Degree Department

Degree Discipline

Degree Level

44 Matching Results

Results open in a new window/tab.

Simulation of Alpha-Channeling in Mirror Machines (open access)

Simulation of Alpha-Channeling in Mirror Machines

Applying α-channeling techniques to mirror machines can significantly increase their effective reactivity, thus making open configurations more advantageous for practical fusion. A large fraction of α particle energy can be extracted using rf waves. Effects employed to cool α particles can also in principle be used to heat the fusion ions; the possibility to design a configuration of rf waves which could be used to perform both tasks is demonstrated.
Date: March 17, 2008
Creator: A.I. Zhmoginov, N.J. Fisch
Object Type: Report
System: The UNT Digital Library
On Sub-linear Convergence for Linearly Degenerate Waves in Capturing Schemes (open access)

On Sub-linear Convergence for Linearly Degenerate Waves in Capturing Schemes

A common attribute of capturing schemes used to find approximate solutions to the Euler equations is a sub-linear rate of convergence with respect to mesh resolution. Purely nonlinear jumps, such as shock waves produce a first-order convergence rate, but linearly degenerate discontinuous waves, where present, produce sub-linear convergence rates which eventually dominate the global rate of convergence. The classical explanation for this phenomenon investigates the behavior of the exact solution to the numerical method in combination with the finite error terms, often referred to as the modified equation. For a first-order method, the modified equation produces the hyperbolic evolution equation with second-order diffusive terms. In the frame of reference of the traveling wave, the solution of a discontinuous wave consists of a diffusive layer that grows with a rate of t{sup 1/2}, yielding a convergence rate of 1/2. Self-similar heuristics for higher order discretizations produce a growth rate for the layer thickness of {Delta}t{sup 1/(p+1)} which yields an estimate for the convergence rate as p/(p+1) where p is the order of the discretization. In this paper we show that this estimated convergence rate can be derived with greater rigor for both dissipative and dispersive forms of the discrete error. In …
Date: March 17, 2008
Creator: Banks, J W; Aslam, T & Rider, W J
Object Type: Article
System: The UNT Digital Library
The Altus Times (Altus, Okla.), Vol. 109, No. 247, Ed. 1 Monday, March 17, 2008 (open access)

The Altus Times (Altus, Okla.), Vol. 109, No. 247, Ed. 1 Monday, March 17, 2008

Daily newspaper from Altus, Oklahoma that includes local, state, and national news along with advertising.
Date: March 17, 2008
Creator: Bush, Michael
Object Type: Newspaper
System: The Gateway to Oklahoma History
The Baytown Sun (Baytown, Tex.), Vol. 88, No. 77, Ed. 1 Monday, March 17, 2008 (open access)

The Baytown Sun (Baytown, Tex.), Vol. 88, No. 77, Ed. 1 Monday, March 17, 2008

Daily newspaper from Baytown, Texas that includes local, state, and national news along with advertising.
Date: March 17, 2008
Creator: Clements, Clifford E.
Object Type: Newspaper
System: The Portal to Texas History
Constitutionality of Applying the FCC’s Indecency Restriction to Cable Television (open access)

Constitutionality of Applying the FCC’s Indecency Restriction to Cable Television

This report examines whether such as extension would violate the First Amendment's guarantee of freedom of speech.
Date: March 17, 2008
Creator: Cohen, Henry
Object Type: Report
System: The UNT Digital Library
Freedom of Speech and Press: Exceptions to the First Amendment (open access)

Freedom of Speech and Press: Exceptions to the First Amendment

This report provides an overview of the major exceptions to the First Amendment.
Date: March 17, 2008
Creator: Cohen, Henry
Object Type: Report
System: The UNT Digital Library
Liability of Interactive Computer Service for Violating the Fair Housing Act (open access)

Liability of Interactive Computer Service for Violating the Fair Housing Act

None
Date: March 17, 2008
Creator: Cohen, Henry
Object Type: Report
System: The UNT Digital Library
Clean Water Act: A Summary of the Law (open access)

Clean Water Act: A Summary of the Law

This report presents a summary of the law, describing the essence of the statute without discussing its implementation. Other CRS products do discuss implementation, including CRS Report RL33800, Water Quality Issues in the 110th Congress: Oversight and Implementation, and numerous products cited in that report.
Date: March 17, 2008
Creator: Copeland, Claudia
Object Type: Report
System: The UNT Digital Library
General Relativistic Effects in Atom Interferometry (open access)

General Relativistic Effects in Atom Interferometry

Atom interferometry is now reaching sufficient precision to motivate laboratory tests of general relativity. We begin by explaining the non-relativistic calculation of the phase shift in an atom interferometer and deriving its range of validity. From this we develop a method for calculating the phase shift in general relativity. This formalism is then used to find the relativistic effects in an atom interferometer in a weak gravitational field for application to laboratory tests of general relativity. The potentially testable relativistic effects include the non-linear three-graviton coupling, the gravity of kinetic energy, and the falling of light. We propose experiments, one currently under construction, that could provide a test of the principle of equivalence to 1 part in 10{sup 15} (300 times better than the present limit), and general relativity at the 10% level, with many potential future improvements. We also consider applications to other metrics including the Lense-Thirring effect, the expansion of the universe, and preferred frame and location effects.
Date: March 17, 2008
Creator: Dimopoulos, Savas; /Stanford U., Phys. Dept.; Graham, Peter W.; /SLAC /Stanford U., Phys. Dept.; Hogan, Jason M.; Kasevich, Mark A. et al.
Object Type: Article
System: The UNT Digital Library
A CCD Camera with Electron Decelerator for Intermediate Voltage Electron Microscopy (open access)

A CCD Camera with Electron Decelerator for Intermediate Voltage Electron Microscopy

Electron microscopists are increasingly turning to Intermediate Voltage Electron Microscopes (IVEMs) operating at 300 - 400 kV for a wide range of studies. They are also increasingly taking advantage of slow-scan charge coupled device (CCD) cameras, which have become widely used on electron microscopes. Under some conditions CCDs provide an improvement in data quality over photographic film, as well as the many advantages of direct digital readout. However, CCD performance is seriously degraded on IVEMs compared to the more conventional 100 kV microscopes. In order to increase the efficiency and quality of data recording on IVEMs, we have developed a CCD camera system in which the electrons are decelerated to below 100 kV before impacting the camera, resulting in greatly improved performance in both signal quality and resolution compared to other CCDs used in electron microscopy. These improvements will allow high-quality image and diffraction data to be collected directly with the CCD, enabling improvements in data collection for applications including high-resolution electron crystallography, single-particle reconstruction of protein structures, tomographic studies of cell ultrastructure and remote microscope operation. This approach will enable us to use even larger format CCD chips that are being developed with smaller pixels.
Date: March 17, 2008
Creator: Downing, Kenneth H; Downing, Kenneth H. & Mooney, Paul E.
Object Type: Article
System: The UNT Digital Library
China-U.S. Relations: Current Issues and Implications for U.S. Policy (open access)

China-U.S. Relations: Current Issues and Implications for U.S. Policy

This report mainly focuses on Current Issues and Implications for U.S. Policy of China-U.S. Relations.U.S relations with China remarkably smooth from 2001-2004 have shown signs of becoming somewhat more problematic again since 2005 as some U.S policymakers.
Date: March 17, 2008
Creator: Dumbaugh, Kerry
Object Type: Report
System: The UNT Digital Library
Beam Dynamics Studies for the SPARC Project (open access)

Beam Dynamics Studies for the SPARC Project

The aim of the SPARC project, is to promote an R&D activity oriented to the development of a high brightness photoinjector to drive SASE-FEL experiments. We discuss in this paper the status of the beam dynamics simulation activities.
Date: March 17, 2008
Creator: Ferrario, M.; Biagini, Maria E.; Boscolo, M.; Fusco, V.; Guiducci, S.; Migliorati, M. et al.
Object Type: Article
System: The UNT Digital Library
DESIGN OF AN OPTICAL DIFFERACTION RADIATION BEAM SIZE MONITOR AT SLAC FETB (open access)

DESIGN OF AN OPTICAL DIFFERACTION RADIATION BEAM SIZE MONITOR AT SLAC FETB

We design a single bunch transverse beam size monitor which will be tested to measure the 28.5 GeV electron/positron beam at the SLAC FFTB beam line. The beam size monitor uses the CCD images of the interference pattern of the optical diffraction radiation from two slit edges which are placed close to the beam path. In this method, destruction of the accelerated electron/positron beam bunches due to the beam size monitoring is negligible, which is vital to the operation of the Linear Collider project.
Date: March 17, 2008
Creator: Fukui, Y.; Cline, D.; Zhou, F.; Tobiyama, M.; Urakawa, J.; Bolton, P. R. et al.
Object Type: Article
System: The UNT Digital Library
The FCC’s Broadcast Media Ownership Rules (open access)

The FCC’s Broadcast Media Ownership Rules

This report provides information about The FCC’s Broadcast Media Ownership Rules which is intended to foster the three long-standing goals of U.S media policy-competition, localism, and diversity of voices.
Date: March 17, 2008
Creator: Goldfarb, Charles B.
Object Type: Report
System: The UNT Digital Library
Vacuum Insulator Development for the Dielectric Wall Accelerator (open access)

Vacuum Insulator Development for the Dielectric Wall Accelerator

At Lawrence Livermore National Laboratory, we are developing a new type of accelerator, known as a Dielectric Wall Accelerator, in which compact pulse forming lines directly apply an accelerating field to the beam through an insulating vacuum boundary. The electrical strength of this insulator may define the maximum gradient achievable in these machines. To increase the system gradient, we are using 'High Gradient Insulators' composed of alternating layers of dielectric and metal for the vacuum insulator. In this paper, we present our recent results from experiment and simulation, including the first test of a High Gradient Insulator in a functioning Dielectric Wall Accelerator cell.
Date: March 17, 2008
Creator: Harris, J. R.; Blackfield, D.; Caporaso, G. J.; Chen, Y.; Hawkins, S.; Kendig, M. et al.
Object Type: Article
System: The UNT Digital Library
Parallel Simulation Algorithms for the Three Dimensional Strong-Strong Beam-Beam Interaction (open access)

Parallel Simulation Algorithms for the Three Dimensional Strong-Strong Beam-Beam Interaction

The strong-strong beam-beam effect is one of the most important effects limiting the luminosity of ring colliders. Little is known about it analytically, so most studies utilize numeric simulations. The two-dimensional realm is readily accessible to workstation-class computers (cf.,e.g.,[1, 2]), while three dimensions, which add effects such as phase averaging and the hourglass effect, require vastly higher amounts of CPU time. Thus, parallelization of three-dimensional simulation techniques is imperative; in the following we discuss parallelization strategies and describe the algorithms used in our simulation code, which will reach almost linear scaling of performance vs. number of CPUs for typical setups.
Date: March 17, 2008
Creator: Kabel, A. C.
Object Type: Article
System: The UNT Digital Library
A Parallel Code for Lifetime Simulations in Hadron Storage Rings in the Presence of Parasitic Beam-Beam Interactions (open access)

A Parallel Code for Lifetime Simulations in Hadron Storage Rings in the Presence of Parasitic Beam-Beam Interactions

The usual approach to predict particle loss in storage rings in the presence of nonlinearities consists in the determination of the dynamic aperture of the machine. This method, however, will not directly predict the lifetimes of beams. We have developed a code which can, by parallelization and careful speed optimization, predict lifetimes in the presence of 100 parasitic beam-beam crossings by tracking > 10{sup 10} particles-turns. An application of this code to the anti-proton lifetime in the Tevatron at injection is discussed.
Date: March 17, 2008
Creator: Kabel, A. C.; Cai, Y.; Erdelyi, B.; Sen, T. & Xiao, M.
Object Type: Article
System: The UNT Digital Library
GAO: Government Accountability Office and General Accounting Office (open access)

GAO: Government Accountability Office and General Accounting Office

This report explains the establishment and evolution of the Government Accountability Office (GAO) and its resources. The Government Accountability Office is the largest of three agencies that provides support staff, research, review, and analysis of congress.
Date: March 17, 2008
Creator: Kaiser, Frederick M.
Object Type: Report
System: The UNT Digital Library
Commerce, Justice, Science, and Related Agencies: FY2008 Appropriations (open access)

Commerce, Justice, Science, and Related Agencies: FY2008 Appropriations

This report is a guide to the regular appropriations bills that Congress consider each year. It lists the key CRS staff relevant to the issues covered and related CRS products.
Date: March 17, 2008
Creator: Krouse, William J.; Murphy, Edward V. & Villarreal, M. Angeles
Object Type: Report
System: The UNT Digital Library
Active Damping of the E-P Instability at the Los Alamos Proton Storage Ring (open access)

Active Damping of the E-P Instability at the Los Alamos Proton Storage Ring

A prototype of an analog, transverse (vertical) feedback system for active damping of the two-stream (e-p) instability has been developed and successfully tested at the Los Alamos Proton Storage Ring (PSR). This system was able to improve the instability threshold by approximately 30% (as measured by the change in RF buncher voltage at instability threshold). The feedback system configuration, setup procedures, and optimization of performance are described. Results of several experimental tests of system performance are presented including observations of instability threshold improvement and grow-damp experiments, which yield estimates of instability growth and damping rates. A major effort was undertaken to identify and study several factors limiting system performance. Evidence obtained from these tests suggests that performance of the prototype was limited by higher instability growth rates arising from beam leakage into the gap at lower RF buncher voltage and the onset of instability in the horizontal plane, which had no feedback.
Date: March 17, 2008
Creator: Macek, R. J.; Assadi, S.; Byrd, J. M.; Deibele, C. E.; Henderson, S. D.; Lee, S. Y. et al.
Object Type: Article
System: The UNT Digital Library
Electron Cloud Generation and Trapping in a Quadrupole Magnet at the Los Alamos Proton Storage Ring (open access)

Electron Cloud Generation and Trapping in a Quadrupole Magnet at the Los Alamos Proton Storage Ring

Recent beam physics studies on the two-stream e-p instability at the LANL proton storage ring (PSR) have focused on the role of the electron cloud generated in quadrupole magnets where primary electrons, which seed beam-induced multipacting, are expected to be largest due to grazing angle losses from the beam halo. A new diagnostic to measure electron cloud formation and trapping in a quadrupole magnet has been developed, installed, and successfully tested at PSR. Beam studies using this diagnostic show that the 'prompt' electron flux striking the wall in a quadrupole is comparable to the prompt signal in the adjacent drift space. In addition, the 'swept' electron signal, obtained using the sweeping feature of the diagnostic after the beam was extracted from the ring, was larger than expected and decayed slowly with an exponential time constant of 50 to 100 {micro}s. Other measurements include the cumulative energy spectra of prompt electrons and the variation of both prompt and swept electron signals with beam intensity. Experimental results were also obtained which suggest that a good fraction of the electrons observed in the adjacent drift space for the typical beam conditions in the 2006 run cycle were seeded by electrons ejected from the …
Date: March 17, 2008
Creator: Macek, Robert J.; Browman, Andrew A.; Ledford, John E.; Borden, Michael J.; O'Hara, James F.; McCrady, Rodney C. et al.
Object Type: Article
System: The UNT Digital Library
Positron Beam Propagation in a Meter Long Plasma Channel (open access)

Positron Beam Propagation in a Meter Long Plasma Channel

Recent experiments and simulations have shown that positron beams propagating in plasmas can be focused and also create wakes with large accelerating gradients. For similar parameters, the wakes driven by positron beams are somewhat smaller compared to the case of an electron beam. Simulations have shown that the wake amplitude can be increased if the positron beam is propagated in a hollow plasma channel (Ref. 1). This paper, compares experimentally, the propagation and beam dynamics of a positron beam in a meter scale homogeneous plasma, to a positron beam hollow channel plasma. The results show that positron beams in hollow channels are less prone to distortions and deflections. Hollow channels were observed to guide the positron beam onto the channel axis. Beam energy loss was also observed implying the formation of a large wake amplitude. The experiments were carried out as part of the E-162 plasma wakefield experiments at SLAC.
Date: March 17, 2008
Creator: Marsh, K. A.; Blue, B. E.; Clayton, C. E.; Joshi, C.; Mori, W. B.; Decker, F. -J. et al.
Object Type: Article
System: The UNT Digital Library
Sapulpa Daily Herald (Sapulpa, Okla.), Vol. 93, No. 107, Ed. 1 Monday, March 17, 2008 (open access)

Sapulpa Daily Herald (Sapulpa, Okla.), Vol. 93, No. 107, Ed. 1 Monday, March 17, 2008

Daily newspaper from Sapulpa, Oklahoma that includes local, state, and national news along with advertising.
Date: March 17, 2008
Creator: Mattox, Jami
Object Type: Newspaper
System: The Gateway to Oklahoma History
The FY2009 Budget Request for the U.S. Department of Agriculture (open access)

The FY2009 Budget Request for the U.S. Department of Agriculture

The report discusses the U.S. Department of Agriculture (USDA) budget request for FY2009. The request includes a $76 billion in mandatory funds for food stamps, child nutrition, and farm subsidies.
Date: March 17, 2008
Creator: Monke, Jim
Object Type: Report
System: The UNT Digital Library