Recent charm mixing results from BABAR, Belle, and CDF (open access)

Recent charm mixing results from BABAR, Belle, and CDF

A summary of the results of several recent studies of charm mixing is presented. A number of different methods were used, including the measurement of lifetime ratios for final states of different CP, time dependence of wrong-sign hadronic decays, fits to time-dependent Dalitz plots, and searches for wrong-sign semi-leptonic decays. Taken together, they suggest mixing is of order 1%. The status of searches for indirect CP violation is also reported.
Date: February 2, 2009
Creator: Charles, M.J. & /SLAC, /Iowa U.
System: The UNT Digital Library
The groundwater-land-surface-atmosphere connection: soil moisture effects on the atmospheric boundary layer in fully-coupled simulations (open access)

The groundwater-land-surface-atmosphere connection: soil moisture effects on the atmospheric boundary layer in fully-coupled simulations

This study combines a variably-saturated groundwater flow model and a mesoscale atmospheric model to examine the effects of soil moisture heterogeneity on atmospheric boundary layer processes. This parallel, integrated model can represent spatial variations in land-surface forcing driven by three-dimensional (3D) atmospheric and subsurface components. The development of atmospheric flow is studied in a series of idealized test cases with different initial soil moisture distributions generated by an offline spin-up procedure or interpolated from a coarse-resolution dataset. These test cases are performed with both the fully-coupled model (which includes 3D groundwater flow and surface water routing) and the uncoupled atmospheric model. The effects of the different soil moisture initializations and lateral subsurface and surface water flow are seen in the differences in atmospheric evolution over a 36-hour period. The fully-coupled model maintains a realistic topographically-driven soil moisture distribution, while the uncoupled atmospheric model does not. Furthermore, the coupled model shows spatial and temporal correlations between surface and lower atmospheric variables and water table depth. These correlations are particularly strong during times when the land surface temperatures trigger shifts in wind behavior, such as during early morning surface heating.
Date: February 2, 2007
Creator: Maxwell, R M; Chow, F K & Kollet, S J
System: The UNT Digital Library
Vector Unparticle Contributions to Lepton g-2 (open access)

Vector Unparticle Contributions to Lepton g-2

The generic unparticle propagator may be modified in two ways. Breaking the conformal symmetry effectively adds a mass term to the propagator, while considering vacuum polarization corrections adds a width-like term. Both of these modifications result naturally from the coupling of the unparticle to standard model (SM) fields. We explore how these modifications to the propagator affect the calculation of the lepton anomalous magnetic moment using an integral approximation of the propagator that is accurate for d {approx}< 1.5, where d is the unparticle dimension. We find that for this range of d and various values of the conformal breaking scale {mu}, the value of g-2 calculated when allowing various SM fermions to run in the unparticle self-energy loops does not significantly deviate from the value of g-2 when the width term is ignored. We also investigate the limits on a characteristic mass scale for the unparticle sector as a function of {mu} and d.
Date: February 2, 2009
Creator: Conley, John A. & Gainer, James S.
System: The UNT Digital Library
Lithium Insertion Chemistry of Some Iron Vanadates (open access)

Lithium Insertion Chemistry of Some Iron Vanadates

Lithium insertion into various iron vanadates has been investigated. Fe{sub 2}V{sub 4}O{sub 13} and Fe{sub 4}(V{sub 2}O{sub 7}){sub 3} {center_dot} 3H{sub 2}O have discharge capacities approaching 200 mAh/g above 2.0 V vs. Li{sup +}/Li. Although the potential profiles change significantly between the first and subsequent discharges, capacity retention is unexpectedly good. Other phases, structurally related to FeVO{sub 4}, containing copper and/or sodium ions were also studied. One of these, {beta}-Cu{sub 3}Fe{sub 4}(VO{sub 4}){sub 6}, reversibly consumes almost 10 moles of electrons per formula unit (ca. 240 mAh g{sup -1}) between 3.6 and 2.0 V vs. Li{sup +}/Li, in a non-classical insertion process. It is proposed that both copper and vanadium are electrochemically active, whereas iron(III) reacts to form LiFe{sup III}O{sub 2}. The capacity of the Cu{sub 3}Fe{sub 4}(VO{sub 4}){sub 6}/Li system is nearly independent of cycling rate, stabilizing after a few cycles at 120-140 mAh g{sup -1}. Iron vanadates exhibit better capacities than their phosphate analogues, whereas the latter display more constant discharge potentials.
Date: February 2, 2007
Creator: Patoux, Sebastien & Richardson, Thomas J.
System: The UNT Digital Library
Status of the International Muon Ionization Cooling Experiment (MICE) (open access)

Status of the International Muon Ionization Cooling Experiment (MICE)

An international experiment to demonstrate muonionization cooling is scheduled for beam at RutherfordAppleton Laboratory (RAL) in 2007. The experimentcomprises one cell of the Study II cooling channel [1],along with upstream and downstream detectors to identifyindividual muons and measure their initial and final 6Dphase-space parameters to a precision of 0.1percent. Magneticdesign of the beam line and cooling channel are completeand portions are under construction. The experiment willbe described, including cooling channel hardware designs,fabrication status, and running plans. Phase 1 of theexperiment will prepare the beam line and providedetector systems, including time-of-flight, Cherenkov,scintillating-fiber trackers and their spectrometersolenoids, and an electromagnetic calorimeter. The Phase2 system will add the cooling channel components,including liquid-hydrogen absorbers embedded insuperconducting Focus Coil solenoids, 201-MHz normalconductingRF cavities, and their surrounding CouplingCoil solenoids. The MICE Collaboration goal is tocomplete the experiment by 2010; progress toward this isdiscussed.
Date: February 2, 2007
Creator: Zisman, Michael S. & Zisman, Michael S.
System: The UNT Digital Library
Investigation of early growth of calcium hydroxide crystals in cement solution by soft x-ray transmission microscopy (open access)

Investigation of early growth of calcium hydroxide crystals in cement solution by soft x-ray transmission microscopy

Research on cement hydration was performed at the full-field soft transmission X-ray microscope XM-1 located at beamline 6.1.2 at the Advanced Light Source (ALS) in Berkeley CA which is operated by the Center for X-ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California. A series of works [1-3] has been conducted using this microscope for the in situ observation and qualitative analysis of through-solution hydration products and products of topochemical reactions, which form in cementitious aqueous solutions. This paper studies the precipitation of the calcium hydroxide (CH) crystals from the cement solution. The analysis of successive images of the hydration process provides critical quantitative information about the growth rate of calcium hydroxide (CH) crystals, the supersaturation ratio, and the kinetic and diffusion coefficients of the growth process. ASTM Type II portland cement and 6% C{sub 4}A{sub 3}{bar S} admixture were mixed in aqueous solution and saturated with respect to CH and gypsum. The C{sub 4}A{sub 3}{bar S} admixture was included in the experimental program because of the general research program on expansive cements, and adding C{sub 4}A{sub 3}{bar S} to portland cement is an efficient method of generating ettringite and significant early-age expansion. The solution/solid materials ratio was 10 cm{sup 3}/g, …
Date: February 2, 2009
Creator: Harutyunyan, V. S.; Kirchheim, A. P.; Monteiro, P. J. M.; Aivazyan, A. P. & Fischer, P.
System: The UNT Digital Library
137Cs and 210Po in Pacific Walrus and Bearded Seal from St. Lawrence Island, Alaska (open access)

137Cs and 210Po in Pacific Walrus and Bearded Seal from St. Lawrence Island, Alaska

The activity concentration of Cesium-137 ({sup 137}Cs) and naturally-occurring Polonium-210 ({sup 210}Po) were measured in the muscle tissue, kidney and liver of Pacific walrus (Odobenus rosmarus divergens) and bearded seal (Erignathus barbatus) collected by native hunters from the Bering Sea. The mean {sup 137}Cs concentrations in muscle, liver and kidney of Pacific walrus were 0.07, 0.09 and 0.07 Bq kg{sup -1} (N= 5, wet weight), respectively, and 0.17, 0.10, and 0.17 Bq kg{sup -1} (N=2, wet weight), respectively, in bearded seal. In general, {sup 137}Cs tissue concentrations are significantly lower than those previously reported for mammals from other regions. By comparison, {sup 210}Po activity concentrations appear to be higher than those reported elsewhere but a larger variation. The mean {sup 210}Po concentration in the muscle tissue, liver and kidney of Pacific walrus (N=5, wet weight) were 28.7, 189, and 174 Bq kg{sup -1}, respectively. This compares with {sup 210}Po concentration values (N=2, wet weight) of 27, 207, and 68 Bq kg{sup -1} measured in the muscle tissue, liver and kidney, of bearded seal, respectively. Estimated bioaccumulation factors--as defined by the radionuclide concentration ratio between the target tissue to that in sea water--were two to three orders of magnitude higher for …
Date: February 2, 2005
Creator: Hamilton, T F; Seagars, D J; Jokela, T & Layton, D
System: The UNT Digital Library
Excitation Function for the 74Se(18O,p3n) Reaction (open access)

Excitation Function for the 74Se(18O,p3n) Reaction

The 74Se(18O,p3n)88gNb excitation function was measured and a maximum cross section of 495+-5 mb was observed at and 18O energy of 74.0 MeV. Experimental cross sections were compared to theoretical calculations using the computer code ALICE-91 and the values were found to be in good agreement. The half life of 88gNb was determined to be around 14.56+-0.11 min.
Date: February 2, 2009
Creator: Gates, Jacklyn; Dragojevic, Irena; Dvorak, Jan; Ellison, Paul; Gregorich, Kenneth; Stavsetra, Liv et al.
System: The UNT Digital Library
Cerocene Revisited: The Electronic Structure of and Interconversion Between Ce2(C8H8)3 and Ce(C8H8)2 (open access)

Cerocene Revisited: The Electronic Structure of and Interconversion Between Ce2(C8H8)3 and Ce(C8H8)2

New synthetic procedures for the preparation of Ce(cot)2, cerocene, from [Li(thf)4][Ce(cot)2], and Ce2(cot)3 in high yield and purity are reported. Heating solid Ce(cot)2 yields Ce2(cot)3 and COT while heating Ce2(cot)3 with an excess of COT in C6D6 to 65oC over four months yields Ce(cot)2. The solid state magnetic susceptibility of these three organocerium compounds shows that Ce(cot)2 behaves as a TIP (temperature independent paramagnet) over the temperature range of 5-300 K, while that of Ce2(cot)3 shows that the spin carriers are antiferromagnetically coupled below 10 K; above 10 K, the individual spins are uncorrelated, and [Ce(cot)2]- behaves as an isolated f1 paramagnet. The EPR at 1.5K for Ce2(cot)3 and [Ce(cot)2]- have ground state of MJ= +- 1/2. The LIII edge XANES of Ce(cot)2 (Booth, C.H.; Walter, M.D.; Daniel, M.; Lukens, W.W., Andersen, R.A., Phys. Rev. Lett. 2005, 95, 267202) and 2Ce2(cot)3 over 30-500 K are reported; the Ce(cot)2 XANES spectra show Ce(III) and Ce(IV) signatures up to a temperature of approximately 500 K, whereupon the Ce(IV) signature disappears, consistent with the thermal behavior observed in the melting experiment. The EXAFS of Ce(cot)2 and Ce2(cot)3 are reported at 30 K; the agreement between the molecular parameters for Ce(cot)2 derived from EXAFS …
Date: February 2, 2009
Creator: Walter, Marc D.; Booth, Corwin H.; Lukens, Wayne W. & Andersen, Richard A.
System: The UNT Digital Library
Uranus in 2003: Zonal Winds, Banded Structure, and Discrete Features (open access)

Uranus in 2003: Zonal Winds, Banded Structure, and Discrete Features

None
Date: February 2, 2005
Creator: Hammel, H B; de Pater, I; Gibbard, S G; Lockwood, G W & Rages, K
System: The UNT Digital Library
Creating Ensembles of Decision Trees Through Sampling (open access)

Creating Ensembles of Decision Trees Through Sampling

Recent work in classification indicates that significant improvements in accuracy can be obtained by growing an ensemble of classifiers and having them vote for the most popular class. This paper focuses on ensembles of decision trees that are created with a randomized procedure based on sampling. Randomization can be introduced by using random samples of the training data (as in bagging or arcing) and running a conventional tree-building algorithm, or by randomizing the induction algorithm itself. The objective of this paper is to describe our first experiences with a novel randomized tree induction method that uses a subset of samples at a node to determine the split. Our empirical results show that ensembles generated using this approach yield results that are competitive in accuracy and superior in computational cost.
Date: February 2, 2001
Creator: Kamath, C & Cantu-Paz, E
System: The UNT Digital Library
Measurement of Black Carbon and Particle Number Emission Factors from Individual Heavy-Duty Trucks (open access)

Measurement of Black Carbon and Particle Number Emission Factors from Individual Heavy-Duty Trucks

Emission factors for black carbon (BC) and particle number (PN) were measured from 226 individual heavy-duty (HD) diesel-fueled trucks driving through a 1 km-long California highway tunnel in August 2006. Emission factors were based on concurrent increases in BC, PN, and CO{sub 2}B concentrations (measured at 1 Hz) that corresponded to the passage of individual HD trucks. The distributions of BC and PN emission factors from individual HD trucks are skewed, meaning that a large fraction of pollution comes from a small fraction of the in-use vehicle fleet. The highest-emitting 10% of trucks were responsible for {approx} 40% of total BC and PN emissions from all HD trucks. BC emissions were log-normally distributed with a mean emission factor of 1.7 g kg {sup -1} and maximum values of {approx} 10 g kg{sup -1}. Corresponding values for PN emission factors were 4.7 x 10{sup 15} and 4 x 10{sup 16} kg{sup -1}. There was minimal overlap among high-emitters of these two pollutants: only 1 of the 226 HD trucks measured was found to be among the highest 10% for both BC and PN. Monte Carlo resampling of the distribution of BC emission factors observed in this study revealed that uncertainties (1{sigma}) …
Date: February 2, 2009
Creator: Ban-Weiss, George A.; Lunden, Melissa M.; Kirchstetter, Thomas W. & Harley, Robert A.
System: The UNT Digital Library
A multi-threshold sampling method for TOF PET signal processing (open access)

A multi-threshold sampling method for TOF PET signal processing

As an approach to realizing all-digital data acquisition for positron emission tomography (PET), we have previously proposed and studied a multithreshold sampling method to generate samples of a PET event waveform with respect to a few user-defined amplitudes. In this sampling scheme, one can extract both the energy and timing information for an event. In this paper, we report our prototype implementation of this sampling method and the performance results obtained with this prototype. The prototype consists of two multi-threshold discriminator boards and a time-to-digital converter (TDC) board. Each of the multi-threshold discriminator boards takes one input and provides up to 8 threshold levels, which can be defined by users, for sampling the input signal. The TDC board employs the CERN HPTDC chip that determines the digitized times of the leading and falling edges of the discriminator output pulses. We connect our prototype electronics to the outputs of two Hamamatsu R9800 photomultiplier tubes (PMTs) that are individually coupled to a 6.25 x 6.25 x 25mm{sup 3} LSO crystal. By analyzing waveform samples generated by using four thresholds, we obtain a coincidence timing resolution of about 340 ps and an {approx}18% energy resolution at 511 keV. We are also able to …
Date: February 2, 2009
Creator: Kim, Heejong; Kao, Chien-Min; Xie, Q.; Chen, Chin-Tu; Zhou, L.; Tang, F. et al.
System: The UNT Digital Library
MOSAIC: a new wavefront metrology (open access)

MOSAIC: a new wavefront metrology

MOSAIC is a new wavefront metrology that enables complete wavefront characterization from print or aerial image based measurements. Here we describe MOSAIC and verify its utility with a model-based proof of principle.
Date: February 2, 2009
Creator: Anderson, Christopher & Naulleau, Patrick
System: The UNT Digital Library
Reaction Selectivity in Heterogeneous Catalysis (open access)

Reaction Selectivity in Heterogeneous Catalysis

The understanding of selectivity in heterogeneous catalysis is of paramount importance to our society today. In this review we outline the current state of the art in research on selectivity in heterogeneous catalysis. Current in-situ surface science techniques have revealed several important features of catalytic selectivity. Sum frequency generation vibrational spectroscopy has shown us the importance of understanding the reaction intermediates and mechanism of a heterogeneous reaction, and can readily yield information as to the effect of temperature, pressure, catalyst geometry, surface promoters, and catalyst composition on the reaction mechanism. DFT calculations are quickly approaching the ability to assist in the interpretation of observed surface spectra, thereby making surface spectroscopy an even more powerful tool. HP-STM has revealed three vitally important parameters in heterogeneous selectivity: adsorbate mobility, catalyst mobility, and selective site-blocking. The development of size controlled nanoparticles from 0.8 to 10 nm, of controlled shape, and of controlled bimetallic composition has revealed several important variables for catalytic selectivity. Lastly, DFT calculations may be paving the way to guiding the composition choice for multi-metallic heterogeneous catalysis for the intelligent design of catalysts incorporating the many factors of selectivity we have learned.
Date: February 2, 2009
Creator: Somorjai, Gabor A. & Kliewer, Christopher J.
System: The UNT Digital Library
Impacts of aerosol-cloud interactions on past and future changes in tropospheric composition (open access)

Impacts of aerosol-cloud interactions on past and future changes in tropospheric composition

The development of effective emissions control policies that are beneficial to both climate and air quality requires a detailed understanding of all the feedbacks in the atmospheric composition and climate system. We perform sensitivity studies with a global atmospheric composition-climate model to assess the impact of aerosols on tropospheric chemistry through their modification on clouds, aerosol-cloud interactions (ACI). The model includes coupling between both tropospheric gas-phase and aerosol chemistry and aerosols and liquid-phase clouds. We investigate past impacts from preindustrial (PI) to present day (PD) and future impacts from PD to 2050 (for the moderate IPCC A1B scenario) that embrace a wide spectrum of precursor emission changes and consequential ACI. The aerosol indirect effect (AIE) is estimated to be -2.0 Wm{sup -2} for PD-PI and -0.6 Wm{sup -2} for 2050-PD, at the high end of current estimates. Inclusion of ACI substantially impacts changes in global mean methane lifetime across both time periods, enhancing the past and future increases by 10% and 30%, respectively. In regions where pollution emissions increase, inclusion of ACI leads to 20% enhancements in in-cloud sulfate production and {approx}10% enhancements in sulfate wet deposition that is displaced away from the immediate source regions. The enhanced in-cloud sulfate …
Date: February 2, 2009
Creator: Unger, N.; Menon, S.; Shindell, D. T. & Koch, D. M.
System: The UNT Digital Library
Carbon contamination of extreme ultraviolet (EUV) mask and its effect on imaging (open access)

Carbon contamination of extreme ultraviolet (EUV) mask and its effect on imaging

Carbon contamination of extreme ultraviolet (EUV) masks and its effect on imaging is a significant issue due to lowered throughput and potential effects on imaging performance. In this work, a series of carbon contamination experiments were performed on a patterned EUV mask. Contaminated features were then inspected with a reticle scanning electron microscope (SEM) and printed with the SEMA TECH Berkeley Microfield-Exposure tool (MET) [1]. In addition, the mask was analyzed using the SEMA TECH Berkeley Actinic-Inspection tool (AIT) [2] to determine the effect of carbon contamination on the absorbing features and printing performance. To understand the contamination topography, simulations were performed based on calculated aerial images and resist parameters. With the knowledge of the topography, simulations were then used to predict the effect of other thicknesses of the contamination layer, as well as the imaging performance on printed features.
Date: February 2, 2009
Creator: Fan, Yu-Jen; Yankulin, Leonid; Antohe, Alin; Garg, Rashi; Thomas, Petros; Mbanaso, Chimaobi et al.
System: The UNT Digital Library
Intercomparison of model simulations of mixed-phase clouds observed during the ARM Mixed-Phase Arctic Cloud Experiment. Part I: Single layer cloud (open access)

Intercomparison of model simulations of mixed-phase clouds observed during the ARM Mixed-Phase Arctic Cloud Experiment. Part I: Single layer cloud

Results are presented from an intercomparison of single-column and cloud-resolving model simulations of a cold-air outbreak mixed-phase stratocumulus cloud observed during the Atmospheric Radiation Measurement (ARM) program's Mixed-Phase Arctic Cloud Experiment. The observed cloud occurred in a well-mixed boundary layer with a cloud top temperature of -15 C. The observed average liquid water path of around 160 g m{sup -2} was about two-thirds of the adiabatic value and much greater than the average mass of ice crystal precipitation which when integrated from the surface to cloud top was around 15 g m{sup -2}. The simulations were performed by seventeen single-column models (SCMs) and nine cloud-resolving models (CRMs). While the simulated ice water path is generally consistent with the observed values, the median SCM and CRM liquid water path is a factor of three smaller than observed. Results from a sensitivity study in which models removed ice microphysics suggest that in many models the interaction between liquid and ice-phase microphysics is responsible for the large model underestimate of liquid water path. Despite this general underestimate, the simulated liquid and ice water paths of several models are consistent with the observed values. Furthermore, there is evidence that models with more sophisticated microphysics …
Date: February 2, 2009
Creator: Klein, Stephen A.; McCoy, Renata B.; Morrison, Hugh; Ackerman, Andrew S.; Avramov, Alexander; de Boer, Gijs et al.
System: The UNT Digital Library
Application of dynamic linear regression to improve the skill of ensemble-based deterministic ozone forecasts (open access)

Application of dynamic linear regression to improve the skill of ensemble-based deterministic ozone forecasts

Forecasts from seven air quality models and surface ozone data collected over the eastern USA and southern Canada during July and August 2004 provide a unique opportunity to assess benefits of ensemble-based ozone forecasting and devise methods to improve ozone forecasts. In this investigation, past forecasts from the ensemble of models and hourly surface ozone measurements at over 350 sites are used to issue deterministic 24-h forecasts using a method based on dynamic linear regression. Forecasts of hourly ozone concentrations as well as maximum daily 8-h and 1-h averaged concentrations are considered. It is shown that the forecasts issued with the application of this method have reduced bias and root mean square error and better overall performance scores than any of the ensemble members and the ensemble average. Performance of the method is similar to another method based on linear regression described previously by Pagowski et al., but unlike the latter, the current method does not require measurements from multiple monitors since it operates on individual time series. Improvement in the forecasts can be easily implemented and requires minimal computational cost.
Date: February 2, 2006
Creator: Pagowski, M O; Grell, G A; Devenyi, D; Peckham, S E; McKeen, S A; Gong, W et al.
System: The UNT Digital Library
What Einstein Did Not Know (open access)

What Einstein Did Not Know

This public lecture is about 100 years of research on elementary particles and fundamental forces, beginning with the identification of the electron about 1900 and extending to the astonishing discovery of Dark Matter in the late 1900s. The author talks about the elementary particle concept; the discoveries of leptons, quarks and force carrying particles; and some of the experimental technology used. The author tells of his own research, the discovery of the tau lepton, the long, inconclusive search for fractional charged particles and his new involvement in astronomical research on Dark Matter. He concludes by looking ahead to old unsolved puzzles and new questions on the fundamental nature of matter and force that face us in the 21st Century.
Date: February 2, 2007
Creator: Perl, Martin L.
System: The UNT Digital Library
Nuclear shape and structure in neutron-rich 110,111Tc (open access)

Nuclear shape and structure in neutron-rich 110,111Tc

The structure of Tc nuclei is extended to the moreneutron-rich regions based on measurements of prompt gamma rays from thespontaneous fission of 252Cf at Gammasphere. The level scheme of N=67neutron-rich (Z=43) 110Tc is established for the first time and that of111Tc is expanded. The ground-state band of 111Tc reaches theband-crossing region and the new observation of the weakly populatedalpha = -1/2 member of the band provides important information ofsignature splitting. The systematics of band crossings in the isotopicand isotonic chains and a CSM calculation suggest that the band crossingof the gs band of 111Tc is due to alignment of a pair of h11/2 neutrons.The best fit to signature splitting, branching ratios, and excitations ofthe ground-state band of 111Tc by RTRP model calculations result in ashape of epsilon2 = 0.32 and gamma = -26 deg. for this nucleus. Itstriaxiality is larger than that of 107Tc, to indicate increasingtriaxiality with increasing neutron number. The identification of theweakly-populated "K+2 satellite" band provides strong evidence for thelarge triaxiality of 111Tc. In 110Tc the four lowest-lying levelsobserved are very similar to those in 108Tc. At an excitation of 478.9keV above the lowest state observed, ten states of a delta I = 1 band areobserved. This …
Date: February 2, 2006
Creator: Luo, Y. X.; Hamilton, J. H.; Rasmussen, J. O.; Ramayya, A. V.; Stefanescu, I.; Hwang, J. K. et al.
System: The UNT Digital Library
Automatic Quenching of High Energy gamma-ray Sources by Synchrotron Photons (open access)

Automatic Quenching of High Energy gamma-ray Sources by Synchrotron Photons

Here we investigate evolution of a magnetized system, in which continuously produced high energy emission undergoes annihilation on a soft photon field, such that the synchrotron radiation of the created electron-positron pairs increases number density of the soft photons. This situation is important in high energy astrophysics, because, for an extremely wide range of magnetic field strengths (nano to mega Gauss), it involves {gamma}-ray photons with energies between 0.3GeV and 30TeV. We derive and analyze the conditions for which the system is unstable to runaway production of soft photons and ultrarelativistic electrons, and for which it can reach a steady state with an optical depth to photon-photon annihilation larger than unity, as well those for which efficient pair loading of the emitting volume takes place. We also discuss the application of our analysis to a realistic situation involving astrophysical sources of a broad-band {gamma}-ray emission and briefly consider the particular case of sources close to active supermassive black holes.
Date: February 2, 2007
Creator: Stawarz, Lukasz; /KIPAC, Menlo Park /SLAC /Jagiellonian U., Astron. Observ.; Kirk, John & /Heidelberg, Max Planck Inst.
System: The UNT Digital Library
FTIR and Raman Study of the LixTiyMn1-yO2 (y = 0, 0.11) Cathodes in Methylpropyl Pyrrolidinium Bis(fluoro-sulfonyl)imide, LiTFSI Electrolyte (open access)

FTIR and Raman Study of the LixTiyMn1-yO2 (y = 0, 0.11) Cathodes in Methylpropyl Pyrrolidinium Bis(fluoro-sulfonyl)imide, LiTFSI Electrolyte

This work demonstrates the protective effect of partial titanium substitution in Li{sub x}Ti{sub 0.11}Mn{sub 0.89}O{sub 2} against surface decomposition in room-temperature ionic liquid (RTILs) cells. Raman microscopy and reflectance Fourier transform IR (FTIR) spectroscopy were used to analyze electrodes recovered from cycled Li/Li{sub x}Ti{sub y}Mn{sub 1-y}O{sub 2} (y=0, 0.11) cells containing the 0.5 mol/kg LiTFSI in P{sub 13}FSI RTIL electrolyte. [TFSI=bis(trifluoromethanesulfonyl)imide.] Raman and FTIR spectra of cycled Li{sub x}MnO{sub 2} cathodes showed many distinct bands that can be attributed to both the electrolyte and electrode decomposition products. The thickness of the amorphous porous layer on the Li{sub x}MnO{sub 2} cathode increased during cycling. The surface degradation of Li{sub x}MnO{sub 2} and precipitation of electrolyte decomposition products contributed to the film growth. Improved cycling behavior was observed in cells containing Li{sub x}Ti{sub 0.11}Mn{sub 0.89}O{sub 2}, yet Raman spectroscopy also showed possible surface degradation. The FTIR spectra of cycled Li{sub x}MnO{sub 2} and Li{sub x}Ti{sub 0.11}Mn{sub 0.89}O{sub 2} cathodes displayed bands characteristic for LiSO{sub 3}CF{sub 3} and Li{sub 2}NSO{sub 2}CF{sub 3}, which originate from the reaction of the TFSI anion with traces of water present in the cell.
Date: February 2, 2009
Creator: Hardwick, L.J.; Lucas, I.T.; Doeff, M.M.; Kostecki, R. & Saint, J.A.
System: The UNT Digital Library
Parallel simulation of beam-beam interaction in high energy accelerators (open access)

Parallel simulation of beam-beam interaction in high energy accelerators

In this paper, we present a self-consistent simulation model of beam-beam interaction in high energy accelerators. Using a parallel particle-in-cell approach, we have calculated the electromagnetic fields between two colliding beams. Dynamic load balance is implemented to improve the parallel efficiency. A preliminary performance test on IBM SP Power3, Cray T3E and PC cluster is presented. As an application, we studied the coherent beam-beam oscillation in the proposed Large Hadron Collider.
Date: February 2, 2002
Creator: Qiang, Ji; Furman, Miguel A. & Ryne, Robert D.
System: The UNT Digital Library