Compressive auto-indexing in femtosecond nanocrystallography (open access)

Compressive auto-indexing in femtosecond nanocrystallography

Ultrafast nanocrystallography has the potential to revolutionize biology by enabling structural elucidation of proteins for which it is possible to grow crystals with 10 or fewer unit cells. The success of nanocrystallography depends on robust orientation-determination procedures that allow us to average diffraction data from multiple nanocrystals to produce a 3D diffraction data volume with a high signal-to-noise ratio. Such a 3D diffraction volume can then be phased using standard crystallographic techniques."Indexing" algorithms used in crystallography enable orientation determination of a diffraction data from a single crystal when a relatively large number of reflections are recorded. Here we show that it is possible to obtain the exact lattice geometry from a smaller number of measurements than standard approaches using a basis pursuit solver.
Date: September 20, 2010
Creator: Maia, Filipe; Yang, Chao & Marchesini, Stefano
Object Type: Article
System: The UNT Digital Library
Evaluation of Alumina-Forming Austenitic Stainless Steel Alloys in Microturbines (open access)

Evaluation of Alumina-Forming Austenitic Stainless Steel Alloys in Microturbines

Oak Ridge National Laboratory (ORNL) and Capstone Turbine Corporation (CTC) participated in an in-kind cost share cooperative research and development agreement (CRADA) effort under the auspices of the Energy Efficiency and Renewable Energy (EERE) Technology Maturation Program to explore the feasibility for use of developmental ORNL alumina-forming austenitic (AFA) stainless steels as a material of construction for microturbine recuperator components. ORNL delivered test coupons of three different AFA compositions to CTC. The coupons were exposed in steady-state elevated turbine exit temperature (TET) engine testing, with coupons removed for analysis after accumulating ~1,500, 3,000, 4,500, and 6,000 hours of operation. Companion test coupons were also exposed in oxidation testing at ORNL at 700-800°C in air with 10% H2O. Post test assessment of the coupons was performed at ORNL by light microscopy and electron probe microanalysis. The higher Al and Nb containing AFA alloys exhibited excellent resistance to oxidation/corrosion, and thus show good promise for recuperator applications.
Date: September 15, 2010
Creator: Brady, M.P. & Matthews, W.J. (Capstone Turbine Corp.)
Object Type: Report
System: The UNT Digital Library
Plasticity and Failure in Nanocrystalline BCC Metals via Molecular Dynamics Simulation (open access)

Plasticity and Failure in Nanocrystalline BCC Metals via Molecular Dynamics Simulation

Advances in the ability to generate extremely high pressures in dynamic experiments such as at the National Ignition Facility has motivated the need for special materials optimized for those conditions as well as ways to probe the response of these materials as they are deformed. We need to develop a much deeper understanding of the behavior of materials subjected to high pressure, especially the effect of rate at the extremely high rates encountered in those experiments. Here we use large-scale molecular dynamics (MD) simulations of the high-rate deformation of nanocrystalline tantalum at pressures less than 100 GPa to investigate the processes associated with plastic deformation for strains up to 100%. We focus on 3D polycrystalline systems with typical grain sizes of 10-20 nm. We also study a rapidly quenched liquid (amorphous solid) tantalum. We apply a constant volume (isochoric), constant temperature (isothermal) shear deformation over a range of strain rates, and compute the resulting stress-strain curves to large strains for both uniaxial and biaxial compression. We study the rate dependence and identify plastic deformation mechanisms. The identification of the mechanisms is facilitated through a novel technique that computes the local grain orientation, returning it as a quaternion for each atom. …
Date: September 29, 2010
Creator: Rudd, R E
Object Type: Article
System: The UNT Digital Library
A new possibility of low-Z gas stripper for high power uranium beam acceleration alternative to C-foil (open access)

A new possibility of low-Z gas stripper for high power uranium beam acceleration alternative to C-foil

The RIKEN accelerator complex started feeding the next-generation exotic beam facility RIBF (RadioIsotope Beam Factory) with heavy ion beams from 2007 after the successful commissioning at the end of 2006. Many elaborating improvements increased the intensity of the various heavy ion beams from 2007 to 2010. However, the available beam intensity especially of uranium beam is far below our goal of 1 p{micro}A (6 x 10{sup 12} particle/s). In order to achieve it, upgrade programs are well in progress, including constructions of a new 28 GHz superconducting ECR ion source and a new injector linac. However, the most serious problem of the charge stripper for uranium beam is still open although many elaborating R&D works for the problems. Equilibrium charge state in gas generally is much lower than that in carbon foil due to its density-effect. But gas stripper is free from the problems originated from its lifetime and uniformity in thickness. Such merits pushed us think about low-Z gas stripper to get higher equilibrium charge state even in gas. Electron loss and capture cross section of U ion beams in He gas were measured as a function of their charge state at 11, 14 and 15 MeV/u. The extracted …
Date: September 27, 2010
Creator: Okuno, H.; Hershcovitch, A.; Fukunishi, N.; Goto, A.; Hasebe, H.; Imao, H. et al.
Object Type: Article
System: The UNT Digital Library
Betatron motion with coupling of horizontal and vertical degrees of freedom (open access)

Betatron motion with coupling of horizontal and vertical degrees of freedom

Presently, there are two most frequently used parameterizations of linear x-y coupled motion used in the accelerator physics. They are the Edwards-Teng and Mais-Ripken parameterizations. The article is devoted to an analysis of close relationship between the two representations, thus adding a clarity to their physical meaning. It also discusses the relationship between the eigen-vectors, the beta-functions, second order moments and the bilinear form representing the particle ellipsoid in the 4D phase space. Then, it consideres a further development of Mais-Ripken parameteresation where the particle motion is described by 10 parameters: four beta-functions, four alpha-functions and two betatron phase advances. In comparison with Edwards-Teng parameterization the chosen parametrization has an advantage that it works equally well for analysis of coupled betatron motion in circular accelerators and in transfer lines. Considered relationship between second order moments, eigen-vectors and beta-functions can be useful in interpreting tracking results and experimental data. As an example, the developed formalizm is applied to the FNAL electron cooler and Derbenev's vertex-to-plane adapter.
Date: September 1, 2010
Creator: Lebedev, V. A. & Bogacz, S. A.
Object Type: Article
System: The UNT Digital Library
Deep-sea oil plume enriches psychrophilic oil-degrading bacteria (open access)

Deep-sea oil plume enriches psychrophilic oil-degrading bacteria

The biological effects and expected fate of the vast amount of oil in the Gulf of Mexico from the Deepwater Horizon blowout are unknown owing to the depth and magnitude of this event. Here, we report that the dispersed hydrocarbon plume stimulated deep-sea indigenous {gamma}-Proteobacteria that are closely related to known petroleum degraders. Hydrocarbon-degrading genes coincided with the concentration of various oil contaminants. Changes in hydrocarbon composition with distance from the source and incubation experiments with environmental isolates demonstrated faster-than-expected hydrocarbon biodegradation rates at 5 C. Based on these results, the potential exists for intrinsic bioremediation of the oil plume in the deep-water column without substantial oxygen drawdown.
Date: September 1, 2010
Creator: Hazen, T. C.; Dubinsky, E. A.; DeSantis, T. Z.; Andersen, G. L.; Piceno, Y. M.; Singh, N. et al.
Object Type: Article
System: The UNT Digital Library
Multiturn injection of EBIS ions in booster (open access)

Multiturn injection of EBIS ions in booster

Ions from EBIS are injected into Booster after acceleration by an RFQ and a Linac. The velocity of the ions at Booster injection is c{beta} where c is the velocity of light and (1) {beta} = 0.0655. The kinetic energy is (2) W = mc{sup 2}({gamma}-1) where m is the ion mass and (3) {gamma} = (1-{beta}{sup 2}){sup -1/2}. Putting in numbers one gets a kinetic energy of approximately 2 MeV per nucleon for each ion. The revolution period at injection is 10.276 {micro}s. The ions in the EBIS trap are delivered in a beam pulse that ranges from 10 to 40 {micro}s in length. This amounts to 1 to 4 turns around the machine. The transverse emittance (un-normalized) of EBIS beams just prior to injection into Booster is 11{pi} mm milliradians in both planes. This is an order of magnitude larger than the nominal 1{pi} mm milliradians for Tandem beams. Injection proceeds by means of an electrostatic inflector in the C3 straight section and four programmable injection dipoles in the C1, C3, C7, and D1 straights. These devices have been in use for many years for the injection of ions from Tandem as described in [1] and [2]. The …
Date: September 1, 2010
Creator: Gardner, C. J.
Object Type: Report
System: The UNT Digital Library
Observation of new resonances decaying to $D\pi$ and $D^*\pi$ in inclusive $e^ e^-$ collisions near $\sqrt{s} (open access)

Observation of new resonances decaying to $D\pi$ and $D^*\pi$ in inclusive $e^ e^-$ collisions near $\sqrt{s}

The authors present a study of the D{sup +}{pi}{sup -}, D{sup 0}{pi}{sup +}, and D*{sup +}{pi}{sup -} systems in inclusive e{sup +}e{sup -} {yields} c{bar c} interactions in a search for new excited D meson states. they use a dataset, consisting of {approx} 454 fb{sup -1}, collected at center-of-mass energies near 10.58 GeV by the BABAR detector at the SLAC PEP-II asymmetric-energy collider. They observe, for the first time, candidates for the radial excitations of the D{sup 0}, D*{sup 0}, and D*{sup +}, as well as the L = 2 excited states of the D{sup 0} and D{sup +}, where L is the orbital angular momentum of the quarks.
Date: September 14, 2010
Creator: del Amo Sanchez, P.; Lees, J. P.; Poireau, V.; Prencipe, E.; Tisserand, V.; Garra Tico, J. et al.
Object Type: Article
System: The UNT Digital Library
Search for the Rare Decay B -> K nu nubar (open access)

Search for the Rare Decay B -> K nu nubar

We present a search for the rare decays B{sup +} {yields} K{sup +}{nu}{bar {nu}} and B{sup 0} {yields} K{sup 0}{nu}{bar {nu}} using 459 million B{bar B} pairs collected with the BABAR detector at the SLAC National Accelerator Laboratory. Flavor-changing neutral-current decays such as these are forbidden at tree level but can occur through one-loop diagrams in the Standard Model (SM), with possible contributions from new physics at the same order. The presence of two neutrinos in the final state makes identification of signal events challenging, so reconstruction in the semileptonic decay channels B {yields} D{sup (*)}l{nu} of the B meson recoiling from the signal B is used to suppress backgrounds. We set an upper limit at the 90% confidence level of 1.3 x 10{sup -5} on the total branching fraction for B{sup +} {yields} K{sup +}{nu}{bar {nu}}, and 5.6 x 10{sup -5} for B{sup 0} {yields} K{sup 0}{nu}{bar {nu}}. We additionally report partial branching fractions in two ranges of di-neutrino mass squared for B{sup +} {yields} K{sup +}{nu}{bar {nu}}.
Date: September 14, 2010
Creator: del Amo Sanchez, P.; Lees, J.P.; Poireau, V.; Prencipe, E.; Tisserand, V.; Garra Tico, J. et al.
Object Type: Article
System: The UNT Digital Library
Measurement of the Decay B to Omega L Nu with the BaBar Detector and Determination of V_Ub (open access)

Measurement of the Decay B to Omega L Nu with the BaBar Detector and Determination of V_Ub

We measure the branching fraction of the exclusive charmless semileptonic decay B {yields} {omega}{ell}{nu}{sub {ell}}, where {ell} is either an electron or a muon, with the charged B meson recoiling against a tag B meson decaying in the charmed semileptonic modes B {yields} D{ell}{nu}{sub {ell}} or B {yields} D*{ell}{nu}{sub {nu}}. The measurement is based on a dataset of 426.1 fb{sup -1} of e{sup +}e{sup -} collisions at a CM energy of 10.58 GeV recorded with the BABAR detector at the PEP-II asymmetric B Factory located at the SLAC National Accelerator Laboratory. We also calculate the relevant B {yields} {omega} hadronic form factors to determine the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element |V{sub ub}|.
Date: September 10, 2010
Creator: Nagel, Martin
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Measurements of B to V(Gamma) Decays (open access)

Measurements of B to V(Gamma) Decays

The standard model has been highly successful at describing current experimental data. However, extensions of the standard model predict particles that have masses at energy scales that are above the electroweak scale. The flavor-changing neutral current processes of the B meson are sensitive to the influences of these new physics contributions. These processes proceed through loop diagrams, thus allowing new physics to enter at the same order as the standard model. New physics may contribute to the enhancement or suppression of rate asymmetries or the decay rates of these processes. The transition B {yields} V{gamma} (V = K*(892), {rho}(770), {omega}(782), {phi}(1020)) represents radiative decays of the B meson that proceed through penguin processes. Hadronic uncertainties limit the theoretical accuracy of the prediction of the branching fractions. However, uncertainties, both theoretical and experimental, are much reduced when considering quantities involving ratios of branching fractions, such as CP or isospin asymmetries. The most dominant exclusive radiative b {yields} s transition is B {yields} K*{gamma}. We present the best measurements of the branching fractions, direct CP, and isospin asymmetries of B {yields} K*{gamma}. The analogous b {yields} d transitions are B {yields} {rho}{gamma} and B {yields} {omega}{gamma}, which are suppressed by a factor …
Date: September 2, 2010
Creator: Yarritu, Aaron K.
Object Type: Report
System: The UNT Digital Library