Time Scale Of Process Research Articles

From division to 'divergence': to understand wood growth across timescales, we need to (learn to) manipulate it.

Wood formation is the Rosetta stone of tree physiology: a traceable, integrated record of physiological and morphological status. It also produces a large and persistent annual sink for terrestrial carbon, motivating predictive understanding. Xylogenesis studies have greatly expanded our knowledge of the intra-annual controls on wood formation, while dendroecology has quantified the environmental drivers of multi-annual variability. But these fields operate on different timescales, making it challenging to predict how short (e.g. turgor) and long timescale processes (e.g. disturbance) interactively influence wood formation. Toward this challenge, wood growth responses to natural climate events provide useful but incomplete explanations of tree growth variability. By contrast, direct manipulations of the tree vascular system have yielded unexpected insights, particularly outside of model species like boreal conifers, but they remain underutilized. To improve prediction of global wood formation, we argue for a new generation of experimental manipulations of wood growth across seasons, species, and ecosystems. Such manipulations should expand inference to diverse forests and capture inter- and intra-specific differences in wood growth. We summarize the endogenous and exogenous factors influencing wood formation to guide future experimental design and hypotheses. We highlight key opportunities for manipulative studies integrating measurements from xylogenesis, dendroanatomy, dendroecology, and ecophysiology.

Direct visualization of electric-field-stimulated ion conduction in a potassium channel.

Understanding protein function would be facilitated by direct, real-time observation of chemical kinetics in the atomic structure. The selectivity filter (SF) of the K+ channel provides an ideal model, catalyzing the dehydration and transport of K+ ions across the cell membrane through a narrow pore. We used a "pump-probe" method called electric-field-stimulated time-resolved X-ray crystallography (EFX) to initiate and observe K+ conduction in the NaK2K channel in both directions on the timescale of the transport process. We observe both known and potentially new features in the high-energy conformations visited along the conduction pathway, including the associated dynamics of protein residues that control selectivity and conduction rate. A single time series of one channel in action shows the orderly appearance of features observed in diverse homologs with diverse methods, arguing for deep conservation of the dynamics underlying the reaction coordinate in this protein family.

Water Electrooxidation Kinetics Clarified by Time‐Resolved X‐Ray Absorption and Electrochemical Impedance Spectroscopy for a Bulk‐Active Cobalt Material

AbstractWater oxidation, the oxygen evolution reaction (OER), is the anodic process in electrocatalytic production of hydrogen and further green fuels. Transition‐metal oxyhydroxides with bulk‐phase OER activity of the complete material or amorphized near‐surface regions are of prime application interest, but their basic electrochemical properties are insufficiently understood. Here the timescale of functional processes is clarified by time‐resolved X‐ray absorption spectroscopy and electrochemical impedance spectroscopy (EIS) for a thickness‐series of cobalt oxyhydroxides films (about 35–550 nm). At the outer material surface, an electric double‐layer is formed in microseconds followed by clearly cobalt‐centered redox‐state changes of the bulk material in the low millisecond domain and a slow chemical step of O2‐formation, within hundreds of milliseconds. Conceptually interesting, the electrode potential likely controls the OER rate indirectly by driving the catalyst material to an increasingly oxidized state which promotes the rate‐limiting chemical step. Rate constants are derived for redox chemistry and catalysis from EIS data of low‐thickness catalyst films; at higher thicknesses, catalyst‐internal charge transport limitations become increasingly relevant. Relations between electrochemically active surface area, double‐layer capacitance, and redox (pseudo‐)capacitance are discussed. These results can increase the power of EIS analyses and support knowledge‐guided optimization of a broader class of OER catalyst materials.

Mechanisms of Separation of the Elastic Step and the Thermal Step

AbstractThe elastic interaction causes a two‐step conversion from the low‐spin (LS) to the high‐spin state (HS) following a femtosecond laser pulse excitation. These steps occur on different timescales: a spin conversion (elastic step) in a short time due to pressure propagation and a late spin conversion (thermal step) resulting from heat diffusion. In this paper, we provide a brief review of models for spin crossover phenomena, emphasizing the role of the difference of degeneracy of the HS state and LS state and elastic interaction due to changes in local structures. We also review theoretical approaches to these effects. Additionally, to analyze the dynamical process of spin conversion after photo‐irradiation, it is necessary to consider mechanisms of heat transfer among spins. Recently, we proposed a two‐temperature model that incorporates both lattice and spin temperatures, which enables us to reproduce the two steps under an early uniformization of the lattice temperature, highlighting the importance of the timescales of these processes. Furthermore, we explore possible mechanisms to separate the two steps by examining the different timescales of processes of spin conversions by mechanical and entropic forces, and also by considering changes of local temperature due to spin conversion.

Li diffusion in plagioclase crystals and glasses – implications for timescales of geological processes

Abstract. The growing interest in Li diffusion as a tool to determine timescales of short-time magmatic events, such as magma ascent during eruption, increases the necessity to better understand Li diffusion in common mineral phases. In this context, well-constrained diffusion coefficients and understanding of kinetic processes specific to mineral phases are of crucial importance. To gain further insight especially into the kinetic processes in plagioclase, we investigated the diffusion of Li between natural An61 plagioclase crystals and synthetic glasses of An80 plagioclase composition. Experiments were conducted at 200 MPa in rapid-heat/rapid-quench cold-seal pressure vessels (RH/RQ CSPVs) and internally heated pressure vessels (IHPVs) at temperatures between 606 and 1114 °C. Concentration and isotope profiles of Li were measured using femtosecond laser ablation multicollector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS). We adopted a multispecies diffusion model and specified boundary conditions for plagioclase of labradoritic composition. Using this model, we were able to distinguish between an interstitial (DLii) and a vacancy process (DLiA), with the interstitial process being 0.2–1 orders of magnitude faster than the vacancy process, depending on temperature. DLii=10-3.76±0.58exp⁡-180.0±12.0kJmol-1RTm2s-1DLiA=10-5.53±0.16exp⁡-151.7±3.2kJmol-1RTm2s-1 Our data indicate charge compensation of Li by Na in both the crystal and the glass. Chemical Li diffusion coefficients in An80 glass are up to 3 orders of magnitude slower compared to Li tracer diffusion in silicate and aluminosilicate glasses and melts, which is attributed to slow Na diffusion at high An content. Our results for chemical diffusion of Li in plagioclase crystals are 1.5–2 orders of magnitude slower than Li tracer diffusion in An- and Ab-rich plagioclase determined in previous studies. This indicates that earlier studies on natural intermediate plagioclase compositions have underestimated timescales by up to 2 orders of magnitude. For accurate determination of timescales from Li diffusion in plagioclase we suggest further exploring the role of Na and a possible dependence on An content.

Shaping Electronic Properties of Metal-Organic Frameworks for Energy Storage Applications

Metal-Organic Frameworks (MOFs) form through self-assembly between metal ions or clusters with multifunctional organic ligands carrying functional groups, resulting in intricate connected structures. Each constituent, whether metal nodes, connecting functional groups, or bridging organic ligands, imparts specific physical and chemical properties to the MOF, including band energy, charge transport characteristics, and photophysical behaviour. In addition, the crystalline structure of MOF defines the exciton transport and dynamic properties, [1] which are critical to evaluate in order to enhance the system’s performance when employed as electrode material or in storage applications including photonic, mechanical or thermal energy conversion. Hence, understanding the dynamic transport properties in MOFs is vital in order to develop real-world industrial-scale applications, where MOF film structures are particularly desired mainly because the pulverous nature of MOFs presents challenges, such as the gradual loss of active material that can undermine performance and conversion efficiencies.Our research aims to unravel the dynamic processes involved during photon- and mechanical energy storage in both, powdered MOFs and their film counterparts [2,3] for which an automated film-fabrication protocol has been developed (Figure 1). [4] We reveal that the efficiency and quantity of stored energy is intricately linked to factors including as the crystallite morphology and chemical composition. To elucidate these complex interdependencies and determine the timescales of dynamic processes during energy storage in crystalline MOFs, we utilize a diverse set of techniques available at facilities like the Elettra synchrotron and the free-electron laser FERMI in Italy. These techniques include time-resolved X-ray scattering, infrared and terahertz spectroscopy. Results show that the energy storage process of MOF powders can be accelerated from hours (>5 h) up to seconds (~6 sec) upon their fabrication as film structures, which additionally guarantee a fully reversible storage/release process initiated remotely. [2,3] Moreover, we show that the storage process rate can be tailored by adjusting the MOF's electronic properties through variations in chemical composition and thickness, [3] with implications for electrode materials and gas sequestration applications. [5]These findings provided valuable insights into energy storage dynamics in MOF systems, paving the way for a deeper understanding of similar or more advanced film systems and offering new avenues for research in this field.[1] Dincă M. and François Léonard, MRS Bulletin, 2016, 41, 854–857.[2] Klokic, S., Naumenko, D., Marmiroli B., Carraro, F., Linares Moreau, M., Dal Zilio, S., Birarda, G., Kargl, R., Falcaro, P., Amenitsch, H., Sci., 2022, 13, 11869-11877.[3] Klokic, S., Marmiroli B., Naumenko, D., Birarda, G., Dal Zilio, S., Velasquez-Hernandez, M.-J., Falcaro, P., Vaccari, L., Amenitsch, H., accepted in CrystEngComm, 2024.[4] Linares‐Moreau, M.; Brandner, L.; Kamencek, T.; Klokic, S.; Carraro, F.; Okada, K.; Takahashi, M.; Zojer, E.; Doonan, C.; Falcaro, P. Mater. Interfaces 2021, 8 (21), 2101039.[5] Klokic, S., Marmiroli B., Birarda, G., Holzer, P., Sartori, B., Asbaghi-NA, B., Dal Zilio, S., Vaccari, L., Amenitsch, H., submitted, April 2024. Figure 1

Mechanism of Hydride-Ion Diffusion in the Oxyhydride of Barium Titanate: Insights from Quasielastic Neutron Scattering

Perovskite type oxyhydrides, of the form ATiO3-xHx (A = Ba, Sr, and Ca, and x < 0.6) are a novel class of mixed-anion materials displaying high hydride-ion conductivity. The high hydride-ion conductivity may be exploited for applications such as in energy storage and conversion devices, and in catalyst technologies for hydrogenation reactions, bu the conductivity mechanism is not fully understood. Here, in a quasielastic neutron scattering study of the oxyhydride of barium titanate, with different levels of anion vacancies, we show that the rate of hydride-ion diffusion increases with an increasing level of anion vacancies, and that the presence of anion vacancies is a necessity for hydride-ion conductivity. The conductivity mechanism is highly temperature dependent. Below 350 K, the hydride ions undergo jumps amongst nearest neighbor anion vacancies acting as jumping sites, whereas at temperatures between 350 and 550 K the hydride ions also undergo jumps amongst second nearest neighbor sites in the material. The jump diffusion dynamics are characterized by an average relaxation time on the order of 10 ps with a diffusion coefficient of the order of 10-5 cm2/s. For temperatures above 300 K, an additional, slower timescale process, on the order of 100 ps, which may be related to nearest neighbour hydride-ion jumps in different types of local structures with different anion and vacancy concentrations and distributions is observed. Tailoring of the local structure with respect to the concentration and distribution of anion vacancies may thus be a promising route towards optimizing the hydride-ion conductivity towards specific applications

(Invited) Engineering Semiconducting and Dielectric Materials and Processes Using Integrative Methods

Plasma-based unit processes are at the core of process technology, enabling future nanosheet and nanowire-based logic. Patterning must deliver pristine surfaces at an atomic scale over films with strict geometric, interfacial, and material property (RI, density, WER, leakage) requirements. Still a silicon world, it is giving way to new materials including 2D structures and dielectrics. Patterning is no longer planar; it is now 3D with plasma process having to grapple with hidden geometries rather than simply lines, spaces, and holes. There is no shortage of challenges to the realization of new device technology. Process hardware options come with increased degrees of freedom. At the same time, however, new options introduce mechanistic complexity that burdens engineering development.Empirical methods alone cannot be used to grapple with current challenges. Integrative methods extend the old concept of concurrent engineering. In this approach, a combination of first principles simulation and experiments targets important unknowns of process and hardware development rather than seek a system level (“simulation-of-everything”) description. First principles simulations include so-called quantum chemistry methods, while first principles experiments include diagnostics that relate species flux directly with surface reactions (for removal or addition) and materials properties. Clarity to the least understood aspects of critical processes is the desired outcome. This leads to a vehicle for understanding what species flux-surface reactions are needed to achieve structures, and films and then ultimately what processes are needed to achieve them. How dielectric films meet many requirements at the same time given process trade-offs is an example of where clarity is needed. From a singular process, geometric requirements, etch resistance, and mechanical and electrical properties must be met and have long lasting integrity. Three component and non-silicon dielectrics, less understood due to their newness in mainstream device manufacturing, are also of current interest. The imperative for a quantitative understanding of process trade-offs for etch is present across all etch technologies.Our integrative approach is described in this presentation. Beyond a discussion of methodology, the presentation will highlight several examples. One related to silicon carbon nitride (SiCN) dielectric film deposition illustrates the trade-offs among leakage current, refractive index, and etch resistance inherent with varying carbon content. We show how precursor-engineered surface matching is critical to achieving desired growth characteristics. Intermediate level theory approaches, such as kinetic Monte Carlo and microkinetic modeling, are used to relate surface kinetics insights to macroscale parameters. Completing the integrative approach are the application of in-situ plasma diagnostics and surface chemistry metrology. These provide a measure of validation and verification. Also, some parameters are more easily measured than computed. Neutral species densities are now measured easily with the combination of computed electron impact cross-sections and advanced mass spectroscopy methods. In another example, the transport of species in narrow spaces is explored with an eye to scaling. Surface diffusion (site to site hopping) becomes important when species are within a nanometer from a surface. Density functional theory (DFT) calculations are used to show the impact of different in-feature transport mechanisms on transport times relative to process timescales. In one final example, we show how optimization algorithms of different levels of complexity may be combined with an integrative approach to understand plasma-based unit processes.

The Role of Spring-Neap Phasing of Intermittent Lateral Exchange in the Ecosystem of a Channel-Shoal Estuary

Lateral variability is a fundamental feature of channel-shoal estuaries, and exchanges between the channel and shoal can play an important role in the dynamics of the ecosystem in each region. This lateral exchange of biomass interacts with vertical structure and variability, particularly in the channel, to define algal biomass accumulation in the estuary. In this paper, we investigate how time-variable lateral exchange affects phytoplankton dynamics with a biophysical model that links two water columns via intermittent exchange. We find that time variability in the exchange influences biomass by increasing concentrations in the shoals and decreasing them in the channel when the time variability happens on a timescale greater than the timescales of biological processes, and the strength of the effect increases with the period of the intermittency. At timescales of variability comparable to the spring-neap cycle, however, the interplay between lateral exchange and the ecosystem response is complicated by the fortnightly development of stratification in the channel and the role that channel-shoal interaction plays in defining that stratification. As a result, for lateral exchange variability with periods of 7 and 14 days, the influence of the shoal ecosystem on the channel ecosystem is sensitive to the phasing of exchange relative to the spring-neap cycle, due to the fact that neap tide exchanges can create stratification events that are larger in magnitude and duration than would occur in the absence of lateral exchange, causing the channel to transition into net positive growth conditions. We conclude that lateral exchange influences the estuarine ecosystem both directly, through the exchange of biomass between shoals with net positive growth and adjoining channels and indirectly through its role in defining stratification events that allow the channel itself to have net positive growth.

The Relationship between Event Boundary Strength and Pattern Shifts across the Cortical Hierarchy during Naturalistic Movie-viewing.

Our continuous experience is spontaneously segmented by the brain into discrete events. However, the beginning of a new event (an event boundary) is not always sharply identifiable: Phenomenologically, event boundaries vary in salience. How are the response profiles of cortical areas at event boundaries modulated by boundary strength during complex, naturalistic movie-viewing? Do cortical responses scale in a graded manner with boundary strength, or do they merely detect boundaries in a binary fashion? We measured "cortical boundary shifts" as transient changes in multivoxel patterns at event boundaries with different strengths (weak, moderate, and strong), determined by across-participant agreement. Cortical regions with different processing timescales were examined. In auditory areas, which have short timescales, cortical boundary shifts exhibited a clearly graded profile in both group-level and individual-level analyses. In cortical areas with long timescales, including the default mode network, boundary strength modulated pattern shift magnitude at the individual participant level. We also observed a positive relationship between boundary strength and the extent of temporal alignment of boundary shifts across different levels of the cortical hierarchy. In addition, hippocampal activity was highest at event boundaries for which cortical boundary shifts were most aligned across hierarchical levels. Overall, we found that event boundary strength modulated cortical pattern shifts strongly in sensory areas and more weakly in higher-level areas and that stronger boundaries were associated with greater alignment of these shifts across the cortical hierarchy.

Geological factors in the sustainable management of mine water heating, cooling and thermal storage resources in the UK

Re-use of the UK's coal mine water heating, cooling and thermal storage resource is increasing in scale and the number of schemes. The upward trajectory requires 3D planning, regulation and licensing to manage sustainable deployment. We review geological factors controlling thermal and flow processes in the anthropogenically-altered subsurface, critical for resource management with multiple users of the same space. Potential interactions of mine water geothermal schemes with the wider environment are also summarized, leading towards concepts of 3D mine water thermal blocks, protection zones, or management strategies integrating heating, cooling and storage demands. Factors such as the magnitude, extent and timescale of thermal processes to underpin management approaches are poorly quantified by data measured at-scale under varying pumping rates and thermal loads. We demonstrate early insights of how two infrastructures, the UK Geoenergy Observatory in Glasgow and the Coal Authority's Mine Water Heat Living Lab in Gateshead, can measure and monitor heat-flow processes in real world settings to provide an evidence base. For example, a thermal storage test at Glasgow showed rapid temperature changes in the rock and mine workings at the re-injection borehole and indicated an influence of lithologically-controlled transmissivity and thermal conductivity on temperature dissipation and recovery.

Diffusion-induced stress in crystals: Implications for timescales of mountain building

Intracrystalline chemical diffusion offers valuable insights into the durations of metamorphic and igneous processes. However, it can yield timescale estimates for orogenic and subduction zone events that are considerably shorter than those obtained via isotopic geochronology. One potential explanation that has been offered for the discrepancy is that the interdiffusion of species with different atomic or ionic radii may generate intracrystalline, compositional stresses that alter or limit diffusional relaxation. In this study we test this idea by developing and applying the compositional stress theory of materials scientists F. Larché and J. Cahn to garnet from the Barrovian sillimanite zone, Scotland. Relaxed contacts from the garnet, independent diffusion chronometers, and thermal modeling all indicate a >100 kyr duration for peak temperature metamorphism. Nonetheless, the garnet records sharp, μm-scale variations in calcium and iron contents that standard diffusion treatments predict should relax in 1–10 kyr at peak temperature conditions. Our results show that the development of compositional stress during diffusional relaxation can explain the preservation of the observed short wavelength compositional oscillations at a >100 kyr timescale. Thus, it may be necessary to account for compositional stress when modeling diffusion in solid solutions with appreciable differences in their endmember molar volumes. This will be particularly relevant when considering sharp, μm-scale chemical gradients involving grossular, the garnet endmember with the largest molar volume relative to pyrope, almandine, and spessartine. Neglecting compositional stress in such cases could result in the underestimation of the timescales of lithospheric processes by potentially orders of magnitude. The effects of compositional stress in garnet are predicted to be the most pronounced under amphibolite and blueschist–eclogite facies conditions. At lower temperatures diffusion is limited, and at higher temperatures both plastic deformation and more ideal solid solution behavior will act to diminish the impact of stress.

Bayesian frameworks for integrating petrologic and geochronologic data

Constraining the absolute time and duration of geologic processes is one of the great challenges and goals in Earth sciences. Increasingly, the integration of geochronologic constraints with petrologic information is being qualitatively applied to understanding the timescales of metamorphic, igneous, tectonic, and fluid-related processes. Many rocks and geochronometers preserve relative age constraints such as compositional zoning or cross cutting relationships. This prior information can be formalized in a Bayesian statistical framework to generate a probabilistic posterior chronology. As we show here, these “age-sequence” models can enhance precision on geochronologic dates and rates and insight into tectonic models. Bayesian modeling of complex, concentrically, zoned monazite from the northern Appalachian orogen was used to develop a detailed temperature-time history through the Acadian (∼405–395 Ma) and Neoacadian (∼380–350 Ma) orogenies with significantly reduced uncertainties (40–70 %). Modeling of zoned monazite from a southern Trans-Hudson orogen granulite yielded durations of 0.5+9/-0.4 Ma and 20+5/-8 Ma for biotite-dehydration melting and suprasolidus conditions, respectively. The relatively short intervals of heating and peak conditions are consistent with a back-arc tectonic setting. A complementary approach, Bayesian change point detection, provides a framework to constrain the timing of compositional changes that can be linked with metamorphic reactions. Applying this approach in the northern Appalachian orogen demonstrates contrasting durations of low-Y monazite crystallization (∼10 vs ∼30 myr) in regions with different pressure-temperature histories. Compositionally distinct monazite domains can be linked with garnet stability, which provides a key constraint on tectonic models. Bayesian statistical analysis represent a powerful tool that can be widely applied to refine the absolute time and duration of geologic processes. A more objective and reproducible set of interpretations are produced by this more formal, although not necessarily complex, statistical analysis.

Time‐Resolved Trigger Processes Leading to the Plinian Eruptions at Sakurajima Volcano, Japan

AbstractMafic magma recharge of crustal reservoirs and subsequent magma mixing has been considered a direct trigger of volcanic eruptions. However, although recharge frequently occurs in many active volcanoes, it rarely leads to an eruption immediately, making its role as a trigger ambiguous. Sakurajima volcano, Japan, has vigorously erupted three times since the 15th century following a common process; mixed magmas after recharge were once stored in a shallow, thick conduit before each eruption (conduit pre‐charge). We reconstructed the magma migration with a high time resolution by diffusion modeling on orthopyroxene and magnetite. Orthopyroxene phenocrysts recorded prolonged diffusive re‐equilibration timescales of years or more after recharge‐and‐mixing. Magnetite, which has the fastest elemental diffusivity among the phenocrysts examined, predominantly lacks zoning. This demonstrates that the mineral phase was re‐equilibrated with surrounding magma and homogenized via elemental diffusion after the final magmatic perturbation, implying the final repose of the shallow pre‐charged magma body for more than several tens of days. After this shallow stagnation period, the Plinian magmas began to ascend and reached the surface within 55 hr. Mass balance calculations show that crystallization‐driven vesiculation upon pre‐charge can produce overpressure sufficient to cause an eruption. The Sakurajima cases demonstrate the hierarchical timescales of trigger processes leading to the explosive eruptions.

Olivine Time-Capsules Constrain the Pre-Eruptive History of Holocene Basalts, Mount Meager Volcanic Complex, British Columbia, Canada

Abstract The Canadian segment of the Cascade Volcanic Arc (i.e. the Garibaldi Volcanic Belt) comprises more than 100 eruptive centres, spanning the entire Quaternary period (Pleistocene to Holocene in age), and with deposits ranging in composition from alkaline basalt to rhyolite. At least one of the volcanoes is currently active; Mount Meager / Q̓welq̓welústen erupted explosively 2360 years BP and has ongoing fumarolic activity. Long-term forecasting of eruption frequency and style depends on reconstruction of the history and timescales of magmatic processes preceding previous volcanic eruptions. Utilising diffusion chronometry, we investigate the Mount Meager Volcanic Complex focusing on Holocene olivine-phyric basalts (Lillooet Glacier basalts) exposed by the retreat of the Lillooet Glacier. We identify two distinct olivine populations in samples of quenched, glassy basalt lavas that record different magmatic processes and histories. Glomerocrysts of Fo83 olivine phenocrysts, entrained and transported by a hot mafic input, form Population 1. These exhibit resorption and normally zoned outermost rim compositions of Fo76–78; a third of them also show interior reverse compositional zoning. A second population of skeletal microphenocrysts have the same composition as the phenocryst rims (i.e. Fo76–78) and are in equilibrium with the adjacent matrix glass. We estimate the pre-eruptive temperature-fO2 conditions in a shallow reservoir (100 MPa; ~3 km) for a melt with H2O content of 0.5 to 1 wt % as ~1097°C to 1106°C (± 30°C), and NNO + 0.5 (±1.1), respectively. Using these input parameters, we report Fe-Mg diffusion chronometry results for 234 normally zoned profiles from 81 olivine phenocrysts. Diffusion modelling of compositional profiles in oriented crystals indicates pre-eruptive magmatic residence times of 1 to 3 months. These remarkably short residence times in shallow reservoirs prior to eruption suggest very short periods of unrest may precede future eruptions.

Transient frequency preference responses in cell signaling systems

Ligand–receptor systems, covalent modification cycles, and transcriptional networks are the fundamental components of cell signaling and gene expression systems. While their behavior in reaching a steady-state regime under step-like stimulation is well understood, their response under repetitive stimulation, particularly at early time stages is poorly characterized. Yet, early-stage responses to external inputs are arguably as informative as late-stage ones. In simple systems, a periodic stimulation elicits an initial transient response, followed by periodic behavior. Transient responses are relevant when the stimulation has a limited time span, or when the stimulated component’s timescale is slow as compared to the timescales of the downstream processes, in which case the latter processes may be capturing only those transients. In this study, we analyze the frequency response of simple motifs at different time stages. We use dose-conserved pulsatile input signals and consider different metrics versus frequency curves. We show that in ligand–receptor systems, there is a frequency preference response in some specific metrics during the transient stages, which is not present in the periodic regime. We suggest this is a general system-level mechanism that cells may use to filter input signals that have consequences for higher order circuits. In addition, we evaluate how the described behavior in isolated motifs is reflected in similar types of responses in cascades and pathways of which they are a part. Our studies suggest that transient frequency preferences are important dynamic features of cell signaling and gene expression systems, which have been overlooked.

A tight N/O–potential relation in star-forming galaxies

ABSTRACT We report a significantly tighter trend between gaseous N/O and $M_*/R_\mathrm{ e}$ (a proxy for gravitational potential) than has previously been reported between gaseous metallicity and $M_*/R_\mathrm{ e}$, for star-forming galaxies in the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. We argue this result to be a consequence of deeper potential wells conferring greater resistance to metal outflows while also being associated with earlier star-formation histories, combined with N/O being comparatively unaffected by metal-poor inflows. The potential–N/O relation thus appears to be both more resistant to short time-scale baryonic processes and also more reflective of a galaxy’s chemical evolution state, when compared to previously considered relations.

Timescales of Ecological Processes, Settling, and Estuarine Transport to Create Estuarine Turbidity Maxima: An Application of the Peter–Parker Model

The estuarine exchange flow increases the longitudinal dispersion of passive tracers and trap sinking particles, potentially creating an estuarine turbidity maximum (ETM): a localized maximum of suspended particulate matter concentration in an estuary. The ETM can have many implications: dead zones due to increased turbidity or hypoxia from organic matter decomposition, naval navigation challenges, and other water quality problems. Using timescales, we investigate how the interaction between exchange flow and particle sinking leads to ETMs by modeling a sinking tracer in an idealized box model of the Total Exchange Flow (TEF) first developed by Parker MacCready. Results indicate that the balance of particle sinking and vertical mixing is critical to determining ETM size and location. We then focus on the role of ecology in ETM formation through the use of the Peter–Parker Model, a new biophysical model which combines the TEF box model with a Nutrient–Phytoplankton–Zooplankton–Detritus (NPZD) model, the likes of which were first developed by Peter J.S. Franks. Detritus sinking rates similarly influence detritus peak concentration and location (an ETM), but detritus ETMs occur in a different location than the sinking tracer due to the influence of biological factors, which create a time lag of about 1 day. Lastly, we characterize the flow of the models with a dimensionless parameter that compares timescales and summarizes the dynamics of the sinking tracer in ETM formation and that can be used across systems.

Exploring temporal sensitivity in the brain using multi-timescale language models: an EEG decoding study

Abstract The brain’s ability to perform complex computations at varying timescales is crucial, ranging from understanding single words to grasping the overarching narrative of a story. Recently, multi-timescale long short-term memory (MT-LSTM) models (Mahto et al. 2020; Jain et al. 2020) have been introduced, which use temporally-tuned parameters to induce sensitivity to different timescales of language processing (i.e. related to near/distant words). However, there has not been an exploration of the relation between such temporally-tuned information processing in MT-LSTMs and the brain’s language processing using high temporal resolution recording modalities, such as electroencephalography (EEG). To bridge this gap, we used an EEG dataset recorded while participants listened to Chapter 1 of “Alice in Wonderland” and trained ridge regression models to predict the temporally-tuned MT-LSTM embeddings from EEG responses. Our analysis reveals that EEG signals can be used to predict MT-LSTM embeddings across various timescales. For longer timescales, our models produced accurate predictions within an extended time window of ±2 s around word onset, while for shorter timescales, significant predictions are confined to a narrow window ranging from −180 ms to 790 ms. Intriguingly, we observed that short timescale information is not only processed in the vicinity of word onset but also at distant time points. These observations underscore the parallels and discrepancies between computational models and the neural mechanisms of the brain. As word embeddings are used more as in silico models of semantic representation in the brain, a more explicit consideration of timescale-dependent processing enables more targeted explorations of language processing in humans and machines.

Linking terrestrial biogeochemical processes and water ages to catchment water quality: A new Damköhler analysis based on coupled modeling of isotope tracers and nitrate dynamics

Catchment-scale nitrate dynamics involve complex coupling of hydrological transport and biogeochemical transformations, imposing challenges for source control of diffuse pollution. The Damköhler number (Da) offers a dimensionless dual-lens concept that integrates the timescales of exposure and processing, but quantifying both timescales in heterogeneous catchments remains methodologically challenging. Here, we propose a novel spatio-temporal framework for catchment-scale quantification of Da based on the ecohydrological modeling platform EcH2O-iso that coupled isotope-aided water age tracking and nitrate modeling. We examined Da variability of soil denitrification in the heterogeneous Selke catchment (456 km2, central Germany). Results showed that warm-season soil denitrification was of catchment-wide significance (Da >1), while its high spatial variations were co-determined by varying exposure times and removal efficiencies (e.g., channel-connected lowland areas are hotspots). Moreover, Da seasonally shifted from processing-dominance to transport-dominance during the wet-spring season (from >1 to <1), implying important linkages between summer terrestrial denitrification and subsequent winter river water quality. Under the prolonged 2018–2019 droughts, denitrification removal generally reduced, resulting in further accumulation in agricultural soils. Moreover, the space-time responses of Da variability indicated important implications for catchment water quality. The older water in lowland areas exhibited extra risks of groundwater contamination, whilst agricultural areas in the hydrologically responsive uplands became sensitive hotspots for export and river water pollution. Importantly, the lowland pixels intersecting river channels exhibited high removal efficiencies, as well as high resilience to the disturbances (wet-spring Da shifted to >1 under drought conditions). The proposed catchment-wide Da framework is implied by mechanistic modeling, which is transferable across various environmental conditions. This could shed light on understanding of catchment N processes, and thus providing site-specific implications of non-point source pollution controls.