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1

Creep Strain and Strain Rate Response of 2219 Al Alloy at High Stress Levels  

NASA Technical Reports Server (NTRS)

As a result of high localized plastic deformation experienced during proof testing in an International Space Station connecting module, a study was undertaken to determine the deformation response of a 2219-T851 roll forging. After prestraining 2219-T851 Al specimens to simulate strains observed during the proof testing, creep tests were conducted in the temperature range from ambient temperature to 107 C (225 F) at stress levels approaching the ultimate tensile strength of 2219-T851 Al. Strain-time histories and strain rate responses were examined. The strain rate response was extremely high initially, but decayed rapidly, spanning as much as five orders of magnitude during primary creep. Select specimens were subjected to incremental step loading and exhibited initial creep rates of similar magnitude for each load step. Although the creep rates decreased quickly at all loads, the creep rates dropped faster and reached lower strain rate levels for lower applied loads. The initial creep rate and creep rate decay associated with primary creep were similar for specimens with and without prestrain; however, prestraining (strain hardening) the specimens, as in the aforementioned proof test, resulted in significantly longer creep life.

Taminger, Karen M. B.; Wagner, John A.; Lisagor, W. Barry

1998-01-01

2

Subcritical crack growth of Ti-6Al-4V at room temperature under high stress-ratio loading  

SciTech Connect

Ti-6Al-4V is a two phase {alpha}-{beta} titanium alloy commonly used for turbine fan and compressor components. The crack growth behavior of Ti-6Al-4V and the role played by various material, mechanical, and environmental factors has been thoroughly investigated. This alloy is also susceptible to crack growth under sustained loading in air (SLC), and both hydrogen assisted cracking and low temperature creep mechanisms have been used to explain this susceptibility. Very little information is available on high R-ratio fatigue crack growth of Ti-6Al-4V and the role played by SLC on the fatigue process. In order to gain better understanding of the cracking behavior of this alloy under ripple loading conditions, room temperature, high stress-ratio (R {ge} 0.9) fatigue and SLC experiments have been conducted on a Ti-6Al-4V plate forging material in the duplex-annealed (DA) condition. The results of this investigation,namely, fatigue crack growth rates (CGR) as a function of stress intensity; SLC data; and scanning electron microscopy of the fatigue and SLC fracture surfaces are reported below.

Thomas, J.P. [Univ. of Notre Dame, IN (United States). Dept. of Aerospace and Mechanical Engineering] [Univ. of Notre Dame, IN (United States). Dept. of Aerospace and Mechanical Engineering

1998-11-13

3

Electric-stress reliability and current collapse of different thickness SiNx passivated AlGaN\\/GaN high electron mobility transistors  

Microsoft Academic Search

This paper investigates the impact of electrical degradation and current collapse on different thickness SiNx passivated AlGaN\\/GaN high electron mobility transistors. It finds that higher thickness SiNx passivation can significantly improve the high-electric-field reliability of a device. The degradation mechanism of the SiNx passivation layer under ON-state stress has also been discussed in detail. Under the ON-state stress, the strong

Ling Yang; Gui-Zhou Hu; Yue Hao; Xiao-Hua Ma; Si Quan; Li-Yuan Yang; Shou-Gao Jiang

2010-01-01

4

Oxidative Stress Biomarkers in Sporadic ALS  

PubMed Central

Objective To investigate oxidative stress biomarkers in a cross-sectional pilot study of 50 participants with sporadic ALS (sALS) compared to 46 control subjects. Methods We measured urinary 8-oxodeoxyguanosine (8-oxodG), urinary 15-F2t-isoprostane (IsoP), and plasma protein carbonyl by ELISA methods. We also determined if ELISA measurement of 8-oxodG could be validated against measures from high pressure liquid chromatography coupled with electrochemical detection, the current standard method. Results 8-oxodG and IsoP levels adjusted for creatinine were significantly elevated in sALS participants. These differences persisted after age and gender were controlled in regression analyses. These markers are highly and positively correlated with each other. 8-oxodG measured by the two techniques from the same urine sample were positively correlated (P < .0001). Protein carbonyl was not different between sALS participants and controls. Conclusion Using ELISA we confirmed that certain oxidative stress biomarkers were elevated in sALS participants. ELISA may be reliable and thus useful in epidemiology studies requiring large numbers of samples to determine the significance of increased oxidative stress markers in sALS. Further studies are required. PMID:18574762

Mitsumoto, Hiroshi; Santella, Regina M.; Liu, Xinhua; Bogdanov, Mikhail; Zipprich, Jennifer; Wu, Hui-Chen; Mahata, Julie; Kilty, Mary; Bednarz, Kate; Bell, Daniel; Gordon, Paul H.; Hornig, Mady; Mehrazin, Mahsa; Naini, Ali; Beal, M. Flint; Factor-Litvak, Pam

2015-01-01

5

Microstructure and Residual Stress of Alumina Scale Formed on Ti2AlC at High Temperature in Air  

SciTech Connect

Ti2AlC ternary carbide is being explored for various high temperature applications owing to its high strength at high temperatures, excellent thermal-shock resistance, and high electrical conductivity. In this study, isothermal oxidation at 1000 XC, 1200 XC, and 1400 XC for up to 25 hours, as well as 1,000 1-hour cyclic oxidation at 1200 XC were performed in air to examine the oxidation behavior of Ti2AlC. Characteristics of the oxide scale developed in air, including mass change, residual stress in the -Al2O3 scale, phase constituents and microstructure, were examined as functions of time and temperature by thermogravimetry, photostimulated luminescence, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy via focused ion beam in-situ lift-out. A continuous and adherent -Al2O3 scale underneath a discontinuous-transient rutile-TiO2 scale was identified in the oxide scale developed at 1000 XC and 1200 XC. At 1400 XC, Al2TiO5 was identified as the discontinuous-transient scale above the continuous and adherent -Al2O3 scale. The -Al2O3 scale thickened to more than 15 m after 25 hours of isothermal oxidation at 1400 XC, and after 1,000 1-hour cyclic oxidation at 1200 XC, yet remained adherent and protective. The compressive residual stress determined by photoluminescence for the -Al2O3 scale remained under 0.65 GPa for the specimens oxidized up to 1400 XC for 25 hours. The small magnitude of the compressive residual stress may impart the high spallation-resistance of the protective -Al2O3 scale developed on Ti2AlC.

Byeon, J [University of Central Florida; Liu, j [University of Central Florida; Hopkins, m [University of Central Florida; Fischer, W [University High School Orlando, FL; Park, K [University of Central Florida; Brady, Michael P [ORNL; Radovic, Miladin [ORNL; Sohn, Yong Ho [University of Central Florida

2007-01-01

6

Influence of stress on structural properties of AlGaN/GaN high electron mobility transistor layers grown on 150 mm diameter Si (111) substrate  

NASA Astrophysics Data System (ADS)

Effects of stress imposed by individual nitride layers on structural properties of an AlGaN/GaN high-electron-mobility-transistor (HEMT) structure, which was grown on a 150 mm diameter Si (111) substrate by metal-organic chemical vapor deposition employing high-temperature step-graded AlxGa1-xN/AlN buffer layers, were studied using transmission electron microscopy, visible micro-Raman spectroscopy, and high-resolution x-ray diffraction. It is revealed that all the nitride layers are more or less tensile strained on the Si (111) substrate; however, strain relaxations occurred at all the heterointerfaces except for the AlGaN/(AlN/)GaN two-dimensional electron gas interface, which is desired for achieving high performance HEMT. The wafer curvature, an important parameter for large area epitaxy of GaN-on-Si, is modeled on the basis of stress distribution within individual layers of the multilayered AlGaN/GaN HEMT structure via the close-form expression developed by Olsen and Ettenberg [J. Appl. Phys. 48, 2543 (1977)]. The evolution of wafer curvature induced by substrate thinning and stress redistribution is predicted by this model, which is further qualitatively confirmed by experimental results.

Liu, H. F.; Dolmanan, S. B.; Zhang, L.; Chua, S. J.; Chi, D. Z.; Heuken, M.; Tripathy, S.

2013-01-01

7

Effect of microstructure on creep deformation of 45XD TiAl alloy at low and high stresses  

Microsoft Academic Search

A stabilized fully lamellar (stabilized FL) structure and a nearly lamellar (NL) structure were prepared by selected heat treatments in a Ti–45Al–2Nb–2Mn (wt.%)+0.8vol.% TiB2 (45XD) alloy. Tensile creep tests were performed at 760°C using applied stresses of 138 and 207MPa. The stabilized FL structure exhibits a lower minimum creep rate and a longer rupture life compared to the NL structure

Hanliang Zhu; D. Y. Seo; K. Maruyama; P. Au

2008-01-01

8

Review of stress-corrosion cracking in high-strength aluminum alloys. [Al alloys 7090, 7091, IN 9052 and Al-Li ingot metallurgy  

Microsoft Academic Search

Developments in understanding the mechanisms of stress-corrosion cracking (SCC) of high-strength aluminum alloys are highlighted from early dissolution models, to present hydrogen embrittlement dominated theories. Uncertainties in the present view of the SCC mechanism are identified. The means by which SCC susceptibility has been reduced in ingot metallurgy (I\\/M) alloys are described. The susceptibility of new powder metallurgy (P\\/M) alloys

J. R. Pickens; L. Christodoulou; T. J. Langan

2008-01-01

9

Dynamic Stress-Strain Behavior in ZrTiCuNiAl Noncrystalline Alloys Pretreated Under High Pressures  

NASA Astrophysics Data System (ADS)

For actual structural engineering applications of materials, many kinds of extreme conditions like high-speed dynamic loading, low temperature, high pressure, other than normal ones should be appreciated. In this paper, the as-casted and high-pressure-treated ZrTiCuNiAl noncrystalline alloys under 0 to 4 GPa at room temperature were investigated by X-ray diffraction, differential scanning calorimetry, and nanoindentation. We find that the nonhydrostatic high pressure does not result in the crystallization but can significantly improve the mechanical performance, in particular the plasticity of the noncrystalline alloys. The investigation concerning the effect of the high pressure treatment on the mechanical behavior of the Zr-based alloy is potentially useful for suggesting possible external means to control the microstructure and mechanical performance of the amorphous materials.

Gao, S. B.; Gao, Y. P.; Yu, P. F.; Feng, S. D.; Li, G.; Liaw, P. K.; Liu, R. P.

2014-08-01

10

Impacts of SiN passivation on the degradation modes of AlGaN/GaN high electron mobility transistors under reverse-bias stress  

NASA Astrophysics Data System (ADS)

Impacts of SiN passivation on the degradation modes of AlGaN/GaN high electron mobility transistors are investigated. The gate leakage current decreases significantly upon removing the SiN layer and no clear critical voltage for the sudden degradation of the gate leakage current can be observed in the reverse-bias step-stress experiments. Gate-lag measurements reveal the decrease of the fast-state surface traps and the increase of slow-state traps after the passivation layer removal. It is postulated that consistent surface charging relieves the electric field peak on the gate edge, thus the inverse piezoelectric effect is shielded.

Chen, Wei-Wei; Ma, Xiao-Hua; Hou, Bin; Zhu, Jie-Jie; Chen, Yong-He; Zheng, Xue-Feng; Zhang, Jin-Cheng; Hao, Yue

2014-10-01

11

On the link between electroluminescence, gate current leakage, and surface defects in AlGaN/GaN high electron mobility transistors upon off-state stress  

NASA Astrophysics Data System (ADS)

The degradation of AlGaN/GaN high electron mobility transistors after off-state stress is studied by means of electroluminescence (EL) analysis, gate leakage current (Ig) monitoring, and atomic force microscopy (AFM) mapping of the semiconductor surface. It is found that the degradation of Ig upon stress is due to the combined effect of the individual defects underlying each of the EL spots, which contribute a few ?A each to the total Ig. After removal of contacts and passivation, a direct one-to-one correspondence between EL spots and pits on the semiconductor surface is found. Reverse bias, conducting-tip AFM imaging showed that these surface pits do indeed act as leakage paths. Thus, the direct relationship between EL hot spots, surface pits, and gate current leakage is demonstrated. Discussion on the morphology of the surface pits and their possible origin is also provided.

Montes Bajo, M.; Hodges, C.; Uren, M. J.; Kuball, M.

2012-07-01

12

ALS and Oxidative Stress: The Neurovascular Scenario  

PubMed Central

Oxidative stress and angiogenic factors have been placed as the prime focus of scientific investigations after an establishment of link between vascular endothelial growth factor promoter (VEGF), hypoxia, and amyotrophic lateral sclerosis (ALS) pathogenesis. Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter and mutant superoxide dismutase 1 (SOD1) which are characterised by atrophy and muscle weakness resulted in phenotype resembling human ALS in mice. This results in lower motor neurodegeneration thus establishing an important link between motor neuron degeneration, vasculature, and angiogenic molecules. In this review, we have presented human, animal, and in vitro studies which suggest that molecules like VEGF have a therapeutic, diagnostic, and prognostic potential in ALS. Involvement of vascular growth factors and hypoxia response elements also highlights the converging role of oxidative stress and neurovascular network for understanding and treatment of various neurodegenerative disorders like ALS. PMID:24367722

Thakur, Keshav; Gupta, Pawan Kumar

2013-01-01

13

Effect of sulfuric acid, oxygen, and hydrogen in high temperature water on stress corrosion cracking of sensitized AlSl 304 stainless steel  

Microsoft Academic Search

The influence of dissolved oxygen and hydrogen and dilute sulfuric acid in 289 C water on the stress corrosion cracking susceptibility of lightly and moderately sensitized AlSl 304 stainless steel was determined in constant extension rate tensile (CERT) tests. The CERT parameters and fracture surface morphologies correlated with the concentrations of dissolved oxygen and sulfate and the electrochemical potentials of

W. E. Ruther; G. Ayrault; T. F. Kassner; W. K. Soppet

1984-01-01

14

Photoluminescence of Al 2O 3 nanocrystals induced by compressive stress  

Microsoft Academic Search

This manuscript presents a study on the growth stress of Al2O3 nanocrystals in Lu2O3 matrix and its resultant effect on the optical properties of Al2O3 nanocrystals. The high-resolution transmission electron microscopy study reveals the complete isolation of Al2O3 nanocrystals embedded in Lu2O3 matrix. Two dimensional finite element calculations clearly demonstrate that Al2O3 nanocrystals certainly experience great compressive stress in Lu2O3

C. L. Yuan; W. Lei

2010-01-01

15

Stress Corrosion Cracking of Al-Mg and Mg-Al Alloys  

SciTech Connect

Aluminum and magnesium based alloys are being used for reducing the weight of automobiles. For structural applications they must have adequate stress corrosion resistance and yet, under some circumstances, stress corrosion cracking can occur in both alloy systems. Precipitation of the Mg rich Beta-phase (Al3Mg2) at grain boundaries of Al-Mg alloys and the Beta-phase (Mg17Al12) at grain boundaries of the Mg-Al alloys are critical factors in their stress corrosion performance. In Mg-Al, the Beta-phase is cathodic to the matrix while in the Al-Mg case, the Beta-phase is anodic to the matrix. These phases produce localized galvanic induced-corrosion that leads to intergranular stress corrosion cracking and cracking growth rates of 5 and 103 times faster than the solution treated condition, for Al-Mg and Mg-Al, respectively.

Jones, Russell H.; Vetrano, John S.; Windisch, Charles F.

2004-12-01

16

ER Dysfunction and Protein Folding Stress in ALS  

PubMed Central

Amyotrophic lateral sclerosis (ALS) is the most frequent paralytic disease in adults. Most ALS cases are considered sporadic with no clear genetic component. The disruption of protein homeostasis due to chronic stress responses at the endoplasmic reticulum (ER) and the accumulation of abnormal protein inclusions are extensively described in ALS mouse models and patient-derived tissue. Recent studies using pharmacological and genetic manipulation of the unfolded protein response (UPR), an adaptive reaction against ER stress, have demonstrated a complex involvement of the pathway in experimental models of ALS. In addition, quantitative changes in ER stress-responsive chaperones in body fluids have been proposed as possible biomarkers to monitor the disease progression. Here we review most recent advances attributing a causal role of ER stress in ALS. PMID:24324498

Matus, Soledad; Valenzuela, Vicente; Medinas, Danilo B.; Hetz, Claudio

2013-01-01

17

Clinical Perspective of Oxidative Stress in Sporadic ALS  

PubMed Central

Sporadic amyotrophic lateral sclerosis (sALS) is one of the most devastating neurological diseases; most patients die within 3 to 4 years after symptom onset. Oxidative stress is a disturbance in the pro-oxidative/anti-oxidative balance favoring the pro-oxidative state. Autopsy and laboratory studies in ALS indicate that oxidative stress plays a major role in motor neuron degeneration and astrocyte dysfunction. Oxidative stress biomarkers in cerebrospinal fluid, plasma, and urine, are elevated, suggesting that abnormal oxidative stress is generated outside of the central nervous system. Our review indicates that agricultural chemicals, heavy metals, military service, professional sports, excessive physical exertion, chronic head trauma, and certain foods might be modestly associated with ALS risk, with a stronger association between risk and smoking. At the cellular level, these factors are all involved in generating oxidative stress. Experimental studies indicate that a combination of insults that induce modest oxidative stress can exert additive deleterious effects on motor neurons, suggesting multiple exposures in real-world environments are important. As the disease progresses, nutritional deficiency, cachexia, psychological stress, and impending respiratory failure may further increase oxidative stress. Moreover, accumulating evidence suggests that ALS is possibly a systemic disease. Laboratory, pathologic, and epidemiologic evidence clearly support the hypothesis that oxidative stress is central in the pathogenic process, particularly in genetically susceptive individuals. If we are to improve ALS treatment, well-designed biochemical and genetic epidemiological studies, combined with a multidisciplinary research approach, are needed and will provide knowledge crucial to our understanding of ALS etiology, pathophysiology, and prognosis. PMID:23797033

D’Amico, Emanuele; Factor-Litvak, Pam; Santella, Regina M.; Mitsumoto, Hiroshi

2013-01-01

18

Profilin 1 Associates with Stress Granules and ALS-Linked Mutations Alter Stress Granule Dynamics  

PubMed Central

Mutations in the PFN1 gene encoding profilin 1 are a rare cause of familial amyotrophic lateral sclerosis (ALS). Profilin 1 is a well studied actin-binding protein but how PFN1 mutations cause ALS is unknown. The budding yeast, Saccharomyces cerevisiae, has one PFN1 ortholog. We expressed the ALS-linked profilin 1 mutant proteins in yeast, demonstrating a loss of protein stability and failure to restore growth to profilin mutant cells, without exhibiting gain-of-function toxicity. This model provides for simple and rapid screening of novel ALS-linked PFN1 variants. To gain insight into potential novel roles for profilin 1, we performed an unbiased, genome-wide synthetic lethal screen with yeast cells lacking profilin (pfy1?). Unexpectedly, deletion of several stress granule and processing body genes, including pbp1?, were found to be synthetic lethal with pfy1?. Mutations in ATXN2, the human ortholog of PBP1, are a known ALS genetic risk factor and ataxin 2 is a stress granule component in mammalian cells. Given this genetic interaction and recent evidence linking stress granule dynamics to ALS pathogenesis, we hypothesized that profilin 1 might also associate with stress granules. Here we report that profilin 1 and related protein profilin 2 are novel stress granule-associated proteins in mouse primary cortical neurons and in human cell lines and that ALS-linked mutations in profilin 1 alter stress granule dynamics, providing further evidence for the potential role of stress granules in ALS pathogenesis. PMID:24920614

Figley, Matthew D.; Bieri, Gregor; Kolaitis, Regina-Maria; Taylor, J. Paul

2014-01-01

19

Stress Development and Relaxation in Al2O3 during Early StageOxidation of beta-NiAl  

SciTech Connect

Using a glancing synchrotron X-ray beam (Advanced Photon Source, Beamline 12BM, Argonne National Laboratory), Debye-Scherrer diffraction patterns from thermally grown oxides on NiAl samples were recorded during oxidation at 1000 or 1100 C in air. The diffraction patterns were analyzed to determine strain and phase changes in the oxide scale as it developed and evolved. Strain was obtained from measurements of the elliptical distortion of the Debye-Scherrer rings, where data from several rings of a single phase were used. Results were obtained from {alpha}-Al{sub 2}O{sub 3} as well as from the transition alumina, in this case {theta}-Al{sub 2}O{sub 3}, which formed during the early stage. Compressive stress was found in the first-formed transition alumina, but the initial stress in {alpha}-Al{sub 2}O{sub 3} was tensile, with a magnitude high enough to cause Al{sub 2}O{sub 3} fracture. New {alpha}-Al{sub 2}O{sub 3} patches nucleated at the scale/alloy interface and spread laterally and upward. This transformation not only puts the alpha alumina in tension, but can also cause the transition alumina to be in tension. After a complete {alpha}-Al{sub 2}O{sub 3} layer formed at the interface, the strain level in {alpha}-Al{sub 2}O{sub 3} became compressive, reaching a steady state level around -75 MPa at 1100 C. To study a specimen's response to stress perturbation, samples with different thickness, after several hours of oxidation at 1100 C, were quickly cooled to 950 C to impose a compressive thermal stress in the scale. The rate of stress relaxation was the same for 1 and 3.5 mm thick samples, having a strain rate of {approx} 1 x 10{sup -8}/s. This behavior indicates that oxide creep is the major stress relaxation mechanism.

Hou, P.Y.; Paulikas, A.P.; Veal, B.W.

2005-04-20

20

On the effect of deep-rolling and laser-peening on the stress-controlled low-and high-cycle fatigue behavior of Ti6Al4V at elevated temperatures  

E-print Network

regimes at temperatures as high as 550 °C. At these temperatures, compressive residual stressesOn the effect of deep-rolling and laser-peening on the stress-controlled low- and high for decades to induce favorable near-surface microstructures and compressive residual stress states [15

Ritchie, Robert O.

21

Residual stress in friction stir-welded Al sheets  

Microsoft Academic Search

Friction stir welding (FSW) is a relatively new joining technique particularly for aluminum alloys that are difficult to fusion weld. Although FSW is as a solid-state joining process which produces low-distortion welds of high quality, significant levels of residual stresses can be present in the weld after fabrication. These residual stresses can influence the service performance of the welded components

P. Staron; M. Koçak; S. Williams; A. Wescott

2004-01-01

22

High Temperature Mechanical Characterization and Analysis of Al2O3 /Al2O3 Composition  

NASA Technical Reports Server (NTRS)

Sixteen ply unidirectional zirconia coated single crystal Al2O3 fiber reinforced polycrystalline Al2O3 was tested in uniaxial tension at temperatures to 1400 C in air. Fiber volume fractions ranged from 26 to 31%. The matrix has primarily open porosity of approximately 40%. Theories for predicting the Young's modulus, first matrix cracking stress, and ultimate strength were applied and evaluated for suitability in predicting the mechanical behavior of Al2O3/Al2O3 composites. The composite exhibited pseudo tough behavior (increased area under the stress/strain curve relative to monolithic alumina) from 22 to 1400 C. The rule-of-mixtures provides a good estimate of the Young's modulus of the composite using the constituent properties from room temperature to approximately 1200 C for short term static tensile tests in air. The ACK theory provides the best approximation of the first matrix cracking stress while accounting for residual stresses at room temperature. Difficulties in determining the fiber/matrix interfacial shear stress at high temperatures prevented the accurate prediction of the first matrix cracking stress above room temperature. The theory of Cao and Thouless, based on Weibull statistics, gave the best prediction for the composite ultimate tensile strength.

Gyekenyesi, John Z.; Jaskowiak, Martha H.

1999-01-01

23

Microstructural Evolution and Stress Corrosion Cracking Behavior of Al-5083  

NASA Astrophysics Data System (ADS)

The fine scale microstructure of Al-5083 (H-131) sensitized at 448 K (175 °C) for 1, 10, 25, 50, 100, 240, 500, and 1000 hours has been investigated using transmission electron microscopy (TEM) to study the evolution of the ? phase (Al3Mg2) at grain boundaries and on pre-existing intragranular particles. In fully sensitized Al-5083, the ? phase (Al3Mg2) forms heterogeneously both at grain boundaries and on pre-existing particles, which are enriched in manganese. TEM observations showed that the grain boundary precipitation of the ? phase initially occurs between 0 to 1 hour of aging at 448 K (175 °C), and that the ? phase grows with a ribbonlike morphology. The grain boundary planes are covered by the ? phase after 240 hours of aging. The contribution of microstructure, defects, and environment on the stress corrosion cracking (SCC) behavior is discussed.

Goswami, R.; Spanos, G.; Pao, P. S.; Holtz, R. L.

2011-02-01

24

Crack propagation in high stress fatigue  

Microsoft Academic Search

An examination of the fracture surfaces of ductile metal specimens broken in high stress fatigue has revealed the occurrence of fracture ripples similar in appearance to those resulting from low stresses, but considerably larger. By sectioning specimens strained to various stages of the fatigue stress cycle, it has been shown that crack propagation and fracture ripple formation are the consequences

C. Laird; G. C. Smith

1962-01-01

25

Stress Histories of Yttria-Stabilized Zirconia and CoNiCrAlY Coatings during Thermal Spraying  

NASA Astrophysics Data System (ADS)

Thermal barrier coating (TBC) systems which are used for insulating the substrates of gas turbine blades from high temperature can be made by thermal spraying. The TBC system has residual stresses because of high temperature deposition and the thermal expansion mismatch in the system. In this study, how the residual stress occurs in TBC system was examined by both experimental measurement and FEM analysis. The Yttria-stabilized zirconia (YSZ) top coating was deposited by atmospheric plasma spraying (APS). CoNiCrAlY bond coatings were deposited by high velocity oxygen-fuel (HVOF) spraying and APS. The temperatures of YSZ, CoNiCrAlYs and substrates were measured during thermal spraying. The temperature of YSZ was the highest and that of CoNiCrAlY(HVOF) was the lowest among the three types of spray processes. The residual stresses were elastically calculated by FEM based on the measured temperature histories. The residual stress of YSZ and CoNiCrAlYs on two types of substrates were also measured by X-ray diffraction method. It was confirmed from FEM analysis that residual stress consisted of primary quench stress and secondary thermal mismatch stress. The quench stress was caused by the quenching of coating particles during deposition which occurs due to the huge thermal capacity of the substrate. The thermal mismatch stress was caused by the difference in linear expansion coefficients between coating and substrate. It was found that not only these two mechanisms but also microcrack formation caused by quench played an important role in the residual stress. The temperatures at which residual stresses might begin to occur in the coatings were shown based on the stress relaxation by microcrack formation. It was also found that peening effect played an important role in the residual stress of HVOF sprayed coating.

Waki, Hiroyuki; Fujioka, Hidenori; Kobayashi, Akira

26

Finite Element Analysis of Stress Evolution in Al-Si Alloy  

NASA Astrophysics Data System (ADS)

A 2D multi-particle model is carried out to understand the effect of microstructural variations and loading conditions on the stress evolution in Al-Si alloy under compression. A total of six parameters are varied to create 26 idealized microstructures: particle size, shape, orientation, matrix temper, strain rate, and temperature. The effect of these parameters is investigated to understand the fracture of Si particles and the yielding of Al matrix. The Si particles are modeled as a linear elastic solid and the Al matrix is modeled as an elasto-plastic solid. The results of the study demonstrate that the increase in particle size decreases the yield strength of the alloy. The particles with high aspect ratio and oriented at 0° and 90° to the loading axis show higher stress values. This implies that the particle shape and orientation are dominant factors in controlling particle fracture. The heat treatment of the alloy is found to increase the stress levels of both particles and matrix. Stress calculations also show that higher particle fracture and matrix yielding is expected at higher strain rate deformation. Particle fracture decreases with increase in temperature and the Al matrix plays an important role in controlling the properties of the alloy at higher temperatures. Further, this strain rate and temperature dependence is more pronounced in the heat-treated microstructure. These predictions are consistent with the experimentally observed Si particle fracture in real microstructure.

Joseph, Sudha; Kumar, S.

2014-11-01

27

Finite Element Analysis of Stress Evolution in Al-Si Alloy  

NASA Astrophysics Data System (ADS)

A 2D multi-particle model is carried out to understand the effect of microstructural variations and loading conditions on the stress evolution in Al-Si alloy under compression. A total of six parameters are varied to create 26 idealized microstructures: particle size, shape, orientation, matrix temper, strain rate, and temperature. The effect of these parameters is investigated to understand the fracture of Si particles and the yielding of Al matrix. The Si particles are modeled as a linear elastic solid and the Al matrix is modeled as an elasto-plastic solid. The results of the study demonstrate that the increase in particle size decreases the yield strength of the alloy. The particles with high aspect ratio and oriented at 0° and 90° to the loading axis show higher stress values. This implies that the particle shape and orientation are dominant factors in controlling particle fracture. The heat treatment of the alloy is found to increase the stress levels of both particles and matrix. Stress calculations also show that higher particle fracture and matrix yielding is expected at higher strain rate deformation. Particle fracture decreases with increase in temperature and the Al matrix plays an important role in controlling the properties of the alloy at higher temperatures. Further, this strain rate and temperature dependence is more pronounced in the heat-treated microstructure. These predictions are consistent with the experimentally observed Si particle fracture in real microstructure.

Joseph, Sudha; Kumar, S.

2015-01-01

28

Effects of stress ratio and temperature on fatigue crack growth in a Ti–6Al–4V alloy  

Microsoft Academic Search

Fatigue thresholds and fatigue crack growth (FCG) rates in corner notched specimens of a forged Ti–6Al–4V aero-engine disk material were investigated at room temperature and 350°C. The threshold stress intensity range, ?Kth, was determined by a method involving a step change in stress ratio (the ‘jump in’ method). It was found that for three high stress ratios (R=0.7–0.9), where crack

J. Ding; R. Hall; J. Byrne

2005-01-01

29

High temperature deformation of NiAl matrix composites  

SciTech Connect

The intermetallic compound, NiAl, has many attractive properties at a high temperature structural materials. However, its lack of creep resistance prevents practical applications. Adding ceramic reinforcements, such as TiB{sub 2} particles, Al{sub 2}O{sub 3} particles or whiskers can significantly improve the strength of binary NiAl at high temperatures. However, the increase in the yield stress of the discontinuous NiAl matrix composites as compared with monolithic NiAl is difficult to explain. The purposes of this research were to understand the deformation mechanisms which cause the increase in strength achieved by adding TiB{sub 2} particles, Al{sub 2}O{sub 3} particles or whiskers to NiAl, and to recognize the principles of the deformation process in NiAl matrix composites. In order to accomplish these objectives, mechanical properties and thermal activation parameters in NiAl matrix composites with different types, shapes and sizes of reinforcements have been systematically evaluated. Microstructures and dislocation structures in NiAl matrix composites have also been thoroughly characterized before and after deformation. It was found that the size of the reinforcement had a large influence on the microstructures of the composites, and the nominal activation energies for all the composites were the same and within the range of the activation energy of self-diffusion for pure NiAl. It was further concluded that the reinforcement addition only increased the non-thermally activated component of the yield stress.

Xu, K.; Arsenault, R.J. [Univ. of Maryland, College Park, MD (United States)] [Univ. of Maryland, College Park, MD (United States)

1999-08-10

30

Nada Al-Alusi Torrey Pines High  

E-print Network

Students Nada Al-Alusi Torrey Pines High Triana Anderson Lowell High Catherine Badart Holy Names Academy Kitae Bae Torrey Pines High Marika Buchholz Louisiana School for Math, Science, and the Arts Royce Temitope Olabinjo Elkins High School Anshul Ramachandran Monta Vista High Daniel Schneller Saint Louis

Shahabi, Cyrus

31

Nada Al-Alusi Torrey Pines High  

E-print Network

Students Nada Al-Alusi Torrey Pines High Triana Anderson Lowell High Catherine Badart Holy Names Academy Kitae Bae Torrey Pines High Marika Buchholz Louisiana School for Math, Science, and the Arts Royce Temitope Olabinjo Elkins High School Anshul Ramachandran Monte Vista High Daniel Schneller Saint Louis

Shahabi, Cyrus

32

Measuring Stress Distributions in Ti-6Al-4V Using Synchrotron X-Ray Diffraction  

NASA Astrophysics Data System (ADS)

This article presents a quantitative strain analysis (QSA) study aimed at determining the distribution of stress states within a loaded Ti-6Al-4V specimen. Synchrotron X-rays were used to test a sample that was loaded to a uniaxial stress of 540 MPa in situ in the A2 experimental station at the Cornell High Energy Synchrotron Source (CHESS). Lattice-strain pole figures (SPFs) were measured and used to construct a lattice strain distribution function (LSDF) over the fundamental region of orientation space for each phase. A high-fidelity geometric model of the experiment was used to drastically improve the signal-to-noise ratio in the data. The three-dimensional stress states at every possible orientation of each ? (hcp) and ? (bcc) crystal within the aggregate were calculated using the LSDF and the single-crystal moduli. The stress components varied by 300 to 500 MPa over the orientation space; it was also found that, in general, the crystal stress states were not uniaxial. The maximum shear stress resolved on the basal and prismatic slip systems of all orientations within the ? phase, hat tau _{{text{rss}}} , was calculated to illustrate the utility of this approach for better identifying “hard” and “soft” orientations within the loaded aggregate. Orientations with low values of hat tau _{{text{rss}}} , which are potential microcrack initiation sites during dwell fatigue conditions, are considered hard and were subsequently illustrated on an electron backscatter diffraction (EBSD) map.

Bernier, J. V.; Park, J.-S.; Pilchak, A. L.; Glavicic, M. G.; Miller, M. P.

2008-12-01

33

Reactive sintering of NiâAl intermetallic alloys under compressive stress  

Microsoft Academic Search

Synthesis of the Ni-25% at. Al intermetallic compound by the thermal explosion mode subject to the application of compressive stress was systematically investigated. The stress was applied prior to the reaction. It was proved that the compressive stress had a profound effect on the reaction, as well as the densification. At a relative low stress, a full reaction could be

K. H. Wu; C. T. Liu

1992-01-01

34

Reactive sintering of Ni[sub 3]Al intermetallic alloys under compressive stress  

Microsoft Academic Search

Synthesis of the Ni-25% at. Al intermetallic compound by the thermal explosion mode subject to the application of compressive stress was systematically investigated. The stress was applied prior to the reaction. It was proved that the compressive stress had a profound effect on the reaction, as well as the densification. At a relative low stress, a full reaction could be

K. H. Wu; C. T. Liu

1992-01-01

35

Transformation toughening of Al 2O 3\\/ZrO 2 laminated ceramics with residual compressive stress  

Microsoft Academic Search

With the help of scanning electronic microscopy and X-ray diffraction, the relationships of microstructure characteristics, phase assemblage, and fracture micrograph of Al2O3\\/ZrO2 laminated ceramics were studied. Compared with monolithic Al2O3\\/ZrO2 ceramics, the existence of surface compressive stresses greatly restrained the growth of ZrO2 and Al2O3 grains at high sinter temperature, fined the grain size, and increased the content of metastable

Bei Chen; Chuan Cheng; Lan Xiong; Li-Ao Wang

2007-01-01

36

Joule-Heating-Induced Damage in Cu-Al Wedge Bonds Under Current Stressing  

NASA Astrophysics Data System (ADS)

Copper wires are increasingly used to replace gold wires in wire-bonding technology owing to their better electrical properties and lower cost. However, not many studies have been conducted on electromigration-induced failure of Cu wedge bonds on Al metallization. In this study, we investigated the failure mechanism of Cu-Al wedge bonds under high current stressing from 4 × 104 A/cm2 to 1 × 105 A/cm2 at ambient temperature of 175°C. The resistance evolution of samples during current stressing and the microstructure of the joint interface between the Cu wire and Al-Si bond pad were examined. The results showed that abnormal crack formation accompanying significant intermetallic compound growth was observed at the second joint of the samples, regardless of the direction of electric current for both current densities of 4 × 104 A/cm2 and 8 × 104 A/cm2. We propose that this abnormal crack formation at the second joint is mainly due to the higher temperature induced by the greater Joule heating at the second joint for the same current stressing, because of its smaller bonded area compared with the first joint. The corresponding fluxes induced by the electric current and chemical potential difference between Cu and Al were calculated and compared to explain the failure mechanism. For current density of 1 × 105 A/cm2, the Cu wire melted within 0.5 h owing to serious Joule heating.

Yang, Tsung-Han; Lin, Yu-Min; Ouyang, Fan-Yi

2014-01-01

37

Modelling Of Residual Stresses Induced By High Speed Milling Process  

SciTech Connect

Maintenance processes used in heavy industries often include high speed milling operations. The reliability of the post-process material state has to be studied. Numerical simulation appears to be a very interesting way to supply an efficient residual stresses (RS) distribution prediction.Because the adiabatic shear band and the serrated chip shaping are features of the austenitic stainless steel high speed machining, a 2D high speed orthogonal cutting model is briefly presented. This finite element model, developed on Forge registered software, is based on data taken from Outeiro and al.'s paper [1]. A new behaviour law fully coupling Johnson-Cook's constitutive law and Latham and Cockcroft's damage model is detailed in this paper. It ensures results that fit those found in literature.Then, the numerical tools used on the 2D model are integrated to a 3D high speed milling model. Residual stresses distribution is analysed, on the surface and into the depth of the material. Various revolutions and passes of the two teeth hemispheric mill on the workpiece are simulated. Thus the sensitivity of the residual stresses generation to the cutting conditions can be discussed. In order to validate the 3D model, a comparison of the cutting forces measured by EDF R and D to those given by numerical simulations is achieved.

Desmaison, Olivier; Mocellin, Katia [Mines ParisTech, CEMEF, Centre of Material Forming, CNRS UMR 7635, BP 207, 1 rue Claude Daunesse, 06904 Sophia Antipolis Cedex (France); Jardin, Nicolas [Industrial Risks Management Dept.-EDF R and D, Chatou-78400 (France)

2011-05-04

38

Functional stress modification after high condylectomy surgery.  

PubMed

Surgical removal of the head of the condyles inevitably leads to radical redistribution of loads applied to the mandible. The nature of this redistribution can have important implications on the surgical approach and subsequent reconstructive procedures. The purpose of this investigation was to visualize photoelastically the functionally delivered stresses after high condylectomy surgery. Three identical models of a dentate human mandible were constructed from a photoelastic material. One mandible simulated a unilateral and the other simulated a bilateral high condylectomy. The third mandible had both condyles intact and served as basis for comparisons. Silicone implants were placed on the sectioned condylar heads. The condyles, with the silicone implants, were fitted into simulated fossae and the mandibles were loaded unilaterally and bilaterally. The resulting stresses were observed and photographed in the field of a circular polariscope. Substantial differences in load-generated stresses were observed as a result of both unilateral and bilateral condylectomies, compared to the normal case. The most severe stress conditions occurred with the unilateral condylectomy, where stresses associated with torsion were most evident. PMID:1890533

Alexandridis, C; Caputo, A A; Eliades, G C

1991-07-01

39

ALS-Associated TDP-43 Induces Endoplasmic Reticulum Stress, Which Drives Cytoplasmic TDP-43 Accumulation and Stress Granule Formation  

PubMed Central

In amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration, TAR DNA binding protein 43 (TDP-43) accumulates in the cytoplasm of affected neurons and glia, where it associates with stress granules (SGs) and forms large inclusions. SGs form in response to cellular stress, including endoplasmic reticulum (ER) stress, which is induced in both familial and sporadic forms of ALS. Here we demonstrate that pharmacological induction of ER stress causes TDP-43 to accumulate in the cytoplasm, where TDP-43 also associates with SGs. Furthermore, treatment with salubrinal, an inhibitor of dephosphorylation of eukaryotic initiation factor 2-?, a key modulator of ER stress, potentiates ER stress-mediated SG formation. Inclusions of C-terminal fragment TDP-43, reminiscent of disease-pathology, form in close association with ER and Golgi compartments, further indicating the involvement of ER dysfunction in TDP-43-associated disease. Consistent with this notion, over-expression of ALS-linked mutant TDP-43, and to a lesser extent wildtype TDP-43, triggers several ER stress pathways in neuroblastoma cells. Similarly, we found an interaction between the ER chaperone protein disulphide isomerase and TDP-43 in transfected cell lysates and in the spinal cords of mutant A315T TDP-43 transgenic mice. This study provides evidence for ER stress as a pathogenic pathway in TDP-43-mediated disease. PMID:24312274

Walker, Adam K.; Soo, Kai Y.; Sundaramoorthy, Vinod; Parakh, Sonam; Ma, Yi; Farg, Manal A.; Wallace, Robyn H.; Crouch, Peter J.; Turner, Bradley J.; Horne, Malcolm K.; Atkin, Julie D.

2013-01-01

40

Acclimatization to oxidative stress at high altitude.  

PubMed

Hypoxia-mediated oxidative stress has been implicated in the pathophysiology of high altitude maladaptations. To explore whether prolonged exposure to high altitude can trigger an adaptive response to oxidative stress and restore redox homeostasis in the body, the study was conducted to evaluate biochemical variables related to oxidative stress and antioxidant status in humans at sea level (190 m) and following 3- and 13- month sojourns at altitude (4,500 m). After 3 months at altitude, whole-blood thiobarbituric acid reactive substances (TBARS) were significantly higher (65.6%), nonenzymatic antioxidants like ascorbic acid and caeruloplasmin were significantly lower (41% and 22%, respectively) and plasma total antioxidant status (TAS), glutathione levels, and superoxide dismutase activity were marginally altered as compared to their basal values. After 13 months at altitude, TBARS levels regressed back to preexposure levels. Plasma total antioxidant status (TAS) improved by 21%, glutathione levels by 32.8%, and plasma bilirubin by 35.8% as compared to sea level. Average concentrations of ascorbic acid and caeruloplasmin were 18% and 37% higher as compared to the subjects studied after a 3-month stay at high altitude. In addition, there was a progressive rise in erythrocytic superoxide dismutase activity and persistent hyperurecemia. The study observed that on prolonged exposure to high altitude humans could mount an effective adaptive response to oxidative stress by activating the antioxidant defense. Hence, strengthening the antioxidant defense could be an effective strategy to prevent free-radical-mediated pathophysiological alterations and quicken acclimatization to oxidative stress. PMID:16351564

Vij, Anjana G; Dutta, Ruma; Satija, Narinder K

2005-01-01

41

Role of microstructure in the mean stress dependence of fatigue strength in Ti-6Al-4V alloy  

SciTech Connect

The high cycle fatigue properties of Ti-6Al-4V alloy with six different microstructure/texture combinations were investigated. Only materials with lamellar and fine bimodal microstructures exhibited linear Goodman relationship on the constant fatigue life diagram. Materials with coarse bimodal and equiaxed microstructures had anomalous mean stress dependency, with HCF strength at intermediate mean stresses being significantly lower than predicted by Goodman relationship, regardless of whether material was forged or cross-rolled. The role of microstructure in mean stress sensitivity behavior of Ti-6Al-4V is studied. Cyclic strain tests were conducted for all microstructures, and the results of strain-controlled and stress-controlled cyclic tests are compared and discussed.

Ivanova, S.G.; Cohen, F.S.; Biederman, R.R.; Sisson, R.D. Jr.

1999-07-01

42

Stress corrosion cracking of Ti-8Al-1 Mo-1V in molten salts  

NASA Technical Reports Server (NTRS)

The stress corrosion cracking (SCC) behavior of Ti-8Al-1 Mo-1V has been studied in several molten salt environments. Extensive data are reported for the alloy in highly pure LiCl-KCl. The influence of the metallurgical heat treatment and texture, and the mechanical microstructure show similarities with aqueous solutions at lower temperature. The fracture path and cracking modes are also similar to that found in other environments. The influence of H2O and H(-) in molten LiCl-KCl lead to the conclusion that hydrogen does not play a major role in crack extension in this environment.

Smyrl, W. H.; Blackburn, M. J.

1975-01-01

43

Effect of base dopants on the bias stress stability of AlGaAs/GaAs HBTs  

NASA Astrophysics Data System (ADS)

The effect of three base dopants C, Be, and Zn on the bias stress stability of non AlGaAs heterojunction bipolar transistors (HBTs) has been investigated. 3 x 30 micron(exp 2) HBTs were fabricated under identical process technology, emitter-base geometry, and layout design. Following 24 h of identical bias stress, it is found that both Be- and Zn-doped devices exhibited current gain degradation as high as 68 and 57%, respectively, compared with only 7% for the C-doped device. The superior bias stress stability of C-doped HBTs is demonstrated.

Ahmad, T.; Rezazadeh, A. A.; Gill, S. S.

1993-09-01

44

Residual stress characterization of Al/SiC nanoscale multilayers using X-ray  

SciTech Connect

Nanolayered composites are used in a variety of applications such as wear resistant coatings, thermal barrier coatings, optical and magnetic thin films, and biological coatings. Residual stresses produced in these materials during processing play an important role in controlling their microstructure and properties. In this paper, we have studied the residual stresses in model metal-ceramic Al/SiC nanoscale multilayers produced by physical vapor deposition (magnetron sputtering). X-ray synchrotron radiation was used to measure stresses in the multilayers using the sin{sup 2} {Psi} technique. The stresses were evaluated as a function of layer thicknesses of Al and SiC and also as a function of the number of layers. The stress state of Al in the multilayer was largely compressive, compared to single layer Al stresses. This is attributed to a peening mechanism due to bombardment of the Al layers by SiC and Ar neutrals during deposition. The stress evolution was numerically modeled by a simplified peening process to qualitatively explain the Al thickness-dependent residual stresses.

Singh, DRP [Arizona State University; Deng, X. [Arizona State University; Chawla, N. [Arizona State University; Bai, J. [Brookhaven National Laboratory (BNL); Hubbard, Camden R [ORNL; Tang, G [University of New Mexico, Albuquerque; Shen, Y-L [University of New Mexico, Albuquerque

2010-01-01

45

Does a threshold stress for creep exist in HfC-dispersed NiAl?  

NASA Technical Reports Server (NTRS)

Recently it was proposed (Jha et al., 1989; Whittenberger et al., 1990) on the basis of constant velocity testing at 1300 K that dispersion strengthened NiAl composites containing about 4 wt pct HfC possess threshold stresses for creep. Further, 1300 K compression testing has been conducted on NiAl+4HfC, and diametrically opposite behavior has been found: for constant load creep tests a normal power law behavior was observed. However, additional constant velocity testing still indicates that the flow stress is essentially independent of strain rate below 10 exp -6/s. Examination of NiAl+4.3HfC specimens deformed under constant velocity conditions revealed that the original hot extruded small grain structure could be converted to large, elongated grains during testing. Such a transformation appears to be responsible for the apparent threshold stress behavior in HfC dispersed NiAl.

Whittenberger, J. D.; Ray, Ranjan; Jha, Sunil C.

1991-01-01

46

Suppression of Crack Generation Using High-Compressive-Strain AlN\\/Sapphire Template for Hydride Vapor Phase Epitaxy of Thick AlN Film  

Microsoft Academic Search

A stress control method was proposed to suppress crack generation in the hydride vapor phase epitaxy (HVPE) of a thick AlN film on an AlN\\/sapphire template, i.e., a high-compressive-strain (HCS) AlN\\/sapphire template was employed as a substrate. The AlN films on the HCS AlN\\/sapphire template were crack-free and very smooth. However, the AlN films on the normal AlN\\/sapphire template (with

Kenichi Tsujisawa; Shinya Kishino; Da-Bing Li; Hideto Miyake; Kazumasa Hiramatsu; Tomohiko Shibata; Mitsuhiro Tanaka

2007-01-01

47

Intrinsic stress evolution during amorphous oxide film growth on Al surfaces  

SciTech Connect

The intrinsic stress evolution during formation of ultrathin amorphous oxide films on Al(111) and Al(100) surfaces by thermal oxidation at room temperature was investigated in real-time by in-situ substrate curvature measurements and detailed atomic-scale microstructural analyses. During thickening of the oxide a considerable amount of growth stresses is generated in, remarkably even amorphous, ultrathin Al{sub 2}O{sub 3} films. The surface orientation-dependent stress evolutions during O adsorption on the bare Al surfaces and during subsequent oxide-film growth can be interpreted as a result of (i) adsorption-induced surface stress changes and (ii) competing processes of free volume generation and structural relaxation, respectively.

Flötotto, D., E-mail: d.floetotto@is.mpg.de; Wang, Z. M.; Jeurgens, L. P. H. [Max Planck Institute for Intelligent Systems (former Max Planck Institute for Metals Research), Heisenbergstraße 3, D-70569 Stuttgart (Germany); Mittemeijer, E. J. [Max Planck Institute for Intelligent Systems (former Max Planck Institute for Metals Research), Heisenbergstraße 3, D-70569 Stuttgart (Germany); Institute for Materials Science, University of Stuttgart (Germany)

2014-03-03

48

Intrinsic stress evolution during amorphous oxide film growth on Al surfaces  

NASA Astrophysics Data System (ADS)

The intrinsic stress evolution during formation of ultrathin amorphous oxide films on Al(111) and Al(100) surfaces by thermal oxidation at room temperature was investigated in real-time by in-situ substrate curvature measurements and detailed atomic-scale microstructural analyses. During thickening of the oxide a considerable amount of growth stresses is generated in, remarkably even amorphous, ultrathin Al2O3 films. The surface orientation-dependent stress evolutions during O adsorption on the bare Al surfaces and during subsequent oxide-film growth can be interpreted as a result of (i) adsorption-induced surface stress changes and (ii) competing processes of free volume generation and structural relaxation, respectively.

Flötotto, D.; Wang, Z. M.; Jeurgens, L. P. H.; Mittemeijer, E. J.

2014-03-01

49

Cu-Al-Ni-SMA-Based High-Damping Composites  

NASA Astrophysics Data System (ADS)

Recently, absorption of vibration energy by mechanical damping has attracted much attention in several fields such as vibration reduction in aircraft and automotive industries, nanoscale vibration isolations in high-precision electronics, building protection in civil engineering, etc. Typically, the most used high-damping materials are based on polymers due to their viscoelastic behavior. However, polymeric materials usually show a low elastic modulus and are not stable at relatively low temperatures (?323 K). Therefore, alternative materials for damping applications are needed. In particular, shape memory alloys (SMAs), which intrinsically present high-damping capacity thanks to the dissipative hysteretic movement of interfaces under external stresses, are very good candidates for high-damping applications. A completely new approach was applied to produce high-damping composites with relatively high stiffness. Cu-Al-Ni shape memory alloy powders were embedded with metallic matrices of pure In, a In-10wt.%Sn alloy and In-Sn eutectic alloy. The production methodology is described. The composite microstructures and damping properties were characterized. A good particle distribution of the Cu-Al-Ni particles in the matrices was observed. The composites exhibit very high damping capacities in relatively wide temperature ranges. The methodology introduced provides versatility to control the temperature of maximum damping by adjusting the shape memory alloy composition.

López, Gabriel A.; Barrado, Mariano; San Juan, Jose; Nó, María Luisa

2009-08-01

50

Stress Corrosion Cracking in Al-Zn-Mg-Cu Aluminum Alloys in Saline Environments  

NASA Astrophysics Data System (ADS)

Stress corrosion cracking of Al-Zn-Mg-Cu (AA7xxx) aluminum alloys exposed to saline environments at temperatures ranging from 293 K to 353 K (20 °C to 80 °C) has been reviewed with particular attention to the influences of alloy composition and temper, and bulk and local environmental conditions. Stress corrosion crack (SCC) growth rates at room temperature for peak- and over-aged tempers in saline environments are minimized for Al-Zn-Mg-Cu alloys containing less than ~8 wt pct Zn when Zn/Mg ratios are ranging from 2 to 3, excess magnesium levels are less than 1 wt pct, and copper content is either less than ~0.2 wt pct or ranging from 1.3 to 2 wt pct. A minimum chloride ion concentration of ~0.01 M is required for crack growth rates to exceed those in distilled water, which insures that the local solution pH in crack-tip regions can be maintained at less than 4. Crack growth rates in saline solution without other additions gradually increase with bulk chloride ion concentrations up to around 0.6 M NaCl, whereas in solutions with sufficiently low dichromate (or chromate), inhibitor additions are insensitive to the bulk chloride concentration and are typically at least double those observed without the additions. DCB specimens, fatigue pre-cracked in air before immersion in a saline environment, show an initial period with no detectible crack growth, followed by crack growth at the distilled water rate, and then transition to a higher crack growth rate typical of region 2 crack growth in the saline environment. Time spent in each stage depends on the type of pre-crack ("pop-in" vs fatigue), applied stress intensity factor, alloy chemistry, bulk environment, and, if applied, the external polarization. Apparent activation energies ( E a) for SCC growth in Al-Zn-Mg-Cu alloys exposed to 0.6 M NaCl over the temperatures ranging from 293 K to 353 K (20 °C to 80 °C) for under-, peak-, and over-aged low-copper-containing alloys (<0.2 wt pct) are typically ranging from 80 to 85 kJ/mol, whereas for high-copper-containing alloys (>~0.8 wt pct), they are typically ranging from 20 to 40 kJ/mol for under- and peak-aged alloys, and based on limited data, around 85 kJ/mol for over-aged tempers. This means that crack propagation in saline environments is most likely to occur by a hydrogen-related process for low-copper-containing Al-Zn-Mg-Cu alloys in under-, peak- and over-aged tempers, and for high-copper alloys in under- and peak-aged tempers. For over-aged high-copper-containing alloys, cracking is most probably under anodic dissolution control. Future stress corrosion studies should focus on understanding the factors that control crack initiation, and insuring that the next generation of higher performance Al-Zn-Mg-Cu alloys has similar longer crack initiation times and crack propagation rates to those of the incumbent alloys in an over-aged condition where crack rates are less than 1 mm/month at a high stress intensity factor.

Holroyd, N. J. Henry; Scamans, G. M.

2013-03-01

51

Residual stress in high modulus carbon fibers  

NASA Technical Reports Server (NTRS)

The modulus and residual strain in carbon fibers are measured by successively electrochemically milling away the fiber surface. Electrochemical etching is found to remove the carbon fiber surface very uniformly, in contrast to air and wet oxidation. The precision of fiber diameter measurements is improved by using a laser diffraction technique instead of optical methods. More precise diameter measurements reveal that past correlations of diameter and fiber modulus are largely measurement artifact. The moduli of most carbon fibers decrease after the outer layers of the fibers are removed. Owing to experimental difficulties, the moduli and strengths of the fibers at their centers are not determined, and moduli are estimated on the basis of microstructure. The calculated residual stresses are found to be insensitive to these moduli estimates as well as the exact form of regression equation used to describe the moduli and residual strain distributions. Axial compressive residual stresses are found to be very high for some higher modulus carbon fibers. It is pointed out that the compressive stress makes the fibers insensitive to surface flaws when loaded in tension but it may initiate failure by buckling when loaded in compression.

Chen, K. J.; Diefendorf, R. J.

1982-01-01

52

Bending fatigue tests on SiC-Al tapes under alternating stress at room temperature  

NASA Technical Reports Server (NTRS)

The development of a testing method for fatigue tests on SiC-Al tapes containing a small amount of SiC filaments under alternating stress is reported. The fatigue strength curves resulting for this composite are discussed. They permit an estimate of its behavior under continuous stress and in combination with various other matrices, especially metal matrices.

Herzog, J. A.

1981-01-01

53

High temperature creep behavior of oxide dispersion strengthened NiAl intermetallics  

SciTech Connect

The intermetallic compound NiAl is a promising candidate material for high-temperature applications, provided its creep strength can be raised by some strengthening strategy. Oxide-dispersion strengthened (ODS) NiAl has been produced by powder-metallurgical methods and its creep behavior at temperatures up to 1,723 K (1,450 C) has been studied. Exceptional creep properties, with high stresses and stress sensitivities when compared to dispersoid-free NiAl, are found, which confirms the effectiveness of dispersion strengthening in this material. The creep behavior is interpreted in the light of creep models. Detachment-controlled models satisfactorily describe the deformation in coarse-grained ODS-NiAl, but modifications are necessary for fine-grained material. In technical terms, ODS-NiAl recommends itself as a strong, light and oxidation-resistant high-temperature alloy for applications up to 1,700 K.

Arzt, E.; Grahle, P. [Univ. of Stuttgart (Germany)] [Univ. of Stuttgart (Germany)

1998-05-01

54

Stress corrosion cracking and hydrogen embrittlement of an Al-Zn-Mg-Cu alloy  

SciTech Connect

The age hardening, stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of an Al-Zn-Mg-Cu 7175 alloy were investigated experimentally. There were two peak-aged states during ageing. For ageing at 413 K, the strength of the second peak-aged state was slightly higher than that of the first one, whereas the SCC susceptibility was lower, indicating that it is possible to heat treat 7175 to high strength and simultaneously to have high SCC resistance. The SCC susceptibility increased with increasing Mg segregation at the grain boundaries. Hydrogen embrittlement (HE) increased with increased hydrogen charging and decreased with increasing ageing time for the same hydrogen charging conditions. Computer simulations were carried out of (a) the Mg grain boundary segregation using the embedded atom method and (b) the effect of Mg and H segregation on the grain boundary strength using a quasi-chemical approach. The simulations showed that (a) Mg grain boundary segregation in Al-Zn-Mg-Cu alloys is spontaneous, (b) Mg segregation decreases the grain boundary strength, and (c) H embrittles the grain boundary more seriously than does Mg. Therefore, the SCC mechanism of Al-Zn-Mg-Cu alloys is attributed to the combination of HE and Mg segregation induced grain boundary embrittlement.

Song, R.G.; Dietzel, W.; Zhang, B.J.; Liu, W.J.; Tseng, M.K.; Atrens, A

2004-09-20

55

High-cycle fatigue characterization of titanium 5Al-2.5Sn alloy  

NASA Technical Reports Server (NTRS)

High-cycle fatigue behavior of titanium 5Al 2.5Sn alloy at room temperature has been studied. S-N curve characterization is performed at different stress ratios ranging from 0 to 0.9 on a subsized fatigue specimen. Both two-stress and three-stress level tests are conducted at different stress ratios to study the cumulative fatigue damage. Life prediction techniques of linear damage rule, double linear damage rule and damage curve approaches are applied, and results are compared with the experimental data. The agreement between prediction and experiment is found to be excellent.

Mahfuz, H.; Xin, Yu T.; Jeelani, S.

1993-01-01

56

Micromechanical stresses in SiC-reinforced Al2O3 composites  

NASA Technical Reports Server (NTRS)

Applying an Eshelby (1957) approach, the internal micromechanical stresses within an SiC-inclusion-reinforced (platelet to whisker geometries) polycrystalline alumina matrix composite were calculated. The results are compared to the experimental residual stress measurements of a SiC-whisker-reinforced Al2O3 by Predecki, et al. (in press) and found to be in excellent agreement. The calculations are then extended to SiC-reinforced composites with polycrystalline mullite, silicon nitride, and cordierite matrices. It is concluded that the internal stresses are significantly influenced by the inclusion geometry as well as the thermoelastic differences between the inclusion and the matrix and also the volume fraction.

Li, Zhuang; Bradt, Richard C.

1989-01-01

57

The Influence of Al-Anon on Stress of Wives of Alcoholics.  

ERIC Educational Resources Information Center

This study assessed Alcoholics Anonymous (Al-Anon) participation as a factor in stress of wives of alcoholics. Additional data focused on attitude and behavior variables. Two groups of 20 subjects each were enlisted from Al-Anon, personal contacts, treatment centers, and referrals in three urban areas in the southeastern United States. Group A…

McGregor, Phyllis W.

58

Stress development in alumina scales formed upon oxidation of (111) NiAl single crystals  

Microsoft Academic Search

Stress evolution in the ? phase of the alumina scale formed on single crystals of (111) NiAl as a function of oxidation time at 1100 °C is reported. The measurements are made at room temperature using the fluorescence from trace Cr3+ impurities in the NiAl that are incorporated into the oxide scale during oxidation. After a short transient period, the

D. M. Lipkin; D. R. Clarke; M. Hollatz; M. Bobeth; W. Pompe

1997-01-01

59

Ab initio local stress and its application to Al (111) surfaces  

NASA Astrophysics Data System (ADS)

A practical way to calculate local quantum stress within the framework of stress density developed by Filippetti and Fiorentini [Phys. Rev. B 61, 8433 (2000)] is proposed and applied to Al (111) surfaces. Through detailed analysis of the gauge-dependent term in the kinetic stress density derived from the kinetic-energy density, it has been shown that the local stress components can be uniquely obtained by defining appropriate local regions where the gauge-dependent term integrates to zero. In Al (111) surface-slab calculations implemented by the projector-augmented-wave method, we have observed Friedel-type oscillation of the layer-by-layer stress, which reveals clear correlation with charge redistribution at the surface.

Shiihara, Yoshinori; Kohyama, Masanori; Ishibashi, Shoji

2010-02-01

60

Tropical soils with high aluminum concentrations cause oxidative stress in two tomato genotypes.  

PubMed

Tropical and subtropical soils are usually acidic and have high concentrations of aluminum (Al). Aluminum toxicity in plants is caused by the high affinity of the Al cation for cell walls, membranes, and metabolites. In this study, the response of the antioxidant-enzymatic system to Al was examined in two tomato genotypes: Solanum lycopersicum var. esculentum (Calabash Rouge) and Solanum lycopersicum var. cerasiforme (CNPH 0082) grown in tropical soils with varying levels of Al. Plant growth; activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPOX), and glutathione reductase (GR) enzymes; stress-indicating compounds (malondialdehyde (MDA) and hydrogen peroxide); and morphology (root length and surface area) were analyzed. Increased levels of Al in soils were correlated with reduced shoot and root biomass and with reduced root length and surface area. Calabash Rouge exhibited low Al concentrations and increased growth in soils with the highest levels of Al. Plants grown in soils with high availability of Al exhibited higher levels of stress indicators (MDA and hydrogen peroxide) and higher enzyme activity (CAT, APX, GPOX, and GR). Calabash Rouge absorbed less Al from soils than CNPH 0082, which suggests that the genotype may possess mechanisms for Al tolerance. PMID:25647795

Nogueirol, Roberta Corrêa; Monteiro, Francisco Antonio; Gratão, Priscila Lupino; Borgo, Lucélia; Azevedo, Ricardo Antunes

2015-03-01

61

The Influence of Hydrogen on the Stress Corrosion Cracking of Low-Strength AL-MG Alloys  

SciTech Connect

There is growing evidence for hydrogen uptake in aluminum alloys and its contribution to the crack growth of high-strength aluminum alloys but less evidence for low-strength alloys. This paper summarizes the evidence for hydrogen uptake in a low-strength alloy AA5083 and its contribution to the stress corrosion cracking of this alloy. A key factor is the anodic dissolution of grain boundary b phase (Al3Mg2) and the associated hydrogen reduction that accompanies this dissolution.

Jones, Russell H.

2003-02-01

62

Growth strains and stress relaxation in alumina scales during high temperature oxidation  

SciTech Connect

A novel X-ray technique was used, exploiting synchrotron radiation at the Advanced Photon Source at Argonne National Laboratory, to investigate the growth stresses in {alpha}-Al{sub 2}O{sub 3}. In-situ measurements of Debye-Scherrer diffraction patterns from the scale were recorded during oxidation and cooling, and the elliptical distortion of the diffraction rings was analyzed to yield the in-plane strain. Fe-28Al, Fe-40Al, Fe-40Al-0.2Hf, Fe-20Cr-10Al and Ni-50Al (at. %) were studied. Data were acquired in air at temperatures between 950-1100 C and during cool down. In all cases, the steady stage growth strain was relatively low (<0.1%) and was either tensile or compressive depending on the alloy. A higher tensile strain often existed during the initial oxidation period when transition alumina was present. Thermal stresses imposed on NiAl by reducing the sample temperature to 950 C for a period of time showed noticeable stress relaxation by creep. Different degrees of relaxation were also found during cooling depending on alloy composition and scale microstructure. On all Fe-based alloys, the first formed {alpha}-Al{sub 2}O{sub 3} was highly textured with the degree of texture decreasing with further oxidation. The relationships between stress development, scale wrinkling, oxide phase changes, and the effect of reactive element addition on growth stresses are discussed. Results are compared with other reports of growth stresses in Al{sub 2}O{sub 3} scales.

Hou, P.Y.; Paulikas, A.P.; Veal, B.W.

2004-03-23

63

Investigation of High-Electric-Field Degradation Effects in AlGaN\\/GaN HEMTs  

Microsoft Academic Search

High-electric-field degradation phenomena are investigated in GaN-capped AlGaN\\/GaN HEMTs by comparing experimental data with numerical device simulations. Under power- and OFF-state conditions, 150-h DC stresses were carried out. Degradation effects characterizing both stress experiments were as follows: a drop in the dc drain current, the amplification of gate-lag effects, and a decrease in the reverse gate leakage current. Numerical simulations

Mustapha Faqir; Giovanni Verzellesi; Gaudenzio Meneghesso; Enrico Zanoni; Fausto Fantini

2008-01-01

64

Determination and Relaxation of Residual Stress in 2024 Al-30 vol.% Magnesium Borate Whisker Composites  

NASA Astrophysics Data System (ADS)

Residual stresses in 30 vol.% magnesium borate whisker-reinforced 2024 aluminum matrix composites have been determined by a nanoindentation method which takes into consideration pile-up and sink-in effects on indentation contact depth. Owing to the thermal mismatch and the large difference in elasticity modulus between the Al matrix and MBO whiskers, tensile residual stress was introduced to Al matrix material during fabrication. It was found that the solution treatment reduced the tensile residual stress by producing interfacial component and dislocations in the composites. Cryogenic cooling released the stress via reversing the tensile residual stress to compression in the matrix, which was more effective than solution treatment to release the tension stress in the composites. The combination of the solution treatment and the cryogenic cooling provided the most effective procedure to release the residual stress in the composites, which reduced the tensile residual stress from 232.6 to 56.5 MPa, i.e., 76% reduction. Meanwhile, no cracks were observed in the composite when processed with such sudden thermal shocking.

Wang, Zhijiang; Jiang, Zhaohua; Hu, Henry; Nie, Xueyuan

2013-10-01

65

Effect of laser spot size on the residual stress field of pure Al treated by laser shock processing: Simulations  

NASA Astrophysics Data System (ADS)

Laser shock processing (LSP) is a unique surface treatment technique. It induces high-depth compressive residual stresses for improved fatigue or stress corrosion cracking resistance. FEM simulation is an effective method to predict material behavior by LSP. A 2D quarter-infinite model was used to simulate the material behaviors of commercially pure Al by LSP. Different peak pressure with different laser spot diameter was applied to surface of pure Al. Each simulation included two steps: (i) explicit dynamics analysis for the analysis of the LSP; (ii) static equilibrium analysis for springback deformation analysis. The following conclusions could be made: (1) Plastically affected depth increased with the increase of laser spot diameter. There was an ultimate value about plastically affected depth when the laser spot diameter increased to some value, and the ultimate value was consistent with Ballard' model. When the laser spot diameter was small, there still existed tensile residual stresses on the surface layer of material although the peak pressure was below 2.5 HEL. When the diameter laser spot diameter was big enough, the tensile residual stresses on the surface layer of material were converted into compressive residual stresses although the peak pressure was higher than 2.5 HEL.

Dai, F. Z.; Lu, J. Z.; Zhang, Y. K.; Wen, D. P.; Ren, X. D.; Zhou, J. Z.

2014-10-01

66

Softening Kinetics in High Al and High Al-Nb-Microalloyed Steels  

NASA Astrophysics Data System (ADS)

Double-hit torsion tests were performed in order to study the effect of high Al levels (up to 2 wt.%) and Nb microalloying (up to 0.07 wt.%) on the static softening kinetics of 0.2%C-2%Mn steels. The addition of 1%Al leads to a delay in the softening kinetics due to solute-drag effect, equivalent to that exerted by 0.027%Nb. For the 2%Al steels, at temperatures below 1000 °C, ? ? ? phase transformation occurs after deformation, resulting in a larger retardation of the softening kinetics. At temperatures higher than 1000 °C, Nb in solid solution also contributes to the retardation of the static softening kinetics, and at lower temperatures NbC strain-induced precipitation leads to incomplete softening for the 1%Al steel, and to a complex interaction between softening, phase transformation, and NbC strain-induced precipitation for the 2%Al-Nb steels. The effect of Al on the static softening kinetics was quantified and introduced in a model developed in previous works for the prediction of the austenite microstructural evolution. In order to validate the results of the model, multipass torsion tests were carried out at conditions representative of hot strip and plate rolling mills. Model predictions show reasonable agreement with the results obtained at different deformation conditions.

Pereda, B.; Aretxabaleta, Z.; López, B.

2015-01-01

67

Response of piezoelectric lead metaniobate to high compressive stresses  

Microsoft Academic Search

The induced polarization, P3(C\\/m2), in piezoelectric lead metaniobate was examined as a function of monotonically increasing uniaxial stress parallel to the poling direction. Comparison to the induced polarization as extrapolated from small oscillating force measurements illustrates, as expected, a nonlinear response at high compressive stress levels. The stress level beyond which nonlinearities occur was determined

A. Amin; S. J. Lukasiewicz

1985-01-01

68

Dynamic deformation behavior of a high reinforcement content TiB 2\\/Al composite at high strain rates  

Microsoft Academic Search

Dynamic compressive properties of a 60vol.% TiB2\\/Al composite fabricated by squeeze casting method were measured using split Hopkinson pressure bar. The 60vol.% TiB2\\/Al composite showed significant strain-rate sensitivity compared with the rate insensitive aluminum alloy matrix. The flow stress and the strain-rate sensitivity both showed rise\\/fall tendency at high strain rates. Moreover, a large plastic strain as 7.8% was obtained

Dezhi Zhu; Gaohui Wu; Guoqin Chen; Qiang Zhang

2008-01-01

69

Effects of intrinsic stress on submicrometer Nb/AlO/sub x//Nb Josephson junctions  

SciTech Connect

The intrinsic stress and its relaxation process are discussed for sputtered Nb films used for the electrodes in Nb/AlOx/Nb Josephson junctions. The stress, optically measured for Nb films, depends on the Ar pressure during sputtering, and changes from compressive to tensile when the Ar pressure is increased. From x-ray diffraction, a shift in the lattice constant was observed to be proportional to the film stress. Changes in the lattice constant were also clearly observed when Nb films were etched to fine patterns. These changes are significant for finer patterns. This suggests that the intrinsic stress in Nb films is relaxed at peripheral areas after patterning processes, and that such relaxation is one cause of deterioration in current-voltage characteristics frequently observed in small Josephson junctions. This emphasizes that stress-free Nb should be employed for submicrometer junctions.

Imamura, T.; Hasuo, S.

1989-03-01

70

Stress investigation of the AlGaN/GaN micromachined circular diaphragms of a pressure sensor  

NASA Astrophysics Data System (ADS)

In this paper, selected mechanical properties of a circular AlGaN/GaN diaphragm with an integrated circular high electron mobility transistor (HEMT) intended for pressure sensing are investigated. Two independent methods were used to determine the residual stress in the proposed diaphragms. The resonant frequency method using laser Doppler vibrometry (LDV) for vibration measurement was chosen to measure the natural frequencies while the diaphragms were excited by acoustic impulse. It is shown that resonant frequency is strongly dependent on the built-in residual stress. The finite element analysis (FEM) in Ansys software was performed to determine the stress value from frequency spectra measured. The transition behavior of proposed diaphragms between the ideal circular membrane and plate is observed and discussed. Secondly, the bulging method and white light interferometry (WLI) are used to determine the stress-dependent deflection response of the AlGaN/GaN diaphragm under static pressure loading. Regarding the results obtained, the optimal design of the sensing electrodes is outlined.

Dzuba, J.; Vanko, G.; Držík, M.; Rýger, I.; Vallo, M.; Kutiš, V.; Haško, D.; Choleva, P.; Lalinský, T.

2015-01-01

71

An investigation of the effects of stress ratio and crack closure on the micromechanisms of fatigue crack growth in Ti-6Al-4V  

SciTech Connect

The effects of positive stress ratios on the fatigue crack growth behavior of a forged, mill-annealed Ti-6Al-4V alloy (with duplex {alpha} + {beta} microstructure) are discussed. Differences between fatigue crack growth rates at low and high stress ratios are shown to be due largely to crack closure. A 1% offset procedure is shown to collapse closure corrected low stress ratio data with the closure-free high stress ratio data. A three parameter multiple regression model is developed for the prediction of the fatigue crack growth rate as a function of stress ratio, crack closure and stress intensity factor range for Ti-6Al-4V. The micromechanisms of fatigue crack growth in the near-threshold and Paris regimes are elucidated via crack tip transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Crack tip TEM shows that Stage II fatigue crack growth in Ti-6Al-4V is crystallographic in nature. Stage II cracks are shown to unzip along intersecting slip bands that are induced as a result of shear localization. The unzipping crack growth mechanism observed in polycrystalline Ti-6Al-4V is shown to be consistent with Neumann`s alternating slip model for the information of striations in single crystals.

Dubey, S.; Soboyejo, A.B.O.; Soboyejo, W.O. [Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering] [Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering

1997-07-01

72

Influence of Ti/TiAlN-multilayer designs on their residual stresses and mechanical properties  

NASA Astrophysics Data System (ADS)

In this research work, Ti/TiAlN multilayers of various designs were deposited onto substrates pretreated by different etching procedures. The influence of multilayer design and substrate pretreatment on multilayers adhesion, hardness, wear and friction coefficients was systematically analyzed and correlated with residual stresses of these multilayers as well as with residual stresses on the coating-near substrate region, which were analyzed by synchrotron X-ray diffraction at HZB-BESSYII. These investigations show that the adhesion can be improved by a specific etching procedure, which cause increased compressive stress in the coating-near the substrate region. Additionally, it was found, that the multilayer with the thickest ceramic layers has the highest hardness and the lowest wear coefficients as well as the lowest compressive residual stress within studied multilayers.

Vogli, E.; Tillmann, W.; Selvadurai-Lassl, U.; Fischer, G.; Herper, J.

2011-08-01

73

High temperature deformation of NiAl and CoAl  

NASA Technical Reports Server (NTRS)

The high temperature mechanical properties of the aluminides are reviewed with respect to their potential as high temperature structural materials. It is shown that NiAl and CoAl are substantially stronger than the pure metals Ni and Co at high temperatures and approach the strength of some superalloys, particularly when those superalloys are tested in "weak" directions. The factors that limit and control the high temperature strengths of NiAl and CoAl are examined to provide a basis for the development of intermetallic alloys of this type.

Nix, W. D.

1982-01-01

74

Thermal stress in high temperature cylindrical fasteners  

NASA Technical Reports Server (NTRS)

Uninsulated structures fabricated from carbon or silicon-based materials, which are allowed to become hot during flight, are attractive for the design of some components of hypersonic vehicles. They have the potential to reduce weight and increase vehicle efficiency. Because of manufacturing contraints, these structures will consist of parts which must be fastened together. The thermal expansion mismatch between conventional metal fasteners and carbon or silicon-based structural materials may make it difficult to design a structural joint which is tight over the operational temperature range without exceeding allowable stress limits. In this study, algebraic, closed-form solutions for calculating the thermal stresses resulting from radial thermal expansion mismatch around a cylindrical fastener are developed. These solutions permit a designer to quickly evaluate many combinations of materials for the fastener and the structure. Using the algebraic equations developed, material properties and joint geometry were varied to determine their effect on thermal stresses. Finite element analyses were used to verify that the closed-form solutions derived give the correct thermal stress distribution around a cylindrical fastener and to investigate the effect of some of the simplifying assumptions made in developing the closed-form solutions for thermal stresses.

Blosser, Max L.

1988-01-01

75

ALS Multicenter Cohort Study of Oxidative Stress (ALS COSMOS): The study methodology, recruitment, and baseline demographic and disease characteristics  

PubMed Central

Objective In a multicenter study of newly diagnosed ALS patients without a reported family history of ALS, we are prospectively investigating whether markers of oxidative stress (OS) are associated with disease progression. Methods An extensive structured telephone interview ascertained environmental, lifestyle, dietary and psychological risk factors associated with OS. Detailed assessments were performed at baseline and at 3 to 6 month intervals during the ensuing 30 months. Our biorepository includes DNA, plasma, urine, and skin. Results 355 patients were recruited. Subjects were enrolled over a 36 month-period at 16 sites. To meet the target number of subjects, the recruitment period was prolonged and additional sites were included. Demographic and disease characteristics were similar between 477 eligible/non-enrolled and enrolled patients, with the only difference being type of health insurance among enrolled patients. Sites were divided into 3 groups by the number of enrolled subjects. Comparing these 3 groups, the Columbia site had fewer “definite ALS” diagnoses. Conclusion This is the first prospective, interdisciplinary, in-depth, multicenter epidemiological investigation of OS related to ALS progression and was accomplished by an aggressive recruitment process. The baseline demographic and disease features of the study sample are now fully characterized. PMID:24564738

Mitsumoto, Hiroshi; Factor-Litvak, Pam; Andrews, Howard; Goetz, Raymond R.; Andrews, Leslie; Rabkin, Judith G.; McElhiney, Martin; Nieves, Jeri; Santella, Regina M.; Murphy, Jennifer; Hupf, Jonathan; Singleton, Jess; Merle, David; Kilty, Mary; Heitzman, Daragh; Bedlack, Richard S.; Miller, Robert G; Katz, Jonathan S.; Forshew, Dallas; Barohn, Richard J.; Sorenson, Eric J.; Oskarsson, Bjorn; Filho, J Americo M. Fernandes; Kasarskis, Edward J.; Lomen-Hoerth, Catherine; Mozaffar, Tahseen; Rollins, Yvonne D.; Nations, Sharon P.; Swenson, Andrea J.; Shefner, Jeremy M.; Andrews, Jinsy A.; Koczon-Jaremko, Boguslawa A.

2015-01-01

76

Sources of Stress and Dissatisfaction in Experienced High School Teachers.  

ERIC Educational Resources Information Center

High school teachers were surveyed to identify sources of stress and dissatisfaction that may induce teachers to leave teaching. Data on perceived role, school climate, coping resources, and specific work problems were canonically correlated to create a construct of teacher stress. Results are discussed. (Author/DF)

Litt, Mark D.; Turk, Dennis C.

1985-01-01

77

Deposition of ultrathin AlN films for high frequency electroacoustic devices  

SciTech Connect

The authors investigate the microstructure, crystal orientation, and residual stress of reactively sputtered aluminum nitride (AlN) films having thicknesses as low as 200 down to 25 nm. A two-step deposition process by the dual cathode ac (40 kHz) powered S-gun magnetron enabling better conditions for AlN nucleation on the surface of the molybdenum (Mo) bottom electrode was developed to enhance crystallinity of ultrathin AlN films. Using the two-step process, the residual in-plane stress as well as the stress gradient through the film thickness can be effectively controlled. X-ray rocking curve measurements have shown that ultrathin films grown on Mo using this technology are highly c-axis oriented with full widths at half maximum of 1.8 deg. and 3.1 deg. for 200- and 25-nm-thick films, respectively, which are equal to or even better than the results previously reported for relatively thick AlN films. High-resolution transmission electron microscopy and fast Fourier transform analyses have confirmed strong grain orientation in 25-100-nm-thick films. A fine columnar texture and a continuous lattice microstructure within a single grain from the interface with the Mo substrate through to the AlN surface have been elicited even in the 25-nm-thick film.

Felmetsger, Valery V.; Laptev, Pavel N.; Graham, Roger J. [OEM Group Incorporated, 2120 W. Guadalupe Road, Gilbert, Arizona 85233 (United States); NanoTEM Analytics Incorporated, 7620 E. McKellips Road, Suite 4109, Scottsdale, Arizona 85257 (United States)

2011-03-15

78

High Al-content AlGaN\\/GaN MODFETs for ultrahigh performance  

Microsoft Academic Search

The use of an AlGaN layer with high Al mole-fraction is proposed to increase the equivalent figures of merit of the AlGaN\\/GaN MODFET structure. It is shown that the room temperature mobility has little degradation with increasing Al mole-fraction up to 50%. 0.7-?m gate-length Al0.5Ga0.5N\\/GaN MODFETs by optical lithography exhibit a current density of 1 A\\/mm and three-terminal breakdown voltages

Y.-F. Wu; B. P. Keller; P. Fini; S. Keller; T. J. Jenkins; L. T. Kehias; S. P. Denbaars; U. K. Mishra

1998-01-01

79

Mechanisms of stress-corrosion cracking and liquid-metal embrittlement in Al-Zn-Mg bicrystals  

Microsoft Academic Search

Metallographic and fractographic studies of intercrystalline fracture in high-purity Al-6Zn-3Mg bicrystals in inert, liquid\\u000a metal, and water environments are described. The effects of variations in grain-boundary microstructure on fracture and the\\u000a effects of cathodically charging specimens with hydrogen prior to testing in inert environments were also investigated. Mechanisms\\u000a of liquid-metal embrittlement, stress-corrosion cracking and pre-exposure embrittlement are discussed in the

S. P. Lynch

1985-01-01

80

Evidence for High Tc Superconducting Transitions in Isolated Al45- and Al47- Nanoclusters  

E-print Network

Heat capacities measured for Al45- and Al47- nanoclusters have reproducible jumps at ~ 200 K. These jumps are consistent with theoretical predictions that some clusters with highly degenerate electronic states near the Fermi level will undergo a transition into a high Tc superconducting state. An analysis based on a theoretical treatment of pairing in Al45- and Al47- agrees well with the experimental data in both the value of the critical temperature and in the size and width of the jumps in the heat capacity.

Cao, Baopeng; Starace, Anne K; Ovchinnikov, Yurii N; Kresin, Vladimir Z; Jarrold, Martin F

2008-01-01

81

Effect of mean stress (stress ratio) and aging on fatigue-crack growth in a metastable beta titanium alloy, Ti10V-2Fe3Al  

Microsoft Academic Search

The effect of mean stress, or the stress ratio (R), on the fatigue-crack growth (FCG) behavior of ?-aged and ?-aged microstructures of the beta titanium alloy Ti-10V-2Fe-3Al was investigated. While the mean stress had a negligible effect\\u000a on the FCG behavior of the ?-aged microstructure, a strong effect was observed in the ?-aged microstructure. In particular, the values of the

S. K. Jha; K. S. Ravichandran

2000-01-01

82

The microstructural characterization of the development of stress corrosion cracks in Al 7010  

SciTech Connect

The stress corrosion cracking (SCC) of underaged, peakaged and overaged Al 7010 in either water vapor, saturated air (WVSA), or in salt water has been investigated using transmission electron microscopy (TEM). The crack tip and near crack tip regions formed in Double Cantilever Beam (DCB) samples are described. A range of behaviors will be outlined in relation to the observed grain boundary microstructures and it will be shown that fracture is caused by either pure mechanical rupture, pure corrosion or SCC.

Deshais, G.; Newcomb, S.B.; Warner, T.J. [Univ. of Cambridge (United Kingdom); [Pechiney Centre de Recherches a Voreppe (France)

1998-12-31

83

Electrical measurements of voltage stressed Al2O3/GaAs MOSFET , P.D. Ye b  

E-print Network

Electrical measurements of voltage stressed Al2O3/GaAs MOSFET Z. Tang a , P.D. Ye b , D. Lee a , C layer deposition deposited Al2O3 gate dielectric have been investigated. The IV characteristics were charges may be first removed from the Al2O3 layer during the initial CVS, while the trapping of electrons

Ye, Peide "Peter"

84

Dislocation bending and tensile stress generation in GaN and AlGaN films  

NASA Astrophysics Data System (ADS)

The growth of GaN and AlGaN films is accompanied by dislocation bending, interaction, density reduction and tensile stress generation to varying degrees. A kinetic model involving outdiffusion of atoms at the growth surface has been adapted to rationalize all of these phenomena using a single platform. Active contribution of dislocation interaction, apart from stress and a surface chemical potential, to the driving force for outdiffusion of atoms from the growth surface has been considered. The kinetic model has then been used to explain stress evolution during growth of GaN films on Si using an AlN buffer layer, an example of a most general case. Stress-thickness relations obtained from the model have been fitted to experimental data to derive basic outdiffusion parameters. These parameters have been used to analyze experimental observations of dislocation structure evolution. The model is able to account for the varying degrees of dislocation bending and interaction observed in these films.

Raghavan, Srinivasan; Manning, Ian C.; Weng, Xiaojun; Redwing, Joan M.

2012-11-01

85

Effect of the N/Al ratio of AlN buffer on the crystal properties and stress state of GaN film grown on Si(1 1 1) substrate  

NASA Astrophysics Data System (ADS)

The effect of the N/Al ratio of AlN buffers on the optical and crystal quality of GaN films, grown by metalorganic chemical vapor deposition on Si(1 1 1) substrates, has been investigated. By optimizing the N/Al ratio during the AlN buffer, the threading dislocation density and the tensile stress have been decreased. High-resolution X-ray diffraction exhibited a (0 0 0 2) full-width at half-maximum as low as 396 acrsec. The variations of the tensile stress existing in the GaN films were approved by the redshifts of the donor bound exiton peaks in the low-temperature photoluminescence measurement at 77 K.

Wu, M.; Zhang, B. S.; Chen, J.; Liu, J. P.; Shen, X. M.; Zhao, D. G.; Zhang, J. C.; Wang, J. F.; Li, N.; Jin, R. Q.; Zhu, J. J.; Yang, H.

2004-01-01

86

Stresses evolution at high temperature (200°C) on the interface of thin films in magnetic components  

NASA Astrophysics Data System (ADS)

In the field of electronics, the increase of operating temperatures is a major industrial and scientific challenge because it allows reducing mass and volume of components especially in the aeronautic domain. So minimizing our components reduce masses and the use of cooling systems. For that, the behaviours and interface stresses of our components (in particular magnetic inductors and transformers) that are constituted of one magnetic layer (YIG) or an alumina substrate (Al2O3) representing the substrate and a thin copper film are studied at high temperature (200°C). COMSOL Multiphysics is used to simulate our work and to validate our measurements results. In this paper, we will present stresses results according to the geometrical copper parameters necessary for the component fabrication. Results show that stresses increase with temperature and copper's thickness while remaining always lower than 200MPa which is the rupture stress value.

Doumit, Nicole; Danoumbé, Bonaventure; Capraro, Stéphane; Chatelon, Jean-Pierre; Nader, Chadi; Habchi, Roland; Piot, Alain; Rousseau, Jean-Jacques

2014-07-01

87

High temperature dispersion strengthening of NiAl  

NASA Technical Reports Server (NTRS)

A potential high temperature strengthening mechanism for alloys based on the intermetallic compound NiAl was investigated. This study forms part of an overall program at NASA Lewis Research Center for exploring the potential of alloys based on NiAl for high temperature applications. An alloy containing 2.26 at% Nb and produced by hot extrusion of blended powders was examined in detail using optical and electron microscopy. Interdiffusion between the blended Nb and NiAl powders results in the formation of intermediate phases. A fine dispersion of precipitates of a hexagonal, ordered NiAlNb phases in a matrix of NiAl can be produced and this results in strengthening of the alloy by interfering with dislocation motion at high temperature. These precipitates are, however, found to coarsen during the high temperature (1300 K) deformation at slow strain rates and this may impose some limitatioins on the use of this strengthening mechanism.

Sherman, M.; Vedula, K.

1986-01-01

88

Dopant-Free GaN/AlN/AlGaN Radial Nanowire Heterostructures as High  

E-print Network

, for the heterostructure. Field-effect transistors fabricated with ZrO2 dielectrics and metal top gates showed excellent for nanoscale electronic devices, including field-effect transistors (FETs),3-5 inverters,6 logic circuits,7Dopant-Free GaN/AlN/AlGaN Radial Nanowire Heterostructures as High Electron Mobility Transistors

Li, Yat

89

Nonuniform magnetic stresses in high temperature superconducting thin films  

NASA Astrophysics Data System (ADS)

We provide an experimental measurement of the magnetic stresses in high temperature superconducting thin films based on the Coherent Gradient Sensor which has many merits such as real time, non-destructive, full field, vibration insensitivity, etc. As an example, the radial stress, hoop stress of the YBa2Cu3O7-x (YBCO) film, and shear stress between the film and the (00l) SrTiO3 substrate subjected to various magnetic fields at 40 K are obtained. For the interfacial shear stress in radial direction between the film and substrate, it is found that the magnitude order of which is at GPa at somewhere under a small magnetic field.

Zhang, Xingyi; Liu, Cong; Zhou, Jun; Zhou, Youhe

2014-01-01

90

High occupational stress and low career satisfaction of korean surgeons.  

PubMed

Surgery is a demanding and stressful field in Korea. Occupational stress can adversely affect the quality of care, decrease job satisfaction, and potentially increase medical errors. The aim of this study was to investigate the occupational stress and career satisfaction of Korean surgeons. We have conducted an electronic survey of 621 Korean surgeons for the occupational stress. Sixty-five questions were used to assess practical and personal characteristics and occupational stress using the Korean occupational stress scale (KOSS). The mean KOSS score was 49.31, which was higher than the average of Korean occupational stress (45.86) or that of other specialized professions (46.03). Young age, female gender, long working hours, and frequent night duties were significantly related to the higher KOSS score. Having spouse, having hobby and regular exercise decreased the KOSS score. Multiple linear regression analysis showed that long working hours and regular exercise were the independent factors associated with the KOSS score. Less than 50% of surgeons answered that they would become a surgeon again. Most surgeons (82.5%) did not want to recommend their child follow their career. Korean Surgeons have high occupational stress and low level of career satisfaction. PMID:25653482

Kang, Sang Hee; Boo, Yoon Jung; Lee, Ji Sung; Han, Hyung Joon; Jung, Cheol Woong; Kim, Chong Suk

2015-02-01

91

Static High Pressure X-Ray Diffraction of TI-6AL-4V  

NASA Astrophysics Data System (ADS)

Ti-6Al-4V was examined under static-high pressure conditions using a diamond anvil cell. The angle-dispersive x-ray diffraction experiments were performed at the Advanced Photon Source, Argonne National Laboratory. Radial and axial geometry were used to examine multiple samples. The purpose of the experiment was to generate pressure-volume data at room temperature (which is non-existent in literature) and to examine deviatoric stress effects on such a hard alloy.

Chesnut, Gary N.; Velisavljevic, Nenad; Sanchez, Lilliana

2007-12-01

92

Proteomics of rice grain under high temperature stress  

PubMed Central

Recent proteomic analyses revealed dynamic changes of metabolisms during rice grain development. Interestingly, proteins involved in glycolysis, citric acid cycle, lipid metabolism, and proteolysis were accumulated at higher levels in mature grain than those of developing stages. High temperature (HT) stress in rice ripening period causes damaged (chalky) grains which have loosely packed round shape starch granules. The HT stress response on protein expression is complicated, and the molecular mechanism of the chalking of grain is obscure yet. Here, the current state on the proteomics research of rice grain grown under HT stress is briefly overviewed. PMID:23508632

Mitsui, Toshiaki; Shiraya, Takeshi; Kaneko, Kentaro; Wada, Kaede

2013-01-01

93

Unusually High Stress Drops Associated with Shallow Moonquakes  

NASA Astrophysics Data System (ADS)

New estimates of stress drops and energy release associated with shallow moonquakes, believed to represent the only lunar seismic events of tectonic origin, have been made, taking into account (1) properties of source spectra, (2) radiation pattern of foci, (3) anelastic attenuation of seismic waves, (4) response of the seismometer, and (5) intense scattering of seismic signals. The results indicate that the three largest events show body wave magnitudes of mB > 5.5 and stress drops of ?? > 100 MPa. The values for stress drops are high compared with those generally associated with most terrestrial events, but they are compatible with results predicted from thermoelastic models of the moon. Presence of high stresses in the lunar crust may indicate that at the beginning of its history the moon was originally molten not only in the outer surface region, but throughout its whole volume.

Oberst, J.

1987-02-01

94

Ab initio local energy and local stress: application to tilt and twist grain boundaries in Cu and Al.  

PubMed

The energy-density and stress-density schemes (Shiihara et al 2010 Phys. Rev. B 81 075441) within the projector augmented wave (PAW) method based on the generalized gradient approximation (GGA) have been applied to tilt and twist grain boundaries (GBs) and single vacancies in Cu and Al. Local energy and local stress at GBs and defects are obtained by integrating the energy and stress densities in each local region by the Bader integration using a recent algorithm (Yu et al 2011 J. Chem. Phys. 134 064111) as well as by the layer-by-layer integration so as to settle the gauge-dependent problem in the kinetic terms. Results are compared with those by the fuzzy-Voronoi integration and by the embedded atom method (EAM). The features of local energy and local stress at GBs and vacancies depend on the bonding nature of each material. Valence electrons in Al mainly located in the interatomic regions show remarkable response to structural disorder as significant valence charge redistribution or bond reconstruction, often leading to long-range variations of charges, energies and stresses, quite differently from d electrons in Cu mainly located near nuclei. All these features can be well represented by our local energy and local stress. The EAM potential for Al does not reproduce correct local energy or local stress, while the EAM potential for Cu provides satisfactory results. PMID:23835349

Wang, Hao; Kohyama, Masanori; Tanaka, Shingo; Shiihara, Yoshinori

2013-07-31

95

Ab initio local energy and local stress: application to tilt and twist grain boundaries in Cu and Al  

NASA Astrophysics Data System (ADS)

The energy-density and stress-density schemes (Shiihara et al 2010 Phys. Rev. B 81 075441) within the projector augmented wave (PAW) method based on the generalized gradient approximation (GGA) have been applied to tilt and twist grain boundaries (GBs) and single vacancies in Cu and Al. Local energy and local stress at GBs and defects are obtained by integrating the energy and stress densities in each local region by the Bader integration using a recent algorithm (Yu et al 2011 J. Chem. Phys. 134 064111) as well as by the layer-by-layer integration so as to settle the gauge-dependent problem in the kinetic terms. Results are compared with those by the fuzzy-Voronoi integration and by the embedded atom method (EAM). The features of local energy and local stress at GBs and vacancies depend on the bonding nature of each material. Valence electrons in Al mainly located in the interatomic regions show remarkable response to structural disorder as significant valence charge redistribution or bond reconstruction, often leading to long-range variations of charges, energies and stresses, quite differently from d electrons in Cu mainly located near nuclei. All these features can be well represented by our local energy and local stress. The EAM potential for Al does not reproduce correct local energy or local stress, while the EAM potential for Cu provides satisfactory results.

Wang, Hao; Kohyama, Masanori; Tanaka, Shingo; Shiihara, Yoshinori

2013-07-01

96

Spallation in Ti-6Al-4V: Stress Measurements and Recovery  

NASA Astrophysics Data System (ADS)

Previous work by a number of authors has shown that the spall strength of the engineering alloy, Ti 6Al - 4V increases markedly with pulse duration. In this paper, we have reproduced those results in a low oxygen variant of the alloy, over a range of impact stresses. The microstructure consisted of a mixture of primary ? grains in a matrix of transformed ?. Samples have also been shock loaded and recovered under conditions of one-dimensional strain, to compliment the results of the stress gauge experiments. In all the recovered samples, complete spallation occurred, but examination of damage at secondary sites showed that this occurred via nucleation and growth of pores. Ductile failure appears to be a mixture of void formation and coalescence within primary ? grains and along primary ? / transformed ? boundaries.

Tyler, C.; Millett, J. C. F.; Bourne, N. K.

2006-07-01

97

High-performance nonvolatile Al/AlO(x)/CdTe:Sb nanowire memory device.  

PubMed

Here we demonstrate a room temperature processed nonvolatile memory device based on an Al/AlO(x)/CdTe:Sb nanowire (NW) heterojunction. Electrical analysis shows an echelon hysteresis composed of a high-resistance state (HRS) and a low-resistance state (LRS), which can allow it to write and erase data from the device. The conductance ratio is as high as 10?, with a retention time of 3 × 10? s. Moreover, the SET voltages ranged from +6 to +8 V, whilst the RESET voltage ?0 V. In addition, flexible memory nano-devices on PET substrate with comparable switching performance at bending condition were fabricated. XPS analysis of the Al/AlO(x)/CdTe:Sb NW heterojunction after controlled Ar? bombardment reveals that this memory behavior is associated with the presence of ultra-thin AlO(x) film. This Al/AlO(x)/CdTe:Sb NW heterojunction will open up opportunities for new memory devices with different configurations. PMID:23924708

Xie, Chao; Nie, Biao; Zhu, Long; Zeng, Long-Hui; Yu, Yong-Qiang; Wang, Xian-He; Fang, Qun-Ling; Luo, Lin-Bao; Wu, Yu-Cheng

2013-09-01

98

Degradation mechanism of enhancement-mode AlGaN/GaN HEMTs using fluorine ion implantation under the on-state gate overdrive stress  

NASA Astrophysics Data System (ADS)

The degradation mechanism of enhancement-mode AlGaN/GaN high electron mobility transistors (HEMTs) fabricated by fluorine plasma ion implantation technology is one major concern of HEMT’s reliability. It is observed that the threshold voltage shows a significant negative shift during the typical long-term on-state gate overdrive stress. The degradation does not originate from the presence of as-grown traps in the AlGaN barrier layer or the generated traps during fluorine ion implantation process. By comparing the relationships between the shift of threshold voltage and the cumulative injected electrons under different stress conditions, a good agreement is observed. It provides direct experimental evidence to support the impact ionization physical model, in which the degradation of E-mode HEMTs under gate overdrive stress can be explained by the ionization of fluorine ions in the AlGaN barrier layer by electrons injected from 2DEG channel. Furthermore, our results show that there are few new traps generated in the AlGaN barrier layer during the gate overdrive stress, and the ionized fluorine ions cannot recapture the electrons. Project supported by the National Natural Science Foundation of China (Grant Nos. 61334002, 61106106, and 61474091), the Opening Project of Science and Techology on Reliability Physics and Application Technology of Electronic Component Laboratory (Grant No. ZHD201206), the New Experiment Development Funds for Xidian University, China (Grant No. SY1213), and the Scientific Research Foundation for the Returned Overseas Chinese Scholars.

Sun, Wei-Wei; Zheng, Xue-Feng; Fan, Shuang; Wang, Chong; Du, Ming; Zhang, Kai; Chen, Wei-Wei; Cao, Yan-Rong; Mao, Wei; Ma, Xiao-Hua; Zhang, Jin-Cheng; Hao, Yue

2015-01-01

99

Influence of compressive stress on stress intensity factor of hole-edge crack by high strain rate laser shock processing  

Microsoft Academic Search

The 2D weight function was integrated with slice synthesis model in order to probe into the influence of compressive stress by high strain rate laser shock processing on stress intensity factor of 3D non-through hole-edge crack. The influence of compressive stress by laser shock of high strain rate on stress intensity factor was deduced by means of slice synthesis model

X. D. Ren; Y. K. Zhang; J. Z. Zhou; J. Z. Lu; L. C. Zhou

2009-01-01

100

Performance of Nb3Sn Quadrupole Under High Stress  

SciTech Connect

Future upgrades of the Large Hadron Collider (LHC) will require large aperture and high gradient quadrupoles. Nb{sub 3}Sn is the most viable option for this application but is also known for its strain sensitivity. In high field magnets, with magnetic fields above 12 T, the Lorentz forces will generate mechanical stresses that may exceed 200 MPa in the windings. The existing measurements of critical current versus strain of Nb{sub 3}Sn strands or cables are not easily applicable to magnets. In order to investigate the impact of high mechanical stress on the quench performance, a series of tests was carried out within a LBNL/CERN collaboration using the magnet TQS03 (a LHC Accelerator Research Program (LARP) 1-meter long, 90-mm aperture Nb{sub 3}Sn quadrupole). The magnet was tested four times at CERN under various pre-stress conditions. The average mechanical compressive azimuthal pre-stress on the coil at 4.2 K ranged from 120 MPa to 200 MPa. This paper reports on the magnet performance during the four tests focusing on the relation between pre-stress conditions and the training plateau.

Felice, H.; Bajko, M.; Bingham, B.; Bordini, B.; Bottura, L.; Caspi, S.; Rijk, G. De; Dietderich, D.; Ferracin, P.; Giloux, C.; Godeke, A.; Hafalia, R.; Milanese, A.; Rossi, L.; Sabbi, G. L.

2010-08-01

101

Effects of high mean stress on the high-cycle fatigue behavior of PWA 1480  

SciTech Connect

PWA 1480 is a potential candidate material for use in the high-pressure fuel turbine blade of the Space Shuttle Main Engine. As an engine material it will be subjected to high-cycle fatigue loading superimposed on a high mean stress due to combined centrifugal and thermal loadings. This paper describes results obtained in an ongoing program to determine the effects of a high mean stress on the high-cycle fatigue behavior of this material.

Majumdar, S.; Antolovich, S.; Milligan, W.

1985-03-01

102

Anodizing of High Electrically Stressed Components  

SciTech Connect

Anodizing creates an aluminum oxide coating that penetrates into the surface as well as builds above the surface of aluminum creating a very hard ceramic-type coating with good dielectric properties. Over time and use, the electrical carrying components (or spools in this case) experience electrical breakdown, yielding undesirable x-ray dosages or failure. The spool is located in the high vacuum region of a rod pinch diode section of an x-ray producing machine. Machine operators have recorded decreases in x-ray dosages over numerous shots using the reusable spool component, and re-anodizing the interior surface of the spool does not provide the expected improvement. A machine operation subject matter expert coated the anodized surface with diffusion pump oil to eliminate electrical breakdown as a temporary fix. It is known that an anodized surface is very porous, and it is because of this porosity that the surface may trap air that becomes a catalyst for electrical breakdown. In this paper we present a solution of mitigating electrical breakdown by oiling. We will also present results of surface anodizing improvements achieved by surface finish preparation and surface sealing. We conclude that oiling the anodized surface and using anodized hot dip sealing processes will have similar results.

Flores, P. [NSTec; Henderson, D. J. [NSTec; Good, D. E. [NSTec; Hogge, K. [NSTec; Mitton, C. V. [NSTec; Molina, I. [NSTec; Naffziger, C. [NSTec; Codova, S. R. [SNL; Ormond, E. U. [SNL

2013-06-01

103

Creep of ultra-high performance concrete under compressive stresses  

Microsoft Academic Search

2 SUMMARY In this paper the creep behavior of the self-compacting ultra-high performance concrete (UHPC) is presented. Experiments were carried out on sealed and free UHPC at the age of 7 days. The results showed that UHPC has a higher creep than conventional high performance concrete C110 loaded at the same stress level. The creep coefficient of UHPC is almost

Jianxin Ma; Holger Schneider

104

Performance of a Nb(3)Sn Quadrupole Under High Stress  

E-print Network

Future upgrades of the Large Hadron Collider (LHC) will require large aperture and high gradient quadrupoles. Nb(3)Sn is the most viable option for this application but is also known for its strain sensitivity. In high field magnets, with magnetic fields above 12 T, the Lorentz forces will generate mechanical stresses that may exceed 200 MPa in the windings. The existing measurements of critical current versus strain of Nb(3)Sn strands or cables are not easily applicable to magnets. In order to investigate the impact of high mechanical stress on the quench performance, a series of tests was carried out within a LBNL/CERN collaboration using the magnet TQS03 (a LHC Accelerator Research Program (LARP) 1-meter long, 90-mm aperture Nb(3)Sn quadrupole). The magnet was tested four times at CERN under various pre-stress conditions. The average mechanical compressive azimuthal pre-stress on the coil at 4.2 K ranged from 120 MPa to 200 MPa. This paper reports on the magnet performance during the four tests focusing on...

Felice, H; Ferracin, P; De Rijk, G; Bajko, M; Caspi, S; Bingham, B; Giloux, C; Bordini, B; Milanese, A; Bottura, L; Sabbi, G L; Hafalia, R; Godeke, A; Dietderich, D

2011-01-01

105

?-MnAl with high coercivity and saturation magnetization  

NASA Astrophysics Data System (ADS)

In this paper, high purity ?-Mn54Al46 and Mn54-xAl46Cxalloys were successfully prepared using conventional arc-melting, melt-spinning, and heat treatment process. The magnetic and the structural properties were examined using x-ray diffraction (XRD), powder neutron diffraction and magnetic measurements. A room temperature saturation magnetization of 650.5 kAm-1, coercivity of 0.5 T, and a maximum energy product of (BH)max = 24.7 kJm-3 were achieved for the pure Mn54Al46 powders without carbon doping. The carbon substituted Mn54-xAl46Cx, however, reveals a lower Curie temperature but similar saturation magnetization as compared to the carbon-free sample. The electronic structure of MnAl shows that the Mn atom possesses a magnetic moment of 2.454 ?B which results from strong hybridization between Mn-Al and Mn-Mn. We also investigated the volume and c/a ratio dependence of the magnetic moments of Mn and Al. The results indicate that an increase in the intra-atomic exchange splitting due to the cell volume expansion, leads to a large magnetic moment for the Mn atom. The Mn magnetic moment can reach a value of 2.9 ?B at a volume expansion rate of ?V/V ? 20%.

Wei, J. Z.; Song, Z. G.; Yang, Y. B.; Liu, S. Q.; Du, H. L.; Han, J. Z.; Zhou, D.; Wang, C. S.; Yang, Y. C.; Franz, A.; Többens, D.; Yang, J. B.

2014-12-01

106

Comparison of the corrosion and stress-corrosion behavior of a ternary Al-Zn-Mg alloy  

Microsoft Academic Search

A comparison has been made of the corrosion and stress-corrosion behavior of an aged Al-5.3 wt pet Zn-2.5 wt pct Mg alloy in aqueous chloride solutions of varying pH (i.e., 1 to 6.2). It is found that lowering the pH to values <4 accelerates corrosion in the absence of stress, due to enhancement of the overall cathodic process, and accelerates

A. J. Sedriks; J. A. S. Green; D. L. Novak

1970-01-01

107

The stress-corrosion behavior of Al-Li-Cu alloys: A comparison of test methods  

NASA Technical Reports Server (NTRS)

Two powder metallurgy processed (Al-Li-Cu) alloys with and without Mg addition were studied in aqueous 3.5% NaCl solution during the alternate immersion testing of tuning fork specimens, slow crack growth tests using fracture mechanics specimens, and the slow strain rate testing of straining electrode specimens. Scanning electron microscopy and optical metallography were used to demonstrate the character of the interaction between the Al-Li-Cu alloys and the selected environment. Both alloys are susceptible to SC in an aqueous 3.5% NaCl solution under the right electrochemical and microstructural conditions. Each test method yields important information on the character of the SC behavior. Under all conditions investigated, second phase particles strung out in rows along the extrusion direction in the alloys were rapidly attacked, and played principal role in the SC process. With time, larger pits developed from these rows of smaller pits and under certain electrochemical conditions surface cracks initiated from the larger pits and contributed directly to the fracture process. Evidence to support slow crack growth was observed in both the slow strain rate tests and the sustained immersion tests of precracked fracture mechanics specimens. The possible role of H2 in the stress corrosion cracking process is suggested.

Rizzo, P. P.; Galvin, R. P.; Nelson, H. G.

1982-01-01

108

Influence of thermal stress on the relative permittivity of the AlGaN barrier layer in an AlGaN/GaN heterostructure Schottky contacts  

NASA Astrophysics Data System (ADS)

Ni Schottky contacts on AlGaN/GaN heterostructures were fabricated. Some samples were thermally treated in a furnace with N2 ambience at 600 °C for different times (0.5 h, 4.5 h, 10.5 h, 18 h, 33 h, 48 h, and 72 h), the others were thermally treated for 0.5 h at different temperatures (500 °C, 600 °C, 700 °C, and 800 °C). With the measured current—voltage (I—V) and capacitance—voltage (C—V) curves and by self-consistently solving Schrodinger's and Poisson's equations, we found that the relative permittivity of the AlGaN barrier layer was related to the piezoelectric and the spontaneous polarization of the AlGaN barrier layer. The relative permittivity was in proportion to the strain of the AlGaN barrier layer. The relative permittivity and the strain reduced with the increased thermal stress time until the AlGaN barrier totally relaxed (after 18 h at 600 °C in the current study), and then the relative permittivity was almost a constant with the increased thermal stress time. When the sample was treated at 800 °C for 0.5 h, the relative permittivity was less than the constant due to the huge diffusion of the contact metal atoms. Considering the relation between the relative permittivity of the AlGaN barrier layer and the converse piezoelectric effect, the conclusion can be made that a moderate thermal stress can restrain the converse piezoelectric effect and can improve the stability of AlGaN/GaN heterostructure devices.

Lü, Yuan-Jie; Lin, Zhao-Jun; Zhang, Yu; Meng, Ling-Guo; Cao, Zhi-Fang; Luan, Chong-Biao; Chen, Hong; Wang, Zhan-Guo

2011-09-01

109

AlGaN/GaN/AlN quantum-well field-effect transistors with highly resistive AlN epilayers  

E-print Network

AlGaN/GaN/AlN quantum-well field-effect transistors with highly resistive AlN epilayers Z. Y. Fana 66506-2601 Received 23 November 2005; accepted 5 January 2006; published online 16 February 2006 AlGaN/GaN/AlN quantum-well field-effect transistors have been demonstrated. By replacing a semi-insulating GaN epilayer

Jiang, Hongxing

110

Effects of residual stress and texture on the high-cycle fatigue properties of light metals  

NASA Astrophysics Data System (ADS)

High cycle fatigue tests were conducted on a commercially pure Ti, a forged Ti-6Al-4V alloy, and newly developed high strength AA2026 and AA2099 Al alloys in four-point bend. The effects of surface compressive residual stress and texture on the fatigue properties of these alloys were systematically investigated. The resistance to fatigue crack growth in an alloy was estimated using a simple model that took into account texture and grain structure. The resistance calculations were able to explain the observed behaviors of fatigue crack growth in planar slip materials. Due to strengthening in the surface by enhancement treatment, fatigue cracks were found to be initiated in the subsurface region in the short peened Ti-6Al-4V alloy and sandblasted CP Ti, in contrast to crack initiation on the surface of the untreated samples. When the shot peened Ti-6A1-4V alloy was tested between 25°C and 200°C, the surface compressive residual stress could only be slightly relaxed due to thermal exposure, which did not deteriorate the fatigue strength of the alloy. Similarly, no obvious redistribution of the residual stress was observed when the sandblasted Ti was annealed below 200°C. With increase in the annealing temperature (300°C˜700°C), the compressive residual stresses were significantly relaxed, leading to relatively a lower fatigue strength. In AA2026 & AA2099 Al alloys, crack growth was found to be in a predominantly crystallographic mode in unrecrystallized regions, and a non-crystallographic mode in recrystallized regions. Fatigue cracks were deflected at grain boundaries usually with small twist angles in the unrecrystallized regions, but with large twist angles in the recrystallized regions. The theoretical analysis verified that a large percentage of recrystallized grains could provide strong resistance to fatigue crack growth by producing larger twist angles of crack deflection at their grain boundaries than those of most of the gains in unrecrystallized regions, and that a <111> fiber texture presented stronger resistance to fatigue crack growth than that of a typical rolling texture. These theoretical analyses provided a quantitative understanding of the effects of macro- and micro textures on the short fatigue crack initiation and propagation in f.c.c. materials. Keywords. Four-point bend fatigue, Surface enhancement treatment, Compressive residual stress, Micro- and Macro-texture effects, Fatigue crack initiation and growth

Jiang, Xiuping

2007-12-01

111

Stress evolution during growth of GaN (0001)/Al2O3(0001) by reactive dc magnetron sputter epitaxy  

NASA Astrophysics Data System (ADS)

We study the real time stress evolution, by in situ curvature measurements, during magnetron sputter epitaxy of GaN (0?0?0?1) epilayers at different growth temperatures, directly on Al2O3(0?0?0?1) substrates. The epilayers are grown by sputtering from a liquid Ga target in a mixed N2/Ar discharge. For 600 °C, a tensile biaxial stress evolution is observed, while for 700 °C and 800 °C, compressive stress evolutions are observed. Structural characterization by cross-sectional transmission electron microscopy, and atomic force microscopy, revealed that films grew at 700 °C and 800 °C in a layer-by-layer mode while a growth temperature of 600 °C led to an island growth mode. High resolution x-ray diffraction data showed that edge and screw threading dislocation densities decreased with increasing growth temperature, with a total density of 5.5 × 1010 cm-2 at 800 °C. The observed stress evolution and growth modes are explained by a high surface mobility during magnetron sputter epitaxy at 700-800 °C. Other possible reasons for the different stress evolutions are also discussed.

Junaid, M.; Sandström, P.; Palisaitis, J.; Darakchieva, V.; Hsiao, C.-L.; Persson, P. O. Å.; Hultman, L.; Birch, J.

2014-04-01

112

Distortion and Residual Stress in High-Pressure Die Castings: Simulation and Measurements  

NASA Astrophysics Data System (ADS)

Two individual high-pressure die casting geometries were developed to study the influence of process parameters and alloy composition on the distortion behavior of aluminum alloy castings. These geometries, a stress lattice and a V-shaped lid, tend to form residual stress due to a difference in wall thickness and a deliberate massive gating system. Castings were produced from two alloys: AlSi12(Fe) and AlSi10MnMg. In the experimental castings, the influence of important process parameters such as die temperature, ejection time, and cooling regime was examined. The time evolution of process temperatures was measured using thermal imaging. Subsequent to casting, distortion was measured by means of a tactile measuring device at ambient temperatures. The measured results were compared against a numerical process and stress simulations of the casting, ejection, and cooling process using the commercial finite element method software ANSYS Workbench. The heat transfer coefficients were adapted to the temperature distributions of the die, and the castings were observed by thermal imaging. A survey of the results of the comparison between simulation and experiment is given for both alloys.

Hofer, P.; Kaschnitz, E.; Schumacher, P.

2014-09-01

113

High stress actuation by dielectric elastomer with oil capsules  

NASA Astrophysics Data System (ADS)

Though capable of generating a large strain, dielectric elastomer actuators (DEAs) generate only a moderate actuation stress not more than 200kPa, which seriously limits its use as artificial muscles for robotic arm. Enhancement of dielectric strength (greater than 500MV/m) by dielectric oil immersion could possibly enable it a larger force generation. Previously, the immersion was done in an oil bath, which limits portability together with DEAs. In this study, we developed portable capsules to enclose oil over the DEA substrate (VHB 4905). The capsules is made of a thinner soft acrylic membrane and they seals dielectric liquid oil (Dow Corning Fluid 200 50cSt). The DEA substrate is a graphiteclad VHB membrane, which is pre-stretched with pure-shear boundary condition for axial actuation. When activated under isotonic condition, the oil-capsule DEA can sustain a very high dielectric field up to 903 MV/m and does not fail; whereas, the dry DEA breaks down at a lower electric field at 570 MV/m. Furthermore, the oil-capsule DEA can produces higher isometric stress change up to 1.05MPa, which is 70% more than the maximum produced by the dry DEA. This study confirmed that oil capping helps DEA achieve very high dielectric strength and generate more stress change for work.

La, Thanh-Giang; Lau, Gih-Keong; Shiau, Li-Lynn; Tan, Adrian W. Y.

2014-03-01

114

High-capacity hydrogen storage in Al-adsorbed graphene  

NASA Astrophysics Data System (ADS)

A high-capacity hydrogen storage medium—Al-adsorbed graphene—is proposed based on density-functional theory calculations. We find that a graphene layer with Al adsorbed on both sides can store hydrogen up to 13.79wt% with average adsorption energy -0.193eV/H2 . Its hydrogen storage capacity is in excess of 6wt% , surpassing U. S. Department of Energy (DOE’s) target. Based on the binding-energy criterion and molecular-dynamics calculations, we find that hydrogen storage can be recycled at near ambient conditions. This high-capacity hydrogen storage is due to the adsorbed Al atoms that act as bridges to link the electron clouds of the H2 molecules and the graphene layer. As a consequence, a two-layer arrangement of H2 molecules is formed on each side of the Al-adsorbed graphene layer. The H2 concentration in the hydrogen storage medium can be measured by the change in the conductivity of the graphene layer.

Ao, Z. M.; Peeters, F. M.

2010-05-01

115

Structural analysis of highly porous ?-Al2O3  

NASA Astrophysics Data System (ADS)

Two highly porous ?-aluminas, a commercial catalyst obtained from the calcination of boehmite and a highly mesoporous product obtained from amorphous aluminum (oxy)hydroxide via a sol-gel-based process were investigated by 27Al nuclear magnetic resonance (NMR), transmission electron microscopy (TEM), and atomic pair distribution function (PDF) analysis of synchrotron powder diffraction data. NMR data showed for both materials a distribution of tetrahedrally and octahedrally coordinated Al at a 0.30:0.70 ratio, which is typical for ?-aluminas. TEM studies revealed that rod-shaped particles with about 5 nm in thickness are the building blocks of the porous structure in both materials. These particles often extend to a length of 50 nm in the commercial catalyst and are considerably shorter in the sol-gel-based material, which has a higher surface area. Refinement of PDFs revealed the presence of a ~1 nm scale local structure and the validity of a tetragonal average structure for both materials. This tetragonal average structure contains a substantial fraction of non-spinel octahedral Al atoms. It is argued that the presence of local structure is a general feature of ?-alumina, independent of precursor and synthesis conditions. The concentration of “non-spinel” Al atoms seems to correlate with surface properties, and increases with increasing pore size/surface area. This should have implications to the catalytic properties of porous ?-alumina.

Samain, Louise; Jaworski, Aleksander; Edén, Mattias; Ladd, Danielle M.; Seo, Dong-Kyun; Javier Garcia-Garcia, F.; Häussermann, Ulrich

2014-09-01

116

STRESS  

NSDL National Science Digital Library

During this activity, students will use the available resources to learn more about stress, the effects of stress and how to handle stress. This activity focuses on the Utah fifth grade health core Standard 1: The students will learn ways to improve mental health and manage stress. During this project, students are given two different scenarios and ...

Hancey, Ms.

2010-04-27

117

Transport Studies of AlGaN\\/GaN Heterostructures of Different Al Mole Fractions With Variable $\\\\hbox{SiN}_{x}$ Passivation Stress  

Microsoft Academic Search

The influence of passivation by silicon nitride (SiNx) of different stress states (compressive, neutral, and tensile) is presented as a function of varying Al mole fraction (x). All types of SiNx passivant induced, as expected, an increase in 2-D elec- tron gas (2DEG) concentration. In addition, however, the 2DEG mobility increased after passivation for the low-x (0.15) sample, and the

Tamara B. Fehlberg; Jason S. Milne; Gilberto A. Umana-Membreno; Stacia Keller; Umesh K. Mishra; Brett D. Nener; Giacinta Parish

2011-01-01

118

High temperature, oxidation resistant noble metal-Al alloy thermocouple  

NASA Technical Reports Server (NTRS)

A thermocouple is disclosed. The thermocouple is comprised of an electropositive leg formed of a noble metal-Al alloy and an electronegative leg electrically joined to form a thermocouple junction. The thermocouple provides for accurate and reproducible measurement of high temperatures (600 - 1300 C) in inert, oxidizing or reducing environments, gases, or vacuum. Furthermore, the thermocouple circumvents the need for expensive, strategic precious metals such as rhodium as a constituent component. Selective oxidation of rhodium is also thereby precluded.

Smialek, James L. (inventor); Gedwill, Michael G. (inventor)

1994-01-01

119

Influence of thermal stress on the characteristic parameters of AlGaN/GaN heterostructure Schottky contacts  

NASA Astrophysics Data System (ADS)

Ni Schottky contacts on AlGaN/GaN heterostructures have been fabricated. The samples are then thermally treated in a furnace with N2 ambient at 600 °C for different times (0.5, 4.5, 10.5, 18, 33, 48 and 72 h). Current—voltage (I—V) and capacitance—voltage (C—V) relationships are measured, and Schrödinger's and Poisson's equations are self-consistently solved to obtain the characteristic parameters related to AlGaN/GaN heterostructure Schottky contacts: the two-dimensional electron gas (2DEG) sheet density, the polarization sheet charge density, the 2DEG distribution in the triangle quantum well and the Schottky barrier height for each thermal stressing time. Most of the above parameters reduce with the increase of stressing time, only the parameter of the average distance of the 2DEG from the AlGaN/GaN interface increases with the increase of thermal stressing time. The changes of the characteristic parameters can be divided into two stages. In the first stage the strain in the AlGaN barrier layer is present. In this stage the characteristic parameters change rapidly compared with those in the second stage in which the AlGaN barrier layer is relaxed and no strain is present.

Lü, Yuan-Jie; Lin, Zhao-Jun; Zhang, Yu; Meng, Ling-Guo; Cao, Zhi-Fang; Luan, Chong-Biao; Chen, Hong; Wang, Zhan-Guo

2011-04-01

120

Defect Band Characteristics in Mg-Al and Al-Si High-Pressure Die Castings  

NASA Astrophysics Data System (ADS)

Bands of positive macrosegregation and porosity commonly follow the surface contour of components produced by high-pressure die casting (HPDC). In this article, Al alloy AlSi7Mg and Mg alloys AZ91 and AM60 were cast into tensile test bars using cold-chamber (cc) HPDC. Microstructural characterization revealed that externally solidified crystals (ESCs) are not necessary for defect band formation, and that defect bands can form both near to and relatively far from any surface layer of different microstructure. The defect bands were 140 to 240 ?m thick. In addition to defect-band-related macrosegregation, the castings also contained inverse segregation and surface segregation. Defect bands are shown to have the characteristics of the dilatant shear bands reported in past rheology studies, indicating that defect bands form due to strain localization in partially solid material during the HPDC process.

Gourlay, C. M.; Laukli, H. I.; Dahle, A. K.

2007-08-01

121

TorsinA rescues ER-associated stress and locomotive defects in C. elegans models of ALS.  

PubMed

Molecular mechanisms underlying neurodegenerative diseases converge at the interface of pathways impacting cellular stress, protein homeostasis and aging. Targeting the intrinsic capacities of neuroprotective proteins to restore neuronal function and/or attenuate degeneration represents a potential means toward therapeutic intervention. The product of the human DYT1 gene, torsinA, is a member of the functionally diverse AAA+ family of proteins and exhibits robust molecular-chaperone-like activity, both in vitro and in vivo. Although mutations in DYT1 are associated with a rare form of heritable generalized dystonia, the native function of torsinA seems to be cytoprotective in maintaining the cellular threshold to endoplasmic reticulum (ER) stress. Here we explore the potential for torsinA to serve as a buffer to attenuate the cellular consequences of misfolded-protein stress as it pertains to the neurodegenerative disease amyotrophic lateral sclerosis (ALS). The selective vulnerability of motor neurons to degeneration in ALS mouse models harboring mutations in superoxide dismutase (SOD1) has been found to correlate with regional-specific ER stress in brains. Using Caenorhabditis elegans as a system to model ER stress, we generated transgenic nematodes overexpressing either wild-type or mutant human SOD1 to evaluate their relative impact on ER stress induction in vivo. These studies revealed a mutant-SOD1-specific increase in ER stress that was further exacerbated by changes in temperature, all of which was robustly attenuated by co-expression of torsinA. Moreover, through complementary behavioral analysis, torsinA was able to restore normal neuronal function in mutant G85R SOD1 animals. Furthermore, torsinA targeted mutant SOD1 for degradation via the proteasome, representing mechanistic insight on the activity that torsinA has on aggregate-prone proteins. These results expand our understanding of proteostatic mechanisms influencing neuronal dysfunction in ALS, while simultaneously highlighting the potential for torsinA as a novel target for therapeutic development. PMID:24311730

Thompson, Michelle L; Chen, Pan; Yan, Xiaohui; Kim, Hanna; Borom, Akeem R; Roberts, Nathan B; Caldwell, Kim A; Caldwell, Guy A

2014-02-01

122

An analysis of the flow stress of a two-phase alloy system, Ti-6Al-4V  

NASA Astrophysics Data System (ADS)

An analysis of the tensile deformation behavior of a two-phase body-centered cubic (bcc)-hexagonal close-packed (hcp) alloy, Ti-6Al-4V, has been made. This has shown that the temperature dependence of the flow stress, the logarithm of the effective stress, and the strain-rate sensitivities can be described by simple analytical equations if the thermally activated strain-rate equation contains the Yokobori activation enthalpy H= H o ln ( ?*0/ ?*), where H o is a constant, ?* the effective stress, and ?*0 its 0 K value. The flow stress-temperature plateau region (500 to 600 K) also can be rationalized analytically in terms of oxygen dynamic strain aging in the alpha phase

Reed-Hill, R. E.; Iswaran, C. V.; Kaufman, M. J.

1996-12-01

123

Uniaxial-Stress-Induced Ferromagnetism in the Itinerant Metamagnetic Compound UCoAl Probed by Magnetostriction Measurements  

NASA Astrophysics Data System (ADS)

Magnetostriction measurements for the Ising-type itinerant metamagnetic compound UCoAl were performed under uniaxial stress for ? || c-axis using an in situ pressure-tuning device. A ferromagnetic transition was clearly observed at zero magnetic field at least above ˜0.05 GPa. For a stress of 0.1 GPa, the FM transition is of 2nd order, since the anomaly of the thermal expansion coefficient does not show any hysteresis at the transition. No step like behavior was observed for the FM transition under uniaxial stress in the present study. From the precise stress dependence of TC, a change of the power (n) law from 3/4 to 1/2 was also found at around 0.1 GPa for the expression of TC(?) ? (? ? ?c)n, where the critical value is ?c ˜ 0.026 GPa.

Shimizu, Yusei; Salce, Bernard; Combier, Tristan; Aoki, Dai; Flouquet, Jacques

2015-02-01

124

Recoverable degradation in InAs/AlSb high-electron mobility transistors: The role of hot carriers and metastable defects in AlSb  

NASA Astrophysics Data System (ADS)

Recent observations of electrical stress-induced recoverable degradation in InAs/AlSb high-electron mobility transistors (HEMTs) have been attributed to metastable defects in the AlSb layer generated by the injected holes. Here we present a detailed theoretical analysis of the degradation mechanism. We show that recoverable degradation does not require the presence of hot carriers in the vicinity of the defects but the degradation is enhanced when the injected holes become more energetic. The metastable degradation arises without the presence of an energy barrier. A comprehensive survey of candidate defects suggest that substitutional and interstitial oxygen are responsible for the degradation. Therefore, reducing the oxygen contamination during device fabrication is likely to significantly improve the reliability of InAs/AlSb HEMTs.

Shen, X.; DasGupta, S.; Reed, R. A.; Schrimpf, R. D.; Fleetwood, D. M.; Pantelides, S. T.

2010-12-01

125

High-Mobility Group Box 1, Oxidative Stress, and Disease  

PubMed Central

Abstract Oxidative stress and associated reactive oxygen species can modify lipids, proteins, carbohydrates, and nucleic acids, and induce the mitochondrial permeability transition, providing a signal leading to the induction of autophagy, apoptosis, and necrosis. High-mobility group box 1 (HMGB1) protein, a chromatin-binding nuclear protein and damage-associated molecular pattern molecule, is integral to oxidative stress and downstream apoptosis or survival. Accumulation of HMGB1 at sites of oxidative DNA damage can lead to repair of the DNA. As a redox-sensitive protein, HMGB1 contains three cysteines (Cys23, 45, and 106). In the setting of oxidative stress, it can form a Cys23-Cys45 disulfide bond; a role for oxidative homo- or heterodimerization through the Cys106 has been suggested for some of its biologic activities. HMGB1 causes activation of nicotinamide adenine dinucleotide phosphate oxidase and increased reactive oxygen species production in neutrophils. Reduced and oxidized HMGB1 have different roles in extracellular signaling and regulation of immune responses, mediated by signaling through the receptor for advanced glycation end products and/or Toll-like receptors. Antioxidants such as ethyl pyruvate, quercetin, green tea, N-acetylcysteine, and curcumin are protective in the setting of experimental infection/sepsis and injury including ischemia-reperfusion, partly through attenuating HMGB1 release and systemic accumulation. Antioxid. Redox Signal. 14, 1315–1335. PMID:20969478

Kang, Rui; Zeh, Herbert J.

2011-01-01

126

Invasive Knotweeds are Highly Tolerant to Salt Stress  

NASA Astrophysics Data System (ADS)

Japanese knotweed s.l. are some of the most invasive plants in the world. Some genotypes are known to be tolerant to the saline concentrations found in salt marshes. Here we focus on tolerance to higher concentrations in order to assess whether the species are able to colonize and establish in highly stressful environments, or whether salt is an efficient management tool. In a first experiment, adult plants of Fallopia japonica, Fallopia × bohemica and Fallopia sachalinensis were grown under salt stress conditions by watering with saline concentrations of 6, 30, 120, or 300 g L-1 for three weeks to assess the response of the plants to a spill of salt. At the two highest concentrations, their leaves withered and fell. There were no effects on the aboveground parts at the lowest concentrations. Belowground dry weight and number of buds were reduced from 30 and 120 g L-1 of salt, respectively. In a second experiment, a single spraying of 120 g L-1 of salt was applied to individuals of F. × bohemica and their stems were clipped to assess the response to a potential control method. 60 % of the plants regenerated. Regeneration was delayed by the salt treatment and shoot growth slowed down. This study establishes the tolerance of three Fallopia taxa to strong salt stress, with no obvious differences between taxa. Their salt tolerance could be an advantage in their ability to colonize polluted environments and to survive to spills of salt.

Rouifed, Soraya; Byczek, Coline; Laffray, Daniel; Piola, Florence

2012-12-01

127

Time-dependent behavior of high-strength concrete sustained compressive stresses  

Microsoft Academic Search

Results are reported of an investigation of the behavior of high-strength concrete under sustained stresses in excess of normal working stress levels. The infuences of drying and of sustained stresses, ranging from 40 percent up to stress levels above which failure occurs under sustained load, on the shrinking and creep properties of three materials are examined. The long-term shrinkage is

M. M. Smadi

1982-01-01

128

Tungsten Behaviour at High Temperature and High Stress At the Neutrino Factory the target operates at very high mean power dissipation and extremely high energy density. This  

E-print Network

Tungsten Behaviour at High Temperature and High Stress At the Neutrino Factory the target operates Doppler Vibrometer Young's modulus of tungsten remains high at high temperature and high stress! Several ­ tungsten bars d. Granular solid target UK activity This conclusion is (partly) based on simulation results

McDonald, Kirk

129

Flow Stress Prediction of SiCp/Al Composites at Varying Strain Rates and Elevated Temperatures  

NASA Astrophysics Data System (ADS)

With isothermal compression tests in the Gleeble-3500 system, the hot deformation behaviors of SiCp/Al composite were studied at a wide range of temperatures from 623 K to 773 K, and strain rates ranging from 0.001 s-1 to 10 s-1. Four different modeling methods such as the modified Zerilli-Armstrong model, the strain compensation Arrhenius-type model, the double multivariate nonlinear regression (DMNR) and the artificial neural model (ANN) were used to predict the flow stress. The suitability levels of these models were evaluated by contrasting both the correlation coefficient R C and the average absolute relative error. The results show that the predictions of these four models can adequately meet the accuracy requirement according to the experimental data of this composite. With the increasing of the numbers of determined material constants and the complexity of computing methods, the predictability of these four methods is enhanced. The deformation parameters in the selected ranges such as strain rate and temperature have non-ignorable effect on predicted results of the previous two methods, while they have slight influence on DMNR and ANN.

Yuan, Zhanwei; Li, Fuguo; Ji, Guoliang; Qiao, Huijuan; Li, Jiang

2014-03-01

130

The Role of PentaCoordinated Al3+ Ions in the High Temperature Phase Transformation of ?-Al2O3  

SciTech Connect

In this work, the structural stability of gamma-alumina (?-Al2O3) was investigated by a combination of XRD and high resolution solid state 27Al MAS NMR at an ultra-high magnetic field of 21.1 tesla. XRD measurements show that ?-Al2O3 undergoes a phase transition to ?-Al2O3 during calcination at 1000oC for 10hr. The formation of the ?-Al2O3 phase is further confirmed by 27Al MAS NMR; additional 27Al peaks centered at 10.5 and ~78 ppm were observed in samples calcined at this high temperature. Both the XRD and NMR results indicate that, after calcination at 1000°C for 10 hrs, the ratio of the ?-Al2O3 phase to the total alumina in samples modified by either BaO or La2O3 is significantly reduced in comparison with ?-Al2O3. 27Al MAS NMR spectra revealed that the reduction in the extent of ?-Al2O3 formation was highly correlated with the reduction in the amount of penta-coordinated aluminum ions, measured after 500°C calcination, in both BaO- and La2O3-modified ?-Al2O3 samples. These results strongly suggest that the penta-coordinated aluminum ions, present exclusively on the surface of ?-Al2O3, play a critical role in the phase transformation of ?-Al2O3 to ?-Al2O3. The role of the modifiers, in our case BaO or La2O3, is to convert the penta-coordinated aluminum ions into octahedral ones, thereby improving the thermal stabilities of the samples. Oxide additives, on the other hand, had no beneficial effect on preventing the specific surface area reduction that occurred during high temperature (?1000°C) calcination.

Kwak, Ja Hun; Hu, Jian Zhi; Lukaski, Adrienne C.; Kim, Do Heui; Szanyi, Janos; Peden, Charles HF

2008-06-26

131

Change in Co/Al-oxide/Co tunneling junction under constant voltage stress  

NASA Astrophysics Data System (ADS)

The tunneling junctions Co(10nm)/Al-oxide/Co(50nm) were fabricated on a glass substrate using a metal mask by ion-beam sputtering. On the bottom Co electrode, a 2.5 nm thick Al film was deposited and was oxidized in pure oxygen gas for 12 - 216 h at 200 C. The electrical properties of the junction were measured by the four-probe method under a constant voltage and the current-voltage characteristics at low voltages were measured every half hour. The barrier parameters of Al-oxide layers are evaluated from a fit to the calculated current-voltage characteristics for the junction by using the Particle Swarm Optimization method with high accuracy. The oxide layer was assumed to comprise two different barriers. In case of the barrier with low potential height, oxidation proceeds by applying the voltage and the resistivity increases. In the case of hard breakdown, the barrier retains uniform at the breakdown with sudden change of the resistivity. In other case of the soft breakdown, the barrier shows segregation just before the breakdown.

Shiiki, K.; Takeda, K.; Horikiri, H.

2011-07-01

132

NiAl-base composite containing high volume fraction of AlN for advanced engines  

NASA Technical Reports Server (NTRS)

A particulate reinforced NiAl-AlN composite alloy has a NiAl matrix and greater than about 13 volume percent fine particles of AlN within the matrix. The particles preferably have a diameter from about 15 nanometers to about 50 nanometers. The particulate reinforced NiAl-AlN composite alloy may be prepared by cryomilling prealloyed NiAl in liquid nitrogen using grinding media having a diameter of from about 2 to 6 mm at an impeller speed of from about 450 RPM to about 800 RPM. The cryomilling may be done for a duration of from about 4 hours to about 20 hours to obtain a cryomilled powder. The cryomilled powder may be consolidated to form the particulate reinforced NiAl-AlN composite alloy. The particulate reinforced alloy can further include a toughening alloy. The toughening alloy may include NiCrAlY, FeCrAlY, and FeAl.

Hebsur, Mohan (inventor); Whittenbeger, John D. (inventor); Lowell, Carl F. (inventor)

1994-01-01

133

Regulation of residual stress in elastic solid component with high-energy acoustic field  

NASA Astrophysics Data System (ADS)

The ultrasonic regulation of internal residual stress in metal and nonmetal elastic solid component has been investigated. High-energy ultrasonic wave is applied to carbon steel and ordinary flat glass for residual stress control. An ultrasonic residual stress measurement device developed with the acoustoelastic theory is used to measure macro residual stress in time, to evaluate the residual stress regulation effectiveness. Based on the essence of residual stress, the interaction between acoustic wave and residual stress is analyzed, and dislocations theory is considered. When the ultrasonic energy supplied to the elastic solid is greater than the energy of dislocation, the internal residual stress will be released. Experiments result shows that as high energy acoustic field is applied, the local residual tensile stress in elastic solid specimen will shift gradually to beneficial compressive stress, thus the component's fatigue strength, corrosion resistance and service life will be greatly improved.

Song, W. T.; Xu, C. G.; Pan, Q. X.; Yang, X. C.; Xu, L.; Guo, J.

2013-01-01

134

Marinesco-Sjögren syndrome protein SIL1 regulates motor neuron subtype-selective ER stress in ALS.  

PubMed

Mechanisms underlying motor neuron subtype-selective endoplasmic reticulum (ER) stress and associated axonal pathology in amyotrophic lateral sclerosis (ALS) remain unclear. Here we show that the molecular environment of the ER between motor neuron subtypes is distinct, with characteristic signatures. We identify cochaperone SIL1, mutated in Marinesco-Sjögren syndrome (MSS), as being robustly expressed in disease-resistant slow motor neurons but not in ER stress-prone fast-fatigable motor neurons. In a mouse model of MSS, we demonstrate impaired ER homeostasis in motor neurons in response to loss of SIL1 function. Loss of a single functional Sil1 allele in an ALS mouse model (SOD1-G93A) enhanced ER stress and exacerbated ALS pathology. In SOD1-G93A mice, SIL1 levels were progressively and selectively reduced in vulnerable fast-fatigable motor neurons. Mechanistically, reduction in SIL1 levels was associated with lowered excitability of fast-fatigable motor neurons, further influencing expression of specific ER chaperones. Adeno-associated virus-mediated delivery of SIL1 to familial ALS motor neurons restored ER homeostasis, delayed muscle denervation and prolonged survival. PMID:25559081

Filézac de L'Etang, Audrey; Maharjan, Niran; Cordeiro Braña, Marisa; Ruegsegger, Céline; Rehmann, Ruth; Goswami, Anand; Roos, Andreas; Troost, Dirk; Schneider, Bernard L; Weis, Joachim; Saxena, Smita

2015-02-01

135

A Study of Relaxation Techniques and Coping Skills with Moderately to Highly Stressed Middle and High School Students.  

ERIC Educational Resources Information Center

This report describes a program for heightening awareness of stress and reducing stress levels while improving learning. The targeted population comprised seventh and ninth grade students in middle schools and high schools located in affluent suburban communities of a large Midwest city. The problem of moderate to high levels of stress was…

Credit, Alison; Garcia, Mary

136

Effect of buffer structures on AlGaN/GaN high electron mobility transistor reliability  

SciTech Connect

AlGaN/GaN high electron mobility transistors (HEMTs) with three different types of buffer layers, including a GaN/AlGaN composite layer, or 1 or 2 lm GaN thick layers, were fabricated and their reliability compared. The HEMTs with the thick GaN buffer layer showed the lowest critical voltage (Vcri) during off-state drain step-stress, but this was increased by around 50% and 100% for devices with the composite AlGaN/GaN buffer layers or thinner GaN buffers, respectively. The Voff - state for HEMTs with thin GaN and composite buffers were 100 V, however, this degraded to 50 60V for devices with thick GaN buffers due to the difference in peak electric field near the gate edge. A similar trend was observed in the isolation breakdown voltage measurements, with the highest Viso achieved based on thin GaN or composite buffer designs (600 700 V), while a much smaller Viso of 200V was measured on HEMTs with the thick GaN buffer layers. These results demonstrate the strong influence of buffer structure and defect density on AlGaN/GaN HEMT performance and reliability.

Liu, L. [University of Florida, Gainesville; Xi, Y. Y. [University of Florida, Gainesville; Ren, F. [University of Florida; Pearton, S. J. [University of Florida; Laboutin, O. [Kopin Corporation, Taunton, MA; Cao, Yu [Kopin Corporation, Taunton, MA; Johnson, Wayne J. [Kopin Corporation, Taunton, MA; Kravchenko, Ivan I [ORNL

2012-01-01

137

Comparison of the corrosion and stress-corrosion behavior of a ternary Al-Zn-Mg alloy  

Microsoft Academic Search

A comparison has been made of the corrosion and stress-corrosion behavior of an aged Al-5.3 wt pet Zn-2.5 wt pct Mg alloy\\u000a in aqueous chloride solutions of varying pH (i.e., 1 to 6.2). It is found that lowering the pH to values ?4 accelerates corrosion\\u000a in the absence of stress, due to enhancement of the overall cathodic process, and accelerates

A. J. Sedriks; J. A. S. Green; D. L. Novak

1970-01-01

138

High lung volume increases stress failure in pulmonary capillaries  

NASA Technical Reports Server (NTRS)

We previously showed that when pulmonary capillaries in anesthetized rabbits are exposed to a transmural pressure (Ptm) of approximately 40 mmHg, stress failure of the walls occurs with disruption of the capillary endothelium, alveolar epithelium, or sometimes all layers. The present study was designed to test whether stress failure occurred more frequently at high than at low lung volumes for the same Ptm. Lungs of anesthetized rabbits were inflated to a transpulmonary pressure of 20 cmH2O, perfused with autologous blood at 32.5 or 2.5 cmH2O Ptm, and fixed by intravascular perfusion. Samples were examined by both transmission and scanning electron microscopy. The results were compared with those of a previous study in which the lung was inflated to a transpulmonary pressure of 5 cmH2O. There was a large increase in the frequency of stress failure of the capillary walls at the higher lung volume. For example, at 32.5 cmH2O Ptm, the number of endothelial breaks per millimeter cell lining was 7.1 +/- 2.2 at the high lung volume compared with 0.7 +/- 0.4 at the low lung volume. The corresponding values for epithelium were 8.5 +/- 1.6 and 0.9 +/- 0.6. Both differences were significant (P less than 0.05). At 52.5 cmH2O Ptm, the results for endothelium were 20.7 +/- 7.6 (high volume) and 7.1 +/- 2.1 (low volume), and the corresponding results for epithelium were 32.8 +/- 11.9 and 11.4 +/- 3.7. At 32.5 cmH2O Ptm, the thickness of the blood-gas barrier was greater at the higher lung volume, consistent with the development of more interstitial edema. Ballooning of the epithelium caused by accumulation of edema fluid between the epithelial cell and its basement membrane was seen at 32.5 and 52.5 cmH2O Ptm. At high lung volume, the breaks tended to be narrower and fewer were oriented perpendicular to the axis of the pulmonary capillaries than at low lung volumes. Transmission and scanning electron microscopy measurements agreed well. Our findings provide a physiological mechanism for other studies showing increased capillary permeability at high states of lung inflation.

Fu, Z.; Costello, M. L.; Tsukimoto, K.; Prediletto, R.; Elliott, A. R.; Mathieu-Costello, O.; West, J. B.

1992-01-01

139

Fabrication of high thermal conductive Al-cBN ceramic sinters by high temperature high pressure method  

NASA Astrophysics Data System (ADS)

Al-cBN ceramic sinters were fabricated by sintering micro-powder mixture of Al and cBN under high temperature and high pressure condition. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electronic microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) elemental mapping analyses and laser flashing thermal conductivity measurements were performed to investigate the sintering properties and thermal conductivity of the Al-cBN ceramic sinters. XRD analysis revealed these Al-cBN ceramic sinters were composed of a large portion of cBN and of a small portion of AlN, and very little amount of AlB 12 and hBN. Formation of boundary phase resulted in the rapid densification of the sinters, as well as the increase of their relative density with increasing Al additions. The Al-cBN ceramic sinters have a maximum thermal conductivity of about 1.94 W/cm K at room temperature and a much higher value of about 2.04 W/cm K at 200 °C. Their high thermal conductivity over that of AlN-hBN composites promise Al-cBN ceramic sinters favorite candidates as high efficiency heat sink materials for wide band gap semiconductors.

Wang, P. F.; Li, Zh. H.; Zhu, Y. M.

2011-05-01

140

Creep deformation and stress-induced structural disorder near Tg in a Zr55Al10Ni5Cu30 glassy alloy  

NASA Astrophysics Data System (ADS)

Creep deformation under a constant applied load in a Zr55Al10Ni5Cu30 glassy alloy at the glass transition region is investigated. At an initial stress, ?0, less than a critical stress, ?c=80 MPa, the glass shows a Newtonian flow. When ?0??c, the flow viscosity, ?, initially decreases and attains a minimum. It then increases as the true stress, ?, decreases with further deformation. The initial decrease in ? and the attendance of viscosity minimum are due to the stress-induced structural disorder and the structural equilibration with the applied stress, respectively. For stress, ?, less than the viscosity minimum stress, the stress dependence of viscosity, ?(?), curves all tend to merge together, and is fitted well with a master curve, ?(?), established previously for the steady-state flow under constant strain-rate experiments. These results render further support to the hypothesis of stress-induced structural disorder and the concept of fictive stress.

Kato, H.; Inoue, A.; Chen, H. S.

2001-12-01

141

Chronic High Pressure-Induced Arterial Oxidative Stress  

PubMed Central

Regardless of the underlying pathological mechanisms oxidative stress seems to be present in all forms of hypertension. Thus, we tested the hypothesis that chronic presence of high pressure itself elicits increased arterial O2.? production. Hypertension was induced in rats by abdominal aortic banding (Ab). Rats with Ab had elevated pressure in vessels proximal and normal pressure in vessels distal to the coarctation, yet both vascular beds were exposed to the same circulating factors. Compared to normotensive hind limb arteries (HLAs) hypertensive forelimb arteries (FLAs) exhibited 1) impaired dilations to acetylcholine and the nitric oxide donor S-nitroso-N-acetyl-d,l-penicillamine that were restored by administration of superoxide dismutase; 2) an increased production of O2.? (measured by lucigenin chemiluminescence and ethidium bromide fluorescence) that was inhibited or reduced by superoxide dismutase, the NAD(P)H oxidase inhibitors diphenyleneiodonium and apocynin, or the protein kinase C (PKC) inhibitors chelerythrine and staurosporine or by the angiotensin-converting enzyme (ACE) inhibitor captopril; and 3) increased ACE activity. In organ culture, exposure of isolated arteries of normotensive rats to high pressure (160 mmHg, for 24 hours) significantly increased O2.? production compared to that in arteries exposed to 80 mmHg. High pressure-induced O2.? generation was reduced by inhibitors of ACE and PKC. Incubation of cultured arteries with angiotensin II elicited significantly increased O2.? generation that was inhibited by chelerythrine. Thus, we propose that chronic presence of high pressure itself can elicit arterial oxidative stress, primarily by activating directly a PKC-dependent NAD(P)H oxidase pathway, but also, in part, via activation of the local renin-angiotensin system. PMID:15215177

Ungvari, Zoltan; Csiszar, Anna; Kaminski, Pawel M.; Wolin, Michael S.; Koller, Akos

2004-01-01

142

Vulnerability to stress among women in chronic pain from fibromyalgia and osteoarthritis davis et al. stress vulnerability  

Microsoft Academic Search

In two investigations, we studied vulnerability to the negative effects of stress among women in chronic pain from 2 types\\u000a of musculoskeletal illnesses, fibromyalgia syndrome (FMS) and osteoarthritis (OA). In Study 1, there were 101 female participants\\u000a 50 to 78 years old: 50 had FMS, 29 had OA knee pain and were scheduled for knee surgery, and 22 had OA

Mary C. Davis; Alex J. Zautra; John W. Reich

2001-01-01

143

Solid-state reaction of Al\\/CuO couple by high-energy ball milling  

Microsoft Academic Search

The solid state reaction of Al\\/CuO induced by high-energy ball milling was studied systematically. When the amount of Al was 20 wt%, only reduction occurred. When the amount of Al exceeded 20 wt%, along with the reduction, a synthesis reaction occurred simultaneously. As the amount of Al increased, the reaction products were Cu9Al4, CuAl2 or a Al(Cu) solid solution, respectively.

Xi Shengqi; Qu Xiaoyan; Ma Mingliang; Zhou Jingen; Zheng Xiulin; Wang Xiaotian

1998-01-01

144

The Voices of High School Counselors: Lived Experience of Job Stress  

ERIC Educational Resources Information Center

There is a paucity of literature addressing high school counselors' experiences of job stress. Our qualitative phenomenological study adds to the professions' knowledge of job stress as experienced by counselors in large suburban high schools. Our study illustrates the job stress phenomenon in the counselors' own voices, identifies situations…

Falls, Leigh; Nichter, Mary

2007-01-01

145

UNIAXIAL STRESS EFFECT ON THE 1A1 ~ 1T1 TRANSITION OF Co3+ IN 03B1-Al2O3  

E-print Network

559 UNIAXIAL STRESS EFFECT ON THE 1A1 ~ 1T1 TRANSITION OF Co3+ IN 03B1-Al2O3 E. DUVAL, R. LOUAT, B'absorption de plus basse énergie de la transition 1A1 ~ 1T1 de Co3+ dans 03B1-Al2O3 est étudié. Les spectres-Al2O3 is studied. The stress spectra are interpreted by a phenomenological matrix based on group

Paris-Sud XI, Université de

146

The behavior of off-state stress-induced electrons trapped at the buffer layer in AlGaN/GaN heterostructure field effect transistors  

SciTech Connect

A measurement methodology involving the synchronous switching of gate to source voltage and drain to source voltage (V{sub DS}) was proposed for determining the shift of threshold voltage after an AlGaN/GaN heterostructure transistor endures high V{sub DS} off-state stress. The measurement results indicated slow electron detrapping behavior. The trap level was determined as (E{sub C}?–?0.6?eV). Simulation tool was used to analyze the measurement results. The simulation results were consistent with the experimental results; and a relationship between the buffer trap and threshold voltage shift over time was observed.

Liao, W. C.; Chen, Y. L.; Chen, C. H.; Chyi, J. I.; Hsin, Y. M. [Department of Electrical Engineering, National Central University, Jhongli, Taiwan (China)

2014-01-20

147

Effect of mean stress (stress ratio) and aging on fatigue-crack growth in a metastable beta titanium alloy, Ti-10V-2Fe-3Al  

SciTech Connect

The effect of mean stress, or the stress ratio (R), on the fatigue-crack growth (FCG) behavior of {alpha}-aged and {omega}-aged microstructures of the beta titanium alloy Ti-10V-2Fe-3Al was investigated. While the mean stress had a negligible effect on the FCG behavior of the {alpha}-aged microstructure, a strong effect was observed in the {omega}-aged microstructure. In particular, the values of the threshold stress-intensity range ({Delta}K{sub th}) exhibited a strong dependence on R in the {omega}-aged microstructure, while this dependence was weak in the {alpha}-aged microstructure. These effects seem to arise primarily from fracture-surface roughness-induced crack closure. The crack closure levels for the {alpha}-aged microstructure were found to be very low compared to those for the {omega}-aged microstructure. Transmission electron microscopy and scanning electron microscopy studies of microstructures and fracture surfaces were performed to gain insight into the deformation characteristics and crack propagation mechanisms, respectively, in these microstructures. The microstructure-induced differences in FCG behavior are rationalized in terms of the effect of aging on slip and crack closure.

Jha, S.K.; Ravichandran, K.S.

2000-03-01

148

The Effect of Ballistic Impacts on the High Cycle Fatigue Properties of Ti-48Al-2Nb-2Cr (at.%)  

NASA Technical Reports Server (NTRS)

The ability of gamma - TiAl to withstand potential foreign and/or domestic object damage is a technical risk to the implementation of gamma - TiAl in low pressure turbine (LPT) blade applications. The overall purpose of the present study was to determine the influence of ballistic impact damage on the high cycle fatigue strength of gamma - TiAl simulated LPT blades. Impact and specimen variables included ballistic impact energy, projectile hardness, impact temperature, impact location, and leading edge thickness. The level of damage induced by the ballistic impacting was studied and quantified on both the impact (front) and backside of the specimens. Multiple linear regression was used to model the cracking and fatigue response as a function of the impact variables. Of the impact variables studied, impact energy had the largest influence on the response of gamma - TiAl to ballistic impacting. Backside crack length was the best predictor of remnant fatigue strength for low energy impacts (<0.74J) whereas Hertzian crack length (impact side damage) was the best predictor for higher energy impacts. The impacted gamma - TiAl samples displayed a classical mean stress dependence on the fatigue strength. For the fatigue design stresses of a 6th stage LPT blade in a GE90 engine, a Ti-48Al-2Nb-2Cr LPT blade would survive an impact of normal service conditions.

Draper, S. L.; Lerch, B. A.; Pereira, J. M.; Nathal, M. V.; Austin, C. M.; Erdman, O.

2000-01-01

149

High pressure X-ray diffraction study of LaAl 2 and LaAl 3  

NASA Astrophysics Data System (ADS)

LaAl 2 and LaAl 3 exhibit MgCu 2 type (space group Fd3m) and Ni 3Sn type (space group P6 3/mmc) structures, respectively, at NTP. High pressure X-ray diffraction studies on these two systems are carried out up to ?35 and ?30 GPa, respectively, with a diamond anvil cell, mounted on a high precision Guinier diffractometer. The volume compression determined at the highest pressures are about 33% for LaAl 2 and 23% for LaAl 3. Neither compound shows any structural transition.

Sekar, M.; Chandra Shekar, N. V.; Sahu, P. Ch.; Sanjay Kumar, N. R.; Rajan, K. Govinda

2002-11-01

150

Growth of crack-free AlGaN film on high-temperature thin AlN interlayer  

Microsoft Academic Search

We report on successful fabrication of crack-free thick AlGaN layers by introducing a thin AlN interlayer at the high temperature of 1000–1100°C on a high quality GaN epitaxial layer. The Al0.52Ga0.48N films grown with the optimized AlN interlayer exhibited mirror-like surface morphology and were free of cracks up to the thickness of 3?m. X-ray analyses and cathodoluminescence spectra showed excellent

In-Hwan Lee; Tae Geun Kim

2002-01-01

151

Review of stress corrosion cracking of pipeline steels in “low” and “high” pH solutions  

Microsoft Academic Search

This paper reviews the current understanding of the mechanisms of stress corrosion cracking of pipeline steels. The similarities, the differences and the influencing factors are considered for the “high pH” stress corrosion cracking caused by a concentrated bicarbonate-carbonate solution, and for the “low pH” stress corrosion cracking due to a diluter solution. For high pH stress corrosion cracking, it is

B. Y. Fang; A. Atrens; J. Q. Wang; E. H. Han; Z. Y. Zhu; W. Ke

2003-01-01

152

Novel self-stressing test structures for realistic high-frequency reliability characterization  

Microsoft Academic Search

A series of self-stressing test structures suitable for investigation of reliability failure mechanisms (hot carriers, electromigration, oxide breakdown) under realistic integrated circuit operating conditions, is described. These structures contain DC-controlled, high-frequency on-chip oscillators, which stress test structures. As a result, high-frequency (>200-MHz) stress-testing can be performed using less expensive DC test systems. In particular, hot-carrier stress-testing was performed at frequencies

Eric S. Snyder; David V. Campbell; Scot E. Swanson; Donald G. Pierce

1993-01-01

153

Magnetic hysteresis under compressive stress at high applied field  

Microsoft Academic Search

n Abstract-The magnetic properties of material are sensitive to applied stress. The aim of this paper is to designed and fabricated a hysteresis imaging apparatus for nondestructive evaluation of stress concentration in ferromagnetic material. It has been applied successfully to measure the hysteresis loops of Q235 steel under various fixed compressive stress. The remanence Br derived from the loops is

Dongyan Huang; Bing Han; Zonggang Wang; Tao Zhang

2011-01-01

154

ALS-linked mutant SOD1 induces ER stress- and ASK1-dependent motor neuron death by targeting Derlin-1  

PubMed Central

Mutation in Cu/Zn-superoxide dismutase (SOD1) is a cause of familial amyotrophic lateral sclerosis (ALS). Mutant SOD1 protein (SOD1mut) induces motor neuron death, although the molecular mechanism of SOD1mut-induced cell death remains controversial. Here we show that SOD1mut specifically interacted with Derlin-1, a component of endoplasmic reticulum (ER)-associated degradation (ERAD) machinery and triggered ER stress through dysfunction of ERAD. SOD1mut-induced ER stress activated the apoptosis signal-regulating kinase 1 (ASK1)-dependent cell death pathway. Perturbation of binding between SOD1mut and Derlin-1 by Derlin-1-derived oligopeptide suppressed SOD1mut-induced ER stress, ASK1 activation, and motor neuron death. Moreover, deletion of ASK1 mitigated the motor neuron loss and extended the life span of SOD1mut transgenic mice. These findings demonstrate that ER stress-induced ASK1 activation, which is triggered by the specific interaction of Derlin-1 with SOD1mut, is crucial for disease progression of familial ALS. PMID:18519638

Nishitoh, Hideki; Kadowaki, Hisae; Nagai, Atsushi; Maruyama, Takeshi; Yokota, Takanori; Fukutomi, Hisashi; Noguchi, Takuya; Matsuzawa, Atsushi; Takeda, Kohsuke; Ichijo, Hidenori

2008-01-01

155

Stress  

NSDL National Science Digital Library

This project collects resources for studying mental health and stress issues with middle schoolers. Teens and stress Science NetLinks: The Laughing Brain 2: A Good Laugh Dealing with anger Stress-o-meter Look at each of the above sites. Choose one and read the content. Write a one-paragraph summary. Play interactive games and take quizzes. Keep a log of what you do. Tell which site you liked best and why. Watch the following video for positive things teens do to reduce the stress ...

Deaton, Mrs.

2011-06-10

156

Ultrafast Bulk Diffusion of AlHxin High-Entropy Dehydrogenation Intermediates of NaAlH4  

SciTech Connect

Using first-principles molecular dynamics (FPMD) and total-energy calculations, we demonstrate low-barrier bulk diffusion of Al-bearing species in ?-NaAlH4, a recently proposed high-entropy polymorph of NaAlH4. For charged AlH4– and neutral AlH3 vacancies, the computed barriers for diffusion are <0.1 eV, and we directly observe the predicted diffusive pathways in FPMD simulations at picosecond time scales. In contrast, such diffusion in the ? phase is inaccessible to FPMD, consistent with much higher barriers. The transport behavior of ?-NaAlH4, in addition to key dynamical and structural signatures, is consistent with experimental observations of high-mobility species, strongly supporting the idea that an intermediate transition from the ? phase to a high-entropy polymorph facilitates the hydrogen-releasing decomposition of NaAlH4. Our results provide an answer to longstanding questions regarding the responsible agent for the experimentally observed efficient Al transport during dehydrogenation and suggest that mass transport and phase transformation kinetics are coupled. Implications for understanding the (de)hydrogenation of undoped and catalyzed NaAlH4 are discussed.

Zhang, Feng [Ames Laboratory; Wood, Brandon C [Lawrence Livermore National Laboratory; Wang, Yan [Georgia Institute of Technology; Wang, Cai-Zhuang [Ames Laboratory; Ho, Kai-Ming [Ames Laboratory; Chou, Mei-Yin [Georgia Institute of Technology

2014-08-14

157

Aggregation-prone c9FTD/ALS poly(GA) RAN-translated proteins cause neurotoxicity by inducing ER stress.  

PubMed

The occurrence of repeat-associated non-ATG (RAN) translation, an atypical form of translation of expanded repeats that results in the synthesis of homopolymeric expansion proteins, is becoming more widely appreciated among microsatellite expansion disorders. Such disorders include amyotrophic lateral sclerosis and frontotemporal dementia caused by a hexanucleotide repeat expansion in the C9ORF72 gene (c9FTD/ALS). We and others have recently shown that this bidirectionally transcribed repeat is RAN translated, and the "c9RAN proteins" thusly produced form neuronal inclusions throughout the central nervous system of c9FTD/ALS patients. Nonetheless, the potential contribution of c9RAN proteins to disease pathogenesis remains poorly understood. In the present study, we demonstrate that poly(GA) c9RAN proteins are neurotoxic and may be implicated in the neurodegenerative processes of c9FTD/ALS. Specifically, we show that expression of poly(GA) proteins in cultured cells and primary neurons leads to the formation of soluble and insoluble high molecular weight species, as well as inclusions composed of filaments similar to those observed in c9FTD/ALS brain tissues. The expression of poly(GA) proteins is accompanied by caspase-3 activation, impaired neurite outgrowth, inhibition of proteasome activity, and evidence of endoplasmic reticulum (ER) stress. Of importance, ER stress inhibitors, salubrinal and TUDCA, provide protection against poly(GA)-induced toxicity. Taken together, our data provide compelling evidence towards establishing RAN translation as a pathogenic mechanism of c9FTD/ALS, and suggest that targeting the ER using small molecules may be a promising therapeutic approach for these devastating diseases. PMID:25173361

Zhang, Yong-Jie; Jansen-West, Karen; Xu, Ya-Fei; Gendron, Tania F; Bieniek, Kevin F; Lin, Wen-Lang; Sasaguri, Hiroki; Caulfield, Thomas; Hubbard, Jaime; Daughrity, Lillian; Chew, Jeannie; Belzil, Veronique V; Prudencio, Mercedes; Stankowski, Jeannette N; Castanedes-Casey, Monica; Whitelaw, Ena; Ash, Peter E A; DeTure, Michael; Rademakers, Rosa; Boylan, Kevin B; Dickson, Dennis W; Petrucelli, Leonard

2014-10-01

158

High-temperature slow crack growth of silicon carbide determined by constant-stress-rate and constant-stress testing  

Microsoft Academic Search

High-temperature slow-crack-growth behaviour of hot-pressed silicon carbide was determined using both constant-stress-rate (“dynamic fatigue”) and constant-stress (“static fatigue”) testing in flexure at 1300 °C in air. Slow crack growth was found to be a governing mechanism associated with failure of the material. Four estimation methods such as the individual data, the Weibull median, the arithmetic mean and the median deviation

SUNG R. CHOI; J. A. SALEM; N. N Nemeth

1998-01-01

159

Effects of high-temperature AIN buffer on the microstructure of AlGaN/GaN HEMTs  

SciTech Connect

Effects on AlGaN/GaN high-electron-mobility transistor structure of a high-temperature AlN buffer on sapphire substrate have been studied by high-resolution x-ray diffraction and atomic force microscopy techniques. The buffer improves the microstructural quality of GaN epilayer and reduces approximately one order of magnitude the edge-type threading dislocation density. As expected, the buffer also leads an atomically flat surface with a low root-mean-square of 0.25 nm and a step termination density in the range of 10{sup 8} cm{sup -2}. Due to the high-temperature buffer layer, no change on the strain character of the GaN and AlGaN epitaxial layers has been observed. Both epilayers exhibit compressive strain in parallel to the growth direction and tensile strain in perpendicular to the growth direction. However, an high-temperature AlN buffer layer on sapphire substrate in the HEMT structure reduces the tensile stress in the AlGaN layer.

Coerekci, S., E-mail: scorekci@kirklareli.edu.tr [K Latin-Small-Letter-Dotless-I rklareli University, Department of Physics (Turkey); Oeztuerk, M. K. [Gazi University, Department of Physics (Turkey); Yu, Hongbo [Bilkent University, Nanotechnology Research Center (Turkey); Cakmak, M.; Oezcelik, S. [Gazi University, Department of Physics (Turkey); Oezbay, E. [Bilkent University, Nanotechnology Research Center, Department of Physics, Department of Electrical and Electronics Engineering (Turkey)

2013-06-15

160

Research on high-resolution distributed fiber optic stress sensor for landslide monitoring  

Microsoft Academic Search

In this paper, an early warning monitoring system for landslides, based on high spatial resolution distributed fiber optic stress sensing and monitoring the intra-stress distribution and changes in landslide bodies, was first presented. The principle of distributed fiber optic stress sensing and the monitoring method for landslides were described in detail. Through measuring the distributed polarization mode coupling in the

Zhiyong Dai; Yongzhi Liu; Lixun Zhang; Zhonghua Ou; Ce Zhou

2008-01-01

161

Fabrication of high compressive stress silicon nitride membrane in strained silicon technology  

Microsoft Academic Search

The mechanism of compressive stress in silicon nitride membrane is studied in this paper. The effects of the various process parameters on the compressive stress in silicon nitride are analyzed and discussed on the basis of the current method using PECVD equipment. The high compressive stress silicon nitride membrane has been fabricated on the optimization of the process parameters, and

Bin Shu; Heming Zhang; Rongxi Xuan; Xianying Dai; Huiyong Hu; Jianjun Song; Liang Liang; Jianan Cui

2009-01-01

162

Thioredoxin 2, an Oxidative Stress-induced Protein, Contains a High Affinity Zinc Binding Site*  

E-print Network

Thioredoxin 2, an Oxidative Stress-induced Protein, Contains a High Affinity Zinc Binding Site, the gene coding for Trx2 is under control of the oxidative stress transcrip- tion factor OxyR in E. coli. This suggests that Trx2 may play a role in the cellular defense against oxidative stress. We show here that Trx2

Bardwell, James

163

High cycle fatigue behavior of implant Ti-6Al-4V in air and simulated body fluid.  

PubMed

Ti-6Al-4V implants that function as artificial joints are usually subjected to long-term cyclic loading. To study long-term fatigue behaviors of implant Ti-6Al-4V in vitro and in vivo conditions exceeding 107 cycles, constant stress amplitude fatigue experiments were carried out at ultrasonic frequency (20 kHz) with two different surface conditions (ground and polished) in ambient air and in a simulated body fluid. The initiation mechanisms of fatigue cracks were investigated with scanning electron microscopy. Improvement of fatigue strength is pronounced for polished specimens below 106 cycles in ambient air since fatigue cracks are initiated from surfaces of specimens. While the cycles exceed 106, surface conditions have no effect on fatigue behaviors because the defects located within the specimens become favorable sites for crack initiation. The endurance limit at 108 cycles of polished Ti-6Al-4V specimens decreases by 7% if it is cycled in simulated body fluid instead of ambient air. Fracture surfaces show that fatigue failure is initiated from surfaces in simulated body fluid. Surface improvement has a beneficial effect on fatigue behaviors of Ti-6Al-4V at high stress amplitudes. The fatigue properties of Ti-6Al-4V deteriorate and the mean endurance limits decrease significantly in simulated body fluid. PMID:24211906

Liu, Yong-jie; Cui, Shi-ming; He, Chao; Li, Jiu-kai; Wang, Qing-yuan

2014-01-01

164

The Effect of High Mechanical Stress on Certain Solid Explosives  

Microsoft Academic Search

Eleven different solid explosives have been subjected at room temperature to stresses of the order of those which prevail in the detonating front. Two types of stress were applied. The first consisted of a hydrostatic pressure of 50,000 kg\\/cm2, on which was superposed a shearing stress sufficient to produce shearing deformations of the order of 60 radians. The second type

P. W. Bridgman

1947-01-01

165

Landslide monitoring based on high-resolution distributed fiber optic stress sensor  

Microsoft Academic Search

We present a landslide monitoring application using a high-resolution distributed fiber optic stress sensor. The sensor is used to monitor the intra-stress distribution and variations in landslide bodies, and can be used for the early warning of the occurrence of the landslides. The principle of distributed fiber optic stress sensing and the intra-stress monitoring method for landslides were described in

Zhi-Yong Dai; Yong Liu; Li-Xun Zhang; Zhong-Hua Ou; Ce Zhou; Yong-Zhi Liu

2008-01-01

166

The characteristics of two-phase Al-Cu and Zn-Al alloys processed by high-pressure torsion  

NASA Astrophysics Data System (ADS)

Experiments were conducted on two different two-phase alloys, the Al-33% Cu eutectic and the Zn-22% Al eutectoid. These alloys were processed by high-pressure torsion (HPT) and then measurements were taken to determine the distributions of hardness values across the disk diameters and tensile tests were conducted to examine the potential for achieving superplastic elongations. Both alloys showed grain refinement through the HPT processing but the Al-Cu alloy exhibited a conventional work-hardening with torsional straining whereas the Zn-Al alloy exhibited a work-softening due to the loss of Zn-rich precipitates under the high imposed pressure. Excellent superplastic elongations were achieved in both alloys when pulled in tension at elevated temperatures with a maximum elongation of 1800% in the Zn-Al alloy.

Kawasaki, Megumi; Langdon, Terence G.

2014-08-01

167

High-cycle fatigue behavior of Ti-5Al-2.5Sn ELI alloy forging at low temperatures  

SciTech Connect

High-cycle fatigue properties of Ti-5Al-2.5Sn Extra Low Interstitial (ELI) alloy forging were investigated at low temperatures. The high-cycle fatigue strength at low temperatures of this alloy was relatively low compared with that at ambient temperature. The crystallographic orientation of a facet formed at a fatigue crack initiation site was determined by electron backscatter diffraction (EBSD) method in scanning electron microscope (SEM) to understand the fatigue crack initiation mechanism and discuss on the low fatigue strength at low temperature. Furthermore, in terms of the practical use of this alloy, the effect of the stress ratio (or mean stress) on the high-cycle fatigue properties was evaluated using the modified Goodman diagram.

Ono, Yoshinori; Yuri, Tetsumi; Ogata, Toshio; Demura, Masahiko [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Matsuoka, Saburo [Kyushu University, 744, Motooka, Nishi-ku, Fukuoka, Fukuoka 819-0395 (Japan); Sunakawa, Hideo [Japan Aerospace Exploration Agency, 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505 (Japan)

2014-01-27

168

Stress  

MedlinePLUS

... breathing exercises at least once a day. Progressive relaxation therapy In this technique, which you can learn ... a new sport, it takes practice to learn relaxation. Dealing with Diabetes-Related Stress Some sources of ...

169

High-Temperature Slow Crack Growth of Silicon Carbide Determined by Constant-Stress-Rate and Constant-Stress Testing  

NASA Technical Reports Server (NTRS)

High-temperature slow-crack-growth behaviour of hot-pressed silicon carbide was determined using both constant-stress-rate ("dynamic fatigue") and constant-stress ("static fatigue") testing in flexure at 1300 C in air. Slow crack growth was found to be a governing mechanism associated with failure of the material. Four estimation methods such as the individual data, the Weibull median, the arithmetic mean and the median deviation methods were used to determine the slow crack growth parameters. The four estimation methods were in good agreement for the constant-stress-rate testing with a small variation in the slow-crack-growth parameter, n, ranging from 28 to 36. By contrast, the variation in n between the four estimation methods was significant in the constant-stress testing with a somewhat wide range of n= 16 to 32.

Choi, Sung H.; Salem, J. A.; Nemeth, N. N.

1998-01-01

170

Electrical and structural degradation of GaN high electron mobility transistors under high-power and high-temperature Direct Current stress  

NASA Astrophysics Data System (ADS)

We have stressed AlGaN/GaN HEMTs (High Electron Mobility Transistors) under high-power and high-temperature DC conditions that resulted in various levels of device degradation. Following electrical stress, we conducted a well-established three-step wet etching process to remove passivation, gate and ohmic contacts so that the device surface can be examined by SEM and AFM. We have found prominent pits and trenches that have formed under the gate edge on the drain side of the device. The width and depth of the pits under the gate edge correlate with the degree of drain current degradation. In addition, we also found visible erosion under the full extent of the gate. The depth of the eroded region averaged along the gate width under the gate correlated with channel resistance degradation. Both electrical and structural analysis results indicate that device degradation under high-power DC conditions is of a similar nature as in better understood high-voltage OFF-state conditions. The recognition of a unified degradation mechanism provides impetus to the development of a degradation model with lifetime predictive capabilities for a broad range of operating conditions spanning from OFF-state to ON-state.

Wu, Y.; Chen, C.-Y.; del Alamo, J. A.

2015-01-01

171

Oxidation and microstructure evolution of Al-Si coated Ni3Al based single crystal superalloy with high Mo content  

NASA Astrophysics Data System (ADS)

A Si modified aluminide (Al-Si) coating was prepared on a Ni3Al based single crystal superalloy with high Mo content by high-activity pack cementation. Cyclic oxidation test at 1150 °C was carried out and the microstructure evolution of the coating was investigated. The results show that the oxidation resistance of the substrate was greatly increased by applying an Al-Si coating. During oxidation, outward diffusion of Mo was effectively blocked due to its high affinity with Si. Besides, a layered structure was formed as a result of the elements inter-diffusion. An obvious degradation of the Al-Si coating was observed after 100 h oxidation. Possible mechanisms related to the oxidation and elements inter-diffusion behaviours were also discussed.

Tu, Xiaolu; Peng, Hui; Zheng, Lei; Qi, Wenyan; He, Jian; Guo, Hongbo; Gong, Shengkai

2015-01-01

172

Improved Performance of Highly Scaled AlGaN/GaN High-Electron-Mobility Transistors Using an AlN Back Barrier  

NASA Astrophysics Data System (ADS)

An ultrathin AlN layer is inserted between the GaN channel and buffer in the fabrication of deep-submicrometer AlGaN/GaN high-electron-mobility transistors (HEMTs). The wide bandgap of AlN establishes a high back barrier and thus enhances the confinement of two-dimensional electron gas under high drain bias voltages. Owning to the effective suppression of short-channel effects in the device with a highly scaled gate length, the fabricated AlN back barrier HEMTs show better pinch-off quality, lower subthreshold current, lower drain-induced barrier lowering factor, and better high-frequency response than the reference device without an AlN back barrier.

Kong, Xin; Wei, Ke; Liu, Guoguo; Liu, Xinyu; Wang, Cuimei; Wang, Xiaoliang

2013-05-01

173

Magnetotransport properties of high equivalent Al composition AlGaN/GaN heterostructures using AlN/GaN superlattice as a barrier  

NASA Astrophysics Data System (ADS)

Magnetotransport properties of the two-dimensional electron gas (2DEG) in high equivalent Al composition AlGaN/GaN heterostructures using AlN/GaN superlattice as a barrier have been studied at low temperatures and high magnetic fields. Well resolved Shubnikov-de Haas oscillations were observed, indicating excellent quality of the quasi-AlGaN/GaN heterostructures. It is measured that the energy separation between the two subbands in the GaN triangular quantum well can be as large as 180.5 meV, depicting strong quantum confinement at the heterointerface. The strong quantum confinement results in a high 2DEG density of 2 × 1013 cm-2. The persistent photoconductivity investigation also indicates that the superlattice barrier layer has a low density of impurities/defects. It is believed that the AlN/GaN superlattice, instead of high Al composition alloy AlGaN layer, could greatly improve the device performance.

Liu, S. D.; Tang, N.; Shen, X. Q.; Duan, J. X.; Lu, F. C.; Yang, X. L.; Xu, F. J.; Wang, X. Q.; Ide, T.; Shimizu, M.; Ge, W. K.; Shen, B.

2013-07-01

174

The influence of buffer layer coalescence on stress evolution in GaN grown on ion implanted AlN/Si(111) substrates  

NASA Astrophysics Data System (ADS)

The effect of AlN buffer layer morphology on the evolution of growth stress in GaN epilayers deposited by metalorganic chemical vapor deposition on N+ ion-implanted AlN/Si(111) substrates was investigated. AlN buffer layers were grown using either a continuous or pulsed source flow process which altered the grain size and extent of coalescence of the films. In situ stress measurements revealed that substrate implantation reduced the initial compressive stress in the GaN epilayers likely due to a decoupling of the AlN lattice from the underlying crystalline Si substrate. The buffer layer morphology was found to significantly alter the influence of ion-implantation on the film properties. GaN epilayers grown on ion-implanted AlN/Si(111) substrates prepared with the pulsed conditions exhibited a 63% decrease in threading dislocation (TD) density compared to unimplanted substrates. In addition, these films were observed to grow under a low overall stress compared to the other samples which exhibited a more typical compressive to tensile stress transition during growth. The low overall growth stress of the GaN grown on the implanted pulsed AlN/Si(111) was explained in terms of a reduced strain gradient from dislocation inclination.

Gagnon, Jarod C.; Leathersich, Jeffrey M.; Shahedipour-Sandvik, Fatemeh (Shadi); Redwing, Joan M.

2014-05-01

175

Thermal Fatigue Life of Glidcop Al-15 High-Heat-Load Components  

SciTech Connect

Shanghai Synchrotron Radiation Facility (SSRF) is a third-generation of synchrotron radiation light source and is presently under construction as a large scale national scientific project in China. Depending on the outstanding thermal and mechanical performance, Glidcop Al-15, a dispersion strengthened copper alloy, is chosen to serve for the high-heat-load components at beam line front end in SSRF. Present study is to investigate the thermal fatigue lives of critical SSRF components. A nonlinear finite element method (FEM) is used to simulate the nonlinear three dimensional stress-strain fields of the critical component-Mask2 at SSRF beam line. The method consists of transient temperature analyses followed by elastic-plastic stress analyses. Then, a critical plane approach is used to predict the thermal fatigue life of mask2. The critical plane approach is appropriate for estimating service life of critical SSRF components since the results are in good consistent with the experimental ones taken at the Advanced Photon Source (APS).

Jin, J. F.; Xiao, W. L.; Chen, H. B. [CAS Key Laboratory Mechanical Behavior and Design of Materials, Department of Modern Mechanics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2010-05-21

176

Stress corrosion cracking of several high strength ferrous and nickel alloys  

NASA Technical Reports Server (NTRS)

The stress corrosion cracking resistance of several high strength ferrous and nickel base alloys has been determined in a sodium chloride solution. Results indicate that under these test conditions Multiphase MP35N, Unitemp L605, Inconel 718, Carpenter 20Cb and 20Cb-3 are highly resistant to stress corrosion cracking. AISI 410 and 431 stainless steels, 18 Ni maraging steel (250 grade) and AISI 4130 steel are susceptible to stress corrosion cracking under some conditions.

Nelson, E. E.

1971-01-01

177

Stress-mapping sensors for high-power adaptive micro-optics  

E-print Network

Stress-mapping sensors for high-power adaptive micro-optics Mohd Suffian B. Zamali and Joseph J in compressive thermal stress to within 80­90 kPa. © 2006 Optical Society of America OCIS codes: 120.6810, 130 with a membrane mirror under tensile stress,1,2 as shown in Fig. 1. Under high-power exci- tation, the mirror

Talghader, Joseph J.

178

Dopant-free GaN/AlN/AlGaN radial nanowire heterostructures as high electron mobility transistors.  

PubMed

We report the rational synthesis of dopant-free GaN/AlN/AlGaN radial nanowire heterostructures and their implementation as high electron mobility transistors (HEMTs). The radial nanowire heterostructures were prepared by sequential shell growth immediately following nanowire elongation using metal-organic chemical vapor deposition (MOCVD). Transmission electron microscopy (TEM) studies reveal that the GaN/AlN/AlGaN radial nanowire heterostructures are dislocation-free single crystals. In addition, the thicknesses and compositions of the individual AlN and AlGaN shells were unambiguously identified using cross-sectional high-angle annular darkfield scanning transmission electron microscopy (HAADF-STEM). Transport measurements carried out on GaN/AlN/AlGaN and GaN nanowires prepared using similar conditions demonstrate the existence of electron gas in the undoped GaN/AlN/AlGaN nanowire heterostructures and also yield an intrinsic electron mobility of 3100 cm(2)/Vs and 21,000 cm(2)/Vs at room temperature and 5 K, respectively, for the heterostructure. Field-effect transistors fabricated with ZrO(2) dielectrics and metal top gates showed excellent gate coupling with near ideal subthreshold slopes of 68 mV/dec, an on/off current ratio of 10(7), and scaled on-current and transconductance values of 500 mA/mm and 420 mS/mm. The ability to control synthetically the electronic properties of nanowires using band structure design in III-nitride radial nanowire heterostructures opens up new opportunities for nanoelectronics and provides a new platform to study the physics of low-dimensional electron gases. PMID:16834431

Li, Yat; Xiang, Jie; Qian, Fang; Gradecak, Silvija; Wu, Yue; Yan, Hao; Blom, Douglas A; Lieber, Charles M

2006-07-01

179

Compressive stress-strain response of directionally aligned SiC w \\/Al composite  

Microsoft Academic Search

A SiCw\\/6061Al composite was fabricated through a squeeze-casting route and hot extruded to obtain a composite with directionally\\u000a aligned whiskers. Based on observed changes in whisker orientation and length before and after deformation, compressive deformation\\u000a behaviour of the directionally aligned SiCw\\/Al composite was investigated. It is found that when the compressive temperature is much lower than the solidus of the

W. L. Zhang; J. X. Wang; D. Z. Wang; M. Y. Gu

2005-01-01

180

Time evolution of off-state degradation of AlGaN/GaN high electron mobility transistors  

SciTech Connect

The evolution of AlGaN/GaN high electron mobility transistors under off-state stress conditions is studied by gate leakage current (I{sub g}) monitoring, electroluminescence (EL), and atomic force microscope (AFM) imaging at room temperature. It is found that the number of off-state failure sites as identified by EL increases over time during stress until it reaches a saturation value. I{sub g} increases accordingly during stress until this saturation number of failure sites is reached. AFM scanning of the device surface stripped of metal contacts and passivation reveals surface pits corresponding to the location of the EL spots. These pits have an elongated shape oriented towards the drain contact whose length is correlated with the distance to the adjacent pits and with the time since their appearance during the stress experiment. A model for the generation and evolution of the off-state stress-related failure sites is proposed consistent with the experimental results, bringing together surface migration of electrochemical species with trap-based leakage mechanisms and resulting in the formation of an exclusion zone around each failure site.

Bajo, M. Montes, E-mail: Miguel.Montes@icfo.es, E-mail: Martin.Kuball@bristol.ac.uk; Sun, H.; Uren, M. J.; Kuball, M., E-mail: Miguel.Montes@icfo.es, E-mail: Martin.Kuball@bristol.ac.uk [Center for Device Thermography and Reliability (CDTR), H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL (United Kingdom)

2014-06-02

181

Time evolution of off-state degradation of AlGaN/GaN high electron mobility transistors  

NASA Astrophysics Data System (ADS)

The evolution of AlGaN/GaN high electron mobility transistors under off-state stress conditions is studied by gate leakage current (Ig) monitoring, electroluminescence (EL), and atomic force microscope (AFM) imaging at room temperature. It is found that the number of off-state failure sites as identified by EL increases over time during stress until it reaches a saturation value. Ig increases accordingly during stress until this saturation number of failure sites is reached. AFM scanning of the device surface stripped of metal contacts and passivation reveals surface pits corresponding to the location of the EL spots. These pits have an elongated shape oriented towards the drain contact whose length is correlated with the distance to the adjacent pits and with the time since their appearance during the stress experiment. A model for the generation and evolution of the off-state stress-related failure sites is proposed consistent with the experimental results, bringing together surface migration of electrochemical species with trap-based leakage mechanisms and resulting in the formation of an exclusion zone around each failure site.

Bajo, M. Montes; Sun, H.; Uren, M. J.; Kuball, M.

2014-06-01

182

High oxidative stress in patients with stable coronary heart disease  

Microsoft Academic Search

Oxidized low density lipoprotein (oxLDL) plays a pivotal role in the development of atherosclerosis. The aim of the study was to investigate the relationship between oxLDL and other oxidative stress biomarkers with stable coronary heart disease (CHD). We compared the degree of oxidative stress in patients with CHD and sex-matched healthy control subjects in a case-control study. The study included

Tanja Weinbrenner; Mercedes Cladellas; Maria Isabel Covas; Montserrat Fitó; Marta Tomás; Mariano Sent??; Jordi Bruguera; Jaume Marrugat

2003-01-01

183

Job Satisfaction, Stress and Coping Strategies among Moroccan High School Teachers.  

ERIC Educational Resources Information Center

Studied job stress, job satisfaction, and coping strategies through self-report measures from 153 Moroccan high school teachers. Results show that 45% of the teachers were satisfied with their jobs, but over half reported high levels of stress, negatively correlated with job satisfaction. Factor analysis of 16 coping strategies produced four…

Benmansour, Naima

1998-01-01

184

Influence of high strain rates on stress–strain relationship, strength and elastic modulus of concrete  

Microsoft Academic Search

Earlier papers showed a method for strength evaluation at high strain rate from the results of static tests, and a method for evaluating modulus of elasticity at static loading from tests based on stress-wave propagation. This paper presents new results on the influence of high strain rates on the stress–strain relationship, strength and modulus of elasticity using the thermofluctuation theory,

I. E. Shkolnik

2008-01-01

185

Highly Conductive Modulation-Doped Graded p-AlGaN\\/(AlN)\\/GaN Multi-Heterostructures  

Microsoft Academic Search

In this study we present theoretical and experimental results regarding modulation doped p-AlGaN\\/(AlN)\\/GaN multi-heterostructures. As the heterostructures should yield both, higher lateral and better vertical conductivity than p-doped GaN, band structure simula- tions have been performed prior to growth experiments. Based on the simulation results several samples were grown by metalorganic vapor phase epitaxy (MOVPE). High reso- lution X-ray diffraction

Joachim Hertkorn; Zhihao Wu

186

Transverse vibrations of embedded nanowires under axial compression with high-order surface stress effects  

NASA Astrophysics Data System (ADS)

Implementing the high-order surface stress model into the Bernoulli-Euler beam theory, the transverse vibration of an axially compressed nanowire embedded in elastic medium is investigated. Closed-form expression is obtained for the natural frequency of a simply supported nanowire. The influences of compressive axial load, high-order surface stress and surrounding elastic medium on the natural frequency are discussed. Additionally, the analytical solution of axial buckling load for the simply supported nanowire is derived, which takes into account the effects of high-order surface stress and surrounding elastic medium. It is concluded from numerical results that the natural frequency of transverse vibration of the nanowire is dependent upon axial load, surrounding elastic medium, and high-order surface stress. Similarly, the dependences of the buckling load on surrounding elastic medium and high-order surface stress are significant.

Zhang, Y. Q.; Pang, M.; Chen, W. Q.

2015-02-01

187

The effect of thermal cycling and stress-assistant ageing twoway shape memory effect in [bar 123]-oriented Co40Ni33Al27 single crystals  

NASA Astrophysics Data System (ADS)

The effect of thermal cycling through an interval of B2-L10 martensitic transformation (MT) under action of external stress and tensile stress-assistant ageing on the two-way shape memory effect in [bar 123]-oriented Co40Ni33Al27 (at.%) single crystals are investigated. For the first time it is experimentally established that tensile stress-assistant 100 MPa ageing at 573 K for 1 h along [bar 123]-direction of Co40Ni33Al27 single crystals creates the necessary conditions for two-way shape memory effect (TWSME) with the reversible strain up to epsilon=2.4 (±0.3)% at cooling/heating. The TWSME in quenched [bar 123]-oriented Co40Ni33Al27 single crystals can be induced by thermal cycling through an interval of B2-L10 MT under action of constant external stress 50 MPa with the reversible strain less than 1%.

Eftifeeva, A. S.; Panchenko, E. Yu; Chumlyakov, Yu I.

2015-01-01

188

Dynamic high-strain-rate mechanical behavior of microstructurally biased two-phase TIB2+AL2O3 ceramics  

NASA Astrophysics Data System (ADS)

The dynamic high-strain-rate behavior of two-phase TiB2+Al2O3 ceramics with biased microstructures was investigated in this study. The microstructural bias includes differences in phase (grain) size and phase distribution such that in one case a continuous (interconnected) TiB2 network surrounds the Al2O3 phase (qualitatively termed "T@A") and in another case the TiB2 and Al2O3 phases are interdispersed and uniformly intertwined with each other (qualitatively termed "TinA"). Quantitative microscopy was used to characterize the phase size and the integral curvature which is taken as a measure of TiB2 phase connectivity around Al2O3. Dynamic compression and tension (spall) properties were measured using plate impact experiments. The measurements used piezoelectric polyvinyldine fluoride stress gauges to obtain the loading profile and to determine the Hugoniot elastic limit. In addition, velocity interferometry system for any reflector interferometry was used to obtain the spall signal and the tensile dynamic strengths of the materials. Experimental results reveal that while the ?HEL and the compressive strengths of TiB2+Al2O3 ceramics are dependent on the average grain (phase) size, the tensile (spall) strength scales with the TiB2-phase connectivity. This result suggests that the interconnected TiB2/Al2O3 microstructural morphology provides a stronger impediment to failure in tension compared with the morphology with simply interdispersed phases.

Kennedy, Greg; Ferranti, Louis; Russell, Rod; Zhou, Min; Thadhani, Naresh

2002-02-01

189

High breakdown voltage in AlGaN/GaN HEMTs using AlGaN/GaN/AlGaN quantum-well electron-blocking layers  

PubMed Central

In this paper, we numerically study an enhancement of breakdown voltage in AlGaN/GaN high-electron-mobility transistors (HEMTs) by using the AlGaN/GaN/AlGaN quantum-well (QW) electron-blocking layer (EBL) structure. This concept is based on the superior confinement of two-dimensional electron gases (2-DEGs) provided by the QW EBL, resulting in a significant improvement of breakdown voltage and a remarkable suppression of spilling electrons. The electron mobility of 2-DEG is hence enhanced as well. The dependence of thickness and composition of QW EBL on the device breakdown is also evaluated and discussed. PMID:25206318

2014-01-01

190

Investigation of trap states in high Al content AlGaN/GaN high electron mobility transistors by frequency dependent capacitance and conductance analysis  

NASA Astrophysics Data System (ADS)

Trap states in Al0.55Ga0.45N/GaN Schottky-gate high-electron-mobility transistors (S-HEMTs) and Al2O3/Al0.55Ga0.45N/GaN metal-oxide-semiconductor HEMTs (MOS-HEMTs) were investigated with conductance method in this paper. Surface states with time constant of (0.09-0.12) ?s were found in S-HEMTs, and electron tunneling rather than emission was deemed to be the dominant de-trapping mechanism due to the high electric field in high Al content barrier. The density of surface states evaluated in S-HEMTs was (1.02-4.67)×1013 eV-1.cm-2. Al2O3 gate insulator slightly reduced the surface states, but introduced low density of new traps with time constant of (0.65-1.29) ?s into MOS-HEMTs.

Zhu, Jie-Jie; Ma, Xiao-Hua; Hou, Bin; Chen, Wei-Wei; Hao, Yue

2014-03-01

191

Influence of Microstructure on Residual Thermal Stresses in TiCxN1-x and -Al2O3 Coatings on WC-Co Tool Inserts  

E-print Network

Influence of Microstructure on Residual Thermal Stresses in TiCxN1-x and -Al2O3 Coatings on WC energy in the -Al2O3 layer are larger than in the TiCxN1-x layer. Furthermore, the mean value. In the present paper, we focus on TiCxN1-x ||-Al2O3||TiN coatings deposited by chemical vapor deposition (CVD

Rohrer, Gregory S.

192

Impact of electrical stress on the electrical characteristics of 2 MeV electron irradiated metal-oxide-silicon capacitors with atomic layer deposited Al2O3, HfO2 and nanolaminated dielectrics  

NASA Astrophysics Data System (ADS)

In this work, the impact of electrical stress on the electrical characteristics of 2 MeV electron irradiated metal-oxide-silicon capacitors with atomic layer deposited (ALD) high permittivity (high-k) dielectric layers of Al2O3, HfO2 and a nanolaminate of them is evaluated. The aim is to investigate the susceptibility to electrical stress of the radiation effects created in irradiated MOS structures, paying especial attention to any possible interaction between the radiation-induced damage and the subsequent electrical stress degradation. For this study, MOS capacitors with a nominal dielectric physical thickness of 10 nm (equivalent oxide thickness (EOT) between 3 nm and 7 nm) on different p-type and n-type silicon substrates were investigated. An exponentially increasing stress current was forced to flow in accumulation through the different dielectric layers, registering the evolution of gate voltage versus stress time until dielectric breakdown occurred. Capacitance-voltage characteristics of the different irradiated and non-irradiated structures are analyzed as a function of electrical stress. Different charge trapping behaviors and significant polarity dependence in interface state generation are observed for the dielectric layers subjected to substrate and gate injections. No clear interaction between radiation and electrical stress damages is noticed under substrate injection (n-type samples). However, higher negative charge trapping near the metal/dielectric interface is registered for the irradiated Al2O3 and nanolaminate layers subjected to gate injection and, in the case of the most irradiated samples, the radiation-induced interface states damage is found to dominate against the damage generated in early stages of the electrical stress.

Rafí, J. M.; González, M. B.; Takakura, K.; Tsunoda, I.; Yoneoka, M.; Beldarrain, O.; Zabala, M.; Campabadal, F.

2013-11-01

193

Stress-induced phase transformation and pseudo-elastic/pseudo-plastic recovery in intermetallic Ni-Al nanowires.  

PubMed

Extensive molecular dynamics (MD) simulations have been performed in a B2-NiAl nanowire using an embedded atom method (EAM) potential. We show a stress induced [Formula: see text]-centered-tetragonal (BCT) phase transformation and a novel temperature and cross-section dependent pseudo-elastic/pseudo-plastic recovery from such an unstable BCT phase with a recoverable strain of approximately 30% as compared to 5-8% in polycrystalline materials. Such a temperature and cross-section dependent pseudo-elastic/pseudo-plastic strain recovery can be useful in various interesting applications of shape memory and strain sensing in nanoscale devices. Effects of size, temperature, and strain rate on the structural and mechanical properties have also been analyzed in detail. For a given size of the nanowire the yield stress of both the B2 and the BCT phases is found to decrease with increasing temperature, whereas for a given temperature and strain rate the yield stress of both the B2 and the BCT phase is found to increase with increase in the cross-sectional dimensions of the nanowire. A constant elastic modulus of approximately 80 GPa of the B2 phase is observed in the temperature range of 200-500 K for nanowires of cross-sectional dimensions in the range of 17.22-28.712 A, whereas the elastic modulus of the BCT phase shows a decreasing trend with an increase in the temperature. PMID:19567964

Sutrakar, Vijay Kumar; Mahapatra, D Roy

2009-07-22

194

An early in-situ stress signature of the AlN-Si pre-growth interface for successful integration of nitrides with (111) Si  

NASA Astrophysics Data System (ADS)

The integration of Metal Organic Chemical Vapor Deposition (MOCVD) grown group III-A nitride device stacks on Si (111) substrates is critically dependent on the quality of the first AlN buffer layer grown. A Si surface that is both oxide-free and smooth is a primary requirement for nucleating such layers. A single parameter, the AlN layer growth stress, is shown to be an early (within 50 nm), clear (<0.5 GPa versus >1 GPa), and fail-safe indicator of the pre-growth surface, and the AlN quality required for successful epitaxy. Grain coalescence model for stress generation is used to correlate growth stress, the AlN-Si interface, and crystal quality.

Chandrasekar, Hareesh; Mohan, Nagaboopathy; Bardhan, Abheek; Bhat, K. N.; Bhat, Navakanta; Ravishankar, N.; Raghavan, Srinivasan

2013-11-01

195

Failure mechanism of coated biomaterials under high impact-sliding contact stresses  

NASA Astrophysics Data System (ADS)

This study uses a newly developed testing method--- inclined cyclic impact-sliding test to investigate the failure behaviors of different types of biomaterials, (SS316L, Ti6Al4V and CoCr) coated by different coatings (TiN, DLC and PEO), under extremely high dynamic contact stress conditions. This test method can simulate the combined impact and sliding/rolling loading conditions, which is very practical in many aspects of commercial usages. During the tests, fatigue cracking, chipping, peeling and material transferring were observed in damaged area. This research is mainly focused on the failure behaviors of load-bearing materials which cyclic impacting and sliding are always involved. This purpose was accomplished in the three stages: First, impact-sliding test was carried out on TiN coated unhardened M2. It was found that soft substrate can cause early failure of coating due to the considerable plastic deformation in the substrate. In this case, stronger substrate is required to support coating better when tested under high contact stresses. Second, PEO coated Ti-6Al-4V was tested under pure sliding and impact-sliding wear conditions. PEO coating was found not strong enough to afford the high contact pressure under cyclic impact-sliding wear test due to its porous surface structure. However, the wear performance of PEO coating was enhanced due to the sub-stoichiometric oxide. To sum up, for load-bearing biomedical implants involved in high impacting movement, PEO coating may not be a promising surface protection. Third, the dense, smooth PVD/CVD bio-inert coatings were reconsidered. DLC and TiN coatings, combined by different substrates together with different interface materials were tested under the cyclic impact-sliding test using a set of proper loading. The results show that to choose a proper combination of coating, interface and substrate based on their mechanical properties is of great importance under the test condition. Hard substrates provide support to coating better and a ductile and adhesive interface layer can delay the cracked coating from peeled-off.

Chen, Ying

196

Optimization of uniaxial stress for high electron mobility on biaxially-strained n-MOSFETs  

NASA Astrophysics Data System (ADS)

The uniaxial stress effect for high electron mobility on biaxially-strained n-MOSFET is investigated by using a one-dimensional self-consistent Schrödinger-Poisson solver. The electron mobility model includes Coulomb, intravalley phonon, intervalley phonon, and surface roughness scattering. We have found that the uniaxial stress effect on biaxially-strained n-MOSFET is significantly different from the uniaxial stress effect on unstrained Si n-MOSFET. It is well known that longitudinal and transverse tensile uniaxial stresses are advantageous for strain-induced high electron mobility. However, we found that the uniaxial strain condition for electron mobility enhancement is changed when it is applied to the biaxially-strained n-MOSFET. To optimize the combined effect of uniaxial and biaxial strain, the longitudinal tensile and transverse compressive uniaxial stresses are advantageous and vertical stress is not helpful for biaxially-strained n-MOSFET.

Sun, Wookyung; Shin, Hyungsoon

2014-04-01

197

Growth of Highly (0002) Oriented InN Films on AlInN/AlN Bilayer  

NASA Astrophysics Data System (ADS)

InN film with an AlInN/AlN bilayer buffer was deposited on Si(111) substrate by radio frequency (RF) magnetron sputtering. X-ray diffraction and Raman spectroscopy measurements reveal that the InN film is of hexagonal wurtzite crystal structure with highly (0002) preferred orientation. An Al0.24In0.76N interface layer of about 50 nm was confirmed by transmission electron microscopy (TEM) and further analyzed by X-ray photoelectron spectroscopy (XPS). The quality of this film is remarkably better than InN films grown directly on Si substrate or with only an AlN buffer, due to the effective accommodation of mismatch between the film and substrate. Our results will be very useful in the fabrication of applicable nitride microelectronic materials.

Dong, C. J.; Xu, M.; Lu, W.; Huang, Q. Z.

2013-04-01

198

Preliminary Thermal Stress Analysis of a High-Pressure Cryogenic Storage Tank  

NASA Technical Reports Server (NTRS)

The thermal stresses on a cryogenic storage tank strongly affect the condition of the tank and its ability to withstand operational stresses. These thermal stresses also affect the growth of any surface damage that might occur in the tank walls. These stresses are particularly of concern during the initial cooldown period for a new tank placed into service, and during any subsequent thermal cycles. A preliminary thermal stress analysis of a high-pressure cryogenic storage tank was performed. Stresses during normal operation were determined, as well as the transient temperature distribution. An elastic analysis was used to determine the thermal stresses in the inner wall based on the temperature data. The results of this elastic analysis indicate that the inner wall of the storage tank will experience thermal stresses of approximately 145,000 psi (1000 MPa). This stress level is well above the room-temperature yield strength of 304L stainless steel, which is about 25,000 psi (170 MPa). For this preliminary analysis, several important factors have not yet been considered. These factors include increased strength of 304L stainless steel at cryogenic temperatures, plastic material behavior, and increased strength due to strain hardening. In order to more accurately determine the thermal stresses and their affect on the tank material, further investigation is required, particularly in the area of material properties and their relationship to stress.

Baker, J. Mark

2003-01-01

199

High-resolution stress mapping of polycrystalline alumina compression using synchrotron X-ray diffraction.  

PubMed

The ability to achieve uniform stress in uniaxial compression tests of polycrystalline alumina is of significance for the calibration of piezospectroscopic coefficients as well as strength studies in ceramics. In this study high-energy X-rays were used to capture powder diffraction profiles over a half-section of a polycrystalline alumina parallelepiped sample under an increasing uniaxial compressive load. The data were converted to strain and results were used for stress mapping of the sample. Stress maps from the study quantify the higher stresses at the sample-platen contact interface and reveal the evolution of the stress distribution in these specimens with load. For the geometry of the samples used, at the center section of the specimen the overall magnitudes of the compressive stresses were found to be 20% higher compared with the average expected theoretical stress based on the applied load and cross-sectional area. The observed compressive stresses at the corners of the parallelepiped specimen were 62% higher and shear stresses were observed at the specimen interface to the load mechanism. The effects, seen at the interface, can lead to premature failure at these locations and can affect the accuracy of calibration of spectral peaks with stress as well as compression strength measurements. The results provide important information that can be used to establish guidelines on material and geometry considerations in developing compression tests on high-strength ceramics. PMID:21525660

Raghavan, Seetha; Imbrie, Peter

2011-05-01

200

Study on Mold Slag with High Al2O3 Content for High Aluminum Steel  

NASA Astrophysics Data System (ADS)

The slag-steel equilibrium reaction between the newly developed mold slag ND-MSL and 20Mn23AlV steel has been studied at high temperatures in the laboratory. The crystal morphology, microanalysis, and phase analysis of the original and final ND-MSL slags were studied by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Results show that, in the final ND-MSL slag, the constitution of SiO2 decreased by 0.7 wt pct and Al2O3 increased by 6.46 wt pct, while the melting temperature, viscosity, and crystallization rate increased by 62 K, 0.66 dPa s, and 15 pct, respectively. NaAlSi3O8 and CaAl2Si2O8 were found to be precipitated in the final ND-MSL slag. Both the original and final ND-MSL slags have a small amount of LiF crystal and good glass form. The ND-MSL slag has little change in the composition and properties compared with the two currently used mold slags.

Wang, Qiang; Sun, Min; Qiu, Shengtao; Tian, Zhiling; Zhu, Guoling; Wang, Longmei; Zhao, Pei

2014-04-01

201

Multicharacterization approach for studying InAl(Ga)N/Al(Ga)N/GaN heterostructures for high electron mobility transistors  

NASA Astrophysics Data System (ADS)

We report on our multi-pronged approach to understand the structural and electrical properties of an InAl(Ga)N(33nm barrier)/Al(Ga)N(1nm interlayer)/GaN(3?m)/ AlN(100nm)/Al2O3 high electron mobility transistor (HEMT) heterostructure grown by metal organic vapor phase epitaxy (MOVPE). In particular we reveal and discuss the role of unintentional Ga incorporation in the barrier and also in the interlayer. The observation of unintentional Ga incorporation by using energy dispersive X-ray spectroscopy analysis in a scanning transmission electron microscope is supported with results obtained for samples with a range of AlN interlayer thicknesses grown under both the showerhead as well as the horizontal type MOVPE reactors. Poisson-Schrödinger simulations show that for high Ga incorporation in the Al(Ga)N interlayer, an additional triangular well with very small depth may be exhibited in parallel to the main 2-DEG channel. The presence of this additional channel may cause parasitic conduction and severe issues in device characteristics and processing. Producing a HEMT structure with InAlGaN as the barrier and AlGaN as the interlayer with appropriate alloy composition may be a possible route to optimization, as it might be difficult to avoid Ga incorporation while continuously depositing the layers using the MOVPE growth method. Our present work shows the necessity of a multicharacterization approach to correlate structural and electrical properties to understand device structures and their performance.

Naresh-Kumar, G.; Vilalta-Clemente, A.; Pandey, S.; Skuridina, D.; Behmenburg, H.; Gamarra, P.; Patriarche, G.; Vickridge, I.; di Forte-Poisson, M. A.; Vogt, P.; Kneissl, M.; Morales, M.; Ruterana, P.; Cavallini, A.; Cavalcoli, D.; Giesen, C.; Heuken, M.; Trager-Cowan, C.

2014-12-01

202

Proppant Fracture Conductivity with High Proppant Loading and High Closure Stress  

E-print Network

conditions improves clean-up of fracture fluid left in the proppant pack compared with using water at ambient temperature. Increasing the proppant concentration in the fracture showed higher conductivity values in some cases even at high closure stress... of fracturing fluids are used with the most common being salt-based polymers with the use of cross-linkers. It was not until the early 1970?s that cross-linkers were introduced with the purpose of increasing the viscosity of gelled water base fracturing...

Rivers, Matthew Charles

2011-08-08

203

Synthesis and stress relaxation of ZnO/Al-doped ZnO core-shell nanowires  

NASA Astrophysics Data System (ADS)

Doping nanostructures is an effective method to tune their electrical and photoelectric properties. Taking ZnO nanowires (NWs) as a model system, we demonstrate that atomic layer deposition (ALD) can be adopted for the realization of a doping process by the homo-epitaxial growth of a doped shell on the NW core. The Al-doped ZnO NWs have a layered superlattice structure with dopants mainly occupying the interstitial positions. After annealing, Al3+ ions diffuse into the ZnO matrix and occupy substitutional locations, which is desirable for dopant activation. The stress accumulated during epitaxial growth is relaxed by the nucleation of dislocations, dislocation dipoles and anti-phase boundaries. We note that the proposed method can be easily adopted for doping different types of nanostructures, and fabricating superlattices and multiple quantum wells on NWs in a controllable way.Doping nanostructures is an effective method to tune their electrical and photoelectric properties. Taking ZnO nanowires (NWs) as a model system, we demonstrate that atomic layer deposition (ALD) can be adopted for the realization of a doping process by the homo-epitaxial growth of a doped shell on the NW core. The Al-doped ZnO NWs have a layered superlattice structure with dopants mainly occupying the interstitial positions. After annealing, Al3+ ions diffuse into the ZnO matrix and occupy substitutional locations, which is desirable for dopant activation. The stress accumulated during epitaxial growth is relaxed by the nucleation of dislocations, dislocation dipoles and anti-phase boundaries. We note that the proposed method can be easily adopted for doping different types of nanostructures, and fabricating superlattices and multiple quantum wells on NWs in a controllable way. Electronic supplementary information (ESI) available: Schematic diagram of the deposition process, TEM images of the as-grown ZnO NWs, the distribution profiles of the elements Zn, O and Al, and the panoramic XPS curves after calibration by C 1s at 284.6 eV. See DOI: 10.1039/c3nr33584d

Wang, Hong-Bo; Ma, Fei; Li, Qian-Qian; Dong, Ce-Zhou; Ma, Da-Yan; Wang, Hong-Tao; Xu, Ke-Wei

2013-03-01

204

Stress corrosion cracking of Alloy 600 in high temperature water  

Microsoft Academic Search

Slow strain rate stress corrosion tests have been performed on specimens cut from four separate heats of alloy 600 steam generator tubing. Material was tested in the mill annealed and thermally stabilized conditions and after various low temperature aging treatments. Only limited cracking was observed, even for tests at 340°C, but the initiation of intergranular cracking was easier on the

J. Congleton; R. N. Parkins; B. Hemsworth

1987-01-01

205

High-intensity acoustic tests of a thermally stressed plate  

Microsoft Academic Search

An investigation was conducted in the Thermal Acoustic Fatigue Apparatus at the Langley Research Center to study the acoustically excited random motion of an aluminum plate which is buckled due to thermal stresses. The thermal buckling displacements were measured and compared with theory. The general trends of the changes in resonances frequencies and random responses of the plate agree with

Chung Fai Ng; Sherman A. Clevenson

1991-01-01

206

Polyaluminum chloride with high Al30 content as removal agent for arsenic-contaminated well water  

E-print Network

Polyaluminum chloride with high Al30 content as removal agent for arsenic-contaminated well water with 75% Al30 nanoclusters (PAClAl30) for the treatment of arsenic-contaminated well water by laboratory. Introduction Arsenic-contaminated groundwater is a major health threat to millions of people worldwide

Wehrli, Bernhard

207

SUPERLINEAR DOSE DEPENDENCE OF HIGH TEMPERATURE THERMOLUMINESCENCE PEAKS IN Al2O3:C  

E-print Network

SUPERLINEAR DOSE DEPENDENCE OF HIGH TEMPERATURE THERMOLUMINESCENCE PEAKS IN Al2O3:C D. Lo1 , J temperature (300­700 C) thermoluminescence (TL) peaks in a-Al2O3:C powder. The main dosimetric peak at $200 C of the strong superlinearity is discussed. INTRODUCTION The thermoluminescence (TL) of Al2O3 samples

Chen, Reuven

208

High Performance Polycrystalline SiGe Thin Film Transistors Using Al2O3 Gate Insulator  

E-print Network

1 High Performance Polycrystalline SiGe Thin Film Transistors Using Al2O3 Gate Insulator Zhonghe. The composition of the deposited aluminum oxide was found to be almost stoichiomertic (i.e. Al2O3), with a very was measured on devices with 50nm thick Al2O3 gate dielectric layers. Typically, a field effect mobility of 47

209

Delineating the genetic heterogeneity of ALS using targeted high-throughput sequencing  

PubMed Central

Background Over 100 genes have been implicated in the aetiology of amyotrophic lateral sclerosis (ALS). A detailed understanding of their independent and cumulative contributions to disease burden may help guide various clinical and research efforts. Methods Using targeted high-throughput sequencing, we characterised the variation of 10 Mendelian and 23 low penetrance/tentative ALS genes within a population-based cohort of 444 Irish ALS cases (50 fALS, 394 sALS) and 311 age-matched and geographically matched controls. Results Known or potential high-penetrance ALS variants were identified within 17.1% of patients (38% of fALS, 14.5% of sALS). 12.8% carried variants of Mendelian disease genes (C9orf72 8.78%; SETX 2.48%; ALS2 1.58%; FUS 0.45%; TARDBP 0.45%; OPTN 0.23%; VCP 0.23%. ANG, SOD1, VAPB 0%), 4.7% carried variants of low penetrance/tentative ALS genes and 9.7% (30% of fALS, 7.1% of sALS) carried previously described ALS variants (C9orf72 8.78%; FUS 0.45%; TARDBP 0.45%). 1.6% of patients carried multiple known/potential disease variants, including all identified carriers of an established ALS variant (p<0.01); TARDBP:c.859G>A(p.[G287S]) (n=2/2 sALS). Comparison of our results with those from studies of other European populations revealed significant differences in the spectrum of disease variation (p=1.7×10?4). Conclusions Up to 17% of Irish ALS cases may carry high-penetrance variants within the investigated genes. However, the precise nature of genetic susceptibility differs significantly from that reported within other European populations. Certain variants may not cause disease in isolation and concomitant analysis of disease genes may prove highly important. PMID:23881933

Kenna, Kevin P; McLaughlin, Russell L; Byrne, Susan; Elamin, Marwa; Heverin, Mark; Kenny, Elaine M; Cormican, Paul; Morris, Derek W; Donaghy, Colette G; Bradley, Daniel G; Hardiman, Orla

2013-01-01

210

ISAP 2012 Brosseaud et al: High modulus asphalt with high rate of recycling 1/13 High modulus asphalt mixes with high rate of RA: what does  

E-print Network

ISAP 2012 Brosseaud et al: High modulus asphalt with high rate of recycling 1/13 High modulus asphalt mixes with high rate of RA: what does it happen? Yves Brosseaud, French Institute of Science Module Elevé (EME - High Modulus Asphalt mixes, in english) give, since more than 20 years, an excellent

Paris-Sud XI, Université de

211

Stress and success: Individual differences in the glucocorticoid stress response predict behavior and reproductive success under high predation risk.  

PubMed

A fundamental element of how vertebrates respond to stressors is by rapidly elevating circulating glucocorticoid hormones. Individual variation in the magnitude of the glucocorticoid stress response has been linked with reproductive success and survival. But while the adaptive value of this response is believed to stem in part from changes in the expression of hormone-mediated behaviors, it is not clear how the behavior of stronger and weaker glucocorticoid responders differs during reproduction, or during exposure to ecologically relevant stressors. Here we report that in a population of barn swallows (Hirundo rustica erythrogaster) experiencing high rates of nest predation, circulating levels of corticosterone (the primary avian glucocorticoid) during exposure to a standardized stressor predict aspects of subsequent behavior and fitness. Individuals that mounted a stronger corticosterone stress response during the early reproductive period did not differ in clutch size, but fledged fewer offspring. Parents with higher stress-induced corticosterone during the early reproductive period later provisioned their nestlings at lower rates. Additionally, in the presence of a model predator stress-induced corticosterone was positively associated with the latency to return to the nest, but only among birds that were observed to return. Model comparisons revealed that stress-induced hormones were better predictors of the behavioral and fitness effects of exposure to transient, ecologically relevant stressors than baseline corticosterone. These findings are consistent with functional links between individual variation in the hormonal and behavioral response to stressors. If such links occur, then selection on the heritable components of the corticosterone stress response could promote adaptation to novel environments or predation regimes. PMID:25461975

Vitousek, Maren N; Jenkins, Brittany R; Safran, Rebecca J

2014-11-01

212

High-stress paleoenvironment during the late Maastrichtian to early Paleocene in Central Egypt  

E-print Network

-stress conditions prevailed in central Egypt as elsewhere in the marginal eastern Tethys. Ã? 2002 Elsevier Science B). In the Eastern Desert, the Sinai and Negev, sediment deposition occurred in a deeper middlHigh-stress paleoenvironment during the late Maastrichtian to early Paleocene in Central Egypt

Keller, Gerta

213

Method for Measuring the Magnetic Properties of High-Density Magnetic Composites Under Compressive Stress  

Microsoft Academic Search

When using a powder magnetic core fabricated from iron powder coated with an insulator in motors, reactors, etc., the effect of stress on its magnetic properties should be considered. In this paper, a system for measuring the magnetic properties of a powder magnetic core under compressive stress was developed and applied to a powder magnetic core, namely a high-density magnetic

N. Takahashi; T. Imahashi; M. Nakano; D. Miyagi; T. Arakawa; H. Nakai; S. Tajima

2007-01-01

214

Analytical model of transient compressive stress evolution during growth of high diffusivity thin films on substrates  

Microsoft Academic Search

We present an analytical model of transient compressive stress evolution during growth of thin films with high surface and grain boundary diffusivities on substrates. The model provides a closed-form analytical solution which compares well with numerical analysis as well as recent experimental data on transient stress evolution during electrodeposition of Sn films on substrates.

Tanmay K. Bhandakkar; Eric Chason; Huajian Gao

2010-01-01

215

An Optical MEMS-Based Shear Stress Sensor for High Reynolds Number Applications  

Microsoft Academic Search

In an effort to extend wall shear stress measurements to high Reynolds number flows, a new MEMS- based optical shear stress sensor was fabricated and tested in the 2 feet wind tunnel at the California Institute of Technology for Reynolds numbers of up to 5.6 x 106. The description of this sensor and the test results are reported in this

D. Fourguette; D. Modarress; D. Wilson; M. Koochesfahani; M. Gharib

216

Residual Stress Distribution of 600MPa Grade High Tensile Strength Steel Pipe Using Welding fe Simulation  

NASA Astrophysics Data System (ADS)

This paper aims to determine the residual stress distribution of 600MPa grade high tensile strength steel pipe (STKT590) by girth welding. Welding FE simulation is achieved considering temperature dependent physical constants and mechanical properties, obtained by the temperature elevated tensile tests. Comparative analyses clarify the characteristics of residual stress profile near weld joint of STKT590 pipe.

Chang, Kyong-Ho; Jang, Gab-Chul

2011-06-01

217

Part two: Early stress and later reproductive performance under conditions of malnutrition and high altitude hypoxia  

Microsoft Academic Search

The phcnotype of the adult organism is dependent upon a host of factors within its developmental framework. Stress acting upon the child during development can alter the adult phenotype in such a way that various functional processes are altered. It is the aim of this paper to explore the role that early exposure to the stresses of malnutrition and high

Ronald S. Weinstein; Jere D. Haas

1977-01-01

218

High stress shallow moonquakes - Evidence for an initially totally molten moon  

NASA Astrophysics Data System (ADS)

Thermoelastic stress calculations show that if the moon was initially molten only in the outer few hundred kilometers, as in the magma ocean model of the moon, the highlands crust should be aseismic. In contrast, if the moon was initially totally molten, high stress (1 to more than about 3 kbar), shallow (0 to about 6 km deep), compressional moonquakes should be occurring in the highlands crust. Calculations of the minimum stress drops made for the 28 observed shallow moonquakes suggest that 3 of them probably have stress drops in the kbar range. Thus, these very limited seismic data are consistent with the model that the moon was initially totally molten.

Binder, A. B.; Oberst, J.

1985-07-01

219

Properties of high-temperature alloys of the system Ni-Al-Nb with a unidirectional eutectic structure  

SciTech Connect

The effects of directional solidification with eutectic crystallization of the gamma- and delta-phases of the ternary alloy Ni-Al-Nb were examined in an attempt to provide better ductility and high temperature oxidation resistance. Specimens of the system examined, Ni-Ni3Al-Ni3Nb, were studied for the variations in the microstructural characteristics in response to variation in the chemical compositions. The Bridgman method was used to effect directional solidification. A unidirectional structure composed of alternating gamma- and delta-phases was observed in specimens with 21-23 percent Nb and 2.0-2.5 percent Al directionally solidified in thermal gradients of 70-80 deg/cm and at a crystallization rate of 0.3-0.4 mm/min. Stress cracking tests of the unidirectional materials yielded a time to failure of 14-24 hr at 1100 C with a 120 MPa stress. The time to failure was extended to 69-81 hr by adding 2-4 percent Cr. 8 references.

Toropov, V.M.; Bondarenko, IU.A.

1985-03-01

220

Mean stress effects on high-cycle fatigue of Alloy 718  

SciTech Connect

This report covers an investigation of the effects of tensile mean stress on the high-cycle fatigue properties of Alloy 718. Three test temperatures (24, 427, and 649{degree}C) were employed, and there were tests in both strain and load control. Results were compared with three different models: linear Modified-Goodman, Peterson cubic, and stress-strain parameter. The linear Modified-Goodman model gave good correlation with actual test data for low and moderate mean stress values, but the stress-strain parameter showed excellent correlation over the entire range of possible mean stresses and therefore is recommended for predicting mean stress effects of Alloy 718. 13 refs., 12 figs.

Korth, G E

1980-07-01

221

Neutron diffraction analysis of residual strain/stress distribution in the vicinity of high strength welds  

NASA Astrophysics Data System (ADS)

Residual stresses resulting from non homogeneous heat distribution during welding process belong to most significant factor influencing behavior of welded structures. These stresses are responsible for defect occurrence during welding and they are also responsible for crack initiation and propagation at the either static or dynamic load. The significant effect of weld metal chemical composition as well as the effect of fatigue load and local plastic deformation on residual stress distribution and fatigue life have been recognized for high strength steels welds. The changes in residual stress distribution have then positive effect on cold cracking behavior and also on fatigue properties of the welds [1-3]. Several experimental methods, both destructive and non-destructive, such as hole drilling method, X-ray diffraction, neutron diffraction and others, have been used to examine residual stress distribution in all three significant orientations in the vicinity of the welds. The present contribution summarizes the results of neutron diffraction measurements of residual stress distribution in the vicinity of single-pass high-strength-steel welds having different chemical composition as well as the influence of fatigue load and local plastic deformation. It has been observed that the chemical composition of the weld metal has a significant influence on the stress distribution around the weld. Similarly, by aplying both cyclic load or pre-stress load on the specimens, stress relaxation was observed even in the region of approximately 40 mm far from the weld toe.

Mráz, L.; Karlsson, L.; Hamák, I.; Vrána, M.; Mikula, P.

2010-06-01

222

Apparatus for Inducing High Uniaxial Compressive Stresses in Crystals  

Microsoft Academic Search

A vise capable of exerting uniaxial forces in excess of 2×109 dynes and operable between 77 and 300 K is described. The strain induced in the crystal being compressed is measured via a strain gauge bonded directly to the surface of the specimen. The applied stress may be varied smoothly to greater than 1010 dynes?cm2 and a resistance bridge resolves

J. F. Schetzina; J. P. McKelvey; M. W. Cresswell

1968-01-01

223

Near ultraviolet InGaN/AlGaN-based light-emitting diodes with highly reflective tin-doped indium oxide/Al-based reflectors.  

PubMed

The enhanced light output power of a InGaN/AlGaN-based light-emitting diodes (LEDs) using three different types of highly reflective Sn-doped indium oxide (ITO)/Al-based p-type reflectors, namely, ITO/Al, Cu-doped indium oxide (CIO)/s-ITO(sputtered)/Al, and Ag nano-dots(n-Ag)/CIO/s-ITO/Al, is presented. The ITO/Al-based reflectors exhibit lower reflectance (76 - 84% at 365 nm) than Al only reflector (91.1%). However, unlike Al only n-type contact, the ITO/Al-based contacts to p-GaN show good ohmic characteristics. Near-UV (365 nm) InGaN/AlGaN-based LEDs with ITO/Al, CIO/s-ITO/Al, and n-Ag/CIO/s-ITO/Al reflectors exhibit forward-bias voltages of 3.55, 3.48, and 3.34 V at 20 mA, respectively. The LEDs with the ITO/Al and CIO/s-ITO/Al reflectors exhibit 9.5% and 13.5% higher light output power (at 20 mA), respectively, than the LEDs with the n-Ag/CIO/s-ITO/Al reflector. The improved performance of near UV LEDs is attributed to the high reflectance and low contact resistivity of the ITO/Al-based reflectors, which are better than those of conventional Al-based reflectors. PMID:24216898

Choi, Chang-Hoon; Han, Jaecheon; Park, Jae-Seong; Seong, Tae-Yeon

2013-11-01

224

In-situ studies of the TGO growth stresses and the martensitic transformation in the B2 phase in commercial Pt-modified NiAl and NiCoCrAlY bond coat alloys.  

SciTech Connect

Oxide growth stresses were measured in situ at 1100 C on commercial Pt-modified NiAl and NiCoCrAlY bond coat alloys using synchrotron X-rays. Measurements were taken on samples that had no preoxidation, as well as on samples that had experienced 24 one-hour thermal exposures at 1150 C, a condition known to induce rumpling in the Pt-modified NiAl alloy, but not in the NiCoCrAlY alloy. The NiCoCrAlY alloy showed continuous stress relaxation under all conditions, whereas the Pt-modified NiAl alloys would typically stabilize at a fixed (often non-zero) stress suggesting a higher creep strength in the 'Thermally Grown Oxide' on the latter alloy, though the precise behavior was dependent on initial surface preparation. The formation of martensite in the Pt-modified NiAl alloys was also observed upon cooling and occurred at temperatures below 200 C for all of the samples observed. Based on existing models, this M{sub s} temperature is too low to account for the rumpling observed in these alloys.

Hovis, D.; Hu, L.; Reddy, A.; Heuer, A. H.; Paulikas, A. P.; Veal, B. W. (Materials Science Division); (Case Western Reserve Univ.)

2007-12-01

225

Stress-corrosion crack-growth study of titanium alloy Ti-6Al-4V exposed to freon PCA and nitrogen tetroxide MON-1  

NASA Technical Reports Server (NTRS)

An experimental fracture mechanics program was performed to determine the stress corrosion crack growth sensitivity of the propellant tank material, titanium alloy Ti-6Al-4V, for aerospace satellite applications involving long term exposure to Freon PCA and nitrogen tetroxide MON-1. Sustained load tests were made at a 49 C (120 F) constant temperature using thin gauge tensile test specimens containing semielliptical surface flaws. Test specimen types included parent metal, center of weld, and weld heat affected zone. It was concluded that Ti-6Al-4V alloy is not adversely affected in a stress environment when exposed to Freon PCA for 1000 hours followed by exposure to nitrogen tetroxide MON-1 for 2000 hours at stress levels up to 80% of the experimental critical plane strain stress intensity factor.

Bjorklund, R. A.

1983-01-01

226

Dielectric stress tests and capacitance-voltage analysis to evaluate the effect of post deposition annealing on Al2O3 films deposited on GaN  

NASA Astrophysics Data System (ADS)

Systematic stress tests that help to evaluate the stability and dielectric performance of Al2O3 films under DC bias conditions are reported. Capacitance-voltage (C-V) curves were monitored for changes after subjecting the dielectric film to constant forward and reverse bias stress. Stress tests, along with C-V analysis, are used to evaluate the effect of post deposition annealing on Metal-Organic Chemical Vapor Deposition) Al2O3 films deposited on GaN. The individual benefits and drawbacks of each film and anneal condition were identified. These suggest that the anneals can be tailored to the unannealed film characteristics to achieve desired improvements in performance. It is found that post deposition annealing in forming gas improves performance under reverse bias stress by reducing the fixed charge and the field in the oxide but does not improve performance under forward bias.

Yeluri, Ramya; Liu, Xiang; Guidry, Matthew; Koksaldi, Onur S.; Lal, Shalini; Kim, Jeonghee; Lu, Jing; Keller, Stacia; Mishra, Umesh K.

2014-12-01

227

Effect of microstructure on high-cycle fatigue properties of Ti-6Al-4V alloy forging at cryogenic temperatures  

NASA Astrophysics Data System (ADS)

The effect of microstructure on the high-cycle fatigue properties of Ti-6Al-4V alloy forging at cryogenic temperature was investigated using four materials with different microstructure. One of them was ?+? annealed and has bimodal microstructure which consists of equiaxed-? and ?+? lamellar microstructure. Three other materials were water quenched (WQ), air cooled (AC) or furnace cooled (FC) after ?-annealing. The ?-annealed materials have lamellar microstructure and ? lamellar width increase in the order of WQ, AC and FC materials. The fatigue test was done with uni-axial load-controlled and a stress ratio of R = ?min/?max = 0.01 at 20 K (in gaseous helium), 77 K (in liquid nitrogen) and 293 K (in laboratory air). The 107-cycles fatigue strengths at 20 K decrease in the order of WQ, AC, FC and the ?+? annealed material. Namely, the ?-annealed Ti-6Al-4V alloys, which has lamellar ? microstructures shows higher fatigue strengths than bimodal microstructure.

Yuri, T.; Ono, Y.; Ogata, T.; Sunakawa, H.

2014-01-01

228

Comparison Between Nb3Al and Nb3Sn Strands and Cables for High Field Accelerator Magnets  

SciTech Connect

The Nb{sub 3}Al small racetrack magnet, SR07, has been successfully built and tested to its short sample limit beyond 10 Tesla without any training. Thus the practical application of Nb{sub 3}Al strands for high field accelerator magnets is established. The characteristics of the representative F4 strand and cable, are compared with the typical Nb{sub 3}Sn strand and cable. It is represented by the OST high current RRP Nb{sub 3}Sn strand with 108/127 configuration. The effects of Rutherford cabling to both type strands are explained and the inherent problem of the Nb{sub 3}Sn strand is discussed. Also the test results of two representative small racetrack magnets are compared from the stand point of Ic values, and training. The maximum current density of the Nb{sub 3}Al strands is still smaller than that of the Nb{sub 3}Sn strands, but if we take into account of the stress-strain characteristics, Nb{sub 3}Al strands become somewhat favorable in some applications.

Yamada, R.; Kikuchi, A.; Barzi, E.; Chlachidze, G.; Rusy, A.; Takeuchi, T.; Tartaglia, M.; Turrioni, D.; Velev, V.; Wake, M.; Zlobin, A.V.; /Fermilab

2010-01-01

229

High Strain, Strain Rate Behavior of PTFE\\/Al\\/W  

Microsoft Academic Search

Conventional dropweight technique was modified to accommodate low amplitude signals from low strength, cold isostatically pressed energetic ``heavy'' composites of polytetrafluoroethylene (PTFE)\\/AL\\/W. The fracture strength, strain and post-critical behaviour of fractured samples were measured for samples of different porosity and W grain size (the masses of each component being the same in each case). Unusual phenomenon of significantly higher strength

John Addiss; Jing Cai; Steve Walley; William Proud; Vitali Nesterenko

2007-01-01

230

Excitation-dependent Polarized Emission from GaN/AlN Quantum Dot Ensembles under In-plane Uniaxial Stresses  

NASA Astrophysics Data System (ADS)

The effects of uniaxial stress and variable excitation on the optical properties of GaN/AlN quantum dots (QDs) grown on Si(111) substrates have been investigated. We show that post-growth microcracks which are created during cooling of the sample serve as excellent stressors through which the strain tensor of the QDs can be modified for studies of strain-induced changes in the optical properties. We have used cathodoluminescence (CL) imaging and spectroscopy with polarization detection to probe limited regions of the sample in which the QDs are subject to in-plane uniaxial stresses of 20 to 30 kbar. CL measurements of the QD excitonic transitions exhibit an in-plane linear polarization anisotropy in close proximity to microcracks that is strongly dependent on the e-beam current used to excite the QD ensemble. Theoretical modeling was performed, as based on self-consistent solutions of the Schrödinger and Poisson equations using the 6×6 k?p and effective mass methods for the calculation of the QD hole and electron states.

Rich, D. H.; Moshe, O.; Damilano, B.; Massies, J.

2011-12-01

231

Ultra-high sensitivity optical stress sensor based on double-layered photonic crystal microcavity.  

PubMed

In this report, we present the design principles to achieve a highly sensitive optical stress sensor. The structure we use is a double-layered (DL) photonic molecule with optical bonding and anti-bonding states based on whispering-gallery mode in photonic crystal microcavity. By applying finite-difference time-domain and finite-element methods, we simulate the change of optical properties (including wavelength and quality (Q) factor) of bonding mode caused by the DL structural variation due to the applied stress in two DL geometries. In the end, we summarize an optical stress sensor design with high Q factor, large structural response due to the applied stress, and large optical spectrum change due to the DL structural variation. The minimum detectable stress variation is estimated to be as small as 0.95 nN. PMID:19188981

Lu, Tsan-Wen; Lee, Po-Tsung

2009-02-01

232

An Inducer of VGF Protects Cells against ER Stress-Induced Cell Death and Prolongs Survival in the Mutant SOD1 Animal Models of Familial ALS  

PubMed Central

Amyotrophic lateral sclerosis (ALS) is the most frequent adult-onset motor neuron disease, and recent evidence has suggested that endoplasmic reticulum (ER) stress signaling is involved in the pathogenesis of ALS. Here we identified a small molecule, SUN N8075, which has a marked protective effect on ER stress-induced cell death, in an in vitro cell-based screening, and its protective mechanism was mediated by an induction of VGF nerve growth factor inducible (VGF): VGF knockdown with siRNA completely abolished the protective effect of SUN N8075 against ER-induced cell death, and overexpression of VGF inhibited ER-stress-induced cell death. VGF level was lower in the spinal cords of sporadic ALS patients than in the control patients. Furthermore, SUN N8075 slowed disease progression and prolonged survival in mutant SOD1 transgenic mouse and rat models of ALS, preventing the decrease of VGF expression in the spinal cords of ALS mice. These data suggest that VGF plays a critical role in motor neuron survival and may be a potential new therapeutic target for ALS, and SUN N8075 may become a potential therapeutic candidate for treatment of ALS. PMID:21151573

Shimazawa, Masamitsu; Tanaka, Hirotaka; Ito, Yasushi; Morimoto, Nobutaka; Tsuruma, Kazuhiro; Kadokura, Michinori; Tamura, Shigeki; Inoue, Teruyoshi; Yamada, Mitsunori; Takahashi, Hitoshi; Warita, Hitoshi; Aoki, Masashi; Hara, Hideaki

2010-01-01

233

Degradation of blue AlGaN/InGaN/GaN LEDs subjected to high current pulses  

SciTech Connect

Short-wavelength, visible-light emitting optoelectronic devices are needed for a wide range of commercial applications, including high-density optical data storage, full-color displays, and underwater communications. In 1994, high-brightness blue LEDs based on gallium nitride and related compounds (InGaN/AlGaN) were introduced by Nichia Chemical Industries. The Nichia diodes are 100 times brighter than the previously available SiC blue LEDs. Group-III nitrides combine a wide, direct bandgap with refractory properties and high physical strength. So far, no studies of degradation of GaN based LEDs have been reported. The authors study, reported in this paper, focuses on the performance of GaN LEDs under high electrical stress conditions. Their observations indicate that, in spite of a high defect density, which normally would have been fatal to other III-V devices, defects in group-III nitrides are not mobile even under high electrical stress. Defect tubes, however, can offer a preferential path for contact metals to electromigrate towards the p-n junction, eventually resulting in a short. The proposed mechanism of GaN diode degradation raises concern for prospects of reliable lasers in the group-III nitrides grown on sapphire.

Barton, D.L. [Sandia National Labs., Albuquerque, NM (United States); Zeller, J.; Phillips, B.S.; Chiu, P.C.; Askar, S.; Lee, D.S.; Osinski, M.; Malloy, K.J. [Univ. of New Mexico, Albuquerque, NM (United States). Center for High Technology Materials

1994-12-31

234

Degradation of blue AlGaN/InGaN/GaN LEDs subjected to high current pulses  

NASA Astrophysics Data System (ADS)

Short-wavelength, visible-light emitting optoelectronic devices are needed for a wide range of commercial applications, including high-density optical data storage, full-color displays, and underwater communications. In 1994, high-brightness blue LED's based on gallium nitride and related compounds (InGaN/AlGaN) were introduced by Nichia Chemical Industries. The Nichia diodes are 100 times brighter than the previously available SiC blue LED's. Group-3 nitrides combine a wide, direct bandgap with refractory properties and high physical strength. So far, no studies of degradation of GaN based LED's have been reported. The authors study, reported in this paper, focuses on the performance of GaN LED's under high electrical stress conditions. Their observations indicate that, in spite of a high defect density, which normally would have been fatal to other 3-5 devices, defects in group-3 nitrides are not mobile even under high electrical stress. Defect tubes, however, can offer a preferential path for contact metals to electromigrate towards the p-n junction, eventually resulting in a short. The proposed mechanism of GaN diode degradation raises concern for prospects of reliable lasers in the group-3 nitrides grown on sapphire.

Barton, Daniel L.; Zeller, Joachim; Phillips, B. Scott; Chiu, Pei-Chih; Askar, Sabrina; Lee, Dong-Seung; Osinski, Lee Marek; Malloy, Kevin J.

1994-12-01

235

LuAlO{sub 3}: A high density, high speed scintillator for gamma detection  

SciTech Connect

We present measurements of the scintillation properties cerium doped lutetium aluminum perovskite, LuAlO{sub 3}:C, new dense ({rho}=8.34 g/cm{sup 3}) inorganic scintillator. This material has a 511 keV interaction length and photoelectric fraction 1.1 cm and 32% respectively, which are well suited to gamma ray detection. In powdered form with 0.5% cerium concentration, the scintillation light output is estimated to be 9,600 photons/MeV of deposited energy, the emission spectrum is a single peak centered at 390 nm, and the fluorescence lifetime is described by the sum of 3 exponential terms, with 60% of the light being emitted with a 11 ns decay time, 26% with a 28 ns decay time, and 13% with a 835 ns decay time. Single crystals contaminated with =10% lutetium aluminum garnet (Lu{sub 3}Al{sub 5}O{sub l2}) have significantly altered scintillation properties. The light output is 26,000 photons/MeV (3.2 times that of BGO), but the decay time increases significantly (1% of the light is emitted with a 10 ns decay time, 15% with a 245 ns decay time, and 85% with a 2010 ns decay time) and the emission spectrum is dominated by a peak centered at 315 nm with a secondary peak centered at 500 rum. The short decay lifetime, high density, and reasonable light output of LuAlO{sub 3}:C (the perovskite phase) suggest that it is useful for applications where high counting rates, good stopping power, good energy resolution, and fast timing are important. However, it is necessary to grow single crystals that are uncontaminated by the garnet phase to realize these properties.

Moses, W.W.; Derenzo, S.E. [Lawrence Berkeley Lab., CA (United States); Fyodorov, A.; Korzhik, M. [Inst. of Nuclear Problems, Minsk (Belarus); Gektin, A.; Minkov, B. [Inst. of Single Crystals, Kharkov (Ukraine); Aslanov, V. [SCITEC RI& NC, Minsk (Belarus)

1994-11-01

236

Genetic dissection of Al tolerance QTLs in the maize genome by high density SNP scan  

PubMed Central

Background Aluminum (Al) toxicity is an important limitation to food security in tropical and subtropical regions. High Al saturation on acid soils limits root development, reducing water and nutrient uptake. In addition to naturally occurring acid soils, agricultural practices may decrease soil pH, leading to yield losses due to Al toxicity. Elucidating the genetic and molecular mechanisms underlying maize Al tolerance is expected to accelerate the development of Al-tolerant cultivars. Results Five genomic regions were significantly associated with Al tolerance, using 54,455 SNP markers in a recombinant inbred line population derived from Cateto Al237. Candidate genes co-localized with Al tolerance QTLs were further investigated. Near-isogenic lines (NILs) developed for ZmMATE2 were as Al-sensitive as the recurrent line, indicating that this candidate gene was not responsible for the Al tolerance QTL on chromosome 5, qALT5. However, ZmNrat1, a maize homolog to OsNrat1, which encodes an Al3+ specific transporter previously implicated in rice Al tolerance, was mapped at ~40 Mbp from qALT5. We demonstrate for the first time that ZmNrat1 is preferentially expressed in maize root tips and is up-regulated by Al, similarly to OsNrat1 in rice, suggesting a role of this gene in maize Al tolerance. The strongest-effect QTL was mapped on chromosome 6 (qALT6), within a 0.5 Mbp region where three copies of the Al tolerance gene, ZmMATE1, were found in tandem configuration. qALT6 was shown to increase Al tolerance in maize; the qALT6-NILs carrying three copies of ZmMATE1 exhibited a two-fold increase in Al tolerance, and higher expression of ZmMATE1 compared to the Al sensitive recurrent parent. Interestingly, a new source of Al tolerance via ZmMATE1 was identified in a Brazilian elite line that showed high expression of ZmMATE1 but carries a single copy of ZmMATE1. Conclusions High ZmMATE1 expression, controlled either by three copies of the target gene or by an unknown molecular mechanism, is responsible for Al tolerance mediated by qALT6. As Al tolerant alleles at qALT6 are rare in maize, marker-assisted introgression of this QTL is an important strategy to improve maize adaptation to acid soils worldwide. PMID:24564817

2014-01-01

237

High strain rate deformation of Ti-48Al-2Cr-2Nb in the duplex morphology  

SciTech Connect

The compressive deformation behavior of Ti-48Al-2Nb-2Cr in the duplex microstructural morphology has been studied at strain rates of 0.001/s and 2000/s over the temperature range from -196 to 1100{degrees}C. The material was cast, homogenized, extruded and heat treated to obtain the duplex microstructure. The yield stress is strain rate sensitive at 25{degrees}C and increases with temperature at a strain rate of 2000/s from 500 to 1100{degrees}C. TEM investigations reveal that deformation occurs in {gamma}-TiAl by means of [111]<112> twinning, 1/2<110> slip, and <101> superdislocations under all conditions depending on the orientation of the grain with respect to the deformation axis. Optical metallography reveals that twinning increases with increasing strain rate. TEM results revealing the dislocation substructure are used to explain the yield stress anomaly.

Maloy, S.A.; Gray, G.T. III

1995-03-01

238

Highly conductive modulation doped composition graded p-AlGaN\\/(AlN)\\/GaN multiheterostructures grown by metalorganic vapor phase epitaxy  

Microsoft Academic Search

In this study, we present theoretical and experimental results regarding highly conductive modulation doped composition graded p-AlGaN\\/(AlN)\\/GaN multiheterostructures. Based on simulation results, several multiheterostructures were grown by metalorganic vapor phase epitaxy. Using high resolution x-ray diffraction and x-ray reflectometry, the abruptness of the AlGaN\\/AlN\\/GaN interfaces could be determined. Using electron holography, the energetic profile of the valence band could be

J. Hertkorn; S. B. Thapa; T. Wunderer; F. Scholz; Z. H. Wu; Q. Y. Wei; F. A. Ponce; M. A. Moram; C. J. Humphreys; C. Vierheilig; U. T. Schwarz

2009-01-01

239

High hemoglobin mixed disulfide content in hemolysates from stressed shark.  

PubMed

1. Hemolysate from heavily stressed smooth hammerhead shark, Sphyrna zygaena, shows three electrophoretic components, SZ I, SZ II and SZ III, whose relative concentrations are 36.4 +/- 6.8, 36.4 +/- 5.0 and 20.8 +/- 5.7%, respectively. After reduction with DTE only SZ I remained. 2. SZ I reacted with glutathione disulfide reconstitute SZ II and SZ III. 3. Non-reduced, DTE-reduced, and denatured hemoglobin were found to have 2.0 +/- 0.4, 3.7 +/- 0.6, and 9.4 +/- 0.7-SH groups, respectively. 4. Erythrocyte non-protein--SH (NPSH), including glutathione present as mixed disulfide with SZ II and SZ III, is 1.7 NPSH/Hb. PMID:2361357

Dafré, A L; Reischl, E

1990-01-01

240

Assessing Cumulative Thermal Stress in Fish During Chronic Exposure to High Temperature  

SciTech Connect

As environmental laws become increasingly protective, and with possible future changes in global climate, thermal effects on aquatic resources are likely to receive increasing attention. Lethal temperatures for a variety of species have been determined for situations where temperatures rise rapidly resulting in lethal effects. However, less is known about the effects of chronic exposure to high (but not immediately lethal) temperatures and even less about stress accumulation during periods of fluctuating temperatures. In this paper we present a modeling framework for assessing cumulative thermal stress in fish. The model assumes that stress accumulation occurs above a threshold temperature at a rate depending on the degree to which the threshold is exceeded. The model also includes stress recovery (or alleviation) when temperatures drop below the threshold temperature as in systems with large daily variation. In addition to non-specific physiological stress, the model also simulates thermal effects on growth.

Bevelhimer, M.S.; Bennett, W.R.

1999-11-14

241

Caffeine prevents cognitive impairment induced by chronic psychosocial stress and/or high fat-high carbohydrate diet.  

PubMed

Caffeine alleviates cognitive impairment associated with a variety of health conditions. In this study, we examined the effect of caffeine treatment on chronic stress- and/or high fat-high carbohydrate Western diet (WD)-induced impairment of learning and memory in rats. Chronic psychosocial stress, WD and caffeine (0.3 g/L in drinking water) were simultaneously administered for 3 months to adult male Wistar rats. At the conclusion of the 3 months, and while the previous treatments continued, rats were tested in the radial arm water maze (RAWM) for learning, short-term and long-term memory. This procedure was applied on a daily basis to all animals for 5 consecutive days or until the animal reaches days to criterion (DTC) in the 12th learning trial and memory tests. DTC is the number of days that the animal takes to make zero error in two consecutive days. Chronic stress and/or WD groups caused impaired learning, which was prevented by chronic caffeine administration. In the memory tests, chronic caffeine administration also prevented memory impairment during chronic stress conditions and/or WD. Furthermore, DTC value for caffeine treated stress, WD, and stress/WD groups indicated that caffeine normalizes memory impairment in these groups. These results showed that chronic caffeine administration prevented stress and/or WD-induced impairment of spatial learning and memory. PMID:23000531

Alzoubi, K H; Abdul-Razzak, K K; Khabour, O F; Al-Tuweiq, G M; Alzubi, M A; Alkadhi, K A

2013-01-15

242

Correlation between biaxial stress and free exciton transition in AlN B. N. Pantha, N. Nepal, T. M. Al Tahtamouni, M. L. Nakarmi, J. Li,  

E-print Network

-ray diffraction XRD studies of AlN epilayers grown on sapphire, SiC, Si, and AlN bulk single crystal sub- strates in AlN/SiC AlN/Si due to a tensile strain. A linear relationship between the FX transition energy peak single crystal substrates.9­11 The use of an AlN bulk single crystal as a substrate is expected

Jiang, Hongxing

243

Complexity of physiological responses decreases in high-stress musical performance  

PubMed Central

For musicians, performing in front of an audience can cause considerable apprehension; indeed, performance anxiety is felt throughout the profession, with wide ranging symptoms arising irrespective of age, skill level and amount of practice. A key indicator of stress is frequency-specific fluctuations in the dynamics of heart rate known as heart rate variability (HRV). Recent developments in sensor technology have made possible the measurement of physiological parameters reflecting HRV non-invasively and outside of the laboratory, opening research avenues for real-time performer feedback to help improve stress management. However, the study of stress using standard algorithms has led to conflicting and inconsistent results. Here, we present an innovative and rigorous approach which combines: (i) a controlled and repeatable experiment in which the physiological response of an expert musician was evaluated in a low-stress performance and a high-stress recital for an audience of 400 people, (ii) a piece of music with varying physical and cognitive demands, and (iii) dynamic stress level assessment with standard and state-of-the-art HRV analysis algorithms such as those within the domain of complexity science which account for higher order stress signatures. We show that this offers new scope for interpreting the autonomic nervous system response to stress in real-world scenarios, with the evolution of stress levels being consistent with the difficulty of the music being played, superimposed on the stress caused by performing in front of an audience. For an emerging class of algorithms that can analyse HRV independent of absolute data scaling, it is shown that complexity science performs a more accurate assessment of average stress levels, thus providing greater insight into the degree of physiological change experienced by musicians when performing in public. PMID:24068177

Williamon, Aaron; Aufegger, Lisa; Wasley, David; Looney, David; Mandic, Danilo P.

2013-01-01

244

High-salt preadaptation of Vibrio parahaemolyticus enhances survival in response to lethal environmental stresses.  

PubMed

Adaptation to changing environmental conditions is an important strategy for survival of foodborne bacterial pathogens. Vibrio parahaemolyticus is a gram-negative seafoodborne enteric pathogen found in the marine environment both free living and associated with oysters. This pathogen is a moderate halophile, with optimal growth at 3% NaCl. Among the several stresses imposed upon enteric bacteria, acid stress is perhaps one of the most important. V. parahaemolyticus has a lysine decarboxylase system responsible for decarboxylation of lysine to the basic product cadaverine, an important acid stress response system in bacteria. Preadaptation to mild acid conditions, i.e., the acid tolerance response, enhances survival under lethal acid conditions. Because of the variety of conditions encountered by V. parahaemolyticus in the marine environment and in oyster postharvest facilities, we examined the nature of the V. parahaemolyticus acid tolerance response under high-salinity conditions. Short preadaptation to a 6% salt concentration increased survival of the wild-type strain but not that of a cadA mutant under lethal acid conditions. However, prolonged exposure to high salinity (16 h) increased survival of both the wild-type and the cadA mutant strains. This phenotype was not dependent on the stress response sigma factor RpoS. Although this preadaptation response is much more pronounced in V. parahaemolyticus, this characteristic is not limited to this species. Both Vibrio cholerae and Vibrio vulnificus also survive better under lethal acid stress conditions when preadapted to high-salinity conditions. High salt both protected the organism against acid stress and increased survival under -20°C cold stress conditions. High-salt adaptation of V. parahaemolyticus strains significantly increases survival under environmental stresses that would otherwise be lethal to these bacteria. PMID:24490918

Kalburge, Sai Siddarth; Whitaker, W Brian; Boyd, E Fidelma

2014-02-01

245

Capabilities of the High Voltage Stress Test System at the Outdoor Test Facility  

SciTech Connect

We illustrate the capabilities of the High Voltage Stress Test (HVST) which operates continuously in the array field east of the Outdoor Test Facility at the National Renewable Energy Laboratory. Because we know that photovoltaic (PV) modules generating electrical power in both residential and utility-scale array installations will develop high-voltage biases approaching 600 VDC and 1,000 VDC, respectively, we expect such high voltages will result in current leakage between cells and ground, typically through the frames or mounts. We know that inevitably such leakage currents are capable of producing electrochemical corrosion that adversely impacts long-term module performance. With the HVST, we stress or operate PV modules under high-voltage bias, to characterize their leakage currents under all prevailing ambient conditions and assess performance changes emanating from high-voltage stress. We perform this test both on single modules and an active array.

del Cueto, J. A.; Trudell, D.; Sekulic, W.

2005-11-01

246

Investigation of trap states in high Al content AlGaN/GaN high electron mobility transistors by frequency dependent capacitance and conductance analysis  

SciTech Connect

Trap states in Al{sub 0.55}Ga{sub 0.45}N/GaN Schottky-gate high-electron-mobility transistors (S-HEMTs) and Al{sub 2}O{sub 3}/Al{sub 0.55}Ga{sub 0.45}N/GaN metal-oxide-semiconductor HEMTs (MOS-HEMTs) were investigated with conductance method in this paper. Surface states with time constant of (0.09–0.12) ?s were found in S-HEMTs, and electron tunneling rather than emission was deemed to be the dominant de-trapping mechanism due to the high electric field in high Al content barrier. The density of surface states evaluated in S-HEMTs was (1.02–4.67)×10{sup 13} eV{sup ?1}·cm{sup ?2}. Al{sub 2}O{sub 3} gate insulator slightly reduced the surface states, but introduced low density of new traps with time constant of (0.65–1.29) ?s into MOS-HEMTs.

Zhu, Jie-Jie; Ma, Xiao-Hua, E-mail: xhma@xidian.edu.cn; Hou, Bin; Chen, Wei-Wei [State Key Discipline Laboratory of Wide Bandgap Semiconductor Technology, School of Advanced Materials and Nanotechnology, Xidian University, Xi'an 710071 (China)] [State Key Discipline Laboratory of Wide Bandgap Semiconductor Technology, School of Advanced Materials and Nanotechnology, Xidian University, Xi'an 710071 (China); Hao, Yue [State Key Discipline Laboratory of Wide Bandgap Semiconductor Technology, School of Advanced Materials and Nanotechnology, Xidian University, Xi'an 710071 (China) [State Key Discipline Laboratory of Wide Bandgap Semiconductor Technology, School of Advanced Materials and Nanotechnology, Xidian University, Xi'an 710071 (China); School of Microelectronics, Xidian University, Xi'an 710071 (China)

2014-03-15

247

High-quality AlN growth on 6H-SiC substrate using three dimensional nucleation by low-pressure hydride vapor phase epitaxy  

NASA Astrophysics Data System (ADS)

There is a method of controlling nucleation and lateral growth using the three-dimensional (3D) and two-dimensional (2D) growth modes to reduce the dislocation density. We performed 3D-2D-AlN growth on 6H-SiC substrates to obtain high-quality and crack-free AlN layers by low-pressure hydride vapor phase epitaxy (LP-HVPE). First, we performed 3D-AlN growth directly on a 6H-SiC substrate. With increasing V/III ratio, the AlN island density decreased and the grain size increased. Second, 3D-2D-AlN layers were grown directly on a 6H-SiC substrate. With increasing the V/III ratio of 3D-AlN, the crystalline qualities of the 3D-2D-AlN layer were improved. Third, we performed 3D-2D-AlN growth on a trench-patterned 6H-SiC substrate. The crack density was reduced to relax the stress by voids. We also evaluated the threading dislocation density by using molten KOH/NaOH etching. As a result, the estimated edge dislocation density of the 3D-2D-AlN sample was 3.9 × 108 cm-2.

Kitagawa, Shin; Miyake, Hideto; Hiramatsu, Kazumasa

2014-01-01

248

Improving the Quality of GaN on Si(111) Substrate with a Medium-Temperature/High-Temperature Bilayer AlN Buffer  

NASA Astrophysics Data System (ADS)

A medium-temperature/high-temperature (MT/HT) bilayer AlN buffer was introduced for GaN grown on Si(111) by metal organic chemical vapor deposition. The properties of the GaN films with a MT/HT bilayer AlN buffer and those with a single-layer HT-AlN buffer were compared and the influence of the growth temperature of the MT-AlN layer was investigated. With a MT-AlN layer grown in the temperature range from 800 to 1000 °C, the crystalline qualities of the subsequent HT-AlN layer and the GaN film were improved. According to the X-ray diffraction results and the transmission electron microscopy images, the dislocation density in GaN film was reduced with a MT/HT bilayer AlN buffer as compared to those with a single-layer HT-AlN buffer. Moreover, photoluminescence and Raman spectra exhibit enhanced optical properties and less tensile stresses of the GaN film. Better surface morphology of GaN was also obtained with a MT/HT bilayer AlN buffer.

Xiang, Peng; Liu, Minggang; Yang, Yibin; Chen, Weijie; He, Zhiyuan; Kuen Leung, Ka; Surya, Charles; Han, Xiaobiao; Wu, Zhisheng; Liu, Yang; Zhang, Baijun

2013-08-01

249

Strain rate sensitivity of a high-strain-rate superplastic Al6061\\/20SiC W composite under uniaxial and equibiaxial tension  

Microsoft Academic Search

Strain rate sensitivity exponent is an important parameter to describe the ability of a material to resist necking. Less research has been done to examine strain rate sensitivity of high-strain-rate superplastic aluminum-based composites under different stress states. In this paper, experimental investigations have been carried out to examine the deformation behavior of Al6061\\/20SiCW composite under both uniaxial and equibiaxial tension.

K. C. Chan; G. Q. Tong

2001-01-01

250

Generation of multiple stress waves in silica glass in high fluence femtosecond laser ablation  

SciTech Connect

Shadowgraphs of dynamic processes outside and inside transparent target during the intense femtosecond laser ablation of silica glass are recorded. Two material ejections outside the target and two corresponding stress waves inside the target are observed at different energy fluences. In particular, a third stress wave can be observed at energy fluence as high as 40 J/cm{sup 2}. The first wave is a thermoelastic wave, while the second and the third may be generated subsequently by the mechanical expansions. In addition, the magnitudes of the three stress waves decrease sequentially based on our analysis.

Hu Haofeng; Wang Xiaolei; Zhai Hongchen; Zhang Nan; Wang Pan [Institute of Modern Optics, Key Laboratory of Opto-electronic Information Science and Technology, Nankai University, Education Ministry of China, Tianjin 300071 (China)

2010-08-09

251

Development of a Fatigue Crack Growth Coupon for Highly Plastic Stress Conditions  

NASA Technical Reports Server (NTRS)

The analytical approach used to develop a novel fatigue crack growth coupon for highly plastic stress field condition is presented in this paper. The flight hardware investigated is a large separation bolt that has a deep notch, which produces a large plastic zone at the notch root when highly loaded. Four test specimen configurations are analyzed in an attempt to match the elastic-plastic stress field and crack constraint conditions present in the separation bolt. Elastic-plastic finite element analysis is used to compare the stress fields and critical fracture parameters. Of the four test specimens analyzed, the modified double-edge notch tension - 3 (MDENT-3) most closely approximates the stress field, J values, and crack constraint conditions found in the flight hardware. The MDENT-3 is also most insensitive to load misalignment and/or load redistribution during crack growth.

Allen, Phillip A.; Aggarwal, Pravin K.; Swanson, Gregory R.

2003-01-01

252

Retinal oxidative stress induced by high intraocular pressure.  

PubMed

Glaucoma is an optic neuropathy in which retinal ganglion cells die probably through an apoptotic process. Apoptosis is known to involve free radicals in several systems including the retina. In this context, the aim of the present work was to analyze retinal oxidative damage in rats with glaucoma induced by the chronic injection of hyaluronic acid in the eye anterior chamber. The results showed a significant decrease in total retinal superoxide dismutase and catalase activities after 6 and 3 weeks of treatment with hyaluronic acid, respectively. Also, although GPX activity increased after 10 weeks of ocular hypertension, GSH levels significantly decreased at 6 weeks of treatment with hyaluronic acid. Moreover, retinal lipid peroxidation significantly increased in a time-of-hypertension-dependent manner. On the other hand, a significant decrease in both diurnal and nocturnal retinal melatonin content was detected at 3, 6, or 10 weeks of treatment with hyaluronic acid. The present results suggest that retinal oxidative stress may be involved in glaucomatous cell death. Thus, manipulation of intracellular redox status using antioxidants may be a new therapeutic tool to prevent glaucomatous neurodegeneration. PMID:15384194

Moreno, María Cecilia; Campanelli, Julieta; Sande, Pablo; Sánez, Daniel A; Keller Sarmiento, María Inés; Rosenstein, Ruth E

2004-09-15

253

Strain and morphology compliance during the intentional doping of high-Al-content AlGaN layers  

NASA Astrophysics Data System (ADS)

This study presents analysis of the residual strain and related surface morphology of high-Al-content Al0.82Ga0.18N layers doped by silicon up to the level of 3 × 1019 cm-3. We focus on understanding the basic mechanisms which underlie the formation of the distinct surface morphology of the Al0.82Ga0.18N:Si layers and their conductivity. We discuss the development of certain facet structure (nanopipes) within the doped layers, which is apparent at the high Si doping levels. The formation of nanopipes influences the conductivity of the layers. It is anticipated to give rise to facets with SiN-related coverage, outcompeting the incorporation of Si at substitutional donor sites in the lattice. We do not find evidence for kinetic stabilization of preferential crystallographic facets when a dopant flow of bis(cyclopentadienyl)magnesium (Cp2Mg), instead of silane (SiH4), is implemented in the doping process.

Nilsson, D.; Janzén, E.; Kakanakova-Georgieva, A.

2014-08-01

254

High-Temperature Oxidation Behavior of Al-Co-Cr-Ni-(Fe or Si) Multicomponent High-Entropy Alloys  

NASA Astrophysics Data System (ADS)

High-entropy alloys (HEAs) are a class of alloys that are being considered for a number of applications. In the present study, the microstructures and 1050°C oxidation behaviors of two HEAs, Al10Cr22.5Co22.5Ni22.5Fe22.5 (at.%) and Al20Cr25Co25Ni25Si5 have been investigated along with Al15Cr10Co35Ni35Si5, which is a high-temperature shape-memory alloy. Oxide formation occurred via selective oxidation in a manner that was consistent with the oxide formation model devised by Giggins and Pettit for model Ni-Cr-Al alloys. The lower Al content alloy formed an external Cr2O3 scale and an internal subscale consisting of Al2O3 and AlN precipitates. The higher Al content alloys exhibited smaller mass gains and formed external Al2O3 scales without any internal oxidation of the alloys.

Butler, T. M.; Alfano, J. P.; Martens, R. L.; Weaver, M. L.

2015-01-01

255

Morphology Control for Al2O3 Inclusion Without Ca Treatment in High-Aluminum Steel  

NASA Astrophysics Data System (ADS)

Nozzle blockage is a major problem during continuous casting of Al-containing steel. Herein, we analyzed the thermodynamic equilibrium behavior between aluminum and oxygen in steel at 1873 K (1600 °C) and demonstrated that, the dissolved [O] initially decreases with increasing the dissolved [Al] until approximately 0.1 wt pct [Al], and after that, the dissolved [O] increases with dissolved [Al]. Thus, for high-aluminum steel with 1.0 wt pct dissolved [Al], the precipitation of Al2O3 inclusion can be avoided during cooling from deoxidation temperature to the liquidus temperature, if the actual dissolved [O] can be kept from increasing when the dissolved [Al] further increases from 0.1 to 1.0 wt pct. Hence, a method of inclusion control for high-aluminum steel without traditional Ca treatment technology was proposed based on the thermodynamic analysis. Industrial tests confirmed that low-melting point Ca-aluminate inclusions were observed typically through a slag washing with SiO2-minimized high-basicity slag during tapping, accompanied by two-step Al-adding process for production of high-aluminum steel. Moreover, there was no nozzle clogging occurred for five heats of continuous casting.

He, Shengping; Chen, Gujun; Guo, Yintao; Shen, Boyi; Wang, Qian

2015-01-01

256

High-Fat Feeding Influences the Endocrine Responses of Pubertal Rats to an Acute Stress  

Microsoft Academic Search

Background\\/Aims: Studies conducted in adult rats have shown that increased fat intake affects brain energy homeostasis and stress response. The neuroendocrine circuits controlling the aforementioned functions continue to mature during puberty. The aim of the present study was to investigate whether post-weaning high-fat consumption can modify the endocrine responses of pubertal rats to an acute stress. Methods: Weaning male and

George Boukouvalas; Kyriaki Gerozissis; Eirini Markaki; Efthimia Kitraki

2010-01-01

257

Heat Stress Activates the Yeast High-Osmolarity Glycerol Mitogen-Activated Protein Kinase Pathway, and Protein Tyrosine Phosphatases Are Essential under Heat Stress  

Microsoft Academic Search

The yeast high-osmolarity glycerol (HOG) mitogen-activated protein kinase (MAPK) pathway has been characterized as being activated solely by osmotic stress. In this work, we show that the Hog1 MAPK is also activated by heat stress and that Sho1, previously identified as a membrane-bound osmosensor, is required for heat stress activation of Hog1. The two-component signaling protein, Sln1, the second osmosensor

Astrid Winkler; Christopher Arkind; Christopher P. Mattison; Anne Burkholder; Kathryn Knoche; Irene Ota

2002-01-01

258

High extensibility of stress fibers revealed by in vitro micromanipulation with fluorescence imaging  

SciTech Connect

Highlights: •We isolate contractile stress fibers from vascular smooth muscle cells. •We measure the extensibility of individual stress fibers. •We present the first direct evidence that individual stress fibers are highly extensible. •We quantitatively determine the local strain along the length of stress fibers. •The high extensibility we found is beyond that explained by a conventional model. -- Abstract: Stress fibers (SFs), subcellular bundles of actin and myosin filaments, are physically connected at their ends to cell adhesions. The intracellular force transmitted via SFs plays an essential role in cell adhesion regulation and downstream signaling. However, biophysical properties intrinsic to individual SFs remain poorly understood partly because SFs are surrounded by other cytoplasmic components that restrict the deformation of the embedded materials. To characterize their inherent properties independent of other structural components, we isolated SFs from vascular smooth muscle cells and mechanically stretched them by in vitro manipulation while visualizing strain with fluorescent quantum dots attached along their length. SFs were elongated along their entire length, with the length being approximately 4-fold of the stress-free length. This surprisingly high extensibility was beyond that explained by the tandem connection of actin filaments and myosin II bipolar filaments present in SFs, thus suggesting the involvement of other structural components in their passive biophysical properties.

Matsui, Tsubasa S. [Department of Biomolecular Sciences, Tohoku University (Japan)] [Department of Biomolecular Sciences, Tohoku University (Japan); Sato, Masaaki [Department of Biomedical Engineering, Tohoku University (Japan) [Department of Biomedical Engineering, Tohoku University (Japan); Department of Bioengineering and Robotics, Tohoku University (Japan); Deguchi, Shinji, E-mail: deguchi@nitech.ac.jp [Department of Bioengineering and Robotics, Tohoku University (Japan)] [Department of Bioengineering and Robotics, Tohoku University (Japan)

2013-05-10

259

A Highly Sensitive Assay for Monitoring the Secretory Pathway and ER Stress  

PubMed Central

Background The secretory pathway is a critical index of the capacity of cells to incorporate proteins into cellular membranes and secrete proteins into the extracellular space. Importantly it is disrupted in response to stress to the endoplasmic reticulum that can be induced by a variety of factors, including expression of mutant proteins and physiologic stress. Activation of the ER stress response is critical in the etiology of a number of diseases, such as diabetes and neurodegeneration, as well as cancer. We have developed a highly sensitive assay to monitor processing of proteins through the secretory pathway and endoplasmic reticulum (ER) stress in real-time based on the naturally secreted Gaussia luciferase (Gluc). Methodology/Principle Findings An expression cassette for Gluc was delivered to cells, and its secretion was monitored by measuring luciferase activity in the conditioned medium. Gluc secretion was decreased down to 90% when these cells were treated with drugs that interfere with the secretory pathway at different steps. Fusing Gluc to a fluorescent protein allowed quantitation and visualization of the secretory pathway in real-time. Expression of this reporter protein did not itself elicit an ER stress response in cells; however, Gluc proved very sensitive at sensing this type of stress, which is associated with a temporary decrease in processing of proteins through the secretory pathway. The Gluc secretion assay was over 20,000-fold more sensitive as compared to the secreted alkaline phosphatase (SEAP), a well established assay for monitoring of protein processing and ER stress in mammalian cells. Conclusions/Significance The Gluc assay provides a fast, quantitative and sensitive technique to monitor the secretory pathway and ER stress and its compatibility with high throughput screening will allow discovery of drugs for treatment of conditions in which the ER stress is generally induced. PMID:17593970

Breakefield, Xandra O.; Tannous, Bakhos A.

2007-01-01

260

Epitaxial growth of ?-Al2O3 on Ti2AlC(0001) by reactive high-power impulse magnetron sputtering  

NASA Astrophysics Data System (ADS)

Al2O3 was deposited by reactive high-power impulse magnetron sputtering at 600 °C onto pre-deposited Ti2AlC(0001) thin films on ?-Al2O3(0001) substrates. The Al2O3 was deposited to a thickness of 65 nm and formed an adherent layer of epitaxial ?-Al2O3(111) as shown by transmission electron microscopy. The demonstration of epitaxial growth of ?-Al2O3 on Ti2AlC(0001) open prospects for growth of crystalline alumina as protective coatings on Ti2AlC and related nanolaminated materials. The crystallographic orientation relationships are ?-Al2O3(111)//Ti2AlC(0001) (out-of-plane) and {{? {- Al}2 {O}3 {(2bar 20)//Ti}2 {AlC(11bar 20)}} (in-plane) as determined by electron diffraction. Annealing in vacuum at 900 °C resulted in partial decomposition of the Ti2AlC by depletion of Al and diffusion into and through the ?-Al2O3 layer.

Eklund, Per; Frodelius, Jenny; Hultman, Lars; Lu, Jun; Magnfält, Daniel

2014-01-01

261

Epitaxial growth of ?-Al{sub 2}O{sub 3} on Ti{sub 2}AlC(0001) by reactive high-power impulse magnetron sputtering  

SciTech Connect

Al{sub 2}O{sub 3} was deposited by reactive high-power impulse magnetron sputtering at 600 °C onto pre-deposited Ti{sub 2}AlC(0001) thin films on ?-Al{sub 2}O{sub 3}(0001) substrates. The Al{sub 2}O{sub 3} was deposited to a thickness of 65 nm and formed an adherent layer of epitaxial ?-Al{sub 2}O{sub 3}(111) as shown by transmission electron microscopy. The demonstration of epitaxial growth of ?-Al{sub 2}O{sub 3} on Ti{sub 2}AlC(0001) open prospects for growth of crystalline alumina as protective coatings on Ti{sub 2}AlC and related nanolaminated materials. The crystallographic orientation relationships are ?-Al{sub 2}O{sub 3}(111)//Ti{sub 2}AlC(0001) (out-of-plane) and ?- Al {sub 2}O{sub 3}(22{sup ¯}0)// Ti {sub 2} AlC (112{sup ¯}0) (in-plane) as determined by electron diffraction. Annealing in vacuum at 900 °C resulted in partial decomposition of the Ti{sub 2}AlC by depletion of Al and diffusion into and through the ?-Al{sub 2}O{sub 3} layer.

Eklund, Per, E-mail: perek@ifm.liu.se; Frodelius, Jenny; Hultman, Lars; Lu, Jun; Magnfält, Daniel [Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden)] [Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden)

2014-01-15

262

Pitting and Stress Corrosion Cracking Susceptibility of Nanostructured Al-Mg Alloys in Natural and Artificial Environments  

NASA Astrophysics Data System (ADS)

The stress corrosion cracking (SCC) behavior of two developmental nanocrystalline 5083 alloys with varied composition and processing conditions was studied. The results were compared to a commercial aluminum AA 5083 (H111) alloy. The pitting densities, size and depths, and residual tensile strengths were measured after alternate immersion in artificial seawater and atmospheric exposure under different loading conditions. Optical and scanning electron microscopy (SEM) with EDX was used to analyze the fracture surfaces of failed specimen after removal at selected intervals and tensile testing. One of the nanostructured Al-Mg alloys exhibited significantly superior pitting resistance when compared to conventional microstructured AA 5083. Under conditions where pitting corrosion showed up as local tunnels toward phase inclusions, transgranular cracking was observed, whereas under conditions when pitting corrosion evolved along grain boundaries, intergranular cracking inside the pit was observed. Pit initiation resistance of the nano alloys appears to be better than that of the conventional alloys. However, long-term pit propagation is a concern and warrants further study. The objective of this investigation was to obtain information regarding the role that ultra-fine microstructures play in their degradation in marine environments and to provide insight into the corrosion mechanisms and damage processes of these alloys.

Sharma, Mala M.; Ziemian, Constance W.

2008-12-01

263

Characteristics of hydrogen embrittlement, stress corrosion cracking and tempered martensite embrittlement in high-strength steels  

Microsoft Academic Search

Characteristics of tempered martensite embrittlement (TME), hydrogen embrittlement (HE), and stress corrosion cracking (SCC) in high-strength steels are reviewed. Often, it is important to determine unambiguously by which of these mechanisms failure occurred, in order to suggest the right actions to prevent failure recurrence. To this aim, samples made of high-strength AISI 4340 alloy steel were embrittled by controlled processes

N. Eliaz; A. Shachar; B. Tal; D. Eliezer

2002-01-01

264

A new piezoresistive high pressure sensor utilizing combination of three-axis normal stress components  

Microsoft Academic Search

A piezoresistive high pressure sensor utilizing a combination of three-axis normal stress components has been developed. Firstly, the principle, FEM analysis, fabrication and characteristics of a newly developed piezoresistive force sensor are briefly summarized. Secondly, the force sensor is adopted as the sensing unit of a high pressure sensor. The pressure sensor is composed of an embedded force sensor unit,

Toshipki Toriyama; Kazuya Sawa; Yasutada Tanimoto; Susumu Sugiyama

1999-01-01

265

Recognition of facial emotions among maltreated children with high rates of post-traumatic stress disorder  

Microsoft Academic Search

ObjectiveThe purpose of this study is to examine processing of facial emotions in a sample of maltreated children showing high rates of post-traumatic stress disorder (PTSD). Maltreatment during childhood has been associated independently with both atypical processing of emotion and the development of PTSD. However, research has provided little evidence indicating how high rates of PTSD might relate to maltreated

Carrie L. Masten; Amanda E. Guyer; Hilary B. Hodgdon; Erin B. McClure; Dennis S. Charney; Monique Ernst; Joan Kaufman; Daniel S. Pine; Christopher S. Monk

2008-01-01

266

High temperature degradation behavior of sputtered nanostructured Co-Al coatings on superalloy  

NASA Astrophysics Data System (ADS)

Microstructure and cyclic high temperature oxidation behavior of nanostructured Co-Al coatings on Superni-718 substrate have been investigated. Cyclic high temperature oxidation tests were conducted on uncoated and coated samples at peak temperatures of 800 °C and 900 °C for up to 100 thermal cycles between the peak and room temperatures. The results showed that bare substrate has higher oxidation resistance at 800 °C as compared to 900 °C and coated sample has slightly higher oxidation resistance at 900 °C. The external scale of both coated sample exhibited good spallation resistance during cyclic oxidation testing at both temperatures. The improvement in oxide scale spallation resistance is believed to be related to the fine-grained structure of the coating. Nanostructured Co-Al coatings on Superni-718 substrate were deposited by DC/RF magnetron sputtering. FE-SEM/EDS and XRD were used to characterize the morphology and formation of different phases in the coatings, respectively. The Co-Al coating on superalloy substrate showed better performance of cyclic high temperature oxidation resistance due to its possession of ?-CoAl phase as Al reservoir and the formation of Al2O3 and spinel phases such as CoCr2O4 and CoAl2O4 in the scale. The oxidation results confirmed an improved oxidation resistance of the Co-Al coating on superalloy as compared to bare substrate up to 100 cycles.

Rahman, Atikur; Jayaganthan, R.; Chandra, Ramesh; Ambardar, R.

2013-01-01

267

Frequency-dependent capacitance reduction in high-k AlTiOx and Al2O3 gate dielectrics from IF to RF frequency range  

Microsoft Academic Search

We have characterized the capacitance and loss tangent for high-k Al2O3 and AlTiOx gate dielectrics from IF (100 KHz) to RF (20 GHz) frequency range. Nearly the same rate of capacitance reduction as SiO2 was demonstrated individually by the proposed Al2O3 and AlTiOx gate dielectrics as frequency was increased. Moreover, both dielectrics preserve the higher k better than SiO2 from

S. B. Chen; C. H. Lai; K. T. Chan; Albert Chin; J. C. Hsieh; J. Liu

2002-01-01

268

A Comprehensive Analysis of the Combined Effects of High Light and High Temperature Stresses on Gene Expression in Sunflower  

PubMed Central

Background and Aims Although high light (HL) and high temperature (HT) stresses have been extensively investigated, a global analysis of their combined effects on the transcriptome of any plant species has not yet been described. Sunflower is an agronomically important oil crop frequently subjected to these stress factors. Because results in model plants may not always translate well to crop plants, responses of sunflower (Helianthus annuus) to HL, HT and a combination of both stresses were analysed by profiling gene expression in leaves and immature seeds. Methods Plants were grown in HL (600 µE m?2 s?1), HT (35 °C) and a combination of HL and HT (HL + HT), and gene expression in leaves and immature seeds was profiled using cDNA microarrays containing more than 8000 putative unigenes. Key Results Using two-way analysis of variance, 105, 55 and 129 cDNA clones were identified showing significant changes in steady-state transcript levels, across the two tissues, in response to HL, HT and HL + HT, respectively. A significant number of these transcripts were found to be specific to each stress. Comparing gene expression profiles between leaves and immature seeds revealed that 89, 113 and 186 cDNA clones can be considered as differentially expressed in response to HL, HT and HL + HT, respectively. More than half of the cDNA clones showing significant differences between embryo and leaf tissues in response to HL + HT were specific to this stress. Significant differences between leaves and seeds shared by all three stress treatments were observed for only eight genes. Conclusions Taken together, these results indicate that vegetative and reproductive tissues employ different transcriptome responses to these stress treatments. Careful examination of the putative functions of these genes revealed novel and specific responses. The potential roles of many of the differentially expressed genes in stress tolerance are mentioned and discussed. PMID:18477560

Hewezi, Tarek; Léger, Mathieu; Gentzbittel, Laurent

2008-01-01

269

Electron and laser beam welding of high strain rate superplastic Al6061\\/SiC composites  

Microsoft Academic Search

The welding characteristics of a fine-grained 6061 Al and three 6061\\/1, 5, and 20 pct SiC composites under high energy electron\\u000a beam welding (EBW) and laser beam welding (LBW) were examined. The three composites exhibited high strain rate superplasticity\\u000a (HSRS). The 6061 Al was more readily welded by EBW than by LBW, and the situation was reversed in the reinforced

R. Y. Huang; J. C. Huang; S. C. Chen

2001-01-01

270

Nucleation Enhancement of Al Alloys by High Intensity Ultrasound  

NASA Astrophysics Data System (ADS)

The utilization of ultrasound is expected to be applied to many casting process because of the high efficiency of ultrasound energy. The present study attempts to evaluate the effect of ultrasound energy on microstructure of castings, and high intensity ultrasound was injected into A356 and A390 alloy melt for refinement of primary phase without adding a chemical refiner. The microstructure refinement, especially primary alpha phase, could not be achieved in A356 alloy with simply ultrasound injection into alloy melt, although ultrasound was injected for 20 min. However, the influence of ultrasound on the microstructure in A390 alloy is very clear. Primary silicon of A390 alloy with ultrasound injection into melt was very small and dispersed uniformly in alloy matrix. In addition, the primary Si size was decreased with an increase the ultrasound injection time from 82 to 8 µm. As compared with A356 alloy, however, A390 alloy shows the nucleation enhancement by ultrasound vibration of melt only. The reason that there is a difference of the refinement of primary phase between A356 and A390 alloy could be explained by solute cluster theory.

Youn, Jeong Il; Jig Kim, Young

2009-07-01

271

High Compressive Stresses Near the Surface of the Sierra Nevada, California  

NASA Astrophysics Data System (ADS)

Observations and stress measurements in granitic rocks of the Sierra Nevada, California reveal strong compressive stresses parallel to the surface of the range at shallow depths. New overcoring measurements show high compressive stresses at three locations along an east-west transect through Yosemite National Park. At the westernmost site (west end of Tenaya Lake), the mean compressive stress is 1.9. At the middle site (north shore of Tenaya Lake) the mean compressive stress is 6.8 MPa. At the easternmost site (south side of Lembert Dome) the mean compressive stress is 3.0 MPa. The trend of the most compressive stress at these sites is within ~30° of the strike of the local topographic surface. Previously published hydraulic fracturing measurements by others elsewhere in the Sierra Nevada indicate surface-parallel compressive stresses of several MPa within several tens of meters of the surface, with the stress magnitudes generally diminishing to the west. Both the new and the previously published compressive stress magnitudes are consistent with the presence of sheeting joints (i.e., "exfoliation joints") in the Sierra Nevada, which require lateral compressive stresses of several MPa to form. These fractures are widespread: they are distributed in granitic rocks from the north end of the range to its southern tip and across the width of the range. Uplift along the normal faults of the eastern escarpment, recently measured by others at ~1-2 mm/yr, probably contributes to these stresses substantially. Geodetic surveys reveal that normal faulting flexes a range concave upwards in response to fault slip, and this flexure is predicted by elastic dislocation models. The topographic relief of the eastern escarpment of the Sierra Nevada is 2-4 km, and since alluvial fill generally buries the bedrock east of the faults, the offset of granitic rocks is at least that much. Compressive stresses of several MPa are predicted by elastic dislocation models of the range front faults of the eastern Sierra Nevada for as little as 100m of slip. The compression is consistent with a concave up flexure of the surface of the range. Conversely, elastic models also predict that markedly lower compressive stresses or even a tension would exist on exposed bedrock on the down-dropped hanging wall east of the range front faults. To test this prediction, we measured stresses at a fourth site, in the granitic rock of the Aeolian Buttes, which is east of the range front faults. The mean compressive stress there is 0.26 MPa, more than an order of magnitude less than the average at the three Yosemite sites. The measured stress magnitudes near the topographic surface of the Sierra, the distribution of sheeting joints west of the range front faults, and elastic model predictions are broadly consistent and indicate that the high compressive stresses at the surface of the Sierra Nevada are largely associated with uplift of the range, although other contributions cannot be excluded.

Martel, S. J.; Logan, J. M.; Stock, G. M.

2012-12-01

272

Bacillus pumilus Reveals a Remarkably High Resistance to Hydrogen Peroxide Provoked Oxidative Stress  

PubMed Central

Bacillus pumilus is characterized by a higher oxidative stress resistance than other comparable industrially relevant Bacilli such as B. subtilis or B. licheniformis. In this study the response of B. pumilus to oxidative stress was investigated during a treatment with high concentrations of hydrogen peroxide at the proteome, transcriptome and metabolome level. Genes/proteins belonging to regulons, which are known to have important functions in the oxidative stress response of other organisms, were found to be upregulated, such as the Fur, Spx, SOS or CtsR regulon. Strikingly, parts of the fundamental PerR regulon responding to peroxide stress in B. subtilis are not encoded in the B. pumilus genome. Thus, B. pumilus misses the catalase KatA, the DNA-protection protein MrgA or the alkyl hydroperoxide reductase AhpCF. Data of this study suggests that the catalase KatX2 takes over the function of the missing KatA in the oxidative stress response of B. pumilus. The genome-wide expression analysis revealed an induction of bacillithiol (Cys-GlcN-malate, BSH) relevant genes. An analysis of the intracellular metabolites detected high intracellular levels of this protective metabolite, which indicates the importance of bacillithiol in the peroxide stress resistance of B. pumilus. PMID:24465625

Jürgen, Britta; Methling, Karen; Schlüter, Rabea; Albrecht, Dirk; van Hijum, Sacha A. F. T.; Bongaerts, Johannes; Maurer, Karl-Heinz; Lalk, Michael; Schweder, Thomas; Hecker, Michael; Voigt, Birgit

2014-01-01

273

Highly cooperative stress relaxation in two-dimensional soft colloidal crystals  

PubMed Central

Stress relaxation in crystalline solids is mediated by the formation and diffusion of defects. Although it is well established how externally generated stresses relax, through the proliferation and motion of dislocations in the lattice, it remains relatively unknown how crystals cope with internal stresses. We investigate, both experimentally and in simulations, how highly localized stresses relax in 2D soft colloidal crystals. When a single particle is actively excited, by means of optical tweezing, a rich variety of highly collective stress relaxation mechanisms results. These relaxation processes manifest in the form of open strings of cooperatively moving particles through the motion of dissociated vacancy-interstitial pairs, and closed loops of mobile particles, which either result from cooperative rotations in transiently generated circular grain boundaries or through the closure of an open string by annihilation of a vacancy-interstitial pair. Surprisingly, we find that the same collective events occur in crystals that are excited by thermal fluctuations alone; a large thermal agitation inside the crystal lattice can trigger the irreversible displacements of hundreds of particles. Our results illustrate how local stresses can induce large-scale cooperative dynamics in 2D soft colloidal crystals and shed light on the stabilization mechanisms in ultrasoft crystals. PMID:25319262

van der Meer, Berend; Qi, Weikai; Fokkink, Remco G.; van der Gucht, Jasper; Dijkstra, Marjolein; Sprakel, Joris

2014-01-01

274

Elite sport is not an additional source of distress for adolescents with high stress levels.  

PubMed

This study examined whether participation in elite sport interacts with stress in decreasing or increasing symptoms of depression and anxiety among adolescents, and further, whether the interplay between participation in high-performance sport and stress is related to the perceived quality of sleep. 434 adolescents (278 girls, 156 boys; age: M = 17.2 yr.) from 15 "Swiss Olympic Sport Classes" and 9 conventional classes answered a questionnaire and completed a 7-day sleep log. Analyses of covariance showed that heightened stress was related to more depressive symptoms and higher scores for trait-anxiety. Moreover, those classified as having poor sleep by a median split cutoff reported higher levels of depressive symptoms. No significant (multivariate) main effects were found for high-performance sport athletes. Similarly, no significant two- or three-way interaction effects were found. These results caution against exaggerated expectations concerning sport participation as a stress buffer. Nevertheless, participation in high-performance sport was not found to be an additional source of distress for adolescents who reported high stress levels despite prior research that has pointed toward such a relationship. PMID:21667766

Gerber, Markus; Holsboer-Trachsler, Edith; Pühse, Uwe; Brand, Serge

2011-04-01

275

Hepatic expression patterns in psychosocially high-stressed pigs suggest mechanisms following allostatic principles.  

PubMed

Psychosocial challenges are known to introduce cellular and humoral adaptations in various tissues and organs, including parts of the sympatho-adrenal-medullary system and hypothalamic-pituitary-adrenal axis as well as other peripheral tissue being responsive to cortisol and catecholamines. The liver is of particular interest given its vital roles in maintaining homeostasis and health as well as regulating nutrient utilization and overall metabolism. We aimed to evaluate whether and how response to psychosocial stress is reflected by physiological molecular pathways in liver tissue. A pig mixing experiment was conducted to induce psychosocial stress culminating in skin lesions which reflect the involvement in aggressive behavior and fighting. At 27 weeks of age, animals prone to psychosocially low- and high-stress were assigned to mixing groups. Skin lesions were counted before mixing and after slaughter on the carcass. Individual liver samples (n=12) were taken. The isolated RNA was hybridized on Affymetrix GeneChip porcine Genome Arrays. Relative changes of mRNA abundances were estimated via variance analyses. Molecular routes related to tRNA charging, urea cycle, acute phase response, galactose utilization, and steroid receptor signaling were found to be increased in psychosocially high-stressed animals, whereas catecholamine degradation and cholesterol biosynthesis were found to be decreased. In particular, psychosocially high-stressed animals show decreased expression of catechol-O-methyltransferase (COMT) which has been linked to molecular mechanisms regulating aggressiveness and stress response. The expression patterns of high-stressed animals revealed metabolic alterations of key genes related to energy-mobilizing processes at the expense of energy consuming processes. Thus, the coping following psychosocial challenges involves transcriptional alterations in liver tissue which may be summarized with reference to the concept of allostasis, a strategy which is critical for survival. PMID:24534173

Oster, M; Muráni, E; Ponsuksili, S; D'Eath, R B; Turner, S P; Evans, G; Thölking, L; Kurt, E; Klont, R; Foury, A; Mormède, P; Wimmers, K

2014-04-10

276

High fat diet aggravates arsenic induced oxidative stress in rat heart and liver.  

PubMed

Arsenic is a well known global groundwater contaminant. Exposure of human body to arsenic causes various hazardous effects via oxidative stress. Nutrition is an important susceptible factor which can affect arsenic toxicity by several plausible mechanisms. Development of modern civilization led to alteration in the lifestyle as well as food habits of the people both in urban and rural areas which led to increased use of junk food containing high level of fat. The present study was aimed at investigating the effect of high fat diet on heart and liver tissues of rats when they were co-treated with arsenic. This study was established by elucidating heart weight to body weight ratio as well as analysis of the various functional markers, oxidative stress biomarkers and also the activity of the antioxidant enzymes. Histological analysis confirmed the biochemical investigations. From this study it can be concluded that high fat diet increased arsenic induced oxidative stress. PMID:24508525

Dutta, Mousumi; Ghosh, Debosree; Ghosh, Arnab Kumar; Bose, Gargi; Chattopadhyay, Aindrila; Rudra, Smita; Dey, Monalisa; Bandyopadhyay, Arkita; Pattari, Sanjib K; Mallick, Sanjaya; Bandyopadhyay, Debasish

2014-04-01

277

Effects of addition of magnesium on interface structure and high-strain-rate superplasticity in Si{sub 3}N{sub 4}-reinforced Al-alloy composites  

SciTech Connect

The mechanical properties and interface structure of fine-grained Al-Cu alloy and Al-Cu-Mg alloy composites, reinforced with Si{sub 3}N{sub 4} whiskers (Si{sub 3}N{sub 4}w) and particles (Si{sub 3}N{sub 4}p), are investigated to reveal the role of magnesium addition in high-strain-rate superplasticity. The Al-Cu alloy composites, which exhibit lower elongations (< 100%), have clear interfaces between the Al-matrix and Si{sub 3}N{sub 4} crystals without any interfacial reaction. On the other hand, the interfaces in the Al-Cu-Mg alloy composites, which exhibit high elongations (> 280%), show strong reaction between the Al-matrix and Si{sub 3}N{sub 4} crystals. The result suggests that the addition of magnesium causes the reaction between the Al-matrix and Si{sub 3}N{sub 4} crystals, and consequently that partially melting of the reaction phases at the tensile-testing temperature results in the relaxation of stress concentration and suppresses the development of microcracks and cavities at the interfaces during superplastic deformation.

Jeong, H.G.; Hiraga, K. [Tohoku Univ., Sendai (Japan). Inst. for Materials Research] [Tohoku Univ., Sendai (Japan). Inst. for Materials Research; Mabuchi, M. [National Industrial Research Inst. of Nagoya (Japan)] [National Industrial Research Inst. of Nagoya (Japan); Higashi, K. [Osaka Prefecture Univ., Sakai, Osaka (Japan). Dept. of Metallurgy and Materials Science] [Osaka Prefecture Univ., Sakai, Osaka (Japan). Dept. of Metallurgy and Materials Science

1998-11-02

278

Effects of suryanamaskar on relaxation among college students with high stress in Pune, India  

PubMed Central

Context: Suryanamaskar is a yogic practice widely practiced across India. Along with the available studies on physiology, there is a need to study its psychological effects. Aims: This research aims at studying the effects of suryanamaskar on relaxation dispositions (R-dispositions) among college students with high stress in Pune, India. Settings and Design: The present study was conducted in a college setting and used a randomized control group design. Materials and Methods: A group of 419 college students (age 17-22 years) were assessed on stress symptoms using the ABC relaxation theory. A total of 124 out of 419 students who were identified as high on stress were randomly assigned to an experimental and control group. And 40 participants each in both the group completed the program and were assessed on R-dispositions and stress dispositions before and after the suryanamaskar program. Statistical Analysis Used: Analysis of covariance (ANCOVA) was used to study the differences in R-dispositions and stress dispositions between the experimental and control groups. Results: The experimental group was found to be higher on the R-dispositions of physical relaxation, mental quiet, at ease/peace, rested and refreshed, strength and awareness and joy and lower on sleepiness, and stress dispositions?somatic stress, worry, and negative emotion compared with the control group. Conclusions: It was concluded that suryanamaskar is effective in leading to R-Dispositions like physical relaxation, mental quiet, at ease/peace, rested and refreshed, strength and awareness and joy and reduces sleepiness, somatic stress, worry and negative emotion at a dispositional level.

Godse, Anand Sharad; Shejwal, Bhaskar R; Godse, Amruta Anand

2015-01-01

279

Effects of Electromagnetic Stirring on the Microstructure and High-Temperature Mechanical Properties of a Hyper-eutectic Al-Si-Cu-Ni Alloy  

NASA Astrophysics Data System (ADS)

A liquid treatment method by electromagnetic stirring was applied to a hyper-eutectic Al-15wt pctSi-4wt pctCu-3wt pctNi alloy for the piston manufacturing with diecasting process in order to improve high-temperature mechanical properties of the piston heads. The mechanical properties, such as hardness, high-temperature tensile stress, thermal expansion, and high-temperature relative wear resistance, were estimated using the specimens taken from the liquid-treated diecast products, and the results were compared with those of a conventional metal-mold-cast piston.

Jang, Youngsoo; Choi, Byounghee; Kang, Byungkeun; Hong, Chun Pyo

2014-12-01

280

Effects of Electromagnetic Stirring on the Microstructure and High-Temperature Mechanical Properties of a Hyper-eutectic Al-Si-Cu-Ni Alloy  

NASA Astrophysics Data System (ADS)

A liquid treatment method by electromagnetic stirring was applied to a hyper-eutectic Al-15wt pctSi-4wt pctCu-3wt pctNi alloy for the piston manufacturing with diecasting process in order to improve high-temperature mechanical properties of the piston heads. The mechanical properties, such as hardness, high-temperature tensile stress, thermal expansion, and high-temperature relative wear resistance, were estimated using the specimens taken from the liquid-treated diecast products, and the results were compared with those of a conventional metal-mold-cast piston.

Jang, Youngsoo; Choi, Byounghee; Kang, Byungkeun; Hong, Chun Pyo

2015-02-01

281

High environmental stress yields greater tocotrienol content while changing vitamin e profiles of wild emmer wheat seeds.  

PubMed

Vitamin E is an essential human nutrient that was first isolated from wheat. Emmer wheat, the cereal of Old World agriculture and a precursor to durum wheat, grows wild in the Fertile Crescent. Evolution Canyon, Israel, provides a microsite that models effects of contrasting environments. The north-facing and south-facing slopes exhibit low and high stress environments, respectively. Wild emmer wheat seeds were collected from both slopes and seed tocochromanol contents measured to test the hypothesis that high stress alters emmer wheat seed tocol-omics. Seeds from high stress areas contained more total vitamin E (108±15?nmol/g) than seeds from low stress environments (80±17?nmol/g, P=.0004). Vitamin E profiles within samples from these different environments revealed significant differences in isoform concentrations. Within each region, ?- plus ?-tocotrienols represented the highest concentration of wheat tocotrienols (high stress, P<.0001; low stress, P<.0001), while ?-tocopherol represented the highest concentration of the tocopherols (high stress, P=.0002; low stress, P<.0001). Percentages of both ?-tocotrienol and ?-tocopherol increased in high stress conditions. Changes under higher stress apparently are due to increased pathway flux toward more tocotrienol production. The production of more ?-isoforms suggests increased flow through a divergent path controlled by the VTE1 gene. Hence, stress conditions alter plant responses such that vitamin E profiles are changed, likely an attempt to provide additional antioxidant activity to promote seed viability and longevity. PMID:25105230

Watts, Emily J; Shen, Yu; Lansky, Ephraim P; Nevo, Eviatar; Bobe, Gerd; Traber, Maret G

2015-02-01

282

Influence of AlGaN barrier thickness on electrical and device properties in Al0.14Ga0.86N/GaN high electron mobility transistor structures  

NASA Astrophysics Data System (ADS)

We investigate the influence of the AlGaN barrier thickness in Al0.14Ga0.86N/GaN heterostructures on both the electrical properties of the heterostructure itself as well as on high electron mobility transistors fabricated on these structures. With increasing barrier thickness, we observe decreasing sheet resistances, transconductances, and threshold voltages. The observed changes are well-described by modelling. We demonstrate that an increase in the barrier thickness in AlGaN/GaN heterostructures results in an increase in available high-frequency input power swing before turn-on of the Schottky gate. The device long-term stability under direct current stress is not affected by the increase in barrier thickness as shown by on-wafer reliability tests at 150 °C base plate temperature. These results pave the way towards AlGaN/GaN transistors offering high robustness under extreme mismatch conditions as well as excellent high-frequency power performance.

Waltereit, P.; Bronner, W.; Musser, M.; Raay, F. van; Dammann, M.; Cäsar, M.; Müller, S.; Kirste, L.; Köhler, K.; Quay, R.; Mikulla, M.; Ambacher, O.

2012-09-01

283

Micromachined stress-free TSV hole for AlGaN/GaN-on-Si (1?1?1) platform-based devices  

NASA Astrophysics Data System (ADS)

This paper presents a micromachined stress-free through silicon via (TSV) backend process for AlGaN/GaN-on-Si (1?1?1) platform-based devices, which was processed by assisted back grinding, chemical mechanical polishing, deep reactive ion etching (DRIE) and copper (Cu) electroplating for the TSV. The metal-filled TSV structure was formed to enhance thermal conduction from the frontend terminal to the backend terminal, especially the source region of the AlGaN/GaN-on-Si (1?1?1) platform-based RF power devices. At the end of a stress-free TSV dry etching process, we have changed RF power 600 W to 300 W to minimize thermal stress of the fabricated TSV electrode pad structure of the AlGaN/GaN-on-Si platform-based devices. Additionally, we have sputtered a multi-metal layer and electroplated Cu metal to interconnect a topside electrode to TSV. To protect the thinned TSV electrode pad structure from water pressure in a sawing process, we have covered photoresist (AZ4330RS) of 3.3 µm thickness on the top area of the structures. We confirmed that the proposed TSV formation method assisted by low-power operation DRIE and protection of the thinned TSV surface by using the thick photoresist is very effective to create minimally stressed TSV structures in AlGaN/GaN-on-Si platform-based devices. The improvement was proved by the yield of dice without bursting the pad structures on a 4 inch AlGaN/GaN-on-Si wafer.

Ko, Sang Choon; Min, Byoung-Gue; Park, Young-Rak; Kim, Jung-Jin; Sung, Ho Kun; Mun, Jae Kyoung; Nam, Eun Soo

2013-03-01

284

High-Temperature Deformation and Ductility of a Modified 5083 Al Alloy  

NASA Astrophysics Data System (ADS)

The high-temperature deformation of a 5.5% Mg and 0.6% Ca modified 5083 aluminum alloy was investigated in the temperature range from 573 to 723 K at strain rates in the range of 10-5-10-1 s-1. Ca was added to form an insoluble second phase in the range of temperatures tested to improve the high-temperature characteristics of this alloy. It was shown that the deformation behavior of the alloy could be divided into two regions with stress exponent, n of 3.5 and 13 at low and high strain rates, respectively. The apparent activation energy determined in both regions suggested that the deformation process is diffusion controlled in both regions. The slightly high value of n at the low-strain rate region (viscous glide) was attributed to the presence of threshold stress. The values of threshold stress showed an exponential increase with decreasing temperature and a dependence with an energy term Qo = 16.5 kJ mol-1. Analysis of creep data in terms of threshold stress and using diffusivity of Mg in normalizing the strain rates, revealed two types of deformation behavior. At high values of normalized strain rate (kT} {DGb}}} > 10^{{ - 9}} ), a high value of stress exponent of n = 10 is observed, and the exponential law creep takes place. At low normalized strain rates ?10-9, the n value is 3 and the true activation energy, Q, is equal to 123 kJ mol-1 suggesting viscous glide of dislocations as rate-controlling mechanism. Enhanced ductility has been observed in the region of viscous-glide controlled deformation as a result of high strain-rate sensitivity.

El-Danaf, Ehab A.; Almajid, Abdulhakim A.; Soliman, Mahmoud S.

2008-08-01

285

Puerarin prevents high glucose-induced apoptosis of Schwann cells by inhibiting oxidative stress?  

PubMed Central

Oxidative stress may be the unifying factor for the injury caused by hyperglycemia in diabetic peripheral neuropathy. Puerarin is the major isoflavonoid derived from Radix puerariae and has been shown to be effective in increasing superoxide dismutase activity. This study sought to investigate the neuroprotective effect of puerarin on high glucose-induced oxidative stress and Schwann cell apoptosis in vitro. Intracellular reactive oxygen radicals and mitochondrial transmembrane potential were detected by flow cytometry analysis. Apoptosis was confirmed by TUNEL and oxidative stress was monitored using an enzyme-linked immunosorbent assay for the DNA marker 8-hydroxy-2-deoxyguanosine. The expression levels of bax and bcl-2 were analyzed by quantitative real-time reverse transcriptase-PCR, while protein expression of cleaved caspase-3 and -9 were analyzed by means of western blotting. Results suggested that puerarin treatment inhibited high glucose-induced oxidative stress, mitochondrial depolarization and apoptosis in a dose-dependent manner. Furthermore, puerarin treatment downregulated Bax expression, upregulated bcl-2 expression and attenuated the activation of caspase-3 and -9. Overall, our results indicated that puerarin antagonized high glucose-induced oxidative stress and apoptosis in Schwann cells. PMID:25368634

Wu, Yingying; Xue, Bing; Li, Xiaojin; Liu, Hongchen

2012-01-01

286

Static contact resistance of usual metal under high compressive stress and for high current densities  

Microsoft Academic Search

Static contact resistance for all combinations of usual metals (cold-drawn copper, brass, aluminum, duraluminum, mild steel, and stainless steel) are measured for stresses of up to 16 kg\\/mm2 and current densities of up to 7.5 kA\\/mm2. A decreasing resistance has been found for increasing compressive stress and increasing current intensity. Very low resistance values have been observed (0.02 mOmega mm2)

C. Boissady; C. Postel; F. Rioux-Damidau

1977-01-01

287

Dynamic tooth loads and stressing for high contact ratio spur gears  

NASA Technical Reports Server (NTRS)

An analysis and computer program were developed for calculating the dynamic gear tooth loading and root stressing for high contact ratio gearing (HCRG) as well as LCRG. The analysis includes the effects of the variable tooth stiffness during the mesh, tooth profile modification, and gear errors. The calculation of the tooth root stressing caused by the dynamic gear tooth loads is based on a modified Heywood gear tooth stress analysis, which appears more universally applicable to both LCRG and HCRG. The computer program is presently being expanded to calculate the tooth contact stressing and PV values. Sample application of the gear program to equivalent LCRG (1.566 contact ratio) and HCRG (2.40 contact ratio) revealed the following: (1) the operating conditions and dynamic characteristics of the gear system an affect the gear tooth loading and root stressing, and therefore, life significantly; (2) the length of the profile modification affect the tooth loading and root stressing significantly, the amount depending on the applied load, speed, and contact ratio; and (3) the effect of variable tooth stiffness is small, shifting and increasing the response peaks slightly from those for constant tooth stiffness.

Cornell, R. W.; Westervelt, W. W.

1983-01-01

288

High Mobility Group Box 1 (HMGB1) Activates an Autophagic Response to Oxidative Stress  

PubMed Central

Abstract Aims Autophagy, the process by which cells break down spent biochemical and damaged components, plays an important role in cell survival following stress. High mobility group box 1 (HMGB1) regulates autophagy in response to oxidative stress. Results Exogenous hydrogen peroxide (H2O2) treatment or knockdown of the major superoxide scavenger enzyme, superoxide dismutase 1 (SOD1), by small interfering RNA (siRNA) increases autophagy in mouse and human cell lines. Addition of either SOD1 siRNA or H2O2 promotes cytosolic HMGB1 expression and extracellular release. Importantly, inhibition of HMGB1 release or loss of HMGB1 decreases the number of autophagolysosomes and autophagic flux under oxidative stress in vivo and in vitro. Innovation: HMGB1 release may be a common mediator of response to oxidative stress. Conclusion HMGB1 is important for oxidative stress-mediated autophagy and serves as a new target for the treatment of stress-associated disorders. Antioxid. Redox Signal. 15, 2185–2195. PMID:21395369

Kang, Rui; Livesey, Kristen M.; Zeh, Herbert J.

2011-01-01

289

Method for improving performance of highly stressed electrical insulating structures  

DOEpatents

Removing the electrical field from the internal volume of high-voltage structures; e.g., bushings, connectors, capacitors, and cables. The electrical field is removed from inherently weak regions of the interconnect, such as between the center conductor and the solid dielectric, and places it in the primary insulation. This is accomplished by providing a conductive surface on the inside surface of the principal solid dielectric insulator surrounding the center conductor and connects the center conductor to this conductive surface. The advantage of removing the electric fields from the weaker dielectric region to a stronger area improves reliability, increases component life and operating levels, reduces noise and losses, and allows for a smaller compact design. This electric field control approach is currently possible on many existing products at a modest cost. Several techniques are available to provide the level of electric field control needed. Choosing the optimum technique depends on material, size, and surface accessibility. The simplest deposition method uses a standard electroless plating technique, but other metalization techniques include vapor and energetic deposition, plasma spraying, conductive painting, and other controlled coating methods.

Wilson, Michael J. (Modesto, CA); Goerz, David A. (Brentwood, CA)

2002-01-01

290

Heat Pipe Embedded AlSiC Plates for High Conductivity - Low CTE Heat Spreaders  

SciTech Connect

Heat pipe embedded aluminum silicon carbide (AlSiC) plates are innovative heat spreaders that provide high thermal conductivity and low coefficient of thermal expansion (CTE). Since heat pipes are two phase devices, they demonstrate effective thermal conductivities ranging between 50,000 and 200,000 W/m-K, depending on the heat pipe length. Installing heat pipes into an AlSiC plate dramatically increases the plate’s effective thermal conductivity. AlSiC plates alone have a thermal conductivity of roughly 200 W/m-K and a CTE ranging from 7-12 ppm/ deg C, similar to that of silicon. An equivalent sized heat pipe embedded AlSiC plate has effective thermal conductivity ranging from 400 to 500 W/m-K and retains the CTE of AlSiC.

Johnson, Matthew (DOE/NNSA Kansas City Plant (United States)); Weyant, J.; Garner, S. (Advanced Cooling Technologies, Inc. (Lancaster, PA (United States)); Occhionero, M. (CPS Technologies Corporation, Norton, MA (United States))

2010-01-07

291

The in uence of residual thermal stresses on the mechanical properties of multilayer -Al2O3/TiCxN1-x coatings on WC/Co cutting tools  

E-print Network

The in uence of residual thermal stresses on the mechanical properties of multilayer -Al2O3/TiCxN1 online 6 November 2012 Keywords: Thermal stresses Al2O3 TiCxN1 - x Hardness Microstructure Channel cracks Orientation maps of the microstructures of four -Al2O3 and TiCxN1-x multilayer coatings on WC­Co cemented

Rohrer, Gregory S.

292

The effect of Mg addition on microstructure and tensile and stress rupture properties of a P/M Al-Fe-Ce alloy  

SciTech Connect

Dispersion strengthened Aluminium alloys based on Al-TM (TM = transition metal) type systems are being developed for elevated temperature structural applications in aerospace at temperatures up to 623K as possible substitutes for the more expensive and refractory Ti alloys currently used. Alloy systems containing transition metals such as Fe, Ni, V, Cr, Zr, Mo and Ti with possible additions of Si and Ce (or misch metal) have been investigated. Al-Fe-Ce alloys belong to this class of dispersion strengthened aluminium alloys which are strengthened primarily by ternary Al-Fe-Ce precipitates. The matrix in this case is almost pure aluminium. Further strengthening of the alloy may therefore be possible by addition of elements such as Mg which impart solid solution strengthening. This should also result in enhancement in elevated temperature strength and stress rupture properties. It is reported that the addition of Mg to Al-Fe-Mm (Mm = misch metal) alloy does not result in formation of new phases in melt spun ribbons even after annealing at 773K thereby confirming that Mg is retained in solid solution. The aim of the present work is to investigate the effect of Mg addition on the microstructure and tensile and stress rupture properties of an Al-Fe-Ce alloy.

Prakash, U.; Raghu, T.; Kamat, S.V.; Gokhale, A.A. [Defence Metallurgical Research Lab., Hyderabad (India)] [Defence Metallurgical Research Lab., Hyderabad (India)

1998-09-04

293

Assessment of microalloying effects on the high temperature fatigue behavior of NiAl  

NASA Technical Reports Server (NTRS)

Binary NiAl suffers from a lack of strength and poor creep properties at and above 1000 K. Poor creep resistance in turn affects low cycle fatigue (LCF) lives at low strain ranges due to the additional interactions of creep damage. One approach for improving these properties involved microalloying with either Zr or N. As an integral part of a much larger alloying program the low cycle fatigue behavior of Zr and N doped nickel aluminides produced by extrusion of prealloyed powders has been investigated. Strain controlled LCF tests were performed in air at 1000 K. The influence of these microalloying additions on the fatigue life and cyclic stress response of polycrystalline NiAl are discussed.

Noebe, R. D.; Lerch, B. A.; Rao, K. B. S.

1995-01-01

294

Top-gate zinc tin oxide thin-film transistors with high bias and environmental stress stability  

SciTech Connect

Top gated metal-oxide thin-film transistors (TFTs) provide two benefits compared to their conventional bottom-gate counterparts: (i) The gate dielectric may concomitantly serve as encapsulation layer for the TFT channel. (ii) Damage of the dielectric due to high-energetic particles during channel deposition can be avoided. In our work, the top-gate dielectric is prepared by ozone based atomic layer deposition at low temperatures. For ultra-low gas permeation rates, we introduce nano-laminates of Al{sub 2}O{sub 3}/ZrO{sub 2} as dielectrics. The resulting TFTs show a superior environmental stability even at elevated temperatures. Their outstanding stability vs. bias stress is benchmarked against bottom-gate devices with encapsulation.

Fakhri, M.; Theisen, M.; Behrendt, A.; Görrn, P.; Riedl, T. [Institute of Electronic Devices, University of Wuppertal, Wuppertal 42119 (Germany)

2014-06-23

295

Top-gate zinc tin oxide thin-film transistors with high bias and environmental stress stability  

NASA Astrophysics Data System (ADS)

Top gated metal-oxide thin-film transistors (TFTs) provide two benefits compared to their conventional bottom-gate counterparts: (i) The gate dielectric may concomitantly serve as encapsulation layer for the TFT channel. (ii) Damage of the dielectric due to high-energetic particles during channel deposition can be avoided. In our work, the top-gate dielectric is prepared by ozone based atomic layer deposition at low temperatures. For ultra-low gas permeation rates, we introduce nano-laminates of Al2O3/ZrO2 as dielectrics. The resulting TFTs show a superior environmental stability even at elevated temperatures. Their outstanding stability vs. bias stress is benchmarked against bottom-gate devices with encapsulation.

Fakhri, M.; Theisen, M.; Behrendt, A.; Görrn, P.; Riedl, T.

2014-06-01

296

Polyaluminum chloride with high Al30 content as removal agent for arsenic-contaminated well water.  

PubMed

Polyaluminum chloride (PACl) is a well-established coagulant in water treatment with high removal efficiency for arsenic. A high content of Al(30) nanoclusters in PACl improves the removal efficiency over broader dosage and pH range. In this study we tested PACl with 75% Al(30) nanoclusters (PACl(Al30)) for the treatment of arsenic-contaminated well water by laboratory batch experiments and field application in the geothermal area of Chalkidiki, Greece, and in the Pannonian Basin, Romania. The treatment efficiency was studied as a function of dosage and the nanoclusters' protonation degree. Acid-base titration revealed increasing deprotonation of PACl(Al30) from pH 4.7 to the point of zero charge at pH 6.7. The most efficient removal of As(III) and As(V) coincided with optimal aggregation of the Al nanoclusters at pH 7-8, a common pH range for groundwater. The application of PACl(Al30) with an Al(tot) concentration of 1-5mM in laboratory batch experiments successfully lowered dissolved As(V) concentrations from 20 to 230 ?g/L to less than 5 ?g/L. Field tests confirmed laboratory results, and showed that the WHO threshold value of 10 ?g/L was only slightly exceeded (10.8 ?g/L) at initial concentrations as high as 2300 ?g/L As(V). However, As(III) removal was less efficient (<40%), therefore oxidation will be crucial before coagulation with PACl(Al30). The presence of silica in the well water improved As(III) removal by typically 10%. This study revealed that the Al(30) nanoclusters are most efficient for the removal of As(V) from water resources at near-neutral pH. PMID:22078251

Mertens, Jasmin; Casentini, Barbara; Masion, Armand; Pöthig, Rosemarie; Wehrli, Bernhard; Furrer, Gerhard

2012-01-01

297

Metallographic assessment of Al-12Si high-pressure die casting escalator steps.  

PubMed

A microstructural characterization study was performed on high-pressure die cast specimens extracted from escalator steps manufactured from an Al-12 wt.% Si alloy designed for structural applications. Black and white, color light optical imaging and scanning electron microscopy techniques were used to conduct the microstructural analysis. Most regions in the samples studied contained globular-rosette primary ?-Al grains surrounded by an Al-Si eutectic aggregate, while primary dendritic ?-Al grains were present in the surface layer. This dendritic microstructure was observed in the regions where the melt did not impinge directly on the die surface during cavity filling. Consequently, microstructures in the surface layer were nonuniform. Utilizing physical metallurgy principles, these results were analyzed in terms of the applied pressure and filling velocity during high-pressure die casting. The effects of these parameters on solidification at different locations of the casting are discussed. PMID:24999947

Vander Voort, George Frederic; Suárez-Peña, Beatriz; Asensio-Lozano, Juan

2014-10-01

298

Effect of nitrogen high temperature plasma based ion implantation on the creep behavior of Ti-6Al-4V alloy  

NASA Astrophysics Data System (ADS)

Nitrogen high temperature plasma based ion implantation (HTPBII) performed on Ti-6Al-4V significantly improved the creep behavior of the alloy. Treatments were performed for 1 h at a working pressure of 4 mbar and negative high voltage pulses of 7.5 kV, 30 ?s and 500 Hz were applied on the specimens heated at 800 °C and 900 °C, respectively. Microstructural characterization of the treated samples revealed the formation of nitrided layers, with simultaneous formation of TiN and Ti2N. The most intense peaks of these compounds were obtained at higher treatment temperature, probably due to the diffusion of nitrogen into titanium. The presence of nitrides caused surface hardening up to three times higher in comparison with untreated alloy. Constant load creep tests were conducted on a standard creep machine in air atmosphere, at stress level of 319 MPa at 600 °C. Significant reductions of the steady-state creep rates (?) were measured for martensitic Ti-6Al-4V treated by nitrogen HTPBII, reaching minimum creep rates of 0.0318 h-1 in comparison with 0.1938 h-1 for untreated sample. The improvement of the creep resistance seems to be associated with the formation of a thick nitrided layer, which acts as a barrier to oxygen diffusion into the material. In addition, the increase of the grain size generated by the heating of the substrate during the treatment can affect some creep mechanisms, leading to a significant reduction of ?.

Oliveira, A. C.; Oliveira, R. M.; Reis, D. A. P.; Carreri, F. C.

2014-08-01

299

Thermal treatment and utilization of Al-rich waste in high calcium fly ash geopolymeric materials  

NASA Astrophysics Data System (ADS)

The Al-rich waste with aluminium and hydrocarbon as the major contaminant is generated at the wastewater treatment unit of a polymer processing plant. In this research, the heat treatment of this Al-rich waste and its use to adjust the silica/alumina ratio of the high calcium fly ash geopolymer were studied. To recycle the raw Al-rich waste, the waste was dried at 110°C and calcined at 400 to 1000°C. Mineralogical analyses were conducted using X-ray diffraction (XRD) to study the phase change. The increase in calcination temperature to 600, 800, and 1000°C resulted in the phase transformation. The more active alumina phase of active ?-Al2O3 was obtained with the increase in calcination temperature. The calcined Al-rich waste was then used as an additive to the fly ash geopolymer by mixing with high calcium fly ash, water glass, 10 M sodium hydroxide (NaOH), and sand. Test results indicated that the calcined Al-rich waste could be used as an aluminium source to adjust the silica/alumina ratio and the strength of geopolymeric materials. The fly ash geopolymer mortar with 2.5wt% of the Al-rich waste calcined at 1000°C possessed the 7-d compressive strength of 34.2 MPa.

Chindaprasirt, Prinya; Rattanasak, Ubolluk; Vongvoradit, Pimdao; Jenjirapanya, Supichart

2012-09-01

300

Are adolescents with high mental toughness levels more resilient against stress?  

PubMed

Mental toughness has been explored predominantly within sport contexts. Nevertheless, it is difficult to conceive mental toughness as only applicable to athletes. This study examines whether mentally tough participants exhibit resilience against stress. This is a cross-sectional study based on two different samples: Sample 1 consisted of 284 high school students (99 males, 185 females, M?=?18.3?years). Sample 2 consisted of 140 first through fifth semester undergraduate students (53 males, 87 females, M?=?20.0?years). Participants provided information about their level of perceived stress (10-item Perceived Stress Scale), mental toughness (48-item Mental Toughness Questionnaire) and depressive symptoms (Beck Depression Inventory). Consistent across the two samples, mental toughness mitigated the relationship between high stress and depressive symptoms. The interaction between stress and mental toughness explained 2% of variance in the adolescent sample and 10% of variance among young adults. The promotion of protective factors that foster resilient adaptation is a relevant issue. Mental toughness may appeal to individuals that are typically difficult to be reached with health interventions. Because mental toughness is part of young people's daily speech, it may serve as a less academic resource than other health psychology concepts. PMID:22941714

Gerber, Markus; Kalak, Nadeem; Lemola, Sakari; Clough, Peter J; Perry, John L; Pühse, Uwe; Elliot, Catherine; Holsboer-Trachsler, Edith; Brand, Serge

2013-04-01

301

Derivation of Apollo 14 High-Al Basalts at Discrete Times: Rb-Sr Isotopic Constraints  

NASA Technical Reports Server (NTRS)

Pristine Apollo 14 (A-14) high-Al basalts represent the oldest volcanic deposits returned from the Moon [1,2] and are relatively enriched in Al2O3 (>11 wt%) compared to other mare basalts (7-11 wt%). Literature Rb-Sr isotopic data suggest there are at least three different eruption episodes for the A-14 high-Al basalts spanning the age range approx.4.3 Ga to approx.3.95 Ga [1,3]. Therefore, the high-Al basalts may record lunar mantle evolution between the formation of lunar crust (approx.4.4 Ga) and the main basin-filling mare volcanism (<3.85 Ga) [4]. The high-Al basalts were originally classified into five compositional groups [5,6], and then regrouped into three with a possible fourth comprising 14072 based on the whole-rock incompatible trace element (ITE) ratios and Rb-Sr radiometric ages [7]. However, Rb-Sr ages of these basalts from different laboratories may not be consistent with each other because of the use of different 87Rb decay constants [8] and different isochron derivation methods over the last four decades. This study involved a literature search for Rb-Sr isotopic data previously reported for the high-Al basalts. With the re-calculated Rb-Sr radiometric ages, eruption episodes of A-14 high-Al basalts were determined, and their petrogenesis was investigated in light of the "new" Rb-Sr isotopic data and published trace element abundances of these basalts.

Hui. Hejiu; Neal, Clive, R.; Shih, Chi-Yu; Nyquist, Laurence E.

2012-01-01

302

A high quality AR coating for AlGaAs/GaAs solar cells  

NASA Astrophysics Data System (ADS)

The AR coating of the AlGaAs/GaAs solar cells should have the characteristics of passivating the surface as well as decreasing optical reflection because they have the chemically active AlGaAs layer. The CVD Si3N4 film has been found to be an excellent AR coating. The CVD Si3N4 presented low reflectance to give high efficiency over 18 percent both in the case of the bare cell and cell with the cover glass opposing to the theoretical prediction. The CVD Si3N4 tightly prevented the water vapor from the corrosion of the AlGaAs layer.

Mitsui, K.; Yoshida, S.; Oda, T.; Kato, M.; Yukimoto, Y.; Matsuda, S.

303

Interfacial characteristics of N-incorporated HfAlO high-k thin films  

Microsoft Academic Search

The characteristics of N-incorporated HfO2–Al2O3 alloy films (HfAlO) were investigated by high-resolution x-ray photoelectron spectroscopy (XPS), near-edge x-ray absorption fine structure (NEXAFS), medium-energy ion scattering (MEIS), and capacitance–voltage measurements. The core-level energy states, Hf 4f and Al 2p peaks of a 15 A? thick film showed a shift to lower binding energy, resulting from the incorporation of nitrogen into the

M.-H. Cho; D. W. Moon; S. A. Park; Y. K. Kim; K. Jeong; S. K. Kang; D.-H. Ko; S. J. Doh; J. H. Lee; N. I. Lee

2004-01-01

304

Interfacial characteristics of N-incorporated HfAlO high-k thin films  

Microsoft Academic Search

The characteristics of N-incorporated HfO2-Al2O3 alloy films (HfAlO) were investigated by high-resolution x-ray photoelectron spectroscopy (XPS), near-edge x-ray absorption fine structure (NEXAFS), medium-energy ion scattering (MEIS), and capacitance-voltage measurements. The core-level energy states, Hf 4f and Al 2p peaks of a 15 A˚ thick film showed a shift to lower binding energy, resulting from the incorporation of nitrogen into the

M.-H. Cho; D. W. Moon; S. A. Park; Y. K. Kim; K. Jeong; S. K. Kang; D.-H. Ko; S. J. Doh; J. H. Lee; N. I. Lee

2004-01-01

305

High-quality NbN nanofilms on a GaN/AlN heterostructure  

NASA Astrophysics Data System (ADS)

We demonstrate high-quality monocrystalline NbN films deposited by DC magnetron sputtering on a GaN/AlN waveguiding heterostructure. NbN layers with a thickness of 8 nm are grown along the [111] direction, and show two orientation domains with NbN(111) [2-1-1]//AlN (0001) [10-10] and NbN(111) [2-1-1]//AlN(0001) [01-10] epitaxial relationships. Our NbN films display a critical temperature of 13.2 K, with the superconducting transition taking place in a temperature range of only 0.7 K.

Sam-Giao, Diane; Pouget, Stéphanie; Bougerol, Catherine; Monroy, Eva; Grimm, Alexander; Jebari, Salha; Hofheinz, Max; Gérard, J.-M.; Zwiller, Val

2014-10-01

306

Highly textured growth of AlN films on sapphire by magnetron sputtering for high temperature surface acoustic wave applications  

SciTech Connect

Piezoelectric aluminum nitride films were deposited onto 3 in. [0001] sapphire substrates by reactive magnetron sputtering to explore the possibility of making highly (002)-textured AlN films to be used in surface acoustic wave (SAW) devices for high temperature applications. The synthesized films, typically 1 {mu}m thick, exhibited a columnar microstructure and a high c-axis texture. The relationship between the microstructures and process conditions was examined by x-ray diffraction (XRD), transmission electron microscopy, and atomic force microscopy analyses. The authors found that highly (002)-textured AlN films with a full width at half maximum of the rocking curve of less than 0.3 deg. can be achieved under high nitrogen concentration and moderate growth temperature, i.e., 250 deg. C. The phi-scan XRD reveals the high in-plane texture of deposited AlN films. The SAW devices, based on the optimized AlN films on sapphire substrate, were characterized before and after an air annealing process at 800 deg. C for 90 min. The frequency response, recorded after the annealing process, confirmed that the thin films were still strong in a high temperature environment and that they had retained their piezoelectric properties.

Aubert, T.; Assouar, M. B.; Legrani, O.; Elmazria, O.; Tiusan, C.; Robert, S. [Institut Jean Lamour, UMR 7198, Nancy University-CNRS, BP 70239, Bd des Aiguillettes, 54506 Vandoeuvre Cedex (France)

2011-03-15

307

Catalytic Transformation of Toluene over High Acidity Y-Zeolite Based S. Al-Khattaf*  

E-print Network

Catalytic Transformation of Toluene over High Acidity Y-Zeolite Based Catalyst S. Al Abstract Catalytic transformation of toluene has been investigated over Y-zeolite based catalysts of the reported studies on toluene disproportionation have been conducted at relatively high pressure

Al-Khattaf, Sulaiman

308

Gate-First AlGaN/GaN HEMT Technology for High-Frequency Applications  

E-print Network

This letter describes a gate-first AlGaN/GaN high-electron mobility transistor (HEMT) with a W/high-k dielectric gate stack. In this new fabrication technology, the gate stack is deposited before the ohmic contacts, and ...

Piner, Edwin L.

309

General High Performance Adaptive Robust Motion Control of Machine Tools Mohammed Al-Majed++  

E-print Network

General High Performance Adaptive Robust Motion Control of Machine Tools Bin Yao + Mohammed Al is applied to the motion control of machine tools, the objective of which is to assure a robust high speed such as machine tools, microelectronics manufacturing equipment, robot manipulators, and automatic inspection

Yao, Bin

310

AlGaAs/GaAs photovoltaic converters for high power narrowband radiation  

NASA Astrophysics Data System (ADS)

AlGaAs/GaAs-based laser power PV converters intended for operation with high-power (up to 100 W/cm2) radiation were fabricated by LPE and MOCVD techniques. Monochromatic (? = 809 nm) conversion efficiency up to 60% was measured at cells with back surface field and low (x = 0.2) Al concentration 'window'. Modules with a voltage of 4 V and the efficiency of 56% were designed and fabricated.

Khvostikov, Vladimir; Kalyuzhnyy, Nikolay; Mintairov, Sergey; Potapovich, Nataliia; Shvarts, Maxim; Sorokina, Svetlana; Luque, Antonio; Andreev, Viacheslav

2014-09-01

311

A high power Tx\\/Rx switch IC using AlGaN\\/GaN HFETs  

Microsoft Academic Search

An extremely high power Tx\\/Rx switch IC based on AlGaN\\/GaN HFETs has been developed for the first time. A low on-state resistance realized by Si doping techniques and a low off-state capacitance by using an Al2O3 substrate led to excellent performance of 0.26 dB insertion loss and 27 dB isolation with the power handling capability of 43 W at 1

H. Ishida; Y. Hirose; T. Murata; A. Kanda; Y. Ikeda; T. Matsuno; K. Inoue; Y. Uemoto; T. Tanaka; T. Egawa; D. Ueda

2003-01-01

312

Heat pipe embedded AlSiC plates for high conductivity - low CTE heat spreaders  

Microsoft Academic Search

Heat pipe embedded aluminum silicon carbide (AlSiC) plates are innovative heat spreaders that provide high thermal conductivity and low coefficient of thermal expansion (CTE). Since heat pipes are two phase devices, they demonstrate effective thermal conductivities ranging between 10,000 and 200,000 W\\/m-K, depending on the heat pipe length. Installing heat pipes into an AlSiC plate dramatically increases the plate's effective

J. Weyant; S. Garner; M. Johnson; M. Occhionero

2010-01-01

313

Effects of Zr on the high strain rate superplasticity of 2124 Al  

Microsoft Academic Search

Many years ago, Nieh and Wadsworth, reported an observation that a 0.6wt%Zr-modified 2124 Al alloy, which has a fine grain size of about 1[mu]m, behaved superplastically at 475 C at high strain rates ([approximately] 10[sup [minus]1]s[sup [minus]1]). The present paper is an extension of the above study, demonstrating the effects of Zr additions to an Al alloy on superplastic strain

T. G. Nieh; J. Wadsworth

1993-01-01

314

STRESS-CORROSION CRACKING OF TYPE 347 STAINLESS STEEL AND OTHER ALLOYS IN HIGH TEMPERATURE WATER  

Microsoft Academic Search

An extensive study was conducted on the susceptibility of Type 347 ; stainless steel to stress-corrosion cracking in high temperature water over wide ; ranges of chloride concentration, temperature, oxygen concentration, and pH. No ; cracking was observed at a chloride concentration of 5 ppm, but cracks were ; observed at 10 ppm and higher at temperatures of 100 deg

P. D. Neumann; J. C. Griess

1963-01-01

315

GROWTH STRESSES ARE HIGHLY CONTROLLED BY THE AMOUNT OF G-LAYER IN POPLAR TENSION WOOD.  

E-print Network

GROWTH STRESSES ARE HIGHLY CONTROLLED BY THE AMOUNT OF G-LAYER IN POPLAR TENSION WOOD. Changhua in tension wood, anatomical measurements of gelatinous fibres were carried out on poplar tension wood wood, poplar hal-00339066,version1-15Nov2008 Author manuscript, published in "IAWA Journal 29, 3 (2008

Paris-Sud XI, Université de

316

CO2 laser scribe of chemically strengthened glass with high surface compressive stress  

Microsoft Academic Search

Chemically strengthened glass is finding increasing use in handheld, IT and TV cover glass applications. Chemically strengthened glass, particularly with high (>600MPa) compressive stress (CS) and deeper depth of layer (DOL), enable to retain higher strength after damage than non-strengthened glass when its surface is abraded. Corning Gorilla® Glass has particularly proven to be advantageous over competition in this attribute.

Xinghua Li; Butchi R. Vaddi

2011-01-01

317

Shear veins observed within anisotropic fabric at high angles to the maximum compressive stress  

Microsoft Academic Search

Some faults seem to slip at unusually high angles (>45°) relative to the orientation of the greatest principal compressive stress. This implies that these faults are extremely weak compared with the surrounding rock. Laboratory friction experiments and theoretical models suggest that the weakness may result from slip on a pre-existing frictionally weak surface, weakening from chemical reactions, elevated fluid pressure

Åke Fagereng; Francesca Remitti; Richard H. Sibson

2010-01-01

318

Tracking-Task Performance during Heat Stress Simulating Cockpit Conditions in High-Performance Aircraft  

Microsoft Academic Search

Heat stress can be a significant problem in high-performance aircraft, where it has a measurable physiological impact on aircrew and may alter the Icarninc curve for novel tasks. In these experiments nine men were trained to plateau performance on a compensatory tracking tusk. They were then tested at the end of 2 h exposures to the following conditions (Tdb\\/Twb, °C):

SARAH A. NUNNELEY; PATRICK J. DOWD; LOREN G. MYHRE; RICHARD F. STRIBLEY; RICHARD C. MCNEE

1979-01-01

319

Factor Structure of Coping: Two Studies of Mothers With High Levels of Life Stress  

Microsoft Academic Search

Exploratory factor analysis (EFA) and confirmatory factor analysis (CFA) were used to investigate the factor structure of coping in mothers with high levels of life stress. In Study 1, EFA of the Coping Orientation to Problems Experienced (C. S. Carver, M. F. Scheier, & J. K. Weintraub, 1989) in a sample of mothers of full-term or very low birth weight

Sheri P. Eisengart; Lynn T. Singer; H. Lester Kirchner; Meeyoung Oh Min; Sarah Fulton; Elizabeth J. Short; Sonia Minnes

2006-01-01

320

FtsH11 Proteases play a critical role in high temperature stress tolerance in plants  

Technology Transfer Automated Retrieval System (TEKTRAN)

FtsHs (Filamentous temperature sensitive H), ATP-dependent zinc metalloproteases of the AAA-superfamily, play essential roles in the turn over of thylakoid proteins damaged by high light stress during photosynthesis. Here, we show that FtsH11, one of the 12 FtsH members in Arabidopsis, plays critic...

321

Recognition of Facial Emotions among Maltreated Children with High Rates of Post-Traumatic Stress Disorder  

ERIC Educational Resources Information Center

Objective: The purpose of this study is to examine processing of facial emotions in a sample of maltreated children showing high rates of post-traumatic stress disorder (PTSD). Maltreatment during childhood has been associated independently with both atypical processing of emotion and the development of PTSD. However, research has provided little…

Masten, Carrie L.; Guyer, Amanda E.; Hodgdon, Hilary B.; McClure, Erin B.; Charney, Dennis S.; Ernst, Monique; Kaufman, Joan; Pine, Daniel S.; Monk, Christopher S.

2008-01-01

322

The Effects of Mindfulness Meditation Training on Multitasking in a High-Stress Information Environment  

E-print Network

The Effects of Mindfulness Meditation Training on Multitasking in a High-Stress Information@uw.edu ABSTRACT We describe an experiment to determine the effects of meditation training on the multitasking who underwent an 8-week training course on mindfulness-based meditation, (2) those who endured a wait

Wobbrock, Jacob O.

323

Traps and defects in pre- and post-proton irradiated AlGaN-GaN high electron mobility transistors and AlGaN Schottky diodes  

NASA Astrophysics Data System (ADS)

High electron mobility transistors (HEMTs) based on AlGaN-GaN hetero-structures are promising for both commercial and military applications that require high voltage, high power, and high efficiency operation. Study of reliability and radiation effects of AlGaN-GaN HEMTs is necessary before solid state power amplifiers based on GaN HEMT technology are successfully deployed in satellite communication systems. Several AlGaN HEMT manufacturers have recently reported encouraging reliability data, but long-term reliability of these devices in the space environment still remains a major concern because a large number of traps and defects are present both in the bulk as well as at the surface leading to undesirable characteristics. This study is to investigate the effects of the AlGaN-GaN HEMTs and AlGaN Schottky diodes irradiated with protons.

Sin, Yongkun; Foran, Brendan; Presser, Nathan; LaLumondiere, Stephen; Lotshaw, William; Moss, Steven C.

2013-03-01

324

Plastic deformation behaviour and deformation substructure in Al-rich TiAl single crystals deformed at high temperatures  

Microsoft Academic Search

Plastic deformation behaviour in Ti–54.7at.%Al and Ti–58.0at.%Al single crystals was examined around and above the anomalous strengthening peak temperature (Tp) focusing on the effect of Al5Ti3 superstructure. The Al5Ti3 superstructure developed in the L10 matrix of Ti–58.0at.%Al, and the size of the Al5Ti3 phase once increased during annealing at 800°C and then decreased with increasing temperature, while no significant evidence

K. Hayashi; T Nakano; Y Umakoshi

2001-01-01

325

Mechanical behavior and cutting performance of nano-multi-layer Ti x Al 1? x N coated tools for high-speed machining of AISI D2 die steel  

Microsoft Academic Search

Nano-multi-layer TixAl1?xN coatings were successfully synthesized on WC–Co substrates by a cathodic arc ion plating (AIP). The synthesized TixAl1?xN films were revealed as nano-multi-layer consisting of nano-sized fine (Ti,Al)N crystallites by characteristics of microstructure, hardness, residual stress and oxidation resistance. The tool performances for the high-hardened AISI D2 die steel (60 HRC) were studied under high-speed cutting conditions. The reliable

Y. G. Jeong; M. C. Kang; J. S. Kim; K. H. Kim; W. G. Kim; I. D. Park; Y. H. Jun

2009-01-01

326

High temperature stability, interface bonding, and mechanical behavior in (beta)-NiAl and Ni3Al matrix composites with reinforcements modified by ion beam enhanced deposition  

NASA Astrophysics Data System (ADS)

Diffusion-bonded NiAl-Al2O3 and Ni3Al-Al2O3 couples were thermally fatigued at 900 C for 1500 and 3500 cycles. The fiber-matrix interface weakened after 3500 cycles for the Saphikon fibers, while the Altex, PRD-166, and FP fibers showed little, if any, degradation. Diffusion bonding of fibers to Nb matrix is being studied. Coating the fibers slightly increases the tensile strength and has a rule-of-mixtures effect on elastic modulus. Push-out tests on Sumitomo and FP fibers in Ni aluminide matrices were repeated. Al2O3 was evaporated directly from pure oxide rod onto acoustically levitated Si carbide particles, using a down-firing, rod-fed electron beam hearth; superior coatings were subsequently produced using concurrent irradiation with 200-eV argon ion-assist beam. The assist beam produced adherent films with reduced tensile stresses. In diffusion bonding in B-doped Ni3Al matrices subjected to compressive bonding at 40 MPa at 1100 C for 1 hr, the diffusion barriers failed to prevent catastrophic particle-matrix reaction, probably because of inadequate film quality. AlN coatings are currently being experimented with, produced by both reactive evaporation and by N(+)-ion enhanced deposition. A 3-kW rod-fed electron-beam-heated evaporation source has been brought into operation.

Grummon, D. S.

1993-01-01

327

High-strain, high-strain-rate flow and failure in PTFE\\/Al\\/W granular composites  

Microsoft Academic Search

Dynamic compression experiments were performed on a pressed PTFE\\/Al\\/W mixture to understand the composite behavior at high-strain and high-strain rate. The high-strain-rate tests were carried out in a drop-weight apparatus at impact velocities of 3.5 and 5m\\/s, providing strain rates of approximately 4×102s?1. Aluminum jackets of varying thickness were used to ensure that specimens underwent confined deformation but did not

J. Cai; S. M. Walley; R. J. A. Hunt; W. G. Proud; V. F. Nesterenko; M. A. Meyers

2008-01-01

328

Oxidative stress plays a role in high glucose-induced activation of pancreatic stellate cells  

SciTech Connect

Highlights: •High glucose increased production of reactive oxygen species in cultured pancreatic stellate cells. •High glucose facilitated the activation of these cells. •Antioxidant treatment attenuated high glucose-induced activation of these cells. -- Abstract: The activation of pancreatic stellate cells (PSCs) is thought to be a potential mechanism underlying islet fibrosis, which may contribute to progressive ?-cell failure in type 2 diabetes. Recently, we demonstrated that antioxidants reduced islet fibrosis in an animal model of type 2 diabetes. However, there is no in vitro study demonstrating that high glucose itself can induce oxidative stress in PSCs. Thus, PSCs were isolated and cultured from Sprague Dawley rats, and treated with high glucose for 72 h. High glucose increased the production of reactive oxygen species. When treated with high glucose, freshly isolated PSCs exhibited myofibroblastic transformation. During early culture (passage 1), PSCs treated with high glucose contained an increased number of ?-smooth muscle actin-positive cells. During late culture (passages 2–5), PSCs treated with high glucose exhibited increases in cell proliferation, the expression of fibronectin and connective tissue growth factor, release of interleukin-6, transforming growth factor-? and collagen, and cell migration. Finally, the treatment of PSCs with high glucose and antioxidants attenuated these changes. In conclusion, we demonstrated that high glucose increased oxidative stress in primary rat PSCs, thereby facilitating the activation of these cells, while antioxidant treatment attenuated high glucose-induced PSC activation.

Ryu, Gyeong Ryul; Lee, Esder; Chun, Hyun-Ji; Yoon, Kun-Ho; Ko, Seung-Hyun; Ahn, Yu-Bae; Song, Ki-Ho, E-mail: kihos@catholic.ac.kr

2013-09-20

329

Al compositional inhomogeneity of AlGaN epilayer with a high Al composition grown by metal-organic chemical vapour deposition.  

PubMed

The Al compositional distribution of AlGaN is investigated by cathodoluminescence (CL). Monochromatic CL images and CL spectra reveal a lateral Al compositional inhomogeneity, which corresponds to surface hexagonal patterns. Cross-sectional CL images show a relatively uniform Al compositional distribution in the growth direction, indicating columnar growth mode of AlGaN films. In addition, a thin AlGaN layer with lower Al composition is grown on top of the buffer AlN layer near the bottom of the AlGaN epilayer because of the larger lateral mobility of Ga adatoms on the growth surface and their accumulation at the grain boundaries. PMID:21690942

Wang, X L; Zhao, D G; Jiang, D S; Yang, H; Liang, J W; Jahn, U; Ploog, K

2007-04-30

330

A New High-Pressure Phase With Mg2Al2O5 Composition  

NASA Astrophysics Data System (ADS)

As MgAl2O4 is one of major components of both spinel phase and calcium ferrite phase in the Earth"fs mantle, many researchers have studied its high-pressure phase relations. However, the high- pressure high-temperature phase relation has been unclear at temperature higher than 2000 °C. By performing high-pressure experiments, we found that MgAl2O4 spinel decomposes to Mg2Al2O5 and Al2O3 at 20-25 GPa and temperature higher than 2000 °C. This is the first report of a compound with the composition of Mg2Al2O5. The powder X-ray diffraction pattern can not be explained by crystal structures of already known high-pressure phases like brownmillerite-type Ca2Al2O5. In this study, we tried to construct a crystal structure model of the new Mg2Al2O5 phase. The obtained structure model was used for structure refinement by the Rietveld analysis. The Mg2Al2O5 phase for a powder XRD measurement was synthesized using a Kawai-type multi-anvil high-pressure apparatus at Gakushuin University. The starting material of a mixture of MgO:Al2O3 = 2:1 (in molar ratio) was hold at 23 GPa and 2500 °C for 10 min. After quenching, the sample was recoverd to ambient pressure. The sintered polycrystalline sample was crushed by a die and ground into powder. The powder X-ray diffraction profile was measured using Rigaku RINT2500V (Cr K?, 45 kV, 250 mA) with the step size of 0.02°. The Rietveld analysis was made using RIETAN-2000 program. The XRD profile showed that symmetry of the Mg2Al2O5 phase is orthorhombic. The extinction rules of the powder XRD peaks suggested the space group of Pba2 or Pbam. Since it was found that the XRD pattern is close to that of (Mg, Fe2+)2(Fe3+, Al)(BO3)O2 ludwigite, a structure model of the Mg2Al2O5 phase was constructed based on it. It should be noted that planner three coordinated sites in ludwigite in which boron places were moved by 0.5 in atomic coordinate along c-axis, because interatomic distances between cation and oxygen in the planner three coordinated sites are too short for Mg2+ and Al3+. In this structure model, (Mg, Al)O6 octahedra connected by edge-sharing and corner-sharing form triangular tunnels along c-axis. Cation sites occupied by only Mg are placed in the tunnels. The sites have a coordination environment of trigonal prism- type MgO6. By the Rietveld analysis, lattice parameters were determined as a = 9.3710(6) Å, b = 12.1952(6) Å, c = 2.7916(2) Å. The calculated density of 3.801(1) g/cm3 is consistent with the high-pressure phase relations. R factor by adopting the space group of Pbam is smaller than that by Pba2. Therefore, it is suggested that the space group of the Mg2Al2O5 phase is Pbam

Kojitani, H.; Enomoto, A.; Tsukamoto, S.; Akaogi, M.; Miura, H.

2008-12-01

331

Search for New Superconductors in RE-Si and Al-B Systems: a High Pressure High Temperature Approach  

NASA Astrophysics Data System (ADS)

We have searched for the presence of superconductivity in the RE-Si and Al-B systems using HP-HT synthesis. The RE-Si system has some of the common features that are present in high TC superconducting materials. We have synthesized Ce, Pr, Nd and Gd silicides undoped and doped with C and B. On the other hand, AlB2 has some similarities with the superconducting MgB2. We have tried to synthesize AlB2 way off stoichiometry using HP-HT and thin films Phase Spread Alloy. The Al0.67 B2 would be the MgB2 equivalent and good reason to expect superconductivity. We discuss the results for both systems after a careful analysis of several physical properties (SQUID, Modulated Microwave Absorption) and x-ray powder diffraction.

Alario-Franco, Miguel Angel; de La Venta, Jose; Basaran, Ali; Schuller, Ivan K.; Grant, Ted; Fisk, Zachary

2012-02-01

332

Sensitivity of on-resistance and threshold voltage to buffer-related deep level defects in AlGaN/GaN high electron mobility transistors  

NASA Astrophysics Data System (ADS)

The influence of deep levels defects located in highly resistive GaN:C buffers on the on-resistance (RON) and threshold voltage (Vth) of AlGaN/GaN high electron mobility transistors (HEMTs) power devices was studied by a combined photocapacitance deep level optical spectroscopy (C-DLOS) and photoconductance deep level optical spectroscopy (G-DLOS) methodology as a function of electrical stress. Two carbon-related deep levels at 1.8 and 2.85 eV below the conduction band energy minimum were identified from C-DLOS measurements under the gate electrode. It was found that buffer-related defects under the gate shifted Vth positively by approximately 10%, corresponding to a net areal density of occupied defects of 8 × 1012 cm-2. The effect of on-state drain stress and off-state gate stress on buffer deep level occupancy and RON was also investigated via G-DLOS. It was found that the same carbon-related deep levels observed under the gate were also active in the access region. Off-state gate stress produced significantly more trapping and degradation of RON (˜140%) compared to on-state drain stress (˜75%). Greater sensitivity of RON to gate stress was explained by a more sharply peaked lateral distribution of occupied deep levels between the gate and drain compared to drain stress. The overall greater sensitivity of RON compared to Vth to buffer defects suggests that electron trapping is significantly greater in the access region compared to under the gate, likely due to the larger electric fields in the latter region.

Armstrong, Andrew M.; Allerman, Andrew A.; Baca, Albert G.; Sanchez, Carlos A.

2013-07-01

333

Compact analytical model for single gate AlInSb/InSb high electron mobility transistors  

NASA Astrophysics Data System (ADS)

We have developed a 2D analytical model for the single gate AlInSb/InSb HEMT device by solving the Poisson equation using the parabolic approximation method. The developed model analyses the device performance by calculating the parameters such as surface potential, electric field distribution and drain current. The high mobility of the AlInSb/InSb quantum makes this HEMT ideal for high frequency, high power applications. The working of the single gate AlInSb/InSb HEMT device is studied by considering the variation of gate source voltage, drain source voltage, and channel length under the gate region and temperature. The carrier transport efficiency is improved by uniform electric field along the channel and the peak values near the source and drain regions. The results from the analytical model are compared with that of numerical simulations (TCAD) and a good agreement between them is achieved.

Chandra, S. Theodore; Balamurugan, N. B.; Subalakshmi, G.; Shalini, T.; Lakshmi Priya, G.

2014-11-01

334

Coenzyme Q10 prevents high glucose-induced oxidative stress in human umbilical vein endothelial cells.  

PubMed

Hyperglycemia-induced oxidative stress plays a crucial role in the pathogenesis of vascular complications in diabetes. Although some clinical evidences suggest the use of an antioxidant reagent coenzyme Q10 in diabetes with hypertension, the direct effect of coenzyme Q10 on the endothelial functions has not been examined. In the present study, we therefore investigated the protective effect of coenzyme Q10 against high glucose-induced oxidative stress in human umbilical vein endothelial cells (HUVEC). HUVEC exposed to high glucose (30 mM) exhibited abnormal properties, including the morphological and biochemical features of apoptosis, overproduction of reactive oxygen species, activation of protein kinase Cbeta2, and increase in endothelial nitric oxide synthase expression. Treatment with coenzyme Q10 strongly inhibited these changes in HUVEC under high glucose condition. In addition, coenzyme Q10 inhibited high glucose-induced cleavage of poly(ADP-ribose) polymerase, an endogenous caspase-3 substrate. These results suggest that coenzyme Q10 prevents reactive oxygen species-induced apoptosis through inhibition of the mitochondria-dependent caspase-3 pathway. Moreover, consistent with previous reports, high glucose caused upregulation of intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) in HUVEC, and promoted the adhesion of U937 monocytic cells. Coenzyme Q10 displayed potent inhibitory effects against these endothelial abnormalities. Thus, we provide the first evidence that coenzyme Q10 has a beneficial effect in protecting against the endothelial dysfunction by high glucose-induced oxidative stress in vitro. PMID:17434478

Tsuneki, Hiroshi; Sekizaki, Naoto; Suzuki, Takashi; Kobayashi, Shinjiro; Wada, Tsutomu; Okamoto, Tadashi; Kimura, Ikuko; Sasaoka, Toshiyasu

2007-07-01

335

Achieving high thermal conductivity from AlN films deposited by high-power impulse magnetron sputtering  

NASA Astrophysics Data System (ADS)

We report on thermal conductivity measurements of aluminum nitride (AlN) films using the fast pulsed photo-thermal technique. The films were deposited by high-power impulse magnetron sputtering with different thicknesses ranging from 1000 to 8000 nm on (1?0?0) oriented silicon substrates. The films were characterized by x-ray diffraction (XRD), Raman spectroscopy, profilometry, scanning electron microscopy and atomic force microscopy. The XRD measurements showed that AlN films were textured along the (0?0?2) direction. Moreover, x-ray rocking curve measurements indicated that the crystalline quality of AlN was improved with the increase in film thickness. The thermal conductivities of the samples were found to rapidly increase when the film thickness increased up to 3300 nm and then showed a tendency to remain constant. A thermal boundary resistance as low as 8 × 10-9 W-1 K m2 and a thermal conductivity as high as 250 ± 50 W K-1 m-1 were obtained for the AlN films, at room temperature. This high thermal conductivity value is close to that of an AlN single crystal and highlights the potential of these films as a dielectric material for thermal management.

Ait Aissa, K.; Semmar, N.; Achour, A.; Simon, Q.; Petit, A.; Camus, J.; Boulmer-Leborgne, C.; Djouadi, M. A.

2014-09-01

336

Evaluation of the stress corrosion cracking resistance of several high strength low alloy steels  

NASA Technical Reports Server (NTRS)

The stress corrosion cracking resistance was studied for high strength alloy steels 4130, 4340, for H-11 at selected strength levels, and for D6AC and HY140 at a single strength. Round tensile and C-ring type specimens were stressed up to 100 percent of their yield strengths and exposed to alternate immersion in salt water, salt spray, the atmosphere at Marshall Space Flight Center, and the seacoast at Kennedy Space Center. Under the test conditions, 4130 and 4340 steels heat treated to a tensile strength of 1240 MPa (180 ksi), H-11 and D6AC heat treated to a tensile strength of 1450 MPa (210 ksi), and HY140 (1020 MPa, 148 ksi) are resistant to stress corrosion cracking because failures were not encountered at stress levels up to 75 percent of their yield strengths. A maximum exposure period of one month for alternate immersion in salt water or salt spray and three months for seacoast is indicated for alloy steel to avoid false indications of stress corrosion cracking because of failure resulting from severe pitting.

Humphries, T. S.; Nelson, E. E.

1980-01-01

337

Static and dynamic stress analyses of the prototype high head Francis runner based on site measurement  

NASA Astrophysics Data System (ADS)

More efforts are put on hydro-power to balance voltage and frequency within seconds for primary control in modern smart grids. This requires hydraulic turbines to run at off-design conditions. especially at low load or speed-no load. Besides. the tendency of increasing power output and decreasing weight of the turbine runners has also led to the high level vibration problem of the runners. especially high head Francis runners. Therefore. it is important to carry out the static and dynamic stress analyses of prototype high head Francis runners. This paper investigates the static and dynamic stresses on the prototype high head Francis runner based on site measurements and numerical simulations. The site measurements are performed with pressure transducers and strain gauges. Based on the measured results. computational fluid dynamics (CFD) simulations for the flow channel from stay vane to draft tube cone are performed. Static pressure distributions and dynamic pressure pulsations caused by rotor-stator interaction (RSI) are obtained under various operating conditions. With the CFD results. static and dynamic stresses on the runner at different operating points are calculated by means of the finite element method (FEM). The agreement between simulation and measurement is analysed with linear regression method. which indicates that the numerical result agrees well with that of measurement. Furthermore. the maximum static and dynamic stresses on the runner blade are obtained at various operating points. The relations of the maximum stresses and the power output are discussed in detail. The influences of the boundary conditions on the structural behaviour of the runner are also discussed.

Huang, X.; Oram, C.; Sick, M.

2014-12-01

338

Fluorescence spectroscopy applied to study cyclic creep behaviour and internal stresses of semi-crystalline high-density polyethylene  

NASA Astrophysics Data System (ADS)

Cyclic creep or ratcheting behaviour has been characterized on semi-crystalline high-density polyethylene (HDPE) at 293 K using in situ extrinsic fluorescence spectroscopy. Fluorescent probe inserted in polymer offers the opportunity to establish a relationship between fluorescence phenomena and mechanical behaviour and more specifically to internal stresses. The influence of mean stress (?m), and stress amplitude (?a), on ratcheting strain (?r) and strain amplitude (?a) was studied in term of internal stresses development. The physical base of internal stress state has been discussed.

Bouvet, G.; Douminge, L.; Feaugas, X.; Touzain, S.; Mallarino, S.

2013-01-01

339

Electrical characteristics of AlGaN-GaN high electron mobility transistors and AlGaN Schottky diodes irradiated with protons  

NASA Astrophysics Data System (ADS)

AlGaN-GaN high electron mobility transistors (HEMTs) are most suitable for commercial and military applications requiring high voltage, high power, and high efficiency operation. In recent years, leading AlGaN HEMT manufacturers have reported encouraging reliability of these devices, but their long-term reliability especially in the space environment still remains a major concern. In addition, degradation mechanisms in AlGaN HEMT devices are still not well understood, and a large number of traps and defects present both in the bulk and at the surface lead to undesirable characteristics. Study of reliability and radiation effects of AlGaN-GaN HEMTs is therefore necessary before GaN HEMT technology is successfully employed in satellite communication systems. For the present study, we investigated electrical characteristics of AlGaN-GaN HEMTs and AlGaN Schottky diodes irradiated with protons. We studied two types of MOCVD-grown AlGaN HEMTs on semi-insulating SiC substrates (HEMT-1 and HEMT-2) as well as MOCVD-grown Al0.27Ga 0.73N Schottky diodes on conducting SiC substrates. Our HEMT-1 structure consisted of a GaN cap, AlGaN/AlN barrier, and 2 ?m GaN buffer layers. Our HEMT-2 structure consisting of undoped AlGaN barrier and GaN buffer layers grown on an AlN nucleation layer showed a charge sheet density of ~1013/cm2 and a Hall mobility of ~1500 cm2 /V.sec. Our HEMT-1 devices had a Pt-Au Schottky gate length of 0.2 ?m, a total gate width of 200-400 ?m periphery, and SiNx passivation. Electrical characteristics of AlGaN-GaN HEMTs and AlGaN Schottky diodes were compared before and after they were proton irradiated with different energies and fluences. Current-mode deep level transient spectroscopy (DLTS) and capacitance-mode DLTS were employed to study pre-proton irradiation trap characteristics in the AlGaN-GaN HEMTs and AlGaN Schottky diodes, respectively. Focused ion beam (FIB) was employed to prepare both cross-sectional and plan view TEM samples for defect analysis using a high resolution TEM. In addition, electrical characteristics of GaAs MESFETs used as reference devices were compared before and after they were proton irradiated.

Sin, Yongkun; Presser, Nathan; Foran, Brendan; LaLumondiere, Stephen; Lotshaw, William; Moss, Steven C.

2014-03-01

340

Trap states in AlGaN channel high-electron-mobility transistors  

SciTech Connect

Frequency dependent capacitance and conductance measurements were performed to analyze the trap states in the AlGaN channel high-electron-mobility transistors (HEMTs). The trap state density in the AlGaN channel HEMTs decreases from 1.26?×?10{sup 13}?cm{sup ?2}eV{sup ?1} at the energy of 0.33?eV to 4.35?×?10{sup 11}?cm{sup ?2}eV{sup ?1} at 0.40?eV. Compared with GaN channel HEMTs, the trap states in the AlGaN channel HEMTs have deeper energy levels. The trap with deeper energy levels in the AlGaN channel HEMTs is another reason for the reduction of the reverse gate leakage current besides the higher Schottky barrier height.

Zhao, ShengLei; Zhang, Kai; Ha, Wei; Chen, YongHe; Zhang, Peng; Zhang, JinCheng; Hao, Yue, E-mail: yhao@xidian.edu.cn [Key Laboratory of Wide Band Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071 (China)] [Key Laboratory of Wide Band Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071 (China); Ma, XiaoHua, E-mail: xhma@xidian.edu.cn [Key Laboratory of Wide Band Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071 (China) [Key Laboratory of Wide Band Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071 (China); School of Advanced Materials and Nanotechnology, Xidian University, Xi'an 710071 (China)

2013-11-18

341

Preliminary study of the characteristics of a high Mg containing Al-Mg-Si alloy  

NASA Astrophysics Data System (ADS)

An Al-20Mg-4Si high Mg containing alloy has been produced and its characteristics investigated. The as-cast alloy revealed primary Mg2Si particles evenly distributed throughout an ?-Al matrix with a ?-Al3Mg2 fully divorced eutectic phase observed in interdendritic regions. The Mg2Si particles displayed octahedral, truncated octahedral, and hopper morphologies. Additions of Sb, Ti and Zr had a refining influence reducing the size of the Mg2Si from 52 ± 4 ?m to 25 ± 0.1 ?m, 35 ± 1 ?m and 34 ± 1 ?m respectively. HPDC tensile test samples could be produced with a 0.6 wt.% Mn addition which prevented die soldering. Solution heating for 1 hr was found to dissolve the majority of the Al3Mg2 eutectic phase with no evidence of any effect on the primary Mg2Si. Preliminary results indicate that the heat treatment has a beneficial effect on the elongation and the UTS.

Yan, F.; McKay, B. J.; Fan, Z.; Chen, M. F.

2012-01-01

342

Internal stress-induced melting below melting temperature at high-rate laser heating  

SciTech Connect

In this Letter, continuum thermodynamic and phase field approaches (PFAs) predicted internal stress-induced reduction in melting temperature for laser-irradiated heating of a nanolayer. Internal stresses appear due to thermal strain under constrained conditions and completely relax during melting, producing an additional thermodynamic driving force for melting. Thermodynamic melting temperature for Al reduces from 933.67?K for a stress-free condition down to 898.1?K for uniaxial strain and to 920.8?K for plane strain. Our PFA simulations demonstrated barrierless surface-induced melt nucleation below these temperatures and propagation of two solid-melt interfaces toward each other at the temperatures very close to the corresponding predicted thermodynamic equilibrium temperatures for the heating rate Q?1.51×10{sup 10}K/s. At higher heating rates, kinetic superheating competes with a reduction in melting temperature and melting under uniaxial strain occurs at 902.1?K for Q?=?1.51?×?10{sup 11?}K/s and 936.9?K for Q?=?1.46?×?10{sup 12?}K/s.

Hwang, Yong Seok, E-mail: yshwang@iastate.edu [Department of Aerospace Engineering, Iowa State University, Ames, Iowa 50011 (United States); Levitas, Valery I., E-mail: vlevitas@iastate.edu [Departments of Aerospace Engineering, Mechanical Engineering, and Material Science and Engineering, Iowa State University, Ames, Iowa 50011 (United States)

2014-06-30

343

RNA-binding ability of FUS regulates neurodegeneration, cytoplasmic mislocalization and incorporation into stress granules associated with FUS carrying ALS-linked mutations  

PubMed Central

Amyotrophic lateral sclerosis (ALS) is an uncommon neurodegenerative disease caused by degeneration of upper and lower motor neurons. Several genes, including SOD1, TDP-43, FUS, Ubiquilin 2, C9orf72 and Profilin 1, have been linked with the sporadic and familiar forms of ALS. FUS is a DNA/RNA-binding protein (RBP) that forms cytoplasmic inclusions in ALS and frontotemporal lobular degeneration (FTLD) patients' brains and spinal cords. However, it is unknown whether the RNA-binding ability of FUS is required for causing ALS pathogenesis. Here, we exploited a Drosophila model of ALS and neuronal cell lines to elucidate the role of the RNA-binding ability of FUS in regulating FUS-mediated toxicity, cytoplasmic mislocalization and incorporation into stress granules (SGs). To determine the role of the RNA-binding ability of FUS in ALS, we mutated FUS RNA-binding sites (F305L, F341L, F359L, F368L) and generated RNA-binding-incompetent FUS mutants with and without ALS-causing mutations (R518K or R521C). We found that mutating the aforementioned four phenylalanine (F) amino acids to leucines (L) (4F-L) eliminates FUS RNA binding. We observed that these RNA-binding mutations block neurodegenerative phenotypes seen in the fly brains, eyes and motor neurons compared with the expression of RNA-binding-competent FUS carrying ALS-causing mutations. Interestingly, RNA-binding-deficient FUS strongly localized to the nucleus of Drosophila motor neurons and mammalian neuronal cells, whereas FUS carrying ALS-linked mutations was distributed to the nucleus and cytoplasm. Importantly, we determined that incorporation of mutant FUS into the SG compartment is dependent on the RNA-binding ability of FUS. In summary, we demonstrate that the RNA-binding ability of FUS is essential for the neurodegenerative phenotype in vivo of mutant FUS (either through direct contact with RNA or through interactions with other RBPs). PMID:23257289

Daigle, J. Gavin; Lanson, Nicholas A.; Smith, Rebecca B.; Casci, Ian; Maltare, Astha; Monaghan, John; Nichols, Charles D.; Kryndushkin, Dmitri; Shewmaker, Frank; Pandey, Udai Bhan

2013-01-01

344

X-ray high-pressure study of Ti2AlN and Ti2AlC  

NASA Astrophysics Data System (ADS)

The lattice parameters of Ti2AlN and Ti2AlC powders were measured as a function of pressure up to ?50 GPa, using a synchrotron radiation source and a diamond anvil cell. No phase transformations were observed. As for most related layered carbides and nitrides, such as Ti4AlN3 and Ti3SiC2, the compressibilities of Ti2AlN and Ti2AlC along the c-axes are larger than those along the a-axes. The bulk modulus of Ti2AlC at 186±2 GPa, is ?10% higher than that of Ti2AlN at 169±3 GPa.

Manoun, Bouchaib; Zhang, F. X.; Saxena, S. K.; El-Raghy, T.; Barsoum, M. W.

2006-09-01

345

A high-density genome-wide association screen of sporadic ALS in US veterans.  

PubMed

Following reports of an increased incidence of amyotrophic lateral sclerosis (ALS) in U.S. veterans, we have conducted a high-density genome-wide association study (GWAS) of ALS outcome and survival time in a sample of U.S. veterans. We tested ?1.3 million single nucleotide polymorphisms (SNPs) for association with ALS outcome in 442 incident Caucasian veteran cases diagnosed with definite or probable ALS and 348 Caucasian veteran controls. To increase power, we also included genotypes from 5909 publicly-available non-veteran controls in the analysis. In the survival analysis, we tested for association between SNPs and post-diagnosis survival time in 639 Caucasian veteran cases with definite or probable ALS. After this discovery phase, we performed follow-up genotyping of 299 SNPs in an independent replication sample of Caucasian veterans and non-veterans (ALS outcome: 183 cases and 961 controls; survival: 118 cases). Although no SNPs reached genome-wide significance in the discovery phase for either phenotype, three SNPs were statistically significant in the replication analysis of ALS outcome: rs6080539 (177 kb from PCSK2), rs7000234 (4 kb from ZNF704), and rs3113494 (13 kb from LOC100506746). Two SNPs located in genes that were implicated by previous GWA studies of ALS were marginally significant in the pooled analysis of discovery and replication samples: rs17174381 in DPP6 (p?=?4.4×10(-4)) and rs6985069 near ELP3 (p?=?4.8×10(-4)). Our results underscore the difficulty of identifying and convincingly replicating genetic associations with a rare and genetically heterogeneous disorder such as ALS, and suggest that common SNPs are unlikely to account for a substantial proportion of patients affected by this devastating disorder. PMID:22470424

Kwee, Lydia Coulter; Liu, Yutao; Haynes, Carol; Gibson, Jason R; Stone, Annjanette; Schichman, Steven A; Kamel, Freya; Nelson, Lorene M; Topol, Barbara; Van den Eeden, Stephen K; Tanner, Caroline M; Cudkowicz, Merit E; Grasso, Daniela L; Lawson, Robert; Muralidhar, Sumitra; Oddone, Eugene Z; Schmidt, Silke; Hauser, Michael A

2012-01-01

346

A High-Density Genome-Wide Association Screen of Sporadic ALS in US Veterans  

PubMed Central

Following reports of an increased incidence of amyotrophic lateral sclerosis (ALS) in U.S. veterans, we have conducted a high-density genome-wide association study (GWAS) of ALS outcome and survival time in a sample of U.S. veterans. We tested ?1.3 million single nucleotide polymorphisms (SNPs) for association with ALS outcome in 442 incident Caucasian veteran cases diagnosed with definite or probable ALS and 348 Caucasian veteran controls. To increase power, we also included genotypes from 5909 publicly-available non-veteran controls in the analysis. In the survival analysis, we tested for association between SNPs and post-diagnosis survival time in 639 Caucasian veteran cases with definite or probable ALS. After this discovery phase, we performed follow-up genotyping of 299 SNPs in an independent replication sample of Caucasian veterans and non-veterans (ALS outcome: 183 cases and 961 controls; survival: 118 cases). Although no SNPs reached genome-wide significance in the discovery phase for either phenotype, three SNPs were statistically significant in the replication analysis of ALS outcome: rs6080539 (177 kb from PCSK2), rs7000234 (4 kb from ZNF704), and rs3113494 (13 kb from LOC100506746). Two SNPs located in genes that were implicated by previous GWA studies of ALS were marginally significant in the pooled analysis of discovery and replication samples: rs17174381 in DPP6 (p?=?4.4×10?4) and rs6985069 near ELP3 (p?=?4.8×10?4). Our results underscore the difficulty of identifying and convincingly replicating genetic associations with a rare and genetically heterogeneous disorder such as ALS, and suggest that common SNPs are unlikely to account for a substantial proportion of patients affected by this devastating disorder. PMID:22470424

Kwee, Lydia Coulter; Liu, Yutao; Haynes, Carol; Gibson, Jason R.; Stone, Annjanette; Schichman, Steven A.; Kamel, Freya; Nelson, Lorene M.; Topol, Barbara; Van Den Eeden, Stephen K.; Tanner, Caroline M.; Cudkowicz, Merit E.; Grasso, Daniela L.; Lawson, Robert; Muralidhar, Sumitra; Oddone, Eugene Z.

2012-01-01

347

Investigation of Aluminate and Al2O3 Crystals and Melts at High Temperature Using XANES Spectroscopy  

SciTech Connect

Using X-ray absorption at the Al K-edge at high temperature, structural information was determined on Al2O3, CaAl2O4 (CA), Ca3Al2O6 (C3A) and CaAl2Si2O8 (anorthite) in the crystalline and liquid states (2380 K). Important changes are observed for Al2O3 where all oscillation in the XANES spectra disappear above the liquidus temperature. For the three other compositions some modifications of the XANES spectra can be attributed to changes in the Al coordination.

Neuville, Daniel R.; Roux, Jacques [Physique des Mineraux et des Magmas, IPGP-CNRS, 4 place Jussieu, 75005 Paris (France); Cormier, Laurent [IMPMC, Universite Pierre et Marie Curie, Universite Denis Diderot, CNRS UMR 7590, 140 rue de Lourmel, 75015 Paris (France); Henderson, Grant S. [Dept of Geology, University of Toronto, 22 Russell St, Toronto (Canada); Ligny, Dominique de [LPCML, UCBL, 12 rue Ampere, 69622 Villeurbanne (France); Flank, Anne-Marie; Lagarde, Pierre [CNRS- UR1 SOLEIL, BP 48, 91192 Gif sur Yvette (France); SLS, 5232 Villigen-PSI (Switzerland)

2007-02-02

348

A unified interpretation of threshold stresses in the creep and high strain rate superplasticity of metal matrix composites  

Microsoft Academic Search

The flow behavior of metal matrix composites is characterized by the presence of a threshold stress under both creep conditions at intermediate temperatures and in high strain rate superplasticity (HSR SP) at very high temperatures near the onset of partial melting. Experiments show the measured threshold stresses decrease with increasing temperature and this trend has been interpreted using an Arrhenius-type

Y. Li; T. G. Langdon

1999-01-01

349

Secondary Al-Si-Mg High-pressure Die Casting Alloys with Enhanced Ductility  

NASA Astrophysics Data System (ADS)

Al-Si-Mg-based secondary cast alloys are attractive candidates for thin-walled high-pressure die castings for applications in the transport industry. The present study investigates the effect of manganese additions at high cooling rates on microstructure, mechanical properties, and on the dominating fracture mechanisms of alloy AlSi10Mg with an elevated iron concentration. Systematic variations of the Mn content from 0.20 to 0.85 wt pct at a constant Fe content of 0.55 wt pct illustrate the key changes in type, phase fraction, and shape of the Fe-containing intermetallic phases, and the corresponding influence on the alloy's ductility. For high-pressure die casting (HPDC), an optimal range of the Mn content between 0.40 and 0.60 wt pct, equivalent to a Mn/Fe ratio of approximately 1, has been identified. At these Mn and Fe contents, the high cooling rates obtained in HPDC result in the formation of fine and homogeneously distributed ?-Al15(Fe,Mn)3Si2 phase, and crack initiation is transferred from AlFeSi intermetallics to eutectic silicon. The study interprets the microstructure-property relationship in the light of thermodynamic calculations which reveal a significant increase in undercooling of the ?-Al15(Fe,Mn)3Si2 phase with increased Mn content. It concludes that the interdependence of the well-defined Mn/Fe ratio and the high cooling rate in HPDC can generate superior ductility in secondary AlSi10Mg cast alloys.

Bösch, Dominik; Pogatscher, Stefan; Hummel, Marc; Fragner, Werner; Uggowitzer, Peter J.; Göken, Mathias; Höppel, Heinz Werner

2014-12-01

350

Stress and Strain Distributions during Machining of Ti-6Al-4V at Ambient and Cryogenic Temperatures  

NASA Astrophysics Data System (ADS)

Dry and liquid nitrogen pre-cooled Ti-6Al-4V samples were machined at a cutting speed of 43.2 m/min and at low (0.1 mm/rev) to high (0.4 mm/rev) feed rates for understanding the effects of temperature and strain rate on chip microstructures. During cryogenic machining, it was observed that between feed rates of 0.10 and 0.30 mm/rev, a 25% pressure reduction on tool occurred. Smaller number of chips and low tool/chip contact time and temperature were observed (compared to dry machining under ambient conditions). An in-situ set-up that consisted of a microscope and a lathe was constructed and helped to propose a novel serrated chip formation mechanism when microstructures (strain localization) and surface roughness were considered. Dimpled fracture surfaces observed in high-speed-machined chips were formed due to stable crack propagation that was also recorded during in-situ machining. An instability criterion was developed that showed easier strain localization within the 0.10-0.30mm/rev feed rate range.

Rahman, Md. Fahim

351

Formation of High Quality AlN Tunnel Barriers via an Inductively Couple Plasma  

NASA Astrophysics Data System (ADS)

Increasing operating frequencies of SIS receivers requires junctions that can operate at higher current densities. A major limiting factor of higher current density junctions is the increase in subgap leakage that occurs in AlOX barriers as current densities approach and exceed 10kA/cm2. AlN insulators are a promising alternative due to their lower leakage current at these high current densities. In this paper we present a more detailed analysis of the formation of AlN barriers using our previously reported inductively coupled plasma (ICP) source growth technique. The ICP allows for independent control of ion energy and current density in the plasma. Additionally, plasmas with very low ion energy (~20eV) and a high degree of dissociation (~80%) can be achieved. This improved control allows for the repeatable formation of high quality barriers. In particular, we report on the relationship between barrier thickness and plasma conditions as determined by in-situ discrete ellipsometry. Ellipsometry results were verified by fabricating Nb/Al-AlN/Nb junctions and measuring current-voltage, I(V), curves. dc I(V) curves for a range of current densities are presented.

Cecil, Thomas W.; Lichtenberger, Arthur W.; Kerr, Anthony R.

2008-04-01

352

Faceted growth of primary Al{sub 2}Cu crystals during directional solidification in high magnetic field  

SciTech Connect

The high magnetic field is widely used to modify the crystal morphology. In this work, the effect of the magnetic field on growing behavior of faceted crystals in the Al-40 wt. %Cu alloy was investigated using directional solidification technique. It was found that the faceted growth of primary Al{sub 2}Cu phase was degraded and the primary spacing was reduced upon applying the magnetic field. Additionally, the length of the mushy zone first decreased and then increased with increase of the magnetic field intensity. The quantitative analysis reveals that the shear stress induced by the fluid motion is insufficient to break the atom bonds at the solid-liquid interface. However, both of the thermoelectric magnetic convection (TEMC) and the thermoelectric magnetic force (TEMF) cause dendrites to fracture and reduce the primary spacing. The two effects also weaken the faceting growth. Moreover, the instability of the solid-liquid interface is generated by the TEMF, which further leads to degrade the faceted growth. The length of mushy zone was changed by the TEMC and reached the minimum in the magnetic field of 0.5 T, which is in good agreement with the predicted value (0.83 T)

Li, Chuanjun; Ren, Zhongming; Shen, Yu [School of Materials Science and Engineering, Shanghai University, Shanghai 200072 (China)] [School of Materials Science and Engineering, Shanghai University, Shanghai 200072 (China); Wang, Qiuliang; Dai, Yinming; Wang, Hui [Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190 (China)] [Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190 (China)

2013-10-21

353

Measurement and interpretation of threshold stress intensity factors for steels in high-pressure hydrogen gas.  

SciTech Connect

Threshold stress intensity factors were measured in high-pressure hydrogen gas for a variety of low alloy ferritic steels using both constant crack opening displacement and rising crack opening displacement procedures. The sustained load cracking procedures are generally consistent with those in ASME Article KD-10 of Section VIII Division 3 of the Boiler and Pressure Vessel Code, which was recently published to guide design of high-pressure hydrogen vessels. Three definitions of threshold were established for the two test methods: K{sub THi}* is the maximum applied stress intensity factor for which no crack extension was observed under constant displacement; K{sub THa} is the stress intensity factor at the arrest position for a crack that extended under constant displacement; and K{sub JH} is the stress intensity factor at the onset of crack extension under rising displacement. The apparent crack initiation threshold under constant displacement, K{sub THi}*, and the crack arrest threshold, K{sub THa}, were both found to be non-conservative due to the hydrogen exposure and crack-tip deformation histories associated with typical procedures for sustained-load cracking tests under constant displacement. In contrast, K{sub JH}, which is measured under concurrent rising displacement and hydrogen gas exposure, provides a more conservative hydrogen-assisted fracture threshold that is relevant to structural components in which sub-critical crack extension is driven by internal hydrogen gas pressure.

Nibur, Kevin A.

2010-11-01

354

The flavoprotein Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells  

SciTech Connect

Highlights: Black-Right-Pointing-Pointer NO is produced from L-arginine in response to elevated temperature in yeast. Black-Right-Pointing-Pointer Tah18 was first identified as the yeast protein involved in NO synthesis. Black-Right-Pointing-Pointer Tah18-dependent NO synthesis confers tolerance to high-temperature on yeast cells. -- Abstract: Nitric oxide (NO) is a ubiquitous signaling molecule involved in the regulation of a large number of cellular functions. In the unicellular eukaryote yeast, NO may be involved in stress response pathways, but its role is poorly understood due to the lack of mammalian NO synthase (NOS) orthologues. Previously, we have proposed the oxidative stress-induced L-arginine synthesis and its physiological role under stress conditions in yeast Saccharomyces cerevisiae. Here, our experimental results indicated that increased conversion of L-proline into L-arginine led to NO production in response to elevated temperature. We also showed that the flavoprotein Tah18, which was previously reported to transfer electrons to the Fe-S cluster protein Dre2, was involved in NO synthesis in yeast. Gene knockdown analysis demonstrated that Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells. As it appears that such a unique cell protection mechanism is specific to yeasts and fungi, it represents a promising target for antifungal activity.

Nishimura, Akira; Kawahara, Nobuhiro [Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan)] [Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan); Takagi, Hiroshi, E-mail: hiro@bs.naist.jp [Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan)] [Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan)

2013-01-04

355

Chronic mild stress induces variations in locomotive behavior and metabolic rates in high fat fed rats.  

PubMed

Chronic mild stress (CMS) has been often associated to the pathogenesis of many diseases including obesity. Indeed, visceral obesity has been linked to the development of metabolic syndrome features and constitutes a serious risk factor for cardiovascular diseases and diabetes. In order to study possible mechanistic relationships between stress and the onset of obesity, we developed during 11 weeks a model of high-fat dietary intake (cafeteria diet) together with a CMS regimen in male Wistar rats. During the experimental period, basal metabolism by indirect calorimetry, rectal temperature, food intake, and locomotive markers were specifically analyzed. After 77 days, animals were sacrificed and body, adiposity and plasma biochemical profiles were also examined. As expected, cafeteria diet in unstressed animals induced a significative increase in body weight, adiposity, and insulin resistance markers. Locomotive variables, specifically distance, rearing and meander, were significantly increased by CMS on the first weeks of stress. Moreover, this model of CMS in Wistar rats increased significantly energy expenditure, and apparently interplayed with the dietary treatment on the muscle weight/fat weight ratio. In summary, this chronic stress model did not affected weight gain in control and high fat fed animals, but induced an interaction concerning the metabolic muscle/fat repartitioning. PMID:18457009

García-Díaz, D F; Campion, J; Milagro, F I; Lomba, A; Marzo, F; Martínez, J A

2007-12-01

356

-Based Mold Flux Used for High Al-TRIP Steel Casting  

NASA Astrophysics Data System (ADS)

An investigation was carried out to study the effect of MnO on crystallization, melting, and heat transfer of lime-alumina-based mold flux used for high Al-TRIP steel casting, through applying the infrared emitter technique (IET) and the double hot thermocouple technique (DHTT). The results of IET tests showed that MnO could improve the general heat transfer rate through promoting the melting and inhibiting the crystallization of mold flux; meanwhile the radiative heat flux was being attenuated. DHTT experiments indicated that the crystallization fraction, melting temperature of mold flux decreased with the addition of MnO. The results of this study can further elucidate the properties of the CaO-Al2O3 slag system and reinforce the basis for the application of lime-alumina system mold fluxes for casting high Al steels.

Zhao, Huan; Wang, Wanlin; Zhou, Lejun; Lu, Boxun; Kang, Youn-Bae

2014-08-01

357

Investigation of trap states under Schottky contact in GaN/AlGaN/AlN/GaN high electron mobility transistors  

SciTech Connect

Forward gate-bias stress experiments are performed to investigate the variation of trap states under Schottky contact in GaN-based high electron mobility transistors. Traps with activation energy E{sub T} ranging from 0.22?eV to 0.31?eV are detected at the gate-semiconductor interface by dynamic conductance technique. Trap density decreases prominently after stressing, particularly for traps with E{sub T}?>?0.24?eV. X-ray photoelectron spectroscopy measurements reveal a weaker Ga-O peak on the stressed semiconductor surface. It is postulated that oxygen is stripped by Ni to form NiO upon electrical stress, contributing to the decrease in O{sub N} donor sates under the gate contact.

Ma, Xiao-Hua, E-mail: xhma@xidian.edu.cn, E-mail: yhao@xidian.edu.cn; Chen, Wei-Wei; Hou, Bin; Zhu, Jie-Jie [School of Advanced Materials and Nanotechnology, Xidian University, Xi'an 710071 (China); Key Lab of Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071 (China); Zhang, Kai; Zhang, Jin-Cheng; Zheng, Xue-Feng; Hao, Yue, E-mail: xhma@xidian.edu.cn, E-mail: yhao@xidian.edu.cn [Key Lab of Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071 (China)

2014-03-03

358

High PAE pseudomorphic InGaAs\\/AlGaAs HEMT X-band high power amplifiers  

Microsoft Academic Search

A systematic experiment was designed and implemented to optimize the 0.25 ?m gate InGaAs\\/AlGaAs pseudomorphic HEMT for the fabrication of high power X-band monolithic amplifiers. The material structure and gate recess process were engineered such that the device breakdown voltage was optimized without sacrificing gain and efficiency. A two-stage high power X-band monolithic amplifier based on the optimized device has

Y. C. Chen; C. S. Wu; C. K. Pao; M. Cole; Z. Bardai; L. D. Hou; T. A. Midford; T. C. Cisco

1995-01-01

359

Amorphous and nanocrystalline phase formation in highly-driven Al-based binary alloys  

SciTech Connect

Remarkable advances have been made since rapid solidification was first introduced to the field of materials science and technology. New types of materials such as amorphous alloys and nanostructure materials have been developed as a result of rapid solidification techniques. While these advances are, in many respects, ground breaking, much remains to be discerned concerning the fundamental relationships that exist between a liquid and a rapidly solidified solid. The scope of the current dissertation involves an extensive set of experimental, analytical, and computational studies designed to increase the overall understanding of morphological selection, phase competition, and structural hierarchy that occurs under far-from equilibrium conditions. High pressure gas atomization and Cu-block melt-spinning are the two different rapid solidification techniques applied in this study. The research is mainly focused on Al-Si and Al-Sm alloy systems. Silicon and samarium produce different, yet favorable, systems for exploration when alloyed with aluminum under far-from equilibrium conditions. One of the main differences comes from the positions of their respective T{sub 0} curves, which makes Al-Si a good candidate for solubility extension while the plunging T{sub 0} line in Al-Sm promotes glass formation. The rapidly solidified gas-atomized Al-Si powders within a composition range of 15 to 50 wt% Si are examined using scanning and transmission electron microscopy. The non-equilibrium partitioning and morphological selection observed by examining powders at different size classes are described via a microstructure map. The interface velocities and the amount of undercooling present in the powders are estimated from measured eutectic spacings based on Jackson-Hunt (JH) and Trivedi-Magnin-Kurz (TMK) models, which permit a direct comparison of theoretical predictions. For an average particle size of 10 {micro}m with a Peclet number of {approx}0.2, JH and TMK deviate from each other. This deviation indicates an adiabatic type solidification path where heat of fusion is reabsorbed. It is interesting that this particle size range is also consistent with the appearance of a microcellular growth. While no glass formation is observed within this system, the smallest size powders appear to consist of a mixture of nanocrystalline Si and Al. Al-Sm alloys have been investigated within a composition range of 34 to 42 wt% Sm. Gas atomized powders of Al-Sm are investigated to explore the morphological and structural hierarchy that correlates with different degrees of departure from full equilibrium conditions. The resultant powders show a variety of structural selection with respect to amount of undercooling, with an amorphous structure appearing at the highest cooling rates. Because of the chaotic nature of gas atomization, Cu-block melt-spinning is used to produce a homogeneous amorphous structure. The as-quenched structure within Al-34 to 42 wt% Sm consists of nanocrystalline fcc-Al (on the order of 5 nm) embedded in an amorphous matrix. The nucleation density of fcc-Al after initial crystallization is on the order of 10{sup 22}-10{sup 23} m{sup -3}, which is 10{sup 5}-10{sup 6} orders of magnitude higher than what classical nucleation theory predicts. Detailed analysis of liquid and as-quenched structures using high energy synchrotron X-ray diffraction, high energy transmission electron microscopy, and atom probe tomography techniques revealed an Al-Sm network similar in appearance to a medium range order (MRO) structure. A model whereby these MRO clusters promote the observed high nucleation density of fcc-Al nanocrystals is proposed. The devitrification path was identified using high temperature, in-situ, high energy synchrotron X-ray diffraction techniques and the crystallization kinetics were described using an analytical Johnson-Mehl-Avrami (JMA) approach.

Kalay, Yunus Eren

2008-10-15

360

Adsorption of methylamine on Ni 3 Al(111) and NiAl(110)--a high resolution photoelectron spectroscopy and density functional theory study.  

PubMed

Methylamine adsorption on the ordered Ni(3)Al(111) and NiAl(110) surfaces has been investigated by high resolution photoelectron spectroscopy and density functional theory calculations. Methylamine adsorbs molecularly at both surfaces at low temperature (90 K). The experiments show that methylamine interacts with the surface aluminium atoms on both surfaces, resulting in a positive binding energy shift relative to the Al 2p bulk contributions. A shift towards lower binding energy is also observed on NiAl(110) attributed to first and second layer surface Al atoms not bonded to methylamine. According to total energy calculations methylamine binds through its N atom to Al on-top sites on NiAl(110) while the Ni on-top site is found to be slightly preferred over the Al on-top site on Ni(3)Al(111). Calculated adsorbate induced shifts are, however, in good agreement with the experimental values only when methylamine is situated in the Al on-top site on both surfaces. In both cases, a lone pair bonding mechanism is found. PMID:21403217

Borck, Ø; Svenum, I-H; Walle, L E; Andersen, T H; Schulte, K; Borg, A

2010-10-01

361

The role of stress waves in thoracic visceral injury from blast loading: modification of stress transmission by foams and high-density materials.  

PubMed

Materials have been applied to the thoracic wall of anaesthetised experimental animals exposed to blast overpressure to investigate the coupling of direct stress waves into the thorax and the relative contribution of compressive stress waves and gross thoracic compression to lung injury. The ultimate purpose of the work is to develop effective personal protection from the primary effects of blast overpressure--efficient protection can only be achieved if the injury mechanism is identified and characterized. Foam materials acted as acoustic couplers and resulted in a significant augmentation of the visceral injury; decoupling and elimination of injury were achieved by application of a high acoustic impedance layer on top of the foam. In vitro experiments studying stress wave transmission from air through various layers into an anechoic water chamber showed a significant increase in power transmitted by the foams, principally at high frequencies. Material such as copper or resin bonded Kevlar incorporated as a facing upon the foam achieved substantial decoupling at high frequencies--low frequency transmission was largely unaffected. An acoustic transmission model replicated the coupling of the blast waves into the anechoic water chamber. The studies suggest that direct transmission of stress waves plays a dominant role in lung parenchymal injury from blast loading and that gross thoracic compression is not the primary injury mechanism. Acoustic decoupling principles may therefore be employed to reduce the direct stress coupled into the body and thus reduce the severity of lung injury--the most simple decoupler is a high acoustic impedance material as a facing upon a foam, but decoupling layers may be optimized using acoustic transmission models. Conventional impacts producing high body wall velocities will also lead to stress wave generation and transmission--stress wave effects may dominate the visceral response to the impact with direct compression and shear contributing little to the aetiology of the injury. PMID:2050704

Cooper, G J; Townend, D J; Cater, S R; Pearce, B P

1991-01-01

362

New insulating materials and their use to achieve high operating stresses in electrostatic machines  

NASA Astrophysics Data System (ADS)

Compressed gas insulation has provided the main insulation for sustaining terminal voltages of electrostatic accelerators. Essentially coaxial geometry is used with mechanical support of the terminal achieved by long columns which also support the acceleration tubes. Because of the vacuum insulation in the acceleration tubes, the electric gradient along the columns is typically 10-20 kV/cm, whereas the radial gas gap can operate at stresses about ten times larger. Until now, the terminal support has always been located in the low stress axial direction along the column and not in the radial high stress region. This paper is concerned with support insulation to be used in the radial direction. Advantages of radial supports include: simpler, more compact column structures, higher total voltages, and support of discrete stress redistribution electrodes such as vivitron. Important factors to the design of radial support insulators include the insulation constraints imposed by the gas gap, mechanical contact to the solid insulator, and basic limits of gas-solid dielectric interfaces. The gas gap insulation strength is shown to be limited by surface microirregularities and this accounts for electrode area and pressure effects. Based on the gas gap requirements, a design strategy for the insulators is developed. Epoxy is employed as the dielectric to allow the use of cast-in metal inserts at the ends. The inserts provide mechanical contact, shielding of the triple junction, and redistribution of the interface electric stresses. By careful design, the electric stress on the interface is made lower than that in the plain coaxial electrode gap. Practical experience shows that voltage increases linearly with insulator length and that designs achieve more than 10 MV/m into the multimegavolt region.

Cooke, Chathan M.

1986-02-01

363

Investigation of thermoelastic stresses induced at high altitudes on aircraft external fuel tanks  

NASA Astrophysics Data System (ADS)

As composite technology has grown over the past several decades, the use of composite materials in military applications has become more feasible and widely accepted. Although composite materials provide many benefits, including strength optimization and reduced weight, damage and repair of these materials creates an additional challenge, especially when operating in a marine environment, such as on a carrier deck. This is evident within the Navy, as excessive damage often leads to the scrapping of F/A-18 External Fuel Tanks. This damage comes in many forms, the most elusive of which is delamination. Often the delamination found on the tanks is beyond repairable limits and the cause unknown, making it difficult to predict and prevent. The purpose of this investigation was to study the structure of the Navy's 330 gallon External Fuel Tanks and investigate one potential cause of delamination, stresses induced at high altitudes by cold temperatures. A stress analysis was completed using finite element software, and validation of the model was accomplished through testing of a scale model specimen. Due to the difficulties in modeling and predicting delamination, such as unknown presence of voids and understanding failure criteria, delamination was not modeled in Abaqus, rather stresses were observed and characteristics were studied to understand the potential for delamination within the layup. In addition, studies were performed to understand the effect of material properties and layup sequence on the stress distribution within the tank. Alternative design solutions are presented which could reduce the radial stresses within the tank, and recommendations are made for further study to understand the trade-offs between stress, cost, and manufacturability.

Mousseau, Stephanie Lynn Steber

364

Effect of high strain rates on peak stress in a Zr-based bulk metallic glass  

NASA Astrophysics Data System (ADS)

The mechanical behavior of Zr41.25Ti13.75Cu12.5Ni10Be22.5 (LM-1) has been extensively characterized under quasistatic loading conditions; however, its mechanical behavior under dynamic loading conditions is currently not well understood. A Split-Hopkinson pressure bar (SHPB) and a single-stage gas gun are employed to characterize the mechanical behavior of LM-1 in the strain-rate regime of 102-105/s. The SHPB experiments are conducted with a tapered insert design to mitigate the effects of stress concentrations and preferential failure at the specimen-insert interface. The higher strain-rate plate-impact compression-and-shear experiments are conducted by impacting a thick tungsten carbide (WC) flyer plate with a sandwich sample comprising a thin bulk metallic glass specimen between two thicker WC target plates. Specimens employed in the SHPB experiments failed in the gage-section at a peak stress of approximately 1.8 GPa. Specimens in the high strain-rate plate-impact experiments exhibited a flow stress in shear of approximately 0.9 GPa, regardless of the shear strain-rate. The flow stress under the plate-impact conditions was converted to an equivalent flow stress under uniaxial compression by assuming a von Mises-like material behavior and accounting for the plane strain conditions. The results of these experiments, when compared to the previous work conducted at quasistatic loading rates, indicate that the peak stress of LM-1 is essentially strain rate independent over the strain-rate range up to 105/s.

Sunny, George; Yuan, Fuping; Prakash, Vikas; Lewandowski, John

2008-11-01

365

Effect of high strain rates on peak stress in a Zr-based bulk metallic glass  

SciTech Connect

The mechanical behavior of Zr{sub 41.25}Ti{sub 13.75}Cu{sub 12.5}Ni{sub 10}Be{sub 22.5} (LM-1) has been extensively characterized under quasistatic loading conditions; however, its mechanical behavior under dynamic loading conditions is currently not well understood. A Split-Hopkinson pressure bar (SHPB) and a single-stage gas gun are employed to characterize the mechanical behavior of LM-1 in the strain-rate regime of 10{sup 2}-10{sup 5}/s. The SHPB experiments are conducted with a tapered insert design to mitigate the effects of stress concentrations and preferential failure at the specimen-insert interface. The higher strain-rate plate-impact compression-and-shear experiments are conducted by impacting a thick tungsten carbide (WC) flyer plate with a sandwich sample comprising a thin bulk metallic glass specimen between two thicker WC target plates. Specimens employed in the SHPB experiments failed in the gage-section at a peak stress of approximately 1.8 GPa. Specimens in the high strain-rate plate-impact experiments exhibited a flow stress in shear of approximately 0.9 GPa, regardless of the shear strain-rate. The flow stress under the plate-impact conditions was converted to an equivalent flow stress under uniaxial compression by assuming a von Mises-like material behavior and accounting for the plane strain conditions. The results of these experiments, when compared to the previous work conducted at quasistatic loading rates, indicate that the peak stress of LM-1 is essentially strain rate independent over the strain-rate range up to 10{sup 5}/s.

Sunny, George; Yuan Fuping; Prakash, Vikas [Department of Mechanical and Aerospace Engineering, Case Western Reserve University, Cleveland, Ohio 44106-7222 (United States); Lewandowski, John [Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106-7222 (United States)

2008-11-01

366

High density GaN/AlN quantum dots for deep UV LED with high quantum efficiency and temperature stability  

PubMed Central

High internal efficiency and high temperature stability ultraviolet (UV) light-emitting diodes (LEDs) at 308?nm were achieved using high density (2.5 × 109?cm?2) GaN/AlN quantum dots (QDs) grown by MOVPE. Photoluminescence shows the characteristic behaviors of QDs: nearly constant linewidth and emission energy, and linear dependence of the intensity with varying excitation power. More significantly, the radiative recombination was found to dominant from 15 to 300?K, with a high internal quantum efficiency of 62% even at room temperature. PMID:24898569

Yang, Weihuang; Li, Jinchai; Zhang, Yong; Huang, Po-Kai; Lu, Tien-Chang; Kuo, Hao-Chung; Li, Shuping; Yang, Xu; Chen, Hangyang; Liu, Dayi; Kang, Junyong

2014-01-01

367

Probing the electronic and vibrational structure of Au2Al2- and Au2Al2 using photoelectron spectroscopy and high resolution photoelectron imaging  

NASA Astrophysics Data System (ADS)

The electronic and vibrational structures of Au2Al2- and Au2Al2 have been investigated using photoelectron spectroscopy (PES), high-resolution photoelectron imaging, and theoretical calculations. Photoelectron spectra taken at high photon energies with a magnetic-bottle apparatus reveal numerous detachment transitions and a large energy gap for the neutral Au2Al2. Vibrationally resolved PE spectra are obtained using high-resolution photoelectron imaging for the ground state detachment transition of Au2Al2- at various photon energies (670.55-843.03 nm). An accurate electron affinity of 1.4438(8) eV is obtained for the Au2Al2 neutral cluster, as well as two vibrational frequencies at 57 ± 8 and 305 ± 13 cm-1. Hot bands transitions yield two vibrational frequencies for Au2Al2- at 57 ± 10 and 144 ± 12 cm-1. The obtained vibrational and electronic structure information is compared with density functional calculations, unequivocally confirming that both Au2Al2- and Au2Al2 possess C2v tetrahedral structures.

Lopez, Gary V.; Czekner, Joseph; Jian, Tian; Li, Wei-Li; Yang, Zheng; Wang, Lai-Sheng

2014-12-01

368

Probing the electronic and vibrational structure of Au2Al2 (-) and Au2Al2 using photoelectron spectroscopy and high resolution photoelectron imaging.  

PubMed

The electronic and vibrational structures of Au2Al2 (-) and Au2Al2 have been investigated using photoelectron spectroscopy (PES), high-resolution photoelectron imaging, and theoretical calculations. Photoelectron spectra taken at high photon energies with a magnetic-bottle apparatus reveal numerous detachment transitions and a large energy gap for the neutral Au2Al2. Vibrationally resolved PE spectra are obtained using high-resolution photoelectron imaging for the ground state detachment transition of Au2Al2 (-) at various photon energies (670.55-843.03 nm). An accurate electron affinity of 1.4438(8) eV is obtained for the Au2Al2 neutral cluster, as well as two vibrational frequencies at 57 ± 8 and 305 ± 13 cm(-1). Hot bands transitions yield two vibrational frequencies for Au2Al2 (-) at 57 ± 10 and 144 ± 12 cm(-1). The obtained vibrational and electronic structure information is compared with density functional calculations, unequivocally confirming that both Au2Al2 (-) and Au2Al2 possess C2v tetrahedral structures. PMID:25494751

Lopez, Gary V; Czekner, Joseph; Jian, Tian; Li, Wei-Li; Yang, Zheng; Wang, Lai-Sheng

2014-12-14

369

Coupled convection, segregation, and thermal stress modeling of low and high pressure Czochralski crystal growth  

NASA Astrophysics Data System (ADS)

Czochralski (Cz) method is a dominant single crystal growth technology for microelectronics applications. The demand for large diameter, low defect density, and uniform single crystals has motivated extensive research on Cz Si growth as well as high pressure liquid-encapsulated Czochralski (HPLEC) growth of III-V compound crystals, e.g., GaAs and InP. The transport phenomena of Cz growth is quite complex, particularly under the industrial growth conditions. The relationship between the process parameters and material properties is further complicated by convective flows of the gas if a high pressure condition is to be maintained for the growth. Two important factors that greatly influence the quality of the crystals, are: (a) impurity and dopant distributions and (b) thermal stresses in the crystal. A comprehensive model which incorporates all of the major physical mechanisms of HPLEC growth, has been developed. For numerical simulation, a novel scheme of combined finite volume (FVM) and finite element (FEM) methods has been devised for thermal-mechanical calculations, that uses multizone adaptive grid generation (MAGG) technique for both FVM and FEM modules. By combining the FVM for thermal transport modeling and FEM for solid stress calculations, valuable experiences in both fields have been employed, and a reliable and robust predictive tool for a large class of problems has been developed. This requires minimum effort and cost in both software development and computing environment and shows a great promise. It makes the investigation of coupled thermal convection and stress phenomena much easier to perform. A two time-scale, mass conserving scheme has also been developed to perform macro-segregation calculations. Both Cz and HPLEC (high pressure liquid-encapsulant Czochralski) processes have been investigated. It is found that both melt and gas convective flows have significant influence on stress distribution in the crystal. It is shown that pure conduction-based models can not make accurate predictions of stresses in as-grown crystals. Use of a heat transfer coefficient to account for gas convection as many investigators have done in the past, is therefore not sufficient. Both melt and gas convection must be accounted in all future models if more accurate flow, temperature and stress calculations are desired. The predicted stress distributions agree qualitatively with experimental results. For macro-segregation analysis, it is found that the dopant distribution is controlled by the melt flow pattern.

Zou, Yunfeng

370

High performance AlScN thin film based surface acoustic wave devices with large electromechanical coupling coefficient  

NASA Astrophysics Data System (ADS)

AlN and AlScN thin films with 27% scandium (Sc) were synthesized by DC magnetron sputtering deposition and used to fabricate surface acoustic wave (SAW) devices. Compared with AlN-based devices, the AlScN SAW devices exhibit much better transmission properties. Scandium doping results in electromechanical coupling coefficient, K2, in the range of 2.0% ˜ 2.2% for a wide normalized thickness range, more than a 300% increase compared to that of AlN-based SAW devices, thus demonstrating the potential applications of AlScN in high frequency resonators, sensors, and high efficiency energy harvesting devices. The coupling coefficients of the present AlScN based SAW devices are much higher than that of the theoretical calculation based on some assumptions for AlScN piezoelectric material properties, implying there is a need for in-depth investigations on the material properties of AlScN.

Wang, Wenbo; Mayrhofer, Patrick M.; He, Xingli; Gillinger, Manuel; Ye, Zhi; Wang, Xiaozhi; Bittner, Achim; Schmid, Ulrich; Luo, J. K.

2014-09-01

371

Characteristics of inclusions in high-Al steel during electroslag remelting process  

NASA Astrophysics Data System (ADS)

The characteristics of inclusions in high-Al steel refined by electroslag remelting (ESR) were investigated by image analysis, scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS). The results show that the size of almost all the inclusions observed in ESR ingots is less than 5 ?m. Inclusions smaller than 3 ?m take nearly 75% of the total inclusions observed in each ingot. Inclusions observed in ESR ingots are pure AlN as dominating precipitates and some fine spherical Al2O3 inclusions with a size of 1 ?m or less. It is also found that protective gas operation and slag deoxidation treatment during ESR process have significant effects on the number of inclusions smaller than 2 ?m but little effects on that of inclusions larger than 2 ?m. Thermodynamic calculations show that AlN inclusions are unable to precipitate in the liquid metal pool under the present experimental conditions, while the precipitation of AlN inclusions could take place at the solidifying front due to the microsegregation of Al and N in liquid steel during solidification.

Shi, Cheng-bin; Chen, Xi-chun; Guo, Han-jie

2012-04-01

372

Low resistance and high reflectivity Al based reflectors for p-GaN flip process  

NASA Astrophysics Data System (ADS)

We report a high-power light-emitting diode (LED) scheme based on aluminum (Al) reflector, commonly used as an n-GaN ohmic contact. The Cu doped In IIO 3 (5nm)/ITO (380nm) interlayer was deposited by electron beam evaporator and subsequently annealed at 500°C After annealing, we sputtered Al (400nm thick)/Ti-W (30nm) on the ITO interlayer to reflect the visible light. From the systematic experiment and the following analyses with InGaN/GaN multiple- quantum-well (MQW) LEDs, the reflectance of electrode based Al was measured to be ~ 90% at a wavelength of 450nm, which is higher than that of the common used Ni/Ag/Pt scheme. The forward- bias voltages of CIO/ITO/Al/Ti-W pelectrodes were as low as 3.2-3.3V. Furthermore, Al reflector showed higher thermal stability and lower leakage currents than those of typical Ag reflector, in which the mean leakage current of Ni/Ag and CIO/ITO/Al/Ti-W contacts were estimated to be 0.54, 0.12uA at an injection current of -5V, respectively.

Chae, Seung Wan; Ko, Kun Yoo; Kim, Dong Woo; Hwang, Seok Min; Park, Hyung Jin; Kim, Je Won; Kim, Yong Chun

2007-02-01

373

Interfacial characteristics of N-incorporated HfAlO high-k thin films  

NASA Astrophysics Data System (ADS)

The characteristics of N-incorporated HfO2-Al2O3 alloy films (HfAlO) were investigated by high-resolution x-ray photoelectron spectroscopy (XPS), near-edge x-ray absorption fine structure (NEXAFS), medium-energy ion scattering (MEIS), and capacitance-voltage measurements. The core-level energy states, Hf4f and Al2p peaks of a 15Å thick film showed a shift to lower binding energy, resulting from the incorporation of nitrogen into the films. Absorption spectra of the OK edge of HfAlO were affected mainly by the Al2O3 in the film, and not by HfO2 after nitridation by NH3 annealing. The NEXAFS of NK edge and XPS data related to the chemical state suggested that the incorporated N atom is dominantly bonded to Al2O3, and not to HfO2. Moreover, MEIS results implied that there is a significant incorporation of N at the interface between the alloy film and Si. The incorporation of N effectively suppressed the leakage current without an increase in interfacial layer thickness, while the interfacial state of the N-incorporated films increased somewhat.

Cho, M.-H.; Moon, D. W.; Park, S. A.; Kim, Y. K.; Jeong, K.; Kang, S. K.; Ko, D.-H.; Doh, S. J.; Lee, J. H.; Lee, N. I.

2004-06-01

374

Precipitation in Al–Mg solid solution prepared by solidification under high pressure  

SciTech Connect

The precipitation in Al–Mg solid solution containing 21.6 at.% Mg prepared by solidification under 2 GPa was investigated. The results show that the ?-Al{sub 12}Mg{sub 17} phase is formed and the ?? phase cannot be observed in the solid solution during ageing process. The precipitation of ? and ? phases takes place in a non-uniform manner during heating process, i.e. the ? and ? phases are first formed in the interdendritic region, which is caused by the inhomogeneous distribution of Mg atoms in the solid solution solidified under high pressure. Peak splitting of X-ray diffraction patterns of Al(Mg) solid solution appears, and then disappears when the samples are aged at 423 K for different times, due to the non-uniform precipitation in Al–Mg solid solution. The direct transformation from the ? to ? phase is observed after ageing at 423 K for 24 h. It is considered that the ? phase is formed through a peritectoid reaction of ? + ? ? ? which needs the diffusion of Mg atoms across the interface of ?/? phases. - Highlights: • The ? phase is formed and the ?? phase is be observed in Al(Mg) solid solution. • Peak splitting of XRD pattern of Al(Mg) solid solution appears during aged at 150 °C. • The ? phase is formed through a peritectoid reaction of ? + ? ? ?.

Jie, J.C., E-mail: jiejc@dlut.edu.cn [Laboratory of Special Processing of Raw Materials and School of Material Science and Engineering, Dalian University of Technology, Dalian, 116024 (China); School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Wang, H.W.; Zou, C.M.; Wei, Z.J. [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Li, T.J. [Laboratory of Special Processing of Raw Materials and School of Material Science and Engineering, Dalian University of Technology, Dalian, 116024 (China)

2014-01-15

375

Hydrogen incorporation in stishovite at high pressure and symmetric hydrogen bonding in N-AlOOH  

E-print Network

Hydrogen incorporation in stishovite at high pressure and symmetric hydrogen bonding in N significant amounts of hydrogen in stishovite under lower-mantle conditions. The enthalpy of solution pressure and temperature. We predict asymmetric hydrogen bonding in the stishovite^N-AlOOH solid solution

Stixrude, Lars

376

Conducting High Cycle Fatigue Strength Step Tests on Gamma TiAl  

NASA Technical Reports Server (NTRS)

High cycle fatigue strength testing of gamma TiAl by the step test method is investigated. A design of experiments was implemented to determine if the coaxing effect occurred during testing. Since coaxing was not observed, step testing was deemed a suitable method to define the fatigue strength at 106 cycles.

Lerch, Brad; Draper, Sue; Pereira, J. Mike

2002-01-01

377

Fabrication of Highly-Oleophobic and Superhydrophobic Surfaces on Microtextured al Substrates  

NASA Astrophysics Data System (ADS)

Theoretical calculations suggest that creating highly-oleophobic surfaces would require a surface energy lower than that of any known materials. In the present work, we demonstrate microtextured Al substrate surfaces with veins-like micro/nanostructures displaying apparent contact angles (CA) greater than 120°, even with nitromethane (surface tension ?1 = 37 mN/m). The Al substrate was microtextured by a chemical solution mixed by zinc nitrate hexahydrate, hexamethyltetramine and a little of hydrofluoric acid. A fluoroalkylsilane (FAS) agent was used to tune the surface wettability. The Al substrates were microtextured by veins-like micro/nanostructures and generating a solid-liquid-vapor composite interface. Combination with FAS modification, the Al surfaces resulted in an oleophobicity with CA for nitromethane was 126.3° (152.7° for diethylene glycol, ?1 = 45.2 mN/m). In addition, the Al surfaces demonstrated a low rolling-off angle with < 6° even for diethylene glycol. However, nitromethane droplet favored to pin on the sample surface even the sample stage is tilted to 90°. It is noted that this highly-oleophobic behavior is induced mainly by topography, which form a composite surface of air and solid with oil drop sitting partially on air. The results are expected to promote the study on self-cleaning applications, especially in the condition with oil contaminations.

Liu, Changsong; Zhou, Jigen; Zheng, Dongmei; Wan, Yong; Li, Zhiwen

2011-06-01

378

A high-throughput virus-induced gene silencing protocol identifies genes involved in multi-stress tolerance  

PubMed Central

Background Understanding the function of a particular gene under various stresses is important for engineering plants for broad-spectrum stress tolerance. Although virus-induced gene silencing (VIGS) has been used to characterize genes involved in abiotic stress tolerance, currently available gene silencing and stress imposition methodology at the whole plant level is not suitable for high-throughput functional analyses of genes. This demands a robust and reliable methodology for characterizing genes involved in abiotic and multi-stress tolerance. Results Our methodology employs VIGS-based gene silencing in leaf disks combined with simple stress imposition and effect quantification methodologies for easy and faster characterization of genes involved in abiotic and multi-stress tolerance. By subjecting leaf disks from gene-silenced plants to various abiotic stresses and inoculating silenced plants with various pathogens, we show the involvement of several genes for multi-stress tolerance. In addition, we demonstrate that VIGS can be used to characterize genes involved in thermotolerance. Our results also showed the functional relevance of NtEDS1 in abiotic stress, NbRBX1 and NbCTR1 in oxidative stress; NtRAR1 and NtNPR1 in salinity stress; NbSOS1 and NbHSP101 in biotic stress; and NtEDS1, NbETR1, NbWRKY2 and NbMYC2 in thermotolerance. Conclusions In addition to widening the application of VIGS, we developed a robust, easy and high-throughput methodology for functional characterization of genes involved in multi-stress tolerance. PMID:24289810

2013-01-01

379

Mosaic-shaped cathode for highly durable solid oxide fuel cell under thermal stress  

NASA Astrophysics Data System (ADS)

In this study, we propose a novel “mosaic structure” for a SOFC (solid oxide fuel cell) cathode with high thermal expansion to improve the stability against thermal stress. Self-organizing mosaic-shaped cathode has been successfully achieved by controlling the amount of binder in the dip-coating solution. The anode-supported cell with mosaic-shaped cathode shows itself to be highly durable performance for rapid thermal cycles, however, the performance of the cell with a non-mosaic cathode exhibits severe deterioration originated from the delamination at the cathode/electrolyte interface after 7 thermal cycles. The thermal stability of an SOFC cathode can be evidently improved by controlling the surface morphology. In view of the importance of the thermal expansion properties of the cathode, the effects of cathode morphology on the thermal stress stability are discussed.

Joo, Jong Hoon; Jeong, Jaewon; Kim, Se Young; Yoo, Chung-Yul; Jung, Doh Won; Park, Hee Jung; Kwak, Chan; Yu, Ji Haeng

2014-02-01

380

SEMICONDUCTOR DEVICES: Analysis of trigger behavior of high voltage LDMOS under TLP and VFTLP stress  

NASA Astrophysics Data System (ADS)

The physical mechanisms triggering electrostatic discharge (ESD) in high voltage LDMOS power transistors (> 160 V) under transmission line pulsing (TLP) and very fast transmission line pulsing (VFTLP) stress are investigated by TCAD simulations using a set of macroscopic physical models related to previous studies implemented in Sentaurus Device. Under VFTLP stress, it is observed that the triggering voltage of the high voltage LDMOS obviously increases, which is a unique phenomenon compared with the low voltage ESD protection devices like NMOS and SCR. The relationship between the triggering voltage increase and the parasitic capacitances is also analyzed in detail. A compact equivalent circuit schematic is presented according to the investigated phenomena. An improved structure to alleviate this effect is also proposed and confirmed by the experiments.

Jing, Zhu; Qinsong, Qian; Weifeng, Sun; Siyang, Liu

2010-01-01

381

Content analysis to detect high stress in oral interviews and text documents  

NASA Technical Reports Server (NTRS)

A system of interrogation to estimate whether a subject of interrogation is likely experiencing high stress, emotional volatility and/or internal conflict in the subject's responses to an interviewer's questions. The system applies one or more of four procedures, a first statistical analysis, a second statistical analysis, a third analysis and a heat map analysis, to identify one or more documents containing the subject's responses for which further examination is recommended. Words in the documents are characterized in terms of dimensions representing different classes of emotions and states of mind, in which the subject's responses that manifest high stress, emotional volatility and/or internal conflict are identified. A heat map visually displays the dimensions manifested by the subject's responses in different colors, textures, geometric shapes or other visually distinguishable indicia.

Thirumalainambi, Rajkumar (Inventor); Jorgensen, Charles C. (Inventor)

2012-01-01

382

Transcriptomic Analysis of Petunia hybrida in Response to Salt Stress Using High Throughput RNA Sequencing  

PubMed Central

Salinity and drought stress are the primary cause of crop losses worldwide. In sodic saline soils sodium chloride (NaCl) disrupts normal plant growth and development. The complex interactions of plant systems with abiotic stress have made RNA sequencing a more holistic and appealing approach to study transcriptome level responses in a single cell and/or tissue. In this work, we determined the Petunia transcriptome response to NaCl stress by sequencing leaf samples and assembling 196 million Illumina reads with Trinity software. Using our reference transcriptome we identified more than 7,000 genes that were differentially expressed within 24 h of acute NaCl stress. The proposed transcriptome can also be used as an excellent tool for biological and bioinformatics in the absence of an available Petunia genome and it is available at the SOL Genomics Network (SGN) http://solgenomics.net. Genes related to regulation of reactive oxygen species, transport, and signal transductions as well as novel and undescribed transcripts were among those differentially expressed in response to salt stress. The candidate genes identified in this study can be applied as markers for breeding or to genetically engineer plants to enhance salt tolerance. Gene Ontology analyses indicated that most of the NaCl damage happened at 24 h inducing genotoxicity, affecting transport and organelles due to the high concentration of Na+ ions. Finally, we report a modification to the library preparation protocol whereby cDNA samples were bar-coded with non-HPLC purified primers, without affecting the quality and quantity of the RNA-seq data. The methodological improvement presented here could substantially reduce the cost of sample preparation for future high-throughput RNA sequencing experiments. PMID:24722556

Villarino, Gonzalo H.; Bombarely, Aureliano; Giovannoni, James J.; Scanlon, Michael J.; Mattson, Neil S.

2014-01-01

383

Effect of aging on the dependence of fatigue crack growth behavior on mean stress (stress ratio) in the {beta}-titanium alloy: Ti-10V-2Fe-3Al  

SciTech Connect

The effect of mean stress or stress ratio, R, on fatigue crack growth (FCG) behavior of {alpha}-aged and {omega}-aged microstructures of the beta titanium alloy Ti-10V-2Fe-3Al was investigated. While the mean stress had a negligible effect on the FCG behavior of the {alpha}-aged microstructure, a strong effect was observed in the {omega}-aged microstructure. In particular the value of threshold stress intensity range ({Delta}K{sub th}) exhibited a strong dependence on R in the {omega}-aged microstructure, while this dependence was weak in the {alpha}-aged microstructure. These effects seem to arise primarily from fracture surface roughness induced crack closure. Crack closure levels for the {alpha}-aged microstructure were found to be very low compared to those for the {omega}-aged microstructure. Transmission and scanning electron microscopic studies of microstructures and fracture surfaces were performed to gain insight into the deformation characteristics and crack propagation mechanisms, respectively in these microstructures. The microstructure-induced differences in fatigue crack growth behavior are rationalized in terms of the effect of aging on slip and crack closure.

Jha, S.K.; Ravichandran, K.S.

1999-07-01

384

High-performance E-mode AlGaN\\/GaN HEMTs  

Microsoft Academic Search

Enhancement-mode AlGaN\\/GaN high electron-mobility transistors have been fabricated with a gate length of 160 nm. The use of gate recess combined with a fluorine-based surface treatment under the gate produced devices with a threshold voltage of +0.1 V. The combination of very high transconductance (> 400 mS\\/mm) and low gate leakage allows unprecedented output current levels in excess of 1.2

T. Palacios; C.-S. Suh; A. Chakraborty; S. Keller; S. P. DenBaars; U. K. Mishra

2006-01-01

385

Tribological adaptability of TiAlCrN PVD coatings under high performance dry machining conditions  

Microsoft Academic Search

The application of ternary nitride (Ti,Cr,Al)N coatings with high aluminum content deposited by a new plasma enhanced cathode method results in a significant cutting tool life improvement. To investigate this improvement the tool life of end milling cutting tools was studied under severe conditions associated with the high speed dry machining of H13 steel (hardness HRC 50). Investigations of the

G. S. Fox-Rabinovich; K. Yamomoto; S. C. Veldhuis; A. I. Kovalev; G. K. Dosbaeva

2005-01-01

386

High-power AlGaN\\/GaN HEMTs for Ka-band applications  

Microsoft Academic Search

We report on the fabrication and high-frequency characterization of AlGaN\\/GaN high-electron mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). In devices with a gate length of 160 nm, a record power density of 10.5 W\\/mm with 34% power added efficiency (PAE) has been measured at 40 GHz in MOCVD-grown HEMTs biased at VDS=30

T. Palacios; A. Chakraborty; S. Rajan; C. Poblenz; S. Keller; S. P. DenBaars; J. S. Speck; U. K. Mishra

2005-01-01

387

Structure and Orientation Behavior of Highly Oriented Polymers Under Tensile and Compressive Stresses  

NASA Astrophysics Data System (ADS)

The birefringence of Kevlar 49^ circler fibers has been shown to decrease with compressive strain, suggesting that structure changes under compression involve decreasing crystallite orientation. This mechanism appears to be the inverse of that occurring under tension, for which increasing crystallite orientation has been reported to occur, leading to non-linear elasticity. A contrast between the effects of both stress modes on structure (orientation) response is presented. While birefringence presents itself as a technically convenient and economically attractive technique for this type of study, caution must be exercised when interpreting results from measurements under stress. For highly crystalline fibers, experiments have led to the attribution of the observed changes in birefringence almost entirely to crystallite orientation. This study presents an analysis of the different contributions to birefringence under stress. X-ray diffraction experiments have been performed for Kevlar 49^ circler fibers under tensile stress. Results from crystal orientation cannot account for changes observed in birefringence. Moreover, they appear to account only for a small fraction of the total change. These observations suggest significant contributions from other sources. Theoretical calculations have been carried out under simulated stress conditions to quantify the effect of molecular deformation on the observed birefringence of Kevlar 49^circler fibers. The results have been obtained using semi-empirical molecular orbital calculations with the AM1 Hamiltonian in MOPAC. This analysis has been applied to poly(p^' -phenylene terephthalamide) (PPTA) and polyethylene (PE) chains. For PE, stress-free computations were performed on segments of up to 50 -(CH_2-CH _2)- units. Strains up to 1% were applied on segments of up to 40 units. For PPTA, segments of up to 5 PTA units were analyzed. Strain-free results indicate a linear dependence of molecular polarizability on chain length. The treatment yields also a linear trend for the effect of strain on the polarizability of PE segments. Thus, the calculations predict a plane in 3-D space for the dependence of molecular polarizability on both chain size and strain. The predicted molecular polarizabilities are used to evaluate the effect of stress on birefringence of the idealized polymers, by applying existing internal-field theory. Results indicate significant effects from molecules deforming under the stress field.

Garcia-Ramirez, Rafael

388

Behavioral effects of adult rats concurrently exposed to high doses of oral manganese and restraint stress  

Microsoft Academic Search

The behavioral effects of concurrent exposure of high doses of manganese (Mn) and restraint stress were assessed in adult rats. Male Sprague-Dawley rats (250–300g) received 0, 275 and 550mg\\/kg\\/day of Mn in the drinking water for 19 weeks. Each group was divided into two subgroups. Animals in one subgroup were restrained for 2h\\/day. During the treatment period, food and water

Margarita Torrente; M. Teresa Colomina; José L. Domingo

2005-01-01

389

Neither Perceived Job Stress Nor Individual Cardiovascular Reactivity Predict High Blood Pressure  

Microsoft Academic Search

We have reported that high job strain was associated with a significantly higher diastolic blood pressure (DBP) of 4.5 mm Hg during the working hours, irrespective of BP reactivity to a stress test. We report the final results of the first 5-year follow-up study, which aimed to assess the respective influences of perception of professional strain and cardiovascular reactivity to

Jean Pierre Fauvel; Pierre Quelin; Jean-Pierre Rigaud; Maurice Laville; Michel Ducher

2010-01-01

390

Muscle-like high-stress dielectric elastomer actuators with oil capsules  

NASA Astrophysics Data System (ADS)

Despite being capable of generating large strains, dielectric elastomer actuators (DEAs) are short of strength. Often, they cannot produce enough stress or as much work as that achievable by human elbow muscles. Their maximum actuation capacity is limited by the electrical breakdown of dielectric elastomers. Often, failures of these soft actuators are pre-mature and localized at the weakest spot under high field and high stress. Localized breakdowns, such as electrical arcing, thermal runaway and punctures, could spread to ultimately cause rupture if they were not stopped. This work shows that dielectric oil immersion and self-clearable electrodes nibbed the buds of localized breakdowns from DEAs. Dielectric oil encapsulation in soft-membrane capsules was found to help the DEA sustain an ultra-high electrical breakdown field of 835\\;MV{{m}^{-1}}, which is 46% higher than the electrical breakdown strength of the dry DEA in air at 570\\;MV{\\mkern 1mu} {{m}^{-1}}. Because of the increased apparent dielectric strength, this oil-capsuled DEA realizes a higher maximum isotonic work density of up to 31.51Jk{{g}^{-1}}, which is 43.8% higher than that realized by the DEA in air. Meanwhile, it produces higher maximum isometric stress of up to 1.05 MPa, which is 75% higher than that produced by the DEA in air. Such improved actuator performances are comparable to those achieved by human flexor muscles, which can exert up to 1.2 MPa during elbow flexion. This muscle-like, high-stress dielectric elastomeric actuation is very promising to drive future human-like robots.

La, Thanh-Giang; Lau, Gih-Keong; Shiau, Li-Lynn; Wei-Yee Tan, Adrian

2014-10-01

391

Sleep disturbances in highly stress reactive mice: Modeling endophenotypes of major depression  

Microsoft Academic Search

Background  Neuronal mechanisms underlying affective disorders such as major depression (MD) are still poorly understood. By selectively\\u000a breeding mice for high (HR), intermediate (IR), or low (LR) reactivity of the hypothalamic-pituitary-adrenocortical (HPA)\\u000a axis, we recently established a new genetic animal model of extremes in stress reactivity (SR). Studies characterizing this\\u000a SR mouse model on the behavioral, endocrine, and neurobiological levels revealed

Thomas Fenzl; Chadi Touma; Christoph PN Romanowski; Jörg Ruschel; Florian Holsboer; Rainer Landgraf; Mayumi Kimura; Alexander Yassouridis

2011-01-01

392

Application of the embedded polariscope photoelastic technique to the stress analysis of a high pressure tee  

E-print Network

temperature analysis which are shown by Table 1. The first of these is the close xnatching of the Poisson's ratios of the resins and the engineering materials at room temperature. At the critical temperature of the resin there is a significant difference... for the degree of MASTER OF SCIENCE May 1969 Major Subject: Aerospace Engineering APPLICATION OF THE EMBEDDED POLARISCOPE PHOTOELASTIC TECHNIQUE TO THE STRESS ANALYSIS OF A HIGH PRESSURE TEE A Thesis by THOMAS ARTHUR DOYLE Approved as to style...

Doyle, Thomas Arthur

1969-01-01

393

Improvement in rolling workability of Fe3Al by high-speed rolling  

NASA Astrophysics Data System (ADS)

High-speed rolling is expected to improve the deformability of difficult-to-work alloys. In this work, high-speed rolling was applied to Fe3Al, and the rolling workability was investigated. Fe-28%Al was prepared by plasma arc melting and multi-pass hot-rolled to a sheet 2 mm in thickness, followed by heat-treatment. Both the hot-rolling and heat-treatment were carried out at 1173 K. These specimens were rolled in a one-pass operation with a thickness reduction of 30 % at 1000 m/min in the temperature range from 573 to 973 K. Rolling at 5 m/min was also conducted for comparison. Sound sheets without defects or cracks were obtained even at 673 K in the high-speed rolling, while sound sheets were obtained only above 1173 K in the low-speed rolling. EBSD analysis showed that fine grains were formed either after the high-speed rolling at 873 K or after the low-speed rolling at 1073 K. Vickers hardness is not sensitive to the rolling speed below 773 K and decreased above 773 K and 1173 K in the high-speed rolling and low-speed rolling, respectively. The rolling workability of Fe3Al was significantly improved by the high-speed rolling.

Muraoka, A.; Utsunomiya, H.; Matsumoto, R.; Sakai, T.

2012-08-01

394

Feasibility study of Nb3Al Rutherford cable for high field accelerator magnet application  

SciTech Connect

Feasibility study of Cu stabilized Nb{sub 3}Al strand and Rutherford cable for the application to high field accelerator magnets are being done at Fermilab in collaboration with NIMS. The Nb{sub 3}Al strand, which was developed and manufactured at NIMS in Japan, has a non-copper Jc of about 844 A/mm{sup 2} at 15 Tesla at 4.2 K, a copper content of 50%, and filament size of about 50 microns. Rutherford cables with 27 Nb{sub 3}Al strands of 1.03 mm diameter were fabricated and tested. Quench tests on a short cable were done to study its stability with only its self field, utilizing a high current transformer. A pair of 2 meter long Nb{sub 3}Al cables was tested extensively at CERN at 4.3 and 1.9 K up to 11 Tesla including its self field with a high transport current of 20.2 kA. In the low field test we observed instability near splices and in the central region. This is related to the flux-jump like behavior, because of excessive amount of Nb in the Nb{sub 3}Al strand. There is possibility that the Nb in Nb{sub 3}Al can cause instability below 2 Tesla field regions. We need further investigation on this problem. Above 8 Tesla, we observed quenches near the critical surface at fast ramp rate from 1000 to 3000 A/sec, with quench velocity over 100 m/sec. A small racetrack magnet was made using a 14 m of Rutherford cable and successfully tested up to 21.8 kA, corresponding to 8.7 T.

Yamada, R.; /Fermilab; Kikuchi, A.; /Tsukuba Magnet Lab.; Ambrosio, G.; Andreev, N.; Barzi, E.; Cooper, C.; Feher, S.; Kashikhin, V.V.; Lamm, M.; Novitski, I.; /Fermilab; Takeuchi, T.; /Tsukuba Magnet Lab.; Tartaglia, M.; Turrioni, D.; /Fermilab; Verweij, A.P.; /CERN; Wake, M.; Willering, G; /Tsukuba Magnet Lab.; Zlobin, A.V.; /Fermilab

2006-08-01

395

AlGaN/GaN High-Electron-Mobility Transistor Employing an Additional Gate for High-Voltage Switching Applications  

E-print Network

AlGaN/GaN High-Electron-Mobility Transistor Employing an Additional Gate for High-Voltage Switching 16, 2004; accepted May 10, 2005; published September 8, 2005) We have proposed and fabricated an AlGaN/GaN: GaN, AlGaN, HEMT, switch 1. Introduction GaN has attracted attention for high-power and high

Seo, Kwang Seok

396

CO2 laser scribe of chemically strengthened glass with high surface compressive stress  

NASA Astrophysics Data System (ADS)

Chemically strengthened glass is finding increasing use in handheld, IT and TV cover glass applications. Chemically strengthened glass, particularly with high (>600MPa) compressive stress (CS) and deeper depth of layer (DOL), enable to retain higher strength after damage than non-strengthened glass when its surface is abraded. Corning Gorilla® Glass has particularly proven to be advantageous over competition in this attribute. However, due to high compressive stress (CS) and Central Tension (CT) cutting ion-exchanged glass is extremely difficult and often unmanageable where ever the applications require dicing the chemically strengthened mother glass into smaller parts. We at Corning have developed a CO2 laser scribe and break method (LSB) to separate a single chemically strengthened glass sheet into plurality of devices. Furthermore, CO2 laser scribe and break method enables debris-free separation of glass with high edge strength due to its mirror-like edge finish. We have investigated laser scribe and break of chemically strengthened glass with surface compressive stress greater than 600 MPa. In this paper we present the results of CO2 scribe and break method and underlying laser scribing mechanisms. We demonstrated cross-scribe repetitively on GEN 2 size chemically strengthened glass substrates. Specimens for edge strength measurements of different thickness and CS/DOL glass were prepared using the laser scribe and break technique. The specimens were tested using the standard 4-point bend method and the results are presented.

Li, Xinghua; Vaddi, Butchi R.

2011-03-01

397

Investigation of the dynamic mechanical behavior of polyetheretherketone (PEEK) in the high stress tensile regime  

NASA Astrophysics Data System (ADS)

Due to its outstanding mechanical performance both in static and dynamic loading and its resistance up to very high temperatures, Polyetheretherketone (PEEK) has attracted many practical applications. The loaded contact state for the application of PEEK rolls as bearing elements was recently analyzed by the corresponding author. High irreversible deformations on the mantle side were caused by the rolling contact and thus the rolling performance is supposed to be strongly affected by the dynamic mechanical properties of this irreversibly deformed material. Tensile fatigue tests at various stress levels up to the thermally dominated fatigue regime were conducted in order to get information regarding the dynamic mechanical material behavior at high stress regimes. Two types of PEEK (annealed and untreated) were investigated and two load ratios, R, were used (0.1 and 0.5). During the fatigue tests extensometer strain, load and surface temperature were recorded and a quantitative hysteresis loop analysis with calculated secant modulus and dynamic modulus was performed. Furthermore, the concept of isocyclic stress-strain diagrams was applied to enlarge and confirm the results obtained from the hysteresis loop analysis. A sharp transition between thermally dominated and mechanically dominated fatigue regimes was found for both PEEK types (annealed and untreated) and for both load ratios. Moreover, the annealed PEEK was stiffer in the tensile fatigue tests than the untreated material. Both examined PEEK types showed distinct hardening throughout the fatigue tests which made them "more elastic" (higher stiffness and less damping).

Berer, M.; Major, Z.; Pinter, G.; Constantinescu, D. M.; Marsavina, L.

2014-11-01

398

Physiological and biochemical responses of Prorocentrum minimum to high light stress  

NASA Astrophysics Data System (ADS)

Prorocentrum minimum is a common bloomforming photosynthetic dinoflagellate found along the southern coast of Korea. To investigate the adaptive responses of P. minimum to high light stress, we measured growth rate, and generation of reactive oxidative species (ROS), superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) in cultures exposed to normal (NL) and high light levels (HL). The results showed that HL (800 ?mol m-2 s-1) inhibited growth of P. minimum, with maximal inhibition after 7-9 days. HL also increased the amount of ROS and MDA, suggesting that HL stress leads to oxidative damage and lipid peroxidation in this species. Under HL, we first detected superoxide on day 4 and H2O2 on day 5. We also detected SOD activity on day 5 and CAT activity on day 6. The level of lipid peroxidation, an indicator of cell death, was high on day 8. Addition of diphenyleneiodonium (DPI), an NAD(P)H inhibitor, decreased the levels of superoxide generation and lipid peroxidation. Our results indicate that the production of ROS which results from HL stress in P. minimum also induces antioxidative enzymes that counteract oxidative damage and allow P. minimum to survive.

Park, So Yun; Choi, Eun Seok; Hwang, Jinik; Kim, Donggiun; Ryu, Tae Kwon; Lee, Taek-Kyun

2009-12-01

399

High strength and utilizable ductility of bulk ultrafine-grained Cu-Al alloys  

NASA Astrophysics Data System (ADS)

Lack of plasticity is the main drawback for nearly all ultrafine-grained (UFG) materials, which restricts their practical applications. Bulk UFG Cu-Al alloys have been fabricated by using equal channel angular pressing technique. Its ductility was improved to exceed the criteria for structural utility while maintaining a high strength by designing the microstructure via alloying. Factors resulting in the simultaneously enhanced strength and ductility of UFG Cu-Al alloys are the formation of deformation twins and their extensive intersections facilitating accumulation of dislocations.

An, X. H.; Han, W. Z.; Huang, C. X.; Zhang, P.; Yang, G.; Wu, S. D.; Zhang, Z. F.

2008-05-01

400

High temperature structural investigation of the delafossite type compound CuAlO2  

Microsoft Academic Search

Crystal structure parameters were determined for the delafossite type compound CuAlO2 at 295, 450, 600, 750, 900, and 1200 K with single crystal high temperature X-ray diffraction technique. Anisotropic refinements result in conventional R values of 0.021, 0.027, 0.029, 0.030, 0.032, and 0.036 at respective temperatures. Crystals of CuAlO2 have the rhombohedral space group R3m with a = 2.8584(7), c

T. Ishiguro; N. Ishizawa; N. Mizutani; M. Kato

1982-01-01

401

High Temperature Aerogels in the Al2O3-SiO2 System  

NASA Technical Reports Server (NTRS)

Al2O3-SiO2 aerogels are of interest as constituents of thermal insulation systems for use at high temperatures. Al2O3 and mullite aerogels are expected to crystallize at higher temperatures than their SiO2 counterparts, hence avoiding the shrinkages that accompany the formation of lower temperature SiO2 phases and preserving pore structures into higher temperature regimes. The objective of this work is to determine the influence of processing parameters on shrinkage, gel structure (including surface area, pore size and distribution) and pyrolysis behavior.

Hurwitz, Frances I.; Aranda, Denisse V.; Gallagher, Meghan E.

2008-01-01

402

Solid state amorphization in the Al-Fe binary system during high energy milling  

SciTech Connect

In the present study, mechanical alloying (MA) of Al75Fe25 elemental powders mixture was carried out in argon atmosphere, using a high energy attritor ball mill. The microstructure of the milled products at different stages of milling was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The results showed that the amorphous phase content increased by increasing the milling time, and after 50 hours the amorphization process became complete. Heating the samples resulted in the crystallization of the synthesized amorphous alloys and the appearance of the equilibrium intermetallic compounds Al{sub 5}Fe{sub 2}.

Urban, P., E-mail: purban@us.es; Montes, J. M.; Cintas, J. [University of Seville, Department of Mechanical and Materials Engineering, ETSI, Camino de los Descubrimientos s/n, Seville, 41092 (Spain); Cuevas, F. G., E-mail: fgcuevas@dqcm.uhu.es [University of Huelva, Department of Chemistry and Materials Science, ETSI, Campus La Rábida, Carretera Palos s/n, Palos de la Frontera, Huelva, 21819 (Spain)

2013-12-16

403

Investigation on compressive behavior of Cu-35Ni-15Al alloy at high temperatures  

NASA Astrophysics Data System (ADS)

Microstructures and mechanical properties of Cu-35Ni-15Al alloy in cast and porous states were studied by scanning electron microscopy and compression tests. The influence of porosity, deformation temperature and loading rate on mechanical properties of the two kinds of alloys was investigated. The results show that the as cast alloy and porous alloys have almost the same phase constitution: Cu rich phase, Ni rich phase and K intermetallics. The yield strength of porous alloys increases continuously with decreasing porosity, the relationship between porosity and yield stress follows Gibson-Ashby equation. With decreasing deformation temperature, the yield strength of as cast alloy and porous alloy increase. With the increase of loading rate, the yield strength of these alloys shows an increasing trend. After compression, the microstructure of as cast alloy is more uniform, and porous alloys are more prone to have localized deformations.

Li, Cong; Chen, Jian; Li, Wei; Hu, Yongle; Ren, Yanjie; Qiu, Wei; He, Jianjun; Chen, Jianlin

2014-08-01

404

Effect of Diffusion Control Layer on Reverse Al-Induced Layer Exchange Process for High-Quality Ge/Al/Glass Structure  

NASA Astrophysics Data System (ADS)

Fabricating large-grained polycrystalline Ge (poly-Ge) thin films on conducting-layer coated glass is a promising approach to lower the manufacturing cost of high-efficiency III-V tandem solar cells. We investigated the self-organizing formation of poly-Ge/Al/glass structures by using Al-induced layer exchange. The layer exchange between amorphous Ge and Al layers was completed at a low temperature of 350°C. Forming the interlayer between Ge and Al, i.e., limiting the diffusion of Ge to Al lowered the Ge nucleation rate and then enlarged the grain size of the resulting poly-Ge layer. The natively oxidized Al interlayer, formed by exposing a thin Al membrane (2-nm thickness) to air for 180 min, led to the poly-Ge with grains 46 ?m in size. Moreover, the Ge layer was highly (111)-oriented. This Ge/Al/glass structure appears promising for use in the bottom cell of the III-V semiconductor based tandem solar cells, as well as in the epitaxial templates for aligned nanowires and other advanced materials.

Nakazawa, K.; Toko, K.; Suemasu, T.

2014-11-01

405

High Temperature Oxidation and Microstructural Evolution of Modified MCrAlY Coatings  

NASA Astrophysics Data System (ADS)

Thermal sprayed MCrAlY coatings are widely used as a bond coat in thermal barrier systems to protect the substrate from corrosion and high temperature oxidation and to improve the compatibility between the ceramic top coat and metallic substrate. In this paper, the high temperature oxidation resistance of MCrAlY coatings with modified compositions was evaluated; in particular, the effect of the addition of reactive and refractory elements (Ta, Re, Si, and Hf) was investigated. MCrAlY coatings were obtained by high velocity oxygen fuel spray and vacuum plasma spray techniques; samples were exposed to air at 1423 K (1150 °C) and the oxidation kinetics were evaluated by measuring the thickness of the thermally grown oxide (TGO) scale at several exposure times. Experimental data confirmed that the oxidation resistance of MCrAlY coatings is strictly related to the amount of the reactive and refractory elements in the starting powders and that a thorough understanding of the microstructural modifications taking place during oxidation is essential for controlling TGO growth and thermal barriers' durability.

Pulci, Giovanni; Tirillò, Jacopo; Marra, Francesco; Sarasini, Fabrizio; Bellucci, Alessandra; Valente, Teodoro; Bartuli, Cecilia

2013-11-01

406

AlN/3C-SiC composite plate enabling high-frequency and high-Q micromechanical resonators.  

PubMed

An AlN/3C-SiC composite layer enables the third-order quasi-symmetric (QS(3)) Lamb wave mode with a high quality factor (Q) characteristic and an ultra-high phase velocity up to 32395 ms(-1). A Lamb wave resonator utilizing the QS(3) mode exhibits a low motional impedance of 91 ? and a high Q of 5510 at a series resonance frequency (f(s)) of 2.92 GHz, resulting in the highest f(s)·Q product of 1.61 × 10(13) Hz among the suspended piezoelectric thin film resonators reported to date. PMID:22495881

Lin, Chih-Ming; Chen, Yung-Yu; Felmetsger, Valery V; Senesky, Debbie G; Pisano, Albert P

2012-05-22

407

High Power Wideband AlGaN/GaN HEMT Feedback Amplifier Module with Drain and Feedback Loop  

E-print Network

High Power Wideband AlGaN/GaN HEMT Feedback Amplifier Module with Drain and Feedback Loop amplifier module using AlGaN/GaN high electron mobility transistor (HEMT) has been developed that covers radars and communications systems. GaN-based HEMT's for high power applications at microwave frequencies

Itoh, Tatsuo

408

High-performance pentacene field-effect transistors using Al2O3 gate dielectrics prepared by atomic  

E-print Network

High-performance pentacene field-effect transistors using Al2O3 gate dielectrics prepared by atomic fabricated using Al2O3 as a gate dielectric material grown by atomic layer deposition (ALD). Hole mobility microscopy (AFM) images of pentacene films on Al2O3 treated with octadecyltrichlorosilane (OTS) revealed well

Wang, Zhong L.

409

In this paper, an AlGaN/GaN high electron mobility transistor (HEMT) device based on a  

E-print Network

205 Abstract In this paper, an AlGaN/GaN high electron mobility transistor (HEMT) device basedBm at 2 GHz have been demonstrated from the fabricated device. 1. Introduction In recent years, AlGaN/GaN noise amplifier and switch. Superior results have been reported in microwave power performance of AlGaN/GaN

Yang, Kyounghoon

410

Low Cost Al-Si Casting Alloy As In-Situ Composite for High Temperature Applications  

NASA Technical Reports Server (NTRS)

A new aluminum-silicon (Al-Si) alloy has been successfully developed at NASA- Marshall Space Flight Center (MSFC) that has significant improvement in tensile and fatigue strength at elevated temperatures (500 F-700 F). The alloy offers a number of benefits such as light weight, high hardness, low thermal expansion and high surface wear resistance. In hypereutectic form, this alloy is considered as an in-situ Al-Si composite with tensile strength of about 90% higher than the auto industry 390 alloy at 600 F. This composite is very economically produced by using either conventional permanent steel molds or die casting. The projected material cost is less than $0.90 per pound, and automotive components such as pistons can be cast for high production rate using conventional casting techniques with a low and fully accounted cost. Key Words: Metal matrix composites, In-situ composite, aluminum-silicon alloy, hypereutectic alloy, permanent mold casting, die casting.

Lee, Jonathan A.

2000-01-01

411

Reproductive parameters and oxidative stress status of male rats fed with low and high salt diet  

PubMed Central

BACKGROUND: Deficiency of minerals and micronutrients has been reported to impair the process of spermatogenesis. Historically, salt has been used by women on their husbands to increase their libido, however, the role of salt diet on sperm parameters are yet to be ascertained. AIM: The present study was designed to determine the effect of low and high salt diet on sperm parameters, oxidative status and reproductive hormone levels of male rats. MATERIALS AND METHODS: A total of 18 rats were divided into three groups: Group I: (control) received 0.3% salt diet, Group II: low salt (received 0.14% salt diet) and Group III: high salt (received 8% salt diet). All animals were treated for 6 weeks; after which epididymal sperm parameters; oxidative stress markers (malondialdehyde, glutathione, catalase and superoxide dismutase) in the testes and epididymal tissues, as well as follicle stimulating hormone (FSH), luteinizing hormone (LH) and testosterone levels were determined. RESULTS: The results showed decreased sperm count in the low salt diet rats while increased sperm count was observed in the high salt diet treated rats. Both low salt and high salt diet fed rats exhibited increased abnormal sperm cells and increased epididymal oxidative stress when compared with their respective control. FSH and testosterone levels were increased in the high salt fed rats while LH level was decreased when compared with the control values. CONCLUSION: This study suggests that both low and high salt diet play a negative role in the fertility of male rats. PMID:24672168

Iranloye, Bolanle O.; Oludare, Gabriel O.; Morakinyo, Ayodele O.; Esume, Naomi A.; Ekeh, Lucy C.

2013-01-01

412

A high quality AR coating for AlGaAs/GaAs solar cells  

SciTech Connect

The AR coating of the AlGaAs/GaAs solar cells should have the characteristics of passivating the surface as well as decreasing optical reflection because they have the chemically active AlGaAs layer. The CVD Si/sub 3/N/sub 4/ film has been found to be an excellent AR coating. The CVD Si/sub 3/N/sub 4/ presented low reflectance to give high efficiency over 18% both in the case of the bare cell and cell with the cover glass opposing to the theoretical prediction. The CVD Si/sub 3/N/sub 4/ tightly prevented the water vapor from the corrosion of the AlGaAs layer.

Mitsui, K.; Kato, M.; Matsuda, S.; Oda, T.; Yoshidu, S.; Yukimoto, Y.

1984-05-01

413

Nano features of Al/Au ultrasonic bond interface observed by high resolution transmission electron microscopy  

SciTech Connect

Nano-scale interfacial details of ultrasonic AlSi1 wire wedge bonding to a Au/Ni/Cu pad were investigated using high resolution transmission electron microscopy (HRTEM). The intermetallic phase Au{sub 8}Al{sub 3} formed locally due to diffusion and reaction activated by ultrasound at the Al/Au bond interface. Multilayer sub-interfaces roughly parallel to the wire/pad interface were observed among this phase, and interdiffusional features near the Au pad resembled interference patterns, alternately dark and bright bars. Solid-state diffusion theory cannot be used to explain why such a thick compound formed within milliseconds at room temperature. The major formation of metallurgical bonds was attributed to ultrasonic cyclic vibration.

Ji Hongjun [Harbin Institute of Technology Shenzhen Graduate School, HIT Campus, Shenzhen University Town, Xili, Shenzhen 518055 (China); State Key Laboratory of Advanced Welding Production Technology, Harbin Institute of Technology, 92, Xidazhi Street, Nangang, Harbin 150001 (China); Li Mingyu [Harbin Institute of Technology Shenzhen Graduate School, HIT Campus, Shenzhen University Town, Xili, Shenzhen 518055 (China)], E-mail: myli@hit.edu.cn; Kim, Jong-Myung; Kim, Dae-Won [Jeonnam Provincial College, Jeonnam 517-802 (Korea, Republic of); Wang Chunqing [State Key Laboratory of Advanced Welding Production Technology, Harbin Institute of Technology, 92, Xidazhi Street, Nangang, Harbin 150001 (China)

2008-10-15

414

High Density Hydrogen Storage System Demonstration Using NaAlH4 Based Complex Compound Hydrides  

SciTech Connect

This final report describes the motivations, activities and results of the hydrogen storage independent project "High Density Hydrogen Storage System Demonstration Using NaAlH4 Based Complex Compound Hydrides" performed by the United Technologies Research Center under the Department of Energy Hydrogen Program, contract # DE-FC36-02AL67610. The objectives of the project were to identify and address the key systems technologies associated with applying complex hydride materials, particularly ones which differ from those for conventional metal hydride based storage. This involved the design, fabrication and testing of two prototype systems based on the hydrogen storage material NaAlH4. Safety testing, catalysis studies, heat exchanger optimization, reaction kinetics modeling, thermochemical finite element analysis, powder densification development and material neutralization were elements included in the effort.

Daniel A. Mosher; Xia Tang; Ronald J. Brown; Sarah Arsenault; Salvatore Saitta; Bruce L. Laube; Robert H. Dold; Donald L. Anton

2007-07-27

415

A new type of Cu-Al-Ta shape memory alloy with high martensitic transformation temperature  

NASA Astrophysics Data System (ADS)

In this study, a new type of Cu-Al-Ta (Cu86Al12Ta2 wt%) shape memory alloy with high martensitic transformation temperature is explored. The microstructure, reversible martensitic transformation and shape memory properties are investigated by means of optical microscopy, back-scattered electron, electron probe microanalysis, x-ray diffraction, differential scanning calorimetry and tensile tests. It is proposed that Cu86Al12Ta2 alloy consists of a mixture of primarily {\\beta }_{1}^{\\prime} martensite and a little {\\gamma }_{1}^{\\prime} martensite and some different precipitates. The tiny thin-striped Ta2(Al,Cu)3 precipitate is predominant in the as-quenched condition, whereas the particle-shaped Cu(Al, Ta) precipitate is dominant after hot-rolling. Additionally, the dendritic-shaped ?1(Cu9Al4) phase begins to appear after hot-rolling, but it disappears when the sample is re-quenched. All studied samples have reversible martensitic transformation temperatures higher than 450?° C. The results show that two-step martensitic transformation behavior is observed for Cu86Al12Ta2 alloy in all three different conditions due to the transformations between ({\\beta }_{1}^{\\prime}+{\\gamma }_{1}^{\\prime}) martensites and the austenite parent phase. The results further show that the recovery ratios are almost 100% when the pre-strains are ?2.5%, then they gradually decrease with further increase of the pre-strains. The shape memory effects clearly increase as a result of increase of the pre-strains, up to a maximum value of 3.2%.

Wang, C. P.; Su, Y.; Y Yang, S.; Shi, Z.; Liu, X. J.

2014-02-01

416

Metagenomic Analysis of Stress Genes in Microbial Mat Communities from Antarctica and the High Arctic  

PubMed Central

Polar and alpine microbial communities experience a variety of environmental stresses, including perennial cold and freezing; however, knowledge of genomic responses to such conditions is still rudimentary. We analyzed the metagenomes of cyanobacterial mats from Arctic and Antarctic ice shelves, using high-throughput pyrosequencing to test the hypotheses that consortia from these extreme polar habitats were similar in terms of major phyla and subphyla and consequently in their potential responses to environmental stresses. Statistical comparisons of the protein-coding genes showed similarities between the mats from the two poles, with the majority of genes derived from Proteobacteria and Cyanobacteria; however, the relative proportions differed, with cyanobacterial genes more prevalent in the Antarctic mat metagenome. Other differences included a higher representation of Actinobacteria and Alphaproteobacteria in the Arctic metagenomes, which may reflect the greater access to diasporas from both adjacent ice-free lands and the open ocean. Genes coding for functional responses to environmental stress (exopolysaccharides, cold shock proteins, and membrane modifications) were found in all of the metagenomes. However, in keeping with the greater exposure of the Arctic to long-range pollutants, sequences assigned to copper homeostasis genes were statistically (30%) more abundant in the Arctic samples. In contrast, more reads matching the sigma B genes were identified in the Antarctic mat, likely reflecting the more severe osmotic stress during freeze-up of the Antarctic ponds. This study underscores the presence of diverse mechanisms of adaptation to cold and other stresses in polar mats, consistent with the proportional representation of major bacterial groups. PMID:22081564

Varin, Thibault; Jungblut, Anne D.; Vincent, Warwick F.; Corbeil, Jacques

2012-01-01

417

High-resolution imagery of active faulting offshore Al Hoceima, Northern Morocco  

NASA Astrophysics Data System (ADS)

Two recent destructive earthquakes in 1994 and 2004 near Al Hoceima highlight that the northern Moroccan margin is one of the most seismically active regions of the Western Mediterranean area. Despite onshore geodetic, seismological and tectonic field studies, the onshore-offshore location and extent of the main active faults remain poorly constrained. Offshore Al Hoceima, high-resolution seismic reflection and swath-bathymetry have been recently acquired during the Marlboro-2 cruise. These data at shallow water depth, close to the coast, allow us to describe the location, continuity and geometry of three active faults bounding the offshore Nekor basin. The well-expressed normal-left-lateral onshore Trougout fault can be followed offshore during several kilometers with a N171°E ± 3° trend. Westward, the Bousekkour-Aghbal normal-left-lateral onshore fault is expressed offshore with a N020°E ± 4° trending fault. The N030°E ± 2° Bokkoya fault corresponds to the western boundary of the Plio-Quaternary offshore Nekor basin in the Al Hoceima bay and seems to define an en échelon tectonic pattern with the Bousekkour-Aghbal fault. We propose that these three faults are part of the complex transtensional system between the Nekor fault and the Al-Idrissi fault zone. Our characterization of the offshore expression of active faulting in the Al Hoceima region is consistent with the geometry and nature of the active fault planes deduced from onshore geomorphological and morphotectonic analyses, as well as seismological, geodetic and geodynamic data.

d'Acremont, E.; Gutscher, M.-A.; Rabaute, A.; Mercier de Lépinay, B.; Lafosse, M.; Poort, J.; Ammar, A.; Tahayt, A.; Le Roy, P.; Smit, J.; Do Couto, D.; Cancouët, R.; Prunier, C.; Ercilla, G.; Gorini, C.

2014-09-01

418

Residual Stresses in Inertia-Friction-Welded Dissimilar High-Strength Steels  

NASA Astrophysics Data System (ADS)

The welding of dissimilar alloys is seen increasingly as a way forward to improve efficiencies in modern aeroengines, because it allows one to tailor varying material property demands across a component. Dissimilar inertia friction welding (IFW) of two high-strength steels, Aermet 100 and S/CMV, has been identified as a possible joint for rotating gas turbine components and the resulting welds are investigated in this article. In order to understand the impact of the welding process and predict the life expectancy of such structures, a detailed understanding of the residual stress fields present in the welded component is needed. By combining energy-dispersive synchrotron X-ray diffraction (EDSXRD) and neutron diffraction, it has been possible to map the variations in lattice spacing of the ferritic phase on both sides of two tubular Aermet 100-S/CMV inertia friction welds (as-welded and postweld heat-treated condition) with a wall thickness of 37 mm. Laboratory-based XRD measurements were required to take into account the variation in the strain-free d-spacing across the weld region. It was found that, in the heat-affected zone (HAZ) slightly away from the weld line, residual stress fields showed tensile stresses increasing most dramatically in the hoop direction toward the weld line. Closer to the weld line, in the plastically affected zone, a sharp drop in the residual stresses was observed on both sides, although more dramatically in the S/CMV. In addition to residual stress mapping, synchrotron XRD measurements were carried out to map microstructural changes in thin slices cut from the welds. By studying the diffraction peak asymmetry of the 200- ? diffraction peak, it was possible to demonstrate that a martensitic phase transformation in the S/CMV is responsible for the significant stress reduction close to the weld line. The postweld heat treatment (PWHT) chosen to avoid any overaging of the Aermet 100 and to temper the S/CMV martensite resulted in little stress relief on the S/CMV side of the weld.

Moat, R. J.; Hughes, D. J.; Steuwer, A.; Iqbal, N.; Preuss, M.; Bray, S. E.; Rawson, M.

2009-09-01

419

Characteristics of High-Temperature Deformation Behavior of Ti-45Al-2Cr-3Ta-0.5W Alloy  

NASA Astrophysics Data System (ADS)

High-temperature deformation behavior tests of as-cast Ti-45Al-2Cr-3Ta-0.5W alloy were conducted over a wide range of strain rates (0.001-1.0 s-1) and temperatures (1150-1300 °C). The flow curves for the current alloy exhibited sharp peaks at low strain levels, followed by pronounced work hardening and flow localization at high strain levels. Phenomenological analysis of the strain rate and temperature dependence of peak stress data yielded an average value of the strain rate sensitivity equal to 0.25 and an apparent activation energy of ~420 kJ/mol. Processing maps were established under different deformation conditions, and the optimal condition for hot work on this material was determined to be 1250 °C/0.001 s-1. The stable deformation region was also found to decrease with increasing strain. Dynamic recrystallization (DRX) was the major softening mechanism controlling the growth of grains at the grain boundary. Meanwhile, local globularization and dynamic recovery (DR) were the main softening mechanisms in the lamellar colony. When deformed at higher temperatures (~1300 °C), the cyclic DRX and DR appeared to dominate the deformation. Moreover, the evolution of the ? phase during hot deformation played an important role in the dynamic softening of the alloy.

Luo, Y. Y.; Xi, Z. P.; Zeng, W. D.; Mao, X. N.; Yang, Y. L.; Niu, H. Z.

2014-10-01

420

Absence of earthquake correlation with Earth tides: An indication of high preseismic fault stress rate  

Microsoft Academic Search

Because the rate of stress change from the Earth tides exceeds that from tectonic stress accumulation, tidal triggering of earthquakes would be expected if the final hours of loading of the fault were at the tectonic rate and if rupture began soon after the achievement of a critical stress level. We analyze the tidal stresses and stress rates on the

John E. Vidale; Duncan Carr Agnew; Malcolm J. S. Johnston; David H. Oppenheimer

1998-01-01