The application of single‐atom catalysts (SACs) to high‐temperature hydrogenation requires materials that thermodynamically favor metal atom isolation over cluster formation. We demonstrate that Pd ...can be predominantly dispersed as isolated atoms onto TiO2 during the reverse water–gas shift (rWGS) reaction at 400 °C. Achieving atomic dispersion requires an artificial increase of the absolute TiO2 surface area by an order of magnitude and can be accomplished by physically mixing a precatalyst (Pd/TiO2) with neat TiO2 prior to the rWGS reaction. The in situ dispersion of Pd was reflected through a continuous increase of rWGS activity over 92 h and supported by kinetic analysis, infrared and X‐ray absorption spectroscopies and scanning transmission electron microscopy. The thermodynamic stability of Pd under high‐temperature rWGS conditions is associated with Pd‐Ti coordination, which manifests upon O‐vacancy formation, and the artificial increase in TiO2 surface area.
Dilution of Pd/TiO2 with neat TiO2 results in the formation of atomically dispersed Pd under reverse water–gas shift (rWGS) reaction conditions at 400 °C and a several fold increase in activity.
Solar-type stars exhibit a rich variety of magnetic activity. Seeking to explore the convective origins of this activity, we have carried out a series of global three-dimensional magnetohydrodynamic ...simulations with the anelastic spherical harmonic code. Here we report on the dynamo mechanisms achieved as the effects of artificial diffusion are systematically decreased. The simulations are carried out at a nominal rotation rate of three times the solar value (3 Omega sub(middot in circle)), but similar dynamics may also apply to the Sun. Our previous simulations demonstrated that convective dynamos can build persistent toroidal flux structures (magnetic wreaths) in the midst of a turbulent convection zone and that high rotation rates promote the cyclic reversal of these wreaths. Here we demonstrate that magnetic cycles can also be achieved by reducing the diffusion, thus increasing the Reynolds and magnetic Reynolds numbers. In these more turbulent models, diffusive processes no longer play a significant role in the key dynamical balances that establish and maintain the differential rotation and magnetic wreaths. Magnetic reversals are attributed to an imbalance in the poloidal magnetic induction by convective motions that is stabilized at higher diffusion levels. Additionally, the enhanced levels of turbulence lead to greater intermittency in the toroidal magnetic wreaths, promoting the generation of buoyant magnetic loops that rise from the deep interior to the upper regions of our simulated domain. The implications of such turbulence-induced magnetic buoyancy for solar and stellar flux emergence are also discussed.
Global 3D simulations of solar giant-cell convection have provided significant insight into the processes which yield the Sun's observed differential rotation and cyclic dynamo action. However, as we ...move to higher-resolution simulations a variety of codes have encountered what has been termed the convection conundrum. As these simulations increase in resolution and hence the level of turbulence achieved, they tend to produce weak or even anti-solar differential rotation patterns associated with a weak rotational influence (high Rossby number) due to large convective velocities. One potential culprit for this convection conundrum is the upper boundary condition applied in most simulations, which is generally impenetrable. Here we present an alternative stochastic plume boundary condition which imposes small-scale convective plumes designed to mimic near-surface convective downflows, thus allowing convection to carry the majority of the outward solar energy flux up to and through our simulated upper boundary. The use of a plume boundary condition leads to significant changes in the convective driving realized in the simulated domain and thus to the convective energy transport, the dominant scale of the convective enthalpy flux, and the relative strength of the strongest downflows, the downflow network, and the convective upflows. These changes are present even far from the upper boundary layer. Additionally, we demonstrate that, in spite of significant changes, giant cell morphology in the convective patterns is still achieved with self-organization of the imposed boundary plumes into downflow lanes, cellular patterns, and even rotationally aligned banana cells in equatorial regions. This plume boundary presents an alternative pathway for 3D global convection simulations where driving is non-local and may provide a new approach toward addressing the convection conundrum.
Spinal cord circuits play crucial roles in transmitting pain, but the underlying activity patterns within and across spinal segments in behaving mice have remained elusive. We developed a wearable ...widefield macroscope with a 7.9-mm
field of view, ~3- to 4-μm lateral resolution, 2.7-mm working distance and <10-g overall weight and show that highly localized painful mechanical stimuli evoke widespread, coordinated astrocyte excitation across multiple spinal segments.
Identifying the role of oxide supports in transition-metal catalysis is critical toward our understanding of heterogeneous catalysis. The water–gas shift (WGS) reaction is a prototypical example ...where the oxide support dictates catalytic activity, yet the cause for this remains uncertain. Herein, we show that a single descriptorthe equilibrium constant for hydroxyl formationrelates the WGS turnover frequency across disparate oxide supports. The dissimilar equilibrium constant, or oxophilicity, between early and late transition metals exemplifies the utility of metal–support interfacial sites to circumvent adsorption-energy scaling restrictions, thereby providing bifunctional gains for the WGS reaction class. In relation, the equilibrium constant for hydroxyl formation is equivalent to the equilibrium constant for the formal heterolytic dissociation of hydrogen and therefore reflects the ability of the metal–support interface to participate in hydrogen heterolysis. The ubiquitous coexistence, yet divergent chemical reactivity of homo- and heterolytically activated hydrogen, renders the identity of the oxide support central toward our understanding of hydrogenation catalysis.
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•Supported iron nanoparticles catalyze the hydrodeoxygenation of fatty acids.•The catalyst favors heavily hydrodeoxygenation over decarbonylation.•The reaction proceeds through a ...reverse Mars–Van-Krevelen mechanism.•The degree of oxidation of Fe controls the selectivity of the reaction.•The Fe catalyst was successfully used for hydroprocessing crude microalgal oil.
Iron nanoparticles supported on mesoporous silica nanoparticles (Fe-MSN) catalyze the hydrotreatment of fatty acids with high selectivity for hydrodeoxygenation over decarbonylation and hydrocracking. The catalysis is likely to involve a reverse Mars–Van Krevelen mechanism, in which the surface of iron is partially oxidized by the carboxylic groups of the substrate during the reaction. The strength of the metal–oxygen bonds that are formed affects the residence time of the reactants facilitating the successive conversion of carboxyl first into carbonyl and then into alcohol intermediates, thus dictating the selectivity of the process. The selectivity is also affected by the pretreatment of Fe-MSN, the more reduced the catalyst the higher the yield of hydrodeoxygenation product. Fe-MSN catalyzes the conversion of crude microalgal oil into diesel-range hydrocarbons.
Augmented renal clearance (ARC), a phenomenon of enhanced elimination of renal solutes, has been described in adult critically ill patients, but little is known about the phenomenon in children. The ...aim of this scoping review was to gather and summarize all evidence on ARC in pediatric patients to examine its breadth and depth including prevalence, risk factors, and pharmacokinetic alterations and identify any gaps for further areas of inquiry. PubMed, Embase, and Web of Science were searched for titles, abstracts, or keywords that focused on ARC. Non-English studies, reviews, and nonhuman studies were excluded. Reporting followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses for Scoping Reviews (PRISMA-ScR) guidelines. Data were extracted on article type, study details, patient population, ARC definition and prevalence, methods of renal function assessment, and study results. A total of 215 citations were found with 25 citations meeting the criteria for inclusion in pediatrics (2102 total patients); the majority of studies (84%) focused on pharmacokinetics (PK) of antimicrobial agents. The median/mean age range was 1.25-12 years. There were a total of 10 different definitions of ARC. The prevalence of ARC ranged from 7.8% to 78%. The most common method for documenting creatinine clearance (CrCl) was the modified Schwartz equation (64%). Only 20% of studies reported risk factors for ARC including low serum creatinine, increasing age, febrile neutropenia, male, septic shock, and treatment with antibiotics. Glycopeptide antimicrobials were the most evaluated class (42.9%) among the 21 antimicrobial drug studies. All studies reported increased drug clearance and/or poor probability of achieving target concentrations of the agents studied. ARC showed variable prevalence in pediatric patients likely due to the lack of a standard definition and many studies not considering age-related changes in CrCl with pediatric intensive care unit (PICU) patients. ARC was shown to impact PK of antibiotics commonly administered to pediatric patients, which may necessitate changes in standard dosing regimens.
While the spinal cord is known to play critical roles in sensorimotor processing, including pain-related signaling, corresponding activity patterns in genetically defined cell types across spinal ...laminae have remained challenging to investigate. Calcium imaging has enabled cellular activity measurements in behaving rodents but is currently limited to superficial regions. Here, using chronically implanted microprisms, we imaged sensory and motor-evoked activity in regions and at speeds inaccessible by other high-resolution imaging techniques. To enable translaminar imaging in freely behaving animals through implanted microprisms, we additionally developed wearable microscopes with custom-compound microlenses. This system addresses multiple challenges of previous wearable microscopes, including their limited working distance, resolution, contrast, and achromatic range. Using this system, we show that dorsal horn astrocytes in behaving mice show sensorimotor program-dependent and lamina-specific calcium excitation. Additionally, we show that tachykinin precursor 1 (Tac1)-expressing neurons exhibit translaminar activity to acute mechanical pain but not locomotion.
The selective hydrogenation of fatty acids to fatty alcohols can be achieved under moderate conditions (180 °C, 30 bar H2) by simultaneously supporting copper and iron oxides on mesoporous silica ...nanoparticles. The activity of the cosupported oxides is significantly higher than that of each supported metal oxide and of a physical mixture of both individually supported metal oxides. A strong interaction between both metal oxides is evident from dispersion, XRD, TPR, and acetic acid TPD measurements, which is likely responsible for the synergistic behavior of the catalyst. Copper oxide is reduced in situ to its metallic form and thereby activates hydrogen. It is proposed that hydrogen spills over to iron oxide where fatty acids bind and are selectively reduced to the alcohol.
The spinal cord is the primary neurological link between the brain and peripheral organs. How important it is in everyday life is apparent in patients with spinal cord injury or motoneuron disease, ...who have dramatically reduced musculoskeletal control or capacity to sense their environment. Despite its crucial role in sensory and motor processing little is known about the cellular and molecular signaling events that underlie spinal cord function under naturalistic conditions. While genetic, electrophysiological, pharmacological, and circuit tracing studies have revealed important roles for different molecularly defined neurons, these approaches insufficiently describe the moment-to-moment neuronal and non-neuronal activity patterns that underlie sensory-guided motor behaviors in health and disease. The recent development of imaging methods for real-time interrogation of cellular activity in the spinal cord of behaving mice has removed longstanding technical obstacles to spinal cord research and allowed new insight into how different cell types encode sensory information from mechanoreceptors and nociceptors in the skin. Here, we review the current state-of-the-art in interrogating cellular and microcircuit function in the spinal cord of behaving mammals and discuss current opportunities and technological challenges.
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