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•Contact-time variation shows ethane is the sole primary product of methane DHA.•Kinetic and thermodynamic formalisms reveal acetylene is a key intermediate.•Degree of reversibility ...control quantifies thermodynamic influence of each step.•Forward rate calculations require spatial-averaging of reaction reversibility.•DHA forward rate is invariant with contact-time and sets upper bounds to net rate.
Acetylene is identified as a key intermediate in methane dehydroaromatization (DHA) reactions present in concentrations O(1) Pascal. The rank of acetylene and other C2 hydrocarbon intermediates is determined by conversion-selectivity profiles collected from 0.01% to 8% methane conversion varied by extent of “non-selective” deactivation of Mo/H-ZSM-5 catalysts. Ethane is shown to be the sole primary product of methane pyrolysis and is sequentially dehydrogenated to ethylene and acetylene – which aromatizes to benzene with rates similar to direct acetylene aromatization measured in the absence of methane. The influence of CH cleavage and CC coupling events to control the rate and reversibility of DHA is assessed by the degree of reversibility control, introduced here for the first time, and the degree of rate control. The approach to equilibrium of the methane to benzene synthesis reaction is length averaged and affinity averaged by the degree of reversibility control of each intervening elementary step to rigorously calculate forward rates of benzene synthesis by use of De Donder relations. Forward rates are found to be invariant along the catalyst bed once the DHA network reaches a pseudo-steady state and methane, ethane, and ethylene form an equilibrated pool.
Hysteretic sorption and desorption of water is observed from 0 to 95% relative humidity and 298-333 K on a glassy polyurethane foam. It is postulated that sorption-induced swelling of the glassy ...polyurethane increases the concentration of accessible hydrogen-bonding adsorption sites for water. The accessibility of sites is kinetically controlled due to the restricted thermal motions of chains in the glassy polymer, causing a difference in accessible site concentrations during sorption and desorption. This discrepancy leads to hysteresis in the sorbed concentrations of water. A coupled chemo-mechanical model relating volumetric strain, adsorption site concentration, and sorbed water concentration is employed to describe water sorption hysteresis in the glassy polyurethane. This model not only describes the final mass uptake for each relative humidity step, but also captures the dynamics of water uptake, which exhibit diffusion and relaxation rate-controlled regimes.
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•Rates of composite reactions are described by a single apparent rate-limiting step.•Sensitivities are the salient parameters that describe rate-control of steps.•Kinetic degrees of ...rate control (DoRC) sum to unity for all reaction networks.•DoRC can be calculated from measured reversibilities for all reaction networks.•Thermodynamic DoRC are proportional to coverages only in ideal cases.
We describe sensitivities of elementary steps as salient parameters in determining the rate determining character of elementary steps within a reaction network and develop a formalism wherein the overall composite reaction is described by an apparent rate-determining step that is a sensitivity-weighted average of the elementary steps that comprise the reaction network. Reaction parameters—apparent reaction orders, apparent enthalpy and entropy of activation—of the composite reaction network are determined within the framework we develop by application of transition state theory to the apparent rate-determining step. From this formalism we develop methods for determination of surface coverages by measuring only reaction orders, methods for discrimination between proposed mechanisms, a proof that the kinetic degrees of rate control sum to unity, and a proof for the relationship between fractional coverages and thermodynamic degrees of rate control. Two complementary formalisms for identifying rate-limiting transition states are broadly employed in chemical kinetics—De Donder relations based on assessing the thermodynamic driving forces of elementary steps during reaction and degrees of rate control based on knowledge of the kinetics of elementary reaction steps. The formalism developed herein unifies these two strategies to elucidate in the most general case a relationship between the thermodynamic driving forces of elementary steps captured by the reversibilities and the kinetic and thermodynamic degrees of rate control.
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•Forward/reverse degrees of rate control (DoRC) are defined for reversible reactions.•Forward/reverse DoRC are constrained by detailed balance at equilibrium.•Forward/reverse DoRC ...give a thermodynamically consistent rate-control formalism.•Reversible reactions behave like pseudo-elementary steps at equilibrium.
The net rate of a composite reaction is the difference between the forward and reverse reaction rates, which are kinetically distinct despite sharing elementary reaction steps and therefore have different rate-controlling transition states and species. Thus, degrees of rate control defined to identify rate-controlling transition states and species for the net rate confound contributions from the forward and reverse reactions. Herein, the forward and reverse degrees of rate control are defined to independently quantify the extent that species and transition states control the forward and reverse rates in reversible reactions. These degrees of rate control are defined as the relative change in the forward and reverse reaction rates per kBT decrease in the standard-state molecular free energies of transition states and species, and they are related to experimentally measurable quantities such as steady-state fractional coverages, reaction orders, and energies and entropies of activation of the forward and reverse reaction rates. The forward/reverse degrees of rate control represent stoichiometric coefficients for species and transition states in an equilibrium between the initial states and transition states of the apparent rate-controlling steps of forward and reverse overall reactions. At equilibrium, the apparent transition states for the forward reaction and reverse reaction converge, and thus the forward and reverse rate-controlling steps combine to form a single apparent rate-controlling step. This apparent rate-controlling step is comprised of an apparent initial state, transition state, and final state, where the apparent final state of the forward reaction is the apparent initial state of the reverse reaction. The apparent rate-controlling step behaves identically to an elementary step reaction at equilibrium with a pseudo-mass-action rate function given by the transition-state-theory (TST) form rate function (Foley and Bhan, 2020) with a stoichiometric number equal to the affinity-averaged stoichiometric number, σ¯. The ratio of the forward and reverse TST-form rate functions is identical to the overall thermodynamic equilibrium relation, consistent with the principles of microscopic reversibility and detailed balance at equilibrium.
Abstract
Background
Animal-borne telemetry instruments (tags) have greatly advanced our understanding of species that are challenging to observe. Recently, non-recoverable instruments attached to ...cetaceans have increased in use, but these devices have limitations in data transmission bandwidth. We analyze trade-offs in the longevity, resolution, and continuity of data records from non-recoverable satellite-linked tags on deep-diving
Ziphius cavirostris
in the context of a behavioral response study of acute noise exposure. We present one data collection programming scheme that balances resolution and continuity against longevity to address specific questions about the behavioral responses of animals to noise exposure in experimental contexts. We compare outputs between two programming regimes on a commercially available satellite-linked tag: (1) dive behavior summary defined by conductivity thresholds and (2) depth time-series at various temporal resolutions.
Results
We found that time-series data vary from the more precisely defined dives from a dive summary record data stream by an acceptable error range for our application. We determined a 5-min time-series data stream collected for 14 days balanced resolution with longevity, achieving complete or nearly complete diving records in 6 out of 8 deployments. We increased our data message reception rate several fold by employing a boat based data capture system. Finally, a tag deployed in a group concurrently with a high-resolution depth recorder showed high depth concordance.
Conclusions
We present the conceptual framework and iterative process for matching telemetry tag programming to research questions that we used and which should be applicable to a wide range of studies. Although designing new hardware for our specific questions was not feasible at the time, we were able to optimize the sampling regime of a commercially available instrument to meet the needs of our research questions and proposed analyses. Nevertheless, for other study species or designs, the complicated intersection between animal behavior and bandwidth of telemetry systems can often create a severe mismatch among research questions, data collection, and analysis tools. More flexible programming and purpose-built instruments will increase the efficacy of these studies and increase the scientific yield relative to the inherently higher risk of invasive studies.
Studies of the social behavior of Cuvier's beaked whales (Ziphius cavirostris) are challenging because of their deep‐water habitat usually far from shore and the limited time they spend at the ...surface. The sociality of these deepest diving mammals is of interest, however, especially for our understanding of how social systems evolve in extreme habitats. High levels of scarring suggest that males compete agonistically for access to females and so we predicted that associations among adult males would be unstable due to competitive exclusion. We tested this prediction by evaluating the diving behavior of animals within social groups off Cape Hatteras, North Carolina, considering diving synchrony a proxy for group membership. Using data from satellite‐linked depth‐recording tags, we found that adult male–male pairs showed extended periods of synchrony in diving behavior, while all pairs that included an adult male with an individual of another age and/or sex dove synchronously for less than a day. We assessed three hypotheses to explain these surprising results: sexual segregation; extended bouts of male–male competition; and the presence of male alliances. Finally, we considered testable predictions to distinguish among these explanations.
Read et al describe one of the most dramatic behavioral responses they have witnessed in more than 200 playback trials with natural and anthropogenic sounds to dozens of marine mammal species. In Aug ...2013, they were conducting controlled playback experiments off Catalina Island CA to determine how Risso's dolphins (Grampus griseus) responded to the sounds of mammal-eating killer whales (Orcinus orca). This was part of a broader study of how social structure influences the behavioral response of odontocetes to these predators. Their observations complement recent studies that have investigated the response of marine mammals to tactical military sonars in the context of anti-predatory behavior.
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