Showing papers by "University of South Carolina published in 2017"

SymPy: Symbolic Computing in Python

Abstract: SymPy is an open source computer algebra system written in pure Python. It is built with a focus on extensibility and ease of use, through both interactive and programmatic applications. These characteristics have led SymPy to become a popular symbolic library for the scientific Python ecosystem. This paper presents the architecture of SymPy, a description of its features, and a discussion of select submodules. The supplementary material provide additional examples and further outline details of the architecture and features of SymPy.

Single Atomic Iron Catalysts for Oxygen Reduction in Acidic Media: Particle Size Control and Thermal Activation.

Abstract: It remains a grand challenge to replace platinum group metal (PGM) catalysts with earth-abundant materials for the oxygen reduction reaction (ORR) in acidic media, which is crucial for large-scale deployment of proton exchange membrane fuel cells (PEMFCs). Here, we report a high-performance atomic Fe catalyst derived from chemically Fe-doped zeolitic imidazolate frameworks (ZIFs) by directly bonding Fe ions to imidazolate ligands within 3D frameworks. Although the ZIF was identified as a promising precursor, the new synthetic chemistry enables the creation of well-dispersed atomic Fe sites embedded into porous carbon without the formation of aggregates. The size of catalyst particles is tunable through synthesizing Fe-doped ZIF nanocrystal precursors in a wide range from 20 to 1000 nm followed by one-step thermal activation. Similar to Pt nanoparticles, the unique size control without altering chemical properties afforded by this approach is able to increase the number of PGM-free active sites. The best O...

Learning Dynamic Siamese Network for Visual Object Tracking

Abstract: How to effectively learn temporal variation of target appearance, to exclude the interference of cluttered background, while maintaining real-time response, is an essential problem of visual object tracking. Recently, Siamese networks have shown great potentials of matching based trackers in achieving balanced accuracy and beyond realtime speed. However, they still have a big gap to classification & updating based trackers in tolerating the temporal changes of objects and imaging conditions. In this paper, we propose dynamic Siamese network, via a fast transformation learning model that enables effective online learning of target appearance variation and background suppression from previous frames. We then present elementwise multi-layer fusion to adaptively integrate the network outputs using multi-level deep features. Unlike state-of-theart trackers, our approach allows the usage of any feasible generally- or particularly-trained features, such as SiamFC and VGG. More importantly, the proposed dynamic Siamese network can be jointly trained as a whole directly on the labeled video sequences, thus can take full advantage of the rich spatial temporal information of moving objects. As a result, our approach achieves state-of-the-art performance on OTB-2013 and VOT-2015 benchmarks, while exhibits superiorly balanced accuracy and real-time response over state-of-the-art competitors.

Big Data and cloud computing: innovation opportunities and challenges

Abstract: Big Data has emerged in the past few years as a new paradigm providing abundant data and opportunities to improve and/or enable research and decision-support applications with unprecedented value for digital earth applications including business, sciences and engineering. At the same time, Big Data presents challenges for digital earth to store, transport, process, mine and serve the data. Cloud computing provides fundamental support to address the challenges with shared computing resources including computing, storage, networking and analytical software; the application of these resources has fostered impressive Big Data advancements. This paper surveys the two frontiers – Big Data and cloud computing – and reviews the advantages and consequences of utilizing cloud computing to tackling Big Data in the digital earth and relevant science domains. From the aspects of a general introduction, sources, challenges, technology status and research opportunities, the following observations are offered: (i...

Understanding differences between summer vs. school obesogenic behaviors of children: the structured days hypothesis

Abstract: Although the scientific community has acknowledged modest improvements can be made to weight status and obesogenic behaviors (i.e., physical activity, sedentary/screen time, diet, and sleep) during the school year, studies suggests improvements are erased as elementary-age children are released to summer vacation. Emerging evidence shows children return to school after summer vacation displaying accelerated weight gain compared to the weight gained occurring during the school year. Understanding how summer days differ from when children are in school is, therefore, essential. There is limited evidence on the etiology of accelerated weight gain during summer, with few studies comparing obesogenic behaviors on the same children during school and summer. For many children, summer days may be analogous to weekend days throughout the school year. Weekend days are often limited in consistent and formal structure, and thus differ from school days where segmented, pre-planned, restrictive, and compulsory components exist that shape obesogenic behaviors. The authors hypothesize that obesogenic behaviors are beneficially regulated when children are exposed to a structured day (i.e., school weekday) compared to what commonly occurs during summer. This is referred to as the ‘Structured Days Hypothesis’ (SDH). To illustrate how the SDH operates, this study examines empirical data that compares weekend day (less-structured) versus weekday (structured) obesogenic behaviors in U.S. elementary school-aged children. From 190 studies, 155 (~80%) demonstrate elementary-aged children’s obesogenic behaviors are more unfavorable during weekend days compared to weekdays. In light of the SDH, consistent evidence demonstrates the structured environment of weekdays may help to protect children by regulating obesogenic behaviors, most likely through compulsory physical activity opportunities, restricting caloric intake, reducing screen time occasions, and regulating sleep schedules. Summer is emerging as the critical period where childhood obesity prevention efforts need to be focused. The SDH can help researchers understand the drivers of obesogenic behaviors during summer and lead to innovative intervention development.

50th Anniversary Perspective: Are Polymer Nanocomposites Practical for Applications?

Abstract: The field of polymer nanocomposites has been at the forefront of research in the polymer community for the past few decades. Foundational work published in Macromolecules during this time has emphasized the physics and chemistry of the inclusion of nanofillers; remarkable early developments suggested that these materials would create a revolution in the plastics industry. After 25 years of innovative and groundbreaking research, PNCs have enabled many niche solutions. To complement the extensive literature currently available, we focus this Perspective on four case studies of PNCs applications: (i) filled rubbers, (ii) continuous fiber reinforced thermoset composites, (iii) membranes for gas separations, and (iv) dielectrics for capacitors and insulation. After presenting synthetic developments we discuss the application of polymer nanocomposites to each of these topic areas; successes will be noted, and we will finish each section by highlighting the various technological bottlenecks that need to be over...

Country-level institutions, firm value, and the role of corporate social responsibility initiatives

Abstract: Drawing on transaction cost theories and the resource-based view of a firm, we posit that the value of corporate social responsibility (CSR) initiatives is greater in countries where an absence of market-supporting institutions increases transaction costs and limits access to resources. Using a large sample of 11,672 firm-year observations representing 2445 unique firms from 53 countries during 2003–2010 and controlling for firm-level unobservable heterogeneity, we find supportive evidence that CSR is more positively related to firm value in countries with weaker market institutions. We also provide evidence on the channels through which CSR initiatives reduce transaction costs. We find that CSR is associated with improved access to financing in countries with weaker equity and credit markets, greater investment and lower default risk in countries with more limited business freedom, and longer trade credit period and higher future sales growth in countries with weaker legal institutions. Our findings provide new insights on non-market mechanisms such as CSR through which firms can compensate for institutional voids.

Microbial Extracellular Polymeric Substances (EPSs) in Ocean Systems.

Abstract: Microbial cells (ie bacteria, archaea, microeukaryotes) in oceans secrete a diverse array of large molecules, collectively called extracellular polymeric substances (EPS) or simply exopolymers These secretions facilitate attachment to surfaces that lead to the formation of structured 'biofilm' communities In open-water environments, they also lead to formation of organic colloids, and larger aggregations of cells, called ‘marine snow’ Secretion of EPS is now recognized as a fundamental microbial adaptation, occurring under many environmental conditions, and one that influences many ocean processes This relatively recent realization has revolutionized our understanding of microbial impacts on ocean systems EPS occur in a range of molecular sizes, conformations and physical/chemical properties, and polysaccharides, proteins, lipids and even nucleic acids are actively-secreted components Interestingly, however, the physical ultrastructure of how individual EPS interact with each other is poorly-understood Together, the EPS matrix molecules form a three-dimensional architecture from which cells may localize extracellular activities and conduct cooperative/ antagonistic interactions that cannot be accomplished efficiently by free-living cells EPS alter optical signatures of sediments and seawater, and are involved in biogeomineral precipitation and the construction of microbial macrostructures, and horizontal-transfers of genetic information In the water-column, they contribute to the formation of marine snow, transparent exopolymer particles (TEP), sea-surface microlayer biofilm, and marine oil snow (MOS) Excessive production of EPS occurs during later-stages of phytoplankton blooms as an excess metabolic byproduct and releases a carbon pool that transitions among dissolved-, colloidal-, and gel-states Some EPS are highly-labile carbon forms, while other forms appear quite refractory to degradation Emerging studies suggest that EPS contribute to efficient trophic-transfer of environmental contaminants, and may provide a protective refugia for pathogenic cells within marine systems; one that enhances their survival/persistence Finally, these secretions are prominent in ‘extreme’ environments ranging from sea-ice communities to hypersaline systems to the high-temperatures/pressures of hydrothermal-vent systems This overview summarizes some of the roles of exopolymer in oceans

SnS nanoparticles electrostatically anchored on three-dimensional N-doped graphene as an active and durable anode for sodium-ion batteries

Abstract: SnS nanoparticles (SnS NPs) electrostatically anchored on a 3D N-doped graphene (3DNG) network exhibit the best cycling performance reported so far for SnS-based anodes. The stronger affinity of 3DNG to SnS NPs and to the discharge product compared to pure graphene is the fundamental reason for achieving a stable electrode architecture during cycling.

Patterns of sedentary behavior and mortality in U.S. middle-aged and older adults a national cohort study

Abstract: Background Excessive sedentary time is ubiquitous in Western societies. Previous studies have relied on self-reporting to evaluate the total volume of sedentary time as a prognostic risk factor for mortality and have not examined whether the manner in which sedentary time is accrued (in short or long bouts) carries prognostic relevance. Objective To examine the association between objectively measured sedentary behavior (its total volume and accrual in prolonged, uninterrupted bouts) and all-cause mortality. Design Prospective cohort study. Setting Contiguous United States. Participants 7985 black and white adults aged 45 years or older. Measurements Sedentary time was measured using a hip-mounted accelerometer. Prolonged, uninterrupted sedentariness was expressed as mean sedentary bout length. Hazard ratios (HRs) were calculated comparing quartiles 2 through 4 to quartile 1 for each exposure (quartile cut points: 689.7, 746.5, and 799.4 min/d for total sedentary time; 7.7, 9.6, and 12.4 min/bout for sedentary bout duration) in models that included moderate to vigorous physical activity. Results Over a median follow-up of 4.0 years, 340 participants died. In multivariable-adjusted models, greater total sedentary time (HR, 1.22 [95% CI, 0.74 to 2.02]; HR, 1.61 [CI, 0.99 to 2.63]; and HR, 2.63 [CI, 1.60 to 4.30]; P for trend < 0.001) and longer sedentary bout duration (HR, 1.03 [CI, 0.67 to 1.60]; HR, 1.22 [CI, 0.80 to 1.85]; and HR, 1.96 [CI, 1.31 to 2.93]; P for trend < 0.001) were both associated with a higher risk for all-cause mortality. Evaluation of their joint association showed that participants classified as high for both sedentary characteristics (high sedentary time [≥12.5 h/d] and high bout duration [≥10 min/bout]) had the greatest risk for death. Limitation Participants may not be representative of the general U.S. population. Conclusion Both the total volume of sedentary time and its accrual in prolonged, uninterrupted bouts are associated with all-cause mortality, suggesting that physical activity guidelines should target reducing and interrupting sedentary time to reduce risk for death. Primary Funding Source National Institutes of Health.

Search for invisible decays of a dark photon produced in e+e- collisions at BaBar

Abstract: We search for single-photon events in 53 fb^{-1} of e^{+}e^{-} collision data collected with the BABAR detector at the PEP-II B-Factory. We look for events with a single high-energy photon and a large missing momentum and energy, consistent with production of a spin-1 particle A^{'} through the process e^{+}e^{-}→γA^{'}; A^{'}→invisible. Such particles, referred to as "dark photons," are motivated by theories applying a U(1) gauge symmetry to dark matter. We find no evidence for such processes and set 90% confidence level upper limits on the coupling strength of A^{'} to e^{+}e^{-} in the mass range m_{A^{'}}≤8 GeV. In particular, our limits exclude the values of the A^{'} coupling suggested by the dark-photon interpretation of the muon (g-2)_{μ} anomaly, as well as a broad range of parameters for the dark-sector models.

Determining Risk of Falls in Community Dwelling Older Adults: A Systematic Review and Meta-analysis Using Posttest Probability.

Abstract: BACKGROUND: Falls and their consequences are significant concerns for older adults, caregivers, and health care providers. Identification of fall risk is crucial for appropriate referral to preventive interventions. Falls are multifactorial; no single measure is an accurate diagnostic tool. There is limited information on which history question, self-report measure, or performance-based measure, or combination of measures, best predicts future falls. Purpose: First, to evaluate the predictive ability of history questions, self-report measures, and performance-based measures for assessing fall risk of community-dwelling older adults by calculating and comparing posttest probability (PoTP) values for individual test/measures. Second, to evaluate usefulness of cumulative PoTP for measures in combination. Data Sources: To be included, a study must have used fall status as an outcome or classification variable, have a sample size of at least 30 ambulatory community-living older adults (>=65 years), and track falls occurrence for a minimum of 6 months. Studies in acute or long-term care settings, as well as those including participants with significant cognitive or neuromuscular conditions related to increased fall risk, were excluded. Searches of Medline/PubMED and Cumulative Index of Nursing and Allied Health (CINAHL) from January 1990 through September 2013 identified 2294 abstracts concerned with fall risk assessment in community-dwelling older adults. Study Selection: Because the number of prospective studies of fall risk assessment was limited, retrospective studies that classified participants (faller/nonfallers) were also included. Ninety-five full-text articles met inclusion criteria; 59 contained necessary data for calculation of PoTP. The Quality Assessment Tool for Diagnostic Accuracy Studies (QUADAS) was used to assess each study's methodological quality. Data Extraction: Study design and QUADAS score determined the level of evidence. Data for calculation of sensitivity (Sn), specificity (Sp), likelihood ratios (LR), and PoTP values were available for 21 of 46 measures used as search terms. An additional 73 history questions, self-report measures, and performance-based measures were used in included articles; PoTP values could be calculated for 35. Data Synthesis: Evidence tables including PoTP values were constructed for 15 history questions, 15 self-report measures, and 26 performance-based measures. Recommendations for clinical practice were based on consensus. Limitations: Variations in study quality, procedures, and statistical analyses challenged data extraction, interpretation, and synthesis. There was insufficient data for calculation of PoTP values for 63 of 119 tests. Conclusions: No single test/measure demonstrated strong PoTP values. Five history questions, 2 self-report measures, and 5 performance-based measures may have clinical usefulness in assessing risk of falling on the basis of cumulative PoTP. Berg Balance Scale score (=12 seconds), and 5 times sit-to-stand times (>=12) seconds are currently the most evidence-supported functional measures to determine individual risk of future falls. Shortfalls identified during review will direct researchers to address knowledge gaps. Copyright (C) 2016 the Section on Geriatrics of the American Physical Therapy Association Language: en

Escaping the iron cage: Liabilities of origin and CSR reporting of emerging market multinational enterprises

Abstract: This article examines the link between the condition of institutional voids in emerging markets and the use of the practice of corporate social responsibility (CSR) reporting by emerging market multinational enterprises (EM-MNEs). Based on neo-institutional theory and in light of the specificity of emerging markets, we propose a positive relationship between institutional voids and CSR reporting. Home-country institutional voids push companies to internationalize as a way to escape the institutional constraints and inefficiencies in their own markets, but at the same time create legitimacy challenges for these companies abroad. In particular, EM-MNEs from less institutionally developed countries are likely to face liabilities of origin – negative perceptions in host countries about these firms’ willingness and ability to conduct legitimate business. CSR reporting is an effective strategy to overcome such liabilities and barriers to legitimation as it conveys to host countries and global stakeholders alignment with global meta-norms and expectations. Internationalization, listing on developed country stock exchanges, and time, further magnify EM-MNEs’ legitimacy challenges and thus the use of CSR reporting to mitigate them. Our hypotheses are supported in a longitudinal study of 157 of the largest EM-MNEs ranked by the United Nations Conference on Trade and Development (UNCTAD) between 2004 and 2011.

Air–Ground Channel Characterization for Unmanned Aircraft Systems—Part I: Methods, Measurements, and Models for Over-Water Settings

Abstract: The use of unmanned aerial systems (UASs), which are also known as unmanned aerial vehicles, and by the term “drones” in the popular press, is growing rapidly. To ensure safety, UAS control and nonpayload communication (CNPC) links must operate very reliably in a variety of conditions. This requires an accurate quantitative characterization of the air–ground (AG) channel, and this channel characterization is the focus of this paper. After providing motivation and background, we describe our methods and modeling approach, followed by a description of our simultaneous dual-band (L-band ∼970 MHz, C-band ∼5 GHz) measurement campaign and the over-water (OW) measurement sites. Example results for path loss and root-mean-square delay spread are provided, as well as the results for channel stationarity distance (SD), used in calculating small-scale Rician $K$ - factor and correlations between the two receiver antennas that we employed in each frequency band. Two distinct SD measures—the power delay profile (PDP) correlation coefficient and the spatial autocorrelation matrix collinearity—were used and found to be of the same order. Path-loss exponents are near that of free space, but significant two-ray cancelation effects for these OW settings warrant more accurate models, which we provide. Delay spreads in the OW channels are also dominated by the two-ray components and are hence typically very small (∼10 ns) but can exceed 350 ns. A third intermittent multipath component (MPC) is also present a nonnegligible fraction of time; hence, we provide statistical wideband AG channel models to represent this. Future papers in this series will report results for the AG channel with ground sites in other types of environments.

Identity-Aware Convolutional Neural Network for Facial Expression Recognition

Abstract: Facial expression recognition suffers under realworldconditions, especially on unseen subjects due to highinter-subject variations. To alleviate variations introduced bypersonal attributes and achieve better facial expression recognitionperformance, a novel identity-aware convolutional neuralnetwork (IACNN) is proposed. In particular, a CNN with a newarchitecture is employed as individual streams of a bi-streamidentity-aware network. An expression-sensitive contrastive lossis developed to measure the expression similarity to ensure thefeatures learned by the network are invariant to expressionvariations. More importantly, an identity-sensitive contrastiveloss is proposed to learn identity-related information from identitylabels to achieve identity-invariant expression recognition.Extensive experiments on three public databases including aspontaneous facial expression database have shown that theproposed IACNN achieves promising results in real world.

Transancestral mapping and genetic load in systemic lupus erythematosus

Abstract: Systemic lupus erythematosus (SLE) is an autoimmune disease with marked gender and ethnic disparities. We report a large transancestral association study of SLE using Immunochip genotype data from 27,574 individuals of European (EA), African (AA) and Hispanic Amerindian (HA) ancestry. We identify 58 distinct non-HLA regions in EA, 9 in AA and 16 in HA (∼50% of these regions have multiple independent associations); these include 24 novel SLE regions (P<5 × 10-8), refined association signals in established regions, extended associations to additional ancestries, and a disentangled complex HLA multigenic effect. The risk allele count (genetic load) exhibits an accelerating pattern of SLE risk, leading us to posit a cumulative hit hypothesis for autoimmune disease. Comparing results across the three ancestries identifies both ancestry-dependent and ancestry-independent contributions to SLE risk. Our results are consistent with the unique and complex histories of the populations sampled, and collectively help clarify the genetic architecture and ethnic disparities in SLE.

International criteria for electrocardiographic interpretation in athletes: Consensus statement

Abstract: Sudden cardiac death (SCD) is the leading cause of mortality in athletes during sport. A variety of mostly hereditary, structural or electrical cardiac disorders are associated with SCD in young athletes, the majority of which can be identified or suggested by abnormalities on a resting 12-lead electrocardiogram (ECG). Whether used for diagnostic or screening purposes, physicians responsible for the cardiovascular care of athletes should be knowledgeable and competent in ECG interpretation in athletes. However, in most countries a shortage of physician expertise limits wider application of the ECG in the care of the athlete. A critical need exists for physician education in modern ECG interpretation that distinguishes normal physiological adaptations in athletes from distinctly abnormal findings suggestive of underlying pathology. Since the original 2010 European Society of Cardiology recommendations for ECG interpretation in athletes, ECG standards have evolved quickly, advanced by a growing body of scientific data and investigations that both examine proposed criteria sets and establish new evidence to guide refinements. On 26-27 February 2015, an international group of experts in sports cardiology, inherited cardiac disease, and sports medicine convened in Seattle, Washington (USA), to update contemporary standards for ECG interpretation in athletes. The objective of the meeting was to define and revise ECG interpretation standards based on new and emerging research and to develop a clear guide to the proper evaluation of ECG abnormalities in athletes. This statement represents an international consensus for ECG interpretation in athletes and provides expert opinion-based recommendations linking specific ECG abnormalities and the secondary evaluation for conditions associated with SCD.

Air–Ground Channel Characterization for Unmanned Aircraft Systems—Part III: The Suburban and Near-Urban Environments

Abstract: Applications for unmanned aircraft systems (UAS), or “drones,” are increasing rapidly. In order to provide safe and reliable links to integrate UAS into the National Airspace System (NAS), control and nonpayload communication (CNPC) system requirements are being specified. A comprehensive knowledge of the air-to-ground (AG) channels in the bands of interest (C-band and L-band) plays an essential role. The NASA Glenn Research Center has sponsored an AG channel measurement campaign for most of the typical ground site (GS) local environments, including over water [8] , hilly/mountainous [9] , suburban, and near-urban. As a continuation of our prior study, this paper addresses the suburban and near-urban scenarios. Our developed AG channel models include path loss, small-scale fading Ricean K factors, spatial and interfrequency correlations for multiple aircraft antennas, root-mean-square (RMS) delay spread, and wideband tapped delay line (TDL) models. The path loss is described by either log-distance or two-ray models, with small corrections for flight direction. The K factors were 12 (14) dB in L-band and 27.4 (28.5) dB in C-band in near-urban (suburban) environments. The interband signals were uncorrelated, but the intra-band signals were highly correlated, with the median correlation coefficient greater than 0.85. The C-band RMS delay spread was on average 10 to 60 ns, with maximum of approximately 4 μs. The TDL models are composed of the line-of-sight (LOS) component, a ground reflection, and up to seven intermittent multipath components (MPCs). Relative power, phase, occurrence probability, duration, and excess delays for these intermittent MPCs are quantified. An algorithm to simulate the AG channel impulse response (CIR) via the TDL models is provided.

A bird's eye view of civilians killed by police in 2015: further evidence of implicit bias

Abstract: Research Summary We analyzed 990 police fatal shootings using data compiled by The Washington Post in 2015. After first providing a basic descriptive analysis of these shootings, we then examined the data for evidence of implicit bias by using multivariate regression models that predict two indicators of threat perception failure: (1) whether the civilian was not attacking the officer(s) or other civilians just before being fatally shot and (2) whether the civilian was unarmed when fatally shot. The results indicated civilians from “other” minority groups were significantly more likely than Whites to have not been attacking the officer(s) or other civilians and that Black civilians were more than twice as likely as White civilians to have been unarmed. Policy Implications We implore the U.S. government to move forward with its publication of a national police use-of-force database, including as much information about the officers involved as possible. We further suggest police departments use training programs and community activities to minimize implicit bias among their officers.

Twenty years of social capital and health research: a glossary

Abstract: Research on social capital in public health is approaching its 20th anniversary. Over this period, there have been rich and productive debates on the definition, measurement and importance of social capital for public health research and practice. As a result, the concepts and measures characterising social capital and health research have also evolved, often drawing from research in the social, political and behavioural sciences. The multidisciplinary adaptation of social capital-related concepts to study health has made it challenging for researchers to reach consensus on a common theoretical approach. This glossary thus aims to provide a general overview without recommending any particular approach. Based on our knowledge and research on social capital and health, we have selected key concepts and terms that have gained prominence over the last decade and complement an earlier glossary on social capital and health.

Probing the electronic and catalytic properties of a bimetallic surface with 3 nm resolution

Abstract: Tip-enhanced Raman spectroscopy in conjunction with scanning tunnelling microscopy can be used to correlate chemical properties and surface topography of bimetallic catalysts with high spatial resolution. An atomic- and molecular-level understanding of heterogeneous catalysis is required to characterize the nature of active sites and improve the rational design of catalysts1,2,3. Achieving this level of characterization requires techniques that can correlate catalytic performances to specific surface structures, so as to avoid averaging effects1. Tip-enhanced Raman spectroscopy4,5,6,7 combines scanning probe microscopy with plasmon-enhanced Raman scattering and provides simultaneous topographical and chemical information at the nano/atomic scale from ambient8,9,10 to ultrahigh-vacuum11,12 and electrochemical environments13,14. Therefore, it has been used to monitor catalytic reactions15,16,17,18 and is proposed to correlate the local structure and function of heterogeneous catalysts19. Bimetallic catalysts, such as Pd–Au, show superior performance in various catalytic reactions20,21, but it has remained challenging to correlate structure and reactivity because of their structural complexity. Here, we show that TERS can chemically and spatially probe the site-specific chemical (electronic and catalytic) and physical (plasmonic) properties of an atomically well-defined Pd(sub-monolayer)/Au(111) bimetallic model catalyst at 3 nm resolution in real space using phenyl isocyanide as a probe molecule ( Fig. 1a ). We observe a weakened N≡C bond and enhanced reactivity of phenyl isocyanide adsorbed at the Pd step edge compared with that at the Pd terrace. Density functional theory corroborates these observations by revealing a higher d-band electronic profile for the low-coordinated Pd step edge atoms. The 3 nm spatial resolution we demonstrate here is the result of an enhanced electric field and distinct electronic properties at the step edges.

V5S8–graphite hybrid nanosheets as a high rate-capacity and stable anode material for sodium-ion batteries

Abstract: Here we report chemically-exfoliated V5S8 and graphite hybrid nanosheets (ce-V5S8–C) as a novel anode material for sodium-ion batteries (SIBs). It exhibits much improved sodiation capacity, rate capability, reversibility and stability compared to other major SIB anode materials.

Self-Assembly: A Facile Way of Forming Ultrathin, High-Performance Graphene Oxide Membranes for Water Purification

Abstract: Single-layer graphene oxide (SLGO) is emerging as a new-generation membrane material for high-flux, high-selectivity water purification, owing to its favorable two-dimensional morphology that allows facile fabrication of ultrathin membranes with subnanometer interlayer channels. However, reliable and precise molecular sieving performance still necessarily depends on thick graphene oxide (GO) deposition that usually leads to low water flux. This trade-off between selectivity and flux significantly impedes the development of ultrathin GO membranes. In this work, we demonstrate that the selectivity/flux trade-off can be broken by self-assembly of SLGO via simple deposition rate control. We find GO membranes, prepared by slow deposition of SLGO flakes, exhibit considerably improved salt rejection, while counterintuitively having 2.5–4 times higher water flux than that of membranes prepared by fast deposition. This finding has extensive implications of designing/tuning interlayer nanostructure of ultrathin GO ...

A New rGO-Overcoated Sb2Se3 Nanorods Anode for Na+ Battery: In Situ X-Ray Diffraction Study on a Live Sodiation/Desodiation Process

Abstract: Sodium ion batteries (SIBs) are a promising alternative to lithium ion batteries for a broader range of energy storage applications in the future. However, the development of high-performance anode materials is a bottleneck of SIBs advancement. In this work, Sb2Se3 nanorods uniformly wrapped by reduced graphene oxide (rGO) as a promising anode material for SIBs are reported. The results show that such Sb2Se3/rGO hybrid anode yields a high reversible mass-specific energy capacity of 682, 448, and 386 mAh g−1 at a rate of 0.1, 1.0, and 2.0 A g−1, respectively, and sustains at least 500 stable cycles at a rate of 1.0 A g−1 with an average mass-specific energy capacity of 417 mAh g−1 and capacity retention of 90.2%. In situ X-ray diffraction study on a live SIB cell reveals that the observed high performance is a result of the combined Na+ intercalation, conversion reaction between Na+ and Se, and alloying reaction between Na+ and Sb. The presence of rGO also plays a key role in achieving high rate capacity and cycle stability by providing good electrical conductivity, tolerant accommodation to volume change, and strong electron interactions to the base Sb2Se3 anode.