260 research outputs found
Reversible and irreversible processes during cyclic voltammetry of an electrodeposited manganese oxide as catalyst for the oxygen evolution reaction
No full textAbstractManganese oxides have received much attention over the years among the wide range of electrocatalysts for the oxygen evolution reaction (OER) due to their low toxicity, high abundance and rich redox chemistry. While many previous studies focused on the activity of these materials, a better understanding of the material transformations relating to activation or degradation is highly desirable, both from a scientific perspective and for applications. We electrodeposited Na-containing MnOx without long-range order from an alkaline solution to investigate these aspects by cyclic voltammetry, scanning electron microscopy and x-ray absorption spectroscopy at the Mn-K and Mn-L edges. The pristine film was assigned to a layered edge-sharing Mn3+/4+ oxide with Mn-O bond lengths of mainly 1.87 Å and some at 2.30 Å as well as Mn-Mn bond lengths of 2.87 Å based on fits to the extended x-ray fine structure. The decrease of the currents at voltages before the onset of the OER followed power laws with three different exponents depending on the number of cycles and the Tafel slope decreases from 186 ± 48 to 114 ± 18 mV dec−1 after 100 cycles, which we interpret in the context of surface coverage with unreacted intermediates. Post-mortem microscopy and bulk spectroscopy at the Mn-K edge showed no change of the microstructure, bulk local structure or bulk Mn valence. Yet, the surface region of MnOx oxidized toward Mn4+, which explains the reduction of the currents in agreement with literature. Surprisingly, we find that MnOx reactivates after 30 min at open-circuit (OC), where the currents and also the Tafel slope increase. Reactivation processes during OC are crucial because OC is unavoidable when coupling the electrocatalysts to intermittent power sources such as solar energy for sustainable energy production.H2020 European Research Councilhttp://dx.doi.org/10.13039/10001066
Electronic Structure of Aqueous [Co bpy 3]2 3 Electron Mediators
Full text linkWe report on the electronic structure of cobalt II tris 2,2 amp; 8242; bipyridine and cobalt III tris 2,2 amp; 8242; bipyridine in aqueous solution using resonant inelastic X ray scattering RIXS spectroscopy at the Co L edge and N K edge resonances. Partial fluorescence yield X ray absorption spectra at both edges were obtained by signal integration of the respective RIXS spectra. Experiments are complemented by calculations of the X ray absorption spectra for high and low spin configurations using density functional theory restricted open shell configuration interaction singles and time dependent density functional theory methods. We find that linear combinations of the simulated X ray absorption spectra for different spin states reproduce the experimental spectra. Best agreement is obtained for measurements at the Co L edge, for both samples. For cobalt II tris 2,2 amp; 8242; bipyridine, our combined experimental and computational study reveals amp; 8764;40 low spin and amp; 8764;60 high spin state components. Much stronger low spin character is found for cobalt III tris 2,2 amp; 8242; bipyridine, amp; 8764;80 low spin and amp; 8764;20 high spin. Prominent energy loss features in the Co RIXS spectra are indicative of d d excitations and charge transfer excitations due to strong mixing between metal and ligand orbitals in both complexes. Analysis of N 1s RIXS data reveals the emission from metal dominated orbitals in the valence region, supporting the strong metal ligand mixin
Larry and Ronny
No full textThis 1955 photograph, taken by Simpson Photographers of Knoxville, Tennessee, shows Larry and Ronny performing. Founder and director of the Mountain Youth Jamboree, Hubert H. Hayes (1901-1964) auditioned and directed youth to perform in folk dance, music, and folk and ballad singing. The jamboree was held in the Asheville City Auditorium (now known as Thomas Wolfe Auditorium) from 1948 to 1973, and Hayes’ wife, Leona Trantham Hayes (1913-1989) continued to direct the program after his death in 1964. Hubert Hayes was an author, playwright, and alumni of Duke University
Investigation of the electronic structure of transition metal-ions in solution from aqua-complexes to porphyrins
No full textInvestigation of the Electronic Structure of Transition Metal Ions in Solution from Aqua Complexes to Porphyrins
No full textUntersuchung der Elektronischen Struktur von Übergangsmetall-Ionen in Lösung, vom aqua-Komplex zu Porphyrinen
No full text1 Introduction 1.1 Porphyrins Role in Nature 1.2 The Study of Solvated
Porphyrins 1.3 Brief Introduction of the Thesis Content 2 Experimental and
Theoretical Methods 2.1 X-ray Spectroscopies 2.1.1 X-ray Interaction with
Matter 2.1.2 X-ray Absorption Coefficients and Cross-Sections 2.1.3 Radiative
and Non-Radiative Decays 2.1.4 X-ray Absorption Spectroscopy (XAS) 2.1.5 X-ray
Emission Spectroscopy (XES) 2.1.6 Resonant Photoelectron Spectroscopy (RPES)
2.2 Experimental Methods and Setups 2.2.1 Synchrotron Facility - BESSY II
2.2.2 Beamline - U41-PGM 2.2.3 Experimental Station - LiXEdrom 2.2.4 Liquid in
Vacuum - Micro-Jet 2.2.5 Liquid in Vacuum - Flow Cell 2.3 Sample Preparation
and Measurement Considerations 2.3.1 Aqueous Ferric Solution 2.3.2 Aqueous
Ferrous Solution 2.3.3 FePPIX-Cl in DMSO 2.3.4 CoPPIX-Cl in DMSO 2.3.5 FePPIX-
Cl in NaOH 2.3.6 MnOEP-Cl and MnTPP-Cl in DCM 2.3.7 FeOEP-Cl and FeTPP-Cl in
DCM 2.4 Theoretical Modeling - ORCA Program Package 2.4.1 [Fe(H2O)6]3+ Complex
2.4.2 [Fe(H2O)6]2+ Complex (MOLCAS 8.0) 2.4.3 Porphyrin Complexes 3 Iron
Chlorides in Aqueous Solution - a Simple Model System 3.1 Undistorted XAS
Probed by Core-Level Emission 3.2 Metal-Ligand Interactions Revealed by
Combined Probing of RIXS and RPES 4 Metalloporphyrins in Solution - a Complex
System 4.1 Solvated Metalloporphyrin Monomers 4.1.1 FePPIX-Cl in DMSO 4.1.2
CoPPIX-Cl in DMSO 4.2 Intermolecular Interactions in FePPIX-Cl Dimer 4.2.1
Local Energy Gap Opening at the Iron Site 4.2.2 Characteristic XA-Feature
Shifting of Nitrogen 4.3 Outer Ligand Effects on Metalloporphyrins in Solution
4.3.1 Outer Ligand Effect on the Metal Center 4.3.2 Metal-Solvent Interaction
Assisted by Porphyrin Outer Ligands 5 Summary and OutlookThis thesis reports how, by the development of the vacuum liquid micro-jet
technique as well as the flow cell technique for soft X-ray spectroscopy,
electronic structure measurements on liquid have advanced to date. My focus is
on investigations of solvated transition metals in both simple and complex
systems. These transition metal systems are at the heart of current research
activities world-wide, in fields including physical chemistry and biology, and
aiming at a molecular level to the understanding of the interactions of metal-
ligand and metal-solvent. For the transition metal aqueous solutions (simple
system) I have systematically compared all possible decay channels upon
resonant excitation at the Fe L-edge, including radiative fluorescence yield
and non-radiative electron yield both for valence and core-level emissions, in
order to discover an undistorted detection method for XAS measurements. Our
analysis suggests a new protocol for investigation of X-ray spectra and its
implications for the study of transition metal solute-solvent electronic
interactions, being important to promote our understanding of the geometric
and electronic structure and the rational design of catalytic and functional
materials. For complex systems the local electronic structure of hemin has
been investigated first by X-ray absorption and emission spectroscopy at the
Fe L-edge and N K-edge. The study was performed for hemin in aqueous solution
where dimerization occurs and in organic solution where the molecule remains
monomer. A local energy gap at the Fe sites was observed for the hemin dimer,
with the occupied valence states shifted to lower binding energies, while the
unoccupied valence states share the same energies as the hemin monomer. In
addition, solute-solvent electronic structure interactions of porphyrin at
very low concentrations in liquid solution are presented. For Mn-
tetraphenylporphyrin chloride and Mn-octaethylporphyrin chloride distinctive
spectral features of metal-to-ligand charge-transfer were observed, when
characterized by resonant inelastic X-ray scattering at the Mn L-edge and N
K-edge. In the case of Fe-octaethylporphyrin chloride and Fe-
tetraphenylporphyrin chloride, it is argued that the Fe center of the Fe
octaethylporphyrin is more capable of binding small solvent molecules, than
the tetraphenylporphyrin complex in solution. The proposed binding mechanism
is through the assistance of the dipole interaction between the porphyrin-
ligand system and the solvent molecule, in a situation where the ligand
structure and arrangement maximize the binding interactions. Our studies
demonstrate that even small ligands, depending on their structure and
arrangement, can have considerable effects on the porphyrin metal center
chemistry in liquid solution. All studies at the porphyrin complexes are
accompanied by the interpretation of density functional theory with restricted
open-shell configuration interaction singles (DFT/ROCIS) calculations.Die vorliegenden, im Rahmen meiner Doktorarbeit durchgeführten Untersuchungen
zeigen, wie sich die Röntgenspektroskopie im weichen Röntgenbereich zur
Analyse der elektronischen Struktur in Lösung, mittels Mikroflüssigkeitsstrahl
und Durchflusszelle im Vakuum, weiterentwickelt hat. Der Fokus meiner
Untersuchungen liegt auf gelöste Übergangsmetall-systeme mit sowohl einfachem
als auch komplexerem Aufbau. Diese Komplexe sind Gegenstand aktueller,
weltweiter wissenschaftlicher Forschungsfelder, wie der physikalischen Chemie
und der Biologie. Bei den relativ einfach aufgebauten Übergansmetall-Wasser-
Komplexen in Lösung, erfolgte ein systematischer Vergleich sämtlicher
elektronischer Wechselwirkungsprozesse, ausgelöst durch resonante Anregung an
der Eisen L-Kante. Der Vergleich basiert auf Messungen mittels partieller
Fluoreszenzausbeute- und Elektronenausbeutetechniken. Das Ziel ist es, eine
Detektionsmethode zu etablieren, die ein störungsfreies
Röntgenabsorptionsspektrum (XAS) liefert. Unsere Ergebnisse sind bedeutend für
die Interpretation von Röntgenspektren und fördern das Verständnis von
elektronischen Wechselwirkungen zwischen den gelösten Komplexen und dem
umgebenden Lösungsmittel in katalytischen und funktionalen Materialien. Als
komplexeres System wurde zuerst die elektronische Struktur von Hemin in Lösung
mittels XAS und XES an der Eisen L-Kante sowie der Stickstoff K-Kante
untersucht. Dabei wurde das Molekül als Dimer in wässriger Lösung und als
Monomer in organischer Lösung (DMSO) analysiert und verglichen. Für das Dimer
wurde eine Energielücke in Valenzzuständen gefunden, wobei die besetzten
Valenzzustände zu niedrigeren Energien verschoben sind, während die
unbesetzten Valenzzustände die gleichen Energien wie das Monomer des Hemins
aufweisen. Zusätzlich werden die Solvat-Solvens-Wechselwirkungen in der
elektronischen Struktur von weiteren Porphyrinen bei niedrigen Konzentrationen
in Dichlormethan vorgestellt. Die Charakterisierung mittels resonanter
unelastischer Röntgenstreuung an der Mangan L-Kante und der Stickstoff K-Kante
liefert markante spektrale Kennzeichen für Metall-zu-Liganden-Ladungstransfer
in Tetraphenyl- und Oktaethylporphyrinen des Mn(III). Im Fall von Tetraphenyl-
und Oktaethyl-porphyrin des Fe(III) tritt eine Interaktion mit den
Lösemittelmolekülen auf, welche für den Oktaethylkomplex stärker ausfällt. Der
vorgeschlagene Bindungsmechanismus wird dabei von Dipolwechselwirkungen des
Porphyrinsystems und den Lösemittelmolekülen gesteuert, wobei die sterische
Anordnung der Alkylgruppen des Porphyrins diesen Vorgang begünstigt. Unsere
Untersuchungen zeigen somit, dass bereits die Variation in kleinen
funktionellen Gruppen des Porphyrinliganden einen messbaren Effekt auf die
elektronische Struktur des Metallzentrums in Lösung haben kann. Sämtliche
Untersuchungen an Porphyrinen wurden durch die Auswertung theoretischer
Berechnungen (DFT/ROCIS) begleitet
Ionic Current Mn K edge X ray Absorption Spectra Obtained in a Flow Cell
No full textXi L, Schellenberger M, Prag RF, Golnak R, Schuck G, Aziz-Lange K. Ionic Current Mn K-Edge X-ray Absorption Spectra Obtained in a Flow Cell. JOURNAL OF PHYSICAL CHEMISTRY C. 2018;122(27):15588-15594.Ionic current X-ray absorption spectroscopy (IC-XAS) relaying on the synchrotron beam-induced ionization current was recently proposed as an alternative approach for XAS detection in flow cells. In this study, we investigate the mechanism behind IC-XAS by varying the spacer thickness and the cell orientation. On the basis of these studies, we propose that the driving force for the ionic current is a beam-induced electric potential between the two electrodes. After that, we attempt to detect IC-XA spectra from the Mn K-edge of several manganese salts, specifically nitrate, chloride, sulfate, acetate, and permanganate. We find that Mn K-edge IC-XAS spectra of aqueous Mn ions can be affected by the mass and concentration of the anions, the substrate as well as the beam intensity. Potential applications and limitations of this method are discussed
Microprocessor energy characterization and optimization through fast, accurate, and flexible simulation
Full text linkThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 99-102).Energy dissipation is emerging as a key constraint for both high-performance and embedded microprocessor designs, requiring computer architects to consider energy in addition to performance when evaluating design decisions. A major limitation is the general difficulty in analyzing the energy impact of architectural and microarchitectural features without constructing detailed implementations and running slow simulations. This thesis first describes the design of a fast, accurate, and flexible circuit simulation tool which enables transition-sensitive studies of microprocessor energy consumption that would otherwise be impossible or impractical. With a simulation infrastructure in place, various optimizations are implemented that target the entire datapath and cache energy consumption. The individual energy optimizations are analyzed in detail, and the microprocessor design is characterized using various energy breakdowns and studies of the bit correlation between data values. This work shows that a few relatively simple energy-saving techniques can have a large impact in the implementation of an energy-efficient microprocessor. By fully characterizing the energy usage, this thesis establishes a coherent vision of microprocessor energy consumption, and serves as a basis and motivation for further energy optimizations.by Ronny Krashinsky.S.M
Oriente Medio, Europa y Estados Unidos se encuentran en Tel Aviv: la poesía de Ronny Someck
Full text linkRonny Someck is one of Israel's best-known poets, both in his own country and abroad. He is a well-established author whose poetry has a very personal tone while forming part of the so-called Postmodernist movement. His geocultural points of reference are Israel, the Arab tradition and the Western combination of Europe and the United States. This article introduces the author, his work and the combination of themes and trends inherent in the characters, places, contexts and situations which appear in his poems. Translated versions of sexteen poems are also included.Ronny Someck es uno de los poetas israelíes más conocidos en su país y en el extranjero. Autor de una ya larga trayectoria, escribe una poesía muy personal, enmarcada en lo que se ha dado en llamar el Postmodernismo. Sus referentes geoculturales son Israel, la tradición árabe y el conjunto occidental Europa-Estados Unidos. El artículo presenta al autor, su obra, y la síntesis de corrientes y tendencias, manifestadas en personajes, escenarios, contextos y situaciones que aparecen en sus poemas. Incluye la traducción de dieciséis poesías
Dataset of continuous human activities performed in arbitrary directions collected with a distributed radar network of five nodes
No full textPlease review the document README_v2.pdf
The data can be extracted with the MATLAB Live Script dataread.mlx.
Referencing the dataset
Guendel, Ronny Gerhard; Unterhorst, Matteo; Fioranelli, Francesco; Yarovoy, Alexander (2021): Dataset of continuous human activities performed in arbitrary directions collected with a distributed radar network of five nodes. 4TU.ResearchData. Dataset. https://doi.org/10.4121/16691500.v3
@misc{Guendel2022,
author = "Ronny Gerhard Guendel and Matteo Unterhorst and Francesco Fioranelli and Alexander Yarovoy",
title = "{Dataset of continuous human activities performed in arbitrary directions collected with a distributed radar network of five nodes}",
year = "2021",
month = "Nov",
url = "https://data.4tu.nl/articles/dataset/Dataset_of_continuous_human_activities_performed_in_arbitrary_directions_collected_with_a_distributed_radar_network_of_five_nodes/16691500",
doi = "10.4121/16691500.v3" }
Paper references are:
Guendel, R.G., Fioranelli, F.,Yarovoy, A.: Distributed radar fusion and recurrent networks for classification of continuous human activities. IET Radar Sonar Navig. 1–18 (2022). https://doi.org/10.1049/rsn2.12249
R. G. Guendel, F. Fioranelli and A. Yarovoy, "Evaluation Metrics for Continuous Human Activity Classification Using Distributed Radar Networks," 2022 IEEE Radar Conference (RadarConf22), 2022, pp. 1-6, doi: 10.1109/RadarConf2248738.2022.9764181.
R. G. Guendel, M. Unterhorst, E. Gambi, F. Fioranelli and A. Yarovoy, "Continuous human activity recognition for arbitrary directions with distributed radars," 2021 IEEE Radar Conference (RadarConf21), 2021, pp. 1-6, doi: 10.1109/RadarConf2147009.2021.9454972.
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