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Charge injection into small semiconductor particles

Description: We report on the effect of the injection of electrons into small CdS particles on their spectroscopy. Solvated electrons were generated pulse radiolytically and their reaction with the particles was monitored. As a result of the excess charge, the absorption by the particle in the exciton region is bleached. The bleaching tacks the shift in band edge as the particle size decreases. However, excess electrons in larger particles are more efficient tan in small particles. It is concluded that the effort originates in the electric field effect generated by the excess charge.
Date: June 1, 1995
Creator: Lawless, D.; Luangdilok, C.; Cook, A.R. & Meisel, D.
Partner: UNT Libraries Government Documents Department
open access

Damping of Dislocation Motion by Conduction Electrons in Metals.

Description: The rate of energy absorption from a moving dislocation by conduction electrons is recalculated using the semiclassical Boltzman transport equation and the model of a free electron gas. Temperature-independent values of the electronic damping coefficients for edge and screw dislations are found in similar magnitudes. The results are compared to previous work by Kravchenko and Brailsford.
Date: October 31, 1972
Creator: Jassby, .K .M & Shull, M.
Partner: UNT Libraries Government Documents Department
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Experimental Research on the Laser Cyclotron Auto-Resonance Accelerator “LACARA”

Description: The Laser Cyclotron Auto-Resonant Accelerator LACARA has successfully operated this year. Results are summarized, an interpretation of operating data is provided in the body of the report, and recommendations are made how the experiment should be carried forward. The Appendix A contains a description of the LACARA apparatus, currently installed at the Accelerator Test Facility, Brookhaven National Laboratory. This report summarizes the project, extending over three grant-years.
Date: November 11, 2008
Creator: Marshall, T C
Partner: UNT Libraries Government Documents Department
open access

Isomorphic classical molecular dynamics model for an excess electronin a supercritical fluid

Description: Ring polymer molecular dynamics (RPMD) is used to directly simulate the dynamics of an excess electron in a supercritical fluid over a broad range of densities. The accuracy of the RPMD model is tested against numerically exact path integral statistics through the use of analytical continuation techniques. At low fluid densities, the RPMD model substantially underestimates the contribution of delocalized states to the dynamics of the excess electron. However, with increasing solvent density, the RPMD model improves, nearly satisfying analytical continuation constraints at densities approaching those of typical liquids. In the high density regime, quantum dispersion substantially decreases the self-diffusion of the solvated electron. In this regime where the dynamics of the electron is strongly coupled to the dynamics of the atoms in the fluid, trajectories that can reveal diffusive motion of the electron are long in comparison to {beta}{h_bar}.
Date: August 4, 2008
Creator: Miller III, Thomas F.
Partner: UNT Libraries Government Documents Department
open access

Model for l/f Flux Noise in SQUIDs and Qubits

Description: We propose a model for 1/f flux noise in superconducting devices (f is frequency). The noise is generated by the magnetic moments of electrons in defect states which they occupy for a wide distribution of times before escaping. A trapped electron occupies one of the two Kramers-degenerate ground states, between which the transition rate is negligible at low temperature. As a result, the magnetic moment orientation is locked. Simulations of the noise produced by a plausible density of randomly oriented defects yield 1/f noise magnitudes in good agreement with experiments.
Date: January 19, 2007
Creator: Koch, Roger H.; DiVincenzo, David P. & Clarke, John
Partner: UNT Libraries Government Documents Department
open access

Electron Cloud Generation And Trapping in a Quadrupole Magnet at the Los Alamos PSR

Description: A diagnostic to measure electron cloud formation and trapping in a quadrupole magnet has been developed, installed, and successfully tested at PSR. Beam studies with this diagnostic show that the electron flux striking the wall in the quadrupole is comparable to or larger than in an adjacent drift. In addition, the trapped electron signal, obtained using the sweeping feature of diagnostic, was larger than expected and decayed very slowly with an exponential time constant of 50 to 100 {micro}s. Experimental results were also obtained which suggest that a significant fraction of the electrons observed in the adjacent drift space were seeded by electrons ejected from the quadrupole.
Date: November 14, 2007
Creator: Macek, R.J.; Browman, A.A.; Ledford, J.E.; /TechSource, Santa Fe /Los Alamos; Borden, M.J.; O'Hara, J.F. et al.
Partner: UNT Libraries Government Documents Department
open access

Efficient multi-exciton emission from quantum dots.

Description: The fundamental spontaneous emission rate an emitter can be modified by its photonic environment. By enhancing the spontaneous emission rate, there is a possibility of extracting multi-exciton energies through radiative decay. In this report, we explore using high Q and small volume cavities to enhance the spontaneous emission rate. We observed greater than 50 folds enhancement in the spontaneous emission from photonic crystal waveguide or microcavity using close-packed monolayer of PbS quantum dot emitters.
Date: September 1, 2010
Creator: Luk, Ting Shan
Partner: UNT Libraries Government Documents Department
open access

Injection Into Electron Plasma Traps

Description: Computational studies and experimental measurements of plasma injection into a Malmberg-Penning trap reveal that the number of trapped particles can be an order of magnitude higher than predicted by a simple estimates based on a ballistic trapping model. Enhanced trapping is associated with a rich nonlinear dynamics generated by the space-charge forces of the evolving trapped electron density. A particle-in-cell simulation is used to identify the physical mechanisms that lead to the increase in trapped electrons. The simulations initially show strong two-stream interactions between the electrons emitted from the cathode and those reflected off the end plug of the trap. This is followed by virtual cathode oscillations near the injection region. As electrons are trapped, the initially hollow longitudinal phase-space is filled, and the transverse radial density profile evolves so that the plasma potential matches that of the cathode. Simple theoretical arguments are given that describe the different dynamical regimes. Good agreement is found between simulation and theory.
Date: December 2, 2003
Creator: Gorgadze, Vladimir; Pasquini, Thomas A.; Fajans, Joel & Wurtele, Jonathan S.
Partner: UNT Libraries Government Documents Department
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Hydromagnetic Instabilities Caused by Runaway Electrons

Description: "The possibility of the excitation of hydromagnetic instabilities caused by a beam of runaway electronics is investigated. It is found that if the wave length and frequency of the wave are such that the Doppler shift of the frequency due to the runaways' motion causes the electrons to see their cyclotron frequency, and if the electric field rotates in the same direction as the electrons do about the confining magnetic field, then an instability occurs."
Date: 1958
Creator: Dawson, J. M. & Bernstein, Ira B.
Partner: UNT Libraries Government Documents Department
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Tables of Electron Radial Functions and Tangents of Phase Shifts for Light Nuclei (Z=1 through 10)

Description: From Introduction: "This Monograph, supplemented by ORNL-3207 [9], should eliminate completely the need for use of approximate formulas (e.g. those of Kotani and Ross [10]). The formulation of the problem has been summarized in sec. II. This is followed in sec. III by a discussion of the methods used in numerical calculations. Sec. IV contains a detailed explanation to facilitate the use of present tables."
Date: August 6, 1964
Creator: Bhalla, C. P.
Partner: UNT Libraries Government Documents Department
open access

Cyclooctatetraenes Tetrakis-Annelated with α-Dithio- or α-Diselenocarbonyl Groups: Diradicals Predicted To Have Ground States with 10 π Electrons in the Eight-Membered Ring and Two-Center, Three-Electron, σ Bonds between Two Pairs of Chalcogen Atoms

Description: Article on cyclooctatetraenes tetrakis-annelated with α-dithio- or α-diselenocarbonyl groups.
Date: February 12, 2010
Creator: Zhou, Xin; Hrovat, David A. & Borden, Weston T.
Partner: UNT College of Arts and Sciences
open access

Emittance and Current of Electrons Trapped in a Plasma Wakefield Accelerator

Description: In recent experiments plasma electrons became trapped in a plasma wakefield accelerator (PWFA). The transverse size of these trapped electrons on a downstream diagnostic yields an upper limit measurement of transverse normalized emittance divided by peak current, {var_epsilon}{sub N,x}/I. The lowest upper limit for {var_epsilon}{sub N,x}/I measured in the experiment is 1.3 {center_dot} 10{sup -10} m/A.
Date: September 24, 2008
Creator: Kirby, N.; Blumenfeld, I.; Clayton, C. E.; Decker, F. J.; Hogan, M. J.; Huang, C. et al.
Partner: UNT Libraries Government Documents Department
open access

Mechanisms of the Bystander Effect

Description: Generations of students in radiation biology have been taught that heritable biological damage requires direct damage to DNA. We now know that this is not true. The Bystander Effect is the name given to the phenomenon whereby biological effects are observed in cells that are not themselves traversed by a charged particle, but are in close proximity to cells that are. Several research groups have convincingly demonstrated a bystander effect for alpha particle, which are heavy and high LET, because charged particles can be focused into a tiny beam that can be directed onto individual cells. The biological effects seen in adjacent non-hit cells clearly represents a bystander effect. It is not so easy to demonstrate a similar effect for x-rays or for the electrons set in motion by the absorption of x-rays. In this project we used two types of cell that could be recognized one from the other. One cell type was fed radioactive tritiated thymidine, which is incorporated into the DNA, . The tritium emits electrons which have a very short range so that they do not even get out of the cell. These cells were then mixed with a different type of cell which are routinely used to assess mutations. The mixed cells formed a cluster, where the two types of cells were in close contact, and left for some hours. Subsequently, the two types of cells were separated and studied. A substantial fraction of the cells that had incorporated the tritiated thymidine were killed by the radiation. The interesting finding is that the cells that had not incorporated tritiated thymidine, but had been in close contact with cells that had, exhibited a significant incidence of mutations. These experiments clearly demonstrated a bystander effect for low LET electrons. In further experiments, it was possible to show …
Date: July 15, 2008
Creator: Hall, Eric J.
Partner: UNT Libraries Government Documents Department
open access

Beat wave injection of electrons into plasma waves using two interfering laser pulses

Description: An electron injector concept that uses a single injection laser pulse colliding with a pump laser pulse in a plasma is analyzed. The pump pulse generates a large amplitude laser wakefield (plasma wave). The counter propagating injection pulse collides with the pump laser pulse to generate a beat wave with a slow phase velocity. The ponderomotive force of the slow beat wave is responsible for injecting plasma electrons into the wakefield near the back of the pump pulse. Test particle simulations indicate that significant amounts of charge can be trapped and accelerated ({approx} 10 pC). For higher charge, beam loading limits the validity of the simulations. The accelerated bunches are ultrashort ({approx} 1 fs) with good beam quality (relative energy spread of a few percent at a mean energy of {approx} 10 MeV and a normalized rms emittance on the order 0.4 mm.mrad). The effects of interaction angle and polarization are also explored, e.g., efficient trapping can occur for near-collinear geometries. Beat wave injection using a single injection pulse has the advantages of simplicity, ease of experimental implementation, and requires modest laser intensity I {approx_equal} 8.8 x 10{sup 17} W/cm{sup 2}.
Date: March 4, 2004
Creator: Fubiani, G.; Esarey, E.; Schroeder, C. B. & Leemans, W. P.
Partner: UNT Libraries Government Documents Department
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