301 Matching Results

Results open in a new window/tab.

Dose dependent effects of exercise training and detraining ontotal and regional adiposity in 4,663 men and 1,743 (open access)

Dose dependent effects of exercise training and detraining ontotal and regional adiposity in 4,663 men and 1,743

Objective: To determine if exercise reduces body weight andto examine the dose-response relationships between changes in exerciseand changes in total and regional adiposity. Methods and Results:Questionnaires on weekly running distance and adiposity from a largeprospective study of 3,973 men and 1,444 women who quit running(detraining), 270 men and 146 women who started running (training) and420 men and 153 women who remained sedentary during 7.4 years offollow-up. There were significant inverse relationships between change inthe amount of vigorous exercise (km/wk run) and changes in weight and BMIin men (slope+-SE:-0.039+-0.005 kg and -0.012+-0.002 kg/m2 per km/wk,respectively) and older women (-0.060+-0.018 kg and -0.022+-0.007 kg/m2per km/wk) who quit running, and in initially sedentary men(-0.098+-0.017 kg and -0.032+-0.005 kg/m2 per km/wk) and women(-0.062+-0.023 kg and -0.021+-0.008 kg/m2 per km/wk) who started running.Changes in waist circumference were also inversely related to changes inrunning distance in men who quit (-0.026+-0.005 cm per km/wk) or startedrunning (-0.078+-0.017 cm per km/wk). Conclusions. The initiation andcessation of vigorous exercise decrease and increase body weight andintra-abdominal fat, respectively, and these changes are proportional tothe change in exercise dose.
Date: January 6, 2006
Creator: Williams, Paul T. & Thompson, Paul D.
System: The UNT Digital Library
Metastable Solid Solution Phases in the LiFePO4/FePO4 System (open access)

Metastable Solid Solution Phases in the LiFePO4/FePO4 System

None
Date: January 2, 2006
Creator: Chen, Guoying Chen; Song, Xiangyun & Richardson, Thomas J.
System: The UNT Digital Library
Long Pulse High Performance Plasma Scenario Development for the National Spherical Torus Experiment (open access)

Long Pulse High Performance Plasma Scenario Development for the National Spherical Torus Experiment

The National Spherical Torus Experiment [Ono et al., Nucl. Fusion, 44, 452 (2004)] is targeting long pulse high performance, noninductive sustained operations at low aspect ratio, and the demonstration of nonsolenoidal startup and current rampup. The modeling of these plasmas provides a framework for experimental planning and identifies the tools to access these regimes. Simulations based on neutral beam injection (NBI)-heated plasmas are made to understand the impact of various modifications and identify the requirements for (1) high elongation and triangularity, (2) density control to optimize the current drive, (3) plasma rotation and/or feedback stabilization to operate above the no-wall limit, and (4) electron Bernstein waves (EBW) for off-axis heating/current drive (H/CD). Integrated scenarios are constructed to provide the transport evolution and H/CD source modeling, supported by rf and stability analyses. Important factors include the energy confinement, Zeff, early heating/H mode, broadening of the NBI-driven current profile, and maintaining q(0) and qmin>1.0. Simulations show that noninductive sustained plasmas can be reached at IP=800 kA, BT=0.5 T, 2.5, N5, 15%, fNI=92%, and q(0)>1.0 with NBI H/CD, density control, and similar global energy confinement to experiments. The noninductive sustained high plasmas can be reached at IP=1.0 MA, BT=0.35 T, 2.5, N9, 43%, …
Date: January 1, 2006
Creator: Kessel, C.E.; Bell, R.E.; Bell, M.G.; Gates, D.A. & Harvey, R.W.
System: The UNT Digital Library
The complete chloroplast genome sequence of Pelargonium xhortorum: Or ganization and evolution of the largest and most highlyrearranged chloroplast genome of land plants (open access)

The complete chloroplast genome sequence of Pelargonium xhortorum: Or ganization and evolution of the largest and most highlyrearranged chloroplast genome of land plants

The chloroplast genome of Pelargonium e hortorum has beencompletely sequenced. It maps as a circular molecule of 217,942 bp, andis both the largest and most rearranged land plant chloroplast genome yetsequenced. It features two copies of a greatly expanded inverted repeat(IR) of 75,741 bp each, and consequently diminished single copy regionsof 59,710 bp and 6,750 bp. It also contains two different associations ofrepeated elements that contribute about 10 percent to the overall sizeand account for the majority of repeats found in the genome. Theyrepresent hotspots for rearrangements and gene duplications and include alarge number of pseudogenes. We propose simple models that account forthe major rearrangements with a minimum of eight IR boundary changes and12 inversions in addition to a several insertions of duplicated sequence.The major processes at work (duplication, IR expansion, and inversion)have disrupted at least one and possibly two or three transcriptionaloperons, and the genes involved in these disruptions form the core of thetwo major repeat associations. Despite the vast increase in size andcomplexity of the genome, the gene content is similar to that of otherangiosperms, with the exceptions of a large number of pseudogenes as partof the repeat associations, the recognition of two open reading frames(ORF56 and ORF42) …
Date: January 20, 2006
Creator: Chumley, Timothy W.; Palmer, Jeffrey D.; Mower, Jeffrey P.; Fourcade, H. Matthew; Calie, Patrick J.; Boore, Jeffrey L. et al.
System: The UNT Digital Library
An analysis of model tropospheric response to various forcings (open access)

An analysis of model tropospheric response to various forcings

None
Date: January 30, 2006
Creator: Hnilo, J J & Christy, J R
System: The UNT Digital Library
MCNP Comparison With Point Source Measurements From a Portable HPGe System (open access)

MCNP Comparison With Point Source Measurements From a Portable HPGe System

The Ortec trans-SPEC is a portable gamma ray spectrometer which is approximately 10.4 kg in total weight and 37 cm × 16 cm × 32 cm in overall size It utilizes a P-type 50 mm diameter and 30 mm height coaxial HPGe detector and has more than 3 hours of battery life when fully charged. This paper details the experimental agreement found for one of these detector units and that of MCNP5 [1] calculations. The purpose of carrying out this work is to evaluate the potential utility of the spectrometer for emergency response (consequence management) applications.
Date: January 1, 2006
Creator: Hayes, Robert
System: The UNT Digital Library
Meta-Analyses of the Associations of Respiratory Health Effectswith Dampness and Mold in Homes (open access)

Meta-Analyses of the Associations of Respiratory Health Effectswith Dampness and Mold in Homes

The Institute of Medicine (IOM) of the National Academy of Sciences recently completed a critical review of the scientific literature pertaining to the association of indoor dampness and mold contamination with adverse health effects. In this paper, we report the results of quantitative meta-analysis of the studies reviewed in the IOM report. We developed point estimates and confidence intervals (CIs) to summarize the association of several respiratory and asthma-related health outcomes with the presence of dampness and mold in homes. The odds ratios and confidence intervals from the original studies were transformed to the log scale and random effect models were applied to the log odds ratios and their variance. Models were constructed both accounting for the correlation between multiple results within the studies analyzed and ignoring such potential correlation. Central estimates of ORs for the health outcomes ranged from 1.32 to 2.10, with most central estimates between 1.3 and 1.8. Confidence intervals (95%) excluded unity except in two of 28 instances, and in most cases the lower bound of the CI exceeded 1.2. In general, the two meta-analysis methods produced similar estimates for ORs and CIs. Based on the results of the meta-analyses, building dampness and mold are associated …
Date: January 1, 2006
Creator: Fisk, William J.; Lei-Gomez, Quanhong & Mendell, Mark J.
System: The UNT Digital Library
Shear-slip analysis in multiphase fluid-flow reservoir engineeringap plications using TOUGH-FLAC (open access)

Shear-slip analysis in multiphase fluid-flow reservoir engineeringap plications using TOUGH-FLAC

This paper describes and demonstrates the use of the coupledTOUGH-FLAC simulator for geomechanical shear-slip (failure) analysis inmultiphase fluid-flow reservoir-engineering applications. Two approachesfor analyzing shear-slip are described, one using continuum stress-strainanalysis and another using discrete fault analysis. The use of shear-slipanalysis in TOUGH-FLAC is demonstrated on application examples related toCO2 sequestration and geothermal energy extraction. In the case of CO2sequestration, the shear-slip analysis is used to evaluate maximumsustainable CO2-injection pressure under increasing reservoir pressure,whereas in the case of geothermal energy extraction, the shear-slipanalysis is used to study induced seismicity during steam productionunder decreasing reservoir pressure and temperature.
Date: January 15, 2006
Creator: Rutqvist, Jonny; Birkholzer, Jens; Cappa, Frederic; Oldenburg,Curt & Tsang, Chin-Fu
System: The UNT Digital Library
Modeling Hydrogeological and Geomenchanical Processes Related toCO2 Injection in a Faulted Multilayer System (open access)

Modeling Hydrogeological and Geomenchanical Processes Related toCO2 Injection in a Faulted Multilayer System

This paper presents a numerical study of coupled hydrological and geomechanical processes during a deep underground injection of supercritical CO{sub 2} in a hypothetical brine aquifer. We consider a multilayer system in which the injection zone is situated below a sequence of caprock and aquifer layers that are intersected by a vertical fault zone. The fault zone consists of highly fractured shale across the first caprock layers that are located just above the injection zone. Initially, the fractured shale zones are considered sealed with minerals, but we allow fractures (and the fractured zones) to open as a result of injection induced reductions in effective stresses. Our results indicate that even when assuming a very sensitive relationship between effective stress and fractured-zone permeability, the injection-induced changes in permeability across are only moderate with largest changes occurring in the first caprock layer, just above the injection zone. As a result, the upward leakage rate remains relatively small and therefore changes in fluid pressure and hydromechanical effects in overlying zones are also relatively small for the case studied in this paper.
Date: January 1, 2006
Creator: Rutqvist, Jonny; Birkholzer, Jens & Tsang, Chin-Fu
System: The UNT Digital Library
Efficient computation of matched solutions of the KV envelope equations for periodic focusing lattices. (open access)

Efficient computation of matched solutions of the KV envelope equations for periodic focusing lattices.

A new iterative method is developed to numerically calculate the periodic, matched beam envelope solution of the coupled Kapchinskij-Vladimirskij (KV) equations describing the transverse evolution of a beam in a periodic, linear focusing lattice of arbitrary complexity. Implementation of the method is straightforward. It is highly convergent and can be applied to all usual parameterizations of the matched envelope solutions. The method is applicable to all classes of linear focusing lattices without skew couplings, and also applies to parameters where the matched beam envelope is strongly unstable. Example applications are presented for periodic solenoidal and quadrupole focusing lattices. Convergence properties are summarized over a wide range of system parameters.
Date: January 17, 2006
Creator: Lund, S M; Chilton, S H & Lee, E P
System: The UNT Digital Library
Causes of Ocean Surface temperature Changes in Atlantic andPacific Topical Cyclogenesis Regions (open access)

Causes of Ocean Surface temperature Changes in Atlantic andPacific Topical Cyclogenesis Regions

Previous research has identified links between changes in sea surface temperature (SST) and hurricane intensity. We use climate models to study the possible causes of SST changes in Atlantic and Pacific tropical cyclogenesis regions. The observed SST increases in these regions range from 0.32 to 0.67 C over the 20th century. The 22 climate models examined here suggest that century-timescale SST changes of this magnitude cannot be explained solely by unforced variability of the climate system, even under conservative assumptions regarding the magnitude of this variability. Model simulations that include external forcing by combined anthropogenic and natural factors are generally capable of replicating observed SST changes in both tropical cyclogenesis regions.
Date: January 31, 2006
Creator: Santer, B. D.; Wigley, T. M. L.; Gleckler, P. J.; Bonfils, C.; Wehner, M. F.; AchutaRao, K. et al.
System: The UNT Digital Library
Complete chloroplast genome of Trachelium caeruleum: extensiverearrangements are associated with repeats and tRNAs (open access)

Complete chloroplast genome of Trachelium caeruleum: extensiverearrangements are associated with repeats and tRNAs

Chloroplast genome structure, gene order and content arehighly conserved in land plants. We sequenced the complete chloroplastgenome sequence of Trachelium caeruleum (Campanulaceae) a member of anangiosperm family known for highly rearranged chloroplast genomes. Thetotal genome size is 162,321 bp with an IR of 27,273 bp, LSC of 100,113bp and SSC of 7,661 bp. The genome encodes 115 unique genes, with 19duplicated in the IR, a tRNA (trnI-CAU) duplicated once in the LSC and aprotein coding gene (psbJ) duplicated twice, for a total of 137 genes.Four genes (ycf15, rpl23, infA and accD) are truncated and likelynonfunctional; three others (clpP, ycf1 and ycf2) are so highly divergedthat they may now be pseudogenes. The most conspicuous feature of theTrachelium genome is the presence of eighteen internally unrearrangedblocks of genes that have been inverted or relocated within the genome,relative to the typical gene order of most angiosperm chloroplastgenomes. Recombination between repeats or tRNAs has been suggested as twomeans of chloroplast genome rearrangements. We compared the relativenumber of repeats in Trachelium to eight other angiosperm chloroplastgenomes, and evaluated the location of repeats and tRNAs in relation torearrangements. Trachelium has the highest number and largest repeats,which are concentrated near inversion endpoints or other rearrangements.tRNAs occur at …
Date: January 9, 2006
Creator: Haberle, Rosemarie C.; Fourcade, Matthew L.; Boore, Jeffrey L. & Jansen, Robert K.
System: The UNT Digital Library
Outrunning major weight gain: a prospective study of 8,340consistent runners during 7 years of follow-up (open access)

Outrunning major weight gain: a prospective study of 8,340consistent runners during 7 years of follow-up

Background: Body weight increases with aging. Short-term,longitudinal exercise training studies suggest that increasing exerciseproduces acute weight loss, but it is not clear if the maintenance oflong-term, vigorous exercise attenuates age-related weight gain inproportion to the exercise dose. Methods: Prospective study of 6,119 maleand 2,221 female runners whose running distance changed less than 5 km/wkbetween their baseline and follow-up survey 7 years later. Results: Onaverage, men who ran modest (0-24 km/wk), intermediate (24-48 km/wk) orprolonged distances (>_48 km/wk) all gained weight throughage 64,however, those who ran ?48 km/wk had one-half the average annual weightgain of those who ran<24 km/wk. Age-related weight gain, and itsreduction by running, were both greater in younger than older men. Incontrast, men s gain in waist circumference with age, and its reductionby running, were the same in older and younger men. Women increased theirbody weight and waist and hip circumferences over time, regardless ofage, which was also reduced in proportion to running distance. In bothsexes, running did not attenuate weight gain uniformly, but ratherdisproportionately prevented more extreme increases. Conclusion: Men andwomen who remain vigorously active gain less weight as they age and thereduction is in proportion to the exercise dose.
Date: January 6, 2006
Creator: Williams, Paul T.
System: The UNT Digital Library
Exaggerated Health Benefits of Physical Fitness and Activity dueto Self-selection. (open access)

Exaggerated Health Benefits of Physical Fitness and Activity dueto Self-selection.

Background: The predicted health benefits of becomingphysically active or fit will be exaggerated if health outcomes causefitness and activity rather than the converse in prospective andcross-sectional epidemiological studies. Objective: Assess whether therelationships of adiposity to fitness and activity are explained byadiposity prior to exercising. Design: Cross-sectional study of physicalfitness (running speed during 10km foot race) and physical activity(weekly running distance) to current BMI (BMIcurrent) and BMI at thestart of running (BMIstarting) in 44,370 male and 25,252 femaleparticipants of the National Runners' Health Study. Results: BMIstartingexplained all of the association between fitness and BMIcurrent in bothsexes, but less than a third of the association between physical activityand BMIcurrent in men. In women, BMIstarting accounted for 58 percent ofthe association between BMIcurrent and activity levels. The 95thpercentile of BMIcurrent showed substantially greater declines withfitness and activity levels than the 5th percentile of BMIcurrent in men(i.e., the negative slope for 95th percentile was 2.6-fold greater thanthe 5th percentile for fitness and 3-fold greater for activity) and women(6-fold and 3.4-fold greater, respectively). At all percentiles, theregression slopes relating BMIstarting to fitness were comparable orgreater (more negative) than the slopes relating BMIcurrent to fitness,whereas the converse was true for activity. Conclusion: Self-selectionbias accounts for all …
Date: January 17, 2006
Creator: Williams, Paul T.
System: The UNT Digital Library
Gel Electrophoresis of Gold-DNA Nano-Conjugates (open access)

Gel Electrophoresis of Gold-DNA Nano-Conjugates

Single stranded DNA of different lengths and different amounts was attached to colloidal phosphine stabilized Au nanoparticles. The resulting conjugates were investigated in detail by a gel electrophoresis study based on 1200 gels. We demonstrate how these experiments help to understand the binding of DNA to Au particles. In particular we compare specific attachment of DNA via gold-thiol bonds with nonspecific adsorption of DNA. The maximum number of DNA molecules that can be bound per particle was determined. We also compare several methods to used gel electrophoresis for investigating the effective diameter of DNA-Au conjugates, such as using a calibration curve of particles with known diameters and Ferguson plots.
Date: January 10, 2006
Creator: Pellegrino, T.; Sperling, R. A.; Alivisatos, A. P. & Parak, W. J.
System: The UNT Digital Library
On-site Analysis of Explosives in Various Matrices (open access)

On-site Analysis of Explosives in Various Matrices

Lawrence Livermore National Laboratory (LLNL) has developed several different strategies and technologies for the on-site detection of explosives. These on-site detection techniques include a colorimetric test, thin layer chromatography (TLC) kit and portable gas chromatography mass spectrometer (GC/MS). The screening of suspicious containers on-site and the search for trace explosive residue in a post-blast forensic investigation are of great importance. For these reasons, LLNL's Forensic Science Center has developed a variety of fieldable detection technologies to screen for a wide range of explosives in various matrices and scenarios. Ideally, what is needed is a fast, accurate, easy-to-use, pocket-size and inexpensive field screening test for explosives.
Date: January 25, 2006
Creator: Reynolds, J. G.; Nunes, P.; Whipple, R. E. & Alcaraz, A.
System: The UNT Digital Library
Chemical Force Microscopy of Chemical and Biological Interactions (open access)

Chemical Force Microscopy of Chemical and Biological Interactions

Interactions between chemical functionalities define outcomes of the vast majority of important events in chemistry, biology and materials science. Chemical Force Microscopy (CFM)--a technique that uses direct chemical functionalization of AFM probes with specific functionalities--allows researchers to investigate these important interactions directly. We review the basic principles of CFM, some examples of its application, and theoretical models that provide the basis for understanding the experimental results. We also emphasize application of modern kinetic theory of non-covalent interactions strength to the analysis of CFM data.
Date: January 2, 2006
Creator: Noy, A
System: The UNT Digital Library
Using higher order modes in superconducting accelerating cavities for beam monitoring (open access)

Using higher order modes in superconducting accelerating cavities for beam monitoring

Dipole modes have been shown to be successful diagnostics for the beam position in superconducting accelerating cavities at the Free Electron Laser in Hamburg (FLASH) facility at DESY. By help of downmixing electronics the signals from the two higher order mode (HOM) couplers mounted on each cavity are monitored. The calibration, based on sigular value decomposition, is more complicated than in standard position monitors. Position like signals based on this calibration are currently being in the process of being included in the control system. A second setup based on digitizing the spectrum from the HOM couplers has been used for monitoring monopole modes. The beam phase with respect to the RF has been thus monitored. The position calibration measurements and phase monitoring made at the FLASH are presented.
Date: January 1, 2006
Creator: Molloy, S.; Baboi, N.; Eddy, N.; Frisch, J.; Hendrickson, L.; Hensler, O. et al.
System: The UNT Digital Library
TEM studies of laterally overgrown GaN layers grown on non-polarsubstrates (open access)

TEM studies of laterally overgrown GaN layers grown on non-polarsubstrates

Transmission electron microscopy (TEM) was used to study pendeo-epitaxial GaN layers grown on polar and non-polar 4H SiC substrates. The structural quality of the overgrown layers was evaluated using a number of TEM methods. Growth of pendeo-epitaxial layers on polar substrates leads to better structural quality of the overgrown areas, however edge-on dislocations are found at the meeting fronts of two wings. Some misorientation between the 'seed' area and wing area was detected by Convergent Beam Electron Diffraction. Growth of pendeo-epitaxial layers on non-polar substrates is more difficult. Two wings on the opposite site of the seed area grow in two different polar directions with different growth rates. Most dislocations in a wing grown with Ga polarity are 10 times wider than wings grown with N-polarity making coalescence of these layers difficult. Most dislocations in a wing grown with Ga polarity bend in a direction parallel to the substrate, but some of them also propagate to the sample surface. Stacking faults formed on the c-plane and prismatic plane occasionally were found. Some misorientation between the wings and seed was detected using Large Angle Convergent Beam Diffraction.
Date: January 5, 2006
Creator: Liliental-Weber, Z.; Ni, X. & Morkoc, H.
System: The UNT Digital Library
Radioanalytical Data Quality Objectives and Measurement Quality Objectives during a Federal Radiological Monitoring and Assessment Center Response (open access)

Radioanalytical Data Quality Objectives and Measurement Quality Objectives during a Federal Radiological Monitoring and Assessment Center Response

During the early and intermediate phases of a nuclear or radiological incident, the Federal Radiological Monitoring and Assessment Center (FRMAC) collects environmental samples that are analyzed by organizations with radioanalytical capability. Resources dedicated to quality assurance (QA) activities must be sufficient to assure that appropriate radioanalytical measurement quality objectives (MQOs) and assessment data quality objectives (DQOs) are met. As the emergency stabilizes, QA activities will evolve commensurate with the need to reach appropriate DQOs. The MQOs represent a compromise between precise analytical determinations and the timeliness necessary for emergency response activities. Minimum detectable concentration (MDC), lower limit of detection, and critical level tests can all serve as measurements reflecting the MQOs. The relationship among protective action guides (PAGs), derived response levels (DRLs), and laboratory detection limits is described. The rationale used to determine the appropriate laboratory detection limit is described.
Date: January 1, 2006
Creator: Nielsen, E. C.
System: The UNT Digital Library
Evaluation of an Unsuccessful Brook Trout Electrofishing Removal Project in a Small Rocky Mountain Stream. (open access)

Evaluation of an Unsuccessful Brook Trout Electrofishing Removal Project in a Small Rocky Mountain Stream.

In the western United States, exotic brook trout Salvelinus fontinalis frequently have a deleterious effect on native salmonids, and biologists often attempt to remove brook trout from streams by means of electrofishing. Although the success of such projects typically is low, few studies have assessed the underlying mechanisms of failure, especially in terms of compensatory responses. A multiagency watershed advisory group (WAG) conducted a 3-year removal project to reduce brook trout and enhance native salmonids in 7.8 km of a southwestern Idaho stream. We evaluated the costs and success of their project in suppressing brook trout and looked for brook trout compensatory responses, such as decreased natural mortality, increased growth, increased fecundity at length, and earlier maturation. The total number of brook trout removed was 1,401 in 1998, 1,241 in 1999, and 890 in 2000; removal constituted an estimated 88% of the total number of brook trout in the stream in 1999 and 79% in 2000. Although abundance of age-1 and older brook trout declined slightly during and after the removals, abundance of age-0 brook trout increased 789% in the entire stream 2 years after the removals ceased. Total annual survival rate for age-2 and older brook trout did not …
Date: January 26, 2006
Creator: Meyer, Kevin A.; Lamansky, Jr., James A. & Schill, Daniel J.
System: The UNT Digital Library
Self-selection contributes significantly to the lower adiposity offaster, longer-distanced, male and female walkers (open access)

Self-selection contributes significantly to the lower adiposity offaster, longer-distanced, male and female walkers

Although cross-sectional studies show active individuals areleaner than their sedentary counterparts, it remains to be determined towhat extent this is due to initially leaner men and women choosing toexercise longer and more intensely (self-selection bias). In this reportwalking volume (weekly distance) and intensity (speed) were compared tocurrent BMI (BMIcurrent) and BMI at the start of walking (BMIstarting) in20,353 women and 5,174 men who had walked regularly for exercise for 7.2and 10.6 years,respectively. The relationships of BMIcurrent andBMIstarting with distance and intensity were nonlinear (convex). Onaverage, BMIstarting explained>70 percent of the association betweenBMIcurrent and intensity, and 40 percent and 17 percent of theassociation between BMIcurrent and distance in women and men,respectively. Although the declines in BMIcurrent with distance andintensity were greater among fatter than leaner individuals, the portionsattributable to BMIstarting remained relatively constant regardless offatness. Thus self-selection bias accounts for most of the decline in BMIwith walking intensity and smaller albeit significant proportions of thedecline with distance. This demonstration of self-selection is germane toother cross-sectional comparisons in epidemiological research, givenself-selection is unlikely to be limited to weight or peculiar tophysical activity.
Date: January 6, 2006
Creator: Williams, Paul T.
System: The UNT Digital Library
Nitrogen as a friendly addition to steel (open access)

Nitrogen as a friendly addition to steel

Interstitial alloying with nitrogen or carbon is a common means of enhancing properties of iron-based alloys. Interstitial nitrogen addition to fcc-phase Fe-Cr-Mn/Ni alloys results in improved mechanical properties, whereas addition of carbon can result in the formation of unwanted carbides. Carbon addition to low alloy, bcc-phase iron alloys significantly improves strength through the formation of carbides, whereas addition of nitrogen in bcc-phase iron alloys can result in porous casting and reduced mechanical properties. This study will show that alloying iron-based alloys with both nitrogen and carbon can produce positive results. Nitrogen addition to Fe-C and Fe-Cr-C alloys, and both nitrogen and nitrogen-carbon additions to Fe-Cr-Mn/Ni alloys altered the microstructure, improved mechanical properties, increased hardness, and reduced wear by stabilizing the fcc-phase and altering (possibly eliminating) precipitate formation.
Date: January 1, 2006
Creator: Rawers, J. C.
System: The UNT Digital Library
Electronic Structure of zinc-blende AlxGa1-xN; Screened-ExchangeStudy (open access)

Electronic Structure of zinc-blende AlxGa1-xN; Screened-ExchangeStudy

We present a first principle investigation of the electronicstructure and the band gap bowing parameter of zinc-blende \AlGaN usingboth local density approximation and screened-exchange density functionalmethod. The calculated sX-LDA band gaps for GaN and AlN are 95 percentand 90 percent of the experimentally observed values, respectively, whileLDA under estimates the gaps to 62 percent and 70 percent. In contrast tothe gap itself, the band gap bowing parameter is found to be very similarin sX-LDA and LDA. Because of the difference in the conduction bandstructure, the direct to indirect band gap crossover is predicted tooccur at different Al concentration.
Date: January 3, 2006
Creator: Lee, Byounghak & Wang, Lin-Wang
System: The UNT Digital Library