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0.7-eV GaInAs Junction for a GaInP/GaAs/GaInAs(1-eV)/GaInAs(0.7-eV) Four-Junction Solar Cell: Preprint

Description: We discuss recent developments in III-V multijunction solar cells, focusing on adding a fourth junction to the Ga0.5In0.5P/GaAs/Ga0.75In0.25As inverted three-junction cell. This cell, grown inverted on GaAs so that the lattice-mismatched Ga0.75In0.25As third junction is the last one grown, has demonstrated 38% efficiency, and 40% is likely in the near future. To achieve still further gains, a lower-bandgap GaxIn1-xAs fourth junction could be added to the three-junction structure for a four-junction cell whose efficiency could exceed 45% under concentration. Here, we present the initial development of the GaxIn1-xAs fourth junction. Junctions of various bandgaps ranging from 0.88 to 0.73 eV were grown, in order to study the effect of the different amounts of lattice mismatch. At a bandgap of 0.88 eV, junctions were obtained with very encouraging {approx}80% quantum efficiency, 57% fill factor, and 0.36 eV open-circuit voltage. The device performance degrades with decreasing bandgap (i.e., increasing lattice mismatch). We model the four-junction device efficiency vs. fourth junction bandgap to show that an 0.7-eV fourth-junction bandgap, while optimal if it could be achieved in practice, is not necessary; an 0.9-eV bandgap would still permit significant gains in multijunction cell efficiency while being easier to achieve than the lower-bandgap junction.
Date: May 1, 2006
Creator: Friedman, D. J.; Geisz, J. F.; Norman, A. G.; Wanlass, M. W. & Kurtz, S. R.
Partner: UNT Libraries Government Documents Department
open access

1,2- Hydroxypyridonates as Contrast Agents for Magnetic ResonanceImaging: TREN-1,2-HOPO

Description: 1,2-Hydroxypyridinones (1,2-HOPO) form very stable lanthanide complexes that may be useful as contrast agents for Magnetic Resonance Imaging (MRI). X-ray diffraction of single crystals established that the solid state structures of the Eu(III) and the previously reported [Inorg. Chem. 2004, 43, 5452] Gd(III) complex are identical. The recently discovered sensitizing properties of 1,2-HOPO chelates for Eu(III) luminescence allow direct measurement of the number if water molecules in the metal complex. Fluorescence measurements of the Eu(III) complex corroborate that in solution two water molecules coordinate the lanthanide (q = 2) as proposed from the analysis of NMRD profiles. In addition, fluorescence measurements have verified the anion binding interactions of lanthanide TREN-1,2-HOPO complexes in solution, studied by relaxivity, revealing only very weak oxalate binding (K{sub A} = 82.7 {+-} 6.5 M{sup -1}). Solution thermodynamic studies of the metal complex and free ligand have been carried out using potentiometry, spectrophotometry and fluorescence spectroscopy. The metal ion selectivity of TREN-1,2-HOPO supports the feasibility of using 1,2-HOPO ligands for selective lanthanide binding [pGd = 19.3 (2); pZn = 15.2 (2), pCa = 8.8 (3)].
Date: May 8, 2007
Creator: Jocher, Christoph J.; Moore, Evan G.; Xu, Jide; Avedano, Stefano; Botta, Mauro; Aime, Silvio et al.
Partner: UNT Libraries Government Documents Department
open access

A 1.5 GeV compact light source with superconducting bending magnets

Description: This paper describes the design of a compact electron synchrotron light source for producing X-rays for medical imaging, protein crystallography, nano-machining and other uses up to 35 keV. The source will provide synchrotron light from six 6.9 tesla superconducting 60{degree} bending magnet stations. In addition the ring, contains conventional quadrupoles and sextupoles. The light source has a circumference of 26 meters, which permits it to be located in a variety of industrial and medical facilities.
Date: May 1995
Creator: Garren, A. A.; Cline, D. B.; Kolonko, J. J.; Green, M. A.; Johnson, D. E.; Leung, E. M. et al.
Partner: UNT Libraries Government Documents Department
open access

A 1.8 Mev K+ injector for the high current beam transport experiment fusion

Description: For the High Current Beam Transport Experiment (HCX) at LBNL, an injector is required to deliver up to 1.8 MV of 0.6 A K{sup +} beam with an emittance of {approx}1 p-mm-mrad. We have successfully operated a 10-cm diameter surface ionization source together with an electrostatic quadrupole (ESQ) accelerator to meet these requirements. The pulse length is {approx}4 {micro}s, firing at once every 10-15 seconds. By optimizing the extraction diode and the ESQ voltages, we have obtained an output beam with good current density uniformity, except for a small increase near the beam edge. Characterization of the beam emerging from the injector included measurements of the intensity profile, beam imaging, and transverse phase space. These data along with comparison to computer simulations provide the knowledge base for designing and understanding future HCX experiments.
Date: May 20, 2002
Creator: Kwan, J. W.; Bieniosek, F. M.; Henestroza, E.; Prost, L. & Seidl, P.
Partner: UNT Libraries Government Documents Department
open access

1 GeV CW nonscaling FFAG for ADS, and magnet parameters

Description: Multi-MW proton driver capability remains a challenging, critical technology for many core HEP programs, particularly the neutrino ones such as the Muon Collider and Neutrino factory, and for high-profile energy applications such as Accelerator Driven Subcritical Reactors (ADS) and Accelerator Transmutation of Waste for nuclear power and waste management. Work is focused almost exclusively on an SRF linac, as, to date, no re-circulating accelerator can attain the 10-20 MW capability necessary for the nuclear applications. Recently, the concept of isochronous orbits has been explored and developed for nonscaling FFAGs using powerful new methodologies in FFAG accelerator design. Work is progressing on a stable, high-intensity, 1 GeV isochronous FFAG. Initial specifications of novel magnets with the nonlinear radial fields required to support isochronous operation are also reported here.
Date: May 20, 2012
Creator: Johnstone, C.; Meot, F.; Snopok, P. & Weng, W.
Partner: UNT Libraries Government Documents Department
open access

1-MeV-Electron Irradiation of GaInAsN Cells: Preprint

Description: This conference paper describes the GaInAsN cells that are measured to retain 933% and 894% of their original efficiency after exposure to 5 X 1014 and 1 X 1015 cm-2 1-MeV electrons, respectively. The rate of degradation is not correlated with the performance at beginning of life (BOL). The depletion width remains essentially unchanged, increasing by< 1%. Temperature-coefficient data for GaInAsN cells are also presented. These numbers are used to project the efficiency of GaInAsN-containing multijunction cells. The GaInAsN junction is not currently predicted to increase the efficiencies of the multijunction cells. Nevertheless, GaInAsN-containing multijunction cell efficiencies are predicted to be comparable to those of the conventional structures, and even small improvements in the GaInAsN cell may lead to higher multijunction cell efficiencies, especially for high-radiation applications and when cell operating temperature is low.
Date: May 1, 2002
Creator: Kurtz, Sarah; King, R. R.; Edmondson, K. M.; Friedman, D. J. & Karam, N. H.
Partner: UNT Libraries Government Documents Department
open access

1 mil gold bond wire study.

Description: In microcircuit fabrication, the diameter and length of a bond wire have been shown to both affect the current versus fusing time ratio of a bond wire as well as the gap length of the fused wire. This study investigated the impact of current level on the time-to-open and gap length of 1 mil by 60 mil gold bond wires. During the experiments, constant current was provided for a control set of bond wires for 250ms, 410ms and until the wire fused; non-destructively pull-tested wires for 250ms; and notched wires. The key findings were that as the current increases, the gap length increases and 73% of the bond wires will fuse at 1.8A, and 100% of the wires fuse at 1.9A within 60ms. Due to the limited scope of experiments and limited data analyzed, further investigation is encouraged to confirm these observations.
Date: May 1, 2013
Creator: Huff, Johnathon; McLean, Michael B.; Jenkins, Mark W. & Rutherford, Brian Milne
Partner: UNT Libraries Government Documents Department
open access

A 2--4 nm Linac Coherent Light Source (LCLS) using the SLAC linac

Description: We describe the use of the SLAC linac to drive a unique, powerful. short wavelength Linac Coherent Light Source (LCLS). Operating as an FEL, lasing would be achieved in a single pass of a high peak current electron beam through a long undulator by self-amplified spontaneous emission (SASE). The main components are a high-brightness rf photocathode electron gun; pulse compressors; about 1/5 of the SLAC linac; and a long undulator with a FODO quadrupole focussing system. Using electrons below 8 GeV, the system would operate at wavelengths down to about 3 nm, producing {ge}10 GW peak power in sub-ps pulses. At a 120 Hz rate the average power is {approx} 1 W.
Date: May 1, 1993
Creator: Winick, H.; Bane, K. & Boyce, R.
Partner: UNT Libraries Government Documents Department
open access

2.5 MHz feedforward beam loading compensation in the Fermilab Main Injector

Description: There are five 2.5 MHz ferrite cavities (h = 28) in the Main Injector with an R/Q of 500 that are presently used for coalescing for the Tevatron. For use with the Fermilab Recycler, feedforward (FF) beam loading compensation (BLC) is required on these cavities because they will be required to operate at a net of 2 kV. Under current Recycler beam conditions, the beam-induced voltage is of this order. Recently a system using a digital bucket delay module operating at 53 MHz (h = 588) was used to produce a one-turn-delay feedforward signal. This signal was then combined with the low level RF signal to the 2.5 MHz cavities to cancel the beam induced voltage. During current operation they have shown consistently to operate with over a 20 dB reduction in beam loading.
Date: May 19, 2003
Creator: Dey, Joseph E.; Kourbanis, Ioanis & Steimel, James
Partner: UNT Libraries Government Documents Department
open access

2-D Simulations of Drainage Winds and Diffusion Compared to Observations

Description: A vertically integrated dynamical drainage flow model is developed from conservation equations for momentum and mass in a terrain-following coordinate system. Wind fields from the dynamical model drive a Monte Carlo transport and diffusion model. The model needs only topographic data, an Eulerian or Lagrangian time scale and a surface drag coefficient for input data, and can be started with a motionless atmosphere. Model wind and diffusion predictions are compared to observations from the rugged Geysers CA area. Model winds generally agree with observed surface winds, and in some cases may give better estimates of area-averaged flow than point observations. Tracer gas concentration contours agree qualitatively with observed contours, and point predictions of maximum concentrations were correctly predicted to within factors of 2 to 10. Standard statistical tests of model skill showed that the accuracy of the predictions varied significantly from canyon to canyon in the Geysers are a. Model wind predictions are also compared to observations from the Savannah River Plant of SC which has gently rolling terrain. The model correctly simulated the slower development of drainage winds and slower deepening of the drainage layer in the Savannah River Valley, relative to the Geysers CA simulations. The SC simulations and observations suggest that drainage winds are more frequent in the southeast United States than is generally recognized. They may be responsible for some of the errors in air pollution concentration predictions made by Gaussian models which assume homogeneous winds and turbulence.
Date: May 29, 2001
Creator: Garrett, A. J.
Partner: UNT Libraries Government Documents Department
open access

A 2-Liter, 2000 MPa Air Source for the Radiatively Driven Hypersonic Wind Tunnel

Description: The A2 LITE is a 2 liter, 2000 MPa, 750 K ultra-high pressure (UHP) vessel used to demonstrate UHP technology and to provide an air flow for wind tunnel nozzle development. It is the largest volume UHP vessel in the world. The design is based on a 100:1 pressure intensification using a hydraulic ram as a low pressure driver and a three-layer compound cylinder UHP section. Active control of the 900 mm piston stroke in the 63.5 mm bore permits pressure-time profiles ranging from static to constant pressure during flow through a 1 mm throat diameter nozzle for 1 second.
Date: May 30, 2002
Creator: Costantino, M & Lofftus, D
Partner: UNT Libraries Government Documents Department
open access

2 {times} 2 TeV {mu}{sup +}{mu}{sup {minus}} collider: Lattice and accelerator-detector interface study

Description: The design for a high-luminosity {mu}{sup +}{mu}{sup {minus}} superconducting storage ring is presented based on first-pass calculations. Special attention is paid to two Iowa interaction regions (IR) whose optics are literally interlaced with the collider detectors. Various sources of backgrounds in IR are explored via realistic Monte Carlo simulations. An improved design of the collider lattice in the neighborhood of the interaction points (EP) is determined by the need to reduce significantly background levels in the detectors.
Date: May 1, 1995
Creator: Gelfand, N. M. & Mokhov, N. V.
Partner: UNT Libraries Government Documents Department
open access

3,2-HOPO Complexes of Near-Infra-Red (NIR) Emitting Lanthanides: Sensitization of Ho(III) and Pr(III) in Aqueous Solution

Description: There is a growing interest in Near Infra-Red (NIR) emission originating from organic complexes of Ln{sup III} cations. As a major impetus, biological tissues are considerably more transparent at these low energy wavelengths when compared to visible radiation, which facilitates deeper penetration of incident and emitted light. Furthermore, the long luminescence lifetimes of Ln{sup III} complexes (eg. Yb{sup III}, {tau}{sub rad} {approx} 1 ms) when compared to typical organic molecules can be utilized to vastly improve signal to noise ratios by employing time-gating techniques. While the improved quantum yield of Yb{sub III} complexes when compared to other NIR emitters favors their use for bioimaging applications, there has also been significant interest in the sensitized emission from other 4f metals such as Ln = Nd, Ho, Pr and Er which have well recognized applications as solid state laser materials (eg. Nd {approx} 1.06 {micro}m, Ho {approx} 2.09 {micro}m), and in telecommunications (eg. Er {approx} 1.54 {micro}m) where they can be used for amplification of optical signals. As a result of their weak (Laporte forbidden) f-f absorptions, the direct excitation of Ln{sup III} cations is inefficient, and sensitization of the metal emission is more effectively achieved using the so-called antenna effect. We have previously examined the properties of several Eu{sup III} complexes which feature 1-hydroxypyridin-2-one (Fig. 1) as the light harvesting chromophore. While the 1,2-HOPO isomer was found to strongly sensitize Eu{sup III}, we noted the analogous Me-3,2-HOPO isomer does not, which prompted further investigation of the properties of this chromophore with other metals.
Date: May 19, 2008
Creator: Moore, Evan G.; Szigethy, Geza; Xu, Jide; Palsson, Lars-Olof; Beeby, Andrew & Raymond, Kenneth N.
Partner: UNT Libraries Government Documents Department
open access

3-D full waveform inversion of seismic data; Part I. Theory

Description: Full waveform inversion of seismic data is a challenging subject partly because of the lack of precise knowledge of the source. Since currently available approaches involve some form of approximations to the source, inversion results are subject to the quality and the choice of the source information used. A new full waveform inversion scheme has been introduced (Lee and Kim, 2003) using normalized wavefield for simple two-dimensional (2-D) scalar problems. The method does not require source information, so potential inversion errors due to source estimation may be eliminated. A gather of seismic traces is first Fourier-transformed into the frequency domain and a normalized wavefield is obtained for each trace in the frequency domain. Normalization is done with respect to the frequency response of a reference trace selected from the gather, so the complex-valued normalized wavefield is source-independent and dimensionless. The inversion algorithm minimizes misfits between measured normalized wavefield and numerically computed normalized wavefield. In this paper the full waveform inversion is extended to three-dimensional (3-D) problems.
Date: May 12, 2003
Creator: Lee, Ki Ha
Partner: UNT Libraries Government Documents Department
open access

3-D Ray-tracing and 2-D Fokker-Planck Simulations of Radiofrequency Application to Tokamak Plasmas

Description: A state of the art numerical tool has been developed to simulate the propagation and the absorption of coexisting different types of waves in a tokamak geometry. The code includes a numerical solution of the three-dimensional (R, Z, {Phi}) toroidal wave equation for the electric field of the different waves in the WKBJ approximation. At each step of integration, the two-dimensional (v{sub {parallel}}, v{sub {perpendicular}}) Fokker-Planck equation is solved in the presence of quasilinear diffusion coefficients. The electron Landau damping of the waves is modeled taking into account the interaction of the wave electric fields with the quasilinearly modified distribution function. Consistently, the code calculates the radial profiles of non-inductively generated current densities, the transmitted power traces and the total power damping curves. Synergistic effects among the different type of waves (e.g., lower hybrid and ion Bernstein waves) are studied through the separation of the contributions of the single wave from the effects due to their coexistence.
Date: May 1, 1999
Creator: Cardinali, A.; Paoletti, F. & Bernabei, S.
Partner: UNT Libraries Government Documents Department
open access

3-D treatment of convective flow in the earth's mantle

Description: A three-dimensional finite-element method is used to investigate thermal convection in the earth's mantle. The equations of motion are solved implicitly by means of a fast multigrid technique. The computational mesh for the spherical problem is derived from the regular icosahedron. The calculation described use a mesh with 43,554 nodes and 81,920 elements and were run on a Cray X. The earth's mantle is modeled as a thick spherical shell with isothermal, free-slip boundaries. The infinite Prandtl number problem is formulated in terms of pressure, density, absolute temperature, and velocity and assumes an isotropic Newtonian rheology. Solutions are obtained for Rayleigh numbers up to approximately 10/sup 6/ for a variety of modes of heating. Cases initialized with a temperature distribution with warmer temperatures beneath speading ridges and cooler temperatures beneath present subduction zones yield whole-mantle convection solutions with surface velocities that correlate well with currently observed plate velocities. 8 references, 6 figures.
Date: May 1, 1984
Creator: Baumgardner, J.R.
Partner: UNT Libraries Government Documents Department
open access

A 3 TeV Muon Collider Lattice Design

Description: A new lattice for 3 TeV c.o.m. energy with {beta}* = 5mm was developed which follows the basic concept of the earlier 1.5 TeV design but uses quad triplets for the final focus in order to keep the maximum magnet strength and aperture close to those in 1.5 TeV case. Another difference is employment of combined-function magnets with the goal to lower heat deposition in magnet cold mass and to eliminate bending field free regions which produce 'hot spots' of neutrino radiation that can be an issue at higher energy. The proposed lattice is shown to satisfy the requirements on luminosity, dynamic aperture and momentum acceptance.
Date: May 1, 2012
Creator: Alexahin, Y. & Gianfelice-Wendt, E.
Partner: UNT Libraries Government Documents Department
open access

4. pi. data of relativistic nuclear collisions. [Plastic ball]

Description: During the past two years, complete events of relativistic nuclear collisions are being studied with the Plastic Ball, the first electronic nonmagnetic particle-identifying 4..pi.. spectrometer. It is well suited to handle the large multiplicities in these reactions and allows collection of data at a rate sufficient to make further software selections to look at rare events. The analysis of the data follows various lines covering topics like thermalization, stopping or transparency, cluster-production mechanism (--can it tell entropy), search for collective flow through various global analyzing methods that allow determination of the scattering plane, projectile fragmentation (--is there a bounce-off), pion distribution, two-particle correlations: Hanbury-Brown Twiss, and excited nuclear states (--nucleosynthesis at the freezeout point or from chemical equilibrium). We will cover in this contribution only two subjects: stopping and thermalization and cluster production.
Date: May 1, 1983
Creator: Gutbrod, H.H.; Gustafsson, H.A. & Kolb, B.
Partner: UNT Libraries Government Documents Department
open access

5 K neutron irradiation and thermal cycling of NbTi superconductors

Description: Simulation experiments of magnet operating conditions in a fusion reactor are reported. After approximately half of the lifetime dose the results on a variety of NbTi superconductors show moderate changes of the critical current density j/sub c/ (approx. 10%), the percentage change of j/sub c/ is always larger at high fields (8 T) than at 5 T. After a rapid initial change the resistivity ratios of the Cu-stabilizer are found to decrease only slowly with increasing neutron fluence.
Date: May 1, 1984
Creator: Hahn, P.; Hoch, H.; Weber, H. W.; Birtcher, R. C. & Brown, B. S.
Partner: UNT Libraries Government Documents Department
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