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  • 1
    Language: English
    In: Nature materials, 2013-10, Vol.12 (10), p.919-924
    Description: The diminished surface-area-normalized catalytic activity of highly dispersed Pt nanoparticles compared with bulk Pt is particularly intricate, and not yet understood. Here we report on the oxygen reduction reaction (ORR) activity of well-defined, size-selected Pt nanoclusters; a unique approach that allows precise control of both the cluster size and coverage, independently. Our investigations reveal that size-selected Pt nanoclusters can reach extraordinarily high ORR activities, especially in terms of mass-normalized activity, if deposited at high coverage on a glassy carbon substrate. It is observed that the Pt cluster coverage, and hence the interparticle distance, decisively influence the observed catalytic activity and that closely packed assemblies of Pt clusters approach the surface activity of bulk Pt. Our results open up new strategies for the design of catalyst materials that circumvent the detrimental dispersion effect, and may eventually allow the full electrocatalytic potential of Pt nanoclusters to be realized.
    ISSN: 1476-1122
    E-ISSN: 1476-4660
    Source: Academic Search Ultimate
    Source: Nature Journals Online
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  • 2
    Language: English
    In: The Journal of chemical physics, 2018-02-07, Vol.148 (5), p.054701-054701
    Description: ZnO nanoparticles are used as catalysts and have potential applications in gas-sensing and solar energy conversion. A fundamental understanding of the exposed crystal facets, their surface chemistry, and stability as a function of environmental conditions is essential for rational design and improvement of synthesis and properties. We study the stability of water adsorbate phases on the non-polar low-index (101¯0) and (112¯0) surfaces from low coverage to multilayers using ab initio thermodynamics. We show that phonon contributions and the entropies due to a 2D lattice gas at low coverage and multiple adsorbate configurations at higher coverage have an important impact on the stability range of water adsorbate phases in the (T,p) phase diagram. Based on this insight, we compute and analyze the possible growth mode of water films for pressures ranging from UHV via ambient conditions to high pressures and the impact of water adsorption on the equilibrium shape of nanoparticles in a humid environment. A 2D variant of the Wulff construction shows that the (101¯0) and (112¯0) surfaces coexist on 12-faceted prismatic ZnO nanoparticles in dry conditions, while in humid environment, the (101¯0) surface is selectively stabilized by water adsorption resulting in hexagonal prisms.
    ISSN: 0021-9606
    E-ISSN: 1089-7690
    Source: American Institute of Physics (AIP) Publications
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  • 3
    Language: English
    In: Physical chemistry chemical physics : PCCP, 2017-01-04, Vol.19 (2), p.1466-1486
    Description: A comprehensive search for stable structures in the low coverage regime (0-1 ML) and at 2 ML and 3 ML using DFT revealed several new aggregation states of water on the non-polar ZnO(101[combining macron]0) surface. Ladder-like structures consisting of half-dissociated dimers, arranged side-by-side along the polar axis, constitute the most stable aggregate at low coverages (≤1 ML) with a binding energy exceeding that of the monolayer. At coverages beyond the monolayer - a regime that has hardly been studied previously - a novel type of structure with a continuous honeycomb-like 2D network of hydrogen bonds was discovered, where each surface oxygen atom is coordinated by additional H-bonding water molecules. This flat double-monolayer has a relatively high adsorption energy, every zinc and oxygen atom is 4-fold coordinated and every hydrogen atom is engaged in a hydrogen bond. Hence this honeycomb double monolayer offers no H-bond donor or acceptor sites for further growth of the water film. At 3 ML coverage, the interface restructures forming a contact layer of half-dissociated water dimers and a liquid-like overlayer of water attached by hydrogen bonds. The structures and their adsorption energies are analysed to understand the driving forces for aggregation and dissociation of water on the surface. We apply a decomposition scheme based on a Born-Haber cycle, discussing difficulties that may occur in applying such an analysis to the adsorption of dissociated molecules and point out alternatives to circumvent the bias against severely stretched bonds. Water aggregation on the ZnO surface is favoured by direct water-water interactions including H-bonds and dipole-dipole interactions and surface- or adsorption-mediated interactions including enhanced water-surface interactions and reduced relaxations of the water molecules and surface. While dissociation of isolated adsorbed molecules is unfavourable, partial or even full dissociation is preferred for aggregates. Nevertheless, direct water-water interactions change very little in the dissociation reaction. Dissociation is governed by a subtle balance between strongly enhanced water-surface interactions and the large energies required for the geometric changes of the water molecule(s) and the surface. Our conclusions are discussed on the background of the current knowledge on water adsorption at metals and non-metallic surfaces.
    ISSN: 1463-9076
    E-ISSN: 1463-9084
    Source: Alma/SFX Local Collection
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  • 4
    Language: English
    In: Journal of the American College of Cardiology, 2010, Vol.56 (15), p.1207-1213
    Description: Objectives The objective of the study was to determine the prevalence of bleeding during continuous-flow left ventricular assist device support and to identify potential mechanisms for those bleeding events. Background Bleeding is frequently reported with continuous-flow left ventricular assist devices and may result from anticoagulation coupled with bleeding diathesis such as acquired von Willebrand syndrome. Accordingly, the prevalence of coagulation abnormalities including laboratory assessment for von Willebrand syndrome, bleeding events during device support, and at heart transplantation were evaluated. Methods A retrospective study in all HeartMate II (HM II) (Thoratec Corp., Pleasanton, California) patients who underwent implantation between April 1, 2004, and August 1, 2009, was performed. Bleeding was defined as the need for transfusion 〉7 days after device insertion of 1 U of packed red blood cells. Transfusion at heart transplantation was compared with that in HeartMate XVE patients. Results Seventy-nine HM II devices were implanted. Anticoagulation included warfarin in 68.3%, aspirin in 55.7%, and dipyridamole in 58.2% of the patients. Of the patients, 44.3% had bleeding episodes at 112 ± 183 days after left ventricular assist device implantation, with 50% experiencing an event within 2 months. Gastrointestinal bleeding was the most frequent event. At the index event, the international normalized ratio averaged 1.67 ± 0.53, and the platelet count was 237 ± 119 × 109 /l. Comparison of the transfusion requirements at heart transplantation of 35 HM II patients with 62 HeartMate XVE patients demonstrated twice the transfusion requirements in HM II patients (packed red blood cells, 6.3 ± 0.8 U vs. 3.8 ± 0.5 U; platelets, 12.5 ± 5.4 U vs. 8.6 ± 6.4 U; fresh frozen plasma, 9.6 ± 4.9 U vs. 4.9 ± 3.6 U; and cryoprecipitate, 4.3 ± 3.6 U vs. 2.2 ± 3.5 U; p 〈 0.05 for all). High molecular weight von Willebrand factor multimers were measured in 31 HM II patients and were reduced in all patients; 18 of these 31 (58%) patients had bleeding. Conclusions Patients with the HM II had a high incidence of bleeding events during device support and at heart transplantation. All HM II patients had reduced high molecular weight von Willebrand factor multimers. The role of these abnormalities in the high incidence of bleeding deserves further investigation. Furthermore, alterations in anticoagulation should be considered during device support and before surgery in patients supported with the HM II.
    Subject(s): Cardiovascular ; Internal Medicine ; heart transplant ; left ventricular assist devices ; bleeding ; von Willebrand syndrome ; Cardiology. Vascular system ; Biological and medical sciences ; Medical sciences ; Intraoperative Complications - blood ; Intraoperative Complications - epidemiology ; Prevalence ; Follow-Up Studies ; Hemorrhage - epidemiology ; Humans ; Middle Aged ; von Willebrand Diseases - epidemiology ; Heart Transplantation - adverse effects ; Male ; Treatment Outcome ; Heart-Assist Devices - adverse effects ; von Willebrand Diseases - etiology ; Young Adult ; Time Factors ; Hemorrhage - etiology ; Intraoperative Complications - etiology ; Adolescent ; Adult ; Female ; Aged ; Retrospective Studies ; Von Willebrand factor ; Prevalence studies (Epidemiology) ; Index Medicus ; Abridged Index Medicus
    ISSN: 0735-1097
    E-ISSN: 1558-3597
    Source: Alma/SFX Local Collection
    Source: © ProQuest LLC All rights reserved〈img src="https://exlibris-pub.s3.amazonaws.com/PQ_Logo.jpg" style="vertical-align:middle;margin-left:7px"〉
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  • 5
    Language: English
    In: Physical chemistry chemical physics : PCCP, 2012, Vol.14 (20), p.7384-7391
    Description: Understanding the hydrogen peroxide electrochemistry on platinum can provide information about the oxygen reduction reaction mechanism, whether H(2)O(2) participates as an intermediate or not. The H(2)O(2) oxidation and reduction reaction on polycrystalline platinum is a diffusion-limited reaction in 0.1 M HClO(4). The applied potential determines the Pt surface state, which is then decisive for the direction of the reaction: when H(2)O(2) interacts with reduced surface sites it decomposes producing adsorbed OH species; when it interacts with oxidized Pt sites then H(2)O(2) is oxidized to O(2) by reducing the surface. Electronic structure calculations indicate that the activation energies of both processes are low at room temperature. The H(2)O(2) reduction and oxidation reactions can therefore be utilized for monitoring the potential-dependent oxidation of the platinum surface. In particular, the potential at which the hydrogen peroxide reduction and oxidation reactions are equally likely to occur reflects the intrinsic affinity of the platinum surface for oxygenated species. This potential can be experimentally determined as the crossing-point of linear potential sweeps in the positive direction for different rotation rates, hereby defined as the "ORR-corrected mixed potential" (c-MP).
    Subject(s): Electrochemistry ; Chemistry ; General and physical chemistry ; Exact sciences and technology
    ISSN: 1463-9076
    E-ISSN: 1463-9084
    Source: Alma/SFX Local Collection
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  • 6
    Language: English
    In: Journal of the American College of Cardiology, 2014, Vol.63 (9), p.880-888
    Description: Objectives This study sought to determine the pre-operative risk factors related to late bleeding, stroke, and pump thrombosis in patients with HeartMate II (HMII) left ventricular assist devices (LVADs) (Thoratec Corporation, Pleasanton, California) that might influence tailored improvements in patient management. Background Adverse events in LVAD patients remain high. It is unclear whether pre-operative characteristics influence the likelihood of the development of post-operative hemorrhagic or thrombotic complications. Knowing which patients are at greater risk might assist in tailoring anticoagulation therapy for certain patients. Methods Advanced heart failure patients (n = 956) discharged from the hospital after LVAD implantation in the HMII bridge to transplantation (n = 405) and destination therapy (n = 551) clinical trials were retrospectively evaluated. Bleeding requiring surgery or transfusion of 〉2 U of packed red blood cells, stroke (hemorrhagic and ischemic), and pump thrombosis were tracked from hospital discharge until patient outcome. Results Adverse event rates for post-discharge bleeding (0.67 events/patient-year) were higher than those for hemorrhagic stroke (0.05), ischemic stroke (0.04), and pump thrombosis (0.03). The main sites of bleeding included gastrointestinal (45% of events), wound (12%), and epistaxis (4%). Older age (〉65 years) (hazard ratio [HR]: 1.31), lower pre-operative hematocrit (≤31%) (HR: 1.31), ischemic etiology (HR: 1.35), and female (HR: 1.45) were statistically significant multivariable risk factors for bleeding. Female (HR: 1.92) and 65 years of age and younger (HR: 1.94) were multivariable risk factors for hemorrhagic stroke, whereas female (HR: 1.84) and history of diabetes (HR: 1.99) were risk factors for ischemic stroke. Female (HR: 1.90) and higher body mass index (HR: 1.71/10 kg/m2 increase) were also multivariable risk factors for pump thrombosis. Conclusions The risk of bleeding and thrombotic events during LVAD support differs by patient demographics, including sex, age, body mass index, and etiology of heart failure. Further studies should focus on the potential of tailored anticoagulation strategies in these subgroups.
    Subject(s): Cardiovascular ; Internal Medicine ; HeartMate II ; heart failure ; bleeding ; stroke ; LVAD ; pump thrombosis ; Stroke (Disease) ; Sects ; Consulting services ; Risk factors
    ISSN: 0735-1097
    E-ISSN: 1558-3597
    Source: Alma/SFX Local Collection
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  • 7
    Language: English
    In: Nature biotechnology, 2015-03, Vol.33 (3), p.277-284
    Description: Brain function depends on simultaneous electrical, chemical and mechanical signaling at the cellular level. This multiplicity has confounded efforts to simultaneously measure or modulate these diverse signals in vivo. Here we present fiber probes that allow for simultaneous optical stimulation, neural recording and drug delivery in behaving mice with high resolution. These fibers are fabricated from polymers by means of a thermal drawing process that allows for the integration of multiple materials and interrogation modalities into neural probes. Mechanical, electrical, optical and microfluidic measurements revealed high flexibility and functionality of the probes under bending deformation. Long-term in vivo recordings, optogenetic stimulation, drug perturbation and analysis of tissue response confirmed that our probes can form stable brain-machine interfaces for at least 2 months. We expect that our multifunctional fibers will permit more detailed manipulation and analysis of neural circuits deep in the brain of behaving animals than achievable before.
    Subject(s): Implants, Experimental ; Mice, Inbred C57BL ; Male ; Mice, Transgenic ; Optogenetics ; Nerve Net - drug effects ; Blood-Brain Barrier - drug effects ; Nerve Net - physiology ; Drug Delivery Systems ; Foreign-Body Reaction - pathology ; Electrodes ; Animals ; Optical Fibers ; Electrophysiological Phenomena - drug effects ; Metals - pharmacology ; Cellular signal transduction ; Neural circuitry ; Research ; Neurological research ; Index Medicus
    ISSN: 1087-0156
    E-ISSN: 1546-1696
    Source: Single Journals
    Source: Academic Search Ultimate
    Source: Nature Journals Online
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  • 8
    Language: English
    In: The New England journal of medicine, 2017-02-02, Vol.376 (5), p.440-450
    Description: In a randomized trial, 294 patients with advanced heart failure were assigned to receive either a new centrifugal-flow pump or an axial-flow pump. At 6 months, the centrifugal-flow pump was associated with better outcomes. A scarcity of effective therapeutic options for advanced heart failure has led to the development of durable mechanical circulatory support devices. Left ventricular assist devices, more accurately known as left ventricular assist systems, increase the rate of survival and improve quality of life among patients with advanced heart failure. However, these clinical benefits are balanced by an increased risk of infection, bleeding, neurologic events, and pump malfunction that is due principally to pump thrombosis. 1 , 2 As adoption of circulatory pumps has expanded, concerns about pump thrombosis have heightened. In 2013, two reports suggested that there has been an increase in . . .
    Subject(s): Humans ; Middle Aged ; Kaplan-Meier Estimate ; Heart-Assist Devices - adverse effects ; Prosthesis Design ; Young Adult ; Disease-Free Survival ; Heart Failure - therapy ; Stroke - etiology ; Prosthesis Failure ; Thrombosis - etiology ; Intention to Treat Analysis ; Aged, 80 and over ; Adult ; Aged ; Heart Failure - mortality ; Heart failure ; Cardiovascular system ; Care and treatment ; Diagnosis ; Cardiopulmonary system ; Stroke ; Transplants & implants ; Transplantation ; Navigation behavior ; Patients ; Thrombosis ; Survival ; Clinical outcomes ; Quality of life ; Motivation ; Surgeons ; Ventricle ; Heart diseases ; Index Medicus ; Abridged Index Medicus
    ISSN: 0028-4793
    E-ISSN: 1533-4406
    Source: Single Journals
    Source: © ProQuest LLC All rights reserved〈img src="https://exlibris-pub.s3.amazonaws.com/PQ_Logo.jpg" style="vertical-align:middle;margin-left:7px"〉
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  • 9
    Language: English
    In: Langmuir, 2012-07-10, Vol.28 (27), p.10192-10208
    Description: Self-assembled monolayers (SAMs) of pentafluorobenzenethiol (PFBT) on Au(111) substrates, prepared with different immersion times (ITs) at room temperature, were studied using scanning tunneling microscopy (STM) and infrared reflection–absorption spectroscopy (IRRAS). In the present study, the focus was on several important points of interest in the field of SAMs. First, the gold islands formed upon adsorption of PFBT molecules on the gold surface were monitored at different ITs in terms of their size, density, and shape. After short ITs (5 to 30 min), small gold islands with rounded shape were formed. These gold islands were arranged in a rather regular fashion and found to be quite mobile under the influence of the STM-tip during the scanning. When the IT was increased to 16 h, the results revealed the formation of highly ordered and orientated gold islands with very unusual shapes with straight edges meeting at 60° or 120° running preferentially along the ⟨11̅0⟩ substrate directions. The density of the gold islands was found to decrease with increasing IT until they almost disappeared from the SAMs prepared after 190 h of IT. On top of the gold islands, the PFBT molecules were found to adopt the closely packed (10√3 × 2) structure. Second, a number of structural defects such as disordered regions at the domain boundaries and dark row(s) of molecules within the ordered domains of the PFBT SAMs were observed at different ITs. The SAMs prepared after 190 h of IT were found to be free of these defects. Third, at low and moderate ITs, a variation in the PFBT molecular contrast was observed. This contrast variation was found to depend mainly on the tunneling parameters. Finally, our results revealed that the organization process of PFBT SAMs is IT-dependent. Consequently, a series of structural phases, namely, α, β, γ, δ, and ε were found. The α-, β-, γ-, and δ-phases were typically accompanied by the ε-phase that appeared on top of gold islands. With increasing IT, the α→β→ γ→δ→ε phase transitions took place. The resulting ε-phase, which covered the entire gold surface after 190 h of IT, yielded well-ordered self-assembled monolayers with large domains having a (10√3 × 2) superlattice structure.
    Subject(s): Surface physical chemistry ; Chemistry ; General and physical chemistry ; Exact sciences and technology ; Gold - chemistry ; Temperature ; Adsorption ; Time Factors ; Microscopy, Scanning Tunneling ; Surface Properties ; Sulfhydryl Compounds - chemistry ; Molecular Structure ; Fluorobenzenes - chemistry ; Spectroscopy, Fourier Transform Infrared ; Phase Transition ; Index Medicus
    ISSN: 0743-7463
    E-ISSN: 1520-5827
    Source: Hellenic Academic Libraries Link
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  • 10
    Language: English
    In: Physical chemistry chemical physics : PCCP, 2013, Vol.15 (21), p.8058-8068
    Description: The impact of electrolyte constituents on the interaction of hydrogen peroxide with polycrystalline platinum is decisive for the understanding of the selectivity of the oxygen reduction reaction (ORR). Hydrodynamic voltammetry measurements show that while the hydrogen peroxide reduction (PRR) is diffusion-limited in perchlorate- or fluoride-containing solutions, kinetic limitations are introduced by the addition of more strongly adsorbing anions. The strength of the inhibition of the PRR increases in the order ClO4(-)≈ F(-) 〈 HSO4(-) 〈 Cl(-) 〈 Br(-) 〈 I(-) as well as with the increase of the concentration of the strongly adsorbing anions. Electronic structure calculations indicate that the dissociation of H2O2 on Pt(111) is always possible, regardless of the coverage of spectator species. However, the adsorption of H2O2 becomes strongly endothermic at high coverage with adsorbing anions. A comparison of our observations on the inhibition of the PRR by spectators with previous studies on the selectivity of the ORR shows that oxygen is reduced to H2O2 only under conditions at which the PRR kinetics is significantly limited, while the ORR proceeds with a complete four-electron reduction only when the PRR is sufficiently fast. Therefore, only a H2O2-mediated pathway that includes a competition between the dissociation and the spectator coverage-dependent desorption of the H2O2 intermediate is enough to explain and unify all the observations that have been made so far on the selectivity of the ORR.
    Subject(s): Electrochemistry ; Chemistry ; General and physical chemistry ; Exact sciences and technology ; Hydrogen Peroxide - chemistry ; Adsorption ; Oxidation-Reduction ; Oxygen - chemistry ; Sulfates - chemistry ; Models, Molecular ; Electrolytes - chemistry ; Platinum - chemistry ; Index Medicus
    ISSN: 1463-9076
    E-ISSN: 1463-9084
    Source: Alma/SFX Local Collection
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