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CONTROL OF NONLINEAR DYNAMICS BY ACTIVE AND PASSIVE METHODS FOR THE NSLS-II INSERTION DEVICES

Description: Nonlinear effects from insertion devices are potentially a limiting factor for the electron beam quality of modern ring-based light sources, i.e., the on and off-dynamical aperture, leading to reduced injection efficiency and beam lifetime. These effects can be modelled by e.g. kick maps ({approx}1/{gamma}{sup 2}) and controlled by e.g. first-order thin or thick magnetic kicks introduced by 'magic fingers,' 'L-shims,' or 'current strips'. However, due to physical or technological constraints, these corrections are typically only partial. Therefore, a precise model is needed to correctly minimize the residual nonlinear effects for the entire system. We outline a systematic method for integrated design and rapid prototyping based on evaluation of the 3D magnetic field and control of the local trajectory with RADIA, and particle tracking with Tracy-3 for validation. The optimal geometry for the compensating magnetic fields is determined from the results of these simulations using a combination of linear algebra and genetic optimization.
Date: May 20, 2012
Creator: J., Bengtsson; Chubar, O.; Kitegi, C. & Tanabe, T.
Partner: UNT Libraries Government Documents Department

Experimental evidence of a dynamic Jahn-Teller effect in C-60(+)

Description: Detailed analysis of the HOMO bandshape in the photoelectron spectrum of gaseous C60 reveals a dynamic Jahn-Teller effect in the ground state of C60+. The direct observation of three tunneling states asserts a D3d geometry for the isolated cation, originating from a strong vibronic coupling. These results show that the ionic motion of the ions plays an important role in the electron-phonon interaction.
Date: May 20, 2002
Creator: Canton, S.E.; Yencha, A.J.; Kukk, E.; Bozek, J.D.; Lopes, M.C.A.; Snell, G. et al.
Partner: UNT Libraries Government Documents Department

On the Euler angles for SU(N)

Description: In this paper we reconsider the problem of the Euler parametrization for the unitary groups. After constructing the generic group element in terms of generalized angles, we compute the invariant measure on SU(N) and then we determine the full range of the parameters, using both topological and geometrical methods. In particular, we show that the given parametrization realizes the group SU(N+1) as a fibration of U(N) over the complex projective space CP{sup n}. This justifies the interpretation of the parameters as generalized Euler angles.
Date: October 20, 2005
Creator: Cerchiai, Bianca L; Bertini, S. & Cacciatori, Sergio L.
Partner: UNT Libraries Government Documents Department

Boltzmann babies in the proper time measure

Description: After commenting briefly on the role of the typicality assumption in science, we advocate a phenomenological approach to the cosmological measure problem. Like any other theory, a measure should be simple, general, well defined, and consistent with observation. This allows us to proceed by elimination. As an example, we consider the proper time cutoff on a geodesic congruence. It predicts that typical observers are quantum fluctuations in the early universe, or Boltzmann babies. We sharpen this well-known youngness problem by taking into account the expansion and open spatial geometry of pocket universes. Moreover, we relate the youngness problem directly to the probability distribution for observables, such as the temperature of the cosmic background radiation. We consider a number of modifications of the proper time measure, but find none that would make it compatible with observation.
Date: December 20, 2007
Creator: Bousso, Raphael; Bousso, Raphael; Freivogel, Ben & Yang, I-Sheng
Partner: UNT Libraries Government Documents Department

TEM Study of Fracturing in Spherical and Plate-like LiFePO4Particles

Description: An investigation of fracturing in LiFePO{sub 4} particles as a function of the particle morphology and history is presented. Two types of samples, one subjected to electrochemical cycling and another to chemical delithiation are compared. We observe the formation of micro fractures parallel to low indexed lattice planes in both samples. The fracture surfaces are predominantly parallel to (100) planes in the chemically delithiated powder and (100) and (010) planes in the electrochemically cycled powder. A consideration of the threshold stresses for dislocation glide shows that particle geometry plays an important role in the observed behavior.
Date: December 20, 2007
Creator: Gabrisch, H.; Wilcox, J. & Doeff, M.M.
Partner: UNT Libraries Government Documents Department

Compositional Modulation in InxGa1-xN

Description: Transmission Electron Microscopy and x-ray diffraction were used to study compositional modulation in In{sub x}Ga{sub 1-x} N layers grown with compositions close to the miscibility gap. The samples (0.34 < x < 0.8) were deposited by molecular beam epitaxy using either a 200-nm-thick AlN or GaN buffer layer grown on a sapphire substrate. In the TEM imaging mode this modulation is seen as black/white fringes which can be considered as self-assembled thin quantum wells. Periodic compositional modulation leads to extra electron diffraction spots and satellite reflections in x-ray diffraction in the {theta}-2{theta} coupled geometry. The modulation period was determined using both methods. Larger modulation periods were observed for layers with higher In content and for those having larger mismatch with the underlying AlN buffer layer. Compositional modulation was not observed for a sample with x = 0.34 grown on a GaN buffer layer. Modulated films tend to have large 'Stokes shifts' between their absorption edge and photoluminescence peak.
Date: July 20, 2005
Creator: Liliental-Weber, Z.; Zakharov, D.N.; Yu, K.M.; Ager III, J.W.; Walukiewicz, W.; Haller, E.E. et al.
Partner: UNT Libraries Government Documents Department

Finite Cosmology and a CMB Cold Spot

Description: The standard cosmological model posits a spatially flat universe of infinite extent. However, no observation, even in principle, could verify that the matter extends to infinity. In this work we model the universe as a finite spherical ball of dust and dark energy, and obtain a lower limit estimate of its mass and present size: the mass is at least 5 x 10{sup 23}M{sub {circle_dot}} and the present radius is at least 50 Gly. If we are not too far from the dust-ball edge we might expect to see a cold spot in the cosmic microwave background, and there might be suppression of the low multipoles in the angular power spectrum. Thus the model may be testable, at least in principle. We also obtain and discuss the geometry exterior to the dust ball; it is Schwarzschild-de Sitter with a naked singularity, and provides an interesting picture of cosmogenesis. Finally we briefly sketch how radiation and inflation eras may be incorporated into the model.
Date: March 20, 2006
Creator: Adler, R.J.; /Stanford U., HEPL; Bjorken, J.D.; /SLAC; Overduin, J.M. & /Stanford U., HEPL
Partner: UNT Libraries Government Documents Department

Impedance Analysis of Electrochemical NOx Sensor Using a Au/Yttria-Stabilized Zirconia (YSZ)/Au cell

Description: An electrochemical cell employing a YSZ electrolyte and two Au electrodes was utilized as a model system for investigating the mechanisms responsible for impedance metric NO{sub x} (NO and NO{sub 2}) sensing. The cell consists of two dense Au electrodes on top of a porous/dense YSZ bilayer structure (with the additional porous layer present only under the Au electrodes). Both electrodes were co-located on the same side of the cell, resulting in an in-plane geometry for the current path. The porous YSZ appears to extend the triple phase boundary and allows for enhanced NO{sub x} sensing performance, although the exact role of the porous layer is not completely understood. Impedance data were obtained over the frequency range of 0.1 Hz to 1 MHz, and over a range of oxygen (2 to 18.9%) and NO{sub x} (10 to 100 ppm) concentrations, and temperatures (600 to 700 C). Data were fit with an equivalent circuit, and the values of the circuit elements were obtained for different concentrations and temperatures. Changes in a single low-frequency arc were found to correlate with concentration changes, and to be temperature dependent. In the absence of NO{sub x}, the effect of O{sub 2} on the low-frequency resistance could be described by a power law, and the temperature dependence described by a single apparent activation energy at all O{sub 2} concentrations. When both O{sub 2} and NO{sub x} were present, however, the power law exponent varied as a function of both temperature and concentration, and the apparent activation energy also showed dual dependence. Adsorption mechanisms are discussed as possibilities for the rate-limiting steps.
Date: November 20, 2006
Creator: Woo, L Y; Martin, L P; Glass, R S & Gorte, R J
Partner: UNT Libraries Government Documents Department

Excitation Curves of C12(p,pn)C11 and B11(p,n)C11 up to 32 MeV.

Description: The reaction C{sup 12} (p,pn)C{sup 11} which has been studied by McMillan, Chubb and Miller for energies up to 100 Mev is an example of a reaction whose high energy behavior cannot be explained by a compound nucleus process. The purpose of the study was to investigate this reaction at the high resolution possible with the Berkeley linear accelerator near the excitation threshold. The excitation curve was obtained by stacking specially molded polystyrene (composition C{sub n}H{sub n}) foils of high uniformity and bombarding them in the proton beam. The resultant activity was then counted on a Geiger counter in standard geometry. The resultant curve is shown in Figure 1. An immediately evident feature is the sharp threshold of the reaction. The second derivative curve, illustrated in Figure 2, of the excitation shows an RMS width of 270 kV, the theoretical straggling width due to the foils of 170 kv, and the remaining width in accordance with the energy spread of approximately {+-} 100 kv half width of the linear accelerator. The data therefore are compatible with a sharp threshold for this reaction. This curve, incidentally, furnishes independent evidence as to the energy homogeneity of the linear accelerator beam.
Date: April 20, 1948
Creator: Phillips, Robert & Panofsky, Wolfgang K.H.
Partner: UNT Libraries Government Documents Department

Supergravity Analysis of Hybrid Inflation Model from D3--D7 System

Description: The slow-roll inflation is a beautiful paradigm, yet the inflaton potential can hardly be sufficiently flat when unknown gravitational effects are taken into account. However, the hybrid inflation models constructed in D = 4 N = 1 supergravity can be consistent with N = 2 supersymmetry, and can be naturally embedded into string theory. This article discusses the gravitational effects carefully in the string model, using D = 4 supergravity description. We adopt the D3--D7 system of Type IIB string theory compactified on K3 x T^2/Z_2 orientifold for definiteness. It turns out that the slow-roll parameter can be sufficiently small despite the non-minimal Kahler potential of the model. The conditions for this to happen are clarified in terms of string vacua. We also find that the geometry obtained by blowing up singularity, which is necessary for the positive vacuum energy, is stabilized by introducing certain 3-form fluxes.
Date: November 20, 2003
Creator: Koyama, Fumikazu; Tachikawa, Yuji & Watari, Taizan
Partner: UNT Libraries Government Documents Department

Progress In NCSX and QPS Design and Construction

Description: The National Compact Stellarator Experiment (NCSX) is being constructed at the Princeton Plasma Physics Laboratory (PPPL) in partnership with the Oak Ridge National Laboratory (ORNL). The stellarator core is designed to produce a compact 3-D plasma that combines stellarator and tokamak physics advantages. The engineering challenges of NCSX stem from its complex geometry. From the project's start in April, 2003 to September, 2004, the fabrication specifications for the project's two long-lead components, the modular coil winding forms and the vacuum vessel, were developed. An industrial manufacturing R&D program refined the processes for their fabrication as well as production cost and schedule estimates. The project passed a series of reviews and established its performance baseline with the Department of Energy. In September 2004, fabrication was approved and contracts for these components were awarded. The suppliers have completed the engineering and tooling preparations and are in production. Meanwhile, the project completed preparations for winding the coils at PPPL by installing a coil manufacturing facility and developing all necessary processes through R&D. The main activities for the next two years will be component manufacture, coil winding, and sub-assembly of the vacuum vessel and coil subsets. Machine sector sub-assembly, machine assembly, and testing will follow, leading to First Plasma in July 2009.
Date: October 20, 2005
Creator: Reiersen, W.; Heitzenroeder, P.; Neilson, G. H.; Nelson, B.; Zarnstorff, M.; Brown, T. et al.
Partner: UNT Libraries Government Documents Department

Bell-Plesset effects for an accelerating interface with contiguous density gradients

Description: A Plesset-type treatment [J. Appl. Phys. 25, 96 (1954)] is used to assess the effects of contiguous density gradients at an accelerating spherical classical interface on Rayleigh-Taylor and Bell-Plesset perturbation growth. Analytic expressions are obtained that describe enhanced Rayleigh-Taylor instability growth from contiguous density gradients aligned with the acceleration and which increase the effective Atwood number of the perturbed interface. A new pathway for geometric amplification of surface perturbations on an accelerating interface with contiguous density gradients is identified. A resonance condition between the density-gradient scalelength and the radius of the interface is also predicted based on a linearized analysis of Bernoulli's equation, potentially leading to enhanced perturbation growth. Comparison of the analytic treatment with detailed two-dimensional single-mode growth-factor simulations shows good agreement for low-mode numbers where the effects of spherical geometry are most manifested.
Date: December 20, 2005
Creator: Amendt, P
Partner: UNT Libraries Government Documents Department

Final Report PetaScale Application Development Analysis Grant Number DE-FG02-04ER25629

Description: The results obtained from this project will fundamentally change the way we look at computer performance analysis. These results are made possible by the precise definition of a consistent system of measurement with a set of primary units designed specifically for computer performance analysis. This system of units, along with their associated dimensions, allows us to apply the methods of dimensional analysis, based on the Pi Theorem, to define scaling and self-similarity relationships. These relationships reveal new insights into experimental results that otherwise seems only vaguely correlated. Applying the method to cache-miss data revealed scaling relationships that were not seen by those who originally collected the data. Applying dimensional analysis to the performance of parallel numerical algorithms revealed that computational force is a unifying concept for understanding the interaction between hardware and software. The efficiency of these algorithms depends, in a very intimate way, on the balance between hardware forces and software forces. Analysis of five different algorithms showed that performance analysis can be reduced to a study of the differential geometry of the efficiency surface. Each algorithm defines a set of curvilinear coordinates, specific to that algorithm, and different machines follow different paths along the surface depending on the difference in balance between hardware forces and software forces. Two machines with the same balance in forces follow the same path and are self-similar. The most important result from the project is the statement of the Principle of Computational Least Action. This principle follows from the identification of a dynamical system underlying computer performance analysis. Instructions in a computer are modeled as a classical system under the influence of computational forces. Each instruction generates kinetic energy during execution, and the sum of the kinetic energy for all instructions produces a kinetic energy spectrum as a function of time. These spectra ...
Date: June 20, 2008
Creator: Numrich, Robert W.
Partner: UNT Libraries Government Documents Department

Final Report for DE-FG02-96ER54370

Description: The work has consisted of three projects. The first one is a continuation of the previous work that was done on the generation of zonal flows due to the four wave modulational instability. In this work, we examined the growth of streamers. This work was done with undergraduate student, and was presented at an APS DPP meeting. A summary of the work is given below. Another project was a study of the stability of curvature driven modes with tied field line geometry. The purpose of this study was to see if this instability was relevant to the observed 'blob' phenomenon in the edge. A summary of this work is given starting in Section II. This work was done with undergraduate student. The final project was an extension of electrostatic work that had been done on the parallel velocity shear instability. In this work, we included electromagnetic effects. We performed the linear stability analysis and discovered a new regime of instability. This work was done in collaboration with undergraduate student, who presented the work at an APS DPP meeting. Details of this are shown in Section III.
Date: November 20, 2008
Creator: McCarthy, Daniel
Partner: UNT Libraries Government Documents Department

Evaluating Cumulative Ecosystem Response to Restoration Projects in the Columbia River Estuary, Annual Report 2005

Description: This report is the second annual report of a six-year project to evaluate the cumulative effects of habitat restoration projects in the Columbia River Estuary, conducted by Pacific Northwest National Laboratory's Marine Sciences Laboratory, NOAA's National Marine Fisheries Service Pt. Adams Biological Field Station, and the Columbia River Estuary Study Taskforce for the US Army Corps of Engineers. In 2005, baseline data were collected on two restoration sites and two associated reference sites in the Columbia River estuary. The sites represent two habitat types of the estuary--brackish marsh and freshwater swamp--that have sustained substantial losses in area and that may play important roles for salmonids. Baseline data collected included vegetation and elevation surveys, above and below-ground biomass, water depth and temperature, nutrient flux, fish species composition, and channel geometry. Following baseline data collection, three kinds of restoration actions for hydrological reconnection were implemented in several locations on the sites: tidegate replacements (2) at Vera Slough, near the city of Astoria in Oregon State, and culvert replacements (2) and dike breaches (3) at Kandoll Farm in the Grays River watershed in Washington State. Limited post-restoration data were collected: photo points, nutrient flux, water depth and temperature, and channel cross-sections. In subsequent work, this and additional post-restoration data will be used in conjunction with data from other sites to estimate net effects of hydrological reconnection restoration projects throughout the estuary. This project is establishing methods for evaluating the effectiveness of individual projects and a framework for assessing estuary-wide cumulative effects including a protocol manual for monitoring restoration and reference sites.
Date: December 20, 2006
Creator: Diefenderfer, Heida L.; Thom, Ronald M.; Borde, Amy B.; Roegner, G. C.; Whiting, Allan H.; Johnson, Gary E. et al.
Partner: UNT Libraries Government Documents Department

Functional Nanostructured Platforms for Chemical and Biological Sensing

Description: The central goal of our work is to combine semiconductor nanotechnology and surface functionalization in order to build platforms for the selective detection of bio-organisms ranging in size from bacteria (micron range) down to viruses, as well as for the detection of chemical agents (nanometer range). We will show on three porous silicon platforms how pore geometry and pore wall chemistry can be combined and optimized to capture and detect specific targets. We developed a synthetic route allowing to directly anchor proteins on silicon surfaces and illustrated the relevance of this technique by immobilizing live enzymes onto electrochemically etched luminescent nano-porous silicon. The powerful association of the specific enzymes with the transducing matrix led to a selective hybrid platform for chemical sensing. We also used light-assisted electrochemistry to produce periodic arrays of through pores on pre-patterned silicon membranes with controlled diameters ranging from many microns down to tens of nanometers. We demonstrated the first covalently functionalized silicon membranes and illustrated their selective capture abilities with antibody-coated micro-beads. These engineered membranes are extremely versatile and could be adapted to specifically recognize the external fingerprints (size and coat composition) of target bio-organisms. Finally, we fabricated locally functionalized single nanopores using a combination of focused ion beam drilling and ion beam assisted oxide deposition. We showed how a silicon oxide ring can be grown around a single nanopore and how it can be functionalized with DNA probes to detect single viral-sized beads. The next step for this platform is the detection of whole viruses and bacteria.
Date: March 20, 2006
Creator: Letant, S E
Partner: UNT Libraries Government Documents Department

Final Report for the grant "Applied Geometry" (DOE DE-FG02-04ER25657)

Description: The primary purpose of this 3-year DOE-funded research effort, now completed, was to develop consistent, theoretical foundations of computations on discrete geometry, to realize the promise of predictive and scalable management of large geometric datasets as handled routinely in applied sciences. Geometry (be it simple 3D shapes or higher dimensional manifolds) is indeed a central and challenging issue from the modeling and computational perspective in several sciences such as mechanics, biology, molecular dynamics, geophysics, as well as engineering. From digital maps of our world, virtual car crash simulation, predictive animation of carbon nano-tubes, to trajectory design of space missions, knowing how to process and animate digital geometry is key in many cross-disciplinary research areas.
Date: May 20, 2009
Creator: Desbrun, Prof. Mathieu
Partner: UNT Libraries Government Documents Department

Changing the PEP-II Center-of-Mass Energy Down to 10 GeV and up to 11 GeV

Description: PEP-II, the SLAC, LBNL, LLNL B-Factory was designed and optimized to run at the Upsilon 4S resonance (10.580 GeV with an 8.973 GeV e- beam and a 3.119 GeV e+ beam). The interaction region (IR) used permanent magnet dipoles to bring the beams into a head-on collision. The first focusing element for both beams was also a permanent magnet. The IR geometry, masking, beam orbits and beam pipe apertures were designed for 4S running. Even though PEP-II was optimized for the 4S, we successfully changed the center-of-mass energy (E{sub cm}) down to the Upsilon 2S resonance and completed an E{sub cm} scan from the 4S resonance up to 11.2 GeV. The luminosity throughout most of these changes remained near 1 x 10{sup 34} cm{sup -2}s{sup -1}. The E{sub cm} was changed by moving the energy of the high-energy beam (HEB). The beam energy differed by more than 20% which produced significantly different running conditions for the RF system. The energy loss per turn changed 2.5 times over this range. We describe how the beam energy was changed and discuss some of the consequences for the beam orbit in the interaction region. We also describe some of the RF issues that arose and how we solved them as the high-current HEB energy changed.
Date: May 20, 2009
Creator: Sullivan, M; Bertsche, K.; Novokhatski, A.; Seeman, J.; Wienands, U. & /SLAC
Partner: UNT Libraries Government Documents Department

Transport of Parallel Momentum by Toroidal Ion Temperature Gradient Instability near Marginality

Description: The turbulent angular momentum flux carried by ions resonant with toroidal ion temperature gradient(ITG) instability is calculated via quasilinear calculation using the phase-space conserving gyrokinetic equation in the laboratory frame. The results near ITG marginality indicate that the inward turbulent equipartition (TEP) momentum pinch [Hahm T.S. et al 2007 Phys. Plasmas 14 072302] remains as the most robust part of pinch. In addition, ion temperature gradient driven momentum flux is inward for typical parameters, while density gradient driven momentum flux is outward as in the previous kinetic result in slab geometry [Diamond P.H. et al 2008 Phys. Plasmas 15 012303].
Date: October 20, 2009
Creator: Yoon, E. S. & Hahm, T. S.
Partner: UNT Libraries Government Documents Department

Downstream Heat Flux Profile vs. Midplane T Profile in Tokamaks

Description: The relationship between the midplane scrape-off-layer electron temperature profile and the parallel heat flux profile at the divertor in tokamaks is investigated. A model is applied which takes into account anisotropic thermal diffusion, in a rectilinear geometry with constant density. Eigenmode analysis is applied to the simplified problem with constant thermal diffusivities. A self-similar nonlinear solution is found for the more realistic problem with anisotropically temperature-dependent thermal diffusivities. Numerical solutions are developed for both cases, with spatially dependent heat flux emerging from the plasma. For both constant and temperature-dependent thermal diffusivities it is found that, below about one-half of its peak, the heat flux profile shape at the divertor, compared with the midplane temperature profile shape, is robustly described by the simplest two-point model. However the physical processes are not those assumed in the simplest two-point model, nor is the numerical coefficient relating q||div to Tmp χ||mp/L|| as predicted. For realistic parameters the peak in the heat flux, moreover, can be reduced by a factor of two or more from the two-point model scaling which fits the remaining profile. For temperature profiles in the SOL region above the x-point set by marginal stability, the heat flux profile to the divertor can be largely decoupled from the prediction of the two-point model. These results suggest caveats for data interpretation, and possibly favorable outcomes for divertor configurations with extended field lines.
Date: August 20, 2009
Creator: Goldston, Robert J.
Partner: UNT Libraries Government Documents Department

Numerical Homogenization on Approach for Stokesian Suspensions.

Description: In this technical report we investigate efficient methods for numerical simulation of active suspensions. The prototypical system is a suspension of swimming bacteria in a Newtonian fluid. Rheological and other macroscopic properties of such suspensions can differ dramatically from the same properties of the suspending fluid alone or of suspensions of similar but inactive particles. Elongated bacteria, such as E. coli or B. subtilis, swim along their principal axis, propelling themselves with the help of flagella, attached at the anterior of the organism and pushing it forward in the manner of a propeller. They interact hydrodynamically with the surrounding fluid and, because of their asymmetrical shape, have the propensity to align with the local flow. This, along with the dipolar nature of bacteria (the two forces a bacterium exerts on a fluid - one due to self-propulsion and the other opposing drag - have equal magnitude and point in opposite directions), causes nearby bacteria to tend to align, resulting in a intermittent local ordering on the mesoscopic scale, which is between the microscopic scale of an individual bacterium and the macroscopic scale of the suspension (e.g., its container). The local ordering is sometimes called a collective mode or collective swimming. Thanks to self-propulsion, collective modes inject momentum into the fluid in a coherent way. This enhances the local strain rate without changing the macroscopic stress applied at the boundary of the container. The macroscopic effective viscosity of the suspension is defined roughly as the ratio of the applied stress to the bulk strain rate. If local alignment and therefore local strain-rate enhancement, are significant, the effective viscosity can be appreciably lower than that of the corresponding passive suspension or even of the surrounding fluid alone. Indeed, a sevenfold decrease in the effective viscosity was observed in experiments with B. subtilis. ...
Date: January 20, 2012
Creator: Haines, Brian M.; Berlyand, Leonid V. & Karpeev, Dmitry A.
Partner: UNT Libraries Government Documents Department

Compressive auto-indexing in femtosecond nanocrystallography

Description: 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
Partner: UNT Libraries Government Documents Department

An embedded boundary method for viscous, conducting compressibleflow

Description: The evolution of an Inertial Fusion Energy (IFE) chamberinvolves a repetition of short, intense depositions of energy (fromtarget ignition) into a reaction chamber, followed by the turbulentrelaxation of that energy through shock waves and thermal conduction tothe vessel walls. We present an algorithm for 2D simulations of the fluidinside an IFE chamber between fueling repetitions. Our finite-volumediscretization for the Navier-Stokes equations incorporates a Cartesiangrid treatment for irregularly-shaped domain boundaries. The discreteconservative update is based on a time-explicit Godunov method foradvection, and a two-stage Runge-Kutta update for diffusion accommodatingstate-dependent transport properties. Conservation is enforced on cutcells along the embedded boundary interface using a local redistributionscheme so that the explicit time step for the combined approach isgoverned by the mesh spacing in the uniform grid. The test problemsdemonstrate second-order convergence of the algorithm on smooth solutionprofiles, and the robust treatment of discontinuous initial data in anIFE-relevant vessel geometry.
Date: October 20, 2004
Creator: Dragojlovic, Zoran; Najmabadi, Farrokh & Day, Marcus
Partner: UNT Libraries Government Documents Department