Transmission from vaccinated individuals in a large SARS-CoV-2 Delta variant outbreak.

An outbreak of over 1,000 COVID-19 cases in Provincetown, Massachusetts (MA), in July 2021-the first large outbreak mostly in vaccinated individuals in the US-prompted a comprehensive public health response, motivating changes to national masking recommendations and raising questions about infection and transmission among vaccinated individuals. To address these questions, we combined viral genomic and epidemiological data from 467 individuals, including 40% of outbreak-associated cases. The Delta variant accounted for 99% of cases in this dataset; it was introduced from at least 40 sources, but 83% of cases derived from a single source, likely through transmission across multiple settings over a short time rather than a single event. Genomic and epidemiological data supported multiple transmissions of Delta from and between fully vaccinated individuals. However, despite its magnitude, the outbreak had limited onward impact in MA and the US overall, likely due to high vaccination rates and a robust public health response.

The Decline of Small Practice in Colorectal Surgery: Practice Consolidation From 2015-2022.

INTRODUCTION: Physicians have gravitated toward larger group practice arrangements in recent years. However, consolidation trends in colorectal surgery have yet to be well described. Our objective was to assess current trends in practice consolidation within colorectal surgery and evaluate underlying demographic trends including age, gender, and geography. METHODS: We performed a retrospective cross-sectional study using the Center for Medicare Services National Downloadable File from 2015 to 2022. Colorectal surgeons were categorized by practice size and by region, gender, and age. RESULTS: From 2015 to 2022, the number of colorectal surgeons in the United States increased from 1369 to 1621 (+18.4%), while the practices with which they were affiliated remained relatively stable (693-721, +4.0%). The proportion of colorectal surgeons in groups of 1-2 members fell from 18.9% to 10.7%. Conversely, those in groups of 500+ members grew from 26.5% to 45.2% (linear trend P < 0.001). The midwest region demonstrated the highest degree of consolidation. Affiliations with group practices of 500+ members saw large increases from both female and male surgeons (+148.9% and +86.9%, respectively). New surgeons joining the field since 2015 overwhelmingly practice in larger groups (5.3% in groups of 1-2, 50.1% in groups of 500+). CONCLUSIONS: Colorectal surgeons are shifting toward larger practice affiliations. Although this change is happening across all demographic groups, it appears unevenly distributed across geography, gender, and age. New surgeons are preferentially joining large group practices.

The interaction of size-selected Ru3 clusters with TiO2: depth-profiling of encapsulated clusters.

Ru is a metal of interest in catalysis. Monodisperse Ru3 clusters as catalytic sites are relevant for the development of catalysts because clusters use significantly lower amounts of precious materials for forming active sites due to the small size of the cluster. However, retaining the mono-dispersity of the cluster size after deposition is a challenge because surface energy could drive both agglomeration and encapsulation of the clusters. In the present work Ru3 clusters are deposited by chemical vapor deposition (CVD) of Ru3(CO)12 and cluster source depositions of bare Ru3 onto radio frequency sputter-deposited TiO2 (RF-TiO2) substrates, TiO2(100), and SiO2. When supported on RF-TiO2, bare Ru3 is encapsulated by a layer of titania substrate material during deposition with a cluster source. Ligated Ru3(CO)12 is also encapsulated by a layer of titania when deposited onto sputter-treated RF-TiO2, but only through heat treatment which is required to remove most of the ligands. The titania overlayer thickness was determined to be 1-2 monolayers for Ru3(CO)12 clusters on RF-TiO2, which is thin enough for catalytic or photocatalytic reactions to potentially occur even without clusters being part of the very outermost layer. The implication for catalysis of the encapsulation of Ru3 into the RF-TiO2 is discussed. Temperature-dependent X-ray photoelectron spectroscopy (XPS), angle-resolved XPS, and temperature-dependent low energy ion scattering (TD-LEIS) are used to probe how the cluster-surface interaction changes due to heat treatment and scanning transmission electron microscopy (STEM) was used to image the depth of the surface from side-on.

Electrocatalytic Hydrogen Evolution at Full Atomic Utilization over ITO-Supported Sub-nano-Ptn Clusters: High, Size-Dependent Activity Controlled by Fluxional Pt Hydride Species.

A combination of density functional theory (DFT) and experiments with atomically size-selected Ptn clusters deposited on indium-tin oxide (ITO) electrodes was used to examine the effects of applied potential and Ptn size on the electrocatalytic activity of Ptn (n = 1, 4, 7, and 8) for the hydrogen evolution reaction (HER). Activity is found to be negligible for isolated Pt atoms on ITO, increasing rapidly with Ptn size such that Pt7/ITO and Pt8/ITO have roughly double the activity per Pt atom compared to atoms in the surface layer of polycrystalline Pt. Both the DFT and experiment find that hydrogen under-potential deposition (Hupd) results in Ptn/ITO (n = 4, 7, and 8) adsorbing ∼2H atoms/Pt atom at the HER threshold potential, equal to ca. double the Hupd observed for Pt bulk or nanoparticles. The cluster catalysts under electrocatalytic conditions are hence best described as a Pt hydride compound, significantly departing from a metallic Pt cluster. The exception is Pt1/ITO, where H adsorption at the HER threshold potential is energetically unfavorable. The theory combines global optimization with grand canonical approaches for the influence of potential, uncovering the fact that several metastable structures contribute to the HER, changing with the applied potential. It is hence critical to include reactions of the ensemble of energetically accessible PtnHx/ITO structures to correctly predict the activity vs Ptn size and applied potential. For the small clusters, spillover of Hads from the clusters to the ITO support is significant, resulting in a competing channel for loss of Hads, particularly at slow potential scan rates.

Trends in Ophthalmology Practice Consolidation: 2015-2022.

PURPOSE: To quantify trends in ophthalmology practice consolidation in the United States. DESIGN: A retrospective cross-sectional study. PARTICIPANTS: Providers in the Centers for Medicare and Medicaid Services (CMS) National Downloadable File with a primary specialty designation of ophthalmology. METHODS: We used the CMS database to determine national practice consolidation trends in ophthalmology on individual physician and group practice levels and analyzed by region, sex, and years spent in practice. We used the Cochran-Armitage test to determine the statistical significance of practice size differences between 2015 and 2022. MAIN OUTCOME MEASURES: Temporal practice size trends for physicians and practices in ophthalmology and regional, sex-specific, and age-related trends. RESULTS: Between 2015 and 2022, the number of ophthalmologists decreased from 17 656 to 17 615 (-0.2%), whereas the number of practices decreased from 7149 to 5890 (-18%). The percentage of ophthalmologists in practices of 1 to 2 members decreased from 35% to 28%, whereas those in groups of 50 or more increased from 7% to 11%. The percentage of practices with 1 to 2 members decreased from 75% to 71%, and those with 50 or more increased from 0.2% to 0.4%. Consolidation trends were significant on individual ophthalmologist (P < 0.001) and group practice (P < 0.001) levels. All regions, sexes, and subgroups of years spent in practice demonstrated consolidation (P < 0.001). The Northeast showed the greatest increase in groups of 50 or more physicians (+7%) between 2015 and 2022. Proportionally fewer female than male ophthalmologists were associated with practice sizes of 1 to 2 members in 2015 (29% and 36%, respectively) and 2022 (23% and 30%, respectively). Proportionally fewer ophthalmologists with 0 to 10 years of experience in practice were associated with practice sizes of 1 to 2 members than those with more than 30 years in practice in 2015 (18% and 48%, respectively) and 2022 (14% and 40%, respectively). CONCLUSIONS: Ophthalmology has undergone practice consolidation from 2015 to 2022. A decrease in the proportion of physicians affiliated with smaller practice sizes seems to have occurred. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Growth and passivation of individual carbon nanoparticles by C2H2 addition at high temperatures: Dependence of growth rate and evolution on material and size.

Absolute kinetics for reactions of C2H2 with a series of ∼60 individual carbon nanoparticles (NPs) from graphite, graphene, graphene oxide, carbon black, diamond, and nano-onion feedstocks were measured for temperatures (TNP) ranging from 1200 to 1700 K. All the NPs were observed to gain mass by carbon addition under conditions that varied with feedstock but with large variations in initial growth rate. Long reaction periods were studied to allow the evolution of growth rates over time to be observed. Diamond NPs were found to passivate against C2H2 addition if heated above ∼1400 K, and the highly variable initial reactivity for carbon nano-onions was found to depend on the presence of non-onion-structure surface carbon. For graphitic and carbon black NPs, three distinct growth modes were observed, correlated with the initial NP mass (Minitial). Smallest graphitic and carbon black NPs, with masses <∼25 MDa, initially grew rapidly but also passivated quickly after adding <4% of Minitial. NPs in the 20-50 MDa range also passivated but only after multiple waves of fast growth separated by periods of low reactivity, with up to ∼11% total mass gain before passivation. The largest carbon black and graphitic NPs, with Minitial >50 MDa, grew rapidly and continuously, adding up to ∼300% of Minitial with no sign of rate slowing as long as C2H2 was present. The efficiencies for C2H2 addition and etching by O2 are strongly correlated, but the correlation changes as the NPs passivate. Growth and passivation mechanisms are discussed.

The Impact of Patient Sex on Outcomes after Endovascular Treatment of Aortoiliac Occlusive Disease.

BACKGROUND: The aim of this study was to explore the effect of patient sex on short-term and long-term outcomes after endovascular treatment for aortoiliac occlusive disease (AIOD). METHODS: A multicenter retrospective analysis was performed on all patients who underwent iliac artery stenting for AIOD across the 3 participating sites from October 1, 2018 to September 21, 2021. Preoperative clinical, operative, and postoperative data were collected on a dedicated database. Demographics and outcomes were compared between male and female patients and the probability of freedom from amputation and freedom from target lesion reintervention were estimated with the Kaplan-Meier method. RESULTS: Of 574 patients, 346 (60%) were male and 228 (40%) were female. Mean follow-up was 12 months. Female patients were significantly older (69.2 ± 10.2 years vs. 67.8 ± 8.9 years, P = 0.025) and more likely to have Trans-Atlantic Inter-Society Consensus II D disease (P = 0.003). The female cohort had significantly less coronary artery disease (40% vs. 50%, P = 0.013), coronary stenting (14% vs. 21%, P = 0.039), and coronary artery bypass grafting (13% vs. 25%, P < 0.001) than the male cohort, as well as less statin use (69% vs. 80%, P = 0.004). There were no differences in stent type, concomitant open surgery, intraoperative events, or hospital length of stay. For 30-day postoperative complications, female patients had a significantly higher rate of thrombotic acute limb ischemia (2% vs. 0%, P = 0.01), while male patients had a higher rate of amputation (4% vs. 9%, P = 0.048). On mid-term outcomes, there was no difference in freedom from amputation or target lesion reintervention between male and female patients (P = 0.14 and P = 0.32, respectively). CONCLUSIONS: Female patients had lower incidence of cardiovascular risk factors but presented with higher Trans-Atlantic Inter-Society Consensus II classification and had higher rates of 30-day thrombotic acute limb ischemia. Male patients were more likely to require amputation within 30 days. Despite no differences in the mid-term, these short-term findings suggest that patient sex may be a relevant consideration in postoperative management and surveillance after endovascular treatment of AIOD.

Recommendations for Medical Discharge Documentation and Academic Supports for University Students Recovering From Concussion.

OBJECTIVE: This study sought to (1) collate the experiences of university students with concussion history and academic stakeholders through interviews and (2) develop concussion management recommendations for institutions of higher learning using a multidisciplinary Delphi procedure. SETTING: Remote semistructured interviews and online surveys. PARTICIPANTS: The first aim of this study included undergraduate university students with concussion history who did not participate in varsity athletics ( n = 21; 57.1% female), as well as academic faculty/staff with experience assisting university students with their postconcussion academic needs ( n = 7; 71.4% female). The second aim enrolled 22 participants (54.5% female) to serve on the Delphi panel including 9 clinicians, 8 researchers, and 5 academic faculty/staff. DESIGN: An exploratory-sequential mixed-methods approach. MAIN MEASURES: Semistructured interviews were conducted to unveil barriers regarding the return-to-learn (RTL) process after concussion, with emergent themes serving as a general framework for the Delphi procedure. Panelists participated in 3 stages of a modified Delphi process beginning with a series of open-ended questions regarding postconcussion management in higher education. The second stage included anonymous ratings of the recommendations, followed by an opportunity to review and/or modify responses based on the group's consensus. RESULTS: The results from the semistructured interviews indicated students felt supported by their instructors; however, academic faculty/staff lacked information on appropriate academic supports and/or pathways to facilitate the RTL process. Of the original 67 statements, 39 achieved consensus (58.2%) upon cessation of the Delphi procedure across 3 main categories: recommendations for discharge documentation (21 statements), guidelines to facilitate a multidisciplinary RTL approach (10 statements), and processes to obtain academic supports for students who require them after concussion (8 statements). CONCLUSIONS: These findings serve as a basis for future policy in higher education to standardize RTL processes for students who may need academic supports following concussion.

Physical Activity Intensity of Singles and Doubles Pickleball in Older Adults.

The purpose of this study was to measure heart rate, activity intensity, and steps in recreational singles and doubles pickleball players. We collected data in 22 singles and 31 doubles players (62.1 ± 9.7 years of age) using Garmin Fenix 5 watches (Garmin International, Inc.) and ActiGraph GT3X+ (ActiGraph LLC) accelerometers. Mean heart rates during singles and doubles were 111.6 ± 13.5 and 111.5 ± 16.2 beats/min (70.3% and 71.2% of predicted maximum heart rate), respectively. Over 70% of singles and doubles playing time was categorized in moderate to vigorous heart rate zones whereas 80.5% of singles time and 50.4% of doubles time were moderate based on Freedson accelerometer cut-points. Steps per hour were higher in singles versus doubles (3,322 ± 493 vs. 2,791 ± 359), t(51) = 4.540, p < .001. Singles and doubles pickleball are moderate- to vigorous-intensity activities that can contribute substantially toward older adults meeting physical activity guidelines.

A general approach for evaluating of the coverage, resolution, and representation of streamflow monitoring networks.

Streamflow monitoring networks provide information for a wide range of public interests in river and streams. A general approach to evaluate monitoring for different interests is developed to support network planning and design. The approach defines three theoretically distinct information metrics (coverage, resolution, and representation) based on the spatial distribution of a variable of interest. Coverage is the fraction of information that a network can provide about a variable when some areas are not monitored. Resolution is the information available from the network relative to the maximum information possible given the number of sites in the network. Representation is the information that a network provides about a benchmark distribution of a variable. Information is defined using Shannon entropy where the spatial discretization of a variable among spatial elements of a landscape or sites in a network indicates the uncertainty in the spatial distribution of the variable. This approach supports the design of networks for monitoring of variables with heterogeneous spatial distributions ("hot spots" and patches) that might otherwise be unmonitored because they occupy insignificant portions of the landscape. Areas where monitoring will maintain or improve the metrics serve as objective priorities for public interests in network design. The approach is demonstrated for the streamflow monitoring network operated by the United States Geological Survey during water year 2020 indicating gaps in the coverage of coastal rivers and the resolution of low flows.

Hydrogen Evolution on Electrode-Supported Ptn Clusters: Ensemble of Hydride States Governs the Size Dependent Reactivity.

We report the size-dependent activity and stability of supported Pt1,4,7,8 for electrocatalytic hydrogen evolution reaction, and show that clusters outperform polycrystalline Pt in activity, with size-dependent stability. To understand the size effects, we use DFT calculations to study the structural fluxionality under varying potentials. We show that the clusters can reshape under H coverage and populate an ensemble of states with diverse stoichiometry, structure, and thus reactivity. Both experiment and theory suggest that electrocatalytic species are hydridic states of the clusters (≈2 H/Pt). An ensemble-based kinetic model reproduces the experimental activity trend and reveals the role of metastable states. The stability trend is rationalized by chemical bonding analysis. Our joint study demonstrates the potential- and adsorbate-coverage-dependent fluxionality of subnano clusters of different sizes and offers a systematic modeling strategy to tackle the complexities.

High-Temperature Oxidation of Single Carbon Nanoparticles: Dependence on the Surface Structure and Probing Real-Time Structural Evolution via Kinetics.

O2 oxidation and sublimation kinetics for >30 individual nanoparticles (NPs) of five different feedstocks (graphite, graphene oxide, carbon black, diamond, and nano-onion) were measured using single-NP mass spectrometry at temperatures (TNP) in the 1100-2900 K range. It was found that oxidation, studied in the 1200-1600 K range, is highly sensitive to the NP surface structure, with etching efficiencies (EEO2) varying by up to 4 orders of magnitude, whereas sublimation rates, significant only for TNP ≥ ∼1700 K, varied by only a factor of ∼3. Its sensitivity to the NP surface structure makes O2 etching a good real-time structure probe, which was used to follow the evolution of the NP surface structures over time as they were either etched or annealed at high TNP. All types of carbon NPs were found to have initial EEO2 values in the range near 10-3 Da/O2 collision, and all eventually evolved to become essentially inert to O2 (EEO2 < 10-6 Da/O2 collision); however, the dependence of EEO2 on time and mass loss was very different for NPs from different feedstocks. For example, diamond NPs evolved rapidly and monotonically toward inertness, and evolution occurred in both oxidizing and inert atmospheres. In contrast, graphite NPs evolved only under oxidizing conditions and were etched with complex time dependence, with multiple waves of fast but non-monotonic etching separated by periods of near-inertness. Possible mechanisms to account for the complex etching behavior are proposed.

Late-onset cutaneous lupus erythematosus patients have distinctive clinical features and demographics versus early-onset patients.

BACKGROUND: Cutaneous lupus erythematosus (CLE) can present later in life, but frequency and risk factors of late-onset CLE patients are not well characterized. The study determined frequency of late-onset CLE and compared the demographic and disease characteristics between early-onset and late-onset CLE in a cohort of patients with CLE. OBJECTIVES: To determine the frequency and compare clinical features of early-onset and late-onset CLE. METHODS: This was a cross-sectional study of CLE patients seen in outpatient dermatology clinics at University of Texas Southwestern Medical Center (UTSW) and Parkland Health and Hospital System, Dallas, TX, from April 2009 to May 2019. The primary outcome was the age of CLE onset, stratified by early-onset (<50 years) and late-onset CLE (≥50 years). Predictor variables significantly associated with CLE onset groups were identified by univariate and multivariable logistic regression analyses. RESULTS: Of the 291 CLE patients studied, 79% were early-onset, and 21% were late-onset. Multivariable logistic regression analyses identified that Caucasian race (odds ratio (OR): 2.23, 95% Confidence Interval (CI): 1.19-4.19, p = 0.013), having a CLE subtype other than chronic (OR: 2.18, 95% CI: 1.02-4.65, p = 0.044), and drug-induced cases (OR: 4.65, 95% CI: 1.18-18.24, p = 0.028) were significantly associated with late-onset CLE. Early-onset CLE patients were more likely to have oral ulcers (OR: 3.58, 95% CI: 1.46-8.78, p = 0.005) and renal disorders (OR: 4.02, 95% CI: 1.10-14.71, p = 0.036). LIMITATIONS: This was a single center study. Age of onset was self-reported and late-onset CLE cohort has a small sample size. CONCLUSIONS: Our diverse cohort of CLE patients had about one out of five patients with CLE experiencing disease onset after 50 years old. These patients have distinct demographic and clinical presentations compared to early-onset CLE patients. Providers should remain mindful of CLE in older patients with photosensitive rashes and mild systemic symptoms.

Drosophila TRF2 is a preferential core promoter regulator.

Transcription of protein-coding genes is highly dependent on the RNA polymerase II core promoter. Core promoters, generally defined as the regions that direct transcription initiation, consist of functional core promoter motifs (such as the TATA-box, initiator [Inr], and downstream core promoter element [DPE]) that confer specific properties to the core promoter. The known basal transcription factors that support TATA-dependent transcription are insufficient for in vitro transcription of DPE-dependent promoters. In search of a transcription factor that supports DPE-dependent transcription, we used a biochemical complementation approach and identified the Drosophila TBP (TATA-box-binding protein)-related factor 2 (TRF2) as an enriched factor in the fractions that support DPE-dependent transcription. We demonstrate that the short TRF2 isoform preferentially activates DPE-dependent promoters. DNA microarray analysis reveals the enrichment of DPE promoters among short TRF2 up-regulated genes. Using primer extension analysis and reporter assays, we show the importance of the DPE in transcriptional regulation of TRF2 target genes. It was previously shown that, unlike TBP, TRF2 fails to bind DNA containing TATA-boxes. Using microfluidic affinity analysis, we discovered that short TRF2-bound DNA oligos are enriched for Inr and DPE motifs. Taken together, our findings highlight the role of short TRF2 as a preferential core promoter regulator.

Perforated Appendicitis During a Pandemic: The Downstream Effect of COVID-19 in Children.

INTRODUCTION: Coronavirus Disease-19 (COVID-19) was declared a pandemic in March 2020. States issued stay-at-home orders and hospitals cancelled non-emergent surgeries. During this time, we anecdotally noticed more admissions for perforated appendicitis. Therefore, we hypothesized that during the months following the COVID-19 pandemic declaration, more children were presenting with perforated appendicitis. MATERIALS AND METHODS: This is a retrospective cohort study reviewing pediatric patients admitted at a single institution with acute and/or perforated appendicitis between October 2019 to May 2020. Interval appendectomies were excluded. COVID-19 months were designated as March, April, and May 2020. Additional analysis of March, April, and May 2019 was performed for comparison purposes. Analyzed data included demographics, symptoms, white blood cell count, imaging findings, procedures performed, and perforation status. Statistical analysis was performed. RESULTS: During the study period, 285 patients were admitted with the diagnosis of acute appendicitis with 95 patients being perforated. We identified a significant increase in perforated appendicitis cases in the three COVID-19 months compared with the preceding five months (45.6% vs 26.4%; P <0.001). In addition, a similar significant increase was identified when comparing to the same months a year prior (P = 0.003). No significant difference in duration of pain was identified (P=0.926). CONCLUSION: The COVID-19 pandemic and its associated stay-at-home orders have had downstream effects on healthcare. Our review has demonstrated a significant increase in the number of children presenting with perforated appendicitis following these stay-at-home ordinances. These results demonstrate that further investigations into the issues surrounding access to healthcare, especially during this pandemic, are warranted.

Mindfulness in Athletes.

ABSTRACT: Interventions to promote athlete health and performance have traditionally been focused on the physical elements of injury and training. More recently, however, increasing attention has been placed on the mental aspects of athlete health, with emerging evidence suggesting that injury risk and athletic performance are significantly affected by athlete well-being. Mindfulness meditation has been shown to have significant benefits for a number of physical and mental health outcomes in various clinical populations, and recent research has explored how mindfulness may enhance athletic performance, improve athlete mental health, reduce injury risk, and perhaps even facilitate recovery from injury. As awareness of mindfulness as a noninvasive, low-risk, and accessible intervention increases in the Western society, use among athletes has increased as well. Health care providers should be aware of this evidence in order to guide athletes regarding the use of mindfulness as an intervention to potentially improve athlete health and performance.

Summit on Exercise Collapse Associated with Sickle Cell Trait: Finding the "Way Ahead".

ABSTRACT: Although largely benign, sickle cell trait (SCT) has been associated with exertion-related events, to include sudden death. In 2011, a summit on SCT introduced the term exercise collapse associated with SCT (ECAST). A series of ECAST deaths in military personnel in 2019 prompted reevaluation of current efforts and led to a second summit in October 2019 hosted by the Consortium for Health and Military Performance of the Uniformed Services University in Bethesda, MD. The goals were to (1) review current service policies on SCT screening, (2) develop draft procedural instructions for executing current policy on SCT within the Department of Defense, (3) develop draft clinical practice guidelines for management of ECAST, (4) establish a framework for education on SCT and ECAST, and (5) prepare a research agenda to address identified gaps.

An Engineered T Cell Receptor Variant Realizes the Limits of Functional Binding Modes.

T cell receptors (TCRs) orchestrate cellular immunity by recognizing peptides presented by a range of major histocompatibility complex (MHC) proteins. Naturally occurring TCRs bind the composite peptide/MHC surface, recognizing peptides that are structurally and chemically compatible with the TCR binding site. Here we describe a molecularly evolved TCR variant that binds the human class I MHC protein HLA-A2 independent of the bound peptide, achieved by a drastic perturbation of the TCR binding geometry that places the molecule far from the peptide binding groove. This unique geometry is unsupportive of normal T cell signaling. A substantial divergence between affinity measurements in solution and in two dimensions between proximal cell membranes leads us to attribute the lack of signaling to steric hindrance that limits binding in the confines of a cell-cell interface. Our results provide an example of how receptor binding geometry can impact T cell function and provide further support for the view that germline-encoded residues in TCR binding loops evolved to drive productive TCR recognition and signaling.

Sublimation Kinetics for Individual Graphite and Graphene Nanoparticles (NPs): NP-to-NP Variations and Evolving Structure-Kinetics and Structure-Emissivity Relationships.

A single nanoparticle (NP) mass spectrometry method was used to measure sublimation rates as a function of nanoparticle temperature (TNP) for sets of individual graphite and graphene NPs. Initially, the NP sublimation rates were ∼400 times faster than those for bulk graphite, and there were large NP-to-NP variations. Over time, the rates slowed substantially, though they remained well above the bulk rate. The initial activation energies (Ea values) were correspondingly low and doubled, as a few monolayers worth of material was sublimed from the surfaces. The high initial rates and low Ea values are attributed to large numbers of edge, defect, and other low coordination sites on the NP surfaces, and the changes are attributed to atomic-scale "smoothing" of the surface by preferential sublimation of the less stable sites. The emissivity of the NPs also changed after heating, more frequently increasing. The emissivity and sublimation rates were anticorrelated, leading to the conclusion that high densities of low-coordination sites on the NP surfaces enhance sublimation but suppress emissivity.

Sn-modification of Pt7/alumina model catalysts: Suppression of carbon deposition and enhanced thermal stability.

An atomic layer deposition process is used to modify size-selected Pt7/alumina model catalysts by Sn addition, both before and after Pt7 cluster deposition. Surface science methods are used to probe the effects of Sn-modification on the electronic properties, reactivity, and morphology of the clusters. Sn addition, either before or after cluster deposition, is found to strongly affect the binding properties of a model alkene, ethylene, changing the number and type of binding sites, and suppressing decomposition leading to carbon deposition and poisoning of the catalyst. Density functional theory on a model system, Pt4Sn3/alumina, shows that the Sn and Pt atoms are mixed, forming alloy clusters with substantial electron transfer from Sn to Pt. The presence of Sn also makes all the thermally accessible structures closed shell, such that ethylene binds only by π-bonding to a single Pt atom. The Sn-modified catalysts are quite stable in repeated ethylene temperature programmed reaction experiments, suggesting that the presence of Sn also reduces the tendency of the sub-nano-clusters to undergo thermal sintering.