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1

Spatial distribution of structural degradation under high-power stress in AlGaN/GaN high electron mobility transistors  

E-print Network

. Figure 1 shows the device structure. An AlGaN/GaN het- erostructure was grown on a SiC substrate usingSpatial distribution of structural degradation under high-power stress in AlGaN/GaN high electron degradation of AlGaN/GaN high electron mobility transistors was investigated under high-power electrical

del Alamo, Jesús A.

2

Spatial distribution of structural degradation under high-power stress in AlGaN/GaN high electron mobility transistors  

E-print Network

The two-dimensional spatial distribution of structural degradation of AlGaN/GaN high electron mobility transistors was investigated under high-power electrical stressing using atomic force and scanning electron microscopy. ...

Li, Libing

3

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

4

Correlating stress generation and sheet resistance in InAlN/GaN nanoribbon high electron mobility transistors  

NASA Astrophysics Data System (ADS)

We report the nanoscale characterization of the mechanical stress in InAlN/GaN nanoribbon-structured high electron mobility transistors (HEMTs) through the combined use of convergent beam electron diffraction (CBED) and elastic mechanical modeling. The splitting of higher order Laue zone lines in CBED patterns obtained along the [540] zone axis indicates the existence of a large strain gradient in the c-direction in both the planar and nanoribbon samples. Finite element models were used to confirm these observations and show that a passivating layer of Al2O3 can induce a tensile stress in the active HEMT layer whose magnitude is dependent on the oxide layer thickness, thus, providing important ramifications for device design and fabrication.

Jones, Eric J.; Azize, Mohamed; Smith, Matthew J.; Palacios, Tomás; Grade?ak, Silvija

2012-09-01

5

High frequency characteristics of FeCoAlO thin films combined the effects of stress and magnetic field  

SciTech Connect

The soft magnetic FeCoAlO thin films with different response at high frequency were prepared by using RF magnetron sputtering. Two different configurations of the sputtering targets were used: the Al{sub 2}O{sub 3} chips were placed on Fe{sub 70}Co{sub 30} disk either uniformly dispersed on the sputtering area (Target-A) or dispersed on the half side of the sputtering area (Target-B). It was found that, although, the films deposited from both of Target A and B possessed good soft magnetic properties and in-plane uniaxial magnetic anisotropy, they showed different behaviors at high frequency. The films deposited by using Target-A have mean permeability of 500 and a cut-off frequency (f{sub r}) of around 780 MHz, while the films deposited by using Target-B have mean permeability of 200 and a f{sub r} of 3.4 GHz. The higher f{sub r} of the later corresponds to the higher uniaxial anisotropic field in the films deposited by using the Target-B, which due to an extra anisotropy induced by the stress resulted from gradient of the Al-O composition. By adjusting the configuration of Target-B, the permeability and f{sub r} can be tuned to satisfy the different requirements for certain industrial applications.

Zheng Fu; Wang Xuan; Li Xu; Bai Jianmin; Wei Fulin [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Wei Dan [Lab of Advanced Materials, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Liu Xiaoxi [Department of Information Engineering, Shinshu University, Nagano 380-8553 (Japan); Xie Wenhui [Department of Physics, East China Normal University, Shanghai 200062 (China)

2011-04-01

6

Transmission electron microscopy characterization of electrically stressed AlGaN/GaN high electron mobility transistor devices  

SciTech Connect

A set of AlGaN/GaN high electron mobility transistor devices has been investigated using step-stress testing, and representative samples of undegraded, source-side-degraded, and drain-side-degraded devices were examined using electron microscopy and microanalysis. An unstressed reference sample was also examined. All tested devices and their corresponding transmission electron microscopy samples originated from the same wafer and thus received nominally identical processing. Step-stressing was performed on each device and the corresponding current voltage characteristics were generated. Degradation in electrical performance, specifically greatly increased gate leakage current, was shown to be correlated with the presence of crystal defects near the gate edges. However, the drain-side-degraded device showed a surface pit on the source side, and another region of the same device showed no evidence of damage. Moreover, significant metal diffusion into the barrier layer from the gate contacts was also observed, as well as thin amorphous oxide layers below the gate metal contacts, even in the unstressed sample. Overall, these observations emphasize that gate-edge defects provide only a partial explanation for device failure.

Johnson, Michael [Arizona State University; Cullen, David A [ORNL; Liu, Lu [University of Florida; Kang, Tsung Sheng [University of Florida, Gainesville; Ren, F. [University of Florida; Chang, C. Y. [University of Florida; Pearton, S. J. [University of Florida; Jang, Soohwan [University of Florida, Gainesville; Johnson, Wayne J. [Kopin Corporation, Taunton, MA; Smith, David J [Arizona State University

2012-01-01

7

Stress-strain behavior of Cu-Al-Ni single-crystal shape memory alloy at high temperature: shape memory effects  

NASA Astrophysics Data System (ADS)

The experimental results of a preliminary study on stress-strain behavior of Cu-13.3% Al- 4% Ni (by wt.) single crystal shape memory alloy grown along the [001] direction at high temperatures are given. An Instron testing machine with a high temperature environmental chamber has been used to study the quasi-static stress-strain response of 1.5 mm diameter Cu-Al-Ni single crystal wires at different ambient temperatures in the range 100 - 160°C. Local strain measurements using a highly sensitive extensometer are compared with overall strain measurements computed from the net displacements between grips. The effect of stress cycles on overall strain on full loading, after unloading and after heating in between stress cycles has been discussed.

Kannarpady, Ganesh K.; Trigwell, Steve; Bhattacharyya, Abhijit; Viahhi, Ivan; Pulnev, Sergei

2004-07-01

8

Formation of Structural Defects in AlGaN/GaN High Electron Mobility Transistors under Electrical Stress  

E-print Network

Formation of Structural Defects in AlGaN/GaN High Electron Mobility Transistors under Electrical of Technology, Cambridge, MA 02139 Gallium nitride (GaN) based devices are of interest for a variety of radar previously carried out extensive electrical reliability characterization of AlGaN/GaN high electron

del Alamo, Jesús A.

9

Time- and space-resolved high-throughput characterization of stresses during sputtering and thermal processing of Al-Cr-N thin films  

NASA Astrophysics Data System (ADS)

(Al100-xCrx)N thin-film materials libraries (x = 31-79 at%) were fabricated on micro-machined cantilever arrays, in order to simultaneously investigate the evolution of stresses during film growth as well as during thermal processing by analysing the changes in cantilever curvature. The issue of the dependence of stress in the growing films on composition, at comparable film thicknesses, was investigated. Among the various experimental parameters studied, it was found that the applied substrate bias has the strongest influence on stress evolution and microstructure formation. The compositions of the films, as well as the applied substrate bias, have a pronounced effect on the lattice parameter and the coherence length. For example, applying a substrate bias in general leads to compressive residual stress, increases the lattice parameter and decreases the coherence length. Moreover, bias can change the film texture from [1?1?1] orientation to [2?0?0]. Further detailed analysis using x-ray diffraction and transmission electron microscopy clearly revealed the presence of a [1?1?1] highly textured face centred cubic (B1 type) Al-Cr-N phase in the as-deposited state as well as the coexistence of the hexagonal [1?1?0] textured Cr2N phase, which forms in the Cr-rich region. These results show that the combinatorial approach provides insight into how stresses and compositions are related to phases and microstructures of different Al-Cr-N compositions fabricated in the form of materials libraries.

Grochla, D.; Siegel, A.; Hamann, S.; Buenconsejo, P. J. S.; Kieschnick, M.; Brunken, H.; König, D.; Ludwig, A.

2013-02-01

10

High-temperature slow crack growth of SiC–Mo 5(Si,Al) 3C composites determined by constant-stress-rate testing  

Microsoft Academic Search

A novel SiC–Mo5(Si,Al)3C composite was fabricated through a melt-infiltration process, and the slow-crack-growth (SCG) behavior of the composite was characterized over four stressing rates ranging from 0.01 to 20 MPa\\/s both at 1200 and 1300°C in 1 atm argon, using the constant-stress-rate (“dynamic fatigue”) test. The composite shows a high resistance to the SCG at 1200°C, where the slow-crack-growth parameter

Qingshan Zhu; Kazuhisa Shobu

2000-01-01

11

Effect of OFF-state stress induced electric field on trapping in AlGaN/GaN high electron mobility transistors on Si (111)  

NASA Astrophysics Data System (ADS)

The influence of electric field (EF) on the dynamic ON-resistance (dyn-RDS[ON]) and threshold-voltage shift (?Vth) of AlGaN/GaN high electron mobility transistors on Si has been investigated using pulsed current-voltage (IDS-VDS) and drain current (ID) transients. Different EF was realized with devices of different gate-drain spacing (Lgd) under the same OFF-state stress. Under high-EF (Lgd = 2 ?m), the devices exhibited higher dyn-RDS[ON] degradation but a small ?Vth (˜120 mV). However, at low-EF (Lgd = 5 ?m), smaller dyn-RDS[ON] degradation but a larger ?Vth (˜380 mV) was observed. Our analysis shows that under OFF-state stress, the gate electrons are injected and trapped in the AlGaN barrier by tunnelling-assisted Poole-Frenkel conduction mechanism. Under high-EF, trapping spreads towards the gate-drain access region of the AlGaN barrier causing dyn-RDS[ON] degradation, whereas under low-EF, trapping is mostly confined under the gate causing ?Vth. A trap with activation energy 0.33 eV was identified in the AlGaN barrier by ID-transient measurements. The influence of EF on trapping was also verified by Silvaco TCAD simulations.

Anand, M. J.; Ng, G. I.; Arulkumaran, S.; Manoj Kumar, C. M.; Ranjan, K.; Vicknesh, S.; Foo, S. C.; Syamal, B.; Zhou, X.

2015-02-01

12

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

13

Stress evolution during ultrasonic Al ribbon bonding  

NASA Astrophysics Data System (ADS)

The present study reveals the stress distribution in the substrate during ultrasonic bonding. The deformations of the Si substrate, Al ribbon, and Al pad were numerically analyzed using a finite element method. Experimental observation of the interface using a highspeed video camera was also conducted to determine the actual interfacial slip amplitude. This amplitude becomes smaller than that of tool-tip with bonding time. It was suggested from the numerical simulations that frictional adhesion enhanced the friction force, resulting in an increase in the equivalent stress in the ribbon and pad. As a result, very large stresses occur in the substrate during ultrasonic bonding. These stresses evolve with the progress of ultrasonic bonding, i.e., frictional adhesion.

Ando, Masaya; Takashima, Kazumasa; Maeda, Masakatsu; Takahashi, Yasuo

2014-08-01

14

Stress-strain rate relations for high-temperature deformation of two-phase Al-Cu alloys  

Microsoft Academic Search

Al-Cu alloys containing 6, 11, 17, 24 and 33 wt% Cu, annealed for 0.5–100 h, were deformed by the differential strain-rate test technique over a strain-rate range of ˜4×10-6 to 3×10-2s-1 at temperatures ranging from 460–540°C. Superplastic behaviour, with strain-rate sensitivity, m˜0.5, and activation energy, Q=171.5 kJ mol-1, is shown by the Al-24Cu and Al-33Cu alloys at lower strain rates

P. K. Bakshi; B. P. Kashyap

1995-01-01

15

Fatigue crack growth at high R ratio in Ti-6Al-4V at 1.5kHz: The effect of periodic removal of mean stress  

SciTech Connect

The components of gas turbine engines operate at high mean stresses due to the centrifugal loads caused by high rotational speeds. The turbine blades also have vibratory stresses that are superimposed on the mean stresses. Any fatigue problems that are experienced by turbine blades are driven by the vibratory stresses, but fatigue phenomena are also well known to depend strongly on mean stress effects. Here, fatigue cracks were grown under high mean stress at {approx}1.5 kHz at rates of 10{sup {minus}10} to 10{sup {minus}12} m/cycle within the scanning electron microscope in vacuum. Periodically, mean stress was removed, then reapplied, and the effect on subsequent crack growth rate was measured. This process has been called HCF/LCF interaction. Detailed crack tip micromechanics analyses were made of these load interactions. The only HCF/LCF effect detected was less than a factor of ten change in crack growth rate, in agreement with expectations from the micromechanics analysis, and previous experimental results in air.

Davidson, D.L.

1999-07-01

16

Degradation analysis and characterization of multifilamentary conduction patterns in high-field stressed atomic-layer-deposited TiO2/Al2O3 nanolaminates on GaAs  

NASA Astrophysics Data System (ADS)

In this paper, the effects of applying a high-field electrical stress on TiO2/Al2O3 nanolaminates grown by atomic layer deposition onto a p-type GaAs substrate are investigated. First, it is shown that the current-time (I-t) characteristic of the devices during a constant voltage stress follows the extended Curie-von Schweidler law for dielectric degradation. The application of voltage sweeps from negative to positive bias and back also reveals an hysteretic behavior of the current-voltage (I-V) characteristic typical of the resistive switching mechanism ocurring in these and others high permittivity oxide films. Second, we show that after the detection of the breakdown event the capacitors exhibit a random spot pattern on the top metal electrode (Al) associated with the generation of multifilamentary conduction paths running across the insulating film. The number of generated spots depends on the magnitude of the electrical stress and for a sufficiently large density, it is possible to demonstrate that they are spatially uncorrelated. The analysis is carried out using spatial statistics techniques such as the intensity plot, the interspot distance histogram, and the pair correlation function.

Miranda, E.; Suñé, J.; Das, T.; Mahata, C.; Maiti, C. K.

2012-09-01

17

Residual stresses in continuous graphite fiber Al metal matrix composites  

NASA Technical Reports Server (NTRS)

The residual stresses in graphite fiber reinforced aluminum (Gr/Al) composites with various thermal histories are measured using X-ray diffraction (XRD) methods. The XRD stress analysis is based on the determination of lattice strains by precise measurements of the interplanar spacings in different directions of the sample. The sample is a plate consisting of two-ply P 100 Gr/Al 6061 precursor wires and Al 6061 overlayers. Prior to XRD measurement, the 6061 overlayers are electrochemically removed. In order to calibrate the relationship between stress magnitude and lattice spacing shift, samples of Al 6061 are loaded at varying stress levels in a three-point bend fixture, while the stresses are simultaneously determined by XRD and surface-attached strain gages. The stresses determined by XRD closely match those determined by the strain gages. Using these calibrations, the longitudinal residual stresses of P 100 Gr/Al 6061 composites are measured for various heat treatments, and the results are presented.

Park, Hun Sub; Zong, Gui Sheng; Marcus, Harris L.

1988-01-01

18

Stress evolution during AlxGa1-xN/AlN growth on sapphire  

NASA Astrophysics Data System (ADS)

In-situ curvature measurements were employed to analyse stress generation and relaxation during epitaxial growth of undoped and Si-doped AlGaN layers on AlN/sapphire templates. While AlGaN films with a lower Al content exhibit a compressive strain during growth including a gradual relaxation, layers with a high Al content (x?0.8) grow under tension due to the AlN/sapphire effective substrate properties. Wafer curvature analysis and accompanying STEM measurements suggest that compressive stress relaxation involves misfit dislocations at or near the heterointerface as well as effective dislocation climb during growth. In addition, introduction of Si as n-type dopant in AlxGa1-xN adds a tensile stress component, most likely driven by a surface-mediated dislocation climb process.

Brunner, F.; Mogilatenko, A.; Kueller, V.; Knauer, A.; Weyers, M.

2013-08-01

19

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

20

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

21

Residual stress in sprayed Ni+5%Al coatings determined by neutron diffraction  

NASA Astrophysics Data System (ADS)

Coatings of nickel-based alloys are used in numerous high-performance applications. Their properties and lifetimes are influenced by factors such as residual stress. Neutron diffraction is a powerful tool for nondestructive residual stress determination. In this study, through-thickness residual stress profiles in Ni+5%Al coatings on steel substrates were determined. Two examples of significantly different spraying techniques - plasma spraying and cold spraying - are highlighted. Different stress-generation mechanisms are discussed with respect to process parameters and material properties.

Mat?jí?ek, J.; Sampath, S.; Gnäupel-Herold, T.; Prask, H. J.

22

High-risk stress fractures  

Microsoft Academic Search

High-risk stress fractures require precise assessment and treatment because of their propensity for delayed union, nonunion,\\u000a or complete fracture and their resulting disabling complications. Proper diagnosis necessitates a thorough clinical evaluation,\\u000a centering on the patient's diet and history, particularly the training regimen. For a definitive diagnosis, plain radiography,\\u000a ultrasound, bone scintigraphy, magnetic resonance imagery (MRI), and computed tomography (CT) are

Steven R. Murray; Michael T. Reeder; Brian E. Udermann; Robert W. Pettitt

2006-01-01

23

Reduction of Residual Stress and Improvement of Dimensional Accuracy by Uphill Quenching for Al6061 Tube  

NASA Astrophysics Data System (ADS)

The purpose of this study is to reduce the residual stress and machining distortion of an Al6061 tube by using uphill quenching. During uphill quenching, solid-solution heat-treated aluminum parts are usually immersed in LN2 at 77 K (-196 °C), followed by the rapid heating of the parts, to produce a new residual stress that is opposite in nature to the original. The uphill quenching method used in this study employed two types of heating methods: boiling water at 373 K (100 °C) and high-velocity steam at 448 K (175 °C). First, FE-simulation coupled with a CFD analysis was performed to predict the residual stress of the backward hot-extruded Al6061 tube with the following dimensions: Ø200 mm × h200 mm × t10 mm. Experiment of uphill quenching was also conducted to measure the residual stress using the boiling water and high-velocity steam uphill quenching methods. The predicted residual stresses were compared with the experimental results obtained via micro-indentation and saw-cutting tests, and a deviation of about 10.4 pct was found. In addition, the experimental results showed that uphill quenching could relieve up to 91 pct of the residual stress induced by water quenching. Finally, the dimensional accuracy of uphill quenched tubes was evaluated by measuring the roundness after the machining process, which showed that the uphill quenching method could improve the dimensional accuracy of an Al6061 tube by reducing the residual stress.

Lim, Hak-Jin; Ko, Dae-Hoon; Ko, Dae-Cheol; Kim, Byung-Min

2014-04-01

24

High temperature creep behaviour of Al-rich Ti-Al alloys  

NASA Astrophysics Data System (ADS)

Compared to Ti-rich ?-TiAl-based alloys Al-rich Ti-Al alloys offer an additional reduction of in density and a better oxidation resistance which are both due to the increased Al content. Polycrystalline material was manufactured by centrifugal casting. Microstructural characterization was carried out employing light-optical, scanning and transmission electron microscopy and XRD analyses. The high temperature creep of two binary alloys, namely Al60Ti40 and Al62Ti38 was comparatively assessed with compression tests at constant true stress in a temperature range between 1173 and 1323 K in air. The alloys were tested in the cast condition (containing various amounts of the metastable phases Al5Ti3 and h-Al2Ti) and after annealing at 1223 K for 200 h which produced (thermodynamically stable) lamellar ?-TiAl + r-Al2Ti microstructures. In general, already the as-cast alloys exhibit a reasonable creep resistance at 1173 K. Compared with Al60Ti40, both, the as-cast and the annealed Al62Ti38 alloy exhibit better creep resistance up to 1323 K which can be rationalized by the reduced lamella spacing. The assessment of creep tests conducted at identical stress levels and varying temperatures yielded apparent activation energies for creep of Q = 430 kJ/mol for the annealed Al60Ti40 alloy and of Q = 383 kJ/mol for the annealed Al62Ti38 material. The latter coincides well with that of Al diffusion in ?-TiAl, whereas the former can be rationalized by the instability of the microstructure containing metastable phases.

Sturm, D.; Heilmaier, M.; Saage, H.; Aguilar, J.; Schmitz, G. J.; Drevermann, A.; Palm, M.; Stein, F.; Engberding, N.; Kelm, K.; Irsen, S.

2010-07-01

25

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

26

Commentary: Beyond Stressful Life Events and Depression?--Reflections on Bogdan et al. (2014)  

ERIC Educational Resources Information Center

In light of continuing disagreement, even at the meta-analytic level, as to whether the gene- × -environment (G×E) interaction involving 5-HTTLPR and stressful life events (SLEs) predicts depression, Bogdan and associates (this issue, Bogdan et al., 2014) sought to extend research on what has become a highly controversial general (GxE) and…

Belsky, Jay

2014-01-01

27

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

28

TRANSCRIPTIONAL ANALYSIS BETWEEN TWO WHEAT NEAR-ISOGENIC LINES CONTRASTING IN ALUMINUM (AL) TOLERANCE UNDER AL STRESS  

Technology Transfer Automated Retrieval System (TEKTRAN)

To understand the mechanisms of aluminum (Al) tolerance and identify genes responsible for Al tolerance in wheat (Triticum aestivum L.), suppression subtractive hybridization (SSH) libraries were constructed from Al-stressed roots for two wheat near- isogenic lines (NILs), Chisholm-T (Al-tolerant) a...

29

High Si and Ge n-type doping of GaN doping -Limits and impact on stress S. Fritze, A. Dadgar, H. Witte, M. Bgler, A. Rohrbeck et al.  

E-print Network

High Si and Ge n-type doping of GaN doping - Limits and impact on stress S. Fritze, A. Dadgar, H://apl.aip.org/about/rights_and_permissions #12;High Si and Ge n-type doping of GaN doping - Limits and impact on stress S. Fritze,1,a) A. Dadgar) We report on GaN n-type doping using silane, germane, and isobutylgermane as Si and Ge dopants

Nabben, Reinhard

30

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

31

Photosynthesis: response to high temperature stress.  

PubMed

Global warming has led to increased temperature of the earth which is a major abiotic stress posing a serious threat to the plants. Photosynthesis is amongst the plant cell functions that is highly sensitive to high temperature stress and is often inhibited before other cell functions are impaired. The primary sites of targets of high temperature stress are Photosystem II (PSII), ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) while Cytochrome b559 (Cytb559) and plastoquinone (PQ) are also affected. As compared to PSII, PSI is stable at higher temperatures. ROS production, generation of heat shock proteins, production of secondary metabolites are some of the consequences of high temperature stress. In this review we have summarized the physiological, biochemical and molecular aspects of high temperature stress on the process of photosynthesis, as well as the tolerance and adaptive mechanisms involved. PMID:24796250

Mathur, Sonal; Agrawal, Divya; Jajoo, Anjana

2014-08-01

32

Non-Algorithmic Stress Optimization Using Simulation for DRAMs Zaid Al-Ars Said Hamdioui  

E-print Network

and temperature [Vollrath00]. Using these stresses during wafer-level testing makes it possible to identify weakNon-Algorithmic Stress Optimization Using Simulation for DRAMs Zaid Al-Ars Said Hamdioui Laboratory Delft, The Netherlands E-mail: z.al-ars@tudelft.nl Abstract: Stress optimization for memory devices

Kuzmanov, Georgi

33

Stress-Induced Grain Growth in an Ultra-Fine Grained Al Alloy  

NASA Astrophysics Data System (ADS)

This paper reports on a study of the stress-induced grain growth phenomenon in the presence of second-phase particles and solutes segregated at grain boundaries (GBs) during high-temperature deformation of an ultra-fine grained (UFG) Al alloy synthesized via the consolidation of mechanically milled powders. Our results show that grain growth was essentially inhibited during annealing at 673 K (400 °C) in the absence of an externally applied stress, whereas in contrast, grain growth was enhanced by a factor of approximately 2.7 during extrusion at 673 K (400 °C). These results suggest that significant grain growth during hot extrusion was attributable to the externally applied stresses stemming from the state of stress imposed during extrusion and that the externally applied stresses can overcome the resistance forces generated by second-phase particles and solutes segregated at GBs. The mechanisms underlying stress-induced grain growth were identified as GB migration and grain rotation, which were accompanied by dynamic recovery and possible geometric dynamic recrystallization, while discontinuous dynamic recrystallization did not appear to be operative.

Lin, Yaojun; Wen, Haiming; Li, Ying; Wen, Bin; Liu, Wei; Lavernia, Enrique J.

2014-06-01

34

Erratum: Erratum to: Stress-Induced Grain Growth in an Ultra-Fine Grained Al Alloy  

NASA Astrophysics Data System (ADS)

This paper reports on a study of the stress-induced grain growth phenomenon in the presence of second-phase particles and solutes segregated at grain boundaries (GBs) during high-temperature deformation of an ultra-fine grained (UFG) Al alloy synthesized via the consolidation of mechanically milled powders. Our results show that grain growth was essentially inhibited during annealing at 673 K (400 °C) in the absence of an externally applied stress, whereas in contrast, grain growth was enhanced by a factor of approximately 2.7 during extrusion at 673 K (400 °C). These results suggest that significant grain growth during hot extrusion was attributable to the externally applied stresses stemming from the state of stress imposed during extrusion and that the externally applied stresses can overcome the resistance forces generated by second-phase particles and solutes segregated at GBs. The mechanisms underlying stress-induced grain growth were identified as GB migration and grain rotation, which were accompanied by dynamic recovery and possible geometric dynamic recrystallization, while discontinuous dynamic recrystallization did not appear to be operative.

Lin, Yaojun; Wen, Haiming; Li, Ying; Wen, Bin; Liu, Wei; Lavernia, Enrique J.

2014-10-01

35

Experimental Evidence for Formation of Ni-Al Compound in Flip-Chip Joints Under Current Stressing  

NASA Astrophysics Data System (ADS)

The materials interactions on the under bump metallization (UBM) side of flip-chip solder joints during current stressing were studied by using high-resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM). Flip-chip solder joints with sputtered Al/Ni(V)/Cu UBM were subjected to current stressing at an ambient temperature of 150°C. It was found that a layer of Ni-Al phase, presumably NiAl3 according to energy-dispersive x-ray spectroscopy (EDX) measurements, was observed at the Al/Ni(V) interface. In addition, evidence for the formation of a nonconductive oxide layer at the NiAl3/Ni(V) interface was observed. This nonconductive oxide layer was responsible for diverting electron current away from the porous region.

Tsai, M. Y.; Lin, Y. L.; Tsai, M. H.; Chen, Y. J.; Kao, C. R.

2011-10-01

36

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

37

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

E-print Network

Dopant-Free GaN/AlN/AlGaN Radial Nanowire Heterostructures as High Electron Mobility Transistors, 2006 ABSTRACT We report the rational synthesis of dopant-free GaN/AlN/AlGaN radial nanowire-organic chemical vapor deposition (MOCVD). Transmission electron microscopy (TEM) studies reveal that the GaN/ AlN/AlGaN

Li, Yat

38

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

39

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

40

Degradation in AlGaN/GaN heterojunction field effect transistors upon electrical stress: Effects of field and temperature  

NASA Astrophysics Data System (ADS)

AlGaN/GaN heterojunction field effect transistors (HFETs) with 2 ?m gate length were subjected to on-state-high-field (high drain bias and drain current) and reverse-gate-bias (no drain current and reverse gate bias) stress at room and elevated temperatures for up to 10 h. The resulting degradation of the HFETs was studied by direct current and uniquely phase noise before and after stress. A series of drain and gate voltages was applied during the on-state-high-field and reverse-gate-bias stress conditions, respectively, to examine the effect of electric field on degradation of the HFET devices passivated with SiNx. The degradation behaviors under these two types of stress conditions were analyzed and compared. In order to isolate the effect of self-heating/temperature on device degradation, stress experiments were conducted at base plate temperatures up to 150 °C. It was found that the electric field induced by reverse-gate-bias mainly generated trap(s), most likely in the AlGaN barrier, which initially were manifested as generation-recombination (G-R) peak(s) in the phase noise spectra near 103 Hz. Meanwhile electric field induced by on-state-high-field stress mainly generated hot-electron and hot-phonon effects, which result in a nearly frequency independent increase of noise spectra. The external base plate temperatures promote trap generation as evidenced by increased G-R peak intensities.

Zhu, C. Y.; Zhang, F.; Ferreyra, R. A.; Avrutin, V.; Özgür, Ü.; Morkoç, H.

2013-10-01

41

Application of multireflection grazing incidence method for stress measurements in polished Al-Mg alloy and CrN coating  

NASA Astrophysics Data System (ADS)

Multi-reflection grazing incidence geometry, referred to as MGIXD, characterized by a small and constant incidence angle, was applied to measure low surface stresses in very thin layers of Al-Mg alloy and CrN coating. These two materials were selected in order to deal with the low and high levels of residual stress, respectively. The influence of different mechanical treatments on residual stresses was studied for Al-Mg samples. It was found that both rolling and mechanical polishing influence the distribution and amplitude of residual stress in surface layers. In the case of CrN coating, a very high compressive stress was generated during the deposition process. The stress distributions determined by the MGIXD method is in good agreement with the classic sin2 ? technique results for all studied samples. In performing stress measurements for a powder sample, it was found that the application of the Göbel mirror in the incident beam strongly reduces statistical and misalignment errors. Additionally, the root mean square values of the third order lattice strain within diffracting grains were determined.

Marciszko, M.; Baczma?ski, A.; Wierzbanowski, K.; Wróbel, M.; Braham, C.; Chopart, J.-P.; Lodini, A.; Bonarski, J.; Tarkowski; Zazi, N. L.

2013-02-01

42

Oxidative stress and mitochondrial damage: importance in non-SOD1 ALS  

PubMed Central

It is well known that mitochondrial damage (MD) is both the major contributor to oxidative stress (OS) (the condition arising from unbalance between production and removal of reactive oxygen species) and one of the major consequences of OS, because of the high dependance of mitochondrial function on redox-sensitive targets such as intact membranes. Conditions in which neuronal cells are not able to cope with MD and OS seem to lead or contribute to several neurodegenerative diseases including Amyotrophic Lateral Sclerosis (ALS), at least in the most studied superoxide dismutase 1 (SOD1)-linked genetic variant. As summarized in this review, new evidence indicates that MD and OS play a role also in non-SOD1 ALS and thus they may represent a target for therapy despite previous failures in clinical trials. PMID:25741238

Carrì, Maria Teresa; Valle, Cristiana; Bozzo, Francesca; Cozzolino, Mauro

2015-01-01

43

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

44

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

45

Utilizing various test methods to study the stress corrosion behavior of Al-Li-Cu alloys  

NASA Technical Reports Server (NTRS)

Recently, much attention has been given to aluminum-lithium alloys because of rather substantial specific-strength and specific-stiffness advantages offered over commercial 2000and 7000-series aluminum alloys. An obstacle to Al-Li alloy development has been inherent limited ductility. In order to obtain a more refined microstructure, powder metallurgy (P/M) has been employed in alloy development programs. As stress corrosion (SC) of high-strength aluminum alloys has been a major problem in the aircraft industry, the possibility of an employment of Al-Li alloys has been considered, taking into account a use of Al-Li-Cu alloys. Attention is given to a research program concerned with the evaluation of the relative SC resistance of two P/M processed Al-Li-Cu alloys. The behavior of the alloys, with and without an addition of magnesium, was studied with the aid of three test methods. The susceptibility to SC was found to depend on the microstructure of the alloys.

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

1984-01-01

46

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

47

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

48

Low-energy deposition of high-strength Al(0) alloys from an ECR plasma  

SciTech Connect

Low-energy deposition of Al(O) alloys from an electron cyclotron resonance (ECR) plasma offers a scaleable method for the synthesis of thick, high-strength Al layers. This work compares alloy layers formed by an ECR-0{sub 2} plasma in conjunction with Al evaporation to 0-implanted Al (ion energies 25-200 keV); and it examines the effects of volume fraction of A1{sub 2}0{sub 3} phase and deposition temperature on the yield stress of the material. TEM showed the Al(O) alloys contain a dense dispersion of small {gamma}-Al{sub 2}0{sub 3} precipitates ({approximately}l nm) in a fine-grain (10-100 nm) fcc Al matrix when deposited at a temperature of {approximately}100C, similar to the microstructure for gigapascal-strength 0-implanted Al. Nanoindentation gave hardnesses for ECR films from 1.1 to 3.2 GPa, and finite-element modeling gave yield stresses up to 1.3 {plus_minus} 0.2 GPa with an elastic modulus of 66 GPa {plus_minus} 6 GPa (similar to pure bulk Al). The yield stress of a polycrystalline pure Al layer was only 0.19 {plus_minus} 0.02 GPa, which was increased to 0.87 {plus_minus} 0.15 GPa by implantation with 5 at. % 0.

Barbour, J.C.; Follstaedt, D.M.; Knapp, J.A.; Myers, S.M. [Sandia National Labs., Albuquerque, NM (United States); Marshall, D.A.; Lad, R.J. [Univ. of Maine, Orono, ME (United States)

1995-12-31

49

Al/C60 Nanocomposites Fabricated by High-Pressure Torsion  

NASA Astrophysics Data System (ADS)

Al-2 vol pct fullerene (C60) composites with relative densities of >0.98 are manufactured by high-pressure torsion of ball-milled powders under an applied pressure of 6 GPa. A considerable Al grain refinement to ~53 nm and a homogeneous distribution of fullerenes give rise to a very high hardness of 152 Hv and yield stress of 405 MPa. Nevertheless, the poor tensile ductility due to the low work-hardening rate is achieved.

Asgharzadeh, Hamed; Joo, Soo-Hyun; Kim, Hyoung Seop

2015-02-01

50

The Alfin-like homeodomain finger protein AL5 suppresses multiple negative factors to confer abiotic stress tolerance in Arabidopsis.  

PubMed

Plant homeodomain (PHD) finger proteins affect processes of growth and development by changing transcription and reading epigenetic histone modifications, but their functions in abiotic stress responses remain largely unclear. Here we characterized seven Arabidopsis thaliana Alfin1-like PHD finger proteins (ALs) in terms of the responses to abiotic stresses. ALs localized to the nucleus and repressed transcription. Except AL6, all the ALs bound to G-rich elements. Mutations of the amino acids at positions 34 and 35 in AL6 caused loss of ability to bind to G-rich elements. Expression of the AL genes responded differentially to osmotic stress, salt, cold and abscisic acid treatments. AL5-over-expressing plants showed higher tolerance to salt, drought and freezing stress than Col-0. Consistently, al5 mutants showed reduced stress tolerance. We used ChIP-Seq assays to identify eight direct targets of AL5, and found that AL5 binds to the promoter regions of these genes. Knockout mutants of five of these target genes exhibited varying tolerances to stresses. These results indicate that AL5 inhibits multiple signaling pathways to confer stress tolerance. Our study sheds light on mechanisms of AL5-mediated signaling in abiotic stress responses, and provides tools for improvement of stress tolerance in crop plants. PMID:25619813

Wei, Wei; Zhang, Yu-Qin; Tao, Jian-Jun; Chen, Hao-Wei; Li, Qing-Tian; Zhang, Wan-Ke; Ma, Biao; Lin, Qing; Zhang, Jin-Song; Chen, Shou-Yi

2015-03-01

51

Compensation effect of bacterium containing biofertilizer on the growth of Cucumis sativus L. under Al-stress conditions.  

PubMed

Biofertilizers are used to improve soil fertility and plant production in sustainable agriculture. However, their applicability depends on several environmental parameters. The aim of our study was to evaluate the effect of free-living bacteria containing fertilizer on the growth of cucumber (Cucumis sativus L. cvs. Delicates) under aluminium (Al) stress. Different responses to Al stress of cucumber growth parameters were examined in terms of root elongation and physiological traits, such as Spad index (relative chlorophyll value), biomass accumulation of root and shoot, Al uptake and selected element contents (Fe, Mn, Zn, Mg) of leaves and root. The applied bacteria containing biofertilizer contains Azotobacter chroococcum and Bacillus megaterium. The dry weights of cucumber shoots and roots decreased in line with the increasing Al concentration. Due to different Al treatments (10-3 M, 10-4 M) higher Al concentration was observed in the leaves, while the amounts of other elements (Fe, Mn, Zn, Mg) decreased. This high Al content of the leaves decreased below the control value when biofertilizer was applied. In the case of the roots the additional biofertilizer treatments compensated the effect of Al. The relative chlorophyll content was reduced during Al-stress in older plants and the biofertilizer moderated this effect. The root/shoot ratio was decreased in all the Al-treatments in comparison to the control. The living bacteria containing fertilizer also had a modifying effect. The root/shoot ratio increased at the 10-4 M Al2(SO4)2 + biofertilizer and 10-4 M Al(NO3)3 + biofertilizer treatments compared to the control and Al-treatments. According to our results the biofertilizer is an alternative nutrient supply for replacing chemical fertilizers because it enhances dry matter production. Biofertilizer usage is also offered under Al polluted environmental conditions. Although, the nutrient solution is a clean system where we can examine the main processes without other effects of natural soils. The soil can modify the results, e.g. the soil-born microorganisms affect nutrient availability, and also can modify the harmful effects of different heavy metals. The understanding of basic processes will help us to know more about the soil behaviour. PMID:23567831

Tóth, Brigitta; Lévai, L; Kovács, B; Varga, Mária Borbélyné; Veres, Szilvia

2013-03-01

52

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.

2015-03-01

53

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

54

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

55

Thermomechanical behavior of Cu-Al-Ni single crystal high-temperature shape memory alloy: reorientation  

NASA Astrophysics Data System (ADS)

Copper-Aluminum-Nickel (Cu-Al-Ni) single crystal shape memory alloy (SMA) wires show great potential in actuator applications due to their high stress-free transformation temperatures and superior mechanical stability compared to common Nickel-Titanium SMAs. In this paper, Cu-13.3%Al-4%Ni (wt %) single crystal wires with stress-free transformation temperatures in the range of 80° C to 120° C were subjected to stress cycling tests at ambient temperatures up to 100° C at low deformation rates. Stress/strain curves up to 9% and 3% strain in the range of the transformation temperatures point to the possibility of phase transformation by detwinning. However, the residual overall strain after unloading decreased significantly at 60° C for both 3% and 9% strains. Accumulation of plastic deformation was observed for subsequent cycles.

Trigwell, Steve; Kannarpady, Ganesh K.; Bhattacharyya, Abhijit; Pulnev, Sergei; Vahhi, Ivan

2004-07-01

56

Creep and rupture of an ods alloy with high stress rupture ductility  

Microsoft Academic Search

The creep and stress rupture properties of an oxide (Y2O3) dispersion strengthened nickel-base alloy, which also is strengthened by ?? precipitates, was studied at 760 °C and 1093\\u000a °C. At both temperatures the alloy YDNiCrAl exhibits unusually high stress rupture ductility as measured by both elongation\\u000a and reduction in area. Failure was transgranular, and different modes of failure were observed

Mona E. McAlarney; Richard M. Arons; Tim E. Howson; John K. Tien; Sanford Baranow

1982-01-01

57

Creep and rupture of an ods alloy with high stress rupture ductility  

Microsoft Academic Search

The creep and stress rupture properties of an oxide (Y2O3) dispersion strengthened nickel-base alloy, which also is strengthened by gamma' precipitates, was studied at 760 °C and 1093 °C. At both temperatures the alloy YDNiCrAl exhibits unusually high stress rupture ductility as measured by both elongation and reduction in area. Failure was transgranular, and different modes of failure were observed

Mona E. McAlarney; Richard M. Arons; Tim E. Howson; John K. Tien; Sanford Baranow

1982-01-01

58

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

59

Impact of high-power stress on dynamic ON-resistance of high-voltage GaN HEMTs  

E-print Network

industrial research AlGaN/GaN HEMTs grown on SiC by MOCVD. The device features an integrated field plateImpact of high-power stress on dynamic ON-resistance of high-voltage GaN HEMTs Donghyun Jin) in high-voltage GaN High-Electron-Mobility Transistors (HEMT). We use a newly proposed dynamic RON

del Alamo, Jesús A.

60

Polar-Molecule-Dominated Electrorheological Fluids Featuring High Yield Stresses  

E-print Network

Polar-Molecule-Dominated Electrorheological Fluids Featuring High Yield Stresses By Rong Shen of the external electric field, and the yield stress displays a quadratic dependence on the field strength been made to improve the performance of ER fluids, however, the yield stresses available were still

Zexian, Cao

61

Evolution of structural defects associated with electrical degradation in AlGaN/GaN high electron mobility transistors  

E-print Network

with electrical degradation. Experimental HEMT devices2,8 with a GaN cap layer and AlGaN/GaN grown on SiC usingEvolution of structural defects associated with electrical degradation in AlGaN/GaN high electron investigated the surface morphology of electrically stressed AlGaN/GaN high electron mobility transistors using

del Alamo, Jesús A.

62

Stress-diffusion interaction during oxidation at high temperature  

NASA Astrophysics Data System (ADS)

Superalloy or other thermal protective materials are often oxidized seriously at high temperature. For most materials diffusion is the controlling step of oxidation. During oxidation, stress would be induced by growth strain and it can affect the diffusion process through chemical potential and diffusivity. Governing equation for diffusion is derived considering chemo-mechanical potential and diffusivity affected by stress. Oxidation kinetics is obtained to interpret the stress-diffusion coupling effects. The stress and its gradient influences on oxidation are also discussed.

Dong, Xuelin; Feng, Xue; Hwang, Keh-Chih

2014-10-01

63

Coping with the Stress of High Stakes Testing  

ERIC Educational Resources Information Center

High stakes testing puts considerable pressure on schools, teachers, and students to achieve at high levels. Therefore, how schools and individuals cope with this major source of stress may have important implications for the success of high stakes testing. This article reviews relevant theory and research on stress as they relate to public…

Kruger, Louis J.; Wandle, Caroline; Struzziero, Joan

2007-01-01

64

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

65

Time-dependent stress concentration and microcrack nucleation in TiAl  

SciTech Connect

Localized stress evolution associated with the interaction of slip or twinning with an interface is treated by means of a superposition of the {open_quotes}internal loading{close_quotes} of a crystalline subsystem by dynamic dislocation pile-up and the stress relaxation by climb of interfacial dislocations. The peak value of a stress concentration factor depends on both the angular function that includes the effect of mode mixity and the ratio of characteristic times for stress relaxation and internal loading. The available experimental data on orientation and strain-rate dependences of interfacial fracture mode in polysynthetically twinned TiAl crystals are discussed in view of the theoretical concepts presented in this paper.

Yoo, M.H.

1995-07-01

66

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

67

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

68

Effect of texture on high temperature deformation behavior at high strain rates in a Mg–3Al–1Zn alloy  

Microsoft Academic Search

The effect of specimen orientation, or texture on high temperature deformation behavior at a high strain rate of 103s?1 was investigated in an extruded Mg–3Al–1Zn alloy rod with ?1?0?1¯?0? fiber texture. Uniaxial compression test data were obtained along two specimen directions (longitudinal and transverse directions). The temperature dependence of yield stress was small up to 673K for both directions, indicating

H. Watanabe; K. Ishikawa

2009-01-01

69

NiAl-Base Composite Containing High Volume Fraction of AIN Particulate for Advanced Engines  

NASA Technical Reports Server (NTRS)

Cryomilling of prealloyed NiAl containing 53 at. % AJ was carried out to achieve high nitrogen levels. The consolidation of cryomilled powder by extrusion or hot pressing/ hot isostatic pressing resulted in a fully dense NiAl-base composite containing 30 vol. % of inhomogeneously distributed, nanosized AIN particulate. The NiAl-30AIN composite exhibited the highest compression yield strengths at all temperatures between 300 and 1300 K as compared with other compositions of NiAl-AIN composite. The NiAl-30AIN specimens tested under compressive creep loading between 1300 and 1500 K also exhibited the highest creep resistance with very little surface oxidation indicating also their superior elevated temperature oxidation resistance. In the high stress exponent regime, the strength is proportional to the square root of the AIN content and in the low stress exponent regime, the influence of AIN content on strength appears to be less dramatic. The specific creep strength of this material at 1300 K is superior to a first generation Ni-base single crystal superalloy. The improvements in elevated temperature creep strength and oxidation resistance have been achieved without sacrificing the room temperature fracture toughness of the NiAl-base material. Based on its attractive combination of properties, the NiAl-30AIN composite is a potential candidate for advanced engine applications,

Hebsur, Mohan G.; Whittenberger, J. D.; Lowell, C. E.; Garg, A.

1995-01-01

70

High-speed High-Stress Ring Shear Tests on Granular Soils and Clayey Soils1  

E-print Network

High-speed High-Stress Ring Shear Tests on Granular Soils and Clayey Soils1 Hiroshi Fukuoka carried out with a newly developed High-speed High-Stress Ring Shear Apparatus to examine was independent of shear speed un- der the normal stress up to 3.8kgf/cm2, 2 N 5 degrees of change in friction

Standiford, Richard B.

71

Numerical models for thermal residual stresses in Al 2O 3 platelets\\/borosilicate glass matrix composites  

Microsoft Academic Search

In this paper, we model and numerically study thermal residual stresses in a borosilicate glass reinforced with Al2O3 platelets. This composite material was experimentally characterized in a previous work. The aim of this paper is to investigate further the thermal residual stresses in these composites that are responsible for toughening and to assess the variation of the thermal residual stresses

Valeria Cannillo; Cristina Leonelli; Aldo R Boccaccini

2002-01-01

72

Breakdown During High-Field Bias-Temperature Stress  

SciTech Connect

Measurements of dielectric breakdown during high-field electrical stress are typically performed at or near room temperature via constant voltage or current stress methods. In this summary they explore whether useful information might also be obtained by performing current measurements during a temperature ramp at high electric field.

Fleetwood, D.M.; Krisch, K.S.; Sexton, F.W.

1999-08-05

73

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

74

Novel high-strength ternary Zr-Al-Sn alloys with martensite structure for nuclear applications  

NASA Astrophysics Data System (ADS)

High strength is essential for the practical application of Zr alloys as structural materials. In this work, Zr-5Al-xSn (x = 2, 3, 4, 5 and 6) alloys have been designed and fabricated through arc melting in order to effectively improve the strength while retaining good ductility. Phase analysis results show that all the samples consist of single phase ?-Zr. The variation trend of lattice constants as a function of Sn content has been analyzed. The microstructural analysis indicates that the Zr-5Al-xSn alloys mainly contain martensite structure. Mechanical tests show that these Zr-5Al-xSn alloys exhibit high compressive strength (1250-1450 MPa), high yield stress (800-1000 MPa), and favorable plastic strain of 18-23%. The fracture mode has been experimentally analyzed. Finally, both Zr-5Al-3Sn and Zr-5Al-5Sn are subjected to heat treatments for further study on the roles of Sn element and controlled heat treatment on the microstructure and mechanical properties of Zr alloys. Sn is found to promote the formation of ZrAl in the Zr-5Al-xSn alloys. Moreover, the martensite laths are observed to evolve into larger strip grains and fine equiaxed grains after heat treatment at 900 °C for 2 h. These factors strengthen the Zr-5Al-xSn alloys.

Nie, Li; Zhan, Yongzhong; Hu, Tong; Chen, Xiaoxian; Wang, Chenghui

2013-11-01

75

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

76

Residual stresses in high-velocity oxy-fuel metallic coatings  

NASA Astrophysics Data System (ADS)

X-ray based residual stress measurements were made on type 316 stainless steel and Fe3Al coatings that were high-velocity oxy-fuel (HVOF) sprayed onto low-carbon and stainless steel substrates. Nominal coating thicknesses varied from 250 to 1500 µm. The effect of HVOF spray particle velocity on residual stress and deposition efficiency was assessed by preparing coatings at three different torch chamber pressures. The effect of substrate thickness on residual stress was determined by spraying coatings onto thick (6.4 mm) and thin (1.4 mm) substrates. Residual stresses were compressive for both coating materials and increased in magnitude with spray velocity. For coatings applied to thick substrates, near-surface residual stresses were essentially constant with increasing coating thickness. Differences in thermal expansion coefficient between low-carbon and stainless steels led to a 180 MPa difference in residual stress for Fe3Al coatings. Deposition efficiency for both materials is maximized at an intermediate (˜600 m/s) velocity. Considerations for X-ray measurement of residual stresses in HVOF coatings are also presented.

Totemeier, T. C.; Wright, R. N.; Swank, W. D.

2004-06-01

77

Model for degradation of GaAs\\/AlGaAs HBTs under temperature and current stress  

Microsoft Academic Search

The similarities between GaAs\\/AlGaAs heterojunction bipolar transistors (HBTs) and GaAs-based light-emitting diodes (LEDs) and laser diodes (LDs) under current and temperature stress are demonstrated. Electroluminescence on HBTs with degraded current gain shows a marked decrease in light emission. One device which suffered rapid degradation in current gain also showed a ?110? dark line defect (DLD). Finally, an equation used to

T. Henderson

1995-01-01

78

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

79

Influence of initial microstructure on the hot working flow stress of Mg–3Al–1Zn  

Microsoft Academic Search

The hot working flow stress is examined for wrought and as-cast magnesium alloy AZ31, deformed in both compression and torsion. It is found that the hot deformation behaviour is sensitive to the deformation conditions, initial microstructure and the deformation mode. The peak stresses in compression are higher for as-cast material at low strain rates and high temperatures, whereas they are

A. G. Beer; M. R. Barnett

2006-01-01

80

Achieving conductive high Al-content AlGaN alloys for deep UV photonics  

NASA Astrophysics Data System (ADS)

Recent progresses in epitaxial growth and fundamental studies on electrical and optical properties of high Al-content AlGaN alloys with Si, Mg, and Zn doping are presented. For Si doped Al xGa1- xN, the Si activation energy was determined for x = 0 up to 1, and the resistivity of n-Al xGa1- xN was found to increases by one order of magnitude when Al content is increased by ~ 8%. From photoluminescence (PL) studies, three groups of deep impurity transitions were observed, related with deep level acceptors involving cation vacancy and its complexes: (VIII) 3-, (VIII-complex)2, and (VIII-complex) 1-, which are electron traps and compensating centers. By optimizing the growth processes to reduce the densities of cation vacancy and its complexes, the n-type conductivity of Al xGa1- xN was significantly improved. A record low room temperature n-type resistivity of 0.0075 ?•cm has been obtained for Al 0.7Ga 0.3N, and n-type conduction in pure AlN has also been achieved. We also review the electrical and optical measurement results of Mgdoped AlGaN and AlN. It was found that the overall material quality and conductivity of Mg-doped AlN are strongly correlated with the PL emission intensity of the nitrogen vacancy (V N 3+) related transition. Improved conductivity was obtained by suppressing the V N 3+ related emission line, which was attributed to the reduced hole compensation by V N 3+. With the identification of the emission peaks associated with V N 3+ hole compensating centers, the p-type conductivity of high Al-content AlGaN alloys was improved by monitoring and suppressing the intensity of the V N 3+ related emission lines. P-type conduction in Al xGa1- xN (x > 0.7) was confirmed at elevated temperatures (> 700 K). The possibility of using Zn as an alternative p-type dopant was also studied. It was found that contrary to the calculation, the energy level of Zn acceptor in AlN was about 0.74 eV, which is 0.23 eV deeper than Mg level in AlN.

Fan, Z. Y.; Lin, J. Y.; Jiang, H. X.

2007-02-01

81

Nrf2/ARE Signaling Pathway: Key Mediator in Oxidative Stress and Potential Therapeutic Target in ALS  

PubMed Central

Nrf2 (nuclear erythroid 2-related factor 2) is a basic region leucine-zipper transcription factor which binds to the antioxidant response element (ARE) and thereby regulates the expression of a large battery of genes involved in the cellular antioxidant and anti-inflammatory defence as well as mitochondrial protection. As oxidative stress, inflammation and mitochondrial dysfunctions have been identified as important pathomechanisms in amyotrophic lateral sclerosis (ALS), this signaling cascade has gained interest both with respect to ALS pathogenesis and therapy. Nrf2 and Keap1 expressions are reduced in motor neurons in postmortem ALS tissue. Nrf2-activating compounds have shown therapeutic efficacy in the ALS mouse model and other neurodegenerative disease models. Alterations in Nrf2 and Keap1 expression and dysregulation of the Nrf2/ARE signalling program could contribute to the chronic motor neuron degeneration in ALS and other neurodegenerative diseases. Therefore, Nrf2 emerges as a key neuroprotective molecule in neurodegenerative diseases. Our recent studies strongly support that the Nrf2/ARE signalling pathway is an important mediator of neuroprotection and therefore represents a promising target for development of novel therapies against ALS, Parkinson's disease (PD), Huntington's disease (HD), and Alzheimer's disease (AD). PMID:23050144

Petri, Susanne; Körner, Sonja; Kiaei, Mahmoud

2012-01-01

82

Low-strain plasticity in a high pressure die cast Mg–Al alloy  

Microsoft Academic Search

The Kocks–Mecking method was used to compare the strain-hardening behavior at low strains of high pressure die cast Mg-9 mass% Al alloy and gravity cast fine grained pure Mg specimens. The alloy specimens exhibited a rounded flow curve in contrast with the pure metal's for which macroscopic yielding occurred at a well-defined stress. Microhardness mapping of the cross-section of an

K Vanna Yang; C H Cáceres; A V Nagasekhar; M A Easton

2012-01-01

83

The high pressure high shear stress rheology of liquid lubricants  

Microsoft Academic Search

A limiting shear stress model of liquid lubricant shear rheology is offered which accurately represents all available primary data. The model is of the nonlinear Maxwell type with shear modulus taken into the time derivative and broadening of the viscous-plastic transition with pressure. Property relations for viscosity, limiting stress and shear modulus are refined for a polyphenyl ether in particular.

S. Bair; W. O. Winer

1992-01-01

84

Structural, microstructural, and residual stress investigations of plasma-sprayed hydroxyapatite on Ti-6Al-4 V.  

PubMed

Plasma-spray (PS) is a classical technique usually employed to cover orthopaedic titanium implant surfaces with hydroxyapatite (HA - Ca(10)(PO(4))(6)(OH)(2)). The objective of the current study is to investigate the structure and microstructure of HA plasma-spray 50 mum thick coating on titanium alloy (Ti-6Al-4 V) and residual stress due to processing in the substrate and in HA coating. The structure of the coatings was determined by high-energy synchrotron X-ray diffraction in energy dispersive (HESXRD), selected area electron diffraction (saed), Scanning Electron Microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). No impurity phases in the HA were identified by HESXRD to keep away from the decomposition of HA at high temperature. hcp phase of HA substrate was detected with slight amorphous background. FTIR spectrum of a HA powder shows a typical spectrum for HA material with the characteristic phosphate peaks for HA at wavenumbers of 1090, 1052, 963, 602, and 573 cm(-1) are present. The morphology of HA powder observed by SEM exhibits grains of ca. 0.1 mum well-adapted for cell proliferation. HA/Ti-6Al-4 V interface observed by cross-section scanning and transmission electron microscopy (TEM) presents microcracks. Residual stresses were analyzed by sin(2) Psi X-ray diffraction method on titanium substrates and HA coating. Although the Ti substrates are in a slightly tensile residual state, the coated ones show a compressive state. PMID:20356205

Carradó, Adele

2010-02-01

85

Effect of Stress in GaN/AlInGaN Grown on GaN Templates with Different Stress States  

NASA Astrophysics Data System (ADS)

We clarify the effect of the stress in GaN templates on the subsequent AlInGaN deposition by simply growing 150nm AlInGaN on a 30 ?m GaN template (sample 1) prepared by hydride vapor phase epitaxy and a 2.3 ?m thin control GaN template (sample 2) prepared by metalorganic chemical vapor deposition. X-ray diffraction and secondary iron mass spectroscopy measurements reveal the stress states (tensile stress and full relaxed for samples 1 and 2, respectively) and compositions (Al0.169In0.01 Ga0.821N, Al0.171In0.006Ga0.823N for samples 1 and 2, respectively) of AlInGaN. By carefully eliminating other possible factor, as template surface roughness, it is concluded that different stress states of AlInGaN should stem from different stress states of GaN templates.

Feng, Xiang-Xu; Liu, Nai-Xin; Zhang, Ning; Wei, Tong-Bo; Wang, Jun-Xi; Li, Jin-Min

2014-05-01

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

Corrosion Fatigue of High-Strength Titanium Alloys Under Different Stress Gradients  

NASA Astrophysics Data System (ADS)

Ti-6Al-4V is the most widely used high strength-to-mass ratio titanium alloy for advanced engineering components. Its adoption in the aerospace, maritime, automotive, and biomedical sectors is encouraged when highly stressed components with severe fatigue loading are designed. The extents of its applications expose the alloy to several aggressive environments, which can compromise its brilliant mechanical characteristics, leading to potentially catastrophic failures. Ti-6Al-4V stress-corrosion cracking and corrosion-fatigue sensitivity has been known since the material testing for pressurized tanks for Apollo missions, although detailed investigations on the effects of harsh environment in terms of maximum stress reduction have been not carried out until recent times. In the current work, recent experimental results from the authors' research group are presented, quantifying the effects of aggressive environments on Ti-6Al-4V under fatigue loading in terms of maximum stress reduction. R = 0.1 axial fatigue results in laboratory air, 3.5 wt.% NaCl solution, and CH3OH methanol solution at different concentrations are obtained for mild notched specimens (K t = 1.18) at 2e5 cycles. R = 0.1 tests are also conducted in laboratory air, inert environment, 3.5 wt.% NaCl solution for smooth, mild and sharp notched specimens, with K t ranging from 1 to 18.65, highlighting the environmental effects for the different load conditions induced by the specimen geometry.

Baragetti, Sergio; Villa, Francesco

2015-03-01

88

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

Microsoft Academic Search

Bands of positive macrosegregation and porosity commonly follow the surface contour of components produced by high-pressure\\u000a die casting (HPDC). In this article, Al alloy AlSi7Mg and Mg alloys AZ91 and AM60 were cast into tensile test bars using cold-chamber\\u000a (cc) HPDC. Microstructural characterization revealed that externally solidified crystals (ESCs) are not necessary for defect\\u000a band formation, and that defect bands

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

2007-01-01

89

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

Microsoft Academic Search

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

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

2007-01-01

90

Effect of Al-Si-Al and Al-Si-Si-Al Pairs in the ZSM-5 Zeolite Framework on the 27 NMR Spectra. A Combined High-Resolution 27  

E-print Network

Effect of Al-Si-Al and Al-Si-Si-Al Pairs in the ZSM-5 Zeolite Framework on the 27 Al NMR Spectra. A Combined High-Resolution 27 Al NMR and DFT/MM Study Jiri´ Dedecek, Stepan Sklenak,*, Chengbin Li, Blanka of the presence of Al-O-Si-O-Al and Al-O-Si-O-Si-O-Al sequences in the ZSM-5 zeolite framework on the local

Sklenak, Stepan

91

Thermal residual stresses and their toughening effect in Al{sub 2}O{sub 3} platelet reinforced glass  

SciTech Connect

Fluorescence spectroscopy has been used to measure the thermal residual stresses in Al{sub 2}O{sub 3}-platelet/borosilicate glass composites. Tensile residual stresses were found in the platelets, implying the presence of compressive residual stresses in the glass matrix. Measurements of stresses in the bulk of the composite could be obtained using fluorescence from platelets below the specimen surface. The measured stresses lay between the predictions of models for spherical particles and thin platelets, but were closer to the former for the range of platelet contents investigated (5--30 vol.%). Estimates of the increase in toughness associated with the compressive residual stresses in the matrix suggest that this mechanism makes a significant contribution to the toughening effect of the Al{sub 2}O{sub 3} platelets.

Todd, R.I.; Sinclair, R.; Yallee, R.B.; Young, R.J. [Univ. of Manchester and UMIST (United Kingdom). Manchester Materials Science Centre] [Univ. of Manchester and UMIST (United Kingdom). Manchester Materials Science Centre; Boccaccini, A.R. [Technische Universitaet Ilmenau (Germany)] [Technische Universitaet Ilmenau (Germany)

1999-09-08

92

High-temperature Oxidation Resistance of Al2O3-Au Laminated Composite Coating Prepared on TiAl-based Alloy  

NASA Astrophysics Data System (ADS)

Novel composite coatings consist of Al2O3 micro-layers alternating with Au nano-layers have been prepared on TiAl-based alloy by magnetron sputtering. The results of high-temperature cyclic oxidation test at 900 °C for 200 h revealed that the multi-sealed ?-Al2O3 and Au layers effectively suppress the inward diffusion of oxygen to a low level. The formed oxide scales and composite coatings are compact and free of cracks. The thermal stress is decreased owing to the increase of thermal-expansion coefficient. And the surface scratch test exhibited that the brittle/ductile laminated structure can remarkably enhance the strength and toughness in combination with improved damage resistance of the Al2O3-Au laminated composite coatings. Consequently, the oxidation and spallation resistance of TiAl-based alloy have been improved significantly.

Ma, Xiaoxu; He, Yedong; Wang, Deren; Lin, Junpin; Gao, Wei

2012-04-01

93

Lateral gradients of phases, residual stress and hardness in a laser heated Ti0.52Al0.48N coating on hard metal  

PubMed Central

The influence of a local thermal treatment on the properties of Ti–Al–N coatings is not understood. In the present work, a Ti0.52Al0.48N coating on a WC–Co substrate was heated with a diode laser up to 900 °C for 30 s and radially symmetric lateral gradients of phases, residual stress and hardness were characterized ex-situ using position-resolved synchrotron X-ray diffraction, Raman spectroscopy, transmission electron microscopy and nanoindentation. The results reveal (i) a residual stress relaxation at the edge of the irradiated area and (ii) a compressive stress increase of few GPa in the irradiated area center due to the Ti–Al–N decomposition, in particular due to the formation of small wurtzite (w) AlN domains. The coating hardness increased from 35 to 47 GPa towards the center of the heated spot. In the underlying heated substrate, a residual stress change from about ? 200 to 500 MPa down to a depth of 6 ?m is observed. Complementary, in-situ high-temperature X-ray diffraction analysis of stresses in a homogeneously heated Ti0.52Al0.48N coating on a WC–Co substrate was performed in the range of 25–1003 °C. The in-situ experiment revealed the origin of the observed thermally-activated residual stress oscillation across the laser heated spot. Finally, it is demonstrated that the coupling of laser heating to produce lateral thermal gradients and position-resolved experimental techniques opens the possibility to perform fast screening of structure–property relationships in complex materials. PMID:23471140

Bartosik, M.; Daniel, R.; Zhang, Z.; Deluca, M.; Ecker, W.; Stefenelli, M.; Klaus, M.; Genzel, C.; Mitterer, C.; Keckes, J.

2012-01-01

94

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

95

Energetic-particle synthesis of high-strength Al(O) alloys  

SciTech Connect

High-strength Al(O) alloys, initially discovered by ion implantation, have now been produced with electron-cyclotron resonance plasma deposition and pulsed-laser deposition. The mechanical properties of these deposited alloy layers were examined with nanoindentation, and finite element modeling of the indented layer on Si substrates was used to determine yield stresses for the alloys of {approximately} 1--5 GPa. The key to these high strengths is the high density of nanometer-size {gamma}-Al{sub 2}O{sub 3} precipitates formed when high concentrations (5--30 at.%) of oxygen are introduced into aluminum as individual atoms or molecules. The strongest alloys have precipitates as small as 1 nm, implying that such small precipitates block dislocation motion. Based upon previous studies with oxygen-implanted aluminum, improved tribological properties are expected for layers made by the two new deposition methods.

Follstaedt, D.M.; Knapp, J.A.; Barbour, J.C.; Myers, S.M.; Dugger, M.T.

1995-09-28

96

Nanotopography and Surface Stress Analysis of Ti6Al4V Bioimplant: An Alternative Design for Stability  

NASA Astrophysics Data System (ADS)

The mechanical stability of biomedical Ti6Al4V rods with vertically aligned nanotubes structure formed on their surface has yet to be fully tested during insertion into the bone. The surface of rods impacted during insertion into a bone makes shear contact with bone, generating an interfacial stress. This stress plays an important role in osseointegration and may contribute to loosening between the bone and the implant during surgery. In the current study, the mechanical stability of various Ti6Al4V surfaces, including machined (M), rough (R), machined-anodized (MA), and rough-anodized (RA) surfaces, were tested and fully analyzed during insertion and pullout test into a simulant bone with densities 15 and 20 pounds per cubic foot (pcf). Our initial results from the field emission scanning electron microscopy images taken before and after insertion reveal that titania nanotubes remained stable and maintained their structural integrity during the insertion and pullout Instron test. Furthermore, from the interfacial stress calculation during the insertion, it was observed that compared with nonanodized rods, a higher force was required to insert the anodized rods. The interfacial stress generated during the insertion of anodized rods was 1.03 ± 0.11 MPa for MA and 1.10 ± 0.36 MPa for RA, which is significantly higher (p < 0.05) than nonanodized rods with 0.36 ± 0.07 MPa for M and 0.36 ± 0.08 MPa for R in simulant bone with density of 15 pcf. Similar behavior was also observed in 20 pcf simulant bone. Energy dissipated during anodized rod insertion (i.e., MA = 1.3 ± 0.04 Nm and RA = 1.23 ± 0.24 Nm) was not significantly different than nonanodized rod insertion (i.e., M = 0.9 ± 0.05 Nm and R = 1.04 ± 0.04 Nm) into 15 pcf simulant bone. The high stress during insertion of anodized rods suggests that the nanotubes on the surface can cause gripping and high friction on the radial side, resisting the counter motion of the bone. The latter may play a beneficial role in preventing micromotion between the bone and implant and therefore reducing the chance of fretting/fatigue corrosion.

Patel, Sweetu; Solitro, Giovanni Francesco; Sukotjo, Cortino; Takoudis, Christos; Mathew, Mathew T.; Amirouche, Farid; Shokuhfar, Tolou

2015-02-01

97

Damage Assessment of Stress-Thermal Cycled High Temperature  

NASA Technical Reports Server (NTRS)

We report on the characterization of bismaleimide and polyimide carbon fiber composite, microcrack development under stress thermal cycling loading. Such cycle range from cryogenic temperatures associated with cryogenic fuel (LN, LOX) containment to high temperatures of 300 degrees associated with future hypervelocity aeropropulsion systems. Microcrack development thresholds as a function of temperature range of the thermal cycle, the number of cycles, and the applied stress level imposed on the composite are reported. We have conducted stress-thermal cycles on thin bismaleimide-woven carbon fiber foils for three temperature range cycles. The principle findings are that the full cycles from -196 degree celsius up to 250 degree celsius cause the most significant microcrack development. These observations indicate that the high temperature portion of the cycle under load causes fiber-matrix interface failure and subsequent exposure to higher stresses at the cryogenic, low temperature region results in composite matrix microcracking as a result of the additional stresses associated with the fiber-matrix thermal expansion mismatch. Our initial studies for 12 ply PMR-II-50 polyimide/M6OJB carbon fabric [0f, 90f, 90f, 0f, 0f, 90f] composites will be presented. The stress-thermal cycle test procedure for these will be described. Moisture absorption characteristics between cycles will be used to monitor interconnected microcrack development. The applied stress level will be 75 percent of the composite cryogenic -196 degree celsius ultimate strength.

Ju, Jach-Yung; Prochazka, Michael; Ronke, Ben; Morgan, Roger; Shin, Eugene

2003-01-01

98

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

99

Uniaxial-stress dependence of Hall effect in an AlGaAs/GaAs modulation-doped heterojunction  

NASA Astrophysics Data System (ADS)

Uniaxial compressive stress was applied to an AlGaAs/GaAs heterojunction. The uniaxial stress coefficients of sheet resistivity, sheet electron concentration, and mobility were obtained. The hydrostatic pressure coefficient of sheet resistivity was also obtained and was used to explain the different magnitude of the uniaxial stress coefficients of sheet electron concentration in the [110] and [11¯0] directions. We obtain a value for the piezoelectric constant e14 of AlAs to be -0.26 C/m2, compared to the value -0.225 C/m2 calculated by K. Hübner [Phys. Status Solidi B 57, 627 (1973)].

Liu, Y.; Rang, Z. L.; Fung, A. K.; Cai, C.; Ruden, P. P.; Nathan, M. I.; Shtrikman, H.

2001-12-01

100

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

101

Microstress prediction in composite laminates with high stress gradients  

Microsoft Academic Search

The objective of this research is to develop a macroscopic theory, which can provide the connection between macro-mechanics and micro-mechanics in characterizing the micro-stress of composite laminates in regions of high macroscopic stress gradients. The micro-polar theory, a class of higher-order elasticity theory, of composite laminate mechanics is implemented in a well-known Pipes–Pagano free edge boundary problem. The micro-polar homogenization

P. Hutapea; F. G. Yuan; N. J. Pagano

2003-01-01

102

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

E-print Network

of the AlGaN/GaN/AlN QW-FET structure used in this study. A Si -doping level of 4.5 10AlGaN/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

Jiang, Hongxing

103

Current Collapse and High-Electric-Field Reliability of Unpassivated GaN\\/AlGaN\\/GaN HEMTs  

Microsoft Academic Search

Long-term ON-state and OFF-state high-electric-field stress results are presented for unpassivated GaN\\/AlGaN\\/GaN high-electron-mobility transistors on SiC substrates. Because of the thin GaN cap layer, devices show minimal current-collapse effects prior to high-electric-field stress, despite the fact that they are not passivated. This comes at the price of a relatively high gate-leakage current. Under the assumption that donor-like electron traps are

Gaudenzio Meneghesso; Fabiana Rampazzo; Peter Kordos; Giovanni Verzellesi; Enrico Zanoni

2006-01-01

104

Flow stress of rapidly solidified Al-5Cr-2Zr alloy as a function of processing variables  

SciTech Connect

In a previous work, Lieblich et al. determined that room temperature hardness and tensile strength of as-extruded Al-5Cr-2Zr (wt.%) alloys obtained by gas atomization increased with decreasing powder particle size and extrusion temperature, and depended only very little on extrusion ratio and ram speed. The aim of the present study was to determine the influence of powder particle diameter and extrusion temperature on the flow stress of Al-5Cr-2Zr at temperatures ranging from 373 to 773 K. The contribution to the flow stress of different strengthening mechanisms is evaluated and related to the processing parameters.

Brahmi, A.; Gerique, T.; Torralba, M.; Lieblich, M. [Centro Nacional de Investigaciones Metalurgicas, Madrid (Spain). Dept. Metalurgia Fisica] [Centro Nacional de Investigaciones Metalurgicas, Madrid (Spain). Dept. Metalurgia Fisica

1997-12-01

105

Uncertainties in obtaining high reliability from stress-strength models  

NASA Technical Reports Server (NTRS)

There has been a recent interest in determining high statistical reliability in risk assessment of aircraft components. The potential consequences are identified of incorrectly assuming a particular statistical distribution for stress or strength data used in obtaining the high reliability values. The computation of the reliability is defined as the probability of the strength being greater than the stress over the range of stress values. This method is often referred to as the stress-strength model. A sensitivity analysis was performed involving a comparison of reliability results in order to evaluate the effects of assuming specific statistical distributions. Both known population distributions, and those that differed slightly from the known, were considered. Results showed substantial differences in reliability estimates even for almost nondetectable differences in the assumed distributions. These differences represent a potential problem in using the stress-strength model for high reliability computations, since in practice it is impossible to ever know the exact (population) distribution. An alternative reliability computation procedure is examined involving determination of a lower bound on the reliability values using extreme value distributions. This procedure reduces the possibility of obtaining nonconservative reliability estimates. Results indicated the method can provide conservative bounds when computing high reliability. An alternative reliability computation procedure is examined involving determination of a lower bound on the reliability values using extreme value distributions. This procedure reduces the possibility of obtaining nonconservative reliability estimates. Results indicated the method can provide conservative bounds when computing high reliability.

Neal, Donald M.; Matthews, William T.; Vangel, Mark G.

1992-01-01

106

Residual Stress on Ti6Al4V Hybrid and Laser Welded Joints  

Microsoft Academic Search

\\u000a Ti6Al4V alloy combines mechanical strength, deformability, excellent fatigue and corrosion resistance and high strength to\\u000a weight ratio. Furthermore, the mechanical behavior remains excellent at high temperature. Such characteristics make this material\\u000a attractive for numerous applications (structural, aerospace and naval) because of recent improvements in welding techniques\\u000a (laser, hybrid laser\\/MIG) that allow realizing high quality titanium welded joints. However some problems

C. Casavola; C. Pappalettere; F. Tursi

107

Relation between surface slip topography and stress corrosion cracking in Ti-8 wt % Al  

NASA Technical Reports Server (NTRS)

The deformation behavior of Ti-8 wt % Al has been investigated in an inert environment (air), and an aggressive environment (salt water). Details of surface slip geometry were examined by high resolution surface replicas at various stages of deformation in both environments. Specimens aged to contain a fine dispersion of Ti3Al precipitates failed by subcritical crack growth in salt water, whereas specimens in the single phase condition showed no effects of environment on the yield or fracture characteristics. The Ti3Al precipitates produce little change in strength level or slip character compared to the single phase alloy, and there is no evidence of any effects of environment on the character of surface slip. Rather, the presence of trenches along slip bands on the surface of aged specimens suggest that the specific effect of the Ti3Al precipitates is to render the surface slip steps chemically active relative to the surrounding matrix by slip induced dissolution of the particles.

Boyd, J. D.; Hoagland, R. G.

1974-01-01

108

Highly thermally conductive, low stress molding compounds  

Microsoft Academic Search

There has been an ongoing interest in highly thermally conductive molding compounds for many years. One major reason is the desire to find a low cost alternative to heat sinks, heat spreaders, and fans for large plastic packages. Of course, the new compound should exhibit the same reliability and attributes as the lower conductivity compound it is replacing. One feature

A. S. Chen; R. H. Y. Lo

1996-01-01

109

High temperature stress-strain analysis  

NASA Technical Reports Server (NTRS)

The objectives of the high temperature structures program are threefold: to assist in the development of analytical tools needed to improve design analysis and procedures for the efficient and accurate prediction of the nonlinear structural response of hot-section components; to aid in the calibration, validation, and evaluation of the analytical tools by comparing predictions with experimental data; and to evaluate existing as well as advanced temperature and strain measurement instrumentation.

Thompson, Robert L.

1985-01-01

110

High p-type conduction in high-Al content Mg-doped AlGaN  

NASA Astrophysics Data System (ADS)

We report on the successful fabrication of highly conductive p-type Mg-doped Al0.7Ga0.3N thin films grown on sapphire substrates by metal-organic chemical vapor deposition. Photoluminescence measurements show that Mg doping for growth with a high V/III ratio and moderate Mg concentration can effectively suppress self-compensation by the formation of nitrogen vacancy complexes. The lowest electrical resistivity was found to be 47 ? cm at room temperature. Moreover, the temperature dependence of the p-type conductivity in these high-Al content AlGaN films shows the extremely small effective activation energies of 47-72 meV at temperatures below 500 K.

Kinoshita, Toru; Obata, Toshiyuki; Yanagi, Hiroyuki; Inoue, Shin-ichiro

2013-01-01

111

High-risk stress fractures: pathogenesis, evaluation, and treatment.  

PubMed

High-risk stress fractures require precise assessment and treatment because of their propensity for delayed union, nonunion, or complete fracture and their resulting disabling complications. Proper diagnosis necessitates a thorough clinical evaluation, centering on the patient's diet and history, particularly the training regimen. For a definitive diagnosis, plain radiography, ultrasound, bone scintigraphy, magnetic resonance imagery (MRI), and computed tomography (CT) are helpful, and each plays a specific role. High-risk stress fractures typically require aggressive treatment such as nonweight-bearing immobilization coupled with therapy and often surgery. PMID:16785578

Murray, Steven R; Reeder, Michael T; Udermann, Brian E; Pettitt, Robert W

2006-01-01

112

High-Temperature Creep Degradation of the AM1/NiAlPt/EBPVD YSZ System  

NASA Astrophysics Data System (ADS)

The failure mechanisms of a NiAlPt/electron beam physical vapor deposition yttria-stabilized-zirconia thermal barrier coating system deposited on the AM1 single crystalline substrate have been investigated under pure creep conditions in the temperature range from 1273 K to 1373 K (1000 °C to 1100 °C) and for durations up to 1000 hours. Doubly tapered specimens were used allowing for the analysis of different stress states and different accumulated viscoplastic strains for a given creep condition. Under such experiments, two kinds of damage mechanisms were observed. Under low applied stress conditions ( i.e., long creep tests), microcracking is localized in the vicinity of the thermally grown oxide (TGO). Under high applied stress conditions, an unconventional failure mechanism at the substrate/bond coat interface is observed because of large creep strains and fast creep deformation, hence leading to a limited TGO growth. This unconventional failure mechanism is observed although the interfacial bond coat/top coat TGO thickening is accelerated by the mechanical applied stress beyond a given stress threshold.

Riallant, Fanny; Cormier, Jonathan; Longuet, Arnaud; Milhet, Xavier; Mendez, José

2014-01-01

113

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

114

High temperature stress-strain analysis  

NASA Technical Reports Server (NTRS)

The objectives of the high-temperature structures program are threefold: to assist in the development of analytical tools needed to improve design analyses and procedures for the efficient and accurate prediction of the nonlinear structural response of hot-section components; to aid in the calibration, validation, and evaluation of the analytical tools by comparing predictions with experimental data; and to evaluate existing as well as advanced temperature and strain measurement instrumentation. As the analytical tools, test methods, tests, instrumentations, as well as data acquisition, management, and analysis methods are developed and evaluated, a proven, integrated analysis and experiment method will result in a more accurate prediction of the cyclic life of hot section components.

Thompson, Robert L.; Moorhead, Paul E.

1986-01-01

115

High fluence nitrogen implantation in Al/Ti multilayers  

NASA Astrophysics Data System (ADS)

We have studied the effects of high fluence nitrogen ion implantation on the structural changes in Al/Ti multilayers, with the aim of achieving multilayered metal-nitrides. The starting structures consisted of 10 alternate sputter-deposited Al and Ti films, with a total thickness of 270 nm, on (1 0 0) Si substrates. They were implanted with 200 keV N2+, to 1 × 10 17 and 2 × 10 17 at/cm 2, the projected range being around half-depth of the multilayers. Structural characterization was performed by Rutherford backscattering, Auger electron spectroscopy and transmission electron microscopy. It was found that ion implantation to the higher fluence induces a full intermixing of Al/Ti layers, resulting in a multilayered structure with different content of Al, Ti and N. The applied method can be interesting for preparation of graded (Al,Ti)N multilayers, with a controlled content of nitrogen and a controlled level of Al-Ti intermixing within the structures.

Peruško, D.; Milosavljevi?, M.; Milinovi?, V.; Timotijevi?, B.; Zalar, A.; Kova?, J.; Pra?ek, B.; Jeynes, C.

2008-05-01

116

Al Coordination Changes in High-Pressure Aluminosilicate Liquids  

Microsoft Academic Search

Understanding the effect of pressure on aluminosilicate glass and liquid structure is critical to understanding magma flow at depth. Aluminum coordination has been predicted by mineral phase analysis and molecular dynamic calculations to change with increasing pressure. Nuclear magnetic resonance studies of glasses quenched from high pressure provide clear evidence for an increase in the average coordination of Al with

J. L. Yarger; K. H. Smith; R. A. Nieman; J. Diefenbacher; G. H. Wolf; B. T. Poe; P. F. McMillan

1995-01-01

117

Strength of VGCF/Al Composites for High Thermal Conductivity  

NASA Astrophysics Data System (ADS)

In this paper, the evaluation of the strength of the VGCF/Aluminum composites which have high thermal conductivity is reported. VGCF (Vapor Growth Carbon Fiber) is a kind of the Carbon nanotube (CNT) which has very high thermal conductivity as well as CNT. The composites are made by spark plasma sintering. The stress-strain curves of the composites are obtained by the tensile tests and show that the composites have brittle behavior. The brittleness of the composites increases with increase in the volume fraction of VGCF. A numerical simulation based on the micromechanics is conducted to estimate nonlinear behavior in the elastic deformation and plastic deformation of the stress-strain relations of the composites. The theories of Eshelby, Mori-Tanaka, Weibull, and Ramberg-Osgood are employed for the numerical simulation. The simulations give some information of the microstructural change in the composite related to the volume fraction of VGCF.

Fukuchi, Kohei; Sasaki, Katsuhiko; Imanishi, Terumitsu; Katagiri, Kazuaki; Kakitsuji, Atsushi; Shimizu, Akiyuki

118

An interpretation of the true stress–true stain behavior for a mechanically milled, superplastic Al(Mg(Cu alloy from a dislocation dynamics viewpoint  

Microsoft Academic Search

Stress–strain curve in tension for a mechanically milled Al-1.5Mg-4.0Cu (mass%) alloy [IN9021] under a high strain rate superplastic condition (temperature:748K, nominal strain rate:10° s?1) was analyzed from a viewpoint of dislocation dynamics by computer-simulation, taking into consideration that the actual true strain rate decreases with straining. The simulation showed a decrease in both the immobilization rate of dislocations U and

Tadashi Hasegawa; Kenji Okazaki

2000-01-01

119

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

120

High-pressure high-temperature phase relations in MgAl2O4  

Microsoft Academic Search

High-pressure high-temperature phase relation experiments in MgAl2O4 were performed in the pressure and temperature ranges of 18-27 GPa and 1400-2500 °C using a Kawai-type multi-anvil high-pressure apparatus. It was clarified that MgAl2O4 spinel directly transforms to the Mg2Al2O5 + Al2O3 assemblage at about 20 GPa and temperature higher than 2100 °C. The experimental results indicates that the phase assemblage of

H. Kojitani; A. Enomoto; S. Tsukamoto; M. Akaogi; H. Miura; H. Yusa

2010-01-01

121

DEFECT AND STRESS CONTROL OF ALGAN AND FABRICATION OF HIGH-EFFICIENCY UV-LED  

E-print Network

was fabricated on the low dislocation density AlGaN. The LED shows strong and sharp UV-emission from GaN and stress are the most serious issues for growth of AlGaN. Low-temperature deposited (LT -) AlN interlayer between AlGaN and GaN is found to reduce tensile stress during growth, and at the same time suppress

Wetzel, Christian M.

122

Damage Assessment of Stress-Thermal Cycled high temperature  

NASA Technical Reports Server (NTRS)

We report on the characterization of bismaleimide and polyimide carbon fiber composite, microcrack development under stress thermal cycling loading. Such cycles range from cryogenic temperatures associated with cryogenic fuel (LN, LOX) containment to high temperatures of 300 degrees Celsius associated with future hypervelocity aeropropulsion systems. Microcrack development thresholds as a function of temperature range of the thermal cycle; the number of cycles; the applied stress level imposed on the composite are reported. We have conducted stress-thermal cycles on thin bismaleimide-woven carbon fiber foils for three temperature range cycles: 1. Ambient temperature - -196 degrees celsius. 2. Ambient temperature - 150 degrees Celsius; 200 degrees Celsius; 250 degrees Celsius. 3. -196 degrees Celsius - 250 degrees Celsius. The Principle findings are that the full cycles from -196 degrees Celsius to to 250 degrees Celsius cause the most significant microcrack of development. These observations indicate that the high temperature portion of the cycle under load causes fiber-matrix interface failure and subsequent exposure to higher stresses at the cryogenic, low temperature region results in composite matrix microcracking as a result of the additional stresses associate with the fiber-matrix thermal expansion mismatch. Our initial studies for 12 ply PMR-II-50 polyimide/M60JB carbon fabric [0f,90f,90f,0f,0f,90f]ls composites will be presented. The stress-thermal cycle test procedure for these will be described. Moisture absorption characteristics between cycles will be used to monitor interconnected microcrack development. The applied stress level will be 75% of the composite cryogenic (-196 degrees Celsius) ultimate strength.

Ju, Jae-Hyung; Prochazka, Michael; Ronke, Ben; Morgan, Roger; Shin, Eugence

2004-01-01

123

Functions of FUS/TLS From DNA Repair to Stress Response: Implications for ALS  

PubMed Central

Fused in sarcoma/translocated in liposarcoma (FUS/TLS or FUS) is a multifunctional DNA-/RNA-binding protein that is involved in a variety of cellular functions including transcription, protein translation, RNA splicing, and transport. FUS was initially identified as a fusion oncoprotein, and thus, the early literature focused on the role of FUS in cancer. With the recent discoveries revealing the role of FUS in neurodegenerative diseases, namely amyotrophic lateral sclerosis and frontotemporal lobar degeneration, there has been a renewed interest in elucidating the normal functions of FUS. It is not clear which, if any, endogenous functions of FUS are involved in disease pathogenesis. Here, we review what is currently known regarding the normal functions of FUS with an emphasis on DNA damage repair, RNA processing, and cellular stress response. Further, we discuss how ALS-causing mutations can potentially alter the role of FUS in these pathways, thereby contributing to disease pathogenesis. PMID:25289647

Sama, Reddy Ranjith Kumar; Ward, Catherine L.

2014-01-01

124

Stress curves and mechanical properties of high performance concrete  

Microsoft Academic Search

In this research, high performance concrete (HPC) was designed by the minimum void ratio method, and slag and silica fumes partially replaced cement, as well as fly ash replacing about 15% of sand. Stress curves for compressive, splitting and flexure strengths of HPC specimens were measured and indicated the experimental concretes had better pastes to void ratios than control batches

2004-01-01

125

Charge trap generation in LPCVD oxides under high field stressing  

Microsoft Academic Search

The degradation of low pressure chemical vapor deposited (LPCVD) oxides, prepared using silane and tetra ethyl ortho silicate (TEOS) as the source, has been investigated under high field stressing. The LPCVD oxides exhibit enhanced conductivity for the Fowler-Nordheim tunneling current, which is modeled as an effective lowering of potential barrier at the injecting electrode. The charge to breakdown (Qbd) of

Navakanta Bhat; Pushkar P. Apte; Krishna C. Saraswat

1996-01-01

126

Creep and rupture of an ODS alloy with high stress rupture ductility. [Oxide Dispersion Strengthened  

NASA Technical Reports Server (NTRS)

The creep and stress rupture properties of an oxide (Y2O3) dispersion strengthened nickel-base alloy, which also is strengthened by gamma-prime precipitates, was studied at 760 and 1093 C. At both temperatures, the alloy YDNiCrAl exhibits unusually high stress rupture ductility as measured by both elongation and reduction in area. Failure was transgranular, and different modes of failure were observed including crystallographic fracture at intermediate temperatures and tearing or necking almost to a chisel point at higher temperatures. While the rupture ductility was high, the creep strength of the alloy was low relative to conventional gamma prime strengthened superalloys in the intermediate temperature range and to ODS alloys in the higher temperature range. These findings are discussed with respect to the alloy composition; the strengthening oxide phases, which are inhomogeneously dispersed; the grain morphology, which is coarse and elongated and exhibits many included grains; and the second phase inclusion particles occurring at grain boundaries and in the matrix. The creep properties, in particular the high stress dependencies and high creep activation energies measured, are discussed with respect to the resisting stress model of creep in particle strengthened alloys.

Mcalarney, M. E.; Arsons, R. M.; Howson, T. E.; Tien, J. K.; Baranow, S.

1982-01-01

127

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

128

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

129

Shot-Peening Effect on High Cycling Fatigue of Al-Cu Alloy  

NASA Astrophysics Data System (ADS)

The present work was aimed at evaluating the effects of shot-peening on the high cycle fatigue performance of the age-hardening aircraft alloy Al 2024 at different almen intensities. Shot-peening to full coverage (100 pct) was performed using spherically conditioned cut wire (SCCW 14) with an average shot size of 0.36 mm and at almen intensities of 0.1, 0.2, and 0.3 mmA. After applying the various mechanical surface treatments, the changes in the surface and near-surface layer properties such as microhardness, residual stress-depth profiles, and surface roughness were determined. The microhardness, surface roughness, and the residual stresses increased proportionally with the almen intensity. Electropolitically polished conditions were used as reference in the mechanically surface treated specimens. A significant improvement was seen in the fatigue performance of the 0.1 mmA.

Fouad, Yasser; Metwally, Mostafa El

2013-12-01

130

Influence of Metalorganic Vapor Phase Epitaxy Regrowth on Characteristics of InAlN/AlGaN/GaN High Electron Mobility Transistors  

NASA Astrophysics Data System (ADS)

We fabricated InAlN/AlGaN/GaN heterostructures using a regrowth technique in order to avoid an unintentional Ga incorporation into the InAlN barrier layer. We prepared two types of samples (S1 and S2) using different regrowth sequences: InAlN regrowth on AlGaN/GaN (S1), and InAlN/AlGaN/GaN regrowth on GaN (S2). The characteristics of the high electron mobility transistors (HEMTs) differed depending on the adopted sequence. In current-voltage characteristics, the kinks appear only for the HEMTs using S1 (HEMT-S1). The current reduction induced by gate-bias stress is as large as 20% in HEMT-S1, while it is only 5% in HEMT-S2. Results of our complementary experiments on AlGaN/GaN heterostructures prepared by various regrowth sequences suggest that the inferior device properties of HEMT-S1 can be attributed to higher trap density at the regrowth interfaces. The higher trap density is most likely a result of the AlGaN surface's being more easily oxidized than the GaN surface. Non-uniform decomposition of the AlGaN surface during the heating process prior to the regrowth may also play a role. The fairly a good device performance of HEMT-S2 indicates that InAlN can actually act as a good barrier for GaN-based HEMTs by careful optimization of the fabrication sequence even with a regrowth process.

Hiroki, Masanobu; Watanabe, Noriyuki; Maeda, Narihiko; Yokoyama, Haruki; Kumakura, Kazuhide; Yamamoto, Hideki

2013-04-01

131

Effect of Stress Ratio on the Fatigue Behavior of a Friction Stir Processed Cast Al-Si-Mg Alloy  

SciTech Connect

The effect of friction stir processing (FSP) on the fatigue life of a cast Al-7Si-0.6Mg alloy at a stress ratio of R=0 was evaluated. Two types of specimen geometry were used for the FSPed condition, through-thickness processed and partial thickness processed. FSP enhanced the fatigue life by a factor of 15 for the through thickness processed samples at lower stress amplitudes. This is different from the FSP specimens tested at R=-1 and similar stress amplitudes where a 5 times improvement in fatigue life was observed. In light of these observations, various closure mechanisms were examined.

Jana, Saumyadeep; Mishra, Rajiv S.; Baumann, John B.; Grant, Glenn J.

2009-11-01

132

High Performance Polarized Electron Photocathodes Based on InGaAlAs/AlGaAs Superlattices  

NASA Astrophysics Data System (ADS)

Highly efficient emitters of polarized electrons based on the InAlGaAs/AlGaAs superlattice give an optimistic prognosis to explorations of such structures as the sources for accelerators. A new set of these SL structures with minimized conduction band offset was designed and recently tested. A new technology of surface protection in MBE growth leads to a significantly reduced heat-cleaning temperature. At these lowered cleaning temperatures, the thermal degradation of the working structure parameters is avoided. As a result a polarization P of up to 91% at corresponding quantum efficiency (QE) of 0.3% was achieved at room temperature. A 50% increase in the photocathode lifetime has been achieved with Sb coverage.

Mamaev, Y. A.; Subashiev, A. V.; Yashin, Y. P.; Gerchikov, L. G.; Luh, D.; Maruyama, T.; Clendenin, J. E.; Ustinov, V. M.; Zhukov, A. E.

2005-08-01

133

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

134

Wear-accelerated corrosion of Ti-6Al-4V and nitrogen-ion-implanted Ti-6Al-4V: mechanisms and influence of fixed-stress magnitude.  

PubMed

Wear-accelerated corrosion rates at constant anodic potentials were evaluated for unimplanted and nitrogen-ion-implanted surgical Ti-6Al-4V while wearing against ultrahigh-molecular-weight polyethylene at stress levels up to 6.90 MPa (1000 psi). The ion implantation processing was found to reduce the wear corrosion rates in both saline and serum solutions at all applied stress levels. During wear testing, all of the ion-implanted surfaces remained visually unchanged from the polished condition. However, many of the unimplanted surfaces developed damage zones characterized by wear tracks and black wear debris. A surface-damage mechanism is proposed and discussed which involves disruption of the Ti-6Al-4V protective oxide film, subsequent entrapment of oxide particles in the polyethylene, then self-perpetuating damage due to the abrasive action of the embedded particles. PMID:3558450

Buchanan, R A; Rigney, E D; Williams, J M

1987-03-01

135

Seasonal changes in stress indicators in high level football.  

PubMed

This study aimed at describing changes in stress and performance indicators throughout a competitive season in high level football. 15 players (19.5±3.0 years, 181±5 cm, 75.7±9.0 kg) competing under professional circumstances were tested at baseline and 3 times during the season 2008/09 (in-season 1, 2, 3). Testing consisted of the Recovery-Stress Questionnaire for Athletes (Total Stress and Recovery score), vertical jump tests (counter movement and drop jump (DJ)), and a maximal ramp-like running test. Average match exposure was higher during a 3-weeks period prior to in-season 3 compared to in-season 1 and 2 (1.5 vs. 1 h/week, p=0.05). Total Stress score was elevated at in-season 1 and 2 compared to baseline (p<0.01) with a further increase at in-season 3 (p<0.03; generalized eta squared (?(2)(g))=0.37). Total Recovery score was decreased at in-season 1 and 3 compared to baseline (p<0.05; ?(2)(g)=0.21). Maximal running velocity (V(max)) and jumping heights were not significantly affected (?(2)(g)?0.04). Changes in DJ height and V (max) between baseline and in-season 3 were correlated with the corresponding changes in Total Stress score (r=-0.55 and r=-0.61, p<0.03). Usual match exposure during a professional football season does not induce relevant changes in performance indicators. Accumulated stress and a lack of recovery towards the end of a season might be indicated by psychometric deteriorations. PMID:21271495

Faude, O; Kellmann, M; Ammann, T; Schnittker, R; Meyer, T

2011-04-01

136

Adolescents' sleep in low-stress and high-stress (exam) times: a prospective quasi-experiment.  

PubMed

This prospective quasi-experiment (N = 175; mean age = 15.14 years) investigates changes in adolescents' sleep from low-stress (regular school week) to high-stress times (exam week), and examines the (moderating) role of chronic sleep reduction, baseline stress, and gender. Sleep was monitored over three consecutive weeks using actigraphy. Adolescents' sleep was more fragmented during the high-stress time than during the low-stress time, meaning that individuals slept more restless during stressful times. However, sleep efficiency, total sleep time, and sleep onset latency remained stable throughout the three consecutive weeks. High chronic sleep reduction was related to later bedtimes, later sleep start times, later sleep end times, later getting up times, and more time spent in bed. Furthermore, low chronic sleep reduction and high baseline stress levels were related to more fragmented sleep during stressful times. This study shows that stressful times can have negative effects on adolescents' sleep fragmentation, especially for adolescents with low chronic sleep reduction or high baseline stress levels. PMID:24786857

Dewald, Julia F; Meijer, Anne Marie; Oort, Frans J; Kerkhof, Gerard A; Bögels, Susan M

2014-01-01

137

Thermal stress and plastic deformation of Al fine line structures: Effects of oxide confinement and line geometry  

Microsoft Academic Search

The effects of oxide confinement on the thermal stress and yield behavior of Al(Cu) line structures have been studied as a function of linewidth to submicron dimensions. Measurements have been carried out on unpassivated and passivated lines during thermal cycling using a bending-beam technique. By measuring periodic line structures with lines oriented parallel and perpendicular to the beam direction, the

P. S. Ho; I.-S. Yeo; S. G. H. Anderson; C. K. Hu

1994-01-01

138

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

139

AlN films deposited by dc magnetron sputtering and high power impulse magnetron sputtering for SAW applications  

NASA Astrophysics Data System (ADS)

In this work, aluminium nitride (AlN) films were deposited on silicon substrates buffered by an epitaxial AlN thin film for surface acoustic wave (SAW) applications. The films were deposited by dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) deposition techniques. The structural properties of AlN films were investigated using x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy and atomic force microscopy. In both cases of films deposited by dcMS and HiPIMS, the XRD results showed that the obtained films are oriented, with full width at half maximum rocking curves of around 1°. Raman spectroscopy revealed higher residual stress relaxation in the AlN epilayers grown by HiPIMS compared to AlN grown by dcMS, highlighted by a blue shift in the E2(high) Raman mode. The SAW measurements indicated an insertion loss of AlN-SAW devices of about 53 and 35?dB for the AlN films deposited by dcMS and HiPIMS respectively. The relation between the structural properties of AlN and the characteristics of AlN-SAW devices were correlated and discussed.

Ait Aissa, K.; Achour, A.; Elmazria, O.; Simon, Q.; Elhosni, M.; Boulet, P.; Robert, S.; Djouadi, M. A.

2015-04-01

140

High-resolution electron microscopy of dislocation cores in NiAl  

SciTech Connect

The atomic structure of dislocation cores in NiAl is studied by high-resolution transmission electron microscopy (HRTEM) and molecular dynamics (MD) calculations. Results are presented on dislocations with Burgers vectors b = a{lt}100{gt} and a{lt}111{gt}. A comparison of HRTEM image simulations indicates that the core of a 45{degree} a{lt}100{gt} dislocation consists of Al atoms. The Burgers vector distribution shows a width of 2.2b. This corresponds very closely to MD results and is consistent with the relatively low Peierls stress of this dislocation. By detailed image analysis the angular dependence of the shear stress components of the dislocation are made visible. MD results obtained from 45{degree} dislocations with opposite screw components suggest, that the helicity of the screw component might be discernible from high-resolution electron micrographs. A a{lt}111{gt} dislocation with {l{underscore}angle}110{r{underscore}angle} line direction is shown which exhibits a rather wide dissociation, probably into two a/2{lt}111{gt} partials.

Stoeckle, D.; Sigle, W.; Seeger, A.

1999-07-01

141

Stress corrosion failure of high-pressure gas pipeline  

Microsoft Academic Search

Incidents of failure due to corrosion\\/stress corrosion cracking of high-pressure gas pipelines in Pakistan have been observed to occur after about 15–20 years of service. The present paper constitutes the failure analysis of an 18-inch diameter electric resistance-welded gas pipeline. The failure was characterized, on the basis of all the available evidence and the metallurgical examination carried out on the

F. Hasan; J. Iqbal; F. Ahmed

2007-01-01

142

On the effect of stress on nucleation and growth of precipitates in an Al-Cu-Mg-Ag alloy  

SciTech Connect

A study has been made of the effect of an externally applied tensile stress on {Omega} and {Theta}{prime} precipitate nucleation and growth in an Al-Cu-Mg-Ag alloy and a binary Al-Cu alloy which was used as a model system. Both solutionized and solutionized and aged conditions were studied. The mechanical properties have been measured and the microstructures have been characterized by transmission electron microscopy (TEM). The volume fraction and number density, as well as the precipitate size, have been experimentally determined. It was found that for as-solutionized samples aged under stress, precipitation occurs preferentially parallel to the stress axis. A threshold stress has to be exceeded before this effect can be observed. The critical stress for influencing the precipitate habit plane is between 120 and 140 MPa for {Omega} and between 16 and 19 MPa for {Theta}{prime} for the aging temperature of 160 C. The major effect of the applied stress is on the nucleation process. The results are discussed in terms of the role of the lattice misfit between the matrix and the precipitate nucleus.

Skrotzki, B. [Rhur-Univ., Bochum (Germany). Inst. fuer Werkstoffe; Shiflet, G.J.; Starke, E.A. Jr. [Univ. of Virginia, Charlottesville, VA (United States). Dept. of Materials Science and Engineering

1996-11-01

143

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

144

Thermal cycling and stress relaxation response of SiAl and SiAl-SiO 2 layered thin films  

Microsoft Academic Search

The deformation of Si-Al and Si-Al-SiO2 multi-layered thin films in response to controlled sequences of constant- and variable-amplitude thermal cycling and isothermal exposures has been studied experimentally by recourse toin situ measurements of curvature changes which made use of the laser scanning technique. In an attempt to systematically isolate salient mechanistic features, a select set of companion experiments have also

Y.-L. Shen; S. Suresh

1995-01-01

145

High quality semipolar (11{sup ¯}02) AlGaN/AlN quantum wells with remarkably enhanced optical transition probabilities  

SciTech Connect

Adjusting the growth conditions from those for c-plane growth realizes high-quality semipolar (11{sup ¯}02) AlGaN/AlN quantum wells (QWs) with atomically smooth surfaces and abrupt interfaces on AlN substrates. Upon comparing the optical properties to those of c-plane QWs using time-integrated and time-resolved photoluminescence spectroscopy, the estimated internal electric field is much smaller in (11{sup ¯}02) AlGaN/AlN QWs than in c-plane QWs. Thus, (11{sup ¯}02) AlGaN/AlN QWs have narrower emission line widths and remarkably faster radiative recombination lifetimes, realizing highly efficient deep ultraviolet emissions.

Ichikawa, S., E-mail: shuhei.ichikawa@optomater.kuee.kyoto-u.ac.jp; Iwata, Y.; Funato, M.; Kawakami, Y., E-mail: kawakami@kuee.kyoto-u.ac.jp [Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510 (Japan); Nagata, S. [JFE Mineral Co. Ltd., Chiba 260-0826 (Japan)

2014-06-23

146

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

147

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

148

Characterization of residual stresses in heat treated Ti6Al4V forgings by machining induced distortion  

Microsoft Academic Search

To provide a solid base for improved material exploitation in dimensioning calculations it is necessary to determine the stress state in the part prior to service loading. In order to achieve higher material strength at elevated temperatures, the surface temperature gradient with respect to time has to be sufficiently high during heat treatment. This results in non-negligable residual stresses that

B. Regener; C. Krempaszky; E. Werner

2010-01-01

149

The response of high and low polyamine-producing cell lines to aluminum and calcium stress.  

PubMed

The diamine putrescine (Put) has been shown to accumulate in tree leaves in response to high Al and low Ca in the soil, leading to the suggestion that this response may provide a physiological advantage to leaf cells under conditions of Al stress. The increase in Put is reversed by Ca supplementation in the soil. Using two cell lines of poplar (Populus nigra x maximowiczii), one with constitutively high Put (resulting from transgenic expression of a mouse ornithine decarboxylase--called HP cells) and the other with low Put (control cells), we investigated the effects of reduced Ca (0.2-0.8 mM vs. 4 mM) and treatment with 0.1 mM Al on several biochemical parameters of cells. We found that in the presence of reduced Ca concentration, the HP cells were at a disadvantage as compared to control cells in that they showed greater reduction in mitochondrial activity and a reduction in the yield of cell mass. Upon addition of Al to the medium, the HP cells, however, showed a reversal of low-Ca effects. We conclude that due to increased ROS production in the HP cells, their tolerance to low Ca is compromised. Contrary to the expectation of deleterious effects, the HP cells showed an apparent advantage in the presence of Al in the medium, which could have come from reduced uptake of Al, enhanced extrusion of Al following its accumulation, and perhaps a reduction in Put catabolism as a result of a reduction in its biosynthesis. PMID:20552726

Mohapatra, Sridev; Cherry, Smita; Minocha, Rakesh; Majumdar, Rajtilak; Thangavel, Palaniswamy; Long, Stephanie; Minocha, Subhash C

2010-07-01

150

Stress Concentration and Fracture at Inter-variant Boundaries in an Al-Li Alloy  

NASA Technical Reports Server (NTRS)

Delamination fracture has limited the use of lightweight Al-Li alloys. Studies of secondary, delamination cracks in alloy 2090, L-T fracture toughness samples showed grain boundary failure between variants of the brass texture component. Although the adjacent texture variants, designated B(sub s1) and B(sub s2), behave similarly during rolling, their plastic responses to mechanical tests can be quite different. EBSD data from through-thickness scans were used to generate Taylor factor maps. When a combined boundary normal and shear tensor was used in the calculation, the delaminating grains showed the greatest Taylor Factor differences of any grain pairs. Kernel Average Misorientation (KAM) maps also showed damage accumulation on one side of the interface. Both of these are consistent with poor slip accommodation from a crystallographically softer grain to a harder one. Transmission electron microscopy was used to confirm the EBSD observations and to show the role of slip bands in the development of large, interfacial stress concentrations. A viewgraph presentation accompanies the provided abstract.

Crooks, Roy; Tayon, Wes; Domack, Marcia; Wagner, John; Beaudoin, Armand

2009-01-01

151

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

152

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

153

Misinformation can influence memory for recently experienced, highly stressful events.  

PubMed

A large body of research has demonstrated that exposure to misinformation can lead to distortions in human memory for genuinely experienced objects or people. The current study examined whether misinformation could affect memory for a recently experienced, personally relevant, highly stressful event. In the present study we assessed the impact of misinformation on memory in over 800 military personnel confined in the stressful, mock POW camp phase of Survival School training. Misinformation introduced after the negatively affected memory for the details of the event (such as the presence of glasses or weapons), and also affected the accuracy of identification of an aggressive interrogator. In some conditions more than half of the subjects exposed to a misleading photograph falsely identified a different individual as their interrogator after the interrogation was over. These findings demonstrate that memories for stressful events are highly vulnerable to modification by exposure to misinformation, even in individuals whose level of training and experience might be thought to render them relatively immune to such influences. PMID:23219699

Morgan, C A; Southwick, Steven; Steffian, George; Hazlett, Gary A; Loftus, Elizabeth F

2013-01-01

154

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

155

Structural Phase Stability of Ti3Al Under High Pressure  

NASA Astrophysics Data System (ADS)

Recently, the structural stability of the high temperature structural intermetallic Ti3Al has been investigated experimentally and a transition from the DO19 to the DO24 structure has been reported. We have performed band structure calculations as a function of reduced volume by tight binding linear muffin-tin orbital (TBLMTO) method to look into these transitions to understand their mechanisms in terms of its electronic structure. The mechanism of the DO19 to the DO24 structure is understood to be due to shifting of the Fermi energy into a valley in the density of states curve, thereby driving the system to a more stable structure.

Rajagopalan, M.; Sahu, P. Ch.; Shekar, N. V. Chandra; Yousuf, Mohammad; Rajan, K. Govinda

156

Computer simulation of stress-oriented nucleation and growth of {theta}{prime} precipitates in Al-Cu alloys  

SciTech Connect

Many structural transformations result in several orientation variants whose volume fractions and distributions can be controlled by applied stresses during nucleation, growth or coarsening. Depending on the type of stress and the coupling between the applied stress and the lattice misfit strain, the precipitate variants may be aligned parallel or perpendicular to the stress axis. This paper reports their studies on the effect of applied stresses on nucleation and growth of coherent {theta}{prime} precipitates in Al-Cu alloys using computer simulations based on a diffuse-interface phase-field kinetic model. In this model, the orientational differences among precipitate variants are distinguished by non-conserved structural field variables, whereas the compositional difference between the precipitate and matrix is described by a conserved field variable. The temporal evolution of the spatially dependent field variables is determined by numerically solving the time-dependent Ginzburg-Landau (TDGL) equations for the structural variables and the Cahn-Hilliard diffusion equation for composition. Random noises were introduced in both the composition and the structural order parameter fields to simulate the nucleation of {theta}{prime} precipitates. It is demonstrated that although an applied stress affects the microstructural development of a two-phase alloy during both the nucleation and growth stages, it is most effective to apply stresses during the initial nucleation stage for producing anisotropic precipitate alignment.

Li, D.Y.; Chen, L.Q. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Materials Science and Engineering] [Pennsylvania State Univ., University Park, PA (United States). Dept. of Materials Science and Engineering

1998-05-01

157

Fundamental studies of stress distributions and stress relaxation in oxide scales on high temperature alloys  

SciTech Connect

The high temperature X-ray diffraction system developed for this program is being used to measure the strains which develop during oxidation. This is being applied to Ni/NiO and Cr/Cr[sub 2]O[sub 3]. Our work suggests tat the oxide and metal crystalline texture, anisotropic elastic modulus and anisotropic thermal expansion can have a pronounced effect on strain state of these systems. Acoustic emission is being used to study oxide scale failure (fracture) during oxidation. AE data from 304 stainless steel are being used to develop a statistical model of fracture process. Strength of metal/scale interface is an important property that has been difficult to quantify. Using Nano-indentation and scratch techniques developed for characterizing thin film interfaces, an effort has begun to measure the fracture toughness of the metal/scale interface. Mathematical modelling of origin and time evolution of growth stresses is an extension and improvement of previous models. The current effort employs a more sophisticated stress analysis and expands the scope to include other stress relaxation process. The interaction between the modeling studies and the X-ray diffraction measurements provides a natural credibility check to both efforts.

Shores, D.A.; Stout, J.H.; Gerberich, W.W.

1992-06-01

158

A High shear stress segment along the San Andreas Fault: Inferences based on near-field stress direction and stress magnitude observations in the Carrizo Plain Area  

SciTech Connect

Nearly 200 new in-situ determinations of stress directions and stress magnitudes near the Carrizo plain segment of the San Andreas fault indicate a marked change in stress state occurring within 20 km of this principal transform plate boundary. A natural consequence of this stress transition is that if the observed near-field ``fault-oblique`` stress directions are representative of the fault stress state, the Mohr-Coulomb shear stresses resolved on San Andreas sub-parallel planes are substantially greater than previously inferred based on fault-normal compression. Although the directional stress data and near-hydrostatic pore pressures, which exist within 15 km of the fault, support a high shear stress environment near the fault, appealing to elevated pore pressures in the fault zone (Byerlee-Rice Model) merely enhances the likelihood of shear failure. These near-field stress observations raise important questions regarding what previous stress observations have actually been measuring. The ``fault-normal`` stress direction measured out to 70 km from the fault can be interpreted as representing a comparable depth average shear strength of the principal plate boundary. Stress measurements closer to the fault reflect a shallower depth-average representation of the fault zone shear strength. If this is true, only stress observations at fault distances comparable to the seismogenic depth will be representative of the fault zone shear strength. This is consistent with results from dislocation monitoring where there is pronounced shear stress accumulation out to 20 km of the fault as a result of aseismic slip within the lower crust loading the upper locked section. Beyond about 20 km, the shear stress resolved on San Andreas fault-parallel planes becomes negligible. 65 refs., 15 figs.

Castillo, D. A., [Department of Geology and Geophysics, University of Adelaide (Australia); Younker, L.W. [Lawrence Livermore National Lab., CA (United States)

1997-01-30

159

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

160

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

161

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

162

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 ...

Ms. Hancey

2010-04-27

163

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

164

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

165

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

166

High quality AlGaN grown on ELO AlN/sapphire templates  

NASA Astrophysics Data System (ADS)

The defect structure and the homogeneity of 1-3 µm thick AlxGa1-xN layers grown on epitaxially laterally overgrown (ELO) AlN on patterned AlN/sapphire templates have been investigated in dependence on the miscut direction of the c-plane sapphire substrates, the etching depth into the sapphire and the Al concentration. It was found that shallowly etched AlN/sapphire templates with a 0.25° miscut toward the a-plane provide a smooth surface of ELO AlN and therefore a good Al homogeneity in the overgrown Al0.8Ga0.2N layer. The threading dislocation density in these layers is as low as 5×108 cm-2.

Zeimer, U.; Kueller, V.; Knauer, A.; Mogilatenko, A.; Weyers, M.; Kneissl, M.

2013-08-01

167

Stress dependence of non-chemical free energy contributions in Cu–Al–Ni shape memory alloy  

Microsoft Academic Search

A Cu–24.0at.% Al–2.2at.% Ni–0.5at.% B shape memory alloy was investigated experimentally under uniaxial tensile stress (?) up to 10MPa. Transformation temperatures and transformation strains as a function of ? were evaluated from the simultaneously measured temperature–elongation and temperature–resistance curves. Using appropriate analysis [Philos. Mag. B 82 (2002) 105; Scripta Mater. 43 (2000) 691; J. Phys. IV 11 (2001) Pr8], it

L. Daróczi; Z. Palánki; S. Szabó; D. L. Beke

2004-01-01

168

Origin of the stress-induced leakage currents in Al -Ta2O5/SiO2-Si structures  

NASA Astrophysics Data System (ADS)

The leakage currents in the Al -Ta2O5/SiO2-Si structures increase as a result of the current stress. The case of the constant current stress was studied and it was found that the I -V characteristics of both unstressed and stressed samples can be described by the previously developed model involving Poole-Frenkel effect in the Ta2O5 and both hopping conductivity and tunneling in the SiO2. After extracting the parameters for both layers from the fitting of the theoretical curves to the experimental results, it was found that the main reason for the increased leakage is the partial destruction of the SiO2 layer.

Novkovski, N.; Atanassova, E.

2005-04-01

169

Electronic and optical properties of GaN/AlN quantum dots on Si(111) subject to in-plane uniaxial stresses and variable excitation  

NASA Astrophysics Data System (ADS)

We have studied the excitation- and polarization-dependent optical properties of GaN/AlN self-assembled quantum dots (QDs) grown on Si(111) substrates. Ensembles of QDs were subject to various external stress configurations that resulted from the thermal expansion coefficient mismatch between the GaN/AlN layers and the Si(111) substrate and ranged from in-plane uniaxial stress, primarily along the ?112¯0? directions, to in-plane biaxial stress, having magnitudes ranging from 20-30 kbar. Limited regions of uniaxial stress were obtained by exploiting naturally occurring microcracks that form during the postgrowth cooling. These microcracks act as stressors in order to create the highly localized regions of uniaxial stress. The local strain tensors for such QDs, which are subject to an interfacial stress perturbation, have been determined by modeling the dependence of the QD excitonic transition energy on the interfacial stress. Cathodoluminescence (CL) measurements of the excitonic transitions exhibit an in-plane linear polarization anisotropy in close proximity to microcracks. The polarization anisotropy is strongly dependent on the sample temperature and the electron beam excitation conditions used to excite the QD ensemble. Localized CL spectroscopy of the QDs exhibits emissions from both the ground and excited states, whose relative contributions depend on the level of excitation and temperature. Experimental results indicate that the polarization anisotropy vanishes at high temperatures (˜300 K) with an increasing excitation of the QDs, while the anisotropy decreases more slowly with excitation at low temperatures (˜60 K). A theoretical modeling of the effect of carrier filling on the polarization anisotropy and the excitonic transition energy was performed, as based on three-dimensional self-consistent solutions of the Schrödinger and Poisson equations using the 6×6 k?p and effective mass methods for calculations of the e-h wave functions and electron and hole quasi-Fermi levels for varying levels of state filling. We attribute carrier filling and a thermal excitation of holes into higher energy QD hole states during excitation to account for the observed gradual decrease in the polarization anisotropy with an increasing electron-hole pair excitation density at T =300 K.

Moshe, O.; Rich, D. H.; Birner, S.; Povolotskyi, M.; Damilano, B.; Massies, J.

2010-10-01

170

Trap states in InAlN/AlN/GaN-based double-channel high electron mobility transistors  

NASA Astrophysics Data System (ADS)

We present a detailed analysis of trap states in InAlN/AlN/GaN double-channel high electron mobility transistors grown by pulsed metal organic chemical vapor deposition. By frequency dependent conductance measurements, trap densities and time constants at both InAlN/AlN/GaN interfaces were determined. Two types of traps, with a high density of up to ˜1014 cm-2 eV-1, were observed existing at the higher InAlN/AlN/GaN interface. On the other hand, the density dramatically decreased to ˜1012 cm-2 eV-1 for traps located at lower InAlN/AlN/GaN interface on which a low-temperature grown GaN (LT-GaN) layer was deposited. Additionally, photo-assisted capacitance-voltage measurements were performed to estimate deep-level defects, yielding a low density of 1.79 × 1011 cm-2 acting as negative fixed charges at the LT-GaN and lower InAlN interface.

Zhang, Kai; Xue, JunShuai; Cao, MengYi; Yang, LiYuan; Chen, YongHe; Zhang, JinCheng; Ma, XiaoHua; Hao, Yue

2013-05-01

171

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

172

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

173

The effects of proton irradiation on the reliability of InAlN/GaN high electron mobility transistors  

NASA Astrophysics Data System (ADS)

We have investigated the effect of proton irradiation on reliability of InAlN/GaN high electron mobility transistors (HEMTs). Devices were subjected to 5-15 MeV proton irradiations with a fixed dose of 5 × 1015 cm-2, or to a different doses of 2 × 1011, 5 × 1013 or 2 × 1015 cm-2 of protons at a fixed energy of 5 MeV. During off-state electrical stressing, the typical critical voltage for un-irradiated devices was 45 to 55 V. By sharp contrast, no critical voltage was detected for proton irradiated HEMTs up to 100 V, which was instrument-limited. After electrical stressing, no degradation was observed for the drain or gate current-voltage characteristics of the proton-irradiated HEMTs. However, the drain current decreased ~12%, and the reverse bias gate leakage current increased more than two orders of magnitude for un-irradiated HEMTs as a result of electrical stressing.

Liu, L.; Lo, C. F.; Xi, Y. Y.; Wang, Y. X.; Kim, H.-Y.; Kim, J.; Pearton, S. J.; Laboutin, O.; Cao, Y.; Johnson, J. W.; Kravchenko, I. I.; Ren, F.

2013-03-01

174

Low-strain plasticity in a high pressure die cast Mg-Al alloy  

NASA Astrophysics Data System (ADS)

The Kocks-Mecking method was used to compare the strain-hardening behavior at low strains of high pressure die cast Mg-9 mass% Al alloy and gravity cast fine grained pure Mg specimens. The alloy specimens exhibited a rounded flow curve in contrast with the pure metal's for which macroscopic yielding occurred at a well-defined stress. Microhardness mapping of the cross-section of an alloy specimen showed a surface layer, or skin, with hardness values ˜20 HV above those of the centre or core region. On the assumption that the core strain hardens at the same rate as the pure Mg specimen, it was estimated that ˜20% of the alloy specimen's cross-section was still elastic when the core reached full plasticity. The micromechanics of the elasto-plastic transition in the alloy specimens are discussed.

Vanna Yang, K.; Cáceres, C. H.; Nagasekhar, A. V.; Easton, M. A.

2012-03-01

175

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

176

High-Efficiency DC-DC Converter With High Voltage Gain and Reduced Switch Stress  

Microsoft Academic Search

In this paper, a high-efficiency dc-dc converter with high voltage gain and reduced switch stress is proposed. Generally speaking, the utilization of a coupled inductor is useful for raising the step-up ratio of the conventional boost converter. However, the switch surge voltage may be caused by the leakage inductor so that it will result in the requirement of high-voltage-rated devices.

Rong-Jong Wai; Chung-You Lin; Rou-Yong Duan; Yung-Ruei Chang

2007-01-01

177

High-pressure and high-temperature stability field of hydrous phase delta-AlOOH  

NASA Astrophysics Data System (ADS)

Stability field of hydrous phases is a key for understanding water concentration in the earth's mantle. ?-AlOOH is a high-pressure polymorph of diaspore (?-AlOOH) and boehmite (?-AlOOH). The space group of this phase is Pnn2 and it is similar to CaCl2-type SiO2 which is a high-pressure polymorph of stishovite; edge-sharing Al-O octahedra make single-chain along c-axis. Although it has a large stability field in pressure range from 18 GPa to 32 GPa and temperature of up to 1473 K, the high-pressure stability limits has not yet clarified. In this study, we investigated the stability field of ?-AlOOH up to 130 GPa. The high-pressure experiments were performed using a laser-heated diamond-anvil cell. Starting material was gibbsite (Al(OH)3) powder mixed with platinum black as a laser absorber. The sample was sandwiched by pure gibbsite layers and loaded into a rhenium gasket. Pressures were measured with ruby-fluorescence technique before and after heating. The sample was heated from both sides by a Nd:YAG laser operated in multimode. After experiment, stable phase in each condition was determined using the X-ray diffraction and Raman spectroscopy method. We also conducted in-situ X-ray diffraction experiments under high-pressure and temperature conditions together with the X-ray diffraction of the recovered samples both at BL10XU in SPring-8 and BL-13A in Photon Factory. In these runs, pressures were also calculated using the equation of state of platinum. The experimental conditions were in the pressures between 50-130 GPa and temperatures to 1800 K. X-ray analysis shows the sample recovered from the pressure and temperature range from 40 GPa and 1577 K to 130 GPa and 1800 K consists of ?-AlOOH. In the in-situ experiments, crystallization of ?-AlOOH was observed at 65 GPa and 1300 K and it was stable up to 1700 K. ?-AlOOH is stable in the large pressure range with a dehydration temperature around 1800K. It can be a water reservoir in subducting slabs in the deep lower mantle conditions beyond the dehydration conditions of the other hydrous phases such as dense hydrous magnesium silicates.

Sano, A.; Ohtani, E.; Kondo, T.; Hirao, N.; Sone, T.; Kikegawa, T.; Sata, N.; Ohishi, Y.

2005-12-01

178

Miniworkshop on effects of stress and strain in high-speed-growth silicon ribbons  

NASA Technical Reports Server (NTRS)

The effects of stress and strain in high speed grown silicon ribbons are discussed. Problems of stress and strain which are limiting to the rate at which SI ribbons of suitable quality for making solar cells are grown, are examined.

Briglio, A., Jr.

1984-01-01

179

Highly Stressed: Stressful and Traumatic Experiences among individuals with HIV/AIDS in the Deep South  

PubMed Central

A history of traumatic and/or stressful experiences is prevalent among HIV-infected individuals and has been consistently associated with poorer health outcomes. However, little is known about incident stressful experiences and the factors that predict these experiences among HIV-infected individuals. Data from a longitudinal study of 611 HIV-infected individuals in the Southeastern US were used to examine the frequency and types of incident stress reported in a 27-month period and to determine predictors associated with 3 incident stress measures (all stressful events, severe stressful events, and traumatic events such as physical assault). Incident stressful experiences frequently occurred among study participants, as 91% reported at least one stressful experience (median= 3.5 experiences) and 10% of study participants reported traumatic stress in any given 9-month reporting period. Financial stressors were the most frequently reported by study participants. Greater emotional distress, substance use, and number of baseline stressful experiences were significantly associated with reporting a greater number of incident stressful experiences and any traumatic experiences. Study results indicate that efforts are needed to identify individuals at risk for traumatic events and/or substantial stressors and to address the factors, including mental health and substance abuse that contribute to these experiences. PMID:21259127

Reif, Susan; Mugavero, Michael; Raper, James; Thielman, Nathan; Leserman, Jane; Whetten, Kathryn; Pence, Brian W.

2013-01-01

180

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

181

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

NASA Astrophysics Data System (ADS)

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; Matsuoka, Saburo; Sunakawa, Hideo

2014-01-01

182

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

183

[Approach to easing occupational stress for high-stress workers: applying the brief job stress questionnaire to workplace mental health promotion].  

PubMed

We investigated job stress among 442 employees from 19 divisions in a Japanese company using the Brief Job Stress Questionnaire. Job stress of the employees was estimated by the score for total health risk. Among the 19 divisions, two divisions showed over 120 points of mean total health risk score. Intervention with a stress-reduction program was carried out in these 2 divisions. First, to assess the job stress, health care staff interviewed all workers in the 2 divisions. Second, the results of the interviews were reported to the divisions' managers. Third, the managers applied the best remedy for job stress in their workplaces. In addition, occupational health staff conducted mental health education as well as individual interviews for the workers from the 2 divisions. At reevaluation one year later, both divisions showed a decreased general health risk (under 120 points). No sick leaves for depression occurred within the 2 divisions during the intervention. The results of the present study suggest that the intervention was effective in easing occupational stress for high-stress workers. The stress reduction program also seemed to have helped managers to change their recognition of occupational mental health and enabled close cooperation with occupational health staff, which may improve mental health in the workplace. PMID:18566525

Hase, Yoko; Hori, Hiroko; Nakayasu, Ikuyo; Matsushita, Yuko; Inagaki, Michiko; Unno, Aiko; Nishigaya, Eri; Nishijima, Chiharu; Enta, Kazuhiko; Sashihara, Shunsuke

2008-07-01

184

Ti/Al/Mo/Au Ohmic contacts to all-binary AlN/GaN high electron mobility transistors  

NASA Astrophysics Data System (ADS)

Electrical and microstructural characterizations of the Ti/Al/Mo/Au Ohmic contacts to ultrathin AlN/GaN heterostructures were carried out. It was found that as-deposited contacts had linear I-V behavior due to high tunneling current across the thin AlN barrier. A contact resistance of 0.455 ? mm was obtained for samples annealed at 800 °C without any premetallization plasma treatment. Transmission electron microscopy studies showed that despite the use of Ti, the AlN layer remained intact. Mushroom-shaped TiN protrusions were formed only along threading dislocations, which terminated in the AlN layer. The TiN protrusions acted as metal plugs/spikes thereby aiding carrier transport.

Wang, Liang; Adesida, Ilesanmi; Dabiran, Amir M.; Wowchak, Andrew M.; Chow, Peter P.

2008-07-01

185

Observations of hydrotectonic stress/strain events at a basement high at the Nicoya outer rise  

NASA Astrophysics Data System (ADS)

There is substantial and growing evidence from heat flow and coring investigations that the oceanic plate off Costa Rica is highly hydrologically active and that this activity is responsible for one of the most anomalously cold thermal environments encountered in the oceanic environment. Recent work by Fisher, et al. has identified limited regions above certain topographic highs with extremely high heat flows. Pore water profiles from cores above these thinly sedimented basement highs suggest upward flow on the order of ~1 cm/yr. These highs may be the principal regions of out-flow from the basement in this region and, thus, can potentially be used to constrain the general level of hydrologic activity. The nine Chemical and Aqueous Transport (CAT) meters we deployed at one of the highest heatflow sites provide a temporal record of both in-flow and out-flow of aqueous fluids at rates as low as 0.1 mm/yr. Our objective was to provide a direct measurement of long term flow rates to address the following questions: (1) What are the characteristic fluid fluxes at basement highs of the low heat flow region of the northern Costa Rican incoming plate, and (2) is this flow temporally variable? The results of the instrument deployments agree quite closely in general with the coring results in that the background rates are on the order of 1 cm/yr or less. There is, however, considerable detail in the temporal records which suggest small scale tectonic stress transients causing temporary increases in flow rate. While this is certainly not an area of major tectonic activity, the site is located at the top of the outer rise where one would expect bending-related stress and fault reactivation to occur. The CAT meters are capable of detecting minute strain events in the underlying sediments and therefore may be detecting small localized strain events. Two periods of increased flow lasting a few weeks each occur during the 5 month deployment and are indicated on all of the instruments. A few indicate downflow while the others show upflow. This sort of response would be expected during a stress event causing regions of compression and dilation. These results suggest that ridge flank basement highs may be good sites to monitor stress/strain events as well as basement hydrology.

Tryon, M. D.; Brown, K. M.

2005-12-01

186

Wear resistant Al-Si\\/TiC coatings prepared by high power laser cladding  

Microsoft Academic Search

High wear resistance Al-based composite coatings were prepared by laser cladding using powder mixtures of Al-12 wt. % Si+40 wt. % TiC and Al-40 wt. % Si+40 wt. % TiC. In the case of the coatings containing 12 % Si, the microstructure consists essentially of TiC particles dispersed in a matrix of primary alpha-Al dendrites and interdendritic alpha-Al+Si eutectic, whereas

Anandkumar Ramasamy; Amelia Almeida; Rui Vilar

2008-01-01

187

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 ...

Mrs. Deaton

2011-06-10

188

Craze nucleation in high-impact polystyrene under biaxial states of stress  

Microsoft Academic Search

Stress concentration factors adjacent to the rubbery particles in high-impact polystyrene have been computed and have been used with general stress criteria for both craze nucleation and plastic flow to predict the onset of crazing and plastic flow adjacent to the particles when the sample as a whole is tested under biaxial states of stress between uniaxial tension and uniaxial

R. J. Oxborough; P. B. Bowden

1974-01-01

189

HIGH-POWER ULTRASOUND TO ASSES THE STRESS STATE IN ROCKS  

Microsoft Academic Search

For security and production reasons, in mining industry, it is of high interest to know the stress state in rocks. The available technology to assess the stress state in rocks consults: strain gage measurements, deformation detection by optical fiber and others. None of these technologies allows the determination of stress state in real time in a suitable way. This paper

Luis Gaete-Garretón

190

Stress reduction in sputter deposited films using nanostructured compliant layers by high working-gas pressures  

E-print Network

Stress reduction in sputter deposited films using nanostructured compliant layers by high working October 2004; accepted 13 December 2004; published 27 June 2005 We present a strategy of stress reduction as a compliant layer to reduce the stress of the subsequently deposited continuous film grown under low gas

Wang, Gwo-Ching

191

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

PubMed

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

Lee, Ya-Ju; Yao, Yung-Chi; Huang, Chun-Ying; Lin, Tai-Yuan; Cheng, Li-Lien; Liu, Ching-Yun; Wang, Mei-Tan; Hwang, Jung-Min

2014-01-01

192

52 Richardson et al.: Drought Stress and Paper Birch (Betula papyrifera) Seedlings To improve the health of urban and ornamental trees, it is  

E-print Network

52 Richardson et al.: Drought Stress and Paper Birch (Betula papyrifera) Seedlings To improve, and leaf reflectance) to assess the level of drought stress in paper birch (Betula papyrifera) seedlings (but still intact) leaf, which is placed in a controlled-environment cuvette. In response to drought

Richardson, Andrew D.

193

Efficient stress relief in GaN heteroepitaxy on Si(1 1 1) using low-temperature AlN interlayers  

Microsoft Academic Search

Low-temperature (LT) AlN interlayers can be applied to reduce the tensile stress and cracks in thick GaN layers on Si. Here, we present an X-ray diffractometry study revealing the influence of metalorganic chemical vapor phase deposition parameters on stress relaxation by these interlayers. The degree of stress relaxation is observed to strongly depend on interlayer deposition temperature. At low temperatures,

A. Reiher; J. Bläsing; A. Dadgar; A. Diez; A. Krost

2003-01-01

194

Back stress evolution and iso-volume fraction lines in a Cr–Ni–Mo–Al–Ti maraging steel in the process of martensitic transformation  

Microsoft Academic Search

The quantitative identification of the back stress evolution is carried out for a Cr–Ni–Mo–Al–Ti maraging steel in the process of martensitic transformation under thermomechanical loading conditions. The evolution depends on the direction of the applied stress: tensile, compressive or shear. The iso-volume fraction lines (the iso-? lines) are determined between the transformation-start and -finish lines on the applied stress–temperature plane.

K. Nagayama; T. Terasaki; S. Goto; K. Tanaka; T. Antretter; F. D. Fischer; G. Cailletaud; F. Azzouz

2002-01-01

195

High-temperature deformation of Al-Li-Cu-Mg-Zr alloys 8090 and 8091  

Microsoft Academic Search

Specimens were prestretched in the range 0 to 7% plastic deformation prior to artificial ageing, or were duplex aged, to investigate\\u000a the effect of dislocation substructure and of S(Al2CuMg) particles on plastic flow during room and elevated temperature tensile tests. The yield stresses increased in Al-Li-Cu-Mg-Zr\\u000a alloys 8090 and 8091 after stretching, due to the dislocation cells introduced by the

Xia Xiaoxin; J. W. Martin

1992-01-01

196

Frequency Comparison of Two High-Accuracy Al+ Optical Clocks  

NASA Astrophysics Data System (ADS)

We have constructed an optical clock with a fractional frequency inaccuracy of 8.6×10-18, based on quantum logic spectroscopy of an Al+ ion. A simultaneously trapped Mg+ ion serves to sympathetically laser cool the Al+ ion and detect its quantum state. The frequency of the S01?P03 clock transition is compared to that of a previously constructed Al+ optical clock with a statistical measurement uncertainty of 7.0×10-18. The two clocks exhibit a relative stability of 2.8×10-15?-1/2, and a fractional frequency difference of -1.8×10-17, consistent with the accuracy limit of the older clock.

Chou, C. W.; Hume, D. B.; Koelemeij, J. C. J.; Wineland, D. J.; Rosenband, T.

2010-02-01

197

Static and kinetic friction of granite at high normal stress  

USGS Publications Warehouse

Frictional sliding on ground surfaces of granite, angle of sliding planes 30?? and 45??, was investigated as a function of confining pressure. Over the normal stress range of 2-12 kb, the static frictional shear stress ??s follows the relationship ??s = 0??5 + 0?? ??n and the kinetic frictional shear stress ??k was calculated to be ??k = 0??25 + 0??47 ??n. ?? 1970.

Byerlee, J.D.

1970-01-01

198

Preparation and Pore Structure Stability at High Temperature of Porous Fe-Al Intermetallics  

NASA Astrophysics Data System (ADS)

Porous Fe-Al intermetallics with different nominal compositions (from Fe-8 wt.% Al to Fe-50 wt.% Al) were fabricated by Fe and Al elemental powders through reaction synthesis. The effects of the Al content on the pore structure properties, and the comparison of pore structure stabilities at high-temperatures among the porous Fe-Al intermetallics and porous Ti, Ni, 316L stainless steel samples, were systematically studied. Results showed that the open porosity, maximum pore size, and permeability vary with the Al content. Porous Fe-(25-30 wt.%) Al intermetallics show good shape controllability and excellent pore structure stability at 1073 K in air, which suggests that these porous Fe-Al intermetallics could be used for filtration at high temperatures.

Shen, P. Z.; Gao, H. Y.; Song, M.; He, Y. H.

2013-12-01

199

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

200

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

201

Quaternary InAlGaN-based deep-UV LED with high-Al-content p-type AlGaN  

NASA Astrophysics Data System (ADS)

For the realization of 250-350 nm band deep ultraviolet (UV) emitters using group III-nitride materials, it is required to obtain high-efficiency UV emission and hole conductivity for wide-bandgap (In)AlGaN. For achieving high-efficiency deep UV emission, it is quite effective to use In segregation effect which has been already used for InGaN blue emitting devices. We have demonstrated high-efficiency UV emission by introducing several percent of In into AlGaN in the wavelength range of 300-360 nm at room temperature with an In segregation effect. The emission fluctuation in the submicron region due to In segregation was clearly observed for the quaternary InAlGaN epitaxial layers. An internal quantum efficiency as high as 15% was estimated from quaternary InAlGaN based single quantum well (SQW) at around 350 nm at room temperature. Such a high efficiency UV emission can be obtained even on high threading dislocation density buffers. Also, hole conductivity was obtained for high Al content (>53%) Mg-doped AlGaN by using alternative gas flow growth process in metal-organic vapor phase epitaxy (MOVPE). Using these techniques we fabricated 310 nm band deep UV light-emitting diodes (LEDs) with quaternary InxAlyGa1-x-yN active region. We achieved output power of 0.4 mW for a 308 nm LED and 0.8 mW for a 314 nm LED under room temperature pulsed operation.

Hirayama, Hideki; Aoyagi, Yoshinobu

2004-07-01

202

Comparison of the transport properties of high quality AlGaN/AlN/GaN and AlInN/AlN/GaN two-dimensional electron gas heterostructures  

NASA Astrophysics Data System (ADS)

The transport properties of high mobility AlGaN/AlN/GaN and high sheet electron density AlInN/AlN/GaN two-dimensional electron gas (2DEG) heterostructures were studied. The samples were grown by metal-organic chemical vapor deposition on c-plane sapphire substrates. The room temperature electron mobility was measured as 1700 cm2/V s along with 8.44×1012 cm-2 electron density, which resulted in a two-dimensional sheet resistance of 435 ?/? for the Al0.2Ga0.8N/AlN/GaN heterostructure. The sample designed with an Al0.88In0.12N barrier exhibited very high sheet electron density of 4.23×1013 cm-2 with a corresponding electron mobility of 812 cm2/V s at room temperature. A record two-dimensional sheet resistance of 182 ?/? was obtained in the respective sample. In order to understand the observed transport properties, various scattering mechanisms such as acoustic and optical phonons, interface roughness, and alloy disordering were included in the theoretical model that was applied to the temperature dependent mobility data. It was found that the interface roughness scattering in turn reduces the room temperature mobility of the Al0.88In0.12N/AlN/GaN heterostructure. The observed high 2DEG density was attributed to the larger polarization fields that exist in the sample with an Al0.88In0.12N barrier layer. From these analyses, it can be argued that the AlInN/AlN/GaN high electron mobility transistors (HEMTs), after further optimization of the growth and design parameters, could show better transistor performance compared to AlGaN/AlN/GaN based HEMTs.

Tülek, Remziye; Ilgaz, Aykut; Gökden, Sibel; Teke, Ali; Öztürk, Mustafa K.; Kasap, Mehmet; Özçelik, Süleyman; Arslan, Engin; Özbay, Ekmel

2009-01-01

203

Chronic Psychological Stress Enhances Nociceptive Processing in the Urinary Bladder in High-Anxiety Rats  

PubMed Central

This study sought to determine whether acute and/or chronic psychological stress produce changes in urinary bladder nociception. Female Sprague-Dawley (SD; low/moderate anxiety) or Wistar-Kyoto (WK; high-anxiety) rats were exposed to either an acute (1 day) or a chronic (10 days) water avoidance stress paradigm or a sham stress paradigm. Paw withdrawal thresholds to mechanical and thermal stimuli and fecal pellet output, were quantified at baseline and after the final stress or sham stress exposure. Rats were then sedated, and visceromotor responses (VMRs) to urinary bladder distension (UBD) were recorded. While acute stress exposure did not significantly alter bladder nociceptive responses in either strain of rats, WK rats exposed to a chronic stress paradigm exhibited enhanced responses to UBD. These high-anxiety rats also exhibited somatic analgesia following acute, but not chronic, stress. Furthermore, WK rats had greater fecal pellet output than SD rats when stressed. Significant stress-induced changes in nociceptive responses to mechanical stimuli were observed in SD rats. That chronic psychological stress significantly enhanced bladder nociceptive responses only in high-anxiety rats provides further support for a critical role of genetics, stress and anxiety as exacerbating factors in painful urogenital disorders such as interstitial cystitis (IC). PMID:17521683

Robbins, M.T.; DeBerry, J.; Ness, T.J.

2007-01-01

204

Internal friction in [gamma]-TiAl at high temperatures  

SciTech Connect

The internal friction in TiAl polycrystals of technical purity was studied in the temperature range of 300--1500 K using an inverted torsion pendulum. Extruded single-phase [gamma]-TiAl with an aluminium content of 54.1 at.% shows a large, frequency-dependent relaxation maximum near 1300 K during cooling from temperatures above 1400 K, which is neither observed during heating from ambient temperature nor in two-phase [alpha][sub 2]/[gamma]-TiAl alloys with a lower Al content. This relaxation maximum is tentatively ascribed to the motion of grain boundaries or dislocations, which are pinned by precipitates in [gamma]-TiAl. The precipitates dissolve at temperatures above 1350 K and form again below 1200 K. No relaxation is observed in polycrystalline TiAl with a carbon content in the range from 0.009 to 0.22 at.% at temperatures below 900 K. This behavior may be an indication of hardening by finely dispersed precipitates, as observed in TEM and SEM micrographs.

Brossmann, U.; Hirscher, M.; Kronmueller, H. (Max-Planck-Inst. fuer Metallforschung, Stuttgart (Germany))

1999-06-22

205

Very high channel conductivity in ultra-thin channel N-polar GaN/(AlN, InAlN, AlGaN) high electron mobility hetero-junctions grown by metalorganic chemical vapor deposition  

NASA Astrophysics Data System (ADS)

Different back barrier designs comprising of AlN, AlGaN, and InAlN layers are investigated for ultra-thin GaN channel N-polar high-electron-mobility-transistors grown by metalorganic chemical vapor deposition. A combinational back barrier with both AlGaN and InAlN materials is proposed. The dependence of channel conductivity on channel thickness is investigated for different back barrier designs. The study demonstrated that the back barrier design of AlN/InAlN/AlGaN is capable of retaining high channel conductivity for ultra-scaled channel thicknesses. For devices with 5-nm-thick channel, a sheet resistance of ˜230 ?/? and mobility ˜1400 cm2/V-s are achieved when measured parallel to the multi-step direction of the epi-surface.

Lu, Jing; Denninghoff, Dan; Yeluri, Ramya; Lal, Shalini; Gupta, Geetak; Laurent, Matthew; Keller, Stacia; DenBaars, Steven P.; Mishra, Umesh K.

2013-06-01

206

The Chinese High School Student's Stress in the School and Academic Achievement  

ERIC Educational Resources Information Center

In a sample of 466 Chinese high school students, we examined the relationships between Chinese high school students' stress in the school and their academic achievements. Regression mixture modelling identified two different classes of the effects of Chinese high school students' stress on their academic achievements. One class contained 87% of…

Liu, Yangyang; Lu, Zuhong

2011-01-01

207

High reflectivity ultraviolet distributed Bragg reflector based on AlGaN/AlGaN multilayer  

NASA Astrophysics Data System (ADS)

AlGaN/AlGaN distributed Bragg reflectors (DBRs) designed for the ultraviolet spectral region have been attained. The crack-free structures were grown on c-plane sapphire by plasma assisted molecular beam epitaxy (MBE). To minimize the built-in strain in DBRs, a thin buffer layer was used directly on c-plane sapphire. A peak reflectivity of 95% at 381 nm with a 21 nm stop band width was obtained at room temperature (RT) using a 32.5 pairs Al 0.7Ga 0.3N/Al 0.15Ga 0.85N DBR. With a driving force for DBRs and emitting regions in wide band gap semiconductor microcavities, such as those based on GaN and ZnO, is the quest for cavity polariton which is the coupled mode between the exciton and photon modes. Moreover, the exploitation of cavity polaritons could be expected in the course of the development of extremely low-threshold optoelectronics devices.

Shimada, Ryoko; Xie, Jinqiao; Morkoç, Hadis

2007-02-01

208

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

209

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

210

High strength and high electrical conductivity of UFG Al-2%Fe alloy achieved by high-pressure torsion and aging  

NASA Astrophysics Data System (ADS)

In this study, Al-2%Fe samples extracted from a cast ingot in the shape of rings were processed by High-Pressure Torsion (HPT) at room temperature. Suitable specimens were extracted for evaluation of mechanical properties and electrical resistivity. High tensile strength of ~600 MPa was attained by HPT due to grain refinement down to an average grain size of ~130 nm and by subsequent aging accompanied by nano-sized (~10 nm) AhFe precipitates. The resulting conductivity (IACS%) was recovered from ~40% in the steady state after HPT to well above 50% in the peak-aged condition, which is in the range of current Al electrical alloys.

Cubero-Sesin, J. M.; Arita, M.; Watanabe, M.; Horita, Z.

2014-08-01

211

A high-content screen identifies novel compounds that inhibit stress-induced TDP-43 cellular aggregation and associated cytotoxicity.  

PubMed

TDP-43 is an RNA binding protein found to accumulate in the cytoplasm of brain and spinal cord from patients affected with amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Nuclear TDP-43 protein regulates transcription through several mechanisms, and under stressed conditions, it forms cytoplasmic aggregates that co-localize with stress granule (SG) proteins in cell culture. These granules are also found in the brain and spinal cord of patients affected with ALS and FTLD. The mechanism through which TDP-43 might contribute to neurodegenerative diseases is poorly understood. To investigate the pathophysiology of TDP-43 aggregation and to isolate potential therapeutic targets, we screened a chemical library of 75,000 compounds using high-content analysis with PC12 cells that inducibly express human TDP-43 tagged with green fluorescent protein (GFP). The screen identified 16 compounds that dose-dependently decreased the TDP-43 inclusions without significant cellular toxicity or changes in total TDP-43 expression levels. To validate the effect, we tested compounds by Western blot analysis and in a Caenorhabditis elegans model that replicates some of the relevant disease phenotypes. The hits from this assay will be useful for elucidating regulation of TDP-43, stress granule response, and possible ALS therapeutics. PMID:24019256

Boyd, Justin D; Lee-Armandt, J Peter; Feiler, Marisa S; Zaarur, Nava; Liu, Min; Kraemer, Brian; Concannon, John B; Ebata, Atsushi; Wolozin, Benjamin; Glicksman, Marcie A

2014-01-01

212

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

213

In-plane uniaxial stress effects of AlGaAs/GaAs modulation doped heterostructures characterized by the transmission line method  

NASA Astrophysics Data System (ADS)

Transmission line method patterns were fabricated on AlGaAs/GaAs heterostructures to measure the effect of uniaxial stress on the heterojunction two-dimensional electron gas resistivity and the contact resistance. Uniaxial compressive stress was applied in the [110] and [11¯0] directions of heterojunctions fabricated on (001)-oriented GaAs substrates. Fitting the measured data to a lumped resistor model yielded normalized sheet resistivity stress coefficients of -3.2%/kbar and 12.6%/kbar for stress in the [110] and [11¯0] directions, respectively. From these coefficients we obtain a value for the piezoelectric constant e14 of Al0.4Ga0.6As to be -0.26 C/m2, which when linearly extrapolated to AlAs gives -0.40 C/m2 compared to the value -0.225 C/m2 calculated by Hübner [Phys. Status Solidi B 57, 627 (1973)].

Fung, A. K.; Albrecht, J. D.; Nathan, M. I.; Ruden, P. P.; Shtrikman, H.

1998-10-01

214

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

Technology Transfer Automated Retrieval System (TEKTRAN)

Aluminum (Al) toxicity is an important limitation to food security in the tropical and subtropical regions. High Al saturation in acid soils limits root development and its ability to uptake water and nutrients. In this study, we present a genome scan for Al tolerance loci with over 50,000 GBS-based...

215

Solar-blind AlGaN-based Schottky photodiodes with low noise and high detectivity  

E-print Network

Solar-blind AlGaN-based Schottky photodiodes with low noise and high detectivity Necmi Biyiklia. The devices were fabricated on n /n AlGaN/GaN heterostructures using a microwave compatible fabrication performance achieved for AlGaN-based solar-blind detectors.15 Dark cur- rents less than 2 pA at 30 V reverse

Aytür, Orhan

216

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 Coagulationeflocculatione sedimentation Water treatment Aggregation a b s t r a c t Polyaluminum chloride (PACl) is a well-established coagulant in water treatment with high removal efficiency for arsenic. A high content of Al30 nanoclusters

Wehrli, Bernhard

217

Stress  

MedlinePLUS

... higher blood glucose levels in people with either type of diabetes. It's easy to find out whether mental stress affects your glucose control. Before checking your glucose levels, write down a number rating ...

218

High-quality Al{sub x}Ga{sub 1{minus}x}N using low temperature-interlayer and its application to UV detector[Ultraviolet  

SciTech Connect

Low-temperature (LT-) AlN interlayer reduces tensile stress during growth of Al{sub x}Ga{sub 1{minus}x}N, while simultaneously acts as the dislocation filter, especially for dislocations of which Burger's vector contains [0001] components. UV photodetectors using thus-grown high quality Al{sub x}Ga{sub 1{minus}x}N layers were fabricated. The dark current below 50 fA at 10 V bias for 10 {micro}m strip allowing a photocurrent to dark current ratio greater than one even at 40 nW/cm{sup 2} have been achieved.

Iwaya, M.; Terao, S.; Hayashi, N.; Kashima, T.; Detchprohm, T.; Amano, H.; Akasaki, I.; Hirano, A.; Pernot, C.

2000-07-01

219

Chinese high school students' academic stress and depressive symptoms: gender and school climate as moderators.  

PubMed

In a sample of 368 Chinese high school students, the present study examined the different effects of Chinese high school students' academic stress on their depressive symptoms and the moderating effects of gender and students' perceptions of school climate on the relationships between their academic stress and depressive symptoms. Regression mixture model identified two different kinds of subgroups in the effects of students' academic stress on their depressive symptoms. One subgroup contained 90% of the students. In this subgroup, the students' perceptions of academic stress from lack of achievement positively predicted their depressive symptoms. For the other 10% of the students, academic stress did not significantly predict their depressive symptoms. Next, multinomial regression analysis revealed that girls or students who had high levels of achievement orientation were more likely to be in the first subgroup. The findings suggested that gender and students' perceptions of school climate could moderate the relationships between Chinese high school students' academic stress and their depressive symptoms. PMID:22190389

Liu, Yangyang; Lu, Zuhong

2012-10-01

220

High-temperature deformation behavior of an Al-8.4Fe-3.6Ce dispersion-strengthened material  

NASA Astrophysics Data System (ADS)

The high-temperature deformation behavior of a dispersion-strengthened Al-8.4Fe-3.6Ce material studied by Yaney and Nix[1] has been reanalyzed using concepts used in the analysis of the creep behavior of Al-Fe-V-Si materials. The Al-8.4Fe-3.6Ce material presents a high volume fraction of submicron dispersoids. The stress exponent and the activation energy values are anomalously high-temperature dependent, as it is usually found in most reinforced materials. Although the creep behavior of this material has been described by the deformation of dispersoids, however, direct evidence of the deformation of the second-phase precipitates was not obtained. In this work, a new approach is further developed. This approach is based on the constant substructure slip creep equation modified by the presence of an interaction between dislocations and dispersoids. This approach is able to satisfactorily predict the creep behavior of the Al-8.4Fe-3.6Ce material.

Carreño, Fernando; Ruano, Oscar A.

1999-02-01

221

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

222

Transient characteristics of AlGaN/GaN high-electron-mobility transistor with bias-controllable field plate  

NASA Astrophysics Data System (ADS)

The trapping and emission of carriers in the gate-to-drain region of an AlGaN/GaN high-electron-mobility transistor (HEMT) have been investigated using a bias-controllable field plate (CFP). Once an instantaneous positive CFP voltage is applied after bias stress in a transient drain current measurement, carrier trapping occurs, which can subsequently be observed as a drain current discontinuity. Numerical analysis of carrier trapping using the Shockley–Read–Hall process also provides a trapped carrier density of 5.1 × 1012 cm?2 and an energy level of 0.6 eV.

Mase, Suguru; Egawa, Takashi; Wakejima, Akio

2015-03-01

223

CaAl 12Si 4O 27, a New High-Pressure Phase Containing Al 6O 19 Clusters  

NASA Astrophysics Data System (ADS)

CaAl12Si4O27, a new high-pressure phase in the CaO-Al2O3-SiO2 system, was prepared at 1550°C and 14 GPa. It has trigonal symmetry, P-3, with a=7.223(1) and c=8.614(3) Å. Its structure was solved using crystal chemistry principles and refined using the Rietveld method applied to powder X-ray diffraction data, Rwp=6.1%, RB=2.7%. The structure is a new type based on a close-packed anion lattice with a mixed layer stacking sequence ABACA?(hc)2 and with Ca atoms ordered in one-seventh of the anion sites in alternate c-stacked layers. The Si atoms are ordered in both octahedral and tetrahedral sites while the Al atoms are ordered in two independent octahedral sites. Octahedral edge-shared clusters, Al6O19, occur in the structure, interconnected within the close-packed layers by corner-linking to SiO4 tetrahedra. The clusters are also connected by corner-sharing to nine-member rings of edge-shared Al- and Si-centered octahedra in adjacent layers. The new phase has structural features in common with the barium titanium ferrite of similar composition, BaFe11Ti3O23, as well as with the mineral simpsonite, Al4Ta3O13(OH), and alkali metal niobates which contain Nb6O19 clusters.

Grey, I. E.; Madsen, I. C.; Hibberson, W. O.; O'Neill, H. St. C.

2000-09-01

224

Itacolumite like High Damping Ceramics in the System Al2O3-TiO2-MgO  

NASA Astrophysics Data System (ADS)

Ceramics is rigid and brittle originally. If the weakness could be overcome, the application will be widely expanded. Itacolumite known as high flexibility rock is the group of sand stone which consist of quartz and slight amount of muscovite. The microstructure of itacolumite has a lot of narrow gaps between the grains, the gap was thought to be formed by the dissolution of minerals in between quartz grains into the groundwater. This narrow space enables a little displacement of the particles, and the rock can bend with stress like plastic deformation. These characters of itacolumite showed the new ceramic functions such as stress relaxation properties and high damping capacity (internal friction Q-1=0.03). The authors tried to develop high damping ceramics by the mimic of itacolumite, and found the Al2O3-TiO2-MgO ceramics. The ceramics had stress relaxation properties and high damping capacity (Q-1=0.01) since microcracks were formed during sintering by the discontinuous grain growth and the anisotropic thermal expansion in the cooling process.

Shimazu, T.; Miura, M.; Isu, N.; Ogawa, T.; Ichikawa, A.; Ishida, E. H.

2006-05-01

225

Oxidative stress and autophagic alteration in brainstem of SOD1-G93A mouse model of ALS.  

PubMed

Amyotrophic lateral sclerosis (ALS) is a progressive and fatal neurodegenerative disease involving both upper and lower motor neurons. The mechanism of motor neuron degeneration is still unknown. Although many studies have been performed on spinal motor neurons, few have been reported on brainstem and its motor nuclei. The aim of this study was to investigate oxidative stress and autophagic changes in the brainstem and representative motor nuclei of superoxide dismutase 1 (SOD1)-G93A mouse model of ALS. The expression levels of cluster of differentiation molecule 11b (CD11b), glial fibrillary acidic protein, glutamate-cysteine ligase catalytic subunit, heme oxygenase-1, NAD(P)H: quinone oxidoreductase 1, voltage-dependent anion-selective channel protein 1, Sequestosome 1/p62 (p62), microtubule-associated protein 1 light chain 3B (LC3), and SOD1 proteins in brainstem were examined by Western blot analysis. Immunohistochemistry and immunofluorescence were performed to identify the cellular localization of SOD1, p62, and LC3B, respectively. The results showed that there were progressive asctrocytic proliferation and microglial activation, induction of antioxidant proteins, and increased p62 and LC3II expression in brainstem of SOD1-G93A mice. Additionally, SOD1 and p62 accumulated in hypoglossal, facial, and red nuclei, but not in oculomotor nucleus. Furthermore, electron microscope showed increased autophagic vacuoles in affected brainstem motor nuclei. Our results indicate that brainstem share similar gliosis, oxidative stress, and autophagic changes as the spinal cord in SOD1-G93A mice. Thus, SOD1 accumulation in astrocytes and neurons, oxidative stress, and altered autophagy are involved in motor neuron degeneration in the brainstem, similar to the motor neurons in spinal cord. Therefore, therapeutic trials in the SOD1G93A mice need to target the brainstem in addition to the spinal cord. PMID:24390572

An, Ting; Shi, Pengxiao; Duan, Weisong; Zhang, Shipan; Yuan, Pin; Li, Zhongyao; Wu, Dongxia; Xu, Zuoshang; Li, Chunyan; Guo, Yansu

2014-06-01

226

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

227

Polarization effects on gate leakage in InAlN/AlN/GaN high-electron-mobility transistors  

NASA Astrophysics Data System (ADS)

Lattice-matched InAlN/AlN/GaN high electron mobility transistors offer high performance with attractive electronic and thermal properties. For high-voltage applications, gate leakage currents under reverse bias voltages remain a serious challenge. This current flow is dominated by field enhanced thermal emission from trap states or direct tunneling. We experimentally measure reverse-bias gate leakage currents in InAlN/AlN/GaN transistors at various temperatures and find that the conventional trap-assisted Frenkel-Poole model fails to explain the experimental data. Unlike the non-polar semiconductors Si, Ge, large polarization-induced electric fields exist in III-nitride heterojunctions. When the large polarization fields are accounted for, a modified Frenkel-Poole model is found to accurately explain the measured data at low reverse bias voltages. At high reverse bias voltages, we identify that the direct Fowler-Nordheim tunneling mechanism dominates. The accurate identification of the gate leakage current flow mechanism in these structures leads to the extraction of several useful physical parameters, highlights the importance of polarization fields, and leads to suggestions for improved behavior.

Ganguly, Satyaki; Konar, Aniruddha; Hu, Zongyang; Xing, Huili; Jena, Debdeep

2012-12-01

228

In situ stress heterogeneity induced by weak natural fractures and faults with high slip-tendency  

NASA Astrophysics Data System (ADS)

In situ stress measurements typically conducted using several geotechnical methods (hydraulic fracturing and overcoring) often show quite scattered and inconsistent stress magnitudes. Would they be artifacts from test errors or genuine stress signals in the crust? I report two field examples of stress measurements, in which lateral stresses represented by maximum (SHmax) and minimum (Shmin) horizontal principal stresses scatter quite widely, to investigate the cause of the observed stress heterogeneity. Hydraulic fracturing stress measurements were conducted in vertical boreholes at two different locations in South Korea. The boreholes are 300 and 400 m deep, respectively, both penetrating granites. Several isolated intervals of intact rocks over depths in the boreholes were vertically fractured by injecting water. Magnitudes of Shmin were determined from shut-in pressures. Magnitudes of SHmax were estimated based on the Hubbert-Willis (1957) equation using reliably determined hydraulic fracturing tensile strengths. The stress states in both locations are in reverse faulting stress regimes, in which vertical stress (Sv) is the least principal stress. The magnitudes of SHmax are generally within or close to stress range limited by frictional coefficients of 0.6-1.0 of nearby faults. However, SHmax do not increase consistently with depth, but rather scatter quite significantly. Over only a few tens of meter depth interval, the SHmax magnitudes jump up and down by an order of ~10 MPa, often resulting in lower SHmax values at deeper depths. Near the depths of relatively low stress, natural fractures and faults with wide apertures (for instance, wider than ~10 mm, observed from borehole image logs) are abundant, and near those of relatively high stress, those wide discontinuities are scarce. Such wide discontinuities are inferred to be filled with weak gouges or rock fragments, and thus tend to have relatively low frictional coefficients. In particular, the wide fractures and faults are oriented predominantly in the directions of high slip-tendency. If excessive stress is exerted, those weak fractures and faults would slip to release the stress, which would reduce the stress magnitudes to the values that can only be sustained by the discontinuities. This observation suggests that stress magnitudes are constrained quite locally by such weak, high slip-tendency discontinuities. Although the remote stress field might be uniformly applied, the stress state in the crust seems inherently heterogeneous because of the heterogeneous distribution of weak natural fractures and faults.

Chang, Chandong

2014-05-01

229

Modeling of high composition AlGaN channel high electron mobility transistors with large threshold voltage  

NASA Astrophysics Data System (ADS)

We report on the potential of high electron mobility transistors (HEMTs) consisting of high composition AlGaN channel and barrier layers for power switching applications. Detailed two-dimensional (2D) simulations show that threshold voltages in excess of 3 V can be achieved through the use of AlGaN channel layers. We also calculate the 2D electron gas mobility in AlGaN channel HEMTs and evaluate their power figures of merit as a function of device operating temperature and Al mole fraction in the channel. Our models show that power switching transistors with AlGaN channels would have comparable on-resistance to GaN-channel based transistors for the same operation voltage. The modeling in this paper shows the potential of high composition AlGaN as a channel material for future high threshold enhancement mode transistors.

Bajaj, Sanyam; Hung, Ting-Hsiang; Akyol, Fatih; Nath, Digbijoy; Rajan, Siddharth

2014-12-01

230

Loss of ALS2 Function Is Insufficient to Trigger Motor Neuron Degeneration in Knock-Out Mice But Predisposes Neurons to Oxidative Stress  

PubMed Central

Amyotrophic lateral sclerosis (ALS), the most common motor neuron disease, is caused by a selective loss of motor neurons in the CNS. Mutations in the ALS2 gene have been linked to one form of autosomal recessive juvenile onset ALS (ALS2). To investigate the pathogenic mechanisms of ALS2, we generated ALS2 knock-out (ALS2?/?) mice. Although ALS2?/? mice lacked obvious developmental abnormalities, they exhibited age-dependent deficits in motor coordination and motor learning. Moreover, ALS2?/? mice showed a higher anxiety response in the open-field and elevated plus-maze tasks. Although they failed to recapitulate clinical or neuropathological phenotypes consistent with motor neuron disease by 20 months of age, ALS2?/? mice or primary cultured neurons derived from these mice were more susceptible to oxidative stress compared with wild-type controls. These observations suggest that loss of ALS2 function is insufficient to cause major motor deficits or motor neuron degeneration in a mouse model but predisposes neurons to oxidative stress. PMID:16107644

Cai, Huaibin; Lin, Xian; Xie, Chengsong; Laird, Fiona M.; Lai, Chen; Wen, Hongjin; Chiang, Hsueh-Cheng; Shim, Hoon; Farah, Mohamed H.; Hoke, Ahmet; Price, Donald L.; Wong, Philip C.

2008-01-01

231

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

232

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

233

High Sensitivity Stress Sensor Based on Hybrid Materials  

NASA Technical Reports Server (NTRS)

A sensing device is used to detect the spatial distributions of stresses applied by physical contact with the surface of the sensor or induced by pressure, temperature gradients, and surface absorption. The sensor comprises a hybrid active layer that includes luminophores doped in a polymeric or organic host, altogether embedded in a matrix. Under an electrical bias, the sensor simultaneously converts stresses into electrical and optical signals. Among many applications, the device may be used for tactile sensing and biometric imaging.

Cao, Xian-An (Inventor)

2014-01-01

234

Metagenomic Analysis of Stress Genes in Microbial Mat Communities from Antarctica and the High Arctic  

E-print Network

mats from Arctic and Antarctic ice shelves, using high-throughput pyrosequencing to test the hypotheses of diverse mechanisms of adaptation to cold and other stresses in polar mats, consistentMetagenomic Analysis of Stress Genes in Microbial Mat Communities from Antarctica and the High

Vincent, Warwick F.

235

Creep strength of high chromium steels welded parts under multiaxial stress conditions  

Microsoft Academic Search

Internal pressure creep tests as well as uniaxial creep tests were conducted on 9Cr and 12Cr steels welded joints in order to evaluate creep strength of the high chromium steels welded parts under multiaxial stress conditions, where a welding direction of the internal pressure specimen was longitudinal one. Except under high stress conditions, cracks occurred at fine grained HAZ region

Masatsugu Yaguchi; Takashi Ogata; Takayuki Sakai

2010-01-01

236

A Study Concerning Stress among High School Students in Selected Rural Schools.  

ERIC Educational Resources Information Center

This study identifies stressful events in the lives of high school students in a rural region of Tennessee. Questionnaires were completed by 240 high school students (144 female and 96 male). The questionnaires included 19 statements to which the participants were to respond concerning their belief about the stressfulness of the situation…

Peach, Larry

237

Improved drought and salt stress tolerance in transgenic tobacco overexpressing a novel A20/AN1 zinc-finger "AlSAP" gene isolated from the halophyte grass Aeluropus littoralis.  

PubMed

We describe here the isolation of a novel gene, designated AlSAP, from A. littoralis in a first step to exploit the potential of this halophyte grass as a genetic resource to improve salt and drought tolerance in plants and, particularly, in cereals. The Aeluropus genome contains a single AlSAP gene which has an intron at its 5'UTR. Sequence homology analysis showed that the AlSAP protein is characterized by the presence of two conserved zinc-finger domains A20 and AN1. AlSAP is induced not only by various abiotic stresses such as salt, osmotic, heat and cold but, also by abscisic acid (ABA) and salicylic acid (SA). Tobacco plants expressing the AlSAP gene under the control of the duplicated CaMV35S promoter exhibited an enhanced tolerance to abiotic stresses such as salinity (350 mM NaCl), drought (soil Relative Water Content (RWC) = 25%), heat (55 degrees C for 2.5 h) and freezing (-20 degrees C for 3 h). Moreover, under high salt and drought conditions, the transgenic plants were able to complete their life cycle and to produce viable seeds while the wild-type plants died at the vegetative stage. Measurements of the leaf RWC and of the root and leaf endogenous Na(+) and K(+) levels in AlSAP transgenic lines compared to wild-type tobacco, showed an evident lower water loss rate and a higher Na(+) accumulation in senescent-basal leaves, respectively. Finally, we found that the steady state levels of transcripts of eight stress-related genes were higher in AlSAP transgenic lines than in wild-type tobacco. Taken together, these results show that AlSAP is a potentially useful candidate gene for engineering drought and salt tolerance in cultivated plants. PMID:19838809

Ben Saad, Rania; Zouari, Nabil; Ben Ramdhan, Walid; Azaza, Jalel; Meynard, Donaldo; Guiderdoni, Emmanuel; Hassairi, Afif

2010-01-01

238

Induction of engineered residual stresses fields and enhancement of fatigue life of high reliability metallic components by laser shock processing  

NASA Astrophysics Data System (ADS)

Laser shock processing (LSP) is being increasingly applied as an effective technology for the improvement of metallic materials mechanical and surface properties in different types of components as a means of enhancement of their corrosion and fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists on the generation of relatively deep compression residual stresses field into metallic alloy pieces allowing an improved mechanical behaviour, explicitly the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Additional results accomplished by the authors in the line of practical development of the LSP technique at an experimental level (aiming its integral assessment from an interrelated theoretical and experimental point of view) are presented in this paper. Concretely, follow-on experimental results on the residual stress profiles and associated surface properties modification successfully reached in typical materials (especially Al and Ti alloys characteristic of high reliability components in the aerospace, nuclear and biomedical sectors) under different LSP irradiation conditions are presented along with a practical correlated analysis on the protective character of the residual stress profiles obtained under different irradiation strategies. Additional remarks on the improved character of the LSP technique over the traditional "shot peening" technique in what concerns depth of induced compressive residual stresses fields are also made through the paper.

Ocaña, J. L.; Porro, J. A.; Díaz, M.; Ruiz de Lara, L.; Correa, C.; Gil-Santos, A.; Peral, D.

2013-02-01

239

Families OverComing under Stress (FOCUS) for Early Childhood: Building Resilience for Young Children in High Stress Families  

ERIC Educational Resources Information Center

Parental distress and trauma affects the entire family, including the youngest children. Families OverComing Under Stress (FOCUS) is a targeted prevention program for high-risk families that aims to enhance family cohesion, support the parent-child relationship, and build emotional regulation, communication, and problem-solving skills across the…

Mogil, Catherine; Paley, Blair; Doud, Tricia; Havens, Linda; Moore-Tyson, Jessica; Beardslee, William R.; Lester, Patricia

2010-01-01

240

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

241

Using a Coupled Thermal/Material Flow Model to Predict Residual Stress in Friction Stir Processed AlMg9Si  

NASA Astrophysics Data System (ADS)

A coupled thermal/material flow model of friction stir processing is developed for friction stir processing of an as-cast AlSi9Mg aluminum alloy. By capturing material flow during processing, an asymmetric temperature distribution is generated with higher processing temperatures on the advancing side than on the retreating side. The temperature distribution from the coupled model is then incorporated into a thermomechanical model to predict the residual stress state after processing. These numerical results are compared with the residual stresses experimentally measured by the trepanation method. Experimental results show that the tensile residual stresses are higher on the advancing side than on the retreating side. The simulation successfully captures the asymmetric behavior of the residual stress profile, and the predicted maximum residual stress values show relatively good agreement with the experimental values. The simulated profile, however, is narrower than the experimental profile, yielding a smaller region of tensile residual stresses around the process zone than experimentally observed.

Hamilton, C.; W?glowski, M. St.; Dymek, S.; Sedek, P.

2015-03-01

242

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

243

Fundamental studies of stress distributions and stress relaxation in oxide scales on high temperature alloys. [Final progress report  

SciTech Connect

This report summarizes a three-year study of stresses arising in the oxide scale and underlying metal during high temperature oxidation and of scale cracking. In-situ XRD was developed to measure strains during oxidation over 1000{degrees}C on pure metals. Acoustic emission was used to observe scale fracture during isothermal oxidation and cooling, and statistical analysis was used to infer mechanical aspects of cracking. A microscratch technique was used to measure the fracture toughness of scale/metal interface. A theoretical model was evaluated for the development and relaxation of stresses in scale and metal substrate during oxidation.

Shores, D.A.; Stout, J.H.; Gerberich, W.W.

1993-06-01

244

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

245

76 FR 45303 - ING Asia Pacific High Dividend Equity Income Fund, et al.; Notice of Application  

Federal Register 2010, 2011, 2012, 2013, 2014

...Company Act Release No. 29735; File No. 812-13909] ING Asia Pacific High Dividend Equity Income Fund, et al.; Notice of...stock that such investment companies may issue. Applicants: ING Asia Pacific High Dividend Equity Income Fund (``IAE''),...

2011-07-28

246

Acute stress differentially affects spatial configuration learning in high and low cortisol-responding healthy adults  

PubMed Central

Background Stress and stress hormones modulate memory formation in various ways that are relevant to our understanding of stress-related psychopathology, such as posttraumatic stress disorder (PTSD). Particular relevance is attributed to efficient memory formation sustained by the hippocampus and parahippocampus. This process is thought to reduce the occurrence of intrusions and flashbacks following trauma, but may be negatively affected by acute stress. Moreover, recent evidence suggests that the efficiency of visuo-spatial processing and learning based on the hippocampal area is related to PTSD symptoms. Objective The current study investigated the effect of acute stress on spatial configuration learning using a spatial contextual cueing task (SCCT) known to heavily rely on structures in the parahippocampus. Method Acute stress was induced by subjecting participants (N = 34) to the Maastricht Acute Stress Test (MAST). Following a counterbalanced within-subject approach, the effects of stress and the ensuing hormonal (i.e., cortisol) activity on subsequent SCCT performance were compared to SCCT performance following a no-stress control condition. Results Acute stress did not impact SCCT learning overall, but opposing effects emerged for high versus low cortisol responders to the MAST. Learning scores following stress were reduced in low cortisol responders, while high cortisol-responding participants showed improved learning. Conclusions The effects of stress on spatial configuration learning were moderated by the magnitude of endogenous cortisol secretion. These findings suggest a possible mechanism by which cortisol responses serve an adaptive function during stress and trauma, and this may prove to be a promising route for future research in this area. PMID:23671762

Meyer, Thomas; Smeets, Tom; Giesbrecht, Timo; Quaedflieg, Conny W. E. M.; Merckelbach, Harald

2013-01-01

247

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

248

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

249

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

250

Stress Fracture of the First Rib in a High School Weight Lifter  

PubMed Central

A 17-year-old boy, who played a weight lifting in high school, sustained stress fracture of the first rib without any causes. We successfully treated first rib stress fracture with limitation of using the upper extremity and with using low-intensity pulsed ultrasound. Key points Stress fracture of the first rib in a weight lifter was successfully treated with limitation of sports activity and with LIPUS treatment. PMID:24149543

Fujioka, Hiroyuki; Kokubu, Takeshi; Makino, Takeshi; Nagura, Issei; Toyokawa, Narikazu; Inui, Atsuyuki; Sakata, Ryosuke; Kurosaka, Masahiro

2009-01-01

251

High Novelty-Seeking Rats Are Resilient to Negative Physiological Effects of the Early Life Stress  

PubMed Central

Exposure to early life stress dramatically impacts adult behavior, physiology, and neuroendocrine function. Using rats bred for novelty-seeking differences and known to display divergent anxiety, depression, and stress vulnerability, we examined the interaction between early life adversity and genetic predisposition for high- versus low-emotional reactivity. Thus, bred Low Novelty Responder (bLR) rats, which naturally exhibit high anxiety- and depression-like behavior, and bred High Novelty Responder (bHR) rats, which show low anxiety/depression together with elevated aggression, impulsivity, and addictive behavior, were subjected to daily 3 h maternal separation (MS) stress postnatal days 1–14. We hypothesized that MS stress would differentially impact adult bHR/bLR behavior, physiology (stress-induced defecation), and neuroendocrine reactivity. While MS stress did not impact bHR and bLR anxiety-like behavior in the open field test and elevated plus maze, it exacerbated bLRs’ already high physiological response to stressstress-induced defecation. In both tests, MS bLR adult offspring showed exaggerated stress-induced defecation compared to bLR controls while bHR offspring were unaffected. MS also selectively impacted bLRs’ (but not bHRs’) neuroendocrine stress reactivity, producing an exaggerated corticosterone acute stress response in MS bLR versus control bLR rats. These findings highlight how genetic predisposition shapes individuals’ response to early life stress. Future work will explore neural mechanisms underlying the distinct behavioral and neuroendocrine consequences of MS in bHR/bLR animals. PMID:24090131

Clinton, Sarah M.; Watson, Stanley J.; Akil, Huda

2014-01-01

252

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

253

Investigation of constant voltage off-state stress on Au-free AlGaN/GaN Schottky barrier diodes  

NASA Astrophysics Data System (ADS)

In this work, we perform an in-depth analysis of electron-trapping in AlGaN/GaN Schottky barrier diodes under constant voltage (VAC = ?100 V) off-state stress conditions. The current–voltage (I–V) characteristics of the diode after stressing show a leakage reduction and on-state degradation due to electron-trapping occurring in the vicinity of the Schottky contact. Capacitance–voltage (C–V) measurements confirm an increase of the barrier height and the on-resistance of the stressed device. Furthermore, the on-resistance increase has been studied with different temperatures and stressing times. By TCAD simulations, a lateral extension of the “trapped region” at the AlGaN/Si3N4 interface has been visualized and can qualitatively explain the phenomenon of higher on-resistance increase at higher temperatures.

Hu, Jie; Stoffels, Steve; Lenci, Silvia; Wu, Tian-Li; Ronchi, Nicolò; You, Shuzhen; Bakeroot, Benoit; Groeseneken, Guido; Decoutere, Stefaan

2015-04-01

254

Performance evaluation of AIP-TiAlN coated tool for high speed machining  

Microsoft Academic Search

Ti0.67Al0.33N single-layered and Ti0.52Al0.48N\\/TiN double-layered coatings were applied to end-mill tools made of WC–Co material by an arc ion plating technique. Their performances under high speed cutting conditions were evaluated about cutting force, tool wear, and surface roughness of workpiece. With Ti–Al–N coatings, tool life and performance were much increased under high speed machining. The Ti0.67Al0.33N single-layer coated tool showed

Myung Chang Kang; In-Wook Park; Kwang Ho Kim

2003-01-01

255

Characterization of residual stresses in heat treated Ti-6Al-4V forgings by machining induced distortion  

NASA Astrophysics Data System (ADS)

To provide a solid base for improved material exploitation in dimensioning calculations it is necessary to determine the stress state in the part prior to service loading. In order to achieve higher material strength at elevated temperatures, the surface temperature gradient with respect to time has to be sufficiently high during heat treatment. This results in non-negligable residual stresses that can reduce the allowable load level upon which yielding occurs. For titanium alloys there are two common heat treatments, namely solution treatment and mill annealing. The latter one is the method of choice within the presented project. Mill annealing is utilized in order to significantly reduce the residual stresses in the parts without loosing much of the improved strength at elevated temperatures. Quantification of residual stresses is done by solving an inverse problem. From the measurement of distortion, induced by dividing the investigated part, the residual stress state can be calculated via analytical modeling or correlation with finite element models. To assure a minimum perturbation of the residual stress state during specimen production, dividing of the part is accomplished by electric discharge machining. The parts of interest are v-shaped prisms with a length of approximatly 450 mm and a thickness in the cross sectional area from about 20 mm to 45 mm. Figure 1(a) shows the forged part and 1(b) the dimensions of the cross section in millimeters as well as the material properties considered in the finite element model. The heat exchange between the part and the environment is modelled as heat transfer by convection superimposed with heat radiation. Since the parts are exposed to air during forging and heat treatment, the surface develops a strongly adhesive oxide layer, the so called alpha-case. After forging the parts are cooled in air and heat treated at a temperature of 720° C for a duration of 120 min. Subsequent air cooling and removing the alpha-case by shot peening and chemical treatment in a mixture of nitric and hydroflouric acid finishes the processing. The residual stress state in the parts is quantified through correlation of results obtained by finite element simulations and high precision deflection experiments. Experimental measuring errors are minimized by using the capability of the wire cutting machine to measure locations on the specimens with respect to the fixed machine coordinate system. A sophisticated design of cutting operations allows an analysis of the part without removing the fixture and hence makes it possible to achieve a very high accuracy of the displacement measurements of about 4 µm. The quality of the obtained results also depends on the finite element models describing the mechanics of the experimental investigations as precise as possible. Since numerical modeling of shot peening and chemical milling is rather complicated, the whole processing route of the shapes is simplified assuming that the individual contribution of all process steps to the residual stress state can be described by virtual heat transfer coefficients. The overall virtual heat transfer coefficient for the whole processing route is calculated from the linear superposition of the individual heat transfer coeffcients for each processing step. Detailed analysis of the obtained overall virtual heat transfer coefficients in comparison with experimentally obtained ones shows, that other processing steps besides the heat treatment considerably influence the residual stress state. In order to make the conducted simulation scheme applicable in practise, advanced finite element modeling techniques are developed. The experimentally derived deflection curves are correlated to the finite element results via a least square fit.

Regener, B.; Krempaszky, C.; Werner, E.

2010-06-01

256

The experimental determination of the stress responses of an Al\\/Mg alloy to a polygonal strain path after three levels of prestraining  

Microsoft Academic Search

A servohydraulic, computer-controlled MTS axial-torsion testing machine with a biaxial clip-on extensometer is employed to test thin-walled tubes of an Al\\/Mg alloy under nonproportional straining. Digital data acquisition is used to record axial and shear stress as well as axial and shear strain. The influence of three levels of prestrain (0%, 1% and 12%) on the subsequent stress response to

E. Krempl; S. Cheng

1993-01-01

257

High temperature deformation behavior in a 2124Al/15vol%SiC[sub w] composite  

SciTech Connect

One of the interesting properties of Al/SiC composites is a superplastic-like behavior or an extended ductility in a two-phase (solid + liquid) region. Mahoney and Ghosh reported that a 7475Al/SiC[sub p] (subscript p represent particulate) could be superplastically deformed up to 450% at 500[degree]C. The matrix itself was a superplastic material, which made it possible for the composite to be superplastically deformed. Wu and Sherby reported a superplasticity in 2024Al/SiC[sub w](subscript w represents whisker) under a thermal cycling condition, which was attributed to internal stresses. The above superplastic behaviors were obtained at very slow strain rates. On the other hand, Chokshi et al. reported that elongation of a 2124Al/SiC[sub w] increased with increasing strain rate up to 10[sup [minus]1]sec[sup [minus]1] at 475[degree]C. Nieh et al. reported an unusual superplasticity, more precisely, superplastic-like behavior that had not been discovered with earlier experimental results. The objectives of this work is to obtain an optimum condition for hot working of a 2124Al/15%SiC[sub w] and to suggest a model which can qualitatively explain the extended ductility in the two-phase(solid and liquid phases) region.

Kim, Jae Hong; Lee, Dong Nyung (Seoul National Univ., Seoul (Korea, Republic of)); Oh, Kyu Hwan (Korea Inst. of Science and Technology, Seoul (Korea, Republic of))

1993-08-01

258

Microstructure Characterization and Stress Corrosion Evaluation of Autogenous and Hybrid Friction Stir Welded Al-Cu-Li 2195 Alloy  

NASA Technical Reports Server (NTRS)

Friction stir welding process is being evaluated for application on the Al-Cu-Li 2195 Super-Light Weight External Tank of the Space Transportation System. In the present investigation Al-Cu-Li 2195 plates were joined by autogenous friction stir welding (FSW) and hybrid FSW (friction stir welding over existing variable polarity plasma arc weld). Optical microscopy and transmission electron microscopy (TEM) were utilized to characterize microstructures of the weldments processed by both welding methods. TEM observations of autogenous FSW coupons in the center section of the dynamically-recrystallized zone showed an equiaxed recrystallized microstructure with an average grain size of approx. 3.8 microns. No T(sub 1), precipitates were present in the above-mentioned zone. Instead, T(sub B) and alpha precipitates were found in this zone with a lower population. Alternate immersion, anodic polarization, constant load, and slow strain tests were carried out to evaluate the general corrosion and stress-corrosion properties of autogenous and hybrid FSW prepared coupons. The experimental results will be discussed.

Li, Zhixian; Arbegast, William J.; Meletis, Efstathios I.

1997-01-01

259

Improved properties of high-Al-composition AlGaN/GaN high electron mobility transistor structures with thin GaN cap layers  

NASA Astrophysics Data System (ADS)

GaN cap layers with thicknesses between 0.6 and 2.4 nm were shown to effectively suppress the degradation of the structural and electrical properties of AlGaN/GaN high electron mobility transistor (HEMT) structures with xAl ˜ 0.5 grown by metal-organic chemical vapor deposition (MOCVD). The formation of platelets and trench networks on free AlGaN surfaces was successfully mitigated by GaN cap layers as thin as 0.6 nm. Simultaneously, a rise in sheet charge density and mobility of the two-dimensional electron gas (2DEG) was observed, the magnitude of which depended on the AlGaN thickness. GaN was also shown to be a superior capping material compared to in-situ grown Si3N4.

Li, Haoran; Keller, Stacia; DenBaars, Steven P.; Mishra, Umesh K.

2014-09-01

260

Overcoming Si3N4 film stress limitations for high quality factor ring resonators  

E-print Network

Overcoming Si3N4 film stress limitations for high quality factor ring resonators Kevin Luke,1 Avik University, Ithaca, New York 14853, USA * ml292@cornell.edu Abstract: Silicon nitride (Si3N4) ring resonators that stress in Si3N4 films can be overcome by introducing mechanical trenches for isolating photonic devices

Lipson, Michal

261

Overcoming Si3N4 film stress limitations for High Quality factor ring resonators  

E-print Network

Overcoming Si3N4 film stress limitations for High Quality factor ring resonators Kevin Luke1 , Avik, Cornell University, Ithaca, NY 14853, USA * ml292@cornell.edu Abstract: Silicon nitride (Si3N4) ring show that stress in Si3N4 films can be overcome by introducing mechanical trenches for isolating

Lipson, Michal

262

Validation of Stress Corrosion Cracking Model for High Level Radioactive-Waste Packages  

Microsoft Academic Search

A stress corrosion cracking (SCC) model has been adapted for performance prediction of high level radioactive-waste packages to be emplaced in the proposed Yucca Mountain radioactive-waste repository. SCC is one form of environmentally assisted cracking resulting from the presence of three factors: metallurgical susceptibility, critical environment, and tensile stresses. For waste packages of the proposed Yucca Mountain repository, the outer

S Lu; G Gordon; P Andresen

2004-01-01

263

A Highly Accurate Stress Measurement System for Producing Precise X-Ray Masks  

Microsoft Academic Search

A new system that measures stress in film deposited on Si wafers has been developed to produce highly accurate X-ray masks. The system consists of very rigid air sliders, an electrostatic sensor, and a soft-handling wafer chuck. With the system, wafer warp is precisely measured before and after film deposition, and the stress distribution is calculated from those measurements. Wafer

Masatoshi Oda; Atsunobu Une; Ikuo Okada; Shinji Shinohara; Yasuo Nakayama; Hideo Yoshihara

1995-01-01

264

Coping Strategies Among Police Recruits in a High-Stress Training Environment  

Microsoft Academic Search

The use and impact of coping strategies were explored in a setting of environmental stress. The sample consisted of 180 police recruits subjected to training stress in a U.S. police academy. Measures of coping, personal distress, and life stressors were used. Recruits who scored high on personal distress tended to use more coping strategies than those who had lower distress

John M. Violanti

1992-01-01

265

Stress fracture of the first rib in a high school weight lifter  

Microsoft Academic Search

A 17-year-old boy, who played a weight lifting in high school, sustained stress fracture of the first rib without any causes. We successfully treated first rib stress fracture with limitation of using the upper extremity and with using low-intensity pulsed ultrasound.

Hiroyuki Fujioka; Takeshi Kokubu; Takeshi Makino; Issei Nagura; Narikazu Toyokawa; Atsuyuki Inui; Ryosuke Sakata; Masahiro Kurosaka

2009-01-01

266

Nano-sized twins induce high rate sensitivity of flow stress in pure copper  

E-print Network

Nano-sized twins induce high rate sensitivity of flow stress in pure copper L. Lu a,b , R sensitivity of flow stress and the extent of strengthening in polycrystalline copper containing dif- ferent volume fractions of nano-sized twins, but having the same average grain size. The specimens were produced

Dao, Ming

267

Fever-range thermal stress promotes lymphocyte trafficking across high endothelial venules via  

E-print Network

Fever-range thermal stress promotes lymphocyte trafficking across high endothelial venules via S Evans1 Fever is an evolutionarily conserved response during acute inflammation, although its physiological benefit is poorly understood. Here we show thermal stress in the range of fever temperatures

von Andrian, Ulrich H.

268

High-temperature strength and creep resistance of FeAl  

Microsoft Academic Search

In an effort to improve the high-temperature mechanical properties of FeAl, we investigated the effects of alloying addition and heat treatment temperature on the tensile and creep properties of Fe–40at.% Al. Alloying of Fe–40Al with titanium, molybdenum, zirconium, boron and carbon, and heat treating at 1300°C resulted in significant improvement in strength and creep resistance due to solid solution and

R. S. Sundar; S. C. Deevi

2003-01-01

269

Charge trapping memory structures with Al 2O 3 trapping dielectric for high-temperature applications  

Microsoft Academic Search

Charge trapping memory structures with Al2O3 dielectrics as a trapping dielectric are investigated in a metal–Al2O3–oxide–silicon configuration with a metal gate of high work function. The devices show very good write\\/erase characteristics, endurance, retention and disturb behaviour. At elevated temperature, devices with an Al2O3 trapping layer are found to have better retention properties than devices with a silicon nitride trapping

M. Specht; H. Reisinger; F. Hofmann; T. Schulz; E. Landgraf; R. J. Luyken; W. Rosner; M. Grieb; L. Risch

2005-01-01

270

Protective SiAlON Coating with Embedded High Temperature Corrosion Sensor  

Microsoft Academic Search

We have fabricated oxidation resistant and wear resistant SiAlON films by RF magnetron co-sputtering of Al and Si targets in Ar\\/O2\\/N2 mixtures. The SiAlON films are amorphous, extremely smooth, and have very low oxygen permeability making them extremely attractive as passivation layers on a variety of sensors and other microelectronic devices used in high-temperature oxidizing environments. To analyze the performance

S. B. Rivers; J. I. Krassikoff; G. Bernhardt; C. J. Bocchino; R. J. Lad

2007-01-01

271

Doped CVD Al 2O 3 coatings for high performance cutting tools  

Microsoft Academic Search

Today, high performance applications of cemented carbide cutting tool inserts demand coatings with enhanced wear resistance. Chemical vapour deposited coatings based on Ti(C,N) and Al2O3 are the systems of choice for these applications. The influence of experimental variables on process stability and Al2O3 modification and structure was investigated. Deposition characteristics of Al2O3 as a function of doping combinations, generated by

M Kathrein; W Schintlmeister; W Wallgram; U Schleinkofer

2003-01-01

272

Estrés, Estilo de Afrontamiento y Adherencia al Tratamiento de Adolescentes Diabéticos Tipo 1. Stress, Copying Style, and Treatment Adherence in Adolescents Sufferingfrom Type I Diabetes  

Microsoft Academic Search

The relationship between stress, coping style, and Type 1 Diabetes Mellitus has been well documented. Due to its chronic nature and its highly demanded treatment, adolescents suffering from Type 1 Diabetes Mellitus may fail when confronting important aspects of the illness, generating high levels of stress and low rates of treatment adherence. In this study, using a non experimental design

Manuel Ortiz Parada

273

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

274

Dynamic Young’s moduli of tungsten and tantalum at high temperature and stress  

NASA Astrophysics Data System (ADS)

Recently reported results of the long lifetime of the tungsten samples under high temperature and high stress conditions expected in the Neutrino Factory target have strengthened the case for a solid target option for the Neutrino Factory. In order to study in more detail the behaviour of the material properties of tungsten, a dynamic method has been used for measurement of Young's modulus at high stress, high-strain-rates (>1000 s -1) and very high temperatures (up to 2650 °C). The method is based on measurements of the surface vibration of thin wires, stressed by a pulsed current, using a Laser Doppler Vibrometer. The measured characteristic frequencies under the thermal excitation have been used to obtain Young's modulus as a function of applied stress and temperature. The same procedure has been used to measure Young's modulus of tantalum up to 2500 °C.

Škoro, G. P.; Bennett, J. R. J.; Edgecock, T. R.; Gray, S. A.; McFarland, A. J.; Booth, C. N.; Rodgers, K. J.; Back, J. J.

2011-02-01

275

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

276

Effects of solidification structure and aging condition on cyclic stress–strain response in Al–7% Si–0.4% Mg cast alloys  

Microsoft Academic Search

Stress–strain response under cyclic loading at fixed plastic strain amplitude condition was examined for age-hardenable Al–7% Si–0.4% Mg (A356) cast alloys. The specimens examined include the cast alloys with ordinary dendrite structure and semi-liquid die-cast alloys with fine effective grain structure. Al–0.5% Mg–0.4% Si (6063) alloy was also tested for comparison. Special attention was paid to the effect of solidification

Sang-Won Han; Koji Katsumata; Shinji Kumai; Akikazu Sato

2002-01-01

277

High-temperature oxidation behavior of pure Ni{sub 3}Al  

SciTech Connect

The high-temperature oxidation behaviour of pure Ni{sub 3}Al alloys in air was studied above 1000{degrees}C. In isothermal oxidation tests between 1000 and 1200{degrees}C, Ni{sub 3}Al showed parabolic oxidation behavior and displayed excellent oxidation resistance. In cyclic oxidation tests between 1000 and 1300{degrees}C, Ni{sub 3}Al exhibited excellent oxidation resistance between 1000 and 1200{degrees}C, but drastic spalling of oxide scales was observed at 1300{degrees}C. When Ni{sub 3}Al was oxidized at 1000{degrees}C, Al{sub 2}O{sub 3} was present as {theta}-Al{sub 2}O{sub 3} in a whisker form. But, at 1100{degrees}C the gradual transformation of initially formed metastable {theta}-Al{sub 2}O{sub 3} to stable {alpha}-Al{sub 2}O{sub 3} was observed after oxidation for about 20 hr. After oxidation at 1200{degrees}C for long times, the formation of a thick columnar-grain layers of {alpha}-Al{sub 2}O{sub 3} was observed beneath a thin and fine-grain outer layer of {alpha}-Al{sub 2}O{sub 3}. The oxidation mechanism of pure Ni{sub 3}Al is described.

Choi, S.C.; Cho, H.J.; Kim, Y.J.; Lee, D.B. [Sung-Kyun-Kwan Univ., Suwon (Korea, Republic of)

1996-08-01

278

Combat high or traumatic stress: violent offending is associated with appetitive aggression but not with symptoms of traumatic stress  

PubMed Central

Former members of armed groups in eastern DR Congo had typically witnessed, experienced, and perpetrated extreme forms of violence. Enhanced trauma-related symptoms had been shown in prior research. But also lashing out in self-defense is a familiar response to threat defined as reactive aggression. Another potential response is appetitive aggression, in which the perpetration of excessive violence is perceived as pleasurable (combat high). What roles do these forms of aggressive behavior play in modern warfare and how are they related to posttraumatic stress symptoms? To answer the question, we sought to determine predictors for appetitive aggressive and trauma-related mental illness, and investigated the frequency of psychopathological symptoms for high- and low-intensity conflict demobilization settings. To this end, we interviewed 213 former members of (para)military groups in the eastern Democratic Republic of Congo in regard to their combat exposure, posttraumatic stress, appetitive aggression, depression, suicidality, and drug dependence. Random forest regression embedded in a conditional inference framework revealed that perpetrated violent acts are not necessarily stressful. In fact, the experience of violent acts that typically implicated salient cues of hunting (e.g., blood, suffering of the victim, etc.) had the strongest association with an appetite for aggression. Furthermore, the number of lifetime perpetrated violent acts was the most important predictor of appetitive aggression. However, the number of perpetrated violent acts did not significantly affect the posttraumatic stress. Greater intensity of conflict was associated with more severe posttraumatic stress symptoms and depression. Psychotherapeutic interventions that address appetitive aggression in addition to trauma-related mental illness, including drug dependence, therefore seem indispensible for a successful reintegration of those who fought in the current civil wars. PMID:25709586

Köbach, Anke; Schaal, Susanne; Elbert, Thomas

2015-01-01

279

Evaluation of Wheat Chromosome Translocation Lines for High Temperature Stress Tolerance at Grain Filling Stage  

PubMed Central

High temperature (HT, heat) stress is detrimental to wheat (Triticum aestivum L.) production. Wild relatives of bread wheat may offer sources of HT stress tolerance genes because they grow in stressed habitats. Wheat chromosome translocation lines, produced by introgressing small segments of chromosome from wild relatives to bread wheat, were evaluated for tolerance to HT stress during the grain filling stage. Sixteen translocation lines and four wheat cultivars were grown at optimum temperature (OT) of 22/14°C (day/night). Ten days after anthesis, half of the plants were exposed to HT stress of 34/26°C for 16 d, and other half remained at OT. Results showed that HT stress decreased grain yield by 43% compared with OT. Decrease in individual grain weight (by 44%) was the main reason for yield decline at HT. High temperature stress had adverse effects on leaf chlorophyll content and Fv/Fm; and a significant decrease in Fv/Fm was associated with a decline in individual grain weight. Based on the heat response (heat susceptibility indices, HSIs) of physiological and yield traits to each other and to yield HSI, TA5594, TA5617, and TA5088 were highly tolerant and TA5637 and TA5640 were highly susceptible to HT stress. Our results suggest that change in Fv/Fm is a highly useful trait in screening genotypes for HT stress tolerance. This study showed that there is genetic variability among wheat chromosome translocation lines for HT stress tolerance at the grain filling stage and we suggest further screening of a larger set of translocation lines. PMID:25719199

Pradhan, Gautam Prasad; Prasad, P. V. Vara

2015-01-01

280

Evaluation of TiN/Cu Gate Metal Scheme for AlGaN/GaN High-Electron-Mobility Transistor Application  

NASA Astrophysics Data System (ADS)

The TiN/Cu metal scheme as gate metal for AlGaN/GaN high-electron-mobility transistors (HEMTs) is investigated. The copper-gated devices show comparable DC characteristics to the conventional Ni/Au-gated devices. No obvious of changes in IDS and IGS were observed for the device after being stressed at VDS=200 and VGS=-5 V for 32 h. The thermal stability test indicates comparable Schottky barrier height for the TiN/Cu gate metal on GaN before and after 250 °C annealing for 1 h. Overall, the AlGaN/GaN HEMT with the TiN/Cu gate metal structure demonstrates excellent device DC characteristics, good thermal stability, and stable performance after a high-voltage stress test.

Lin, Yueh-Chin; Chang, Chih-Hsiang; Li, Fang-Ming; Hsu, Li-Han; Chang, Edward Yi

2013-09-01

281

Laminated metal composite formed from low flow stress layers and high flow stress layers using flow constraining elements and making same  

DOEpatents

A laminated metal composite of low flow stress layers and high flow stress layers is described which is formed using flow constraining elements, preferably in the shape of rings, individually placed around each of the low flow stress layers while pressure is applied to the stack to bond the layers of the composite together, to thereby restrain the flow of the low flow stress layers from the stack during the bonding. The laminated metal composite of the invention is made by the steps of forming a stack of alternate layers of low flow stress layers and high flow stress layers with each layer of low flow stress material surrounded by an individual flow constraining element, such as a ring, and then applying pressure to the top and bottom surfaces of the resulting stack to bond the dissimilar layers together, for example, by compression rolling the stack. In a preferred embodiment, the individual flow constraining elements surrounding the layers of low flow stress material are formed of a material which may either be the same material as the material comprising the high flow stress layers, or have similar flow stress characteristics to the material comprising the high flow stress layers. Additional sacrificial layers may be added to the top and bottom of the stack to avoid damage to the stack during the bonding step; and these additional layers may then be removed after the bonding step.

Syn, Chol K. (Moraga, CA); Lesuer, Donald R. (Livermore, CA)

1995-01-01

282

Laminated metal composite formed from low flow stress layers and high flow stress layers using flow constraining elements and making same  

DOEpatents

A laminated metal composite of low flow stress layers and high flow stress layers is described which is formed using flow constraining elements, preferably in the shape of rings, individually placed around each of the low flow stress layers while pressure is applied to the stack to bond the layers of the composite together, to thereby restrain the flow of the low flow stress layers from the stack during the bonding. The laminated metal composite of the invention is made by the steps of forming a stack of alternate layers of low flow stress layers and high flow stress layers with each layer of low flow stress material surrounded by an individual flow constraining element, such as a ring, and then applying pressure to the top and bottom surfaces of the resulting stack to bond the dissimilar layers together, for example, by compression rolling the stack. In a preferred embodiment, the individual flow constraining elements surrounding the layers of low flow stress material are formed of a material which may either be the same material as the material comprising the high flow stress layers, or have similar flow stress characteristics to the material comprising the high flow stress layers. Additional sacrificial layers may be added to the top and bottom of the stack to avoid damage to the stack during the bonding step; and these additional layers may then be removed after the bonding step. 5 figs.

Syn, C.K.; Lesuer, D.R.

1995-07-04

283

High shear stress can initiate both platelet aggregation and shedding of procoagulant containing microparticles.  

PubMed

Previous studies have demonstrated that a high level of shear stress can produce platelet aggregation without the addition of any agonist. We investigated whether high shear stress could cause both platelet aggregation and shedding of microparticles from the platelet plasma membrane. A coneplate viscometer was used to apply shear stress and microparticle formation was measured by flow cytometry. It was found that microparticle formation increased as the duration of shear stress increased. Both microparticles and the remnant platelets showed the exposure of procoagulant activity on their surfaces. Investigation of the mechanisms involved in shear-dependent microparticle generation showed that binding of von Willebrand factor (vWF) to platelet glycoprotein lb, influx of extracellular calcium, and activation of platelet calpain were required to generate microparticles under high shear stress conditions. Activation of protein kinase C (PKC) promoted shear-dependent microparticle formation. Epinephrine did not influence microparticle formation, although it enhanced platelet aggregation by high shear stress. These findings suggest the possibility that local generation of microparticles in atherosclerotic arteries, the site that pathologically high shear stress could occur, may contribute to arterial thrombosis by providing and expanding a catalytic surface for the coagulation cascade. PMID:8896411

Miyazaki, Y; Nomura, S; Miyake, T; Kagawa, H; Kitada, C; Taniguchi, H; Komiyama, Y; Fujimura, Y; Ikeda, Y; Fukuhara, S

1996-11-01

284

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

285

Structural and optical properties of direct current sputtered zinc aluminum oxides with a high Al concentration  

Microsoft Academic Search

Zinc aluminum oxide films were deposited by reactive dc magnetron sputtering from Zn\\/Al target containing 30 wt.% Al. Sputtering was carried out on glass and Si(100) substrates held at room temperature. The effect of oxygen flow on structural and optical properties was studied. The properties of the films were strongly dependent on oxygen flow. Amorphous, highly transparent and very smooth

S. H. Mohamed; R. Drese

2006-01-01

286

Si-doped high Al-content AlGaN epilayers with improved quality and conductivity using indium as a surfactant  

E-print Network

Si-doped high Al-content AlGaN epilayers with improved quality and conductivity using indium online 4 March 2008 Effects of indium as a surfactant for the growth of Si-doped Al0.75Ga0.25N epilayers by metal organic chemical vapor deposition have been studied. It was found that the use of indium

Jiang, Hongxing

287

High Rate Deposition of High Quality ZnO:Al by Filtered Cathodic Arc  

SciTech Connect

High quality ZnO:Al (AZO) thin films were prepared on glass substrates by direct current filtered cathodic arc deposition. Substrate temperature was varied from room temperature to 425oC, and samples were grown with and without the assistance of low power oxygen plasma (75W). For each growth condition, at least 3 samples were grown to give a statistical look at the effect of the growth environment on the film properties and to explore the reproducibility of the technique. Growth rate was in the 100-400 nm/min range but was apparently random and could not be easily traced to the growth conditions explored. For optimized growth conditions, 300-600 nm AZO films had resistivities of 3-6 x 10-4 ?Omega cm, carrier concentrations in the range of 2-4 x 1020 cm3, Hall mobility as high as 55 cm2/Vs, and optical transmittance greater than 90percent. These films are also highly oriented with the c-axis perpendicular to the substrate and a surface roughness of 2-4 nm.

Mendelsberg, Rueben J.; Lim, S.H.N.; Milliron, D.J.; Anders, Andre

2010-11-18

288

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

289

Advanced technologies for improving high frequency performance of AlGaN/GaN high electron mobility transistors  

E-print Network

In this thesis, we have used a combination of physical analysis, numerical simulation and experimental work to identify and overcome some of the main challenges in AlGaN/GaN high electron mobility transistors (HEMTs) for ...

Chung, Jinwook W. (Jinwook Will)

2008-01-01

290

Transient high-pressure stress relaxation of prestressing tendons in unbonded construction   

E-print Network

of construction. One concern for these structures in fire is that high temperature stress relaxation of the unbonded prestressed reinforcement may cause considerable and irrecoverable prestress loss, with subsequent structural consequences. This paper uses a...

Gales, John; Bisby, Luke; MacDougall, Colin; MacLean, Kevin

291

Stress Management as an Enabling Technology for High-Field Superconducting Dipole Magnets  

E-print Network

This dissertation examines stress management and other construction techniques as means to meet future accelerator requirement demands by planning, fabricating, and analyzing a high-field, Nb_(3)Sn dipole. In order to enable future fundamental...

Holik, Eddie Frank

2014-06-03

292

Occupational Stress and Cardiovascular Risk Factors in High-Ranking Government Officials and Office Workers  

PubMed Central

Background: Cardiovascular diseases are among the most important sources of mortality and morbidity, and have a high disease burden. There are some major well-known risk factors, which contribute to the development of these diseases. Occupational stress is caused due to imbalance between job demands and individual’s ability, and it has been implicated as an etiology for cardiovascular diseases. Objectives: This study was conducted to evaluate the cardiovascular risk factors and different dimensions of occupational stress in high-ranking government officials, comparing an age and sex-matched group of office workers with them. Patients and Methods: We invited 90 high-ranking officials who managed the main governmental offices in a city, and 90 age and sex-matched office workers. The subjects were required to fill the occupational role questionnaire (Osipow) which evaluated their personal and medical history as well as occupational stress. Then, we performed physical examination and laboratory tests to check for cardiovascular risk factors. Finally, the frequency of cardiovascular risk factors and occupational stress of two groups were compared. Results: High-ranking officials in our study had less work experience in their current jobs and smoked fewer pack-years of cigarette, but they had higher waist and hip circumference, higher triglyceride level, more stress from role overload and responsibility, and higher total stress score. Our group of office workers had more occupational stress because of role ambiguity and insufficiency, but their overall job stress was less than officials. Conclusions: The officials have higher scores in some dimensions of occupational stress and higher overall stress score. Some cardiovascular risk factors were also more frequent in managers. PMID:25389469

Mirmohammadi, Seyyed Jalil; Taheri, Mahmoud; Mehrparvar, Amir Houshang; Heydari, Mohammad; Saadati Kanafi, Ali; Mostaghaci, Mehrdad

2014-01-01

293

A study on stress affecting the microwave surface resistance of YBCO high temperature superconducting thin films  

Microsoft Academic Search

We calculate stress in YBa2Cu3O7?x\\/MgO (YBCO\\/MgO) and YBa2Cu3O7?x\\/LaAlO3 (YBCO\\/LAO) by XRD of the sample, ?1=?1.2GPa and ?2=?1.4GPa, respectively, which shows that the stress in YBCO\\/LAO is stronger than that in YBCO\\/MgO. In addition, microwave response of the two pieces of thin films is also investigated by microstrip resonator technique. Surface resistance and penetration depth of the films are obtained by

Li-Bin Shi; Cui-Yan Xu; Guo-Hua Zhang

2008-01-01

294

High-temperature mechanical properties of SiC whisker reinforced Al sub 2 O sub 3 composites  

SciTech Connect

High-temperature constant strain rate compressive tests have been performed on Al{sub 2}O{sub 3} reinforced with different concentrations of SiC whiskers. The samples were obtained from three sources, but contained whiskers from the same source. The temperature range was from 1300 to 1500{degree}C and experiments were conducted in air and argon. Strain rates varied from 3 {times} 10{sup {minus}8} to 5 {times} 10{sup {minus}5} s{sup {minus}1} with stresses between 3 and 500 MPa. Stress exponents were fond to vary between 1 and 5 and depended on microstructure, whisker concentration and stress, indicating a change in the mechanism controlling plastic deformation. Change from diffusional creep to a damage accumulation mechanism was supported by TEM observations on samples as-received and deformed both in the n = 1 regime and in the n = 5 regime. Degradation of SiC whiskers occurred when testing in air. 12 refs., 1 tab., 7 figs.

DeArellano-Lopez, A.R.; Dominguez-Rodriguez, A. (Seville Univ. (Spain). Dept. Materia Condensada); Goretta, K.C.; Routbort, J.L. (Argonne National Lab., IL (USA))

1990-01-01

295

Investigation of smooth specimen scc test procedures; variations in environment, specimen size, stressing frame, and stress state. [for high strength aluminum alloys  

NASA Technical Reports Server (NTRS)

The variables studied in the stress-corrosion cracking performance of high strength aluminum alloys were: (1) corrosiveness of the environment, (2) specimen size and stiffness of the stressing system, (3) interpretation of transgranular cracking, and (4) interaction of the state of stress and specimen orientation in a product with an anisotropic grain structure. It was shown that the probability of failure and time to fracture for a specimen loaded in direct tension are influenced by corrosion pattern, the stressing assembly stiffness, and the notch tensile strength of the alloy. Results demonstrate that the combination of a normal tension stress and a shear stress acting on the plane of maximum susceptibility in a product with a highly directional grain cause the greatest tendency for stress-corrosion cracking.

Lifka, B. W.; Sprowls, D. O.; Kelsey, R. A.

1975-01-01

296

Application of the embedded polariscope photoelastic technique to the stress analysis of a high pressure tee  

E-print Network

APPLICATION OF THE EMBEDDED POLARISCOPE PHOTOELASTIC TECHNIQUE TO THE STRESS ANALYSIS OF A HIGH PRESSURE TEE A Thesis by THOMAS ARTHUR DOYLE Submitted to the Graduate College of Texas ASM University in partial fulfillment of the requirements... 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

297

High frequency noise in deep-submicron NMOSFETs under different hot carrier stresses  

Microsoft Academic Search

Degradation mechanisms contributing to the increased high frequency noise of deep-submicrometer NMOSFETs after different hot-carrier (HC) stresses are investigated. It is demonstrated that device noise parameters, such as NFmin and Rn degrade most under maximum substrate-current (IB,max) stress. On the other hand, hot electron and hot hole injection have much lower degradation on device noise performance. The high frequency noise

Hao Su; Hong Wang; Zhiyong Sun; Tao Xu

2009-01-01

298

Responses of High Biomass Rice (Oryza sativa L.) to Various Abiotic Stresses  

E-print Network

iii RESPONSES OF HIGH BIOMASS RICE (ORYZA SATIVA L.) TO VARIOUS ABIOTIC STRESSES A Thesis by ADITI NITINKUMAR KONDHIA Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE August 2010 Major Subject: Plant Breeding iv Responses of High Biomass Rice (Oryza sativa L.) to Various Abiotic Stresses Copyright 2010 Aditi...

Kondhia, Aditi Nitinkumar

2011-10-21

299

A high accuracy ultrasonic measurement method for nondestructive evaluation of residual stress in welded pipings  

SciTech Connect

Today`s nuclear power plants are marked by increasing needs for non-destructive inspection techniques in preventive maintenance programs. Additionally, it is becoming more important to evaluate residual stress which may be a key parameter for crack propagations in welded pipings. The authors have developed an ultrasonic velocity measurement method which obtains ultrasonic velocity changes by residual stress with a high accuracy. The ultrasonic velocity measurement is composed of three procedures. They are as follows. (1) Highly accurate propagation time measurements; (2) Pipe thickness correction; (3) Residual stress evaluation. The ultrasonic velocity measurements have been applied to the residual stress evaluation of carbon steel welded pipings. Destructive testing using stress strain gauges was done after the ultrasonic non-destructive evaluation of the residual stress. The experimental results verified that residual stress in carbon steel welded pipings can be measured by the ultrasonic method within an error of 40MPa, and the non-destructive values are equivalent to the average between inner and outer surface stresses measured by strain gauges.

Takahashi, F.; Koike, M.; Oda, M. [Hitachi, Ltd. (Japan); Mochizuki, M. [Hitachi, Ltd., Tsuchiura (Japan)

1995-08-01

300

High speed twin roll casting of recycled Al3Si0.6Mg strip  

Microsoft Academic Search

Purpose: Purpose of this paper is to clear the possibility of high speed roll casting of thin strip of recycled Al- 3%Si-0.6%Mg alloy. Investigation of the mechanical properties of the roll cast recycled Al-3%Si-0.6%Mg strip was purpose, too. Design\\/methodology\\/approach: Method used in the present study was high speed twin roll caster and low temperature casting. These methods were used to

T. Haga; M. Ikawa; H. Watari; S. Kumai

2007-01-01

301

Ascast microstructure and solidification behavior of a high Al and Nb-containing superalloy  

Microsoft Academic Search

This study investigated the as-cast microstructure and solidification behavior of a high Al- and Nb-containing low thermal\\u000a expansion IN783 alloy. By analyzing the as-cast microstructure, the quenched microstructure after soaking at high temperature\\u000a and differential scanning calorimeter (DSC) results, the solidification sequence of IN783 alloy was determined as follows:\\u000a L ? L + ? ? L + ? + ? ? ? + ? + Laves. Segregation of Al and Nb promoted the formation of Al-enriched

Lianxu Yu; Yating Zhao; Shulin Yang; Wenru Sun; Shouren Guo; Xiaofeng Sun; Zhuangqi Hu

2010-01-01

302

Aftershocks are well aligned with the background stress field, contradicting the hypothesis of highly-heterogeneous crustal stress  

USGS Publications Warehouse

It has been proposed that the crustal stress field contains small-length-scale heterogeneity of much larger amplitude than the uniform background stress. This model predicts that earthquake focal mechanisms should reflect the loading stress rather than the uniform background stress. So, if the heterogeneous stress hypothesis is correct, focal mechanisms before and after a large earthquake should align with the tectonic loading and the earthquake-induced static stress perturbation, respectively. However, I show that the off-fault triggered aftershocks of the 1992 M7.3 Landers, California, earthquake align with the same stress field as the pre-Landers mechanisms. The aftershocks occurred on faults that were well oriented for failure in the pre-Landers stress field and then loaded by the Landers-induced static stress change. Aftershocks in regions experiencing a 0.05 to 5 MPa coseismic differential stress change align with the modeled Landers-induced static stress change, implying that they were triggered by the stress perturbation. Contrary to the heterogeneous stress hypothesis, these triggered aftershocks are also well aligned with the pre-Landers stress field obtained from inverting the pre-Landers focal mechanisms. Therefore, the inverted pre-Landers stress must represent the persistent background stress field. Earthquake focal mechanisms provide an unbiased sample of the spatially coherent background stress field, which is large relative to any small-scale stress heterogeneity. The counterexample provided by the Landers earthquake is strong evidence that the heterogeneous stress model is not widely applicable.

Hardebeck, Jeanne L.

2010-01-01

303

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

304

Electrical properties of Si-implanted AlxGa1-xN with high Al mole fraction  

Microsoft Academic Search

Ion implanted AlGaN has not been well investigated, in particular AlGaN with high Al mole fraction, compared to the research of ion-implanted GaN. Therefore, a systematic electrical activation study of Si-implanted AlGaN with Al mole fraction from 0.1 to 0.5 has been made as a function of ion dose and anneal temperature. The AlGaN wafers were grown on sapphire substrates

Elizabeth Moore; Mee-Yi Ryu; Yung Kee Yeo; Robert Hengehold

2007-01-01

305

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

306

State of the art in high accuracy high detail DTMs derived from ALS  

NASA Astrophysics Data System (ADS)

High-resolution Digital Terrain Models (DTMs) representing the bare Earth are a fundamental input for various applications in geomorphology. Airborne laser scanning (ALS) is established as a standard tool for deriving DTMs over large areas with unprecedented accuracy. Due to advances in sensor technology and in processing algorithms in the recent years the obtainable accuracy is still increasing. Accuracy is understood as the deviation from the elevation at one specified point to its true value. These advances may lead to a more efficient data acquisition, if reduced accuracy is targeted, but also allow data acquisition schemes with more detail becoming visible, i.e. small features of the relief. For the latter a high internal precision, i.e. repeatability, is necessary. The essential advances in the technologies are improvements in ranging through the introduction of full-waveform (FWF) laser scanning and rigorous models of strip adjustment. In FWF laser scanning the time-dependent strength of the backscattered signal is recorded. This is opposed to the analogue processing of the incoming energy and storage of one arrival time of discrete-return systems. In a simple one-echo situation, the arrival time corresponds to the maximum of the waveform. By applying a decomposition of the full waveform into single echoes, which are transformed copies of the emitted signal, it is possible to retrieve more echoes per shot. Additionally, if echoes of individual scatterers are overlapping, FWF sensors might be able to separate them, whereas discrete return systems might rather only be able to derive one collective arrival time. Finally, the overlay of two echoes does not have the maxima at the same positions as the individual echoes. Additionally, the pulse repetition rate of laser scanners has increased, which allows higher point densities and therefore higher richness of detail. These advances in data acquisition increase the precision within one ALS strip. Deficiencies in the calibration of the multi-sensor system ALS, consisting of laser range finder, scanner, inertial measurement unit (IMU), and global navigation satellite system (GNSS), lead to a decrease in overall accuracy, which becomes apparent in discrepancies between overlapping strips. Especially small features of the relief are distorted by these discrepancies and therefore appear blurred or undiscernible from the noise. Strip adjustment algorithms are targeted at removing these discrepancies by improving the calibration of the single components of the measurement system, and estimating the relative orientation (offset and angular attitude) between the components. These improvements in precision allow filtering algorithms, i.e. the classification of the acquired points into ground points and off-terrain points, to perform better in the separation of random measurement noise, small terrain features, and off terrain points. The first one shall be reduced by suitable averaging, the second are to be maintained, and the third to be removed. Filtering is also improved by considering the shape of the recorded echoes. Near ground vegetation often leads to an increase in echo width, which is an indicator for a reflection from objects above the terrain. These advances in sensor technology and processing methodology lead to improved DTMs with respect to accuracy, precision, and terrain detail. Therefore, geomorphological features and processes can be identified more reliably. The improvement of "raw" point clouds and DTMs also enables advances in automatic lineament extraction and data reduction.

Pfeifer, N.; Briese, C.; Mandlburger, G.; Höfle, B.; Ressl, C.

2009-04-01

307

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

308

Fundamental studies of stress distributions and stress relaxation in oxide scales on high temperature alloys. Progress report  

SciTech Connect

The high temperature X-ray diffraction system developed for this program is being used to measure the strains which develop during oxidation. This is being applied to Ni/NiO and Cr/Cr{sub 2}O{sub 3}. Our work suggests tat the oxide and metal crystalline texture, anisotropic elastic modulus and anisotropic thermal expansion can have a pronounced effect on strain state of these systems. Acoustic emission is being used to study oxide scale failure (fracture) during oxidation. AE data from 304 stainless steel are being used to develop a statistical model of fracture process. Strength of metal/scale interface is an important property that has been difficult to quantify. Using Nano-indentation and scratch techniques developed for characterizing thin film interfaces, an effort has begun to measure the fracture toughness of the metal/scale interface. Mathematical modelling of origin and time evolution of growth stresses is an extension and improvement of previous models. The current effort employs a more sophisticated stress analysis and expands the scope to include other stress relaxation process. The interaction between the modeling studies and the X-ray diffraction measurements provides a natural credibility check to both efforts.

Shores, D.A.; Stout, J.H.; Gerberich, W.W.

1992-06-01

309

High density Al2O3/TaN-based metal insulator metal capacitors in application to radio frequency integrated circuits  

NASA Astrophysics Data System (ADS)

Metal-insulator-metal (MIM) capacitors with atomic-layer-deposited Al2O3 dielectric and reactively sputtered TaN electrodes in application to radio frequency integrated circuits have been characterized electrically. The capacitors exhibit a high density of about 6.05 fF/?m2, a small leakage current of 4.8×10-8 A/cm2 at 3V, a high breakdown electric field of 8.61MV/cm as well as acceptable voltage coefficients of capacitance (VCCs) of 795 ppm/V2 and 268ppm/V at 1 MHz. The observed properties should be attributed to high-quality Al2O3 film and chemically stable TaN electrodes. Further, a logarithmically linear relationship between quadratic VCC and frequency is observed due to the change of relaxation time with carrier mobility in the dielectric. The conduction mechanism in the high field ranges is dominated by the Poole-Frenkel emission, and the leakage current in the low field ranges is likely to be associated with trap-assisted tunnelling. Meanwhile, the Al2O3 dielectric presents charge trapping under low voltage stresses, and defect generation under high voltage stresses, and it has a hard-breakdown performance.

Ding, Shi-Jin; Huang, Yu-Jian; Huang, Yue; Pan, Shao-Hui; Zhang, Wei; Wang, Li-Kang

2007-09-01

310

Work at high altitude and oxidative stress: antioxidant nutrients  

Microsoft Academic Search

A significant portion of the world's geography lies above 10,000 feet elevation, an arbitrary designation that separates moderate and high altitude. Although the number of indigenous people living at these elevations is relatively small, many people travel to high altitude for work or recreation, exposing themselves to chronic or intermittent hypoxia and the associated risk of acute mountain sickness (AMS)

E. W. Askew

2002-01-01

311

High electric stress and insulation challenges in integrated microelectronic circuits  

Microsoft Academic Search

The insulating layer in the transistor has decreased from 100 nm in the early 1970s to only a few nanometers today. This thin insulating layer gives rise to very high electric fields approaching 1000 kV\\/mm for an operating voltage of 1 V. Degradation of the insulation during ageing takes place due to the high field and may eventually lead to

Frøydis Oldervoll

2002-01-01

312

HIGH TEMPERATURE STRESS ON FLORAL DEVELOPMENT AND YIELD OF COTTON  

Technology Transfer Automated Retrieval System (TEKTRAN)

Because a number of reproductive processes must occur in highly concerted fashion during the progamic phase (from pollination to fertilization) for successful fertilization and seed production to occur, final yield in cotton is exceptionally sensitive to high temperatures during the flowering period...

313

New facility for neutron diffraction studies of residual stresses in highly radioactive materials in NPI ?ež  

NASA Astrophysics Data System (ADS)

A dedicated shielding box enabling safe manipulation with highly radioactive specimens was developed as an auxiliary equipment of neutron diffraction stress/strain scanners available in NPI ?ež. The box was designed to provide the following functions-an easy specimen installation in the hot cells, a remote control of specimen positioning, input and output beam shutters and collimators. Employing this facility, the stress mapping experiments on radioactive components can be then realized by means of the current stress/strain scanners. The results of testing experiments on the irradiated CT specimen of austenitic stainless steel are presented.

Lukáš, Petr; Vrána, Miroslav; Mikula, Pavel; Brožová, Anna; Ernestová, Miroslava

2006-11-01

314

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

315

Low-temperature plasma-assisted growth of optically transparent, highly oriented nanocrystalline AlN  

NASA Astrophysics Data System (ADS)

Optically transparent, highly oriented nanocrystalline AlN(002) films have been synthesized using a hybrid plasma enhanced chemical vapor deposition and plasma-assisted radio frequency (rf) magnetron sputtering process in reactive Ar+N2 and Ar+N2+H2 gas mixtures at a low Si(111)/glass substrate temperature of 350 °C. The process conditions, such as the sputtering pressure, rf power, substrate temperature, and N2 concentration were optimized to achieve the desired structural, compositional, and optical characteristics. X-ray diffractometry reveals the formation of highly c-oriented AlN films at a sputtering pressure of 0.8 Pa. Field emission scanning electron microscopy suggests the uniform distribution of AlN grains over large surface areas and also the existence of highly oriented in the (002) direction columnar structures of a typical length ˜100-500 nm with an aspect ratio of ˜7-15. X-ray photoelectron and energy dispersive x-ray spectroscopy suggest that films deposited at a rf power of 400 W feature a chemically pure and near stoichiometric AlN. The bonding states of the AlN films have been confirmed by Raman and Fourier transform infrared spectroscopy showing strong E2 (high) and E1 transverse optical phonon modes. Hydrogenated AlN films feature an excellent optical transmittance of ˜80% in the visible region of the spectrum, promising for advanced optical applications.

Mirpuri, C.; Xu, S.; Long, J. D.; Ostrikov, K.

2007-01-01

316

Cast Aluminum Alloys for High Temperature Applications Using Nanoparticles Al2O3 and Al3-X Compounds (X = Ti, V, Zr)  

NASA Technical Reports Server (NTRS)

In this paper, the effect of nanoparticles Al2O3 and Al3-X compounds (X = Ti, V, Zr) on the improvement of mechanical properties of aluminum alloys for elevated temperature applications is presented. These nanoparticles were selected based on their low cost, chemical stability and low diffusions rates in aluminum at high temperatures. The strengthening mechanism at high temperature for aluminum alloy is based on the mechanical blocking of dislocation movements by these nanoparticles. For Al2O3 nanoparticles, the test samples were prepared from special Al2O3 preforms, which were produced using ceramic injection molding process and then pressure infiltrated by molten aluminum. In another method, Al2O3 nanoparticles can also be homogeneously mixed with fine aluminum powder and consolidated into test samples through hot pressing and sintering. With the Al3-X nanoparticles, the test samples are produced as precipitates from in-situ reactions with molten aluminum using conventional permanent mold or die casting techniques. It is found that cast aluminum alloy using nanoparticles Al3-X is the most cost effective method to produce high strength aluminum alloys for high temperature applications in comparison to nanoparticles Al2O3. Furthermore, significant mechanical properties retention in high temperature environment could be achieved with Al3-X nanoparticles, resulting in tensile strength of nearly 3 times higher than most 300- series conventional cast aluminum alloys tested at 600 F.

Lee, Jonathan A.

2009-01-01

317

Dual stress liner for high performance sub-45nm gate length SOI CMOS manufacturing  

Microsoft Academic Search

For the first time, tensile and compressively stressed nitride contact liners have been simultaneously incorporated into a high performance CMOS flow. This dual stress liner (DSL) approach results in NFET\\/PFET effective drive current enhancement of 15%\\/32% and saturated drive current enhancement of 11%\\/20%. Significant hole mobility enhancement of 60% is achieved without using SiGe. Inverter ring oscillator delay is reduced

H. S. Yang; R. Malik; S. Narasimha; Y. Li; R. Divakaruni; P. Agnello; S. Allen; A. Antreasyan; J. C. Arnold; K. Bandy; M. Belyansky; A. Bonnoit; G. Bronner; V. Chan; X. Chen; Z. Chen; D. Chidambarrao; A. Chou; W. Clark; S. W. Crowder; B. Engel; H. Harifuchi; S. F. Huang; R. Jagannathan; F. F. Jamin; Y. Kohyama; H. Kuroda; C. W. Lai; H. K. Lee; W.-H. Lee; E. H. Lim; W. Lai; A. Mallikarjunan; K. Matsumoto; A. McKnight; J. Nayak; H. Y. Ng; S. Panda; R. Rengarajan; M. Steigerwalt; S. Subbanna; K. Subramanian; J. Sudijono; G. Sudo; S.-P. Sun; B. Tessier; Y. Toyoshima; P. Tran; R. Wise; R. Wong; I. Y. Yang; C. H. Wann; L. T. Su; M. Horstmann; Th. Feudel; A. Wei; K. Frohberg; G. Burbach; M. Gerhardt; M. Lenski; R. Stephan; K. Wieczorek; M. Schaller; H. Salz; J. Hohage; H. Ruelke; J. Klais; P. Huebler; S. Luning; R. van Bentum; G. Grasshoff; C. Schwan; E. Ehrichs; S. Goad; J. Buller; S. Krishnan; D. Greenlaw; M. Raab; N. Kepler

2004-01-01

318

Viscoelastic analysis of mismatch stresses in ceramic matrix composites under high-temperature neutron irradiation  

Microsoft Academic Search

Fiber-reinforced ceramic matrix composites, such as SiC?SiC, are proposed for structural applications in future fusion energy systems. In a fusion nuclear reactor environment time-dependent inelastic effects are induced by irradiation and hence mismatch stresses are expected to change in time. The time evolution of the internal mismatch stresses in ceramic fiber composites under high-temperature neutron irradiation is presented, with application

A. El-Azab; N. M. Ghoniem

1995-01-01

319

Proteins responding to drought and high-temperature stress in Populus × euramericana cv. ‘74\\/76’  

Microsoft Academic Search

Proteomic analysis provides a powerful method of studying plant responses to stress at the protein level. In order to study\\u000a stress-responsive molecular mechanisms for Populus × euramericana cv. ‘74\\/76’, one of the most important forest plantation tree species in subtropical and temperate regions, we analyzed the\\u000a response of 2-year-old cuttings of P. × euramericana cv. ‘74\\/76’ to drought and high

Caiyun He; Jianguo Zhang; Aiguo Duan; Shuxing Zheng; Honggang Sun; Lihua Fu

2008-01-01

320

Response of Chickpea Yield to High Temperature Stress during Reproductive Development  

Microsoft Academic Search

Minimizing the exposure of an annual crop to abiotic stresses may increase seed yield. A study was conducted to determine the effect of high temperature stress during reproductive development on pod fer- tility, seed set, and seed yield of chickpea (Cicer arietinum L). 'Myles' desi and 'Xena' kabuli chickpea were grown in a controlled envi- ronment under 20\\/16C day\\/night air

J. Wang; Y. T. Gan; F. Clarke; C. L. McDonald

2006-01-01

321

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

322

The millimeter-wave spectrum of AlOH. [in relevance to its high cosmic abundance  

NASA Technical Reports Server (NTRS)

The pure rotational spectrum of the AlOH and AlOD molecules in their X 1Sigma(+) (v = 0) ground electric states has been measured in the laboratory using direct absorption millimeter/submillimeter spectroscopy. The species were produced by the reaction of aluminum vapor, created in a Broida-type oven, with hydrogen peroxide or D2O2. Eight rotational transitions of AlOH and five transitions for AlOD were measured in the frequency range of 157-378 GHz to an accuracy better than +/- 75 kHz. Electric quadrupole interactions, arising from the aluminum nuclear spin of 5/2, were observed in the J = 4 - 5 and the J = 5 - 6 transitions of AlOH. The rotational constants of these molecules have been determined from a nonlinear least-squares fit to the data. The electric quadrupole coupling constant, eqQ, has been measured as well, and was found to have a value of -42.4 +/- 4.3 MHz. The spectra are consistent with quasi-linear ground states for AlOH and AlOD, as predicted by theory. AlOH is of astrophysical interest because of the relatively high cosmic abundance of aluminum.

Apponi, A. J.; Barclay, W. L., Jr.; Ziurys, L. M.

1993-01-01

323

Single Discharge Machining Insulating Al2O3 Ceramic with High Instantaneous Pulse Energy in Kerosene  

Microsoft Academic Search

A technique of machining insulating Al2O3 ceramic with a thin copper sheet assisting electrode and high instantaneous pulse energy is developed. The process uses the high peak voltage and large capacitor with high instantaneous pulse energy, and there is no current-limiting resistor in the discharge circuit, so the discharge energy and discharge explosive force are high, and the process is

Renjie Ji; Yonghong Liu; Yanzhen Zhang; Fei Wang; Baoping Cai; Xingsheng Fu

2012-01-01

324

Single Discharge Machining Insulating Al2O3 Ceramic with High Instantaneous Pulse Energy in Kerosene  

Microsoft Academic Search

A technique of machining insulating Al2O3 ceramic with a thin copper sheet assisting electrode and high instantaneous pulse energy is developed. The process uses the high peak voltage and large capacitor with high instantaneous pulse energy, and there is no current-limiting resistor in the discharge circuit, so the discharge energy and discharge explosive force are high, and the process is

Renjie Ji; Yonghong Liu; Yanzhen Zhang; Fei Wang; Baoping Cai; Xingsheng Fu

2011-01-01

325

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

326

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

327

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

328

Optical investigation of strong exciton localization in high Al composition AlxGa?-xN alloys.  

PubMed

The exciton localization in wurtzite AlxGa?-xN alloys with x varying from 0.41 to 0.63 has been studied by deep-ultraviolet photoluminescence (PL) spectroscopy and picosecond time-resolved PL spectroscopy. Obvious S-shape temperature dependence was observed indicating that the strong exciton localization can be formed in high Al composition AlxGa?-xN alloys. It was also found that the Al composition dependence of exciton localization energy of AlGaN alloys is inconsistent with that of the excitonic linewidth. We contribute the inconsistency to the strong zero-dimensional exciton localization. PMID:24150295

Fan, Shunfei; Qin, Zhixin; He, Chenguang; Hou, Mengjun; Wang, Xinqiang; Shen, Bo; Li, Wei; Wang, Weiying; Mao, Defeng; Jin, Peng; Yan, Jianchang; Dong, Peng

2013-10-21

329

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

330

Pb nanowire formation on Al/lead zirconate titanate surfaces in high-pressure hydrogen  

SciTech Connect

Thin films of Al on lead zirconate titanate (PZT) annealed in high-pressure hydrogen at 100C exhibit surface Pb nanowire growth. Wire diameter is approximately 80 nm and length can exceed 100 microns. Based on microstructural analysis using electron microscopy and ion scattering, a vapor-solid scheme with hydrogen as a carrier gas was proposed as a growth mechanism. We expect that these observations may lead to controlled Pb nanowires growth through pattering of the Al film.

Alvine, Kyle J.; Shutthanandan, V.; Arey, Bruce W.; Wang, Chong M.; Bennett, Wendy D.; Pitman, Stan G.

2012-07-12

331

AlGaAs/GaAs photovoltaic converters for high power narrowband radiation  

SciTech Connect

AlGaAs/GaAs-based laser power PV converters intended for operation with high-power (up to 100 W/cm{sup 2}) 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; Andreev, Viacheslav [Ioffe Physical-Technical Institute, 26 Polytechnicheskaya, St. Petersburg, 194021 (Russian Federation); Luque, Antonio [Ioffe Physical-Technical Institute, 26 Polytechnicheskaya, St. Petersburg, 194021, Russia and Instituto de Energia Solar, Universidad Politecnica de Madrid, Madrid (Spain)

2014-09-26

332

An Electrochemical Framework to Explain Intergranular Stress Corrosion Cracking in an Al-5.4%Cu-0.5%Mg-0.5%Ag Alloy  

NASA Technical Reports Server (NTRS)

A modified version of the Cu-depletion electrochemical framework was used to explain the metallurgical factor creating intergranular stress corrosion cracking susceptibility in an aged Al-Cu-Mg-Ag alloy, C416. This framework was also used to explain the increased resistance to intergranular stress corrosion cracking in the overaged temper. Susceptibility in the under aged and T8 condition is consistent with the grain boundary Cu-depletion mechanism. Improvements in resistance of the T8+ thermal exposure of 5000 h at 225 F (T8+) compared to the T8 condition can be explained by depletion of Cu from solid solution.

Little, D. A.; Connolly, B. J.; Scully, J. R.

2001-01-01

333

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.

334

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 in the temperature range of 400-500o C to understand the transformation of toluene over high acidity Y-based zeolite Abstract Catalytic transformation of toluene has been investigated over Y-zeolite based catalysts

Al-Khattaf, Sulaiman

335

High brightness AlGaInP light-emitting diodes  

Microsoft Academic Search

This paper reviews the recent progress of AlGaInP high brightness light-emitting diodes. After the discussion of some basic material properties and the general problem of light extraction we will discuss several approaches of high efficiency devices

Klaus Streubel; Norbert Linder; Ralph Wirth; Arndt Jaeger

2002-01-01

336

INFLUENCE OF HIGH ENERGY BALL MILLING ON REACTIVITY IN NI-AL  

E-print Network

INFLUENCE OF HIGH ENERGY BALL MILLING ON REACTIVITY IN NI-AL GASLESS HETEROGENEOUS SYSTEM #12;Motivation of the Research Reactive exothermic mixtures of nickel and aluminum may be applied for · chemical at which the self-propagating reaction initiates. Microstructural control - high energy ball milling (HEBM

Mukasyan, Alexander

337

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

338

Improvement of the interfacial integrity of (Ti,Al)N hard coatings deposited on high speed steel cutting tools  

Microsoft Academic Search

With improved microhardness and high temperature resistance, the advanced (Ti,Al)N hard coating has now been successfully applied to carbide tools for high speed machining, although problems with adhesion at the interface are inevitable when the (Ti,Al)N hard coating is applied to high-speed steel cutting tools. This study investigated a series of multi-layered interfaces consisting of TiAl, TiN and TiAlN in

D.-Y Wang; C.-L Chang; K.-W Wong; Y.-W Li; W.-Y Ho

1999-01-01

339

High quality AlN and GaN grown on Si(111) by gas source molecular beam epitaxy with ammonia  

SciTech Connect

The authors describe the growth of high quality AlN and GaN on Si(111) by gas source molecular beam epitaxy (GSMBE) with ammonia (NH{sub 3}). The initial nucleation (at 1130--1190K) of an AlN monolayer with full substrate coverage resulted in a very rapid transition to two-dimensional (2D) growth mode of AlN. The rapid transition to the 2D growth mode of AlN is essential for the subsequent growth of high quality GaN, and complete elimination of cracking in thick (>2 {micro}m) GaN layers. The authors show, using Raman scattering (RS) and photoluminescence (PL) measurements, that the tensile stress in the GaN is due to thermal expansion mismatch, is below the ultimate strength of breaking of GaN, and produces a sizable shift in the bandgap. They show that the GSMBE AlN and GaN layers grown on Si can be used as a substrate for subsequent deposition of thick AlN and GaN layers by hydride vapor phase epitaxy (HVPE).

Nikishin, S.A.; Faleev, N.N.; Antipov, V.G. [and others

2000-07-01

340

Continuous deformation versus episodic deformation at high stress - the microstructural record  

NASA Astrophysics Data System (ADS)

The microstructural record of continuous high stress deformation is compared to that of episodic high stress deformation on two examples: 1. Folding of quartz veins in metagreywacke from Pacheco Pass, California, undergoing deformation by dissolution precipitation creep at temperatures of 300 ± 50°C. The microfabric of the folded quartz veins indicates deformation by dislocation creep accompanied by subgrain rotation. The small recrystallized grain size of ~8±6 µm in average implies relatively high differential stresses of a few hundred MPa. The stress concentration in the vein is due to a high contrast in effective viscosities between the single phase material and the polyphase fine-grained host metagreywacke deforming by dissolution precipitation creep. Smoothly curved, but generally not sutured, grain boundaries as well as the small size and a relatively high dislocation density of recrystallized grains suggest that strain-induced grain boundary migration was of minor importance. This is suspected to be a consequence of low strain gradients, which are due to the relative rates of dynamic recovery and continuous dislocation production during climb-controlled creep, at high stress and the given low temperature. Subgrain rotation recrystallization is thus proposed to be characteristic for continuous deformation at high differential stress. 2. Episodic deformation in the middle crust at the tip of a seismic active fault zone. The microfabric of mid-crustal rocks exhumed in tectonically active regions can record episodic high stress deformation at the base of the seismogenic layer. The quartz veins from St. Paul la Roche in the Massif Central, France, are very coarse grained. On the scale of a thin section they are basically single crystalline. However, they show a very heterogeneous microstructure with a system of healed microcracks that are decorated by subgrains and more rarely by small recrystallized grains. Undulating deformation lamellae that do not show a preferred crystallographic orientation are found by transmission electron microscopy to represent dislocation walls with a high density of dislocations. They are interpreted as a modified microstructure that reflects a stage of initial high stress deformation with restricted dynamic recovery. The missing aggregates of recrystallized grains rule out dynamic recrystallization, which is proposed to be due to a high strain rate, preventing effective dislocation climb. Instead, localized single grains in random orientations that are aligned along fractures indicate quasi-static recrystallization and recovery at a subsequent stage of low stress and temperatures of ~300 ± 50°C. Such a microstructure is characteristic of initial short-term high stress glide-controlled deformation accompanied by microcracking during coseismic loading and subsequent modification by recovery and recrystallization at rapidly decreasing stresses during postseismic relaxation in the middle crust below the seismogenic layer. Both examples indicate deformation of quartz at similar conditions in terms of temperature (~300 ± 50°C) and high stress. However, the deformation and recrystallization processes and the resulting microfabrics are completely different due to the different loading time and rate.

Trepmann, C. A.; Stöckhert, B.

2009-04-01

341

Intermittent short-duration exposure to low wall shear stress induces intimal thickening in arteries exposed to chronic high shear stress  

Microsoft Academic Search

We sought to determine whether intermittent short-duration exposure to low wall shear stress could induce intimal thickening in arteries chronically exposed to high shear stress. An arteriovenous fistula (AVF) was created between the left common carotid artery and the corresponding external jugular vein in 20 Japanese white male rabbits. After 4 weeks, blood flow was increased 10-fold to 182 T

Hiroshi Nanjo; Eiketsu Sho; Masayo Komatsu; Mien Sho; Christopher K. Zarins; Hirotake Masuda

342

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

343

Control of Al2O3/InAlN interface by two-step atomic layer deposition combined with high-temperature annealing  

NASA Astrophysics Data System (ADS)

An attempt was made to control the Al2O3/InAlN interface by the phase change of the Al2O3 layer formed by atomic layer deposition (ALD). The electrical properties of an InAlN metal-oxide-semiconductor (MOS) diode with a sufficiently thick ALD-Al2O3 layer deteriorated following conventional postdeposition annealing (PDA) at 850 °C, which is sufficiently high for microcrystallization of the ALD-Al2O3 layer. However, X-ray photoelectron spectroscopy showed no evidence of an interface disorder in the ultrathin ALD-Al2O3/InAlN structure annealed at 850 °C. Two-step ALD interrupted by annealing at 850 °C right after the formation of the initial ultrathin Al2O3 layer improved the electrical properties of the MOS diode with reduced interface state density (Dit) and leakage current. A weak crystallization of the ultrathin Al2O3 layer was confirmed by transmission electron microscopy. Improvement of the interface disorder by high-temperature annealing is discussed as the origin of the Dit reduction.

Nakano, Takuma; Chiba, Masahito; Akazawa, Masamichi

2014-04-01

344

Time exposure studies on stress corrosion cracking of aluminum 2014-T6, 2219-T87, 2014-T651, 7075-T651, and titanium 6Al-4V  

NASA Technical Reports Server (NTRS)

The effect of a constant applied stress in crack initiation of aluminum 2014-T6, 2219-T87, 2014-T651, 7075-T651 and titanium 6Al-4V has been investigated. Aluminum c-ring specimens (1-inch diameter) and u-band titanium samples were exposed continuously to a 3.5% NaCl solution (pH 7) and organic fluids of ethyl, methyl, and iso-propyl alcohol (reagent purity), and demineralized distilled water. Corrosive action was observed to begin during the first and second day of constant exposure as evidenced by accumulation of hydrogen bubbles on the surface of stressed aluminum samples. However, titanium stressed specimens showed no reactions to its environment. Results of this investigation seems to suggest that aluminum 2014-T6, aluminum 7075-T651 and aluminum 2014-T651 are susceptible to stress corrosion cracking in chloride solution (NaCl), while aluminum 2219-T87 seem to resist stress corrosion cracking in sodium chloride at three levels of stress (25%, 50%, and 75% Y.S.). In organic fluids of methyl, ethyl, and iso-propyl alcohol, 2014-T6 and 7075-T651 did not fail by SCC; but 2014-T651 was susceptible to SCC in methly alcohol, but resistant in ethyl alcohol, iso-propyl alcohol and demineralized distilled water.

Terrell, J.

1973-01-01

345

Quantitative high content imaging of cellular adaptive stress response pathways in toxicity for chemical safety assessment.  

PubMed

Over the past decade, major leaps forward have been made on the mechanistic understanding and identification of adaptive stress response landscapes underlying toxic insult using transcriptomics approaches. However, for predictive purposes of adverse outcome several major limitations in these approaches exist. First, the limited number of samples that can be analyzed reduces the in depth analysis of concentration-time course relationships for toxic stress responses. Second these transcriptomics analysis have been based on the whole cell population, thereby inevitably preventing single cell analysis. Third, transcriptomics is based on the transcript level, totally ignoring (post)translational regulation. We believe these limitations are circumvented with the application of high content analysis of relevant toxicant-induced adaptive stress signaling pathways using bacterial artificial chromosome (BAC) green fluorescent protein (GFP) reporter cell-based assays. The goal is to establish a platform that incorporates all adaptive stress pathways that are relevant for toxicity, with a focus on drug-induced liver injury. In addition, cellular stress responses typically follow cell perturbations at the subcellular organelle level. Therefore, we complement our reporter line panel with reporters for specific organelle morphometry and function. Here, we review the approaches of high content imaging of cellular adaptive stress responses to chemicals and the application in the mechanistic understanding and prediction of chemical toxicity at a systems toxicology level. PMID:24450961

Wink, Steven; Hiemstra, Steven; Huppelschoten, Suzanna; Danen, Erik; Niemeijer, Marije; Hendriks, Giel; Vrieling, Harry; Herpers, Bram; van de Water, Bob

2014-03-17

346

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

347

Piriformospora indica rescues growth diminution of rice seedlings during high salt stress  

PubMed Central

Piriformospora indica association has been reported to increase biotic as well as abiotic stress tolerance of its host plants. We analyzed the beneficial effect of P. indica association on rice seedlings during high salt stress conditions (200 and 300 mM NaCl). The growth parameters of rice seedlings such as root and shoot lengths or fresh and dry weights were found to be enhanced in P. indica-inoculated rice seedlings as compared with non-inoculated control seedlings, irrespective of whether they are exposed to salt stress or not. However, salt-stressed seedlings performed much better in the presence of the fungus compared with non-inoculated control seedlings. The photosynthetic pigment content [chlorophyll (Chl) a, Chl b, and carotenoids] was significantly higher in P. indica-inoculated rice seedlings under high salt stress conditions as compared with salt-treated non-inoculated rice seedlings, in which these pigments were found to be decreased. Proline accumulation was also observed during P. indica colonization, which may help the inoculated plants to become salt tolerant. Taken together, P. indica rescues growth diminution of rice seedlings under salt stress.

Jogawat, Abhimanyu; Saha, Shreya; Bakshi, Madhunita; Dayaman, Vikram; Kumar, Manoj; Dua, Meenakshi; Varma, Ajit; Oelmüller, Ralf; Tuteja, Narendra; Johri, Atul Kumar

2013-01-01

348

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

349

High reflectance-low stress Mo-Si multilayer reflective coatings  

DOEpatents

A high reflectance-low stress Mo-Si multilayer reflective coating particularly useful for the extreme ultraviolet (EUV) wavelength region. While the multilayer reflective coating has particular application for EUV lithography, it has numerous other applications where high reflectance and low stress multilayer coatings are utilized. Multilayer coatings having high near-normal incidence reflectance (R.gtoreq.65%) and low residual stress (.ltoreq.100 MPa) have been produced using thermal and non-thermal approaches. The thermal approach involves heating the multilayer coating to a given temperature for a given time after deposition in order to induce structural changes in the multilayer coating that will have an overall "relaxation" effect without reducing the reflectance significantly.

Montcalm, Claude (Livermore, CA); Mirkarimi, Paul B. (Sunol, CA)

2000-01-01

350

Process for fabricating high reflectance-low stress Mo--Si multilayer reflective coatings  

DOEpatents

A high reflectance-low stress Mo--Si multilayer reflective coating particularly useful for the extreme ultraviolet (EUV) wavelength region. While the multilayer reflective coating has particular application for EUV lithography, it has numerous other applications where high reflectance and low stress multilayer coatings are utilized. Multilayer coatings having high near-normal incidence reflectance (R.gtoreq.65%) and low residual stress (.ltoreq.100 MPa) have been produced using thermal and non-thermal approaches. The thermal approach involves heating the multilayer coating to a given temperature for a given time after deposition in order to induce structural changes in the multilayer coating that will have an overall "relaxation" effect without reducing the reflectance significantly.

Montcalm, Claude (Livermore, CA); Mirkarimi, Paul B. (Sunol, CA)

2001-01-01

351

Growth and annealing conditions of high Al-content p-type AlGaN for deep-UV LEDs  

NASA Astrophysics Data System (ADS)

We report on growth and annealing conditions for high Al-content p-type AlGaN that is required to achieve deep-ultraviolet (UV) light-emitting diodes (LEDs) or laser diodes (LDs). Mg-doped AlGaN epilayers with the Al-contents between 0 and 40% were grown by low-pressure (LP) metalorganic chemical vapor deposition (MOCVD). We found that the suitable annealing temperature for p-Al0.22Ga0.78N is around 900 °C, which is approximately 50 °C higher than that for p-GaN. We also demonstrated that the use of a lower V/III ratio and a higher growth temperature are preferable for the growth of high Al-content p-AlGaN, in comparison with the case of p-GaN. By controlling the growth and annealing conditions, we have achieved hole concentrations as high as 2.0 × 1018 cm-3 for Mg-doped AlGaN with an Al-content of 32% as determined by Hall effect measurement.

Obata, Toshiyuki; Hirayama, Hideki; Aoyagi, Yoshinobu; Ishibashi, Koji

2004-09-01

352

Resistance to oxidative stress shows low heritability and high common environmental variance in a wild bird.  

PubMed

Oxidative stress was recently demonstrated to affect several fitness-related traits and is now well recognized to shape animal life-history evolution. However, very little is known about how much resistance to oxidative stress is determined by genetic and environmental effects and hence about its potential for evolution, especially in wild populations. In addition, our knowledge of phenotypic sexual dimorphism and cross-sex genetic correlations in resistance to oxidative stress remains extremely limited despite important evolutionary implications. In free-living great tits (Parus major), we quantified heritability, common environmental effect, sexual dimorphism and cross-sex genetic correlation in offspring resistance to oxidative stress by performing a split-nest cross-fostering experiment where 155 broods were split, and all siblings (n = 791) translocated and raised in two other nests. Resistance to oxidative stress was measured as both oxidative damage to lipids and erythrocyte resistance to a controlled free-radical attack. Both measurements of oxidative stress showed low additive genetic variances, high common environmental effects and phenotypic sexual dimorphism with males showing a higher resistance to oxidative stress. Cross-sex genetic correlations were not different from unity, and we found no substantial heritability in resistance to oxidative stress at adult age measured on 39 individuals that recruited the subsequent year. Our study shows that individual ability to resist to oxidative stress is primarily influenced by the common environment and has a low heritability with a consequent low potential for evolution, at least at an early stage of life. PMID:25040169

Losdat, S; Helfenstein, F; Blount, J D; Richner, H

2014-09-01

353

Testing the accelerating moment release (AMR) hypothesis in areas of high stress  

NASA Astrophysics Data System (ADS)

Several retrospective analyses have proposed that significant increases in moment release occurred prior to many large earthquakes of recent times. However, the finding of accelerating moment release (AMR) strongly depends on the choice of three parameters: (1) magnitude range, (2) area being considered surrounding the events and (3) the time period prior to the large earthquakes. Consequently, the AMR analysis has been criticized as being a posteriori data-fitting exercise with no new predictive power. As AMR has been hypothesized to relate to changes in the state of stress around the eventual epicentre, we compare here AMR results to models of stress accumulation in California. Instead of assuming a complete stress drop on all surrounding fault segments implied by a back-slip stress lobe method, we consider that stress evolves dynamically, punctuated by the occurrence of earthquakes, and governed by the elastic and viscous properties of the lithosphere. We study the seismicity of southern California and extract events for AMR calculations following the systematic approach employed in previous studies. We present several sensitivity tests of the method, as well as grid-search analyses over the region between 1955 and 2005 using fixed magnitude range, radius of the search area and period of time. The results are compared to the occurrence of large events and to maps of Coulomb stress changes. The Coulomb stress maps are compiled using the coseismic stress from all M > 7.0 earthquakes since 1812, their subsequent post-seismic relaxation, and the interseismic strain accumulation. We find no convincing correlation of seismicity rate changes in recent decades with areas of high stress that would support the AMR hypothesis. Furthermore, this indicates limited utility for practical earthquake hazard analysis in southern California, and possibly other regions.

Guilhem, Aurélie; Bürgmann, Roland; Freed, Andrew M.; Ali, Syed Tabrez

2013-11-01

354

A comparative study of the stress-rupture lifetimes of high-strength carbon fibers  

NASA Astrophysics Data System (ADS)

Stress-rupture life is the time a composite can survive under load at an assigned risk level. The stress-rupture lifetimes of high-strength PAN-based carbon fibers are important to the development and use of lightweight composite structures such as composite overwrapped pressure vessels (COPVs). To quantify appropriate stress-rupture risk levels based on available models, quantification of single fiber variability and lifetime is necessary to understand the variability observed in larger composite structures. In the present work, three PAN-based carbon fibers commonly used in COPV technology were examined, Hexcel IM9, Toray T700, and Toray T1000. The diameter of each fiber type was quantified by measuring samples in the scanning electron microscope and failure loads were determined by performing tensile tests on single fibers. Weibull statistics were used to describe the results. Fractography was performed on IM9 and T1000 fibers after tensile failure. The fracture surfaces are consistent with crack growth from a volume or surface defect. Stress-rupture testing was completed at two stress levels at each fiber type, 97% and 93% of the mean fiber strength for each of the fiber types. The results indicate that differences in stress-rupture life performance exist between the three fiber types. Differences in stress ratio of between 5 and 10% were observed, which may translate to significant difference in stress-rupture life behavior for larger composite structures. The results indicate that a relationship may exist between strength and stress-rupture life. However, if this relationship exists, it is not a simple one, and the relationship is likely complicated by manufacturing.

Grimes-Ledesma, Lorie

355

Abstract--Frequency dispersion of transconductance and output conductance in AlInN/GaN high electron mobility  

E-print Network

1 Abstract--Frequency dispersion of transconductance and output conductance in AlInN/GaN high is compared to experimental data for several bias conditions and different types of dispersion. Index Terms--AlInN/GaN in recent years on nearly lattice-matched AlInN/GaN high electron mobility transistors (HEMTs

Paris-Sud XI, Université de

356

Deformation behavior and microstructural evolution of Al-Zn-Cu-Mg-Sc-Zr alloy during high temperature compression  

Microsoft Academic Search

The deformation behavior of a new Al-Zn-Cu-Mg-Sc-Zr alloy was investigated with compression tests in temperature range of\\u000a 380–470 °C and strain rate range of 0.001–10 s?1 using Gleeble 1500 system, and the associated microstructural evolutions were studied by metallographic microscopy and transmission\\u000a electron microscopy. The results show that true stress—strain curves exhibit a peak stress, followed by a dynamic flow

Wen-bin Li; Qing-lin Pan; Jun-sheng Liu; Wen-jie Liang; Yun-bin He; Xiao-yan Liu

2009-01-01

357

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

358

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. PMID:25558129

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

2015-01-01

359

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

360

Effects of residual stress on the performance of plasma sprayed functionally graded ZrO 2\\/NiCoCrAlY coatings  

Microsoft Academic Search

Functionally graded ZrO2\\/NiCoCrAlY coatings were produced by plasma spraying using pre-mixed and spheroidized powders as the feedstock. The microstructure, density, elastic modulus, thermal conductivity\\/diffusivity, microhardness and coefficient of thermal expansion were found to change gradually through the five-layer functionally graded coatings which was beneficial for the improvement of mechanical and thermal properties of the coatings. The residual stresses of the

K. A Khor; Y. W Gu

2000-01-01

361

Effect of back stress evolution due to martensitic transformation on iso-volume fraction lines in a Cr–Ni–Mo–Al–Ti maraging steel  

Microsoft Academic Search

The effect of the back stress evolution on the iso-martensite volume fraction lines (the iso-? lines) is experimentally investigated in a Cr–Ni–Mo–Al–Ti maraging steel in the process of martensitic transformation by identifying the iso-? lines inside the transformation zone bounded by the martensite-start and -finish lines. Each iso-? line is composed of a tensile-branch and a compressive-branch, which are parallel

K Tanaka; T Terasaki; S Goto; T Antretter; F. D Fischer; G Cailletaud

2003-01-01

362

Reproduction in high altitude Aymara: physiological stress and fertility planning?  

PubMed

Reproductive characteristics at high altitude are described based on the reproductive histories of 720 Aymara women, collected in 1998 and 1999 in a group of twelve peasant communities at a mean altitude of 4000 m in the Bolivian Altiplano. The reproductive pattern is shaped by a late onset of childbearing, associated with a rather short reproductive span and large birth intervals. Environmental conditions could explain the particularly late age at menarche of rural girls compared with their urban counterparts, whereas the age at first birth is likely to be under cultural control. The short reproductive span appears to result from a large mean interval between last birth and menopause, which is essentially determined by cultural decisions. The birth intervals, which are longer than in many traditional societies, could be the result of a slower restoration of postpartum fecundability induced by the hard way of life inherent in the Altiplano (including poor sanitary and nutritional conditions and high workload), perhaps aggravated by hypoxia. However, a secular trend in fertility is perceptible, towards earlier menarche, earlier age at first birth, increasing reproductive span and a slight increase in live births and surviving offspring, which is probably the result of a slow improvement in living conditions. The existence of birth control on the one hand, and a total fertility rate averaging six live births among the couples who do not practise contraception on the other, are other arguments against the hypothesis of a low natural fecundity in these Aymara groups. PMID:12395863

Crognier, E; Villena, M; Vargas, E

2002-10-01

363

Electron mobility increase in submicronic transistors integrated on ultrathin silicon membranes subjected to high mechanical stress  

NASA Astrophysics Data System (ADS)

In this contribution we investigate an original method to apply high values of biaxial stress: The integration of submicronic fully depleted silicon on insulator transistors on ultrathin silicon membranes. The membranes are micromachined in the device substrate, the buried oxide facilitating the control of the membrane thickness below 1 ?m. High values of biaxial stress can thus be applied on the transistor channel without the drawbacks of conventional methods. The experimental results obtained using 750 nm thick membranes are presented. The piezoresistive longitudinal coefficient obtained for strained silicon on insulator wafer (240×10-12 Pa-1) is in good agreement with the results obtained by the four-probe bending method.

Bercu, Bogdan; Montès, Laurent; Rochette, Florent; Mouis, Mireille; Xin, Xu; Morfouli, Panagiota

2010-03-01

364

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

365

Investigation of Aluminate and Al2O3 Crystals and Melts at High Temperature Using XANES Spectroscopy  

NASA Astrophysics Data System (ADS)

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.; Cormier, Laurent; Roux, Jacques; Henderson, Grant S.; de Ligny, Dominique; Flank, Anne-Marie; Lagarde, Pierre

2007-02-01

366

An Empirical Test of a Cognitive Social Learning Model for Stress Moderation with Junior High School Students.  

ERIC Educational Resources Information Center

A cognitive social learning model for stress moderation was tested using 531 junior high school students. Higher levels of stress were found for younger students, White students, females, and those with upsetting life events. Locus of control, Type A personality, and knowledge of stress did not appear to moderate levels. (Author/MT)

Price, James H.; And Others

1985-01-01

367

Adaptation of Beef Cattle to Stressful Environments and Integrated Beef Systems for Production of Consistently Distinctive High-quality Beef  

E-print Network

Adaptation of Beef Cattle to Stressful Environments and Integrated Beef Systems for Production of Consistently Distinctive High-quality Beef Adaptation of Beef Cattle to Stressful Environments Evaluation of cattle phenotypes and genotypes as to adaptation to stressful environments involves Characterization

368

High-throughput screening of microbial adaptation to environmental stress.  

PubMed

We developed a microwell plate, high-throughput, screening method aimed at quantitating the tolerance of a panel of Gram-positive and Gram-negative bacteria to metals (Frankia sp., Escherichia coli, Cupriavidus metallidurans, Rhizobium leguminosarum, and Streptomyces scabies). Microbial viability was quantified using MTS; a tetrazolium salt converted to a water-soluble formazan through microbial reduction. In this paper, we present the stepwise development of the method, highlighting the main elements underlying its reliability, and compare results obtained with literature. We conclude the method is well suited to efficiently screen bacteria, including those that are filamentous and slow-growing, without the need for large amounts of inoculum which may not always be available. The method allows testing of compound gradients with sufficient replicates to generate statistically robust results, and is transposable to other types of cell proliferation assays such as those for antimicrobial susceptibility, and chemoresistance. PMID:21315114

Bélanger, Pier-Anne; Beaudin, Julie; Roy, Sébastien

2011-05-01

369

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

2015-03-01

370

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

371

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

372

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

373

Hot-Carrier- and Constant-Voltage-Stress-Induced Low-Frequency Noise in Nitrided High Dielectric MOSFETs  

Microsoft Academic Search

Understanding and minimization of low-frequency noise (LFN) originating from high- k (HK) gate dielectrics in new generation MOSFETs are of critical importance to applications in RF, analog, and digital circuits. To understand the effect of stress conditions on noise, nMOSFETs were subjected to accelerated hot-carrier stress (HCS) and positive constant-voltage stress (CVS). The additional LFN introduced through stressing was evaluated

M. Shahriar Rahman; Tanvir Hasan Morshed; Zeynep Celik-Butler; M. A. Quevedo-Lopez; A. Shanware; Luigi Colombo

2009-01-01

374

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

375

Solution-processed Al-chelated gelatin for highly transparent non-volatile memory applications  

NASA Astrophysics Data System (ADS)

Using the biomaterial of Al-chelated gelatin (ACG) prepared by sol-gel method in the ITO/ACG/ITO structure, a highly transparent resistive random access memory (RRAM) was obtained. The transmittance of the fabricated device is approximately 83% at 550 nm while that of Al/gelatin/ITO is opaque. As to the ITO/gelatin/ITO RRAM, no resistive switching behavior can be seen. The ITO/ACG/ITO RRAM shows high ON/OFF current ratio (>105), low operation voltage, good uniformity, and retention characteristics at room temperature and 85 °C. The mechanism of the ACG-based memory devices is presented. The enhancement of these electrical properties can be attributed to the chelate effect of Al ions with gelatin. Results show that transparent ACG-based memory devices possess the potential for next-generation resistive memories and bio-electronic applications.

Chang, Yu-Chi; Wang, Yeong-Her

2015-03-01

376

-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

377

High-precision half-life measurement for the superallowed ?+ emitter ²?Al(m).  

PubMed

A high-precision half-life measurement for the superallowed ?+ emitter 26Al(m) was performed at the TRIUMF-ISAC radioactive ion beam facility yielding T 1/2 6346.54 ± 0.46(stat) ± 0.60 (syst) ms, consistent with, but 2.5 times more precise than, the previous world average. The 26Al(m) half-life and ft value, 3037.53(61) s, are now the most precisely determined for any superallowed ? decay. Combined with recent theoretical corrections for isospin-symmetry-breaking and radiative effects, the corrected Ft value for (26)Al(m), 3073.0(12) s, sets a new benchmark for the high-precision superallowed Fermi ?-decay studies used to test the conserved vector current hypothesis and determine the V(ud) element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. PMID:21405268

Finlay, P; Ettenauer, S; Ball, G C; Leslie, J R; Svensson, C E; Andreoiu, C; Austin, R A E; Bandyopadhyay, D; Cross, D S; Demand, G; Djongolov, M; Garrett, P E; Green, K L; Grinyer, G F; Hackman, G; Leach, K G; Pearson, C J; Phillips, A A; Sumithrarachchi, C S; Triambak, S; Williams, S J

2011-01-21

378

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

379

High temperature properties of equiatomic FeAl with ternary additions  

NASA Technical Reports Server (NTRS)

The aluminide intermetallic compounds are considered potential structural materials for aerospace applications. The B2 binary aluminide FeAl has a melting point in excess of 1500 K, is of simple cubic structure, exists over a wide range of composition with solubility for third elements and is potentially self-protecting in extreme environments. The B2 FeAl compound has been alloyed with 1 to 5 at. pct ternary additions of Si, Ti, Zr, Hf, Cr, Ni, Co, Nb, Ta, Mo, W, and Re. The alloys were prepared by blending a third elemental powder with pre-alloyed binary FeAl powder. Consolidation was by hot extrusion at 1250 K. Annealing studies on the extruded rods showed that the third element addition can be classified into three categories based upon the amount of homogenization and the extent of solid solutioning. Constant strain rate compression tests were performed to determine the flow stress as a function of temperature and composition. The mechanical strength behavior was dependent upon the third element homogenization classification.

Titran, R. H.; Vedula, K. M.; Anderson, G. G.

1985-01-01

380

High temperature properties of equiatomic FeAl with ternary additions  

NASA Technical Reports Server (NTRS)

The aluminide intermetallic compounds are considered potential structural materials for aerospace applications. The B2 binary aluminide FeAl has a melting point in excess of 1500 K, is of simple cubic structure, exits over a wide range of composition with solubility for third elements and is potentially self-protecting in extreme environments. The B2 FeAl compound has been alloyed with 1 to 5 at % ternary additions of Si, Ti, Zr, Hf, Cr, Ni, Co, Nb, Ta, Mo, W, and Re. The alloys were prepared by blending a third elemental powder with prealloyed binary FeAl powder. Consolidation was by hot extrusion at 1250 K. Annealing studies on the extruded rods showed that the third element addition can be classified into three categories based upon the amount of homogenization and the extent of solid solutioning. Constant strain rate compression tests were performed to determine the flow stress as a function of temperature and composition. The mechanical strength behavior was dependent upon the third element homogenization classification.

Titran, R. H.; Vedula, K. M.; Anderson, G. G.

1984-01-01

381

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

382

High-Temperature Thermometer Using Cr-Doped GdAlO3 Broadband Luminescence  

NASA Technical Reports Server (NTRS)

A new concept has been developed for a high-temperature luminescence-based optical thermometer that both shows the desired temperature sensitivity in the upper temperature range of present state-of-the-art luminescence thermometers (above 1,300 C), while maintaining substantial stronger luminescence signal intensity that will allow these optical thermometers to operate in the presence of the high thermal background radiation typical of industrial applications. This objective is attained by using a Cr-doped GdAlO3 (Cr:GdAlO3) sensor with an orthorhombic perovskite structure, resulting in broadband luminescence that remains strong at high temperature due to the favorable electron energy level spacing of Cr:GdAlO3. The Cr:GdAlO3 temperature (and pressure) sensor can be incorporated into, or applied onto, a component s surface when a non-contact surface temperature measurement is desired, or alternatively, the temperature sensor can be attached to the end of a fiber-optic probe that can then be positioned at the location where the temperature measurement is desired. In the case of the fiber-optic probe, both the pulsed excitation and the luminescence emission travel through the fiber-optic light guide. In either case, a pulsed light source provides excitation of the luminescence, and the broadband luminescence emission is collected. Real-time temperature measurements are obtain ed using a least-squares fitting algorithm that determines the luminescence decay time, which has a known temperature dependence established by calibration. Due to the broad absorption and emission bands for Cr:GdAlO3, there is considerable flexibility in the choice of excitation wavelength and emission wavelength detection bands. The strategic choice of the GdAlO3 host is based on its high crystal field, phase stability, and distorted symmetry at the Cr3+ occupation sites. The use of the broadband emission for temperature sensing at high temperatures is a key feature of the invention and is novel since broadband luminescence emission normally shows severe thermal quenching. The tightly bound AlO6 octahedra in GdAlO3 results in a larger energy barrier to nonradiative decays than in other materials and therefore makes using broadband emission for temperature sensing possible at high temperatures. This approach results in a substantial increase in temperature capability. For example, the most commonly used Cr-doped crystal used for luminescence-based temperature measurements, ruby, has only been demonstrated up to 600 C, whereas the Cr:GdAlO3 optical thermometer under development has already been shown to exhibit useful luminescence up to 1,300 C. Because GdAlO3 is non-reactive and is stable in harsh, high-temperature environments, sensors composed of Cr:GdAlO3 will be very well suited for remote high-temperature measurements in engine or industrial environments where its intense high-temperature luminescence will stand out above significant thermal radiation background levels.

Eldridge, Jeffrey; Chambers, Matthew

2011-01-01

383

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

384

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

385

Structural and optical properties of nearly stress-free m-plane ZnO film on (1 0 0) ?-LiAlO 2 with a GaN buffer layer by metal-organic chemical vapor deposition  

NASA Astrophysics Data System (ADS)

(1 0 1¯ 0)m-plane ZnO film was epitaxially deposited on (1 0 0) ?-LiAlO 2 by metal-organic chemical vapor deposition at 600 °C with a GaN buffer layer. The epitaxial relationships between ZnO and GaN, GaN and (1 0 0) ?-LiAlO 2 were determined by X-ray diffraction ?-scans. There exhibits very small decrease for the E 2 mode shift (0.3 cm -1) of ZnO in the Raman spectrum, which indicates the epitaxial ZnO film was under a slight tensile stress (5.77 × 10 7 Pa). Unlike the highly strained a-plane ZnO, temperature dependent photoluminescence spectra show that the free A exiton emission was observed with the temperature ?138 K.

Lin, Hui; Zhou, Shengming; Teng, Hao; Hou, Xiaorui; Jia, Tingting; Gu, Shulin; Zhu, Shunming; Xie, Zili; Han, Ping; Zhang, Rong; Xu, Ke

2009-08-01

386

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

387

Schottky-Drain Technology for AlGaN/GaN High-Electron Mobility Transistors  

E-print Network

In this letter, we demonstrate 27% improvement in the buffer breakdown voltage of AlGaN/GaN high-electron mobility transistors (HEMTs) grown on Si substrate by using a new Schottky-drain contact technology. Schottky-drain ...

Lu, Bin

388

Invited Paper AlGaN-based high-performance metalsemiconductormetal  

E-print Network

¨kkavas a,*, Serkan Butun a , Turgut Tut a , Necmi Biyikli b , Ekmel Ozbay a a Nanotechnology Research, Bilkent, Ankara 06800, Turkey b Department of Electrical and Computer Engineering, Virginia Commonwealth three orders of magnitude. High-speed measurements of Al0.38Ga0.62N MSM PD resulted in fast responses

Ozbay, Ekmel

389

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

390

HIGH TEMPERATURE SULFIDATION BEHAVIOR OF LOW Al IRON-ALUMINUM COMPOSITIONS  

E-print Network

HIGH TEMPERATURE SULFIDATION BEHAVIOR OF LOW Al IRON-ALUMINUM COMPOSITIONS S.W. Banovic, J.N. Du (Received January 5, 1998) (Accepted March 23, 1998) Introduction Iron-aluminum weld overlay coatings, the application of iron-aluminum alloys is currently limited due to hydrogen cracking susceptibility subsequent

DuPont, John N.

391

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

392

High density GaN/AlN quantum dots for deep UV LED with high quantum efficiency and temperature stability.  

PubMed

High internal efficiency and high temperature stability ultraviolet (UV) light-emitting diodes (LEDs) at 308?nm were achieved using high density (2.5 × 10(9)?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

393

High density GaN/AlN quantum dots for deep UV LED with high quantum efficiency and temperature stability  

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

394

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

395

Effect of high intensity ultrasound on Al?Ni?, Al?Ni crystallite size in binary AlNi (50 wt% of Ni) alloy.  

PubMed

Crystallite size of the intermetallics is one of the most important parameters that can influence kinetics of catalytic reactions. Analysis of the crystallite sizes of Al?Ni and Al?Ni? intermetallic phases using Scherrer and Williamson-Hall methods reveals that the sonomechanical impact of ultrasound on suspensions of AlNi particles in ethanol results in crystallites growth and microstrain reduction. PMID:25171834

Cherepanov, Pavel V; Melnyk, Inga; Andreeva, Daria V

2015-03-01

396

A method of calculating the safe fatigue life of compact, highly-stressed components  

NASA Technical Reports Server (NTRS)

This paper describes a method which has been developed for estimating the safe fatigue life of compact, highly-stressed and inaccessible components for aeroplanes and helicopters of the Royal Air Force. It is explained why the Design Requirements for British Military Aircraft do not favor the use of a damage-tolerance approach in these circumstances.

Cardick, Arthur W.; Pike, Vera J.

1994-01-01

397

Stress analysis of carotid plaque rupture based on in vivo high resolution MRI  

Microsoft Academic Search

Atheromatous carotid plaque rupture is responsible for the majority of ischaemic strokes in the developed world. Plaque rupture has been associated with plaque morphology, plaque components’ properties, inflammation and local stress concentration. High resolution multi-spectral magnetic resonance imaging (MRI) has allowed the plaque components to be visualized in vivo. This study combined the recent advances in finite element analysis (FEA)

Zhi-Yong Li; Simon Howarth; Rikin A. Trivedi; Jean M. U-King-Im; Martin J. Graves; Andrew Brown; Liqun Wang; Jonathan H. Gillard

2006-01-01

398

Patellar polyethylene spinout after low-contact stress, high-congruity, mobile-bearing patellofemoral arthroplasty.  

PubMed

A low-contact stress, high-congruity, mobile-bearing patellofemoral joint arthroplasty decreases the contact force in the patellofemoral joint, theoretically reducing patellar polyethylene wear and increasing implant longevity. This article describes the case of a 47-year-old obese woman who presented with pain and loss of extension after a low-contact stress, high-congruity, mobile-bearing patellofemoral joint arthroplasty. Radiographs revealed dislocation (ie, spinout) of the patellar polyethylene. Patellar polyethylene spinout is a rare complication of metal-backed, mobile-bearing patellar resurfacing. Theoretically, patellar polyethylene spinout in low-contact stress, high-congruity, mobile-bearing patellofemoral arthroplasty is related to implant design and the placement of the metal base plate. Ultimately, the articulation of low-contact stress, high-congruity, mobile-bearing patellofemoral arthroplasty may be too congruent to resist the forces of the patellofemoral joint, particularly in patients who are obese, and the patellar rotation allowed by this articulation may not be sufficient for all patients. Should patellar spinout occur, replacement of the polyethylene is not sufficient to correct the problem; hence, revision of the patellar and trochlear components is required because it remains unclear whether failure is secondary to patellar or trochlear design deficiencies. PMID:22310419

Amanatullah, Derek F; Jamali, Amir A

2012-02-01

399

A novel high-efficiency single-stage PFC converter with reduced voltage stress  

Microsoft Academic Search

In this paper, a novel single-stage power-factor-correction converter is proposed, which employs two auxiliary windings to achieve low input current total harmonic distortion, low voltage stress across the bulk capacitor, and high efficiency. The improved performance was experimentally verified

Miaosen Shen; Zhaoming Qian

2002-01-01

400

High-throughput analysis of thin-film stresses using arrays of micromachined cantilever beams  

E-print Network

High-throughput analysis of thin-film stresses using arrays of micromachined cantilever beams Hyun tool for the combinatorial analysis of phase transformations in thin films, especially when combined to evaluate the thermomechanical behavior of Fe­Pd binary alloys as a function of composition. © 2008 American

401

Stress corrosion behavior of stainless steel welds in high temperature water containing chlorides  

Microsoft Academic Search

The effects of delta ferrite, carbon content and postweld heat treatment on the stress corrosion susceptibility of AISI Types 308, 309, and 316 stainless steel surfacing welds in high temperature water have been investigated. For each type of stainless steel, the initial ferrite level was controlled at three predetermined levels in the range 1 to 10%, and the carbon content

R. Viswanathan; J. I. Nurminen; R. G. Aspden

1979-01-01

402

High-Stakes Testing and Its Relationship to Stress Levels of Secondary Teachers  

ERIC Educational Resources Information Center

This study investigated the relationship between high-stakes testing and the stress levels of secondary teachers in Jackson's Jackson Public School District. The independent variables of age, gender, subject taught, teaching experience, degree and school level were used to determine the differences of the various groups. A survey was piloted and…

Christian, Sonya Colman

2010-01-01

403

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...

404

High performance 65 nm SOI technology with dual stress liner and low capacitance SRAM cell  

Microsoft Academic Search

A high performance 65 nm SOI CMOS technology is presented featuring 35 nm gate length, 1.05 nm gate oxide, performance enhancement from dual stress nitride liners (DSL), and 10 wiring levels with low-k dielectric offered in the first 8 levels. DSL enhancement is shown to scale well to 65 nm with larger enhancement seen than at 90 nm design rules.

E. Leobandung; H. Nayakama; D. Mocuta; K. Miyamoto; M. Angyal; H. V. Meer; K. McStay; I. Ahsan; S. Allen; A. Azuma; M. Belyansky; R.-V. Bentum; J. Cheng; D. Chidambarrao; B. Dirahoui; M. Fukasawa; M. Gerhardt; M. Gribelyuk; S. Halle; H. Harifuchi; D. Harmon; J. Heaps-Nelson; H. Hichri; K. Ida; M. Inohara; I. C. Inouc; K. Jenkins; T. Kawamura; B. Kim; S.-K. Ku; M. Kumar; L. Liebmann; R. Logan; I. Melville; K. Miyashita; A. Mocuta; P. O'Neil; M.-F. Ng; T. Nogami; A. Nomura; C. Norris; E. Nowak; M. Ono; S. Panda; C. Penny; C. Radens; R. Ramachandran; A. Ray; S.-H. Rhee; D. Ryan; T. Shinohara; G. Sudo; F. Sugaya; J. Strane; Y. Tan; L. Tsou; L. Wang; F. Wirbeleit; S. Wu; T. Yamashita; H. Yan; Q. Ye; D. Yoneyama; D. Zamdmer; H. Zhong; H. Zhu; W. Zhu; P. Agnello; S. Bukofsky; G. Bronner; E. Crabbe; G. Freeman; S.-F. Huang; T. Ivers; H. Kuroda; D. McHerron; J. Pellerin; Y. Toyoshima; S. Subbanna; N. Kepler; L. Su

2005-01-01

405

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

406

A method of calculating the safe fatigue life of compact, highly-stressed components  

NASA Astrophysics Data System (ADS)

This paper describes a method which has been developed for estimating the safe fatigue life of compact, highly-stressed and inaccessible components for aeroplanes and helicopters of the Royal Air Force. It is explained why the Design Requirements for British Military Aircraft do not favor the use of a damage-tolerance approach in these circumstances.

Cardick, Arthur W.; Pike, Vera J.

1994-09-01

407

The Role of High-Field Stress in the Negative-Bias Temperature Instability  

Microsoft Academic Search

In this paper, a fast drain-current measurement methodology which supports the standard threshold voltage and transconductance extractions associated with the fast dynamic negative-bias temperature instability (NBTI) is presented. Using this methodology, we show that production quality transistors exhibit only minimal degradation after a brief stress at moderate to high dielectric fields (contrary to the excessive degradation reported in the recent

J. P. Campbell; Kin P. Cheung; John S. Suehle; Anthony S. Oates

2010-01-01

408

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.

409

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

E-print Network

High-stress paleoenvironment during the late Maastrichtian to early Paleocene in Central Egypt 01003, USA d Department of Geology, Faculty of Science, South Valley University, Aswan 81528, Egypt of central Egypt indicate a depositional environment interrupted by periods of erosion due to local tectonic

Keller, Gerta

410

X-ray diffraction and high resolution transmission electron microscopy of 3C-SiC/AlN/6H-SiC(0001)  

NASA Astrophysics Data System (ADS)

The structure and crystal quality of epitaxial films of SiC/AlN/6H-SiC(0001) prepared by chemical vapor deposition were evaluated by high resolution transmission electron microscopy (HRTEM) and x-ray diffraction techniques. Cross-sectional HRTEM revealed an abrupt AlN layer-6H-SiC substrate junction, but the transition between the AlN and SiC layers was much rougher, leading to the formation of a highly disordered SiC region adjacent to the interface. The AlN layer was relatively defect free, while the SiC layer contained many microtwins and stacking faults originating at the top SiC/AlN interface. The SiC layer was the 3C-polytype, as determined by double crystal x-ray rocking curves. The SiC layers were under in-plane compressive stress, with calculated defect density between 2 4×107 defects/cm-2.

Edgar, J. H.; Yu, Z. J.; Smith, David J.; Chaudhuri, J.; Cheng, X.

1997-12-01

411

High Power Wideband AlGaN\\/GaN HEMT Feedback Amplifier Module  

Microsoft Academic Search

A high power wideband feedback amplifier module using AlGaN\\/GaN high electron mobility transistor (HEMT) has been developed that covers the frequency range of DC to 5 GHz with small signal gain of 9 dB. Shunt feedback topology is employed by adding inductive components to increase the bandwidth. At midband frequency, power added efficiency (PAE) of 20 % and saturation power

Y. Chung; S. Cai; W. Lee; Y. Lin; C. P. Wen; K. L. Wang; T. Itoh

1980-01-01

412

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

413

An 8 GHz high power AlGaN\\/GaN HEMT VCO  

Microsoft Academic Search

A high power X-band hybrid microwave integrated voltage controlled oscillator (VCO) based on AlGaN\\/GaN HEMT is presented. The oscillator design utilizes a common-gate negative resistance structure with open and short-circuit stub microstrip lines as the main resonator for a high Q factor. The VCO operating at 20 V drain bias and -1.9 V gate bias exhibits an output power of

Chen Huifang; Wang Xiantai; Chen Xiaojuan; Luo Weijun; Liu Xinyu

2010-01-01

414

Solid-solution hardening of a high-Entropy AlTiVCrNbMo alloy  

NASA Astrophysics Data System (ADS)

The nature of solid-solution hardening of high-entropy alloys is discussed using an equiatomic bcc AlTiVCrNbMo alloy as an example. The hardening of the alloy is found to be characterized by an increase in the temperature dependence of the component of the critical shear strength and by anomalously high athermic hardening due to the perpendicular slip plane of the Burgers vector component. A relatively simple expression is proposed to estimate the detected hardening ? H(??).

Firstov, S. A.; Rogul', T. G.; Krapivka, N. A.; Ponomarev, S. S.; Tkach, V. N.; Kovylyaev, V. V.; Gorban', V. F.; Karpets, M. V.

2014-04-01

415

High-brightness AlGaInP light emitting diodes  

Microsoft Academic Search

First commercially introduced in 1990, AlGaInP light emitting diodes (LEDs) currently are the highest (luminous) efficiency visible solid-state emitters produced to date in the red through yellow spectral regime. The attainment of this high-efficiency performance is a result of the development of advanced metalorganic chemical vapor deposition crystal growth techniques, which have facilitated the high-quality growth of this quaternary alloy

D. A. Vanderwater; I.-H. Tan; G. E. Hofler; D. C. Defevere; F. A. Kish

1997-01-01

416

Al2O3 surface passivation and MOS-gate fabrication on AlGaN/GaN high-electron-mobility transistors without Al2O3 etching process  

NASA Astrophysics Data System (ADS)

Al2O3 passivation by thermal oxidation of aluminium on AlGaN/GaN high-electron-mobility transistors (HEMTs) without Al2O3 etching is proposed. The deposition of a 5-nm-thick Al film was carried out, followed by a lift-off process to remove Al from the ohmic and contact pad area. Subsequently, the Al film was annealed under O2 ambient. When the gate bias was ?7 V, the gate leakage currents of a conventional nonpassivated HEMT, a surface-passivated Schottky-gate HEMT, and a surface-passivated MOS-HEMT were determined as 140, 96, and 4.1 µA/mm, respectively. The current collapse phenomenon in the Al2O3-surface-passivated devices was evidently suppressed compared with that in the nonpassivated HEMT.

Kim, Jeong-Jin; Park, Young-Rak; Jang, Hyun-Gyu; Na, Je-Ho; Lee, Hyun-Soo; Ko, Sang-Choon; Jung, Dong-Yun; Lee, Hyung-Seok; Mun, Jae-Kyoung; Lim, Jing-Hong; Yang, Jeon-Wook

2015-03-01

417

Microstructure/processing relationships in high-energy high-rate consolidated powder composites of Nb-stabilized Ti3Al+TiAl  

SciTech Connect

A new approach to powder processing is employed in forming titanium aluminide composites. The processing consists of internal heating of a customized powder blend by a fast electrical discharge of a homopolar generator. The high-energy high-rate '1MJ in 1s' pulse permits rapid heating of an electrically conducting powder mixture in a cold wall die. This short time at temperature approach offers the opportunity to control phase transformations and the degree of microstructural coarsening not readily possible with standard powder-processing approaches. This paper describes the consolidation results of titanium aluminide-based powder-composite materials. The focus of this study was the definition of microstructure/processing relationships for each of the composite constituents, first as monoliths and then in composite forms. Non-equilibrium phases present in rapidly solidified TiAl powders are transformed to metastable intermediates en route to the equilibrium gamma phase.

Persad, C.; Lee, B.; Hou, C.; Eliezer, Z.; Marcus, H.L.

1989-01-01

418

Highly selective and low damage atomic layer etching of InP\\/InAlAs heterostructures for high electron mobility transistor fabrication  

Microsoft Academic Search

Highly selective, low damage atomic layer etching (ALET) technology was developed for dry gate recess during the fabrication of InGaAs\\/InP\\/InAlAs high electron mobility transistors lattice matched to InP substrates. Etching characteristics of InP layer on top of InAlAs layer and the surface chemistry of the exposed InAlAs layer were investigated by utilizing angular resolved x-ray photoelectron spectroscopy. Finally, InAlAs Schottky

S. D. Park; C. K. Oh; W. S. Lim; H. C. Lee; J. W. Bae; G. Y. Yeom; T. W. Kim; J. I. Song; J. H. Jang

2007-01-01

419

Highly selective and low damage atomic layer etching of InP?InAlAs heterostructures for high electron mobility transistor fabrication  

Microsoft Academic Search

Highly selective, low damage atomic layer etching (ALET) technology was developed for dry gate recess during the fabrication of InGaAs?InP?InAlAs high electron mobility transistors lattice matched to InP substrates. Etching characteristics of InP layer on top of InAlAs layer and the surface chemistry of the exposed InAlAs layer were investigated by utilizing angular resolved x-ray photoelectron spectroscopy. Finally, InAlAs Schottky

S. D. Park; C. K. Oh; W. S. Lim; H. C. Lee; J. W. Bae; G. Y. Yeom; T. W. Kim; J. I. Song; J. H. Jang

2007-01-01

420

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

421

Phase separation in equiatomic AlCoCrFeNi high-entropy alloy.  

PubMed

The microstructure of the as-cast AlCoCrFeNi high entropy alloy has been investigated by transmission electron microscopy and atom probe tomography. The alloy shows a very pronounced microstructure with clearly distinguishable dendrites and interdendrites. In both regions a separation into an Al-Ni rich matrix and Cr-Fe-rich precipitates can be observed. Moreover, fluctuations of single elements within the Cr-Fe rich phase have been singled out by three dimensional atom probe measurements. The results of investigations are discussed in terms of spinodal decomposition of the alloying elements inside the Cr-Fe-rich precipitates. PMID:23352803

Manzoni, A; Daoud, H; Völkl, R; Glatzel, U; Wanderka, N

2013-09-01

422

Isentropic Compression Driven by High-Explosive Application to TI-6AL-4V  

NASA Astrophysics Data System (ADS)

We report on an isentropic compression experiment of Ti-6Al-4V alloy based on the use of the release of detonation products from a high-explosive to generate a ramp wave compression in a multisteps target. VISAR and DLI measurements of the rear free surface velocities of the different steps allow computing the sound velocity of the material during its compression, which is characteristic of the EOS of the material. The experimental device is described and the sound velocity measurements are analyzed. We obtain Ti-6Al-4V strength along the compression up to 15 GPa. The results are compared with two dimensional elastic-plastic simulations.

Voltz, C.; Sollier, A.; Maillet, J.-B.; Bouyer, V.

2009-12-01

423

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

424

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

425

Analysis of thermal residual stress in a thick-walled ring of Duralcan-base Al-SiC functionally graded material  

SciTech Connect

A ring-cutting test and an elastic theory were applied to evaluate the macroscopic residual stress in a thick-walled ring made of Al-SiC functionally graded material (FGM). The FGM ring specimens, with outer diameter 90 mm, radial thickness approximately 8.4 to 10 mm, and width 30 mm, were fabricated by the centrifugal casting method from an ingot of Duralcan F3D.20S of Al-20 vol pct SiC master composite. Because of a difference in centrifugal forces of SiC particles and of molten aluminum alloy, the rings had a graded composition of SiC particles in the radial direction. The volume fractions of SiC particles in each ring specimen varied in the range of 0 to 43 vol pct from the inner to the outer surface of the ring, depending on the applied mold spin speed. A ring diametral compression test was performed to validate an analytical formula based on the curved beam theory that can account for the graded properties of the material. Excellent agreement between the theory that can account for the graded properties of the material. Excellent agreement between the theory and the experiment was found. The residual stress was found to be generated by a cooling of {Delta}T = 140 K, which was from half the melting point corresponding stress-free condition to the ambient temperature. The hoop residual stresses in the FGM ring varied in the range of {minus}50 to +35 MPa and from tension at the inner surface to compression at the outer space because of the graded composition. With an increase in wall thickness and/or composition gradation, the residual stresses were found to increase.

Fukui, Yasuyoshi [Kagoshima Univ. (Japan). Dept. of Mechanical Engineering; Watanabe, Yoshimi [Shinshu Univ., Ueda (Japan). Faculty of Textile Science and Technology

1996-12-01

426

High-resolution interferometric imaging of stress propagation in pediatric and adult skulls  

NASA Astrophysics Data System (ADS)

Variations based on bone growth and development make stress and fracture propagation differ greatly in pediatric skulls as compared to adult skulls. Differentiating the stress propagation between the pediatric and adult skulls can improve diagnostic prediction when presented with direct frontal impact on a pediatric skull, a fairly common occurrence in the clinical environment. Critical diagnostic information can be learned from an in depth study of stress propagation as a function of impact force at critical locations on the periorbital region of the human skull. The Division of Pediatric Otolaryngology at Albany Medical College and InterScience, Inc. are utilizing electronic speckle pattern interferometry detection (ESPI) and high resolution imaging to evaluate and compare stress propagation in pediatric and adult skulls. A dual detection ESPI system was developed which integrates a medium resolution (2/3') CCD capable of real-time image processing, with a high resolution, megapixel detector capable of limited real time acquisition and image processing in software. Options to allow for high speed detection include integrating a custom, high performance image intensifier with the megapixel detector leg to be used as a high speed gate. The dual optical layout will allow for continuous and pulsed ESPI evaluation of calibrated impacts at specific landmarks on the skull. The goal of this work is to produce a full quantitative analysis of the stress propagation in pediatric versus adult skulls for a better understanding of bone dynamics. The work presented below concentrates on the development of the dual detection ESPI system and initial results achieved with an adult cadaver skull.

Conerty, Michelle D.; Castracane, James; Clow, Lawrence P., Jr.; Koltai, Peter J.; Mouzakes, Jason

1997-05-01

427

Size-dependent resonance and buckling behavior of nanoplates with high-order surface stress effects  

NASA Astrophysics Data System (ADS)

This work presents a theoretical study of the resonance frequency and buckling load of nanoplates with high-order surface stress model. A classical thin plate theory based on Kirchhoff-Love assumption is implemented with surface effects. Circular and rectangular nanoplates with simply supported end conditions are exemplified. The size-dependent solutions are compared with the simplified solutions based on simple surface stress model, and also on the classical theory of elasticity. We aim to explore the scope of applicability so that the modified continuum mechanics model could serve as a refined approach in the prediction of mechanical behavior of nanoplates.

Cheng, Chih-Hao; Chen, Tungyang

2015-03-01

428

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

429

Stress Corrosion Cracking Model for High Level Radioactive-Waste Packages  

Microsoft Academic Search

A stress corrosion cracking (SCC) model has been adapted for performance prediction of high level radioactive-waste packages to be emplaced in the proposed Yucca Mountain repository. For waste packages of the proposed Yucca Mountain repository, the outer barrier material is the highly corrosion-resistant Alloy UNS-N06022 (Alloy 22), the environment is represented by aqueous brine films present on the surface of

P. Andresen; G. Gordon; S. Lu

2004-01-01

430

Weight Gain Induced by High-Fat Feeding Involves Increased Liver Oxidative Stress  

Microsoft Academic Search

Objective: To assess the effects of high-fat feeding on white adipose tissue gene expression and liver oxidative stress.Research Methods and Procedures: Male Wistar rats were fed on standard pelleted or high-fat diet to produce a diet-induced obesity model. Therefore, body composition, serum biochemical values and liver malondialdehyde (MDA) were determined after 56 days of feeding. Expression (mRNA) values of three

Fermín I. Milagro; Javier Campión; J. Alfredo Martínez

2006-01-01

431

Boundary layer Reynolds stress composition at high and low Reynolds numbers  

Microsoft Academic Search

Properties of the motions contributing to the Reynolds stresses (-\\\\overlineuv) in high and low Reynolds number (R_theta) turbulent boundary layers are studied through physical experiments. The low R_theta measurements (R_theta = 2870) were acquired in a laboratory wind tunnel, while the high R_theta data (R_theta ~= 5 × 10^6) were acquired at the SLTEST site, Utah. At each R_theta, comparisons

Paththage Priyadarshana; Joseph Klewicki

2003-01-01

432

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

Microsoft Academic Search

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

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

2005-01-01

433

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

434

High-Al gabbros in the Laramie Anorthosite Complex, Wyoming: implications for the composition of melts parental to Proterozoic anorthosite  

Microsoft Academic Search

High-Al gabbro represents one of the latest phases of magmatism in the 1.43 Ga Laramie anorthosite complex (LAC) in southeastern Wyoming. This lithology, which is mineralogically and geochemically the most primitive in the