain behavior
prior to the peak stress state and a DSC approach to capture the post-peak
softening and dilation response. Furthermore, the model is rigorously
validated by utilizing multiple sets of triaxial experimental data
of gas hydrate sediments under different initial conditions. This
comprehensive validation process ensured the robustness and reliability
of the proposed model. Finally, the efficacy of the model is analyzed
based on the energy absorption capacity and index of agreement approach
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