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Hydrodynamics Determine Tafel Slopes in Electrochemical CO₂ Reduction on Copper
No full textThe hydrodynamics of electrochemical CO₂ reduction (CO₂) systems is an insufficiently investigated area of research that has broad implications on catalyst activity and selectivity. While most previous reports are limited to laminar and CO₂-sparged systems, herein we address a wide range of hydrodynamics via electrolyte recirculation systems. We find that increased hydrodynamics at the electrode surface results directly in changes to the ethylene and methane Tafel slopes, demonstrating that mass transport is on equal footing with catalyst active sites in determining reaction mechanisms and the ensuing product distribution. Mass transport is traditionally considered to be in the purview of systems-level engineering, yet the present work shows that CO₂R mechanistic work must be considered in the context of the mass transport conditions. We extend our analysis to organic coatings, demonstrating that the films shield the active sites from variability in hydrodynamics and increase the residence time of CO so that it may be further reduced to desirable products
Flux exponent control predicts metabolic dynamics from network structure
No full textMetabolic dynamics such as stability of steady states, oscillations, lags and growth arrests in stress responses are important for microbial communities in human health, ecology, and metabolic engineering. Yet it is hard to model due to sparse data available on trajectories of metabolic fluxes. For this reason, a constraint-based approach called flux control (e.g., flux balance analysis) was invented to split metabolic systems into known stoichiometry (plant) and unknown fluxes (controller), so that data can be incorporated as refined constraints, and optimization can be used to find behaviors in scenarios of interest. However, flux control can only capture steady state fluxes well, limiting its application to scenarios with days or slower timescales. To overcome this limitation and capture dynamic fluxes, this work proposes a novel constraint-based approach, flux exponent control (FEC). FEC uses a different plant-controller split between the activities of catalytic enzymes and their regulation through binding reactions. Since binding reactions effectively regulate fluxes' exponents (from previous works), this yields the rule of FEC, that cells regulate fluxes' exponents, not the fluxes themselves as in flux control. In FEC, dynamic regulations of metabolic systems are solutions to optimal control problems that are computationally solvable via model predictive control. Glycolysis, which is known to have minute-timescale oscillations, is used as an example to demonstrate FEC can capture metabolism dynamics from network structure. More generally, FEC brings metabolic dynamics to the realm of control system analysis and design
Characterization of Transitional, High-Enthalpy Boundary Layers on a Slightly-Blunted Cone. Part I: Schlieren Imaging
No full textThis paper presents an experimental investigation into the boundary-layer stability of a slender cone in hypervelocity flow within the T5 reflected-shock tunnel. Schlieren imaging was utilized to characterize the frequency content and disturbance structures experienced within the boundary layer of a 5◦ cone in a Mach-5 freestream with high reservoir enthalpy, 8-10 MJ/kg. The effects of varying freestream Reynolds number and nose bluntness were examined. Second-mode frequency peaks between 1200-1300 kHz were identified in all cases, but they persisted over a longer extent in the sharper-nose cases. The bluntest nosetip case exhibited unique nonmodal structures which extended into the freestream, and the signature of the second-mode appeared limited to the near-wall region. N factors contours suggested interplay between second-mode content and frequency content outside the second-mode band. Cross-bicoherence calculations indicated that, for the sharper nosetip, nonlinear interactions between the second-mode fundamental and its first harmonic persisted to the point of breakdown. For the blunter nosetip, dominant nonlinear interactions involved low-frequency content
The Influence of Tidal Heating on the Habitability of Planets Orbiting White Dwarfs
No full textIn recent years, there have been a growing number of observations indicating the presence of rocky material in short-period orbits around white dwarfs. In this Letter, we revisit the prospects for habitability around these post-main-sequence star systems. In addition to the typically considered radiative input luminosity, potentially habitable planets around white dwarfs are also subjected to significant tidal heating. The combination of these two heating sources can, for a narrow range of planetary properties and orbital parameters, continuously maintain surface temperatures amenable for habitability for planets around white dwarfs over timescales up to 10 Gyr. We show that for a specific locus of orbital parameter space, tidal heating can substantially extend the timescale of continuous habitability for a planet around a white dwarf
Time-domain source parameter estimation of M_w 3–7 earthquakes in Japan from a large database of moment-rate functions
No full textTime-domain analyses of seismic waveforms have revealed diverse source complexity in large earthquakes (M_w > 7). However, source characteristics of small earthquakes have been studied by assuming a simple rupture pattern on the frequency domain. This study utilizes high-quality seismic network data from Japan to systematically address the source complexities and radiated energies of M_w 3–7 earthquakes on the time domain. We first determine the apparent moment-rate functions (AMRFs) of the earthquakes using the empirical Green's functions. Some of the AMRFs show multiple peaks, suggesting complex ruptures at multiple patches. We then estimate the radiated energies (E_R) of 1736 events having more than ten reliable AMRFs. The scaled energy (e_R = E_R/M₀) does not strongly depend on the seismic moment (M₀), focal mechanisms, or depth. The median value of e_R is 3.7 × 10⁻⁵, which is comparable to those of previous studies; however, e_R varies by approximately one order of magnitude among earthquakes. We measure the source complexity based on the radiated energy enhancement factor (REEF). The values of REEF differ among earthquakes, implying diverse source complexity. The values of REEF do not show strong scale dependence for M_w 3–7 earthquakes, suggesting that the source diversity of smaller earthquakes is similar to that of larger earthquakes at their representative spatial scales. Applying a simple spectral model (e.g. the ω²-source model) to complex ruptures may produce substantial estimation errors in source parameters
Mesoscale shock structure in particulate composites
No full textMultiscale experiments in heterogeneous materials and the knowledge of their physics under shock compression are limited. This study examines the multiscale shock response of particulate composites comprised of soda-lime glass particles in a PMMA matrix using full-field high speed digital image correlation (DIC) for the first time. Normal plate impact experiments, and complementary numerical simulations, are conducted at stresses ranging from 1.1 - 3.1 GPa to elucidate the mesoscale mechanisms responsible for the distinct shock structure observed in particulate composites. The particle velocity from the macroscopic measurement at continuum scale shows a relatively smooth velocity profile, with shock thickness decreasing with an increase in shock stress, and the composite exhibits strain rate scaling as the second power of the shock stress. In contrast, the mesoscopic response was highly heterogeneous, which led to a rough shock front and the formation of a train of weak shocks traveling at different velocities. Additionally, the normal shock was seen to diffuse the momentum in the transverse direction, affecting the shock rise and the rounding-off observed at the continuum scale measurements. The numerical simulations indicate that the reflections at the interfaces, wave scattering, and interference of these reflected waves are the primary mechanisms for the observed rough shock fronts
Synchronous motor imagery and visual feedback of finger movement elicit the moving rubber hand illusion, at least in illusion-susceptible individuals
No full textRecent evidence suggests that imagined auditory and visual sensory stimuli can be integrated with real sensory information from a different sensory modality to change the perception of external events via cross-modal multisensory integration mechanisms. Here, we explored whether imagined voluntary movements can integrate visual and proprioceptive cues to change how we perceive our own limbs in space. Participants viewed a robotic hand wearing a glove repetitively moving its right index finger up and down at a frequency of 1 Hz, while they imagined executing the corresponding movements synchronously or asynchronously (kinesthetic-motor imagery); electromyography (EMG) from the participants’ right index flexor muscle confirmed that the participants kept their hand relaxed while imagining the movements. The questionnaire results revealed that the synchronously imagined movements elicited illusory ownership and a sense of agency over the moving robotic hand—the moving rubber hand illusion—compared with asynchronously imagined movements; individuals who affirmed experiencing the illusion with real synchronous movement also did so with synchronous imagined movements. The results from a proprioceptive drift task further demonstrated a shift in the perceived location of the participants’ real hand toward the robotic hand in the synchronous versus the asynchronous motor imagery condition. These results suggest that kinesthetic motor imagery can be used to replace veridical congruent somatosensory feedback from a moving finger in the moving rubber hand illusion to trigger illusory body ownership and agency, but only if the temporal congruence rule of the illusion is obeyed. This observation extends previous studies on the integration of mental imagery and sensory perception to the case of multisensory bodily awareness, which has potentially important implications for research into embodiment of brain–computer interface controlled robotic prostheses and computer-generated limbs in virtual reality
A comprehensive re-look into Jurassic-Cretaceous Neotethyan active margin in Iran: Evidence of deep mantle flow into subduction magma factory and formation of transitional basalts
No full textSubduction zones display the most diverse magma compositions from various calc-alkaline differentiates to alkaline mafic associations, but mechanisms generating Nb-Enriched Basalts (NEB) and High-Nb Basalts (HNB) in such settings have received less attention from the researchers. Occurrences of NEB and HNB magmas in the Mesozoic Neotethyan active margin in Iran, known as the Sanandaj-Sirjan Zone, provide an excellent natural lab for examining this interesting petrologic puzzle. The Middle-Jurassic typical calc-alkaline arc plutons exhibit a NW-SE subduction parallel trend. In the northwestern sector of the zone, the Late Jurassic–Early Cretaceous magmatic rocks (JCMR) define a chain that transects the Middle-Jurassic arc trend. The two cross-cutting magmatic chains are chemically and genetically different. The JCMR include three distinct compositional groups: (i) tholeiites that are depleted in high-field-strength elements (HFSE) and show subduction-related geochemical fingerprints, (ii) NEB with higher abundances of Nb and other HFSE, and (iii) HNB with the highest abundances of Nb and other HFSE. The latter two groups do not display typical arc signatures and are transitional between arc and plume-type magmas. These three groups of rocks show linear major and trace element, and Sr–Nd isotopic variation trends extending from Mid-Ocean Ridge Basalts-like tholeiites to Oceanic Island Basalts-like HNB. Hence, a two-component mixing process is suggested for explaining the compositional variation of the JCMR. We propose that a vertical window resulted from slab tear created the geodynamic environment for juxtaposition of magmas originated at different mantle depths and formation of the transitional basalts by magma mixing
Rotation Periods, Inclinations, and Obliquities of Cool Stars Hosting Directly Imaged Substellar Companions: Spin-Orbit Misalignments Are Common
No full textThe orientation between a star’s spin axis and a planet’s orbital plane provides valuable information about the system’s formation and dynamical history. For non-transiting planets at wide separations, true stellar obliquities are challenging to measure, but lower limits on spin–orbit orientations can be determined from the difference between the inclination of the star’s rotational axis and the companion’s orbital plane (Δi). We present results of a uniform analysis of rotation periods, stellar inclinations, and obliquities of cool stars (SpT ≳ F5) hosting directly imaged planets and brown dwarf companions. As part of this effort, we have acquired new v sin i_* values for 22 host stars with the high-resolution Tull spectrograph at the Harlan J. Smith telescope. Altogether our sample contains 62 host stars with rotation periods, most of which are newly measured using light curves from the Transiting Exoplanet Survey Satellite. Among these, 53 stars have inclinations determined from projected rotational and equatorial velocities, and 21 stars predominantly hosting brown dwarfs have constraints on Δi. Eleven of these (52₋₁₁⁺¹⁰% of the sample) are likely misaligned, while the remaining 10 host stars are consistent with spin–orbit alignment. As an ensemble, the minimum obliquity distribution between 10 and 250 au is more consistent with a mixture of isotropic and aligned systems than either extreme scenario alone—pointing to direct cloud collapse, formation within disks bearing primordial alignments and misalignments, or architectures processed by dynamical evolution. This contrasts with stars hosting directly imaged planets, which show a preference for low obliquities. These results reinforce an emerging distinction between the orbits of long-period brown dwarfs and giant planets in terms of their stellar obliquities and orbital eccentricities
Editorial: Advanced water splitting technologies development: Best practices and protocols
No full textAs the level of deployment and utilization of renewable energy sources, including wind and solar, continues to rise, large-scale, long-term energy storage technologies that could accommodate weekly and seasonal energy fluctuations will play a significant role in the overall deployment of renewable energies in the future. Harnessing and storing renewable energy resources via electrochemical, photoelectrochemical, or thermochemical processes by converting renewable energy into sustainable (energy storage) fuels have the potential to meet the long-term, terawatt scale energy storage challenge. Renewable hydrogen production is the cornerstone for sustainable fuel production and deep decarbonization of multiple sectors in our society. Cost-competitive clean hydrogen provides value to applications, such as 1) in the transportation sector for fuel cell vehicles, 2) in the electric grid sector for system stability and load balancing, and 3) in the industrial sector with metal refineries, cement production, and biomass upgrading (carbon-free fertilizer production). In addition, coupling clean renewable hydrogen with the carbon and nitrogen cycles enables known and well-established thermal-chemical processes to generate renewable hydrocarbon fuels and ammonia. The Advanced Water Splitting Technologies (AWST): low temperature electrolysis (LTE), high temperature electrolysis (HTE), photoelectrochemical (PEC) and solar thermo-chemical hydrogen (STCH) provide four unique and parallel approaches to produce low cost, low greenhouse gas (GHG) emission hydrogen at scale (Figure 1). Cost competitive clean hydrogen production using these four technologies is a current high priority focus for governments and industry. In June of 2022, the U.S. Department of Energy (DOE) launched the first in a series of Earthshot Initiatives. The Hydrogen Shot, “1 1 1” aims to reduce the cost of clean hydrogen by more than 80% to one dollar per one kilogram in 1 decade ($1/kg H₂). The European Green Deal and the International Energy Agency (IEA) have implemented a strong focus on green hydrogen production for a clean and secure energy future