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Where Water is Oxidized to Dioxygen: Structure of the Photosynthetic Mn4Ca Cluster from X-ray Spectroscopy

Description: Light-driven oxidation of water to dioxygen in plants, algae and cyanobacteria iscatalyzed within photosystem II (PS II) by a Mn4Ca cluster. Although the cluster has been studied by many different methods, the structure and the mechanism have remained elusive. X-ray absorption and emission spectroscopy and EXAFS studies have been particularly useful in probing the electronic and geometric structure, and the mechanism of the water oxidation reaction. Recent progress, reviewed here, includes pola… more
Date: October 24, 2007
Creator: Yano, Junko; Yano, Junko & Yachandra, Vittal K.
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Partner: UNT Libraries Government Documents Department
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Numerical Study of Coulomb Scattering Effects on Electron Beamfrom a Nano-Tip

Description: Nano-tips with high acceleration gradient around the emission surface have been proposed to generate high brightness beams. However, due to the small size of the tip, the charge density near the tip is very high even for a small number of electrons. The stochastic Coulomb scattering near the tip can degrade the beam quality and cause extra emittance growth and energy spread. In the paper, we present a numerical study of these effects using a direct relativistic N-body model. We found that emitt… more
Date: June 25, 2007
Creator: Qiang, Ji; Corlett, John N.; Lidia, Steven M.; Padmore, HowardA.; Wan, Weishi; Zholent, Andrew A. et al.
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Partner: UNT Libraries Government Documents Department
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Design of an electro-optical sampling experiment at the AWA facility

Description: The free space electro-optical (EO) sampling technique is a powerful tool for analyzing the longitudinal charge density of an ultrashort e-beam. In this paper, we present (1) experimental results for a laser-based mock-up of the EO experiment [1] and (2) a design for a beam-based, single-shot, EO sampling experiment using the e-beam from the Argonne Wakefield Accelerator (AWA) RF photoinjector. For the mock-up, a tabletop terahertz experiment is conducted in the AWA laser room. The mock-up uses… more
Date: June 1, 2007
Creator: Ruan, J.; Edwards, H.; Tan, Cheng Yang; Thurman-Keup, R.; Scarpine, V.; /Fermilab et al.
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Partner: UNT Libraries Government Documents Department
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A Vlasov Solver for Longitudinal Dynamics in Beam Delivery Systems for X-Ray FELs

Description: Direct numerical methods for solving the Vlasov equationoffer some advantages over macroparticle simulations, as they do notsuffer from the consequences of the statistical fluctuations inherent inusing a number of macroparticles smaller than thebunch population.Unfortunately these methods are more time-consuming and generallyconsidered impractical in a full 6D phase space. However, in alower-dimension phase space they may become attractive if the beamdynamics is sensitive to the presence of sma… more
Date: May 9, 2007
Creator: Venturini, Marco; Warnock, Robert & Zholents, Alexander
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Partner: UNT Libraries Government Documents Department
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Error-Induced Beam Degradation in Fermilab's Accelerators

Description: In Part I, three independent models of Fermilab's Booster synchrotron are presented. All three models are constructed to investigate and explore the effects of unavoidable machine errors on a proton beam under the influence of space-charge effects. The first is a stochastic noise model. Electric current fluctuations arising from power supplies are ubiquitous and unavoidable and are a source of instabilities in accelerators of all types. A new noise module for generating the Ornstein-Uhlenbeck (… more
Date: August 1, 2007
Creator: Yoon, Phil S.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries Government Documents Department
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Development of Carbon Based optically Transparent Electrodes from Pyrolyzed Photoresist for the Investigation of Phenomena at Electrified Carbon-Solution Interfaces

Description: The work presented herein describes a fundamental investigations of carbon as electrode material by using the pyrolysis of photoresist to create an optically transparent material. The development of these carbon-based optically transparent electrodes (C-OTEs) enables investigations of molecular interactions within the electrical double layer, processes that are central to a wide range of important phenomena, including the impact of changes in the surface charge density on adsorption. The electr… more
Date: December 1, 2007
Creator: Donner, Sebastian
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries Government Documents Department
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Modeling the Pulse Line Ion Accelerator (PLIA): an algorithm for quasi-static field solution.

Description: The Pulse-Line Ion Accelerator (PLIA) is a helical distributed transmission line. A rising pulse applied to the upstream end appears as a moving spatial voltage ramp, on which an ion pulse can be accelerated. This is a promising approach to acceleration and longitudinal compression of an ion beam at high line charge density. In most of the studies carried out to date, using both a simple code for longitudinal beam dynamics and the Warp PIC code, a circuit model for the wave behavior was employe… more
Date: June 18, 2007
Creator: Friedman, A; Briggs, R J; Grote, D P; Henestroza, E & Waldron, W L
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Partner: UNT Libraries Government Documents Department
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Origin of Charge Density at LaAlO3 on SrTiO3 Heterointerfaces: Possibility of Intrinsic Doping

Description: As discovered by Ohtomo and Hwang, a large sheet charge density with high mobility exists at the interface between SrTiO{sub 3} and LaAlO{sub 3}. Based on transport, spectroscopic, and oxygen-annealing experiments, we conclude that extrinsic defects in the form of oxygen vacancies introduced by the pulsed laser deposition process used by all researchers to date to make these samples is the source of the large carrier densities. Annealing experiments show a limiting carrier density. We also pres… more
Date: June 14, 2007
Creator: Siemons, W.; /Stanford U., Geballe Lab. /Twente U., Enschede; Koster, Gertjan; /Stanford U., Geballe Lab.; Yamamoto, Hideki; /Stanford U., Geballe Lab. /NTT Basic Res. Lab. et al.
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Partner: UNT Libraries Government Documents Department
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Parametic Study of the current limit within a single driver-scaletransport beam line of an induction Linac for Heavy Ion Fusion

Description: The High Current Experiment (HCX) at Lawrence Berkeley National Laboratory is part of the US program that explores heavy-ion beam as the driver option for fusion energy production in an Inertial Fusion Energy (IFE) plant. The HCX is a beam transport experiment at a scale representative of the low-energy end of an induction linear accelerator driver. The primary mission of this experiment is to investigate aperture fill factors acceptable for the transport of space-charge-dominated heavy-ion bea… more
Date: February 14, 2007
Creator: Prost, Lionel Robert
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries Government Documents Department
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Electronic Structure and Oxidation State Changes in the Mn4Ca Cluster of Photosystem II

Description: Oxygen-evolving complex (Mn4Ca cluster) of Photosystem II cycles through five intermediate states (Si-states, i =0-4) before a molecule of dioxygen is released. During the S-state transitions, electrons are extracted from the OEC, either from Mn or alternatively from a Mn ligand. The oxidation state of Mn is widely accepted as Mn4(III2,IV2) and Mn4(III,IV3) for S1 and S2 states, while it is still controversial for the S0 and S3 states. We used resonant inelastic X-ray scattering (RIXS) to study… more
Date: August 3, 2007
Creator: Yano, Junko; Pushkar, Yulia; Messinger, Johannes; Bergmann, Uwe; Glatzel, Pieter & Yachandra, Vittal K
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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STM Studies of TbTe3: Evidence for a Fully Incommensurate Charge Density Wave

Description: We observe unidirectional charge density wave ordering on the cleaved surface of TbTe{sub 3} with a Scanning Tunneling Microscope at {approx}6 K. The modulation wave-vector q{sub CDW} as determined by Fourier analysis is 0.71 {+-} 0.02 x2{pi}/c. (Where c is one edge of the in-plane 3D unit cell.) Images at different tip-sample voltages show the unit cell doubling effects of dimerization and the layer below. Our results agree with bulk X-ray measurements, with the addition of (1/3) x2{pi}/a orde… more
Date: September 28, 2007
Creator: Fang, A.; Ru, N.; Fisher, I.R.; /Stanford U., Appl. Phys. Dept.; Kapitulnik, A. & /Stanford U., Appl. Phys. Dept. /Stanford U., Phys. Dept.
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Partner: UNT Libraries Government Documents Department
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