Reaction Time Scale Research Articles

The propagation characteristics of particle-laden two-phase detonation waves in pyrolysis mixtures of C(s)/H2/CO/CH4/O2/N2

In this paper, numerical simulations are carried out to study the propagation characteristics of detonation waves in carbon particle-laden two-phase pyrolysis mixtures consisting of C(s)/H2/CO/CH4/O2/N2. The results show that the hydrodynamic thickness of the detonation waves changes non-monotonically with the carbon particle mass loading ratio and particle diameter. Both the aerodynamic relaxation time and heterogeneous reaction time increase drastically by enlarging the carbon particles. Small particles with the diameter of less than 1 μm gather and then react near the detonation front, which significantly enhances the propagation velocity of the detonation waves. Under such conditions, the aerodynamic relaxation time scale is smaller than the detonation wave characteristic time scale, which causes both the velocities and temperatures of gas and particles to reach the maximum values at the detonation front. However, such effects diminish gradually as the particles enlarge in size. The investigations show that 50 μm-sized particles have almost no effect on the detonation wave, for which the aerodynamic relaxation and heterogeneous reaction time scales are considerably larger than the detonation wave characteristic time scale. The propagation velocity of the detonation wave in the presence of 50 μm-sized particles is close to the value of the gaseous case. The results also show that increasing the particle mass loading ratio induces nonlinear changes in the detonation propagation velocity, due to changes in the global equivalence ratio of the two-phase mixtures.

Observational constraints on the sensitivity of two calving glaciers to external forcings

AbstractFuture mass loss projections of the Greenland ice sheet require understanding of the processes at a glacier terminus, especially of iceberg calving. We present detailed and high-rate terrestrial radar interferometer observations of Eqip Sermia and Bowdoin Glacier, two outlet glaciers in Greenland with comparable dimensions and investigate iceberg calving, surface elevation, velocity, strain rates and their links to air temperature, tides and topography. The results reveal that the two glaciers exhibit very different flow and calving behaviour on different timescales. Ice flow driven by a steep surface slope with several topographic steps leads to high velocities, areas of extension and intense crevassing, which triggers frequent but small calving events independent of local velocity gradients. In contrast, ice flow under smooth surface slopes leaves the ice relatively intact, such that sporadic large-scale calving events dominate, which initiate in areas with high shearing. Flow acceleration caused by enhanced meltwater input and tidal velocity variations were observed for terminus sections close to floatation. Firmly grounded terminus sections showed no tidal signal and a weak short-term reaction to air temperature. These results demonstrate reaction timescales to external forcings from hours to months, which are, however, strongly dependent on local terminus geometry.

In Situ Ternary Adduct Formation of Yttrium Polyaminocarboxylates Leads to Small Molecule Capture and Activation.

In this work the chemistry of yttrium complexes is exploited for small molecule capture and activation. Nuclear magnetic resonance (NMR) and density functional theory (DFT) studies were used to investigate the in situ formation of solution state ternary yttrium-acetate, yttrium-bicarbonate, and yttrium-pyruvate adducts with a range of polyaminocarboxylate chelates. These studies reveal that [Y(DO3A)(H2 O)2 ] (H3 DO3A - 1,4,7,10-tetraazacyclododecane-1,4,7-tricarboxylic acid) and [Y(EDTA)(H2 O)q ]- (H4 EDTA - ethylenediaminetetraacetic acid, q = 2 and 3) are able to form ternary adducts with bicarbonate and pyruvate. In the latter, unusual decarboxylation of pyruvate to form acetic acid and CO2 was observed and further studied using SABRE-hyperpolarised 13 C NMR (SABRE - signal amplification by reversible exchange) to provide information about the reaction timescale and lifetime of intermediates involved in this conversion. The work presented demonstrates that yttrium complexes can capture and activate small molecules, which may lead to novel and useful applications of this metal in catalysis and medical imaging.

Fully resolved direct numerical simulation of single coal particle gasification in supercritical water

Supercritical water gasification is a promising technology in the context of carbon neutrality, since it converts coal into hydrogen and easily-captured CO2. A fully resolved direct numerical simulation of single particle gasification in supercritical water is conducted in this paper in order to investigate process details at particle scale. To handle the shrinking reactive particle, a directional ghost-cell immersed boundary method is used with a general Robin-type boundary condition at the interface. Detailed flow field and interphase heat/mass transfer near the reactive coal particle are revealed and compared with standard non-reactive cases – used for validation. They are found to be significantly affected by the combined effect of the reaction-induced Stefan flow, particle shrinking, species generation or destruction, and reaction heat release. The chemical processes are then studied with special attention on the gas-phase reaction time-scale. This study delivers a detailed understanding of coal particle gasification in supercritical water, and provides a first successful test of efficient numerical methods needed for large-scale supercritical water gasification simulations.

It started with a Cys: Spontaneous cysteine modification during cryo-EM grid preparation.

Advances in single particle cryo-EM data collection and processing have seen a significant rise in its use. However, the influences of the environment generated through grid preparation, by for example interactions of proteins with the air-water interface are poorly understood and can be a major hurdle in structure determination by cryo-EM. Initial interactions of proteins with the air-water interface occur quickly and proteins can adopt preferred orientation or partially unfold within hundreds of milliseconds. It has also been shown previously that thin-film layers create hydroxyl radicals. To investigate the potential this might have in cryo-EM sample preparation, we studied two proteins, HSPD1, and beta-galactosidase, and show that cysteine residues are modified in a time-dependent manner. In the case of both HSPD1 and beta-galactosidase, this putative oxidation is linked to partial protein unfolding, as well as more subtle structural changes. We show these modifications can be alleviated through increasing the speed of grid preparation, the addition of DTT, or by sequestering away from the AWI using continuous support films. We speculate that the modification is oxidation by reactive oxygen species which are formed and act at the air-water interface. Finally, we show grid preparation on a millisecond timescale outruns cysteine modification, showing that the reaction timescale is in the range of 100s to 1,000s milliseconds and offering an alternative approach to prevent spontaneous cysteine modification and its consequences during cryo-EM grid preparation.

From ensemble electrochemistry to nanoparticle-impact electrochemistry: Altered reaction process and possible applications

Nanoparticle-impact electrochemistry (NIE) is an electroanalytical method based on the stochastic collisions of individual nanoparticles onto an inert ultramicroelectrode. In this article, we overview different characteristics of NIE-based reactions from their ensemble counterpart, that is, enhanced mass transport, intermittent working mode, and reduced reaction time scale. A particular interest is focused on the survey of the resulting changes in the reaction process regarding enhanced reaction efficiency and rate, altered selectivity, and improved catalyst stability. A summary of the application prospect of NIE is followed, and existing challenges are provided.

Designed Synthesis of Fe x Co100−x Alloy Nanoparticles by Polyol Reduction: An Evolution of Structural, Morphological and Magnetic Properties

Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">100−<i>x</i></sub> nanoparticles with different stoichiometry ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x = 0$ </tex-math></inline-formula> –100) have been prepared by a facile synthesis process and compositions confirmed using X-ray fluorescence spectroscopy. X-ray diffraction measurements suggest alloy formation in the body-centered cubic (BCC) phase, with a progressive shift of peak positions to account for the stoichiometric changes. The evolution of nanoparticle morphology is from cubic for iron to hexagonal for cobalt, and the entire composition range has been examined. Magnetic behavior has been accessed by Mössbauer spectroscopy and vibrating sample magnetometric measurements, which suggests an increase of magnetization values of iron upon alloying with cobalt. A detailed account of the synthesis scheme has been presented, to achieve uniform alloy nanoparticles in the pristine state with minimum aggregation and surface oxidation, by carefully adjusting the reaction timescales.

Coupled Interfacial and Bulk Kinetics Govern the Timescales of Multiphase Ozonolysis Reactions.

Chemical transformations in aerosols impact the lifetime of particle phase species, the fate of atmospheric pollutants, and both climate- and health-relevant aerosol properties. Timescales for multiphase reactions of ozone in atmospheric aqueous phases are governed by coupled kinetic processes between the gas phase, the particle interface, and its bulk, which respond dynamically to reactive consumption of O3. However, models of atmospheric aerosol reactivity often do not account for the coupled nature of multiphase processes. To examine these dynamics, we use new and prior experimental observations of aqueous droplet reaction kinetics, including three systems with a range of surface affinities and ozonolysis rate coefficients (trans-aconitic acid (C6H6O6), maleic acid (C4H4O4), and sodium nitrite (NaNO2)). Using literature rate coefficients and thermodynamic properties, we constrain a simple two-compartment stochastic kinetic model which resolves the interface from the particle bulk and represents O3 partitioning, diffusion, and reaction as a coupled kinetic system. Our kinetic model accurately predicts decay kinetics across all three systems, demonstrating that both the thermodynamic properties of O3 and the coupled kinetic and diffusion processes are key to making accurate predictions. An enhanced concentration of adsorbed O3, compared to gas and bulk phases is rapidly maintained and remains constant even as O3 is consumed by reaction. Multiphase systems dynamically seek to achieve equilibrium in response to reactive O3 loss, but this is hampered at solute concentrations relevant to aqueous aerosol by the rate of O3 arrival in the bulk by diffusion. As a result, bulk-phase O3 becomes depleted from its Henry's law solubility. This bulk-phase O3 depletion limits reaction timescales for relatively slow-reacting organic solutes with low interfacial affinity (i.e., trans-aconitic and maleic acids, with krxn ≈ 103-104 M-1 s-1), which is in contrast to fast-reacting solutes with higher surface affinity (i.e., nitrite, with krxn ≈ 105 M-1 s-1) where surface reactions strongly impact the observed decay kinetics.

Structural dynamics: review of time-resolved cryo-EM.

The structural determination of biological macromolecules has been transformative for understanding biochemical mechanisms and developing therapeutics. However, the ultimate goal of characterizing how structural dynamics underpin biochemical processes has been difficult. This is largely due to significant technical challenges that hinder data collection and analysis on the native timescales of macromolecular dynamics. Single-particle cryo-EM provides a powerful platform to approach this challenge, since samples can be frozen faster than the single-turnover timescales of most biochemical reactions. In order to enable time-resolved analysis, significant innovations in the handling and preparation of cryo-EM samples have been implemented, bringing us closer to the goal of the direct observation of protein dynamics in the milliseconds to seconds range. Here, the current state of time-resolved cryo-EM is reviewed and the most promising future research directions are discussed.

ANALYTICAL SINGULAR VALUE DECOMPOSITION FOR A CLASS OF STOICHIOMETRY MATRICES.

We present the analytical singular value decomposition of the stoichiometry matrix for a spatially discrete reaction-diffusion system. The motivation for this work is to develop a matrix decomposition that can reveal hidden spatial flux patterns of chemical reactions. We consider a 1D domain with two subregions sharing a single common boundary. Each of the subregions is further partitioned into a finite number of compartments. Chemical reactions can occur within a compartment, whereas diffusion is represented as movement between adjacent compartments. Inspired by biology, we study both (1) the case where the reactions on each side of the boundary are different and only certain species diffuse across the boundary and (2) the case where reactions and diffusion are spatially homogeneous. We write the stoichiometry matrix for these two classes of systems using a Kronecker product formulation. For the first scenario, we apply linear perturbation theory to derive an approximate singular value decomposition in the limit as diffusion becomes much faster than reactions. For the second scenario, we derive an exact analytical singular value decomposition for all relative diffusion and reaction time scales. By writing the stoichiometry matrix using Kronecker products, we show that the singular vectors and values can also be written concisely using Kronecker products. Ultimately, we find that the singular value decomposition of the reaction-diffusion stoichiometry matrix depends on the singular value decompositions of smaller matrices. These smaller matrices represent modified versions of the reaction-only stoichiometry matrices and the analytically known diffusion-only stoichiometry matrix. Lastly, we present the singular value decomposition of the model for the Calvin cycle in cyanobacteria and demonstrate the accuracy of our formulation. The MATLAB code, available at www.github.com/MathBioCU/ReacDiffStoicSVD, provides routines for efficiently calculating the SVD for a given reaction network on a 1D spatial domain.

The Importance of Physiochemical Processes in Decarbonisation Technology Applications Utilizing the Subsurface: A Review

The Earth’s subsurface not only provides a wide range of natural resources but also contains large pore volume that can be used for storing both anthropogenic waste and energy. For example, geothermal energy may be extracted from hot water contained or injected into deep reservoirs and disused coal mines; CO2may be stored within depleted petroleum reservoirs and deep saline aquifers; nuclear waste may be disposed of within mechanically stable impermeable strata; surplus heat may be stored within shallow aquifers or disused coal mines. Using the subsurface in a safe manner requires a fundamental understanding of the physiochemical processes which occur when decarbonising technologies are implemented and operated. Here, thermal, hydrological, mechanical and chemical perturbations and their dynamics need to be considered. Consequently, geoscience will play a central role in Society’s quest to reduce greenhouse gas emissions. This contribution provides a review of the physiochemical processes related to key technologies that utilize the subsurface for reducing greenhouse gas emissions and the resultant challenges associated with these technologies. Dynamic links between the geomechanical, geochemical and hydrological processes differ between technologies and the geology of the locations in which such technologies are deployed. We particularly focus on processes occurring within the lithologies most commonly considered for decarbonisation technologies. Therefore, we provide a brief comparison between the lithologies, highlighting the main advantages and disadvantages of each, and provide a list of key parameters and properties which have first order effects on the performance of specific rock types, and consequently should be considered during reservoir evaluation for decarbonising technology installation. The review identifies several key knowledge gaps that need to be filled to improve reservoir evaluation and performance prediction to be able to utilize the subsurface efficiently and sustainably. Most importantly, the biggest uncertainties emerge in prediction of fracture pattern development and understanding the extent and timescales of chemical reactions that occur within the decarbonising applications where external fluid or gas is cyclically injected and invariably causes disequilibrium within the system. Furthermore, it is clear that whilst geoscience can show us the opportunities to decarbonise our cities and industries, an interdisciplinary approach is needed to realize these opportunities, also involving social science, end-users and stakeholders.

0020 Investigation of Seasonal Changes in Self-Reported Sleep Quality and Psychomotor Vigilance Task Outcomes: Results From the Ultra Long-Term Sleep (ULTS) Study

Abstract Introduction Although sleep is fundamental for human well-being, factors that contribute to an individual’s experience and report of sleep quality remain poorly understood. Utilizing that sleepiness is known to impact vigilance performance, this study sets out to explore how self-reported sleep quality changes with behavioral performance and how this variation is affected by seasonal changes. Methods This work is an interim analysis of self-reported sleep quality and behavioral performance data collected in the Ultra Long-term Sleep (ULTS) study (ClinicalTrials.gov Identifier: NCT04513743). In the study 20 healthy participants (average 33±13 years of age) were enrolled for 365 continuous days to observe the seasonal variation in sleep and cognitive performance. The outcome from the daily psychomotor vigilance task (PVT) and sleep questionnaire is analyzed and reported. The sleep questionnaire is a composite of questions from the Sleep Satisfaction Tool, the Karolinska Sleep Diary, questions regarding feelings of pain and outside disturbances, easiness of waking up, and the Karolinska Sleepiness Scale (KSS). The PVT was designed for self-administered high-frequency testing and has a short 3-minute test period. Monthly changes were examined from June to November. This period was chosen since all subjects were active. Results The first eight participants have now completed the study. Repeated measures correlations between KSS and mean PVT reaction time showed moderate but highly robust associations between the two measures over time (r=0.2; 95% CI 0.18-0.23). From the data collected thus far from the entire population, fastest PVT mean reaction times were found on Saturdays and slowest on Tuesdays. Similarly, KSS had best scores in weekends. There was an overall increase in mean PVT reaction time during the investigated period from June to November. This was also observed in KSS. Conclusion Our findings show a moderate correlation between the mean PVT reaction time and Karolinska Sleepiness Scale with up to 365 datapoints per subject with weekly and seasonal trends observed. Support (If Any) This research is supported by Innovation Fund Denmark.

Optimization of silicon etch rate in a CF4/Ar/O2 inductively coupled plasma

We use a fluid plasma model coupled with Maxwell's equations to analyze the influence of various parameters on the silicon etching rate by inductively coupled low-pressure plasma (ICP) generated in a CF4/O2/Ar mixture. These parameters include different argon and oxygen fractions in the feedgas, the gas residence time, and the discharge power. The simulation results show that the optimal etching rate is obtained when the gas residence time in the reactor is comparable to the time scale of dissociation reactions of feedgas CF4. We find that the etch rate remains almost constant for argon fraction in the mixture &amp;lt;50% and decreases for larger argon fractions. Based on these results, we discuss the influence of the argon fraction on the energy efficiency of the fluorine atoms formation in the ICP reactor. It is found that, for the conditions of our studies, there is the optimal etch rate for the oxygen fraction in the mixture of ∼5%. We demonstrate that the conventional explanation of this result is not applicable to the diffusion-controlled discharges and propose an alternative explanation. Finally, the increasing etching rate is obtained for the discharge power in the range of 102–103 W.

Semiclassical Real-Time Nuclear-Electronic Orbital Dynamics for Molecular Polaritons: Unified Theory of Electronic and Vibrational Strong Couplings.

Molecular polaritons have become an emerging platform for remotely controlling molecular properties through strong light-matter interactions. Herein, a semiclassical approach is developed for describing molecular polaritons by self-consistently propagating the real-time dynamics of classical cavity modes and a quantum molecular subsystem described by the nuclear-electronic orbital (NEO) method, where electrons and specified nuclei are treated quantum mechanically on the same level. This semiclassical real-time NEO approach provides a unified description of electronic and vibrational strong couplings and describes the impact of the cavity on coupled nuclear-electronic dynamics while including nuclear quantum effects. For a single o-hydroxybenzaldehyde molecule under electronic strong coupling, this approach shows that the cavity suppression of excited state intramolecular proton transfer is influenced not only by the polaritonic potential energy surface but also by the time scale of the chemical reaction. This work provides the foundation for exploring collective strong coupling in nuclear-electronic quantum dynamical systems within optical cavities.

Global Controls on DOC Reaction Versus Export in Watersheds: A Damköhler Number Analysis

AbstractThe relative capacity for watersheds to eliminate or export reactive constituents has important implications on aquatic ecosystem ecology and biogeochemistry. Removal efficiency depends on factors that affect either the reactivity or advection of a constituent within river networks. Here, we characterized Damköhler number (Da) for dissolved organic carbon (DOC) uptake in global river networks. Da equals the advection to reaction timescale ratio and thus provides a unitless indicator for DOC reaction intensity during transport within river networks. We aim to demonstrate the spatial and temporal patterns and interplays among factors that determine DOC uptake across global river networks. We show that watershed size imposes a primary control on river network DOC uptake due to a three orders of magnitude difference in water residence time (WRT) between the smallest and largest river networks. DOC uptake capacity in tropical river networks is 2–6 times that in temperate and the Arctic river networks, coinciding with larger DOC removals in warm than in cold watersheds. River damming has a profound impact on DOC uptake due to significantly extended WRTs, particularly in temperate watersheds where most constructed dams are situated. Global warming is projected to increase river network DOC uptake by ca. 19% until year 2100 under the RCP4.5 scenario.

Benthic Biolayer Structure Controls Whole‐Stream Reactive Transport

AbstractHyporheic zone reaction rates are highest just below the sediment‐water interface, in a shallow region called the benthic biolayer. Vertical variability of hyporheic reaction rates leads to unexpected reaction kinetics for stream‐borne solutes, compared to classical model predictions. We show that deeper, low‐reactivity locations within the hyporheic zone retain solutes for extended periods, which delays reactions and causes solutes to persist at higher concentrations in the stream reach than would be predicted by classical approaches. These behaviors are captured by an upscaled model that reveals the fundamental physical and chemical processes in the hyporheic zone. We show how time scales of transport and reaction within the biolayer control solute retention and transformation at the stream scale, and we demonstrate that accurate assessment of stream‐scale reactivity requires methods that integrate over all travel times.

Vertical Transport Timescale of Surface‐Produced Particulate Material in the Chesapeake Bay

AbstractAccumulation and remineralization of surface‐produced particulate organic matter (POM) in the water column and seabed link closely to hypoxia and the health of aquatic ecosystems. The POM retention time provides a key timescale to interpret biochemical reaction processes. In this study, we investigated the spatiotemporal variations in the vertical particulate age (VPA) of surface‐produced POM, which is the mean time elapsed since the particulates last contact the surface, by incorporating major physical processes including sinking, resuspension, and deposition in the Chesapeake Bay. It was found that the vertical transport time for the particulates (i.e., VPA) is much longer than the dissolved counterparts as the former consists of new material from the surface and the resuspended aged material that has elongated resting on the seabed after deposition. The VPA is sensitive to settling velocity, especially in low‐frequent resuspension environments, and varies over 2 orders of magnitude with settling velocity from 0 to 10 m/day. Slow‐sinking material can remain in suspension and seldom settle to the seabed, thus mainly contribute to pelagic processes, while the fast‐sinking material connects closely with benthic processes. The seasonality of VPA decreases as the settling velocity increases. No significant difference in VPA was found between wet and dry years, yet the episodic strong flood events entrain old materials from the depositional lateral shoals to increase VPA in the channel. The transport age bridges cross disciplinaries by providing the fourth‐dimensional age information as a common currency to compare the physical transport timescale with the timescales for biochemical reactions.

The Importance of Decarbonylation Mechanisms in the Atomic Layer Deposition of High-Quality Ru Films by Zero-Oxidation State Ru(DMBD)(CO)3.

Achieving facile nucleation of noble metal films through atomic layer deposition (ALD) is extremely challenging. To this end, η4 -2,3-dimethylbutadiene ruthenium(0) tricarbonyl (Ru(DMBD)(CO)3 ), a zero-valent complex, has recently been reported to achieve good nucleation by ALD at relatively low temperatures and mild reaction conditions. The authors study the growth mechanism of this precursor by in situ quartz-crystal microbalance and quadrupole mass spectrometry during Ru ALD, complemented by ex situ film characterization and kinetic modeling. These studies reveal that Ru(DMBD)(CO)3 produces high-quality Ru films with excellent nucleation properties. This results in smooth, coalesced films even at low film thicknesses, all important traits for device applications. However, Ru deposition follows a kinetically limited decarbonylation reaction scheme, akin to typical chemical vapor deposition processes, with a strong dependence on both temperature and reaction timescale. The non-self-limiting nature of the kinetically driven mechanism presents both challenges for ALD implementation and opportunities for process tuning. By surveying reports of similar precursors, it is suggested that the findings can be generalized to the broader class of zero-oxidation state carbonyl-based precursors used in thermal ALD, with insight into the design of effective saturation studies.

The Limitation of the Combination of Transition State Theory and Thermodynamics for the Reactions of Proteins and Nucleic Acids.

When a reaction is accompanied by a change with the speed close to or slower than the reaction rate, a circulating reaction flow can exist among the reaction states in the macroscopic stationary state. If the accompanying change were at equilibrium in the timescale of the relevant reaction, the transition-state theory would hold to eliminate the flow.

Semi-Crystalline Poly(thioether) Prepared by Visible-Light-Induced Organocatalyzed Thiol-ene Polymerization in Emulsion.

A photocatalytic thiol-ene aqueous emulsion polymerization under visible-light is described to prepare linear semicrystalline latexes using 2,2'-dimercaptodiethyl sulfide as dithiol and various dienes. The procedure involves low irradiance (3mW cm-2 ), LED irradiation source, eosin-Y disodium as organocatalyst, low catalyst loading (<0.05%mol), and short reaction time scales (<1 h). The resulting latexes have molecular weights of about 10kg mol-1 , average diameters of 100nm, and a linear structure consisting only of thioether repeating units. Electron-transfer reaction from a thiol to the triplet excited state of the photocatalyst is suggested as the primary step of the mechanism (type I), whereas oxidation by singlet oxygen generated by energy transfer has a negligible effect (type II). Only polymers prepared with aliphatic dienes such as diallyl adipate or di(ethylene glycol) divinyl ether exhibit a high crystallization tendency as revealed by differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction. Ordering and crystallization are driven by molecular packing of poly(thioether) chains combining structural regularity, compactness, and flexibility.