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A Compact X-Band Linac for an X-Ray FEL
With the growing demand for FEL light sources, cost issues are being reevaluated. To make the machines more compact, higher frequency room temperature linacs are being considered, specifically ones using C-band (5.7 GHz) rf technology, for which 40 MV/m gradients are achievable. In this paper, we show that an X-band (11.4 GHz) linac using the technology developed for NLC/GLC can provide an even lower cost solution. In particular, stable operation is possible at gradients of 100 MV/m for single bunch operation and 70 MV/m for multibunch operation. The concern, of course, is whether the stronger wakefields will lead to unacceptable emittance dilution. However, we show that the small emittances produced in a 250 MeV, low bunch charge, LCLS-like S-band injector and bunch compressor can be preserved in a multi-GeV X-band linac with reasonable alignment tolerances. The successful lasing and operation of the LCLS [1] has generated world-wide interest in X-ray FELs. The demand for access to such a light source by researchers eager to harness the capabilities of this new tool far exceeds the numbers that can be accommodated, spurring plans for additional facilities. Along with cost, spatial considerations become increasingly important for a hard X-ray machine driven by a …
Date:
September 12, 2011
Creator:
Adolphsen, Chris; Huang, Zhirong; Bane, Karl L. F.; Li, Zenghai; Zhou, Feng; Wang, Faya et al.
Object Type:
Article
System:
The UNT Digital Library
It's On: Early Interpretations of ATLAS Results in Jets and Missing Energy
The first search for supersymmetry from ATLAS with 70 nb{sup -1} of integrated luminosity extends the Tevatron's reach for colored particles that decay into jets plus missing transverse energy. For gluinos that decay directly or through a one step cascade into the LSP and two jets, the mass range m{sub {bar g}} {le} 205 GeV is disfavored by the ATLAS searches, regardless of the mass of the LSP. In some cases the coverage extends up to m{sub {bar g}} {approx_equal} 295 GeV, already surpassing the Tevatron's reach for compressed supersymmetry spectra.
Date:
August 12, 2011
Creator:
Alves, Daniele S. M.; Izaguirre, Eder & Wacker, Jay G.
Object Type:
Article
System:
The UNT Digital Library
Poker Face of Inelastic Dark Matter: Prospects at Upcoming Direct Detection Experiments
The XENON100 and CRESST experiments will directly test the inelastic dark matter explanation for DAMA's 8.9{sigma} anomaly. This article discusses how predictions for direct detection experiments depend on uncertainties in quenching factor measurements, the dark matter interaction with the Standard Model and the halo velocity distribution. When these uncertainties are accounted for, an order of magnitude variation is found in the number of expected events at CRESST and XENON100. The process of testing the DAMA anomaly highlights many of the challenges inherent to direct detection experiments. In addition to determining the properties of the unknown dark matter particle, direct detection experiments must also consider the unknown flux of the incident dark matter, as well as uncertainties in converting a signal from one target nucleus to another. The predictions for both the CRESST 2009 run and XENON100 2010 run show an order of magnitude uncertainty. The nuclear form factor for {sup 184}W, when combined with additional theoretical and experimental uncertainties, will likely prevent CRESST from refuting the iDM hypothesis with an exposure of {Omicron}(100 kg-d) in a model-independent manner. XENON100, on the other hand, will be able to make a definitive statement about a spin-independent, inelastically scattering dark matter candidate. Still, …
Date:
August 12, 2011
Creator:
Alves, Daniele S.M.; Lisanti, Mariangela; /SLAC /Stanford U., Phys. Dept.; Wacker, Jay G. & /SLAC
Object Type:
Article
System:
The UNT Digital Library
Demonstration of a 17 cm robust carbon fiber deformable mirror for adaptive optics
Carbon-fiber reinforced polymer (CFRP) composite is an attractive material for fabrication of optics due to its high stiffness-to-weight ratio, robustness, zero coefficient of thermal expansion (CTE), and the ability to replicate multiple optics from the same mandrel. We use 8 and 17 cm prototype CFRP thin-shell deformable mirrors to show that residual CTE variation may be addressed with mounted actuators for a variety of mirror sizes. We present measurements of surface quality at a range of temperatures characteristic of mountaintop observatories. For the 8 cm piece, the figure error of the Al-coated reflective surface under best actuator correction is {approx}43 nm RMS. The 8 cm mirror has a low surface error internal to the outer ring of actuators (17 nm RMS at 20 C and 33 nm RMS at -5 C). Surface roughness is low (< 3 nm P-V) at a variety of temperatures. We present new figure quality measurements of the larger 17 cm mirror, showing that the intra-actuator figure error internal to the outer ring of actuators (38 nm RMS surface with one-third the actuator density of the 8 cm mirror) does not scale sharply with mirror diameter.
Date:
September 12, 2011
Creator:
Ammons, S. M.; Hart, M.; Coughenour, B.; Romeo, R.; Martin, R. & Rademacher, M.
Object Type:
Article
System:
The UNT Digital Library
Two-Dimensional Dirac Fermions in a Topological Insulator: Transport in the Quantum Limit
Pulsed magnetic fields of up to 55T are used to investigate the transport properties of the topological insulator Bi{sub 2}Se{sub 3} in the extreme quantum limit. For samples with a bulk carrier density of n = 2.9 x 10{sup 16} cm{sup -3}, the lowest Landau level of the bulk 3D Fermi surface is reached by a field of 4T. For fields well beyond this limit, Shubnikov-de Haas oscillations arising from quantization of the 2D surface state are observed, with the {nu} = 1 Landau level attained by a field of {approx} 35T. These measurements reveal the presence of additional oscillations which occur at fields corresponding to simple rational fractions of the integer Landau indices.
Date:
August 12, 2011
Creator:
Analytis, J. G.; McDonald, R. D.; Riggs, S. C.; Chu, J.-H.; Boebinger, G. S. & Fisher, I. R.
Object Type:
Article
System:
The UNT Digital Library
Recovery Act: Energy Efficiency of Data Networks through Rate Adaptation (EEDNRA) - Final Technical Report
This Concept Definition Study focused on developing a scientific understanding of methods to reduce energy consumption in data networks using rate adaptation. Rate adaptation is a collection of techniques that reduce energy consumption when traffic is light, and only require full energy when traffic is at full provisioned capacity. Rate adaptation is a very promising technique for saving energy: modern data networks are typically operated at average rates well below capacity, but network equipment has not yet been designed to incorporate rate adaptation. The Study concerns packet-switching equipment, routers and switches; such equipment forms the backbone of the modern Internet. The focus of the study is on algorithms and protocols that can be implemented in software or firmware to exploit hardware power-control mechanisms. Hardware power-control mechanisms are widely used in the computer industry, and are beginning to be available for networking equipment as well. Network equipment has different performance requirements than computer equipment because of the very fast rate of packet arrival; hence novel power-control algorithms are required for networking. This study resulted in five published papers, one internal report, and two patent applications, documented below. The specific technical accomplishments are the following: • A model for the power consumption …
Date:
July 12, 2011
Creator:
Andrews, Matthew; Antonakopoulos, Spyridon; Fortune, Steve; Francini, Andrea & Zhang, Lisa
Object Type:
Report
System:
The UNT Digital Library
Accelerated Gibbs Sampling for Infinite Sparse Factor Analysis
The Indian Buffet Process (IBP) gives a probabilistic model of sparse binary matrices with an unbounded number of columns. This construct can be used, for example, to model a fixed numer of observed data points (rows) associated with an unknown number of latent features (columns). Markov Chain Monte Carlo (MCMC) methods are often used for IBP inference, and in this technical note, we provide a detailed review of the derivations of collapsed and accelerated Gibbs samplers for the linear-Gaussian infinite latent feature model. We also discuss and explain update equations for hyperparameter resampling in a 'full Bayesian' treatment and present a novel slice sampler capable of extending the accelerated Gibbs sampler to the case of infinite sparse factor analysis by allowing the use of real-valued latent features.
Date:
September 12, 2011
Creator:
Andrzejewski, D M
Object Type:
Report
System:
The UNT Digital Library
Dispersion in the Presence of Strong Transverse Wakefields
To minimize emittance growth in a long linac, it is necessary to control the wakefields by correcting the beam orbit excursions. In addition, the particle energy is made to vary along the length of the bunch to introduce a damping, known as the BNS damping, to the beam break-up effect. In this paper, we use a two-particle model to examine the relative magnitudes of the various orbit and dispersion functions involved. The results are applied to calculate the effect of a closed orbit bump and a misaligned structure. It is shown that wake-induced dispersion is an important contribution to the beam dynamics in long linacs with strong wakefields like SLC.
Date:
August 12, 2011
Creator:
Assmann, Ralph & Chao, Alex
Object Type:
Article
System:
The UNT Digital Library
Heavy octets and Tevatron signals with three or four b jets
Hypothetical color-octet particles of spin 0, pair-produced at hadron colliders through their QCD coupling, may lead to final states involving three or four b jets. We analyze kinematic distributions of the 3b final state that differentiate the scalar octets from supersymmetric Higgs bosons. Studying the scalar sector that breaks an SU(3) x SU(3) gauge symmetry down to the QCD gauge group, we find that the scalar octet is resonantly produced in pairs via a spin-1 octet (coloron). A scalar octet of mass in the 140-150 GeV range can explain the nonstandard shape of the b-jet transverse energy distributions reported by the CDF Collaboration, especially when the coloron mass is slightly above twice the scalar mass. The dominant decay mode of the scalar octet is into a pair of gluons, so that the production of a pair of dijet resonances is large in this model, of about 40 pb at the Tevatron. Even when a W boson is radiated from the initial state, the inclusive cross section for producing a dijet resonance near the scalar octet mass remains sizable, around 0.15 pb.
Date:
August 12, 2011
Creator:
Bai, Yang & Dobrescu, Bogdan A.
Object Type:
Article
System:
The UNT Digital Library
LHC Predictions from a Tevatron Anomaly in the Top Quark Forward-Backward Asymmetry
We examine the implications of the recent CDF measurement of the top-quark forward-backward asymmetry, focusing on a scenario with a new color octet vector boson at 1-3 TeV. We study several models, as well as a general effective field theory, and determine the parameter space which provides the best simultaneous fit to the CDF asymmetry, the Tevatron top pair production cross section, and the exclusion regions from LHC dijet resonance and contact interaction searches. Flavor constraints on these models are more subtle and less severe than the literature indicates. We find a large region of allowed parameter space at high axigluon mass and a smaller region at low mass; we match the latter to an SU(3){sub 1} x SU(3){sub 2}/SU(3){sub c} coset model with a heavy vector-like fermion. Our scenario produces discoverable effects at the LHC with only 1-2 inverse femtobarns of luminosity at 7-8 TeV. Lastly, we point out that a Tevatron measurement of the b-quark forward-backward asymmetry would be very helpful in characterizing the physics underlying the top-quark asymmetry.
Date:
August 12, 2011
Creator:
Bai, Yang; Hewett, JoAnne L.; Kaplan, Jared & Rizzo, Thomas G.
Object Type:
Article
System:
The UNT Digital Library
Final Report - Summer Visit 2010
During my visit to LLNL during the summer of 2010, I worked on algebraic multilevel solvers for large sparse systems of linear equations arising from discretizations of partial differential equations. The particular solver of interest is based on ILU decomposition. The setup phase for this AMG solve is just the single ILU decomposition, and its corresponding error matrix. Because the ILU uses a minimum degree or similar sparse matrix ordering, most of the fill-in, and hence most of the error, is concentrated in the lower right corner of the factored matrix. All of the major multigrid components - the smoother, the coarse level correction matrices, and the fine-to-coarse and coarse-to-fine rectangular transfer matrices, are defined in terms of various blocks of the ILU factorization. Although such a strategy is not likely to be optimal in terms of convergence properties, it has a relatively low setup cost, and therefore is useful in situations where setup costs for more traditional AMG approaches cannot be amortized over the solution of many linear systems using the same matrix. Such a situation arises in adaptive methods, where often just one linear system is solved at each step of an adaptive feedback loop, or in solving …
Date:
September 12, 2011
Creator:
Bank, R
Object Type:
Report
System:
The UNT Digital Library
The Rambler (Fort Worth, Tex.), Vol. 94, No. 19, Ed. 1 Wednesday, October 12, 2011
Weekly student newspaper from Texas Wesleyan University in Fort Worth, Texas that includes campus and local news along with advertising.
Date:
October 12, 2011
Creator:
Banks, Shauna
Object Type:
Newspaper
System:
The Portal to Texas History
Stimulated Superconductivity at Strong Coupling
Stimulating a system with time dependent sources can enhance instabilities, thus increasing the critical temperature at which the system transitions to interesting low-temperature phases such as superconductivity or superfluidity. After reviewing this phenomenon in non-equilibrium BCS theory (and its marginal fermi liquid generalization) we analyze the effect in holographic superconductors. We exhibit a simple regime in which the transition temperature increases parametrically as we increase the frequency of the time-dependent source.
Date:
August 12, 2011
Creator:
Bao, Ning; Dong, Xi; Silverstein, Eva; Torroba, Gonzalo & /Stanford U., ITP /Stanford U., Phys. Dept. /SLAC
Object Type:
Report
System:
The UNT Digital Library
A Benchmark Model for Parallel ns3
None
Date:
December 12, 2011
Creator:
Barnes, P. D.
Object Type:
Article
System:
The UNT Digital Library
Precision Equation-of-State Measurements on NIF ablator materials from 1 to 12 Mbar Using Laser-Driven Shock Waves
None
Date:
October 12, 2011
Creator:
Barrios, M. A.; Boehly, T. R.; Hicks, D. G.; Fratanduono, D. E.; Eggert, J. H.; Collins, G. et al.
Object Type:
Article
System:
The UNT Digital Library
Single-Sector Supersymmetry Breaking, Chirality, and Unification
Calculable single-sector models provide an elegant framework for generating the flavor textures via compositeness, breaking supersymmetry, and explaining the electroweak scale. Such models may be realized naturally in supersymmetric QCD with additional gauge singlets (SSQCD), though it remains challenging to construct models without a surfeit of light exotic states where the Standard Model index emerges naturally. We classify possible single-sector models based on Sp confining SSQCD according to their Standard Model index and number of composite messengers. This leads to simple, calculable models that spontaneously break supersymmetry, reproduce the fermion flavor hierarchy, and explain the Standard Model index dynamically with little or no additional matter. At low energies these theories realize a 'more minimal' soft spectrum with direct mediation and a gravitino LSP.
Date:
August 12, 2011
Creator:
Behbahani, Siavosh R.; /SLAC /Stanford U., Phys. Dept.; Craig, Nathaniel; /Stanford U., Phys. Dept. /Princeton, Inst. Advanced Study /Rutgers U., Piscataway; Torroba, Gonzalo & /SLAC /Stanford U., Phys. Dept.
Object Type:
Article
System:
The UNT Digital Library
Nearly Supersymmetric Dark Atoms
Theories of dark matter that support bound states are an intriguing possibility for the identity of the missing mass of the Universe. This article proposes a class of models of supersymmetric composite dark matter where the interactions with the Standard Model communicate supersymmetry breaking to the dark sector. In these models supersymmetry breaking can be treated as a perturbation on the spectrum of bound states. Using a general formalism, the spectrum with leading supersymmetry effects is computed without specifying the details of the binding dynamics. The interactions of the composite states with the Standard Model are computed and several benchmark models are described. General features of non-relativistic supersymmetric bound states are emphasized.
Date:
August 12, 2011
Creator:
Behbahani, Siavosh R.; Jankowiak, Martin; /SLAC /Stanford U., ITP; Rube, Tomas; /Stanford U., ITP; Wacker, Jay G. et al.
Object Type:
Article
System:
The UNT Digital Library
Direct Imaging of the Coexistence of Ferromagnetism and Superconductivity at the LaA1O3/SrTiO3 Interface
LaAlO{sub 3} and SrTiO{sub 3} are insulating, nonmagnetic oxides, yet the interface between them exhibits a two-dimensional electron system with high electron mobility, superconductivity at low temperatures, and electric-field-tuned metal-insulator and superconductor-insulator phase transitions. Bulk magnetization and magnetoresistance measurements also suggest some form of magnetism depending on preparation conditions and suggest a tendency towards nanoscale electronic phase separation. Here we use local imaging of the magnetization and magnetic susceptibility to directly observe a landscape of ferromagnetism, paramagnetism, and superconductivity. We find submicron patches of ferromagnetism in a uniform background of paramagnetism, with a nonuniform, weak diamagnetic superconducting susceptibility at low temperature. These results demonstrate the existence of nanoscale phase separation as suggested by theoretical predictions based on nearly degenerate interface subbands associated with the Ti orbitals. The magnitude and temperature dependence of the paramagnetic response suggests that the vast majority of the electrons at the interface are localized, and do not contribute to transport measurements. In addition to the implications for magnetism, the existence of a 2D superconductor at an interface with highly broken inversion symmetry and a ferromagnetic landscape in the background suggests the potential for exotic superconducting phenomena.
Date:
August 12, 2011
Creator:
Bert, Julie
Object Type:
Article
System:
The UNT Digital Library
Director of National Intelligence Statutory Authorities: Status and Proposals
This report discusses the Director of National Intelligence (DNI) position created by the Intelligence Reform and Terrorism Prevention Act of 2004 (P.L. 108-458). It includes an overview of the authorities granted to the DNI by legislation in 2004 and later as well as the varying opinions of Congress regarding new DNI authorities, as well as related legislation from FY2010 through FY2012.
Date:
January 12, 2011
Creator:
Best, Richard A., Jr. & Cumming, Alfred
Object Type:
Report
System:
The UNT Digital Library
Tax Gap: Should the 3% Withholding Requirement on Payments to Contractors by Government Be Repealed?
This reports discusses tax gaps and withholding, and concerns and legislation regarding these issues in the 112th Congress.
Date:
September 12, 2011
Creator:
Bickley, James M.
Object Type:
Report
System:
The UNT Digital Library
Tax Gap: Should the 3% Withholding Requirement on Payments to Contractors by Government Be Repealed?
This brief discusses the Joint Committee on Taxation (JCT) report titled Options to Improve Tax Compliance and Reform Tax Expenditures. The JCT report identified many options, including several to increase withholding.
Date:
September 12, 2011
Creator:
Bickley, James M.
Object Type:
Report
System:
The UNT Digital Library
Closing Remarks
Presentation for the 2011 International Internet Preservation Consortium General Assembly. Presentation covers closing remarks for the conference and provides general updates on upcoming IIPC events.
Date:
May 12, 2011
Creator:
Binns, Aaron
Object Type:
Presentation
System:
The UNT Digital Library
United Nations System Efforts to Address Violence Against Women
This report provides an overview of recent U.N. efforts to address violence against women (VAW) and highlights key U.N. interagency efforts. It also discusses selected U.N. funds, programs, and agencies that address international violence against women. It does not assess the extent to which VAW is directly addressed or is part of a larger initiative or program.
Date:
July 12, 2011
Creator:
Blanchfield, Luisa
Object Type:
Report
System:
The UNT Digital Library
Bioinformatics tools for cancer metabolomics
This review focuses on the use of different bioinformatics tools in cancer metabolomics studies.
Date:
January 12, 2011
Creator:
Blekherman, Grigoriy; Laubenbacher, Reinhard; Cortes, Diego F.; Mendes, Pedro; Torti, Frank M.; Akman, Steven et al.
Object Type:
Article
System:
The UNT Digital Library