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19,014 Matching Results
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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
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.
Object Type:
Article
System:
The UNT Digital Library
The 0.22 Percent Across-the-Board Cut in FY2001 Appropriations
Report describing changes that affected the government budget for the 2001 fiscal year under the Consolidated Appropriations Act.
Date:
May 31, 2001
Creator:
Keith, Robert
Object Type:
Report
System:
The UNT Digital Library
1,2- Hydroxypyridonates as Contrast Agents for Magnetic ResonanceImaging: TREN-1,2-HOPO
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.
Object Type:
Article
System:
The UNT Digital Library
A 1.8 Mev K+ injector for the high current beam transport experiment fusion
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.
Object Type:
Article
System:
The UNT Digital Library
1-MeV-Electron Irradiation of GaInAsN Cells: Preprint
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.
Object Type:
Article
System:
The UNT Digital Library
2.5 MHz feedforward beam loading compensation in the Fermilab Main Injector
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
Object Type:
Article
System:
The UNT Digital Library
2-D Simulations of Drainage Winds and Diffusion Compared to Observations
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 …
Date:
May 29, 2001
Creator:
Garrett, A. J.
Object Type:
Article
System:
The UNT Digital Library
A 2-Liter, 2000 MPa Air Source for the Radiatively Driven Hypersonic Wind Tunnel
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
Object Type:
Article
System:
The UNT Digital Library
3,2-HOPO Complexes of Near-Infra-Red (NIR) Emitting Lanthanides: Sensitization of Ho(III) and Pr(III) in Aqueous Solution
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 …
Date:
May 19, 2008
Creator:
Moore, Evan G.; Szigethy, Geza; Xu, Jide; Palsson, Lars-Olof; Beeby, Andrew & Raymond, Kenneth N.
Object Type:
Article
System:
The UNT Digital Library
3-Center-4-Electron Bonding in [(silox)2Mo=NtBu]2(μ-Hg) Controls Reactivity while Frontier Orbitals Permit a Dimolybdenum π-Bond Energy Estimate
Article describing research on 3-center-4-electron bonding in [(silox)2Mo=NtBu]2(mu-Hg).
Date:
May 18, 2005
Creator:
Rosenfeld, Devon C.; Wolczanski, Peter T.; Barakat, Khaldoon A.; Buda, Corneliu & Cundari, Thomas R., 1964-
Object Type:
Article
System:
The UNT Digital Library
3-D full waveform inversion of seismic data; Part I. Theory
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
Object Type:
Article
System:
The UNT Digital Library
''6-Degrees of Freedom'' Single Crystal Plasticity Experiments
A deformation experiment has been developed specifically for the purpose of validation of dislocation dynamics simulations of plastic flow up to strains on the order of 1% [1]. The experiment has been designed so that a compressive uniaxial stress field is essentially super imposed on the test sample, and the crystal is free to deform with 3 orthogonal translation directions, and 3 rotation/tilt axes of freedom and has been given the name ''6-degrees of freedom'' (6DOF) experiment. The rotation, tilt and translation of the crystal are monitored by 5 laser displacement gages and 3 extensometers. Experiments are being performed on high purity Mo single crystals orientated for ''single slip''. All of the experiments are performed in pairs, with one test sample having highly polished surfaces for optical light and AFM slip-trace analyses, and the other having 4 strain gage rosettes mounted on the sides for measurement of the bi-axial surface strains during testing. All of the experimental data is used together to determine the slip activity of the orientated single crystal during deformation. Experimental results on high-purity Mo single crystals are presented. The results of these experiments show that slip behavior is in substantial deviation from the expected ''Schmid'' behavior. …
Date:
May 21, 2003
Creator:
Lassila, D. H.; Florando, J. N.; LeBlanc, M. M.; Arsenlis, T. & Rhee, M.
Object Type:
Article
System:
The UNT Digital Library
8 GeV H- ions: Transport and injection
Fermilab is working on the design of an 8 GeV superconducting RF H{sup -} linac called the Proton Driver. The energy of H{sup -} beam will be an order of magnitude higher than the existing ones. This brings up a number of technical challenges to transport and injection of H{sup -} ions. This paper will focus on the subjects of stripping losses (including stripping by blackbody radiation, field and residual gas) and carbon foil stripping efficiency, along with a brief discussion on other issues such as Stark states lifetime of hydrogen atoms, single and multiple Coulomb scattering, foil heating and stress, radiation activation, collimation and jitter correction, etc.
Date:
May 1, 2005
Creator:
Chou, W.; Bryant, H.; Drozhdin, A.; Hill, C.; Kostin, M.; Macek, R. et al.
Object Type:
Article
System:
The UNT Digital Library
An 8-Step Program: Shaping and Fixed-Time Food Delivery Effects on Several Approximations and Undesired Responses in Goats.
This study investigated the effects of a shaping program for halter training across 8 steps in the program and 4 trial-terminating, or "undesirable," responses. Three La Mancha goats (Capra hircus) located at the Frank Buck Zoo in Gainesville, Texas were used for the study. A fixed-time 15 s (FT-15 s) was used during the baseline conditions, to examine the effects of response contingent and response-independent food deliveries, as well as to examine what preliminary steps might not necessarily have to be shaped. All 3 goats successfully learned to allow the halter to be placed on them and to lead on the halter, although 2 of the 3 goats required an additional task analysis for the fifth step to further break down that approximation. Several of the early steps selected by the researchers were not necessary to complete the program, as determined by the baseline condition.
Date:
May 2003
Creator:
Fernandez, Eduardo J.
Object Type:
Thesis or Dissertation
System:
The UNT Digital Library
9-11 Commission Hearing #2, May 22, 2003, Part 1
Recording of the second public hearing held by the National Commission on Terrorist Attacks Upon the United States on May 22, 2003 at the Hart Senate Office Building in Washington, D.C. This hearing addresses four topics, which include the commission mandate and objectives, intelligence oversight and the joint inquiry, affected constituencies, and the state of civil aviation security on September 11th. This section includes the first panel on the commission mandate and objectives, with testimony from Congresswoman Nancy Pelosi, Senator John McCain, and Senator Joseph Lieberman.
Date:
May 22, 2003
Creator:
National Commission on Terrorist Attacks upon the United States
Object Type:
Video
System:
The UNT Digital Library
9-11 Commission Hearing #2, May 22, 2003, Part 2
Recording of the second public hearing held by the National Commission on Terrorist Attacks upon the United States on May 22, 2003 at the Hart Office Senate Building in Washington, D.C. This hearing addresses four topics, which include the commission mandate and objectives, intelligence oversight and the joint inquiry, affected constituencies, and the state of civil aviation security on September 11th. This section includes the second panel on intelligence oversight and the joint inquiry with testimony from Senators Bob Graham and Richard Shelby and Representatives Porter Goss and Jane Harman.
Date:
May 22, 2003
Creator:
National Commission on Terrorist Attacks upon the United States
Object Type:
Video
System:
The UNT Digital Library
9-11 Commission Hearing #2, May 22, 2003, Part 3
Recording of the second public hearing held by the National Commission on Terrorist Attacks upon the United States on May 22, 2003 at the Hart Senate Office Building in Washington, D.C. This hearing addresses four topics, which include the commission mandate and objectives, intelligence oversight and the joint inquiry, affected constituencies, and the state of civil aviation security on September 11th. This section contains the third panel on affected constituencies with testimony from Senators Schumer, Clinton, Corzine and Lautenberg, and Representatives Nadler, Shays, and Smith.
Date:
May 22, 2003
Creator:
National Commission on Terrorist Attacks upon the United States
Object Type:
Video
System:
The UNT Digital Library
9-11 Commission Hearing #2, May 22, 2003, Part # 4
Recording of the second public hearing held by the National Commission on Terrorist Attacks upon the United States on May 22, 2003 at the Hart Senate Office Building in Washington, D.C. This hearing addresses four topics, which include the commission mandate and objectives, intelligence oversight and the joint inquiry, affected constituencies, and the state of civil aviation security on September 11th. This section includes the panel on civil aviation security with testimony from representatives of the Federal Aviation Administration, the Department of Transportation, the Air Transport Association of America, and the Transportation Security Agency.
Date:
May 22, 2003
Creator:
National Commission on Terrorist Attacks upon the United States
Object Type:
Video
System:
The UNT Digital Library
9-11 Commission Hearing #2, May 23, 2003, Part 1
Recording of the second public hearing held by the National Commission on Terrorist Attacks upon the United States on May 23 in Washington, D.C. This hearing addresses four topics, which include the commission mandate and objectives, intelligence oversight and the joint inquiry, affected constituencies, and the state of civil aviation security on September 11th. This section includes the panel on civil aviation security, with testimony from Norman Mineta, Major General Craig McKinley, and Lieutenant General Mike Canavan on the attacks and the response to the 9/11 attacks.
Date:
May 23, 2003
Creator:
National Commission on Terrorist Attacks upon the United States
Object Type:
Video
System:
The UNT Digital Library
9-11 Commission Hearing #2, May 23, 2003, Part 2
Recording of the second public hearing held by the National Commission on Terrorist Attacks upon the United States on May 23, 2003 in Washington, D.C. This hearing addresses four topics, which include the commission mandate and objectives, intelligence oversight and the joint inquiry, affected constituencies, and the state of civil aviation security on September 11th. This section concludes the panel on civil aviation security, with testimony from Stephen McHale, Major General O.K. Steele, and Mary Schiavo on reforming civil aviation security.
Date:
May 23, 2003
Creator:
National Commission on Terrorist Attacks upon the United States
Object Type:
Video
System:
The UNT Digital Library
9-11 Commission Hearing #11, May 18, 2004, Part 1
Recording of the eleventh public hearing held by the National Commission on Terrorist Attacks upon the United States on May 18, 2004 at New School University in New York City. The two-day hearing examined the response of local and federal emergency response departments on September 11, 2001, and considered how to improve these critical functions in the event of future terrorist attacks. Two staff statements were presented during the course of the hearing. This section includes the staff statement on emergency preparedness and response.
Date:
May 18, 2004
Creator:
National Commission on Terrorist Attacks upon the United States
Object Type:
Video
System:
The UNT Digital Library
9-11 Commission Hearing #11, May 18, 2004, Part 2
Recording of the eleventh public hearing held by the National Commission on Terrorist Attacks upon the United States on May 18, 2004 at New School University in New York City. The two-day hearing examined the response of local and federal emergency response departments on September 11, 2001, and considered how to improve these critical functions in the event of future terrorist attacks. Two staff statements were presented during the course of the hearing. This section includes the first panel, with testimony from Alan Reiss and Joseph Morris.
Date:
May 18, 2004
Creator:
National Commission on Terrorist Attacks upon the United States
Object Type:
Video
System:
The UNT Digital Library
9-11 Commission Hearing #11, May 18, 2004, Part 3
Recording of the eleventh public hearing held by the National Commission on Terrorist Attacks upon the United States on May 18, 2004 at New School University in New York City. The two-day hearing examined the response of local and federal emergency response departments on September 11, 2001, and considered how to improve these critical functions in the event of future terrorist attacks. Two staff statements were presented during the course of the hearing. This section includes the second panel with testimony from Bernard B. Kerik, Thomas Von Essen, and Richard Sheirer.
Date:
May 18, 2004
Creator:
National Commission on Terrorist Attacks upon the United States
Object Type:
Video
System:
The UNT Digital Library
9-11 Commission Hearing #11, May 18, 2004, Part 4
Recording of the eleventh public hearing held by the National Commission on Terrorist Attacks upon the United States on May 18, 2004 at New School University in New York City. The two-day hearing examined the response of local and federal emergency response departments on September 11, 2001, and considered how to improve these critical functions in the event of future terrorist attacks. Two staff statements were presented during the course of the hearing.This section includes the beginning of the third panel, with testimony from Raymond W. Kelly.
Date:
May 18, 2004
Creator:
National Commission on Terrorist Attacks upon the United States
Object Type:
Video
System:
The UNT Digital Library