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- 1/N expansion for the degenerate Anderson model in the mixed-valence regimeZhang, F. C.; Lee, T. K. (American Physical Society, 1983-07)The 1N expansion method for the degenerate Anderson model is formulated. N is the degeneracy factor of one of the f-electron configurations. Various ground-state properties are calculated. Excellent agreement with the result of Bethe ansatz for N=6 is shown. The rate of convergence of the series is analyzed. The merit and inadequacy of the method are discussed. At zero temperature the ratio of the magnetic susceptibility and the specific-heat linear coefficient is shown to lie within a range of 1 and 1+(N-1)-1.
- 10 kpc Scale Seyfert Galaxy Outflow: HST/COS Observations of IRAS F22456-5125Borguet, Benoit C. J.; Edmonds, Douglas; Arav, Nahum; Dunn, Jay; Kriss, Gerard A. (IOP Publishing Ltd., 2012-06)We present analysis of the UV spectrum of the low-z AGN IRAS F22456-5125 obtained with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. The spectrum reveals six main kinematic components, spanning a range of velocities of up to 800 km s (1), which for the first time are observed in troughs associated with C II, C IV, N V, Si II, Si III, Si IV, and S IV. We also obtain data on the O VI troughs, which we compare to those available from an earlier Far Ultraviolet Spectroscopic Explorer epoch. Column densities measured from these ions allow us to derive a well-constrained photoionization solution for each outflow component. Two of these kinematic components show troughs associated with transitions from excited states of Si II and C II. The number density inferred from these troughs, in combination with the deduced ionization parameter, allows us to determine the distance to these outflow components from the central source. We find these components to be at a distance of similar to 10 kpc. The distances and the number densities derived are consistent with the outflow being part of a galactic wind.
- 14-year program monitoring the flux densities of 33 radio sources at low frequenciesSalgado, José Francisco; Altschuler, Daniel R.; Ghosh, Tapasi; Dennison, Brian K.; Mitchell, Kenneth J.; Payne, Harry E. (IOP PUBLISHING LTD, 1999-01)We present the results of a low-frequency flux density monitoring program of 33 extragalactic radio sources. The light curves at 318 and 430 MHz over a 14 yr period are presented. The measurements were made with the NAIC Arecibo 305 m radio telescope at approximately bimonthly intervals between 1980 January and 1989 February and at less regular intervals between 1989 October and 1993 October, for a total of 64 observing sessions. In addition, we provide a first discussion of the results, pointing out several source properties and interesting objects.
- The 2015 landslide and tsunami in Taan Fiord, AlaskaHigman, Bretwood; Shugar, Dan H.; Stark, Colin P.; Ekstrom, Goran; Koppes, Michele N.; Lynett, Patrick; Dufresne, Anja; Haeussler, Peter J.; Geertsema, Marten; Gulick, Sean; Mattox, Andrew; Venditti, Jeremy G.; Walton, Maureen A. L.; McCall, Naoma; Mckittrick, Erin; MacInnes, Breanyn; Bilderback, Eric L.; Tang, Hui; Willis, Michael J.; Richmond, Bruce; Reece, Robert S.; Larsen, Chris; Olson, Bjorn; Capra, James; Ayca, Aykut; Bloom, Colin; Williams, Haley; Bonno, Doug; Weiss, Robert; Keen, Adam; Skanavis, Vassilios; Loso, Michael (Springer Nature, 2018-09-06)Glacial retreat in recent decades has exposed unstable slopes and allowed deep water to extend beneath some of those slopes. Slope failure at the terminus of Tyndall Glacier on 17 October 2015 sent 180 million tons of rock into Taan Fiord, Alaska. The resulting tsunami reached elevations as high as 193 m, one of the highest tsunami runups ever documented worldwide. Precursory deformation began decades before failure, and the event left a distinct sedimentary record, showing that geologic evidence can help understand past occurrences of similar events, and might provide forewarning. The event was detected within hours through automated seismological techniques, which also estimated the mass and direction of the slide - all of which were later confirmed by remote sensing. Our field observations provide a benchmark for modeling landslide and tsunami hazards. Inverse and forward modeling can provide the framework of a detailed understanding of the geologic and hazards implications of similar events. Our results call attention to an indirect effect of climate change that is increasing the frequency and magnitude of natural hazards near glaciated mountains.
- 2D Hierarchical Microbarcodes with Expanded Storage Capacity for Optical Multiplex and Information EncryptionWorch, Josh; Xie, Yujie; Tong, Zaizai; Rho, Julia; Dove, Andrew; O'Reilly, Rachel (2023-11-28)The design of nanosegregated fluorescent tags/barcodes by geometrical patterning with precise dimensions and hierarchies could integrate multilevel optical information within one carrier and enhance microsized barcoding techniques for ultrahigh-density optical data storage and encryption. However, precise control of the spatial distribution in micro/nanosized matrices intrinsically limits the accessible barcoding applications in terms of material design and construction. Here, crystallization forces are leveraged to enable a rapid, programmable molecular packing and rapid epitaxial growth of fluorescent units in 2D via crystallization-driven self-assembly. The fluorescence encoding density, scalability, information storage capacity, and decoding techniques of the robust 2D polymeric barcoding platform are explored systematically. These results provide both a theoretical and an experimental foundation for expanding the fluorescence storage capacity, which is a longstanding challenge in state-of-the-art microbarcoding techniques and establish a generalized and adaptable coding platform for high-throughput analysis and optical multiplexing.
- (2S,4R)-4-Fluoro-pyrrolidinium-2-carboxyl-ate.Hobart, David B. Jr.; Merola, Joseph S. (International Union of Crystallography, 2012-08-01)The crystal structure of the title compound, C(5)H(8)FNO(2), at 100 K, displays inter-molecular N-H⋯O hydrogen bonding between the ammonium and carboxyl-ate groups as a result of its zwitterionic nature in the solid state. The five-membered ring adopts an envelope conformation with the C atom at the 3-position as the flap. The compound is of inter-est with respect to the synthesis and structural properties of synthetic collagens. The absolute structure was determined by comparison with the commercially available material.
- 3D electron microscopy and volume-based bouton sorting reveal the selectivity of inputs onto geniculate relay cell and interneuron dendrite segmentsMaher, Erin E.; Briegel, Alex C.; Imtiaz, Shahrozia; Fox, Michael A.; Golino, Hudson; Erisir, Alev (Frontiers, 2023-03)IntroductionThe visual signals evoked at the retinal ganglion cells are modified and modulated by various synaptic inputs that impinge on lateral geniculate nucleus cells before they are sent to the cortex. The selectivity of geniculate inputs for clustering or forming microcircuits on discrete dendritic segments of geniculate cell types may provide the structural basis for network properties of the geniculate circuitry and differential signal processing through the parallel pathways of vision. In our study, we aimed to reveal the patterns of input selectivity on morphologically discernable relay cell types and interneurons in the mouse lateral geniculate nucleus. MethodsWe used two sets of Scanning Blockface Electron Microscopy (SBEM) image stacks and Reconstruct software to manually reconstruct of terminal boutons and dendrite segments. First, using an unbiased terminal sampling (UTS) approach and statistical modeling, we identified the criteria for volume-based sorting of geniculate boutons into their putative origins. Geniculate terminal boutons that were sorted in retinal and non-retinal categories based on previously described mitochondrial morphology, could further be sorted into multiple subpopulations based on their bouton volume distributions. Terminals deemed non-retinal based on the morphological criteria consisted of five distinct subpopulations, including small-sized putative corticothalamic and cholinergic boutons, two medium-sized putative GABAergic inputs, and a large-sized bouton type that contains dark mitochondria. Retinal terminals also consisted of four distinct subpopulations. The cutoff criteria for these subpopulations were then applied to datasets of terminals that synapse on reconstructed dendrite segments of relay cells or interneurons. ResultsUsing a network analysis approach, we found an almost complete segregation of retinal and cortical terminals on putative X-type cell dendrite segments characterized by grape-like appendages and triads. On these cells, interneuron appendages intermingle with retinal and other medium size terminals to form triads within glomeruli. In contrast, a second, presumed Y-type cell displayed dendrodendritic puncta adherentia and received all terminal types without a selectivity for synapse location; these were not engaged in triads. Furthermore, the contribution of retinal and cortical synapses received by X-, Y- and interneuron dendrites differed such that over 60% of inputs to interneuron dendrites were from the retina, as opposed to 20% and 7% to X- and Y-type cells, respectively. ConclusionThe results underlie differences in network properties of synaptic inputs from distinct origins on geniculate cell types.
- A 4-year longitudinal neuroimaging study of cognitive control using latent growth modeling: developmental changes and brain-behavior associationsKim-Spoon, Jungmeen; Herd, Toria; Brieant, Alexis; Elder, Jacob; Lee, Jacob; Deater-Deckard, Kirby; Casas, Brooks (2021-08-15)Despite theoretical models suggesting developmental changes in neural substrates of cognitive control in adolescence, empirical research has rarely examined intraindividual changes in cognitive control-related brain activation using multi-wave multivariate longitudinal data. We used longitudinal repeated measures of brain activation and behavioral performance during the multi-source interference task (MSIT) from 167 adolescents (53% male) who were assessed annually over four years from ages 13 to 17 years. We applied latent growth modeling to delineate the pattern of brain activation changes over time and to examine longitudinal associations between brain activation and behavioral performance. We identified brain regions that showed differential change patterns: (1) the fronto-parietal regions that involved bilateral insula, bilateral middle frontal gyrus, left pre-supplementary motor area, left inferior parietal lobule, and right precuneus; and (2) the rostral anterior cingulate cortex (rACC) region. Longitudinal confirmatory factor analyses of the fronto-parietal regions revealed strong measurement invariance across time implying that multivariate functional magnetic resonance imaging data during cognitive control can be measured reliably over time. Latent basis growth models indicated that fronto-parietal activation decreased over time, whereas rACC activation increased over time. In addition, behavioral performance data, age-related improvement was indicated by a decreasing trajectory of intraindividual variability in response time across four years. Testing longitudinal brain-behavior associations using multivariate growth models revealed that better behavioral cognitive control was associated with lower fronto-parietal activation, but the change in behavioral performance was not related to the change in brain activation. The current findings suggest that reduced effects of cognitive interference indicated by fronto-parietal recruitment may be a marker of a maturing brain that underlies better cognitive control performance during adolescence.
- 5-year follow-up of adolescents with social anxiety disorder: Current functioning during COVID-19Carlton, Corinne N.; Garcia, Katelyn M.; Honaker, Makayla; Richey, John A.; Ollendick, Thomas H. (Elsevier, 2023-04)The present study followed-up adolescents with social anxiety disorder (SAD) during the COVID-19 pandemic, approximately 5-years following their participation in an Attention Bias Modification Training (ABMT) program (Ollendick et al., 2019). The current study aimed to evaluate current functioning and quality of life (QoL) during the emerging adulthood period. Participants included 27 young adults who completed a randomized controlled trial of ABMT and were available for follow-up. Participants filled out self-report measures of QoL and functioning and underwent a clinical interview to assess current severity of social anxiety. Clinician-rated symptoms of SAD significantly decreased from post-treatment to 5-year follow-up. Additionally, results demonstrated that social anxiety severity was significantly related to poorer self-reported physical and psychological health as well as poorer functioning with regard to social distancing fears during COVID-19. Lastly, when evaluating change in symptoms over time, increases in social anxiety severity over a 5-year period significantly predicted worsened social distancing fears during COVID-19.
- The 750 GeV diphoton excess in unified SU(2)(L) x SU(2)(R) x SU(4) models from noncommutative geometryAydemir, U.; Minic, Djordje; Sun, C.; Takeuchi, Tatsu (World Scientific, 2016-06-14)
- A machine-learning approach for differentiating borderline personality disorder from community participants with brain-wide functional connectivityLahnakoski, Juha M.; Nolte, Tobias; Solway, Alec; Vilares, Iris; Hula, Andreas; Feigenbaum, Janet; Lohrenz, Terry; Casas, Brooks; Fonagy, Peter; Montague, P. Read; Schilbach, Leonhard (Elsevier, 2024-05-26)Background: Functional connectivity has garnered interest as a potential biomarker of psychiatric disorders including borderline personality disorder (BPD). However, small sample sizes and lack of within-study replications have led to divergent findings with no clear spatial foci. Aims: Evaluate discriminative performance and generalizability of functional connectivity markers for BPD. Method: Whole-brain fMRI resting state functional connectivity in matched subsamples of 116 BPD and 72 control individuals defined by three grouping strategies. We predicted BPD status using classifiers with repeated cross-validation based on multiscale functional connectivity within and between regions of interest (ROIs) covering the whole brain—global ROI-based network, seed-based ROI-connectivity, functional consistency, and voxel-to-voxel connectivity—and evaluated the generalizability of the classification in the left-out portion of non-matched data. Results: Full-brain connectivity allowed classification (∼70 %) of BPD patients vs. controls in matched inner cross-validation. The classification remained significant when applied to unmatched out-of-sample data (∼61–70 %). Highest seed-based accuracies were in a similar range to global accuracies (∼70–75 %), but spatially more specific. The most discriminative seed regions included midline, temporal and somatomotor regions. Univariate connectivity values were not predictive of BPD after multiple comparison corrections, but weak local effects coincided with the most discriminative seed-ROIs. Highest accuracies were achieved with a full clinical interview while self-report results remained at chance level. Limitations: The accuracies vary considerably between random sub-samples of the population, global signal and covariates limiting the practical applicability. Conclusions: Spatially distributed functional connectivity patterns are moderately predictive of BPD despite heterogeneity of the patient population.
- A naturally derived biomaterial formulation for improved menstrual careBataglioli, Rogerio Aparecido; Kaur, Harsimran; Muller, John; Geddes, Elizabeth; Champine, Carrie; Hsu, Bryan B. (Cell Press, 2024-07-10)Adequately managing menstruation is an important factor in the overall quality of life for women. With a growing discussion of the global need for its improvement, it is clear that better management of menstruation can positively influence social, educational, and professional outcomes. Herein, we describe a biopolymer-based formulation that gels blood in a mechanism alternative to coagulation. We first tested several biopolymer mixtures with blood and quantified increases in viscosity, finding that high-molecular-weight alginate in combination with glycerol could rapidly absorb and gel blood. We then demonstrated that this powder could be deployed both as a traditional menstrual pad filler and as an additive to menstrual cups to reduce leakage and spillage, respectively. Finally, we include an antimicrobial polymer to impair the growth of Staphylococcus aureus, a bacterium associated with toxic shock syndrome. Collectively, our work describes a biodegradable formulation derived from renewable resources that can improve menstrual care.
- A-site doping-induced renormalization of structural transformations in the PbSc0.5Nb0.5O3 relaxor ferroelectric under high pressureMaier, B. J.; Welsch, A. M.; Angel, R. J.; Mihailova, B.; Zhao, J.; Engel, J. M.; Schmitt, L. A.; Paulmann, C.; Gospodinov, M.; Friedrich, A.; Bismayer, U. (American Physical Society, 2010-05-01)The effect of A-site incorporated Ba2+ and Bi3+ on the pressure-driven structural transformations in Pb-based perovskite-type relaxor ferroelectrics has been studied with in situ x-ray diffraction and Raman scattering of PbSc0.5Nb0.5O3, Pb0.93Ba0.07Sc0.5Nb0.5O3, and Pb0.98Bi0.02Sc0.51Nb0.49O3 in the range from ambient pressure to 9.8 GPa. The substitution of Ba2+ for Pb2+ represents the case in which A-site divalent cations with stereochemically active lone-pair electrons are replaced by isovalent cations with a larger ionic radius and no active lone pairs, leading to formation of strong local elastic fields. In contrast, substitution of Bi3+ for Pb2+ involves the replacement of divalent A-site cations with active lone-pair electrons by aliovalent cations with nearly the same ionic radius and active lone pairs so it induces local electric fields but not strong elastic fields. The two types of dopants have rather distinct effects on the changes in the atomic structure under pressure. The embedding of Ba2+ and associated elastic fields hinders the development of pressure-induced ferroic ordering and thus smears out the phase transition. The addition of Bi3+ enlarges the fraction of spatial regions with a pressure-induced ferroic distortion, resulting in a more pronounced phase transition of the average structure, i.e., the preserved lone-pair order and the absence of strong local elastic fields enhances the development of the ferroic phase at high pressure. For all compounds studied, the high-pressure structure exhibits glide-plane pseudosymmetry associated with a specific octahedral tilt configuration.
- Abacus proofs of Schur function identitiesLoehr, N. A. (Siam Publications, 2010)This article uses combinatorial objects called labeled abaci to give direct combinatorial proofs of many familiar facts about Schur polynomials. We use abaci to prove the Pieri rules, the Littlewood-Richardson rule, the equivalence of the tableau definition and the determinant definition of Schur polynomials, and the combinatorial interpretation of the inverse Kostka matrix (first given by Egecioglu and Remmel). The basic idea is to regard formulas involving Schur polynomials as encoding bead motions on abaci. The proofs of the results just mentioned all turn out to be manifestations of a single underlying theme: when beads bump, objects cancel.
- Aberrant early growth of individual trigeminal sensory and motor axons in a series of mouse genetic models of 22q11.2 deletion syndromeMotahari, Zahra; Maynard, Thomas M.; Popratiloff, Anastas; Moody, Sally A.; LaMantia, Anthony-Samuel (2020-09-15)We identified divergent modes of initial axon growth that prefigure disrupted differentiation of the trigeminal nerve (CN V), a cranial nerve essential for suckling, feeding and swallowing (S/F/S), a key innate behavior compromised in multiple genetic developmental disorders including DiGeorge/22q11.2 Deletion Syndrome (22q11.2 DS). We combined rapid in vivo labeling of single CN V axons in LgDel(+/-) mouse embryos, a genomically accurate 22q11.2DS model, and 3D imaging to identify and quantify phenotypes that could not be resolved using existing methods. We assessed these phenotypes in three 22q11.2-related genotypes to determine whether individual CN V motor and sensory axons wander, branch and sprout aberrantly in register with altered anterior-posterior hindbrain patterning and gross morphological disruption of CN V seen in LgDel(+/-). In the additional 22q11.2-related genotypes: Tbx1(+/-), Ranbp1(+/-), Ranbp1(+/-) and LgDel(+/-):Raldh2(+/-); axon phenotypes are seen when hindbrain patterning and CN V gross morphology is altered, but not when it is normal or restored toward WT. This disordered growth of CN V sensory and motor axons, whose appropriate targeting is critical for optimal S/F/S, may be an early, critical determinant of imprecise innervation leading to inefficient oropharyngeal function associated with 22q11.2 deletion from birth onward.
- Above-ground tree carbon storage in response to nitrogen deposition in the US is heterogeneous and may have weakenedClark, Christopher M.; Thomas, R. Quinn; Horn, Kevin J. (Springer Nature, 2023-02-14)Long-term nitrogen deposition may not provide sustained stimulation of tree carbon storage, suggest analyses of a tree inventory and growth for the contiguous US between 2000 and 2016, compared to data for the 1980s and 1990s. Changes in nitrogen (N) availability affect the ability for forest ecosystems to store carbon (C). Here we extend an analysis of the growth and survival of 94 tree species and 1.2 million trees, to estimate the incremental effects of N deposition on changes in aboveground C (dC/dN) across the contiguous U.S. (CONUS). We find that although the average effect of N deposition on aboveground C is positive for the CONUS (dC/dN = +9 kg C per kg N), there is wide variation among species and regions. Furthermore, in the Northeastern U.S. where we may compare responses from 2000-2016 with those from the 1980s-90s, we find the recent estimate of dC/dN is weaker than from the 1980s-90s due to species-level changes in responses to N deposition. This suggests that the U.S. forest C-sink varies widely across forests and may be weakening overall, possibly necessitating more aggressive climate policies than originally thought.
- Absence of Mycobacterium intracellulare and Presence of Mycobacterium chimaera in Household Water and Biofilm Samples of Patients in the United States with Mycobacterium avium Complex Respiratory DiseaseWallace, Richard J. Jr.; Iakhiaeva, Elena; Williams, Myra D.; Brown-Elliott, Barbara A.; Vasireddy, Sruthi; Vasireddy, Ravikiran; Lande, Leah; Peterson, Donald D.; Sawicki, Janet; Kwait, Rebecca; Tichenor, Wellington S.; Turenne, Christine; Falkinham, Joseph O. III (American Society for Microbiology, 2013-03-27)Recent studies have shown that respiratory isolates from pulmonary disease patients and household water/biofilm isolates of Mycobacterium avium could be matched by DNA fingerprinting. To determine if this is true for Mycobacterium intracellulare, household water sources for 36 patients with Mycobacterium avium complex (MAC) lung disease were evaluated. MAC household water isolates from three published studies that included 37 additional MAC respiratory disease patients were also evaluated. Species identification was done initially using nonsequencing methods with confirmation by internal transcribed spacer (ITS) and/or partial 16S rRNA gene sequencing. M. intracellulare was identified by nonsequencing methods in 54 respiratory cultures and 41 household water/biofilm samples. By ITS sequencing, 49 (90.7%) respiratory isolates were M. intracellulare and 4 (7.4%) were Mycobacterium chimaera. In contrast, 30 (73%) household water samples were M. chimaera, 8 (20%) were other MAC X species (i.e., isolates positive with a MAC probe but negative with species-specific M. avium and M. intracellulare probes), and 3 (7%) were M. avium; none were M. intracellulare. In comparison, M. avium was recovered from 141 water/biofilm samples. These results indicate that M. intracellulare lung disease in the United States is acquired from environmental sources other than household water. Nonsequencing methods for identification of nontuberculous mycobacteria (including those of the MAC) might fail to distinguish closely related species (such as M. intracellulare and M. chimaera). This is the first report of M. chimaera recovery from household water. The study underscores the importance of taxonomy and distinguishing the many species and subspecies of the MAC.
- Abstracts from the 3rd Conference on Aneuploidy and Cancer: Clinical and Experimental AspectsCornish-Bowden, Athel; Rasnick, David; Heng, Henry H.; Horne, Steven; Abdallah, Batoul; Liu, Guo; Ye, Christine J.; Bloomfield, Mathew; Vincent, Mark D.; Aldaz, C. M.; Karlsson, Jenny; Valind, Anders; Jansson, Caroline; Gisselsson, David; Graves, Jennifer A. M.; Stepanenko, Aleksei A.; Andreieva, Svitlana V.; Korets, Kateryna V.; Mykytenko, Dmytro O.; Huleyuk, Nataliya L.; Baklaushev, Vladimir P.; Kovaleva, Oksana A.; Chekhonin, Vladimir P.; Vassetzky, Yegor S.; Avdieiev, Stanislav S.; Bakker, Bjorn; Taudt, Aaron S.; Belderbos, Mirjam E.; Porubsky, David; Spierings, Diana C. J.; de Jong, Tristan V.; Halsema, Nancy; Kazemier, Hinke G.; Hoekstra-Wakker, Karina; Bradley, Allan; de Bont, Eveline S. J. M.; van den Berg, Anke; Guryev, Victor; Lansdorp, Peter M.; Tatché, Maria C.; Foijer, Floris; Liehr, Thomas; Baudoin, Nicolaas C.; Nicholson, Joshua M.; Soto, Kimberly; Quintanilla, Isabel; Camps, Jordi; Cimini, Daniela; Dürrbaum, M.; Donnelly, N.; Passerini, V.; Kruse, C.; Habermann, B.; Storchová, Z.; Mandrioli, Daniele; Belpoggi, Fiorella; Silbergeld, Ellen K.; Perry, Melissa J.; Skotheim, Rolf I.; Løvf, Marthe; Johannessen, Bjarne; Hoff, Andreas M.; Zhao, Sen; SveeStrømme, Jonas M.; Sveen, Anita; Lothe, Ragnhild A.; Hehlmann, R.; Voskanyan, A.; Fabarius, A.; Böcking, Alfred; Biesterfeld, Stefan; Berynskyy, Leonid; Börgermann, Christof; Engers, Rainer; Dietz, Josef; Fritz, A.; Sehgal, N.; Vecerova, J.; Stojkovicz, B.; Ding, H.; Page, N.; Tye, C.; Bhattacharya, S.; Xu, J.; Stein, G.; Stein, J.; Berezney, R.; Gong, Xue; Grasedieck, Sarah; Swoboda, Julian; Rücker, Frank G.; Bullinger, Lars; Pollack, Jonathan R.; Roumelioti, Fani-Marlen; Chiourea, Maria; Raftopoulou, Christina; Gagos, Sarantis; Duesberg, Peter; Bloomfield, Mathew; Hwang, Sunyoung; Gustafsson, Hans T.; O’Sullivan, Ciara; Acevedo-Colina, Aracelli; Huang, Xinhe; Klose, Christian; Schevchenko, Andrej; Dickson, Robert C.; Cavaliere, Paola; Dephoure, Noah; Torres, Eduardo M.; Stampfer, Martha R.; Vrba, Lukas; LaBarge, Mark A.; Futscher, Bernard; Garbe, James C.; Trinh, Andrew L.; Zhou, Yi-Hong; Digman, Michelle (2017-06-22)
- Abundance and Size Distribution of Particulate Matter Fractions Near a Caribbean Bank Barrier ReefSimmons, George M. Jr. (Inter-Research, 1979)Recent research indicates that corals have the ability to occupy several trophic levels and that particulate matter (PM) appears to play a major role in meeting their daily energy requirements. A study was undertaken to determine the amount and size distribution of PM near a bank barrier reef off the West Indies Laboratory on St. Croix, U.S.V.I. Size distributions were determined by filtration through selected sieves and filters ranging between 250 and 0.45 μm. Results showed that PM was greater in back-reef than fore-reef areas and greater during day than night hours. The PM collected on the smallest filters (0.45μm) remained constant during both sampling periods and could potentially supply 60 % of the daily energy requirements for corals. Inclusion of the PM on the next size filter (8.0 μm) would more than account for their daily energy requirements. The mean PM abundance found in this study (1.1 mg 1^-1) is the same as that reported at another Caribbean laboratory in the West Indies.
- Abundance and Speciation of Surface Oxygen on Nanosized Platinum Catalysts and Effect on Catalytic ActivitySerra-Maia, Rui; Winkler, Christopher; Murayama, Mitsuhiro; Tranhuu, Kevin; Michel, F. Marc (2018-06-18)Oxygen at the surface of nanosized platinum has a direct effect on catalytic activity of oxidation−reduction chemical reactions. However, the abundance and speciation of oxygen remain uncertain for platinum with different particle size and shape characteristics, which has hindered the development of fundamental property−activity relationships. We have characterized two commercially available platinum nanocatalysts known as Pt black and Pt nanopowder to evaluate the effects of synthesis and heating conditions on the physical and surface chemical properties, as well as on catalytic activity. Characterization using complementary electron microscopy, X-ray scattering, and spectroscopic methods showed that the larger average crystallite size of Pt nanopowder (23 nm) compared to Pt black (11 nm) corresponds with a 70% greater surface oxygen concentration. Heating the samples in air resulted in an increase in surface oxygen concentration for both nanocatalysts. Surface oxygen associated with platinum is in the form of chemisorbed oxygen, and no significant amounts of chemically bonded platinum oxide were found for any of the samples. The increase in surface oxygen abundance during heating depends on the initial size and surface oxygen content. Hydrogen peroxide decomposition rate measurements showed that larger particle size and higher surface chemisorbed oxygen correlate with enhanced catalytic activity. These results are particularly important for future studies that aim to relate the properties of platinum, or other metal nanocatalysts, with surface reactivity.