Variations in water economy traits in two Sphagnum species across their distribution boundaries.

PREMISE: We assessed changes in traits associated with water economy across climatic gradients in the ecologically similar peat mosses Sphagnum cuspidatum and Sphagnum lindbergii. These species have parapatric distributions in Europe and have similar niches in bogs. Sphagnum species of bogs are closely related, with a large degree of microhabitat niche overlap between many species that can be functionally very similar. Despite this, ecologically similar species do have different distributional ranges along climatic gradients that partly overlap. These gradients may favor particular Sphagnum traits, especially in relation to water economy, which can be hypothesized to drive species divergence by character displacement. METHODS: We investigated traits relevant for water economy of two parapatric bryophytes (Sphagnum cuspidatum and S. lindbergii) across the border of their distributional limits. We included both shoot traits and canopy traits, i.e., collective traits of the moss surface, quantified by photogrammetry. RESULTS: The two species are ecologically similar and occur at similar positions along the hydrological gradient in bogs. The biggest differences between the species were expressed in the variations of their canopy surfaces, particularly surface roughness and in the responses of important traits such as capitulum mass to climate. We did not find support for character displacement, because traits were not more dissimilar in sympatric than in allopatric populations. CONCLUSIONS: Our results suggest that parapatry within Sphagnum can be understood from just a few climatic variables and that climatic factors are stronger drivers than competition behind trait variation within these species of Sphagnum.

Size-dependent diffusion of supported metal nanoclusters: mean-field-type treatments and beyond for faceted clusters.

Nanostructured systems are intrinsically metastable and subject to coarsening. For supported 3D metal nanoclusters (NCs), coarsening can involve NC diffusion across the support and subsequent coalescence (as an alternative to Ostwald ripening). When used as catalysts, this leads to deactivation. The dependence of diffusivity, DN, on NC size, N (in atoms), controls coarsening kinetics. Traditional mean-field (MF) theory for DNversus N assumes that NC diffusion is mediated by independent random hopping of surface adatoms with low coordination, and predicts that DN ∼ hN-4/3neq. Here, h = ν exp[-Ed/(kBT)] denotes the hop rate, and neq = exp[-Eform/(kBT)] the density of those adatoms. The adatom formation energy, Eform, approaches a finite large-N limit, as does the effective barrier, Eeff = Ed + Eform, for NC diffusion. This MF theory is critically assessed for a realistic stochastic atomistic model for diffusion of faceted fcc metal NCs with a {100} facet epitaxially attached to a (100) support surface. First, the MF formulation is refined to account for distinct densities and hop rates for surface adatoms on different facets and along the base contact line, and to incorporate the exact values of Eform and neqversus N for our model. MF theory then captures the occurrence of local minima in DNversus N at closed-shell sizes, as shown by KMC simulation. However, the MF treatment also displays fundamental shortcomings due to the feature that diffusion of faceted NCs is actually dominated by a cooperative multi-step process involving disassembling and reforming of outer layers on side facets. This mechanism leads to an Eeff which is well above MF values, and which increases with N, features captured by a beyond-MF treatment.

The use of autorefractors using the image-size principle in determining on-axis and off-axis refraction. Part 1: Analysis of optical principles of autorefractors.

PURPOSE: To study the optical principles and properties of autorefractors that use the image-size principle in which the size of the reimaged retinal image determines refraction. METHODS: The retinal illumination and reimaging of the retinal image were described, as were variations in the basic system. Imaging was determined for systems in which the light source is either diverging or converging as it passes into the eye. Equations were determined to describe the dependence of refraction on the heights and angles of incoming and outgoing beams, and refraction error was determined when eye position was not correct. RESULTS: The fundamental refraction equation is DE=±(α+θ)/h1 where DE is refraction, h1 is the beam height entering the eye, and θ and α are the angles of the incoming and outgoing beams, respectively. The negative sign outside the brackets applies if the beam focuses before entering the eye, while the positive sign applies if the beam focuses after entering the eye. When light is diverging as it reaches the anterior eye, hyperopia produces greater retinal image sizes than myopia. The opposite is the case when light is converging as it reaches the anterior eye. The effect of incorrect ocular longitudinal position on the measured refraction was determined; this produced errors identical to those for vertex errors with ophthalmic lenses. CONCLUSION: For image-size principle autorefractors, simple equations describe the dependence of measured refraction on the height and angle of the instrument beam as it enters the eye and the angle of the light, reflected back from the retina, after it exits the eye. Further work will investigate the validity of such instruments for determining peripheral refraction.

The use of autorefractors using the image-size principle in determining on-axis and off-axis refraction. Part 2: Theoretical study of peripheral refraction with the Grand Seiko AutoRef/Keratometer WAM-5500.

PURPOSE: To determine, through simulations, the likely validity of Grand-Seiko autorefractors with annular targets in peripheral refraction. METHODS: Using a physical model eye, the distance inside the eye to which the Grand Seiko AutoRef/Keratometer WAM-5500 beam was converging and the effective size of its outer diameter at the cornea were determined. Grand-Seiko refraction was calculated from Rx  = (θ + α)/h1 , where θ is the angle of the ingoing radiation beam, h1 is the height of the beam at the anterior cornea and α is the angle of the beam emerging from the eye following reflection at the retina. Two eye models were used: a Navarro schematic eye and a Navarro schematic eye with a contact lens having a highly positive aspheric front surface. RESULTS: The instrument beam was determined to be converging towards the eye to a distance of 24.4 mm behind the corneal vertex, with a 2.46 mm effective size outer diameter of the beam at the anterior cornea. The Grand-Seiko refractions provided accurate estimates of peripheral refraction for the model eyes. The results were closer to Zernike refractions than to Zernike paraxial refraction. Spherical aberration influenced refraction by up to 0.5 D, and peripheral coma had limited influence. CONCLUSION: Grand-Seiko autorefractors in current use, and having a circular annulus with an ingoing effective outer diameter at the front of the eye of about 2.4 mm, are likely to give valid peripheral refractions.

Nature of the Active Sites on Ni/CeO2 Catalysts for Methane Conversions.

Effective catalysts for the direct conversion of methane to methanol and for methane's dry reforming to syngas are Holy Grails of catalysis research toward clean energy technologies. It has recently been discovered that Ni at low loadings on CeO2(111) is very active for both of these reactions. Revealing the nature of the active sites in such systems is paramount to a rational design of improved catalysts. Here, we correlate experimental measurements on the CeO2(111) surface to show that the most active sites are cationic Ni atoms in clusters at step edges, with a small size wherein they have the highest Ni chemical potential. We clarify the reasons for this observation using density functional theory calculations. Focusing on the activation barrier for C-H bond cleavage during the dissociative adsorption of CH4 as an example, we show that the size and morphology of the supported Ni nanoparticles together with strong Ni-support bonding and charge transfer at the step edge are key to the high catalytic activity. We anticipate that this knowledge will inspire the development of more efficient catalysts for these reactions.

High Resource Utilization in Emergent Versus Elective General Surgery.

BACKGROUND: In an era of pay for performance metrics, we sought to increase understanding of factors driving high resource utilization (HRU) in emergent (EGS) versus same-day elective (SDGS) general surgery patients. METHODS: General surgery procedures from the 2016 ACS-NSQIP public use file were grouped according to the first four digits of the primary procedure CPT code. Groups having at least 100 of both elective and emergent cases were included (22 groups; 83,872 cases). HRU patients were defined as those in-hospital >7D, returned to the OR, readmitted, and/or had morbidity likely requiring an intensive care unit (ICU)stay. Independent NSQIP predictors of HRU were identified through forward regression; P for entry < 0.05, for exit > 0.10. RESULTS: Of all patients, 33% were HRU. The three highest HRU procedures (total colectomy, enterolysis, and ileostomy) comprised a higher proportion of EGS than SDGS cases (10.3 versus 2.6%, P < 0.001). The duration of operation was 40 Min lower in EGS after adjustment. Thirty-nine of the remaining 40 HRU predictors were higher in EGS including preoperative SIRS/Sepsis (50 versus 2%), ASA classification IV-V (31 versus 5%), albumin <3.5 g/dL (40 versus 12%), transfers (26 versus 2%, P's < 0.001), septuagenarians (35 versus 25%) and disseminated cancer (6.3 versus 4.8%, P's < 0.001); while sex did not differ. After adjustment, EGS patients remained more likely to be HRU (odds ratio 2.5, 95% CI 2.4 - 2.6, P < 0.001). CONCLUSIONS: EGS patients utilize significantly more resources than SDGS patients above what can be adjusted for in the clinically robust ACS-NSQIP dataset. Distinctive payment and value-based performance models are necessary for EGS.

Cortical Presynaptic Boutons Progressively Engulf Spinules as They Mature.

Despite decades of discussion in the neuroanatomical literature, the role of the synaptic "spinule" in synaptic development and function remains elusive. Canonically, spinules are finger-like projections that emerge from postsynaptic spines and can become enveloped by presynaptic boutons. When a presynaptic bouton encapsulates a spinule in this manner, the membrane apposition between the spinule and surrounding bouton can be significantly larger than the membrane interface at the synaptic active zone. Hence, spinules may represent a mechanism for extrasynaptic neuronal communication and/or may function as structural "anchors" that increase the stability of cortical synapses. Yet despite their potential to impact synaptic function, we have little information on the percentages of developing and adult cortical bouton populations that contain spinules, the percentages of these cortical spinule-bearing boutons (SBBs) that contain spinules from distinct neuronal/glial origins, or whether the onset of activity or cortical plasticity are correlated with increased prevalence of cortical SBBs. Here, we employed 2D and 3D electron microscopy to determine the prevalence of spinules in excitatory presynaptic boutons at key developmental time points in the primary visual cortex (V1) of female and male ferrets. We find that the prevalence of SBBs in V1 increases across postnatal development, such that ∼25% of excitatory boutons in late adolescent ferret V1 contain spinules. In addition, we find that a majority of spinules within SBBs at later developmental time points emerge from postsynaptic spines and adjacent boutons/axons, suggesting that synaptic spinules may enhance synaptic stability and allow for axo-axonal communication in mature sensory cortex.

Silver Adsorption on Calcium Niobate(001) Nanosheets: Calorimetric Energies That Explain Sinter-Resistant Support.

Metal nanoparticles deposited on oxide supports are essential to many technologies, including catalysts, fuel cells, and electronics. Therefore, understanding the chemical bonding strength between metal nanoparticles and oxide surfaces is of great interest. The adsorption energetics, adhesion energy, and adsorbate structure of Ag on dehydrated HCa2Nb3O10(001) nanosheets at 300 K have been studied using metal adsorption calorimetry and surface spectroscopies. These dehydrated ("dh") calcium niobate nanosheets (dh-HCa2Nb3O10(001)) have the stoichiometry Ca4Nb6O19. They impart unusual stability to metal nanoparticles when used as catalyst supports and are easy-to-prepare by Langmuir-Blodgett (LB) techniques, highly ordered, and essentially single-crystal surfaces of mixed oxides with a huge ratio of terrace to edge sites. Below the monolayer coverage, Ag grows on dh-HCa2Nb3O10(001) as 2D islands of thickness ∼2 layers. The differential heat of Ag adsorption is initially ∼303 kJ/mol, increasing slowly to ∼338 kJ/mol by 0.8 ML. At higher coverages, Ag atoms mainly add on top of these 2D islands, growing 3D nanoparticles of increasing thickness, as the heat decreases asymptotically toward silver's heat of sublimation (285 kJ/mol). The adhesion energy of Ag(s) to this Ca niobate surface is estimated to be 4.33 J/m2, larger than that on any oxide surface previously measured. This explains the sinter resistance reported for metal nanoparticles on this support. Electron transfer from Ag into the calcium niobate is also measured. These results demonstrate an easy way to do single-crystal-type surface science studies-and especially thermochemical measurements-on the complex surfaces of mixed oxides: using LB-deposited perovskite nanosheets and ultrahigh-vacuum annealing in O2.

Reduction of the therapeutic dose of silencing RNA by packaging it in extracellular vesicles via a pre-microRNA backbone.

A small percentage of the short interfering RNA (siRNA) delivered via passive lipid nanoparticles and other delivery vehicles reaches the cytoplasm of cells. The high doses of siRNA and delivery vehicle that are thus required to achieve therapeutic outcomes can lead to toxicity. Here, we show that the integration of siRNA sequences into a Dicer-independent RNA stem-loop based on pre-miR-451 microRNA-which is highly enriched in small extracellular vesicles secreted by many cell types-reduces the expression of the genes targeted by the siRNA in the liver, intestine and kidney glomeruli of mice at siRNA doses that are at least tenfold lower than the siRNA doses typically delivered via lipid nanoparticles. Small extracellular vesicles that efficiently package siRNA can significantly reduce its therapeutic dose.

Prognostic Role of Elevated Myeloperoxidase in Patients with Acute Coronary Syndrome: A Systemic Review and Meta-Analysis.

BACKGROUND: Myocardial inflammation following acute ischemic injury has been linked to poor cardiac remodeling and heart failure. Many studies have linked myeloperoxidase (MPO), a neutrophil and inflammatory marker, to cardiac inflammation in the setting of acute coronary syndrome (ACS). However, the prognostic role of MPO for adverse clinical outcomes in ACS patients has not been well established. METHODS: MEDLINE and Cochrane databases were searched for studies from 1975 to March 2018 that investigated the prognostic value of serum MPO in ACS patients. Studies which have dichotomized patients into a high MPO group and a low MPO group reported clinical outcomes accordingly and followed up patients for at least 30 days to be eligible for enrollment. Data were analyzed using random-effects model. Sensitivity analyses were conducted for quality control. RESULTS: Our meta-analysis included 13 studies with 9090 subjects and a median follow-up of 11.4 months. High MPO level significantly predicted mortality (odds ratio (OR) 2.03; 95% confidence interval (CI): 1.40-2.94; P < 0.001), whereas it was not significantly predictive of major adverse cardiac events and recurrent myocardial infarction (MI) (OR 1.28; CI: 0.92-1.77, P = 0.14 and OR 1.23; CI: 0.96-1.58, P = 0.101, respectively). Hypertension, diabetes mellitus, and age did not affect the prognostic value of MPO for clinical outcomes, whereas female gender and smoking status have a strong influence on the prognostic value of MPO in terms of mortality and recurrent MI (metaregression coefficient -8.616: 95% CI -14.59 to -2.633, P = 0.0048 and 4.88: 95% CI 0.756 to 9.0133, P = 0.0204, respectively). CONCLUSIONS: Our meta-analysis suggests that high MPO levels are associated with the risk of mortality and that MPO can be incorporated in risk stratification models that guide therapy of high-risk ACS patients.

Energies of Adsorbed Catalytic Intermediates on Transition Metal Surfaces: Calorimetric Measurements and Benchmarks for Theory.

Better catalysts and electrocatalysts are essential for the production and use of clean fuels with less pollution and improved energy efficiency, for making chemicals with less energy and environmental impact, for pollution abatement, and for many other future technologies needed to achieve environmentally friendlier energy supply and chemicals industry. Crucial for rational design of better catalyst and electrocatalyst materials is knowledge of the energies of elementary chemical reactions on late transition metal surfaces. This knowledge would also aid in designing more efficient and stable photocatalysts and batteries for harvesting and storing solar energy. These are all crucial for sustainable living with high quality. Herein, I review measurements of surface reaction energies involving many of the most common adsorbates formed as intermediates on late transition metal surfaces in catalytic and electrocatalytic reactions of interest for energy and environmental technologies. I focus on calorimetric measurements of the heat of molecular and dissociative adsorption of gases on single crystals (i.e., single crystal adsorption calorimetry, or SCAC) that allow the heats of formation of adsorbed intermediates in well-defined structures to be directly determined. Adsorption reactions are often irreversible, and in such cases SCAC is required to get these heats, since the other methods for measuring adsorption energies (equilibrium adsorption isotherms and temperature-programmed desorption) work only for reversible adsorption. Common examples of irreversible adsorption reactions are ones that produce adsorbed molecular fragments or adsorbed molecules such as olefins and aromatic molecules that bind very strongly to non-noble metals. When the heats of formation of different adsorbed molecular fragments are compared to each other, and to their values on different metal surfaces, they reveal which properties of the metal surface and the molecular fragments determine metal-adsorbate bond strengths, and clarify differences in catalytic reactivity between different metals. When combined with earlier adsorption energy measurements, these heats also provide a database of reliable energies of adsorbed catalytic intermediates that serve as crucial benchmarks to guide the development of improved computational methods for calculating the energetics of elementary steps on late transition metal surfaces (i.e., reaction energies and activation barriers), such as density functional theory. The energy accuracy of such computational estimates is crucial for the future of catalysis research and catalyst discovery.

Origin of Thermal and Hyperthermal CO2 from CO Oxidation on Pt Surfaces: The Role of Post-Transition-State Dynamics, Active Sites, and Chemisorbed CO2.

The post-transition-state dynamics in CO oxidation on Pt surfaces are investigated using DFT-based ab initio molecular dynamics simulations. While the initial CO2 formed on a terrace site on Pt(111) desorbs directly, it is temporarily trapped in a chemisorption well on a Pt(332) step site. These two reaction channels thus produce CO2 with hyperthermal and thermal velocities with drastically different angular distributions, in agreement with recent experiments (Nature, 2018, 558, 280-283). The chemisorbed CO2 is formed by electron transfer from the metal to the adsorbate, resulting in a bent geometry. While chemisorbed CO2 on Pt(111) is unstable, it is stable by 0.2 eV on a Pt(332) step site. This helps explain why newly formed CO2 produced at step sites desorbs with far lower translational energies than those formed at terraces. This work shows that steps and other defects could be potentially important in finding optimal conditions for the chemical activation and dissociation of CO2 .

Bond Energies of Adsorbed Intermediates to Metal Surfaces: Correlation with Hydrogen-Ligand and Hydrogen-Surface Bond Energies and Electronegativities.

Understanding what controls the strength of bonding of adsorbed intermediates to transition-metal surfaces is of central importance in many technologies, especially catalysis and electrocatalysis. Our recently measured bond enthalpies of -OH, -OCH3 , -O(O)CH and -CH3 to Pt(111) and Ni(111) surfaces are fit well (standard deviation of 7.2 kJ mol-1 ) by a predictive equation involving only known parameters (gas-phase ligand-hydrogen bond enthalpies, bond enthalpies of adsorbed H atoms to that surface, electronegativities of the elements, and group electronegativities of the ligands). This equation is based upon Pauling's equation, with improvements introduced by Matcha, derived here following manipulations of Matcha's equation similar to (but going beyond) those introduced by Schock and Marks to explain ligand-metal bond enthalpy trends in organometallic complexes.

Velocity-resolved kinetics of site-specific carbon monoxide oxidation on platinum surfaces.

Catalysts are widely used to increase reaction rates. They function by stabilizing the transition state of the reaction at their active site, where the atomic arrangement ensures favourable interactions 1 . However, mechanistic understanding is often limited when catalysts possess multiple active sites-such as sites associated with either the step edges or the close-packed terraces of inorganic nanoparticles2-4-with distinct activities that cannot be measured simultaneously. An example is the oxidation of carbon monoxide over platinum surfaces, one of the oldest and best studied heterogeneous reactions. In 1824, this reaction was recognized to be crucial for the function of the Davy safety lamp, and today it is used to optimize combustion, hydrogen production and fuel-cell operation5,6. The carbon dioxide products are formed in a bimodal kinetic energy distribution7-13; however, despite extensive study 5 , it remains unclear whether this reflects the involvement of more than one reaction mechanism occurring at multiple active sites12,13. Here we show that the reaction rates at different active sites can be measured simultaneously, using molecular beams to controllably introduce reactants and slice ion imaging14,15 to map the velocity vectors of the product molecules, which reflect the symmetry and the orientation of the active site 16 . We use this velocity-resolved kinetics approach to map the oxidation rates of carbon monoxide at step edges and terrace sites on platinum surfaces, and find that the reaction proceeds through two distinct channels11-13: it is dominated at low temperatures by the more active step sites, and at high temperatures by the more abundant terrace sites. We expect our approach to be applicable to a wide range of heterogeneous reactions and to provide improved mechanistic understanding of the contribution of different active sites, which should be useful in the design of improved catalysts.

The physical chemistry and materials science behind sinter-resistant catalysts.

Catalyst sintering, a main cause of the loss of catalytic activity and/or selectivity at high reaction temperatures, is a major concern and grand challenge in the general area of heterogeneous catalysis. Although all heterogeneous catalysts are inevitably subjected to sintering during their operation, the immediate and drastic consequences can be mitigated by carefully engineering the catalytic particles and their interactions with the supports. In this tutorial review, we highlight recent progress in understanding the physical chemistry and materials science involved in sintering, including the discussion of advanced techniques, such as in situ microscopy and spectroscopy, for investigating the sintering process and its rate. We also discuss strategies for the design and rational fabrication of sinter-resistant catalysts. Finally, we showcase recent success in improving the thermal stability and thus sinter resistance of supported catalytic systems.

Energetics of van der Waals Adsorption on the Metal-Organic Framework NU-1000 with Zr6-oxo, Hydroxo, and Aqua Nodes.

We report measurements of adsorption isotherms and the determination of the isosteric heats of adsorption of several small gases (H2, D2, Ne, N2, CO, CH4, C2H6, Ar, Kr, and Xe) on the metal-organic framework (MOF) NU-1000, which is one of the most thermally stable MOFs. It has transition-metal nodes of formula Zr6(µ3-OH)4(µ3-O)4(OH)4(OH2)4 that resemble hydrated ZrO2 clusters and can serve as catalysts or catalyst supports. The linkers in this MOF are pyrenes linked to the nodes via the carboxylate groups of benzoates. The broad range of adsorbates studied here allows us to compare trends both with adsorption on other surfaces and with density functional calculations also presented here. The experimental isotherms indicate similar filling of the MOF surface by the different gases, starting with strong adsorption sites near the Zr atoms, a result corroborated by the density functional calculations. This adsorption is followed by the filling of other adsorption sites on the nodes and organic framework. Capillary condensation occurs in wide pores after completion of a monolayer. The total amount adsorbed for all the gases is the equivalent of two complete monolayers. The experimental isosteric heats of adsorption are nearly proportional to the atom-atom (or molecule-molecule) Lennard-Jones well-depth parameters of the adsorbates but ∼13-fold larger. The density functional calculations show a similar trend but with much more scatter and heats that are usually greater (by 30%, on average).