Protein-DNA charge transport: Redox activation of a DNA repair protein by guanine radical

DNA charge transport (CT) chemistry provides a route to carry out oxidative DNA damage from a distance in a reaction that is sensitive to DNA mismatches and lesions. Here, DNA-mediated CT also leads to oxidation of a DNA-bound base excision repair enzyme, MutY. DNA-bound Ru(III), generated through a flash/quench technique, is found to promote oxidation of the [4Fe-4S](2+) cluster of MutY to [4Fe-4S](3+) and its decomposition product [3Fe-4S](1+). Flash/quench experiments monitored by EPR spectroscopy reveal spectra with g = 2.08, 2.06, and 2.02, characteristic of the oxidized clusters. Transient absorption spectra of poly(dGC) and [Ru(phen)(2)dppz](3+) (dppz = dipyridophenazine), generated in situ, show an absorption characteristic of the guanine radical that is depleted in the presence of MutY with formation instead of a long-lived species with an absorption at 405 nm; we attribute this absorption also to formation of the oxidized [4Fe-4S](3+) and [3Fe4S](1+) clusters. In ruthenium-tethered DNA assemblies, oxidative damage to the 5'-G of a 5'-GG-3' doublet is generated from a distance but this irreversible damage is inhibited by MutY and instead EPR experiments reveal cluster oxidation. With ruthenium-tethered assemblies containing duplex versus single-stranded regions, MutY oxidation is found to be mediated by the DNA duplex, with guanine radical as an intermediate oxidant; guanine radical formation facilitates MutY oxidation. A model is proposed for the redox activation of DNA repair proteins through DNA CT, with guanine radicals, the first product under oxidative stress, in oxidizing the DNA-bound repair proteins, providing the signal to stimulate DNA repair

Anti-Hyperon Enhancement through Baryon Junction Loops

The baryon junction exchange mechanism recently proposed to explain valence baryon number transport in nuclear collisions is extended to study midrapidity anti-hyperon production. Baryon junction-anti-junction (J anti-J) loops are shown to enhance anti-Lambda, anti-Xi, anti-Omega yields as well as lead to long range rapidity correlations. Results are compared to recent WA97 Pb + Pb -> Y + anti-Y + X data.Comment: 10 pages, 4 figure

Crystallographic Analysis of Nucleation at Hardness Indentations in High-Purity Aluminum

Nucleation at Vickers hardness indentations has been studied in high-purity aluminum cold-rolled 12 pct. Electron channeling contrast was used to measure the size of the indentations and to detect nuclei, while electron backscattering diffraction was used to determine crystallographic orientations. It is found that indentations are preferential nucleation sites. The crystallographic orientations of the deformed grains affect the hardness and the nucleation potentials at the indentations. Higher hardness gives increased nucleation probabilities. Orientation relationships between nuclei developed at different indentations within one original grain are analyzed and it is found that the orientation distribution of the nuclei is far from random. It is suggested that it relates to the orientations present near the indentation tips which in turn depend on the orientation of the selected grain in which they form. Finally, possible nucleation mechanisms are briefly discussed. © 2016, The Minerals, Metals &amp; Materials Society and ASM International.</p

RK-TBA studies at the RTA test facility

Construction of a prototype RF power source based on the RK-TBA concept, called the RTA, has commenced at the Lawrence Berkeley National Laboratory. This prototype will be used to study physics, engineering, and costing issues involved in the application of the RK-TBA concept to linear colliders. The status of the prototype is presented, specifically the 1-MV, 1.2-kA induction electron gun and the pulsed power system that are in assembly. The RTA program theoretical effort, in addition to supporting the development of the prototype, has been studying optimization parameters for the application of the RK-TBA concept to higher-energy linear colliders. An overview of this work is presented. 1 fig

Neutralized transport of high intensity beams

The NTX experiment at the Heavy Ion Fusion Virtual National Laboratory is exploring the performance of neutralized final focus systems for high perveance heavy ion beams. A converging ion beam at the exit of the final focus magnetic system is injected into a neutralized drift section. The neutralization is provided by a metal arc source and an RF plasma source. Effects of a ''plasma plug'', where electrons are extracted from a localized plasma in the upstream end of the drift section, and are then dragged along by the ion potential, as well as the ''volumetric plasma'', where neutralization is provided by the plasma laid down along the ion path, are both studied and their relative effects on the beam spot size are compared. Comparisons with 3-D PIC code predictions will also be presented

The Electrical-Thermal Switching in Carbon Black-Polymer Composites as a Local Effect

Following the lack of microscopic information about the intriguing well-known electrical-thermal switching mechanism in Carbon Black-Polymer composites, we applied atomic force microscopy in order to reveal the local nature of the process and correlated it with the characteristics of the widely used commercial switches. We conclude that the switching events take place in critical interparticle tunneling junctions that carry most of the current. The macroscopic switched state is then a result of a dynamic-stationary state of fast switching and slow reconnection of the corresponding junctions.Comment: 14 pages, 5 figures,Typographic correctio

Non-universal current flow near the metal-insulator transition in an oxide interface

In systems near phase transitions, macroscopic properties often follow algebraic scaling laws, determined by the dimensionality and the underlying symmetries of the system. The emergence of such universal scaling implies that microscopic details are irrelevant. Here, we locally investigate the scaling properties of the metal-insulator transition at the LaAlO3/SrTiO3 interface. We show that, by changing the dimensionality and the symmetries of the electronic system, coupling between structural and electronic properties prevents the universal behavior near the transition. By imaging the current flow in the system, we reveal that structural domain boundaries modify the filamentary flow close to the transition point, preventing a fractal with the expected universal dimension from forming. Our results offer a generic platform to engineer electronic transitions on the nanoscale.Comment: 19 pages, 6 figure

Stacked insulator induction accelerator gaps

Stacked insulators, with alternating layers of insulating material and conducting film, have been shown to support high surface electrical field stresses. We have investigated the application of the stacked insulator technology to the design of induction accelerator modules for the Relativistic-Klystron Two-Beam Accelerator program. The rf properties of the accelerating gaps using stacked insulators, particularly the impedance at frequencies above the beam pipe cutoff frequency, are investigated. Low impedance is critical for Relativistic-Klystron Two-Beam Accelerator applications where a high current, bunched beam is trsnsported through many accelerating gaps. An induction accelerator module designs using a stacked insulator is presented

Tensile and fatigue strength of hydrogen-treated Ti-6Al-4V alloy

Tensile, fatigue and fractographic data on Ti-6Al-4V microstructures attained through a series of post-β-annealing treatments which used hydrogen as a temporary alloying element are presented. Hydrogen-alloying treatments break up the continuous grain boundary α and colony structure, and produce a homogeneous microstructure consisting of refined α-grains in a matrix of discontinuous β. These changes in microstructural morphology result in significant increases of the yield strength (974 to 1119 MPa), ultimate strength (1025 to 1152 MPa) and high cycle fatigue strength (643 to 669 MPa) compared to respective values for lamellar microstructures (902, 994, 497 MPa). The strengths are also significantly greater than the strengths of equiaxed microstructures (914, 1000, 590 MPa). The strengths of hydrogen-alloy treated samples are therefore superior to strengths attainable via other thermal cycling techniques.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44703/1/10853_2004_Article_BF00576523.pd