Fast odour dynamics are encoded in the olfactory system and guide behaviour.

Odours are transported in turbulent plumes, which result in rapid concentration fluctuations1,2 that contain rich information about the olfactory scenery, such as the composition and location of an odour source2-4. However, it is unclear whether the mammalian olfactory system can use the underlying temporal structure to extract information about the environment. Here we show that ten-millisecond odour pulse patterns produce distinct responses in olfactory receptor neurons. In operant conditioning experiments, mice discriminated temporal correlations of rapidly fluctuating odours at frequencies of up to 40 Hz. In imaging and electrophysiological recordings, such correlation information could be readily extracted from the activity of mitral and tufted cells-the output neurons of the olfactory bulb. Furthermore, temporal correlation of odour concentrations5 reliably predicted whether odorants emerged from the same or different sources in naturalistic environments with complex airflow. Experiments in which mice were trained on such tasks and probed using synthetic correlated stimuli at different frequencies suggest that mice can use the temporal structure of odours to extract information about space. Thus, the mammalian olfactory system has access to unexpectedly fast temporal features in odour stimuli. This endows animals with the capacity to overcome key behavioural challenges such as odour source separation5, figure-ground segregation6 and odour localization7 by extracting information about space from temporal odour dynamics.

Wireless monitoring of respiration with EEG reveals relationships between respiration, behavior, and brain activity in freely moving mice.

Active sampling in the olfactory domain is a fundamental aspect of mouse behavior, and there is increasing evidence that respiration-entrained neural activity outside of the olfactory system sets an important global brain rhythm. It is therefore crucial to accurately measure breathing during natural behaviors. We develop a new approach to do this in freely moving animals, by implanting a telemetry-based pressure sensor into the right jugular vein, which allows for wireless monitoring of thoracic pressure. After verifying this technique against standard head-fixed respiration measurements, we combined it with EEG and EMG recording and used evolving partial coherence analysis to investigate the relationship between respiration and brain activity across a range of experiments in which the mice could move freely. During voluntary exploration of odors and objects, we found that the association between respiration and cortical activity in the delta and theta frequency range decreased, whereas the association between respiration and cortical activity in the alpha range increased. During sleep, however, the presentation of an odor was able to cause a transient increase in sniffing without changing dominant sleep rhythms (delta and theta) in the cortex. Our data align with the emerging idea that the respiration rhythm could act as a synchronizing scaffold for specific brain rhythms during wakefulness and exploration, but suggest that respiratory changes are less able to impact brain activity during sleep. Combining wireless respiration monitoring with different types of brain recording across a variety of behaviors will further increase our understanding of the important links between active sampling, passive respiration, and neural activity.NEW & NOTEWORTHY Animals can alter their respiration rate to actively sample their environment, and increasing evidence suggests that neurons across the brain align their firing to this changing rhythm. We developed a new approach to measure sniffing in freely moving mice while simultaneously recording brain activity, and uncovered how specific cortical rhythms changed their coherence with respiration rhythm during natural behaviors and across arousal states.

Coherent olfactory bulb gamma oscillations arise from coupling independent columnar oscillators.

Spike timing-based representations of sensory information depend on embedded dynamical frameworks within neuronal networks that establish the rules of local computation and interareal communication. Here, we investigated the dynamical properties of olfactory bulb circuitry in mice of both sexes using microelectrode array recordings from slice and in vivo preparations. Neurochemical activation or optogenetic stimulation of sensory afferents evoked persistent gamma oscillations in the local field potential. These oscillations arose from slower, GABA(A) receptor-independent intracolumnar oscillators coupled by GABA(A)-ergic synapses into a faster, broadly coherent network oscillation. Consistent with the theoretical properties of coupled-oscillator networks, the spatial extent of zero-phase coherence was bounded in slices by the reduced density of lateral interactions. The intact in vivo network, however, exhibited long-range lateral interactions that suffice in simulation to enable zero-phase gamma coherence across the olfactory bulb. The timing of action potentials in a subset of principal neurons was phase-constrained with respect to evoked gamma oscillations. Coupled-oscillator dynamics in olfactory bulb thereby enable a common clock, robust to biological heterogeneities, that is capable of supporting gamma-band spike synchronization and phase coding across the ensemble of activated principal neurons.NEW & NOTEWORTHY Odor stimulation evokes rhythmic gamma oscillations in the field potential of the olfactory bulb, but the dynamical mechanisms governing these oscillations have remained unclear. Establishing these mechanisms is important as they determine the biophysical capacities of the bulbar circuit to, for example, maintain zero-phase coherence across a spatially extended network, or coordinate the timing of action potentials in principal neurons. These properties in turn constrain and suggest hypotheses of sensory coding.

Balloon-expandable transcatheter heart valves for treatment of aortic valve stenosis in patients with large aortic annuli: Evaluation of deployment balloon overfilling strategies.

OBJECTIVES: Transcatheter aortic valve implantation (TAVI) using balloon-expandable (BE) transcatheter heart valves (THV) in aortic annuli above 29 mm includes particular procedural steps, mainly involving overfilling of the deployment balloon. Data on overfilling strategies in clinical daily practice is scarce. We herein aimed for a retrospective description of utilized overfilling strategies in those patients. METHODS: Between January 2016 and December 2022, 45 patients (100% male, 76.9 ± 6.1 years) received TAVI in aortic annuli above 29 mm using a BE THV. Overfilling volumina of the deployment balloon were left to operators' discretion. Clinical and multislice computed tomography data were retrospectively collected. Clinical endpoints were adjudicated in accordance with the updated standardized VARC-3 definitions. RESULTS: Profound overfilling (+4/5 mL) was used in patients with a mild calcium burden (˂750 mm³) even in aortic annuli of 29.0-30.0 mm. Nominal/slight overfilling (+1 mL) was used in aortic annuli up to 32.5 mm but an intermediate to severe calcific burden (>750-3200 mm³). Accordingly, a low calcification group (˂750 mm³, n = 17) compared to a significant calcification group (≥750 mm³, n = 28), presented with higher overfilling volumina (2.1 ± 1.4 vs. 0.8 ± 1.0; p ˂ 0.001), although aortic annulus diameter was not different (29.8 ± 0.8 vs. 29.9 ± 0.9 mm; p = 0.7). All-cause 30-day mortality was 0%. Device success was 97.8%. Transvalvular mean pressure gradient at discharge was 9.5 ± 3.6 mmHg. No case of PVL >mild was documented. CONCLUSION: Extent of overfilling of the deployment balloon largely depends on calcification burden in addition to aortic annulus diameter with significant and profound overfilling particularly in patients with a calcification burden of the aortic valve complex ˂750 mm³.

Coupling of Mouse Olfactory Bulb Projection Neurons to Fluctuating Odor Pulses.

Odors are transported by turbulent air currents, creating complex temporal fluctuations in odor concentration that provide a potentially informative stimulus dimension. We have shown that mice are able to discriminate odor stimuli based on their temporal structure, indicating that information contained in the temporal structure of odor plumes can be extracted by the mouse olfactory system. Here, using in vivo extracellular and intracellular electrophysiological recordings, we show that mitral cells (MCs) and tufted cells (TCs) of the male C57BL/6 mouse olfactory bulb can encode the dominant temporal frequencies present in odor stimuli up to at least 20 Hz. A substantial population of cell-odor pairs showed significant coupling of their subthreshold membrane potential with the odor stimulus at both 2 Hz (29/70) and the suprasniff frequency 20 Hz (24/70). Furthermore, mitral/tufted cells (M/TCs) show differential coupling of their membrane potential to odor concentration fluctuations with tufted cells coupling more strongly for the 20 Hz stimulation. Frequency coupling was always observed to be invariant to odor identity, and M/TCs that coupled well to a mixture also coupled to at least one of the components of the mixture. Interestingly, pharmacological blocking of the inhibitory circuitry strongly modulated frequency coupling of cell-odor pairs at both 2 Hz (10/15) and 20 Hz (9/15). These results provide insight into how both cellular and circuit properties contribute to the encoding of temporal odor features in the mouse olfactory bulb.SIGNIFICANCE STATEMENT Odors in the natural environment have a strong temporal structure that can be extracted and used by mice in their behavior. Here, using in vivo extracellular and intracellular electrophysiological techniques, we show that the projection neurons in the olfactory bulb can encode and couple to the dominant frequency present in an odor stimulus. Furthermore, frequency coupling was observed to be differential between mitral and tufted cells and was odor invariant but strongly modulated by local inhibitory circuits. In summary, this study provides insight into how both cellular and circuit properties modulate encoding of odor temporal features in the mouse olfactory bulb.

Sparse connectivity for MAP inference in linear models using sister mitral cells.

Sensory processing is hard because the variables of interest are encoded in spike trains in a relatively complex way. A major goal in studies of sensory processing is to understand how the brain extracts those variables. Here we revisit a common encoding model in which variables are encoded linearly. Although there are typically more variables than neurons, this problem is still solvable because only a small number of variables appear at any one time (sparse prior). However, previous solutions require all-to-all connectivity, inconsistent with the sparse connectivity seen in the brain. Here we propose an algorithm that provably reaches the MAP (maximum a posteriori) inference solution, but does so using sparse connectivity. Our algorithm is inspired by the circuit of the mouse olfactory bulb, but our approach is general enough to apply to other modalities. In addition, it should be possible to extend it to nonlinear encoding models.

Synthesis and Characterization of Catalytically Active Au Core─Pd Shell Nanoparticles Supported on Alumina.

A two-step seeded-growth method was refined to synthesize Au@Pd core@shell nanoparticles with thin Pd shells, which were then deposited onto alumina to obtain a supported Au@Pd/Al2O3 catalyst active for prototypical CO oxidation. By the strict control of temperature and Pd/Au molar ratio and the use of l-ascorbic acid for making both Au cores and Pd shells, a 1.5 nm Pd layer is formed around the Au core, as evidenced by transmission electron microscopy and energy-dispersive spectroscopy. The core@shell structure and the Pd shell remain intact upon deposition onto alumina and after being used for CO oxidation, as revealed by additional X-ray diffraction and X-ray photoemission spectroscopy before and after the reaction. The Pd shell surface was characterized with in situ infrared (IR) spectroscopy using CO as a chemical probe during CO adsorption-desorption. The IR bands for CO ad-species on the Pd shell suggest that the shell exposes mostly low-index surfaces, likely Pd(111) as the majority facet. Generally, the IR bands are blue-shifted as compared to conventional Pd/alumina catalysts, which may be due to the different support materials for Pd, Au versus Al2O3, and/or less strain of the Pd shell. Frequencies obtained from density functional calculations suggest the latter to be significant. Further, the catalytic CO oxidation ignition-extinction processes were followed by in situ IR, which shows the common CO poisoning and kinetic behavior associated with competitive adsorption of CO and O2 that is typically observed for noble metal catalysts.

On-Line Composition Analysis of Complex Hydrocarbon Streams by Time-Resolved Fourier Transform Infrared Spectroscopy and Ion-Molecule Reaction Mass Spectrometry.

On-line composition analysis of complex hydrocarbon mixtures is highly desirable to determine the composition of process streams and to study chemical reactions in heterogeneous catalysis. Here, we show how the combination of time-resolved Fourier transform infrared spectroscopy and ion-molecule-reaction mass spectrometry (IMR-MS) can be used for compositional analysis of processed plant biomass streams. The method is based on the biomass-derived model compound 2,5-dimethylfuran and its potential catalytic conversion to valuable green aromatics, for example, benzene, toluene, and xylenes (BTX) over zeolite ß. Numerous conversion products can be determined and quantified simultaneously in a temporal resolution of 4 min-1 without separation of individual compounds. The realization of this method enables us to study activity, selectivity, and changes in composition under transient reaction conditions. For example, increasing isomerization of 2,5-dimethylfuran to 2,4-dimethylfuran, 2-methyl-2-cyclopenten-1-one, and 2-methyl-2-cyclopenten-1-one is observed as the catalyst is exposed to the reactant, while BTX and olefin formation is decreasing.

Spatial information from the odour environment in mammalian olfaction.

The sense of smell is an essential modality for many species, in particular nocturnal and crepuscular mammals, to gather information about their environment. Olfactory cues provide information over a large range of distances, allowing behaviours ranging from simple detection and recognition of objects, to tracking trails and navigating using odour plumes from afar. In this review, we discuss the features of the natural olfactory environment and provide a brief overview of how odour information can be sampled and might be represented and processed by the mammalian olfactory system. Finally, we discuss recent behavioural approaches that address how mammals extract spatial information from the environment in three different contexts: odour trail tracking, odour plume tracking and, more general, olfactory-guided navigation. Recent technological developments have seen the spatiotemporal aspect of mammalian olfaction gain significant attention, and we discuss both the promising aspects of rapidly developing paradigms and stimulus control technologies as well as their limitations. We conclude that, while still in its beginnings, research on the odour environment offers an entry point into understanding the mechanisms how mammals extract information about space.

TAVI in Patients with Mitral Annular Calcification and/or Mitral Stenosis.

BACKGROUND: We herein aimed for analysis of influence of mitral annular calcification (MAC) and mitral stenosis (MS) on outcomes in transcatheter aortic valve implantation (TAVI). METHODS: Between 11/2009 and 06/2017, 1,058 patients underwent TAVI in the presence of concomitant MAC or MS at our center. Subgroups were built and multivariate logistic regression, COX regression, Kaplan-Meier survival analyses, and receiver operating characteristics method were performed. RESULTS: Thirty-day mortality was 7.5% (79/1,058) with highest mortality in patients severe MS (MAC: 3.4% vs. mild MS: 5.9% vs. moderate MS: 15.0% vs. severe MS: 72.7%; p < 0.001). Moderate-to-severe MS (odds ratio [OR]: 7.75, confidence interval [CI]: 3.94-16.26, p < 0.001), impaired left ventricular ejection fraction (OR: 1.38, CI: 1.10-1.72, p < 0.01), and coronary artery disease (OR: 1.36, CI: 1.11-1.67, p < 0.01) were predictive of 30-day survival. Left ventricular systolic/end-diastolic pressure drop of <59.5 mm Hg / <19.5 mm Hg was associated with increased mortality. CONCLUSIONS: TAVI in the presence of MAC and mild MS is associated with acceptable acute outcomes but should be considered high-risk procedures in patients with moderate and especially those with severe MS. Our results suggest adverse hemodynamics after TAVI with concomitant MS, which may be caused by underfilling of the left ventricle leading to low-cardiac output.

Transcatheter Aortic Valve Implantation in Bicuspid Aortic Valve Pathology: Current Evidence and Technical Challenges.

Transcatheter aortic valve implantation (TAVI) is an established therapy for severe symptomatic aortic valve stenosis (AS) in patients at high and intermediate risk for surgical aortic valve replacement (SAVR). Current evidence also suggests at least non-inferiority of TAVI in low-risk patients compared to SAVR. However, there are special subsets of patients and anatomical circumstances in which TAVI is traditionally considered a suboptimal treatment strategy due to procedure inherent increased risks (e.g., rupture of cardiac chambers in patients with severe calcifications of the left ventricular outflow tract, valve migration in very large aortic annuli). One of these special subsets is bicuspid AS. Bicuspid aortic valve disease is the most common congenital heart defect and most frequent reason for AS in patients <70 years of age. Bicuspid aortic valve pathology is characterized by special anatomical complexities like asymmetrical cusp proportion and calcium distribution, a more pronounced annular ellipticity compared to tricuspid aortic valves and concomitant dilation of the thoracic aorta. These factors have led physicians to traditionally indicate TAVI more reluctantly in those patients in the past. In this article, current evidence for TAVI for bicuspid AS is discussed and technical challenges are highlighted.

Randomized trial of ticagrelor vs. aspirin in patients after coronary artery bypass grafting: the TiCAB trial.

AIMS: The antiplatelet treatment strategy providing optimal balance between thrombotic and bleeding risks in patients undergoing coronary artery bypass grafting (CABG) is unclear. We prospectively compared the efficacy of ticagrelor and aspirin after CABG. METHODS AND RESULTS: We randomly assigned in double-blind fashion patients scheduled for CABG to either ticagrelor 90 mg twice daily or 100 mg aspirin (1:1) once daily. The primary outcome was the composite of cardiovascular death, myocardial infarction (MI), repeat revascularization, and stroke 12 months after CABG. The main safety endpoint was based on the Bleeding Academic Research Consortium classification, defined as BARC ≥4 for periprocedural and hospital stay-related bleedings and BARC ≥3 for post-discharge bleedings. The study was prematurely halted after recruitment of 1859 out of 3850 planned patients. Twelve months after CABG, the primary endpoint occurred in 86 out of 931 patients (9.7%) in the ticagrelor group and in 73 out of 928 patients (8.2%) in the aspirin group [hazard ratio 1.19; 95% confidence interval (CI) 0.87-1.62; P = 0.28]. All-cause mortality (ticagrelor 2.5% vs. aspirin 2.6%, hazard ratio 0.96, CI 0.53-1.72; P = 0.89), cardiovascular death (ticagrelor 1.2% vs. aspirin 1.4%, hazard ratio 0.85, CI 0.38-1.89; P = 0.68), MI (ticagrelor 2.1% vs. aspirin 3.4%, hazard ratio 0.63, CI 0.36-1.12, P = 0.12), and stroke (ticagrelor 3.1% vs. 2.6%, hazard ratio 1.21, CI 0.70-2.08; P = 0.49), showed no significant difference between the ticagrelor and aspirin group. The main safety endpoint was also not significantly different (ticagrelor 3.7% vs. aspirin 3.2%, hazard ratio 1.17, CI 0.71-1.92; P = 0.53). CONCLUSION: In this prematurely terminated and thus underpowered randomized trial of ticagrelor vs. aspirin in patients after CABG no significant differences in major cardiovascular events or major bleeding could be demonstrated. CLINICALTRIALS.GOV IDENTIFIER: NCT01755520.

Transcatheter Mitral Valve Replacement for Degenerated Bioprosthetic Valves and Failed Annuloplasty Rings.

The risk of recurrent mitral regurgitation after surgical mitral valve repair for ischemic functional mitral regurgitation is 28 % at 10 years. Also, an increasing number of patients with degenerated mitral bioprostheses are seen in daily clinical practice due to a dramatic shift from mechanical to biological bioprostheses over the past few decades. Therefore, it can be anticipated that there will be growing need for therapy options to treat high-risk patients in case of recurrent mitral regurgitation subsequent to surgical mitral valve repair or replacement. Interventional therapy for failing surgical mitral valve replacement and repair is an appealing option in patients who are ineligible for redo surgery. The efficacy and safety of transcatheter mitral valve replacement have been reported in patients with failing mitral rings or degenerated mitral bioprostheses. However, crucial limitations remain, including possible device malpositioning, left ventricular outflow tract obstruction and postprocedural mitral regurgitation. Partially, these complications can be explained by the most frequently used transcatheter heart valves, which are balloon-expanding bioprostheses intended for transcatheter aortic valve implantation that cannot be repositioned. Currently, frequently used approaches for transcatheter mitral valve replacement include retrograde transapical and antegrade transseptal techniques, most often with the use of transcatheter heart valves from the Sapien family (Edwards Lifesciences Inc., Irvine, CA, USA) followed by the mechanical expandable Lotus valve (Boston Scientific, Marlborough, MS, USA). Anecdotal reports have described the application of self-expandable transcatheter heart valves (Centera; Edwards) or dedicated transcatheter mitral valve replacement devices. In this report, we give an overview of current interventional techniques, available evidence and reported outcomes for transcatheter mitral valve replacement for degenerated bioprosthetic valves and failed annuloplasty rings.

Quantitative Association of Anatomical and Functional Classes of Olfactory Bulb Neurons.

Juxtaglomerular cells (JGCs) of the olfactory bulb (OB) glomerular layer (GL) play a fundamental role in olfactory information processing. Their variability in morphology, physiology, and connectivity suggests distinct functions. The quantitative understanding of population-wise morphological and physiological properties and a comprehensive classification based on quantitative parameters, however, is still lacking, impeding the analysis of microcircuits. Here, we provide multivariate clustering of 95 in vitro sampled cells from the GL of the mouse (male or female C57BL/6) OB and perform detailed morphological and physiological characterization for the seven computed JGC types. Using a classifier based on a subselection of parameters, we identified the neuron types in paired recordings to characterize their functional connectivity. We found that 4 of the 7 clusters comply with prevailing concepts of GL cell types, whereas the other 3 represent own distinct entities. We have labeled these entities horizontal superficial tufted cell (hSTC), vertical superficial tufted cell, and microglomerular cell (MGC): The hSTC is a tufted cell with a lateral dendrite that much like mitral cells and tufted cells receives excitatory inputs from the external tufted cell but likewise serves as an excitatory element for glomerular interneurons. The vertical superficial tufted cell, on the other hand, represents a tufted cell type with vertically projecting basal dendrites. We further define the MGC, characterized by a small dendritic tree and plateau action potentials. In addition to olfactory nerve-driven and external tufted cell driven interneurons, these MGCs represent a third functionally distinct type, the hSTC-driven interneurons. The presented correlative analysis helps to bridge the gap between branching patterns and cellular functional properties, permitting the integration of results from in vivo recordings, advanced morphological tools, and connectomics.SIGNIFICANCE STATEMENT The variance of neuron properties is a feature across mammalian cerebral circuits, contributing to signal processing and adding computational robustness to the networks. It is particularly noticeable in the glomerular layer of the olfactory bulb, the first site of olfactory information processing. We provide the first unbiased population-wise multivariate analysis to correlate morphological and physiological parameters of juxtaglomerular cells. We identify seven cell types, including four previously described neuron types, and identify further three distinct classes. The presented correlative analysis of morphological and physiological parameters gives an opportunity to predict morphological classes from physiological measurements or the functional properties of neurons from morphology and opens the way to integrate results from in vivo recordings, advanced morphological tools, and connectomics.

Sensory-evoked synaptic integration in cerebellar and cerebral cortical neurons.

Neurons integrate synaptic inputs across time and space, a process that determines the transformation of input signals into action potential output. This article explores how synaptic integration contributes to the richness of sensory signalling in the cerebellar and cerebral cortices. Whether a neuron receives a few or a few thousand discrete inputs, most evoked synaptic activity generates only subthreshold membrane potential fluctuations. Sensory tuning of synaptic inputs is typically broad, but short-term dynamics and the interplay between excitation and inhibition restrict action potential firing to narrow windows of opportunity. We highlight the challenges and limitations of the use of somatic recordings in the study of synaptic integration and the importance of active dendritic mechanisms in sensory processing.

Pharmacological inhibition of DNA methylation attenuates pressure overload-induced cardiac hypertrophy in rats.

BACKGROUND: Heart failure is associated with altered gene expression and DNA methylation. De novo DNA methylation is associated with gene silencing, but its role in cardiac pathology remains incompletely understood. We hypothesized that inhibition of DNA methyltransferases (DNMT) might prevent the deregulation of gene expression and the deterioration of cardiac function under pressure overload (PO). To test this hypothesis, we evaluated a DNMT inhibitor in PO in rats and analysed DNA methylation in cardiomyocytes. METHODS AND RESULTS: Young male Wistar rats were subjected to PO by transverse aortic constriction (TAC) or to sham surgery. Rats from both groups received solvent or 12.5 mg/kg body weight of the non-nucleosidic DNMT inhibitor RG108, initiated on the day of the intervention. After 4 weeks, we analysed cardiac function by MRI, fibrosis with Sirius Red staining, gene expression by RNA sequencing and qPCR, and DNA methylation by reduced representation bisulphite sequencing (RRBS). RG108 attenuated the ~70% increase in heart weight/body weight ratio of TAC over sham to 47% over sham, partially rescued reduced contractility, diminished the fibrotic response and the downregulation of a set of genes including Atp2a2 (SERCA2a) and Adrb1 (beta1-adrenoceptor). RG108 was associated with significantly lower global DNA methylation in cardiomyocytes by ~2%. The differentially methylated pathways were "cardiac hypertrophy", "cell death" and "xenobiotic metabolism signalling". Among these, "cardiac hypertrophy" was associated with significant methylation differences in the group comparison sham vs. TAC, but not significant between sham+RG108 and TAC+RG108 treatment, suggesting that RG108 partially prevented differential methylation. However, when comparing TAC and TAC+RG108, the pathway cardiac hypertrophy was not significantly differentially methylated. CONCLUSIONS: DNMT inhibitor treatment is associated with attenuation of cardiac hypertrophy and moderate changes in cardiomyocyte DNA methylation. The potential mechanistic link between these two effects and the role of non-myocytes need further clarification.

Steps Control the Dissociation of CO2 on Cu(100).

CO2 reduction reactions, which provide one route to limit the emission of this greenhouse gas, are commonly performed over Cu-based catalysts. Here, we use ambient pressure X-ray photoelectron spectroscopy together with density functional theory to obtain an atomistic understanding of the dissociative adsorption of CO2 on Cu(100). We find that the process is dominated by the presence of steps, which promote both a lowering of the dissociation barrier and an efficient separation between adsorbed O and CO, reducing the probability for recombination. The identification of steps as sites for efficient CO2 dissociation provides an understanding that can be used in the design of future CO2 reduction catalysts.

Valve-in-valve-in-valve: Balloon expandable transcatheter heart valve in failing self-expandable transcatheter heart valve in deteriorated surgical bioprosthesis.

Valve-in-valve (ViV) procedures for failing bioprostheses carry a certain risk for device malfunction. We herein report a case of a failing Evolut R in a deteriorated Mitroflow, treated with a Sapien 3. An 81 year old female patient received surgical aortic valve replacement and was treated by ViV due to deterioration. Three years later, echocardiography revealed a pressure gradient of peak/mean 105/63 mmHg. Subsequently, a second ViV procedure with initial intentional rupture of the bioprosthetic stent was performed. Immediate stent recoil of the Evolut R prompted implantation of a Sapien 3. In 30-day follow-up, mean pressure gradient of 30 mmHg and nearly complete symptom relief was documented. Fracture of a surgical bioprosthetic stent is feasible in a ViV configuration. Supra-annular placement of a balloon-expandable THV as ViV-in-valve is feasible with suboptimal hemodynamic results in this case. Risk of re-do surgery should be weighted against anticipated hemodynamic and clinical results.

Thermal reduction of ceria nanostructures on rhodium(111) and re-oxidation by CO2.

The thermal reduction of cerium oxide nanostructures deposited on a rhodium(111) single crystal surface and the re-oxidation of the structures by exposure to CO2 were investigated. Two samples are compared: a rhodium surface covered to ≈60% by one to two O-Ce-O trilayer high islands and a surface covered to ≈65% by islands of four O-Ce-O trilayer thickness. Two main results stand out: (1) the thin islands reduce at a lower temperature (870-890 K) and very close to Ce2O3, while the thicker islands need higher temperature for reduction and only reduce to about CeO1.63 at a maximum temperature of 920 K. (2) Ceria is re-oxidized by CO2. The rhodium surface promotes the re-oxidation by splitting the CO2 and thus providing atomic oxygen. The process shows a clear temperature dependence. The maximum oxidation state of the oxide reached by re-oxidation with CO2 differs for the two samples, showing that the thinner structures require a higher temperature for re-oxidation with CO2. Adsorbed carbon species, potentially blocking reactive sites, desorb from both samples at the same temperature and cannot be the sole origin for the observed differences. Instead, an intrinsic property of the differently sized CeOx islands must be at the origin of the observed temperature dependence of the re-oxidation by CO2.

Structure of the SnO_{2}(110)-(4×1) Surface.

Using surface x-ray diffraction (SXRD), quantitative low-energy electron diffraction (LEED), and density-functional theory (DFT) calculations, we have determined the structure of the (4×1) reconstruction formed by sputtering and annealing of the SnO_{2}(110) surface. We find that the reconstruction consists of an ordered arrangement of Sn_{3}O_{3} clusters bound atop the bulk-terminated SnO_{2}(110) surface. The model was found by application of a DFT-based evolutionary algorithm with surface compositions based on SXRD, and shows excellent agreement with LEED and with previously published scanning tunneling microscopy measurements. The model proposed previously consisting of in-plane oxygen vacancies is thus shown to be incorrect, and our result suggests instead that Sn(II) species in interstitial positions are the more relevant features of reduced SnO_{2}(110) surfaces.