Reversible Guest Exchange Mechanisms in Supramolecular Host-Guest Assemblies (open access)

Reversible Guest Exchange Mechanisms in Supramolecular Host-Guest Assemblies

Synthetic chemists have provided a wide array of supramolecular assemblies able to encapsulate guest molecules. The scope of this tutorial review focuses on supramolecular host molecules capable of reversibly encapsulating polyatomic guests. Much work has been done to determine the mechanism of guest encapsulation and guest release. This review covers common methods of monitoring and characterizing guest exchange such as NMR, UV-VIS, mass spectroscopy, electrochemistry, and calorimetry and also presents representative examples of guest exchange mechanisms. The guest exchange mechanisms of hemicarcerands, cucurbiturils, hydrogen-bonded assemblies, and metal-ligand assemblies are discussed. Special attention is given to systems which exhibit constrictive binding, a motif common in supramolecular guest exchange systems.
Date: September 1, 2006
Creator: Pluth, Michael D. & Raymond, Kenneth N.
Object Type: Article
System: The UNT Digital Library
Optomechanical considerations for the VISAR diagnostic at the National Ignition Facility (NIF) (open access)

Optomechanical considerations for the VISAR diagnostic at the National Ignition Facility (NIF)

The National Ignition Facility (NIF) requires optical diagnostics for measuring shock velocities in shock physics experiments. The velocity interferometer for any reflector measures shock velocities at a location remote to the NIF target chamber. Our team designed two systems, one for a polar port orientation, and the other to accommodate two equatorial ports. The polar-oriented design requires a 48-m optical relay to move the light from inside the target chamber to a separately housed measurement and laser illumination station. The currently operational equatorial design requires a much shorter relay of 21 m. Both designs posed significant optomechanical challenges due to the long optical path length, large quantity of optical elements, and stringent NIF requirements. System design had to tightly control the use of lubricants and materials, especially those inside the vacuum chamber; tolerate earthquakes and radiation; and consider numerous other tolerance, alignment, and steering adjustment issues. To ensure compliance with NIF performance requirements, we conducted a finite element analysis.
Date: September 1, 2006
Creator: Kaufman, Morris I.; Celeste, John R.; Frogget, Brent C.; Lee, Tony L.; GacGowan, Brian J.; Malone, Robert M. et al.
Object Type: Article
System: The UNT Digital Library
Use of simulated data sets to evaluate the fidelity of Metagenomic processing methods (open access)

Use of simulated data sets to evaluate the fidelity of Metagenomic processing methods

Metagenomics is a rapidly emerging field of research for studying microbial communities. To evaluate methods presently used to process metagenomic sequences, we constructed three simulated data sets of varying complexity by combining sequencing reads randomly selected from 113 isolate genomes. These data sets were designed to model real metagenomes in terms of complexity and phylogenetic composition. We assembled sampled reads using three commonly used genome assemblers (Phrap, Arachne and JAZZ), and predicted genes using two popular gene finding pipelines (fgenesb and CRITICA/GLIMMER). The phylogenetic origins of the assembled contigs were predicted using one sequence similarity--based (blast hit distribution) and two sequence composition--based (PhyloPythia, oligonucleotide frequencies) binning methods. We explored the effects of the simulated community structure and method combinations on the fidelity of each processing step by comparison to the corresponding isolate genomes. The simulated data sets are available online to facilitate standardized benchmarking of tools for metagenomic analysis.
Date: December 1, 2006
Creator: Mavromatis, Konstantinos; Ivanova, Natalia; Barry, Kerri; Shapiro, Harris; Goltsman, Eugene; McHardy, Alice C. et al.
Object Type: Article
System: The UNT Digital Library
Microprocessor-controlled, wide-range streak camera (open access)

Microprocessor-controlled, wide-range streak camera

Bechtel Nevada/NSTec recently announced deployment of their fifth generation streak camera. This camera incorporates many advanced features beyond those currently available for streak cameras. The arc-resistant driver includes a trigger lockout mechanism, actively monitors input trigger levels, and incorporates a high-voltage fault interrupter for user safety and tube protection. The camera is completely modular and may deflect over a variable full-sweep time of 15 nanoseconds to 500 microseconds. The camera design is compatible with both large- and small-format commercial tubes from several vendors. The embedded microprocessor offers Ethernet connectivity, and XML [extensible markup language]-based configuration management with non-volatile parameter storage using flash-based storage media. The camera’s user interface is platform-independent (Microsoft Windows, Unix, Linux, Macintosh OSX) and is accessible using an AJAX [asynchronous Javascript and XML]-equipped modem browser, such as Internet Explorer 6, Firefox, or Safari. User interface operation requires no installation of client software or browser plug-in technology. Automation software can also access the camera configuration and control using HTTP [hypertext transfer protocol]. The software architecture supports multiple-simultaneous clients, multiple cameras, and multiple module access with a standard browser. The entire user interface can be customized.
Date: September 1, 2006
Creator: Amy E. Lewis, Craig Hollabaugh
Object Type: Article
System: The UNT Digital Library
Radial Particle Flux in the SOL of DIII-D During ELMing H-Mode (open access)

Radial Particle Flux in the SOL of DIII-D During ELMing H-Mode

The radial particle flux in the scrape-off-layer (SOL) during ELMing H-mode is examined in DIII-D as a function of density. The global radial particle flux in the outboard far SOL is determined by a window frame technique. Between ELMs the outboard far SOL particle flux increases strongly with density but remains similar to the particle flux across the separatrix as estimated by the pedestal density and temperature gradients. At low density the steep density gradient of the pedestal extends up to 2 cm outside the separatrix. At high density the density gradient flattens just outside the separatrix making this region critical for assessment of the far SOL particle flux. During ELMs the far SOL particle flux becomes localized to the outboard midplane and the assumptions for the window frame analysis break down. Implications for scaling of main chamber wall particle flux and pedestal fueling are explored.
Date: June 1, 2006
Creator: Leonard, A. W.; Boedo, J. A.; Groth, M.; Lipschultz, B. L.; Porter, G. D.; Rudakov, D. L. et al.
Object Type: Article
System: The UNT Digital Library
Cracking and Corrosion of Composite Tubes in Black Liquor Recovery Boiler Primary Air Ports (open access)

Cracking and Corrosion of Composite Tubes in Black Liquor Recovery Boiler Primary Air Ports

This report addresses the cracking and corrosion of composite tubes in black liquor recovery boiler primary air ports.
Date: October 1, 2006
Creator: Keiser, James R.; Singbeil, Douglas; Gorti, Sarma B.; Kish, Joseph R.; Yuan, Jianwei; Frederick, Laurel A. et al.
Object Type: Report
System: The UNT Digital Library
Deployment Notes for Sodars at the Stevens Institute of Technology during the March 2005 Urban Dispersion Program Field Campaign (MSG05) (open access)

Deployment Notes for Sodars at the Stevens Institute of Technology during the March 2005 Urban Dispersion Program Field Campaign (MSG05)

This report documents the deployment of two sodars at the Stevens Institute of Technology (SIT) in Hoboken, New Jersey, during the March 2005 Madison Square Garden Urban Dispersion Field Campaign (MSG05) conducted in the vicinity of Madison Square Garden in Midtown Manhattan. One sodar was a Scintec MFAS sodar that was operated on a dock along the Hudson River. This sodar was only operated during Intensive Observation Periods (IOPs). The other sodar was an AeroVironment (AV) Model 3000 MiniSodar that was located on top of the Howe Center at SIT. This sodar was operated continually, but there were data quality issues in the lowest three and upper seven range gates during non-IOP periods. The IOP data from the AeroVironment was reprocessed so that only data from the lowest three and highest seven range gates was removed. Measurements from both sodars were compared to measurements made using a propeller and vane anemometer that was also located on top of the Howe Center. This report also describes the quality control methods applied to data from each sodar and the structure of the data files available. The agreement between the sodars is generally good, and we recommend using either the AV data or …
Date: August 1, 2006
Creator: Berg, Larry K. & Allwine, K Jerry
Object Type: Report
System: The UNT Digital Library
Performance Modeling and Optimization of a High Energy Colliding Beam Simulation Code (open access)

Performance Modeling and Optimization of a High Energy Colliding Beam Simulation Code

An accurate modeling of the beam-beam interaction is essential to maximizing the luminosity in existing and future colliders. BeamBeam3D was the first parallel code that can be used to study this interaction fully self-consistently on high-performance computing platforms. Various all-to-all personalized communication (AAPC) algorithms dominate its communication patterns, for which we developed a sequence of performance models using a series of micro-benchmarks. We find that for SMP based systems the most important performance constraint is node-adapter contention, while for 3D-Torus topologies good performance models are not possible without considering link contention. The best average model prediction error is very low on SMP based systems with of 3% to 7%. On torus based systems errors of 29% are higher but optimized performance can again be predicted within 8% in some cases. These excellent results across five different systems indicate that this methodology for performance modeling can be applied to a large class of algorithms.
Date: June 1, 2006
Creator: Shan, Hongzhang; Strohmaier, Erich; Qiang, Ji; Bailey, David H. & Yelick, Kathy
Object Type: Article
System: The UNT Digital Library
Corrosion Performance of Ferritic Steel for SOFC Interconnect Applications (open access)

Corrosion Performance of Ferritic Steel for SOFC Interconnect Applications

Ferritic stainless steels have been identified as potential candidates for interconnects in planar-type solid oxide fuel cells (SOFC) operating below 800ºC. Crofer 22 APU was selected for this study. It was studied under simulated SOFC-interconnect dual environment conditions with humidified air on one side of the sample and humidified hydrogen on the other side at 750ºC. The surfaces of the oxidized samples were studied by scanning electron microscopy (SEM) equipped with microanalytical capabilities. X-ray diffraction (XRD) analysis was also used in this study.
Date: November 1, 2006
Creator: Ziomek-Moroz, M.; Holcomb, G. R.; Covino, B. S., Jr.; Bullard, S. J.; Jablonski, P. D. & Alman, D. E.
Object Type: Article
System: The UNT Digital Library
Quantum Mechanical Single Molecule Partition Function from Path Integral Monte Carlo Simulations (open access)

Quantum Mechanical Single Molecule Partition Function from Path Integral Monte Carlo Simulations

An algorithm for calculating the partition function of a molecule with the path integral Monte Carlo method is presented. Staged thermodynamic perturbation with respect to a reference harmonic potential is utilized to evaluate the ratio of partition functions. Parallel tempering and a new Monte Carlo estimator for the ratio of partition functions are implemented here to achieve well converged simulations that give an accuracy of 0.04 kcal/mol in the reported free energies. The method is applied to various test systems, including a catalytic system composed of 18 atoms. Absolute free energies calculated by this method lead to corrections as large as 2.6 kcal/mol at 300 K for some of the examples presented.
Date: October 1, 2006
Creator: Chempath, Shaji; Bell, Alexis T. & Predescu, Cristian
Object Type: Article
System: The UNT Digital Library
National Emission Standards for Hazardous Air Pollutants Calendar Year 2005 (open access)

National Emission Standards for Hazardous Air Pollutants Calendar Year 2005

The Nevada Test Site (NTS) is operated by the U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office (NNSA/NSO). From 1951 through 1992, the NTS was operated as the nation’s site for nuclear weapons testing. The release of man-made radionuclides from the NTS as a result of testing activities has been monitored since the first decade of atmospheric testing. After 1962, when nuclear tests were conducted only underground, the radiation exposure to the public surrounding the NTS was greatly reduced. After the 1992 moratorium on nuclear testing, radiation monitoring on the NTS focused on detecting airborne radionuclides that are resuspended into the air (e.g., by winds, dust-devils) along with historically-contaminated soils on the NTS. To protect the public from harmful levels of man-made radiation, the Clean Air Act, National Emission Standards for Hazardous Air Pollutants (NESHAP) (40 Code of Federal Regulations 61 Subpart H) limits the release of radioactivity from a U. S. Department of Energy (DOE) facility (e.g., the NTS) to 10 millirem per year (mrem/yr) effective dose equivalent (EDE) to any member of the public. This is the dose limit established for someone living off of the NTS for inhaling radioactive particles that may be carried …
Date: June 1, 2006
Creator: Bechtel Nevada (Firm)
Object Type: Report
System: The UNT Digital Library
An Aerial Radiological Survey of the Yucca Mountain Project Proposed Land Withdrawal and Adjacent Areas (open access)

An Aerial Radiological Survey of the Yucca Mountain Project Proposed Land Withdrawal and Adjacent Areas

An aerial radiological survey of the Yucca Mountain Project (YMP) proposed land withdrawal was conducted from January to April 2006, and encompassed a total area of approximately 284 square miles (73,556 hectares). The aerial radiological survey was conducted to provide a sound technical basis and rigorous statistical approach for determining the potential presence of radiological contaminants in the Yucca Mountain proposed Land withdrawal area. The survey site included land areas currently managed by the Bureau of Land Management, the U.S. Air Force as part of the Nevada Test and Training Range or the U.S. Department of Energy (DOE), National Nuclear Security Administration Nevada Site Office (NNSA/NSO) as part of the Nevada Test Site (NTS). The survey was flown at an approximate ground speed of 70 knots (36 meters per second), at a nominal altitude of 150 ft (46 m) above ground level, along a set of parallel flight lines spaced 250 ft (76 m) apart. The flight lines were oriented in a north-south trajectory. The survey was conducted by the DOE NNSA/NSO Remote Sensing Laboratory-Nellis, which is located in Las Vegas, Nevada. The aerial survey was conducted at the request of the DOE Office of Civilian Radioactive Waste Management. The …
Date: July 1, 2006
Creator: Craig Lyons, Thane Hendricks
Object Type: Report
System: The UNT Digital Library
Systematics and limit calculations (open access)

Systematics and limit calculations

This note discusses the estimation of systematic uncertainties and their incorporation into upper limit calculations. Two different approaches to reducing systematics and their degrading impact on upper limits are introduced. An improved {chi}{sup 2} function is defined which is useful in comparing Poisson distributed data with models marginalized by systematic uncertainties. Also, a technique using profile likelihoods is introduced which provides a means of constraining the degrading impact of systematic uncertainties on limit calculations.
Date: December 1, 2006
Creator: Fisher, Wade
Object Type: Report
System: The UNT Digital Library
STROBOSCOPIC IMAGE CAPTURE: REDUCING THE DOSE PER FRAME BY AFACTOR OF 30 DOES NOT PREVENT BEAM-INDUCED SPECIMEN MOVEMENT INPARAFFIN (open access)

STROBOSCOPIC IMAGE CAPTURE: REDUCING THE DOSE PER FRAME BY AFACTOR OF 30 DOES NOT PREVENT BEAM-INDUCED SPECIMEN MOVEMENT INPARAFFIN

Beam-induced specimen movement may be the major factor that limits the quality of high-resolution images of organic specimens. One of the possible measures to improve the situation that was proposed by Henderson and Glaeser (Henderson and Glaeser, 1985), which we refer to here as 'stroboscopic image capture', is to divide the normal exposure into many successive frames, thus reducing the amount of electron exposure--and possibly the amount of beam-induced movement--per frame. The frames would then be aligned and summed. We have performed preliminary experiments on stroboscopic imaging using a 200-kV electron microscope that was equipped with a high dynamic range CCD camera for image recording and a liquid N{sub 2}-cooled cryoholder. Single-layer paraffin crystals on carbon film were used as a test specimen. The ratio F(g)/F(0) of paraffin reflections, calculated from the images, serves as our criterion for the image quality. In the series that were evaluated, no significant improvement of the F{sub image}(g)/F{sub image}(0) ratio was found, even though the electron exposure per frame was reduced by a factor of 30. A frame-to-frame analysis of image distortions showed that considerable beam-induced movement had still occurred during each frame. In addition, the paraffin crystal lattice was observed to move relative …
Date: August 1, 2006
Creator: Typke, Dieter; Gilpin, Christopher J.; Downing, Kenneth H. & Glaeser, Robert M.
Object Type: Article
System: The UNT Digital Library
Developement of a same-side kaon tagging algorithm of B^0_s decays for measuring delta m_s at CDF II (open access)

Developement of a same-side kaon tagging algorithm of B^0_s decays for measuring delta m_s at CDF II

The authors developed a Same-Side Kaon Tagging algorithm to determine the production flavor of B{sub s}{sup 0} mesons. Until the B{sub s}{sup 0} mixing frequency is clearly observed the performance of the Same-Side Kaon Tagging algorithm can not be measured on data but has to be determined on Monte Carlo simulation. Data and Monte Carlo agreement has been evaluated for both the B{sub s}{sup 0} and the high statistics B{sup +} and B{sup 0} modes. Extensive systematic studies were performed to quantify potential discrepancies between data and Monte Carlo. The final optimized tagging algorithm exploits the particle identification capability of the CDF II detector. it achieves a tagging performance of {epsilon}D{sup 2} = 4.0{sub -1.2}{sup +0.9} on the B{sub s}{sup 0} {yields} D{sub s}{sup -} {pi}{sup +} sample. The Same-Side Kaon Tagging algorithm presented here has been applied to the ongoing B{sub s}{sup 0} mixing analysis, and has provided a factor of 3-4 increase in the effective statistical size of the sample. This improvement results in the first direct measurement of the B{sub s}{sup 0} mixing frequency.
Date: June 1, 2006
Creator: Menzemer, Stephanie & U., /Heidelberg
Object Type: Article
System: The UNT Digital Library
Results of the 2004 Knowledge and Opinions Surveys for the Baseline Knowledge Assessment of the U.S. Department of Energy Hydrogen Program (open access)

Results of the 2004 Knowledge and Opinions Surveys for the Baseline Knowledge Assessment of the U.S. Department of Energy Hydrogen Program

The U.S. Department of Energy (DOE) Hydrogen Program focuses on overcoming critical barriers to the widespread use of hydrogen fuel cell technology. The transition to a new, hydrogen-based energy economy requires an educated human infrastructure. With this in mind, the DOE Hydrogen Program conducted statistical surveys to measure and establish baselines for understanding and awareness about hydrogen, fuel cells, and a hydrogen economy. The baseline data will serve as a reference in designing an education program, and it will be used in comparisons with future survey results (2008 and 2011) to measure changes in understanding and awareness. Scientific sampling was used to survey four populations: (1) the general public, ages 18 and over; (2) students, ages 12-17; (3) state and local government officials; and (4) potential large-scale hydrogen users. It was decided that the survey design should include about 1,000 individuals in each of the general public and student categories, about 250 state and local officials, and almost 100 large-scale end users. The survey questions were designed to accomplish specific objectives. Technical questions measured technical understanding and awareness of hydrogen technology. Opinion questions measured attitudes about safety, cost, the environment, and convenience, as well as the likelihood of future applications …
Date: April 1, 2006
Creator: Schmoyer, Richard L; Truett, Lorena Faith & Cooper, Christy
Object Type: Report
System: The UNT Digital Library
Studying High pT muons in Cosmic-Ray Air Showers (open access)

Studying High pT muons in Cosmic-Ray Air Showers

Most cosmic-ray air shower arrays have focused on detectingelectromagnetic shower particles and low energy muons. A few groups (mostnotably MACRO + EASTOP and SPASE + AMANDA) have studied the high energymuon component of showers. However, these experiments had small solidangles, and did not study muons far from the core. The IceTop + IceCubecombination, with its 1 km$^2$ muon detection area can study muons farfrom the shower core. IceCube can measure their energy loss ($dE/dx$),and hence their energy. With the energy, and the known distribution ofproduction heights, the transverse momentum ($p_T$) spectrum of high$p_T$ muons can be determined. The production of the semuons iscalculable in perturbative QCD, so the measured muon spectra can be usedto probe the composition of incident cosmic-rays.
Date: December 1, 2006
Creator: Klein, Spencer R.
Object Type: Article
System: The UNT Digital Library
Laser sheet light flow visualization for evaluating room air flowsfrom Registers (open access)

Laser sheet light flow visualization for evaluating room air flowsfrom Registers

Forced air heating and cooling systems and whole house ventilation systems deliver air to individual rooms in a house via supply registers located on walls ceilings or floors; and occasionally less straightforward locations like toe-kicks below cabinets. Ideally, the air velocity out of the registers combined with the turbulence of the flow, vectoring of air by register vanes and geometry of register placement combine to mix the supply air within the room. A particular issue that has been raised recently is the performance of multiple capacity and air flow HVAC systems. These systems vary the air flow rate through the distribution system depending on the system load, or if operating in a ventilation rather than a space conditioning mode. These systems have been developed to maximize equipment efficiency, however, the high efficiency ratings do not include any room mixing effects. At lower air flow rates, there is the possibility that room air will be poorly mixed, leading to thermal stratification and reduced comfort for occupants. This can lead to increased energy use as the occupants adjust the thermostat settings to compensate and parts of the conditioned space have higher envelope temperature differences than for the well mixed case. In addition, …
Date: April 1, 2006
Creator: Walker, Iain S.; Claret, Valerie & Smith, Brian
Object Type: Report
System: The UNT Digital Library
Traveling waves and the renormalization group improvedBalitsky-Kovchegov equation (open access)

Traveling waves and the renormalization group improvedBalitsky-Kovchegov equation

I study the incorporation of renormalization group (RG)improved BFKL kernels in the Balitsky-Kovchegov (BK) equation whichdescribes parton saturation. The RG improvement takes into accountimportant parts of the next-to-leading and higher order logarithmiccorrections to the kernel. The traveling wave front method for analyzingthe BK equation is generalized to deal with RG-resummed kernels,restricting to the interesting case of fixed QCD coupling. The resultsshow that the higher order corrections suppress the rapid increase of thesaturation scale with increasing rapidity. I also perform a "diffusive"differential equation approximation, which illustrates that someimportant qualitative properties of the kernel change when including RGcorrections.
Date: December 1, 2006
Creator: Enberg, Rikard
Object Type: Article
System: The UNT Digital Library
Search for New Physics in the Jets + Missing ET topology (open access)

Search for New Physics in the Jets + Missing ET topology

Although the standard model of particle physics agrees perfectly with experimental data, it is unlikely the final theory describing particles and their interactions. New phenomena has been searched in the jets and missing transverse energy topology. Such phenomena may be due to the pair production of leptoquarks decaying into a quark and a neutrino or the pair production of stops decaying into a charm and a neutralino which is assumed to be the lightest supersymmetric particle. These searches have been performed with the D0 detector at hadronic collider TeVatron with a center of mass energy of 1.96 TeV. This kind of search needs a good understanding of the jet energy calibration. The determination of the relative jet energy scale has allowed them to reduce the systematic uncertainties on the jet energy measurement when comparing the data and the simulation. Moreover a new method has been developed in order to correct simulated jets for the differences observed in the jet energy scale, the jet energy resolution and the jet reconstruction efficiency between the data and the simulation. The data analysis, performed with an integrated luminosity of 310 pb{sup -1}, has not observed any excess. This result is interpreted in terms of …
Date: May 1, 2006
Creator: Makovec, Nikola Michel & /Orsay
Object Type: Thesis or Dissertation
System: The UNT Digital Library
Shillapoo Wildlife Area, Annual Report 2006-2007. (open access)

Shillapoo Wildlife Area, Annual Report 2006-2007.

This report summarizes accomplishments, challenges and successes on WDFW's Shillapoo Wildlife Area funded under Bonneville Power Administration's (BPA) Wildlife Mitigation Program (BPA project No.2003-012-00) during the Fiscal Year 07 contract period October 1, 2006-September 30, 2007. The information presented here is intended to supplement that contained in BPA's PISCES contract development and reporting system. The organization below is by broad categories of work but references are made to individual work elements in the PISCES Statement of Work as appropriate. The greatest success realized during this contract period was significant positive changes in the vegetative community in several wetland basins throughout the wildlife area. This major goal is being achieved in part by new equipment and operation capability funded under the BPA contract, state capital and migratory bird stamp funds, and the past or ongoing investment of other partners including Ducks Unlimited, The Natural Resources Conservation Service (NRCS), Clark Public Utilities and others. We continue to be challenged by requirements under the archaeological and historic preservation act necessary to protect many sensitive sites known to occur within the wildlife area. The problems encountered to date have been largely administrative in nature and those experienced this year were unforeseen and probably unavoidable. …
Date: October 1, 2006
Creator: Calkins, Brian
Object Type: Report
System: The UNT Digital Library
The structure of a-C: What NEXAFS and EXAFS see (open access)

The structure of a-C: What NEXAFS and EXAFS see

Mechanically hard ha-C and soft sa-C amorphous carbon films of 2.9 and 2.2 g cm-3 approximate densities were prepared by filtered cathodic arc deposition and analyzed by near-edge x-ray absorption spectroscopy NEXAFS and extended x-ray absorption spectroscopy EXAFS to determine their structure. The analysis observed an insignificant level of pi bond conjugation in both kind of films. EXAFS distinguished two types of atomic environments in them: one semiordered with well defined bond lengths, and the other with so strong bond disorder that its contribution to EXAFS was undetectable. The proportion of atoms in the semiordered atomic environments was of less than 40percent in both films. Their bond lengths were similar to those of diamond in the ha-C films and to graphite in the sa-C. NEXAFS spectra analysis was based on the linear relation between sigma* energy and bond length. It served to quantify the proportion of sp3 bonded atoms in a-C, to deduce the average bond length of the atoms undetected by EXAFS, and to determine the level of bond conjugation in the films. The sp3 concentration estimated with the proposed method was of 44percent in the ha-C films and 10percent in the sa-C films. These values were consistent with …
Date: August 1, 2006
Creator: Hussain, Zahid; Diaz, J.; Monteiro, O.R. & Hussain, Z.
Object Type: Article
System: The UNT Digital Library
Rolling Contact Fatigue of Ceramics (open access)

Rolling Contact Fatigue of Ceramics

High hardness, low coefficient of thermal expansion and high temperature capability are properties also suited to rolling element materials. Silicon nitride (Si{sub 3}N{sub 4}) has been found to have a good combination of properties suitable for these applications. However, much is still not known about rolling contact fatigue (RCF) behavior, which is fundamental information to assess the lifetime of the material. Additionally, there are several test techniques that are employed internationally whose measured RCF performances are often irreconcilable. Due to the lack of such information, some concern for the reliability of ceramic bearings still remains. This report surveys a variety of topics pertaining to RCF. Surface defects (cracks) in Si{sub 3}N{sub 4} and their propagation during RCF are discussed. Five methods to measure RCF are then briefly overviewed. Spalling, delamination, and rolling contact wear are discussed. Lastly, methods to destructively (e.g., C-sphere flexure strength testing) and non-destructively identify potential RCF-limiting flaws in Si{sub 3}N{sub 4} balls are described.
Date: September 1, 2006
Creator: Wereszczak, Andrew A.; Wang, W.; Wang, Y.; Hadfield, M.; Kanematsu, W.; Kirkland, Timothy Philip et al.
Object Type: Report
System: The UNT Digital Library
Material Removal and Specific Energy in the Dynamic Scratching of Gamma Titanium Aluminides (open access)

Material Removal and Specific Energy in the Dynamic Scratching of Gamma Titanium Aluminides

Mechanical responses of three gamma titanium aluminides (TiAls) (denoted as Alloy A, Alloy B and Alloy C) subjected to dynamic scratching were studied by using a single-grit pendulum (rotating) scratch tester. The maximum depth of groove was ~ 0.07 mm, and the scratch velocity used was ~ 1.0 m/s. Normal and tangential forces were monitored. The material removal mechanisms were examined using a scanning electron microscope (SEM) and the scratches were measured by using a laser profilometer. The mechanical properties of the tested TiAls were characterized by the instantaneous specific energy, scratch resistance and scratch hardness as related to the depth of groove. Extensive thermal softening was observed in the dynamic scratch of the tested TiAls, which facilitated both the detachments of developing chips and the pile-ups of materials on side ridges. Sizable fractures were observed in the transverse direction on the tested TiAls; these fractures tended to participate in the chip formation, depending on the microstructure of the TiAl and the size of the scratch groove. Specific energy and scratch hardness are depth-dependent to various degrees for the tested TiAls. The materiel removal might be subjected to different mechanisms, but the overall response of materials can be effectively characterized …
Date: November 1, 2006
Creator: Wang, Hong; Lin, Hua-Tay & Wereszczak, Andrew A.
Object Type: Report
System: The UNT Digital Library