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1

Effects of high electrical stress on GaN\\/InGaN\\/AlGaN single-quantum-well light-emitting diodes  

Microsoft Academic Search

We report on high-electrical-stress testing of Nichia GaN\\/InGaN\\/AlGaN single-quantum-well (SQW) light-emitting diodes. In contrast to our earlier experiments with double-heterostructure LEDs, the present SQW devices have been improved to the point that the encapsulating plastic fails under high electrical stress earlier than the diode itself.

Marek Osi?ski; Daniel L Barton; Piotr Perlin; Jinhyun Lee

1998-01-01

2

The yield stress anomaly in stoichiometric FeAl at high strain rate  

Microsoft Academic Search

Single crystals and large-grained polycrystals of B2-structured FeAl containing initially low vacancy concentrations exhibit a so-called yield anomaly, with a yield strength peak at typically â¼0.40--0.45 of the absolute melting point. If the grain size in a polycrystal is fine, declining Hall-Petch strengthening with increasing temperature can obscure this yield anomaly. Similarly, vacancies retained after elevated temperature annealing can raise

Y. Yang; I. Baker; G. T Gray III; C. Cady

1999-01-01

3

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

4

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

SciTech Connect

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

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

2007-01-01

5

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

6

Oxidative stress biomarkers in sporadic ALS.  

PubMed

We aimed to investigate oxidative stress biomarkers in a cross-sectional pilot study of 50 participants with sporadic ALS (SALS) compared to 46 control subjects. We measured urinary 8-oxodeoxyguanosine (8-oxodG), urinary 15-F(2t)-isoprostane (IsoP), and plasma protein carbonyl by ELISA methods. We also determined if ELISA measurement of 8-oxodG could be validated against measures from high-pressure liquid chromatography coupled with electrochemical detection, the current standard method. We found that 8-oxodG and IsoP levels adjusted for creatinine were significantly elevated in SALS participants. These differences persisted after age and gender were controlled in regression analyses. These markers are highly and positively correlated with each other. 8-oxodG measured by the two techniques from the same urine sample were positively correlated (p<.0001). Protein carbonyl was not different between SALS participants and controls. In conclusion, using ELISA, we confirmed that certain oxidative stress biomarkers were elevated in SALS participants. ELISA may be reliable and thus useful in epidemiology studies requiring large numbers of samples to determine the significance of increased oxidative stress markers in SALS. Further studies are required. PMID:18574762

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

2008-06-01

7

Localization of off-stress-induced damage in AlGaN/GaN high electron mobility transistors by means of low frequency 1/f noise measurements  

NASA Astrophysics Data System (ADS)

The location of the time dependent degradation in OFF-state stressed AlGaN/GaN high electron mobility transistors is studied using low frequency 1/f noise measurements, with additional electroluminescence analysis. The gate bias dependence of the 1/f noise is shown to be a powerful tool to illustrate that in addition to the gate edge breakdown, progressive time-dependent trap generation occurs underneath the gate area, possibly extending in the gate-drain access region due to the electric field peak associated with the gate field plate.

Silvestri, Marco; Uren, Michael J.; Killat, Nicole; Marcon, Denis; Kuball, Martin

2013-07-01

8

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

9

Tree fine root Ca\\/Al molar ratio – Indicator of Al and acidity stress  

Microsoft Academic Search

High soil acidity and elevated soil Al concentrations limit plant growth in many terrestrial ecosystems. Aluminium toxicity can be ameliorated by Ca. Thus, Ca\\/Al molar ratios in soil solution and in plant tissues have been proposed as superior indicators than Al concentration itself for evaluating the Al toxicity stress to trees (Cronan & Grigal, J Environ Qual 1995;24:209 – 226). This article

E. I. Vanguelova; Y. Hirano; T. D. Eldhuset; L. Sas-Paszt; M. R. Bakker; Ü. Püttsepp; I. Brunner; K. Lõhmus; D. Godbold

2007-01-01

10

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

11

Improved Off-State Stress Critical Voltage on AlGaN/GaN High Electron Mobility Transistors Utilizing Pt/Ti/Au Based Gate Metallization  

SciTech Connect

The critical voltage for degradation of AlGaN/GaN high electron mobility transistors (HEMTs) employed with the Pt/Ti/Au gate metallization instead of the commonly used Ni/Au was significantly increased during the off-state stress. The typical critical voltage for HEMTs with Ni/Au gate metallization was around -60V. By sharp contrast, no critical voltage was observed for the HEMTs with Pt/Ti/Au gate metallization, even up to -100V, which was the instrumental limitation in this experiment. Both Schottky forward and reverse gate characteristics of the Ni/Au degraded once the gate voltage passed the critical voltage of around -60V. There was no degradation exhibited for the HEMTs with Pt-gated HEMTs.

Lo, C. F. [University of Florida; Liu, L. [University of Florida, Gainesville; Kang, Tsung Sheng [University of Florida, Gainesville; Davies, Ryan [University of Florida; Gila, Brent P. [University of Florida, Gainesville; Pearton, S. J. [University of Florida; Kravchenko, Ivan I [ORNL; Laboutin, O. [Kopin Corporation, Taunton, MA; Cao, Yu [Kopin Corporation, Taunton, MA; Johnson, Wayne J. [Kopin Corporation, Taunton, MA; Ren, F. [University of Florida

2011-01-01

12

Improvement of Off-State Stress Critical Voltage by Using Pt-gated AlGaN/GaN High Electron Mobility Transistors  

SciTech Connect

By replacing the commonly used Ni/Au gate metallization with Pt/Ti/Au, the critical voltage for degradation of AlGaN/GaN High Electron Mobility Transistors (HEMTs) during off-state biasing stress was significantly increased. The typical critical voltage for the HEMTs with Ni/Au gate metallization was around -55V. By sharp contrast, no critical voltage was observed for the HEMTs with Pt/Ti/Au gate metallization, even up -100V, which was the instrumental limitation in this experiment. Both Schottky forward and reverse gate characteristics of the Ni/Au degraded once the gate voltage passed the critical voltage of -55V. There was no degradation exhibited for the HEMTs with Pt/Ti/Au gate metallization.

Lo, C. F. [University of Florida; Liu, L. [University of Florida, Gainesville; Kang, Tsung Sheng [University of Florida, Gainesville; Gila, Brent P. [University of Florida, Gainesville; Pearton, S. J. [University of Florida; Kravchenko, Ivan I [ORNL; Laboutin, O. [Kopin Corporation, Taunton, MA; Cao, Yu [Kopin Corporation, Taunton, MA; Johnson, Wayne J. [Kopin Corporation, Taunton, MA; Ren, F. [University of Florida

2011-01-01

13

Stress granules as crucibles of ALS pathogenesis  

PubMed Central

Amyotrophic lateral sclerosis (ALS) is a fatal human neurodegenerative disease affecting primarily motor neurons. Two RNA-binding proteins, TDP-43 and FUS, aggregate in the degenerating motor neurons of ALS patients, and mutations in the genes encoding these proteins cause some forms of ALS. TDP-43 and FUS and several related RNA-binding proteins harbor aggregation-promoting prion-like domains that allow them to rapidly self-associate. This property is critical for the formation and dynamics of cellular ribonucleoprotein granules, the crucibles of RNA metabolism and homeostasis. Recent work connecting TDP-43 and FUS to stress granules has suggested how this cellular pathway, which involves protein aggregation as part of its normal function, might be coopted during disease pathogenesis. PMID:23629963

King, Oliver D.

2013-01-01

14

Local stress-induced effects on AlGaAs/AlOx oxidation front shape  

NASA Astrophysics Data System (ADS)

The lateral oxidation of thick AlGaAs layers (>500 nm) is studied. An uncommon shape of the oxide tip is evidenced and attributed to the embedded stress distribution, inherent to the oxidation reaction. Experimental and numerical studies of the internal strain in oxidized AlxGa1-xAs/GaAs structures were carried out by dark-field electron holography and finite element methods. A mapping of the strain distribution around the AlGaAs/oxide interface demonstrates the main role of internal stress on the shaping of the oxide front. These results demonstrate the high relevance of strain in oxide-confined III-V devices, in particular, with over-500-nm thick AlOx confinement layers.

Chouchane, F.; Almuneau, G.; Cherkashin, N.; Arnoult, A.; Lacoste, G.; Fontaine, C.

2014-07-01

15

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

SciTech Connect

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

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

2004-12-01

16

Effect of Stress Level on the High Temperature Deformation and Fracture Mechanisms of Ti-45Al-2Nb-2Mn-0.8 vol. pct TiB2: An In Situ Experimental Study  

NASA Astrophysics Data System (ADS)

The effect of the applied stress on the deformation and crack nucleation and propagation mechanisms of a ?-TiAl intermetallic alloy (Ti-45Al-2Nb-2Mn (at. pct)-0.8 vol. pct TiB2) was examined by means of in situ tensile (constant strain rate) and tensile-creep (constant load) experiments performed at 973 K (700 °C) using a scanning electron microscope. Colony boundary cracking developed during the secondary stage in creep tests at 300 and 400 MPa and during the tertiary stage of the creep tests performed at higher stresses. Colony boundary cracking was also observed in the constant strain rate tensile test. Interlamellar ledges were only found during the tensile-creep tests at high stresses ( ? > 400 MPa) and during the constant strain rate tensile test. Quantitative measurements of the nature of the crack propagation path along secondary cracks and along the primary crack indicated that colony boundaries were preferential sites for crack propagation under all the conditions investigated. The frequency of interlamellar cracking increased with stress, but this fracture mechanism was always of secondary importance. Translamellar cracking was only observed along the primary crack.

Muñoz-Moreno, Rocío; Pérez-Prado, M. Teresa; Llorca, Javier; Ruiz-Navas, Elisa María; Boehlert, Carl J.

2013-04-01

17

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

18

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

19

Internal stress superplasticity in directionally solidified Al-Al{sub 3}Ni eutectic composite  

SciTech Connect

Thermal cycling creep behavior in fiber-reinforced composites was investigated using a directionally solidified Al-Al{sub 3}Ni eutectic composite. A superplastic elongation of 120% was obtained during a thermal cycling tensile creep test. Compression creep tests were performed under an external stress applied either parallel or perpendicular to the growth direction. The average strain rates for the two directions exhibited the characteristics of internal stress superplasticity: those at low stresses were much higher than the corresponding isothermal creep rates and were proportional to the applied stress. In the case of transverse loading, the thermal cycling creep rate was explained quantitatively using the previously reported internal stress superplasticity model for particle-dispersed composite. In the case of longitudinal loading, it was much lower than that predicted using the model because of the difference in the stress state and the relaxation process. However, thermal cycling creep had very low activation energy, which is a unique characteristic of internal stress superplasticity.

Kitazono, K. [Inst. of Space and Astronautical Science, Sagamihara, Kanagawa (Japan)] [Inst. of Space and Astronautical Science, Sagamihara, Kanagawa (Japan); [Univ. of Tokyo, Hongo, Bunkyo (Japan). Dept. of Materials Science; Sato, E. [Inst. of Space and Astronautical Science, Sagamihara, Kanagawa (Japan)] [Inst. of Space and Astronautical Science, Sagamihara, Kanagawa (Japan)

1998-12-11

20

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

21

Stress change and its implication for the reduction of primary creep in gamma-TiAl  

SciTech Connect

Current research on {gamma}-TiAl is primarily focused on improving its room-temperature ductility, toughness and high-temperature creep resistance. For engineering applications such as turbine engine components, creep properties are of primary concern. The creep properties, and particularly the steady state creep, of TiAl-based alloys have been studied extensively. However, the results showed that the stress exponent, n, of steady state creep varied from 1--7, depending upon the applied stress (or strain rate). The reported creep mechanisms, deduced primarily from the measured stress exponent, are therefore different. The objective of the present study is to use stress reduction techniques to characterize the creep transient behavior of TiAl, and thus to shed light on the creep mechanisms. In addition, the significance of the experimental results from stress reduction to primary creep will also be addressed.

Nieh, T.G.; Wang, J.N. [Lawrence Livermore National Lab., CA (United States)] [Lawrence Livermore National Lab., CA (United States)

1995-10-01

22

PHOTOSYNTHESIS AND HIGH LIGHT STRESS  

Microsoft Academic Search

Summary. Exposure of plants to irradiances far above the light saturation point of photosynthesis, known as high-light stress, induces various respon- ses including light adaptation of the photosynthetic apparatus and chloroplast ultrastructure by formation of sun-type chloroplasts. The latter possess a low- er cross section for light absorption (less light-harvesting chlorophyll prote- ins) and higher rates of photosynthetic quantum conversion

Hartmut K. Lichtenthaler; Stefan Burkart

1999-01-01

23

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

24

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

25

Rye oxidative stress under long term Al exposure.  

PubMed

Aluminium (Al) toxicity decreases plant growth. Secale cereale L. is among the most Al-tolerant crop species. In order to study the response to Al-long term exposure, two rye genotypes with different Al sensitivity ('D. Zlote' and 'Riodeva') were exposed to 1.11 and 1.85mM Al and the antioxidant responses were followed for 2 and 3 weeks in roots and leaves. Al toxicity signals, such as a severe decrease in root growth, occurred sooner in 'Riodeva.' The antioxidant response was dependent on the genotype, the organ, Al concentration and the exposure period. Al-exposed roots of 'D. Zlote' showed earlier enhancements of APX, SOD and G-POX activities than those of 'Riodeva.' 'D. Zlote' roots showed stimulation of the AsA-GSH cycle after the second week (when root growth inhibition was less severe), while later (when severe root growth inhibition was observed), oxidation of AsA and GSH pools was observed. In leaves of both genotypes, CAT, SOD and G-POX activities increased with Al exposure. In these leaves, the effect of AsA-GSH was time dependent, with maximum oxidation at the second week, followed by recovery. We confirmed that the oxidation state of AsA and GSH pools is involved in the detoxification of Al-induced oxidative stress. Moreover, our data demonstrate that the production of ROS does not correlate with the Al-induced root growth decrease. Finally, the differences observed over time indicate that long term exposure may provide additional information on rye sensitivity to Al, and contribute to a better understanding of this species' mechanisms of Al tolerance. PMID:23537706

Silva, Sónia; Pinto, Glória; Correia, Barbara; Pinto-Carnide, Olinda; Santos, Conceição

2013-07-01

26

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

27

Ghabezloo et al.: Effective stress law for the permeability of a limestone Effective stress law for the permeability of a  

E-print Network

few bars. The test results are well reproduced using the proposed permeability-effective stress lawGhabezloo et al.: Effective stress law for the permeability of a limestone Effective stress law, MSRGI, 58, boulevard Lefebvre, 75015 Paris Cedex 15, France Abstract The effective stress law

Paris-Sud XI, Université de

28

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

29

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

30

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

31

Characterization of Quench-Extracted High Pressure Stressed Microorganisms  

NASA Astrophysics Data System (ADS)

In-situ high pressure microbiology work by Sharma et al (2002) presented a unique approach with diamond anvil cells to the study of microbes under environmental stress. This study focused on high pressure exposure as the stress component and provided a technique to directly monitor microbial activity. However, it lacked the much desired biochemical and biophysical information that could reflect the state of surviving microorganisms with insights into the process of adaptation at extreme. More recent work (Sharma et al 2011) expands on the previous study by including synergistic effect of high temperature with increased pressures along variable time scale. With the cell extraction and subsequent cell growth demonstrated, Sharma et al. (2011) show that more than pressure, temperature remains the environmental variable that defines the limits of life's survival. In this study we have refined the extraction process from the diamond anvil cell such that the stressed microorganisms can be routinely available for in-depth physiological study using conventional and state-of-the-art high resolution imaging tools. Here we present some recent in-depth FESEM, AFM and optical spectroscopy data to study the effect of stress on Escherichia coli. Contrary to earlier studies where various cell membrane ruptures were reported after moderate pressure exposure, we find that most cells remain viable and except for some occasional anomalous morphology, the surviving cells were similar to the unstressed state. Preliminary results suggest that the stress response in Escherichia coli exposed to short term extreme pressures (ranging from 1 -24 hrs) seems rapidly reversible. Biophysical entities such as the cell membrane, therefore, remain intact in the whole organism (and colony of microorganisms) at significantly higher pressure conditions than 300 MPa as reported in previous biophysics literature.

Sharma, P.; Sharma, A.

2011-12-01

32

Size and volume distributions of thermally induced stress voids in AlCu metallization  

Microsoft Academic Search

AlCu integrated circuit interconnect lines are stressed at 200 °C for a variable duration of time. The number of stress voids and the total void volume are measured. The number of voids saturates between 0.1 and 1 day of stress, and reaches a constant value. The total void volume continues to rise and saturates between 30 and 100 days of

Srdjan Kordic; Jan Engel; Rob A. M. Wolters

1996-01-01

33

Oxidative stress is an early symptom triggered by aluminum in Al-sensitive potato plantlets  

Microsoft Academic Search

The objective of this study was to evaluate whether the oxidative stress caused by aluminum (Al) toxicity is an early symptom that can trigger root growth inhibition in Macaca (Al-sensitive) and SMIC148-A (Al-tolerant) potato clones. Plantlets were grown in a nutrient solution (pH 4.00) with 0, 100 and 200mg Al L?1. At 24, 72, 120 and 168h after Al addition,

Luciane Almeri Tabaldi; Denise Cargnelutti; Jamile Fabbrin Gonçalves; Luciane Belmonte Pereira; Gabriel Y Castro; Joseila Maldaner; Renata Rauber; Liana Verônica Rossato; Dilson Antônio Bisognin; Maria Rosa Chitolina Schetinger; Fernando Teixeira Nicoloso

2009-01-01

34

STRESS ANNEALING INDUCED DIFFUSE SCATTERING FROM Ni3(Al,Si) PRECIPITATES  

SciTech Connect

Diffuse scattering caused by L12 type Ni3 (Al,Si) precipitates after stress annealing of Ni-Al-Si alloys is studied. Experimental reciprocal space maps are compared to the theoretical ones. Oscillations of diffuse scattering due to Ni3 (Al,Sc) precipitates are observed. Peculiarities of diffuse scattering in asymptotic region as compared to Huang scattering region are discussed. Coupling between the stress annealing direction and the precipitate shape is demonstrated.

Barabash, Rozaliya [ORNL; Ice, Gene E [ORNL; Karapetrova, Evgenia [University of Illinois, Urbana-Champaign; Zschack, P. [Argonne National Laboratory (ANL)

2012-01-01

35

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

SciTech Connect

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

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

2010-01-01

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

Modelling Of Residual Stresses Induced By High Speed Milling Process  

NASA Astrophysics Data System (ADS)

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® software, is based on data taken from Outeiro & 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&D to those given by numerical simulations is achieved.

Desmaison, Olivier; Mocellin, Katia; Jardin, Nicolas

2011-05-01

38

Changes in antioxidant gene expression and induction of oxidative stress in pea (Pisum sativum L.) under Al stress.  

PubMed

Aluminium toxicity has been recognized as a primary growth-limiting factor in acid soil, resulting in a decrease in plant growth and production. In this experiment we have studied the induction of oxidative stress and changes in antioxidant gene expression in pea (var. ALASKA) under aluminium (Al) stress. We have found that Al treatment affected the growth of pea plant and induced oxidative stress with a change in antioxidant gene expression profile. While the expression of glutathione-s-transferase (GST) and catalase (CAT) was more in root, cytosolic Ascorbate peroxidase (cAPX) expression increased in shoot under aluminium stress. Copper- Zinc Superoxide dismutase (Cu-Zn SOD) gene expression was higher after 24 h but decreased after 48 h along with elevated expression of manganese superoxide dismutase (MnSOD) and iron-superoxide dismutase (FeSOD) at higher aluminium concentrations after 24 and 48 h. Aluminium stress elevated hydrogen peroxide (H(2)O(2)) level and affected the growth. The proline content did not change significantly, whereas glutathione content increased with a decreased ascorbate content under Al stress. The present study indicates that aluminium treatment affected the antioxidant gene expression and induced oxidative stress in pea plant. PMID:20505982

Panda, Sanjib Kumar; Matsumoto, Hideki

2010-08-01

39

Formation of stress-induced 9R structure in a hot-deformed Ti-45Al-10Nb alloy  

SciTech Connect

Two-phase {gamma}-TiAl alloys composed of {gamma}-TiAl and {alpha}{sub 2}-Ti{sub 3}Al are currently under extensive investigation because their mechanical properties are superior to both single-phase {alpha}{sub 2} and {gamma} alloys. The deformation induced microstructures of two-phase {gamma}-TiAl was investigated by many researchers using scanning and transmission electron microscopy (TEM). Various deformation modes were found to contribute to plastic deformation of two-phase alloys at different temperatures. More recently, some researchers also reported stress-induced phase transformations to occur during deformation of two-phase {gamma}-TiAl alloys. However, the mechanisms of these stress-induced phase transformations in two-phase {gamma}-TiAl alloys have not been studied in detail. In this paper, the formation of 9R structure in a hot-worked Ti-45Al-10Nb alloy with nearly fully-lamellar microstructure is studied using high-resolution transmission electron microscopy. The mechanism of the stress induced {gamma} {yields} 9R phase transformation will be discussed.

Wang, J.G. [Univ. of Science and Technology, Beijing (China). State Key Lab. for Advanced Metals and Materials] [Univ. of Science and Technology, Beijing (China). State Key Lab. for Advanced Metals and Materials; [Academia Sinica, Shenyang (China). Lab. of Atomic Imaging of Solids; Zhang, L.C.; Chen, G.L. [Univ. of Science and Technology, Beijing (China). State Key Lab. for Advanced Metals and Materials] [Univ. of Science and Technology, Beijing (China). State Key Lab. for Advanced Metals and Materials; Ye, H.Q. [Academia Sinica, Shenyang (China). Lab. of Atomic Imaging of Solids] [Academia Sinica, Shenyang (China). Lab. of Atomic Imaging of Solids

1997-07-15

40

Stress control in AlN and Mo films for electro-acoustic devices  

Microsoft Academic Search

Piezoelectric AlN films with strong (002) crystal orientation are widely used in various resonator-based applications such as BAW and FBAR filters, oscillators and resonating sensors. Low intrinsic stress is one of the important requirements for the thin film stacks employed in electro-acoustic devices. In this paper, we describe technical and technological solutions enabling effective stress control in piezoelectric AlN films

Valery V. Felmetsger; P. N. Laptev

2008-01-01

41

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

42

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

NASA Technical Reports Server (NTRS)

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

Herzog, J. A.

1981-01-01

43

The variation in flow stress and microstructure during superplastic deformation of the Al-Cu eutectic  

Microsoft Academic Search

Stress-strain curves have been obtained for the superplastically deformed Al-Cu eutectic tested in tension under constant true strain-rate conditions. It is shown that constant flow stress conditions do not obtain and that, after an initial transient, the flow stress is linearly related to natural tensile strain. Optical metallography has been employed to follow the variation of both inter-phase particle separation

B. M. Watts; M. J. Stowell; D. M. Cottingham

1971-01-01

44

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

45

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

E-print Network

(Mali and Mehta, 1977), Nootripathu, an indica landrace adapted to rainfed condition, (Babu et al., 2001), and Apo (IR55423-01), an improved indica upland variety with high-yield potential under aerobic soil condition (George et al., 2002). Recent... efforts have been put to understand the genetics of drought adaptive traits in some of these varieties but it has been difficult to identify the genetic segments that influence the yield under stress (Babu et al., 2003). Several studies provide...

Kondhia, Aditi Nitinkumar

2011-10-21

46

Analysis of residual stresses in Al-Li repair welds and mitigation techniques  

SciTech Connect

In this paper, the recent results based on a comprehensive study on repair weld residual stresses are presented. Advanced finite element techniques were used to characterize the residual stress evolution in Al-Li alloy weldments, particularly under repair welding conditions. The present analysis procedures considered three-dimensional residual stress characteristics in the repair welds using a shell element model. Local residual stress details were analyzed by a generalized plane-strain model with prescribed translation and rotation conditions established from the global shell element model. Experimental residual stress measurements were conducted using X-ray diffraction methods. A good agreement between the finite element results and experimental measurements was obtained. Finally, a novel welding repair procedure (termed as a thermal stretching technique) was proposed to mitigate the weld residual stresses in repair.

Dong, P.; Hong, J.K. [Battelle, Columbus, OH (United States). Center for Welded Structures Research; Rogers, P. [Marshall Space Flight Center, Huntsville, AL (United States)

1998-11-01

47

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

48

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

49

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

50

Effects of Thermal Stress on the Performance of Benzocyclobutene-Passivated In0:52Al0:48As/In0:53Ga0:47As High Electron Mobility Transistors  

E-print Network

. As passivation layers, which can guarantee a long-term reliability of devices, silicon nitride (SiNx), polyimide, it is important to investigate the effects of thermal stress on the device performance for long-term reliability mobility transistors (HEMTs) were investigated and compared with those on silicon nitride and polyimide

Yang, Kyounghoon

51

Internal stress superplasticity in Al-Be eutectic alloy during triangular temperature profile  

SciTech Connect

Materials containing second phases show superplastic behavior during thermal cycling (internal stress superplasticity). In the present study, this behavior has been investigated by thermal cycling creep tests with a triangular wave having fixed heating and cooling rates, using a Be-particle-dispersed Al matrix alloy. The thermal cycling creep rates were much higher than the isothermal creep rates and proportional to the applied stress at intermediate stresses. It was interpreted by the previous theoretical model of internal stress superplasticity, and the values of the thermal cycling creep rate were about 60% of the theoretical one. The discrepancy was explained by the transition after each temperature reversal until achieving the quasi-steady state stress distribution during thermal cycling.

Kitazono, K.; Sato, E. [Inst. of Space and Astronautical Science, Sagamihara, Kanagawa (Japan)

1997-12-19

52

High Stress, Hostility, Depression Linked with Increased Stroke Risk  

MedlinePLUS

... on Heart.org Learn More High stress, hostility, depression linked with increased stroke risk American Heart Association ... a Stroke? Stress and Heart Health How does depression affect the heart? Ischemic Stroke Animation and photos ...

53

On the high-stress region stress exponent during creep  

Microsoft Academic Search

The creep behavior of pure metal and solid solution alloys has been reasonably defined. A power law in the form of ε = A Ïⁿ usually describes the steady state creep of these materials where the stress exponent n is between 3 to 5. Precipitation hardened alloys, however, creep quite differently. The zinc alloy used contains 1wt%Cu and 0.15wt%Ti which

Z. F. Zhou; B. A. Parker

1995-01-01

54

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

E-print Network

control in order to discern the cyclic softening or hardening behavior as a function of fatigue cycles-cycle fatigue behavior of Ti­6Al­4V at elevated temperatures up to 550 °C Igor Altenberger a,1 , Ravi K. Nalla b April 2012 Keywords: Fatigue Titanium alloys Surface treatments Deep-rolling Laser shock peening a b

Ritchie, Robert O.

55

Thermal residual stresses in functionally graded and layered 6061 Al/SiC materials  

SciTech Connect

The thermal residual stresses that develop in spray atomized and codeposited functionally graded and layered 6061 Al/SiC metal-matrix composites (MMCs) during cooling from the codeposition temperature to ambient temperature were studied using thermo-elastoplastic finite element analysis. In an effort to investigate the effect of layered and graded structures on the residual stress distribution, the composites with homogeneous distribution of SiC particulates were also analyzed. The effect of SiC composites with homogeneous distribution of SiC particulates were also analyzed. The effect of SiC volume fraction in the SiC-rich layers and the effect of SiC-rich layer thickness on the residual stresses were investigated. Based on the present study, it was found that the residual stress distribution is very distinct for the aluminum and the SiC-rich layers in the layered materials. As the volume fraction of SiC increases in the SiC-rich layer, the magnitude of residual stresses also increases. The radial stress was found to be tensile in the aluminum layers and compressive in the SiC-rich layers. It was also found that, as the thickness of the SiC-rich layer increases, the magnitude of radial stress in the aluminum layers increases, and that in the SiC-rich layers decreases. In the graded material, the lower region of each layer exhibits tensile radial stress, and the upper region of each layer shows compressive radial stress in order to maintain continuity between layers during cooldown. In general, the layered and the graded materials have greater residual stresses and more complicated stress distribution, as compared with those in the composite materials with homogeneous distribution of SiC particulates.

Ho, S.; Lavernia, E.J. [Univ. of California, Irvine, CA (United States). Dept. of Chemical Engineering and Materials Science

1996-10-01

56

Evolution of residual stresses in micro-arc oxidation ceramic coatings on 6061 Al alloy  

NASA Astrophysics Data System (ADS)

Most researches on micro-arc oxidation mainly focus on the application rather than discovering the evolution of residual stresses. However, residual stresses in the surface coatings of structural components have adverse effects on their properties, such as fatigue life, dimensional stability and corrosion resistance, etc. The micro-arc oxidation ceramic coatings are produced on the surfaces of 6061 aluminum alloy by a homemade asymmetric AC type of micro-arc oxidation equipment of 20 kW. A constant current density of 4.4±0.1 A/dm2 and a self-regulated composite electrolyte are used. The micro-arc oxidation treatment period ranges from 10 min to 40 min, and the thickness of the ceramic coatings is more than 20 ?m. Residual stresses attributed to ?-Al2O3 constituent in the coatings at different micro-arc oxidation periods are analyzed by an X-ray diffractometer using the sin2 ? method. The analysis results show that the residual stress in the ceramic coatings is compressive in nature, and it increases first and then decreases with micro-arc oxidation time increase. The maximum stress value is 1 667±20 MPa for period of 20 min. Through analyzing the coating thickness, surface morphology and phase composition, it is found that the residual stress in the ceramic coatings is linked closely with the coating growth, the phase composition and the micro cracks formed. It is also found that both the heat treatment and the ultrasonic action release remarkably the residual compressive stress. The heat treatment makes the residual compressive stress value decrease 1 378 MPa. The ultrasonic action even alters the nature of the residual stress, making the residual compressive stress change into a residual tensile stress.

Shen, Dejiu; Cai, Jingrui; Guo, Changhong; Liu, Peiyu

2013-11-01

57

Residual stresses in high-velocity oxy-fuel metallic coatings  

Microsoft Academic Search

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.

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

2004-01-01

58

Residual stresses in high-velocity oxy-fuel metallic coatings  

Microsoft Academic Search

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\\u000a 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\\u000a at three different torch chamber pressures.

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

2004-01-01

59

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

PubMed

Abstract 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 utilize an extensive structured telephone interview ascertaining environmental, lifestyle, dietary and psychological risk factors associated with OS. Detailed assessments were performed at baseline and at 3-6 month intervals during the ensuing 30 months. Our biorepository includes DNA, plasma, urine, and skin. Three hundred and fifty-five 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. Results showed that demographic and disease characteristics were similar between 477 eligible/non-enrolled and enrolled patients, the only difference being type of health insurance among enrolled patients. Sites were divided into three groups by the number of enrolled subjects. Comparing these three groups, the Columbia site had fewer 'definite ALS' diagnoses. This is the first prospective, interdisciplinary, in-depth, multicenter epidemiological investigation of OS related to ALS progression and has been 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; Fernandes Filho, J Americo M; 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

2014-06-01

60

Stress and the High School Senior: Implications for Instruction.  

ERIC Educational Resources Information Center

A recent survey found that 90 percent of high school seniors/respondents perceived the world as stressful and the majority of people as phony. These views may partly explain the high suicide, pregnancy, dropout, and drug usage rates among high school seniors. Teachers can help students overcome stress by modeling coping strategies and providing…

Amen, John; Reglin, Gary

1992-01-01

61

High-temperature deformation of uniaxially aligned lamellar TiAl/Ti{sub 3}Al  

SciTech Connect

Uniaxially aligned polysynthetically twinned two-phase TiAl/Ti{sub 3}Al material is produced by induction zone melting and deformed in uniaxial compression. Above 1,000 K the strain rate sensitivity is independent of the lamellar orientation and increases strongly with increasing deformation temperature. Results for the strain rate sensitivity parameters are somewhat lower than those obtained for {gamma}-TiAl single- and polycrystals. If the lamellae are oriented parallel or perpendicular to the deformation axis, the flow stress decreases with increasing strain. After plastic deformation the dislocation density in the lamellae is remarkably low indicating recovery processes. At the lamellar interfaces misfit dislocations and periodic arrangements of dislocations with Burgers vectors inclined to the lamellar boundaries are found. In contrast to deformation at lower temperatures, deformation twinning is rare.

Heinrich, H.; Abaecherli, V.; Wilkins, D.J.; Kostorz, G.

1999-07-01

62

Effect of an overheating temperature on cyclic isothermal stress-induced transformations in single crystal Cu–13.3Al–4.0Ni (wt.%) shape memory alloys  

Microsoft Academic Search

Motivated by eventual applications as high temperature actuators, cyclic isothermal stress-induced transformations of Cu–13.3Al–4.0Ni (wt.%) single crystal wires with stress-free transformation temperatures: Mf=80°C, Ms=100.5°C, As=104.5°C and Af=117°C were studied under the two adverse conditions of high overall strain (9%) and an overheating temperature (175°C for 30min). Wires were subjected to isothermal stress cycling at 25°C using an Instron testing machine

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

2006-01-01

63

The rate dependence of the saturation flow stress of Cu and 1100 Al  

SciTech Connect

The strain-rate dependence of the saturation flow stress of OFHC Cu and 1100 Al from 10{sup {minus}3}s{sup {minus}1} to nearly to 10{sup 12}s{sup {minus}1} is examined. The flow stress above 10{sup 9}s{sup {minus}1} is estimated using Wallace's theory of overdriven shocks in metals. A transition to the power-law behavior {Psi} {approximately} {tau}{sub s}{sup 5} occurs at a strain rate of order 10{sup 5}s{sup {minus}1}. 10 refs., 2 figs.

Preston, D.L.; Tonks, D.L.; Wallace, D.C.

1991-01-01

64

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

E-print Network

DEFECT AND STRESS CONTROL OF ALGAN AND FABRICATION OF HIGH-EFFICIENCY UV-LED H. AMANO, M. IWAYA, S was fabricated on the low dislocation density AlGaN. The LED shows strong and sharp UV-emission from Ga the propagation of dislocations having screw components, by which UV-photodetector showing very-low-dark current

Wetzel, Christian M.

65

Temperature dependence of yield stress, deformation mode and deformation structure in single crystals of TiAl (Ti56 at.% Al)  

Microsoft Academic Search

The plastic deformation behaviour of single crystals of TiAl with a composition of Ti-56 at.% Al has been studied in compression as a function of crystal orientation in the temperature range from ?196 to 1100°C. The profile of yield stress-temperature curves for all orientations studied can be divided into three temperature regions; the yield stress rapidly decreases with increasing temperature

H. Inui; M. Matsumuro; D.-H. Wu; M. Yamaguchi

1997-01-01

66

Influence of stress state on cavitation during hot working of Ti-6Al-4V  

NASA Astrophysics Data System (ADS)

Notched-tension tests were conducted on Ti-6Al-4V samples with a colony-alpha microstructure to determine the effect of the stress state on cavitation during hot working of alpha/beta titanium alloys. The experiments were complemented by finite-element-method analyses to establish the local stress state, strain, and damage factor for different areas within each sample. A critical damage factor, defined by a modified Cockcroft-and-Latham criterion, was found to be applicable for the prediction of cavity initiation for the different notch geometries. Measured cavity growth rates were also correlated to the stress state ( i.e., ratio of mean-to-effective stress, ? M /? e ) and compared to predictions of prior models. Model predictions showed reasonable agreement with measurements at low levels of stress triaxiality, but exhibited some deviations at higher values of ? M /? e . The differences were attributed to differences in the properties of the present material and those assumed in deriving the models as well as the neglect of cavity interaction in one of the models. The results were summarized in terms of a processing map, which delineates the initiation of cavities and their size as a function of the stress state and effective strain.

Nicolaou, P. D.; Goetz, R. L.; Semiatin, S. L.

2004-02-01

67

Thermal stress in high temperature cylindrical fasteners  

SciTech Connect

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, M.L.

1988-05-01

68

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

69

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

70

Sputter deposition of stress-controlled piezoelectric AlN and AlScN films for ultrasonic and energy harvesting applications.  

PubMed

This paper reports on the deposition and characterization of piezoelectric AlN and AlXSc1-XN layers. Characterization methods include XRD, SEM, active thermo probe, pulse echo, and piezometer measurements. A special focus is on the characterization of AlN regarding the mechanical stress in the films. The stress in the films changed between -2.2 GPa (compressive) and 0.2 GPa (tensile) and showed a significant dependence on film thickness. The cause of this behavior is presumed to be the different mean grain sizes at different film thicknesses, with bigger mean grain sizes at higher thicknesses. Other influences on film stress such as the sputter pressure or the pulse mode are presented. The deposition of gradient layers using those influences allowed the adjustment of film stress while retaining the piezoelectric properties. PMID:25073140

Barth, Stephan; Bartzsch, Hagen; Gloess, Daniel; Frach, Peter; Herzog, Thomas; Walter, Susan; Heuer, Henning

2014-08-01

71

Dependence of the yield stress of Fe3Al on heat treatment  

SciTech Connect

The room-temperature yield strength of quenched FeAl-based iron aluminides depends strongly on the temperature from which the quench occurs. There is evidence that Fe{sub 3}Al-based iron aluminides show similar behavior, albeit not as pronounced. The purpose of this work was to carry out quenching and annealing experiments to clearly demonstrate this effect, as well as to study its kinetics. Room-temperature compression tests were performed using cast Fe-28at%Al and Fe-30at%Al after quenching from temperatures in the range 300-1000 C. Kinetic studies were carried out to assess the reduction of the yield stress by subsequent annealing for various times at relatively low temperatures. Results from the present study are compared with data available in the literature and explanations for the dependence of room-temperature mechanical behavior on annealing history are evaluated. It is concluded that room-temperature strengthening in Fe{sub 3}Al-based iron aluminides is consistent with behavior expected for quenched-in thermal vacancies and this could be an important strengthening mechanism in Fe{sub 3}Al.

Hasemann, G [University of Magdeburg, Germany; Schneibel, Joachim H [ORNL; George, Easo P [ORNL

2012-01-01

72

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

73

ICP etching of high Al mole fraction AlGaN  

NASA Astrophysics Data System (ADS)

The etching process has great influence on the performance of solar blind detector based on AlxGa1-xN epitaxial layers on sapphire substrate with high Al mole fraction grown by metal organic chemical vapor deposition (MOCVD) method. Traditional etching methods, including wet or reactive ion etching (RIE) are hard to achieve good result due to the high chemical-stability of AlGaN films with high Al mole fraction. In this paper, we studied on the inductively coupled plasma reactive ion etching (ICP-RIE) of high Al mole fraction AlxGa1-xN films (x>0.4) for fabricating high performance solar blind detectors. SiN was used as mask, and Cl2 and BCl3 were used as etching gas. Etching systems was selected from Oxford Inc. DC bias was controlled automatically. A 2.5:1 of selectivity on AlGaN and SiN was obtained with suitable flux and component of etching gas, RF power and ICP power. Etching velocity was adjusted mainly by RF power. The role of Ar, Cl2, and BCl3 in the etching process was also discussed.

Meng, Zhao; Yu, Libo; Li, Xiao; Liu, Qibin; Duan, Huiqiang; Yu, Chenhui; Chen, Changqing

2009-08-01

74

High strain-rate plastic flow in Al and Fe  

NASA Astrophysics Data System (ADS)

Thin Fe and Al foils were ramp-compressed over several to tens of ns timescales to study the time-dependence associated with the onset of plastic flow. Peak stress states of 15-200 GPa were achieved through laser ramp-compression where the strain rate was varied, shot-to-shot, between 106 to 108 s-1. Our data combined with data from other dynamic compression platforms reveals a strong correlation between the peak elastic precursor stress, ?E, and the strain rate at the onset of plastic flow, ?.p. In fcc Al, phonon drag dislocation flow dominates above ?.p~103s-1 and ?E ˜ 0.03 GPa where ?E scales as ?.p0.43. By contrast, the Al alloy 6061-T6 exhibits a relatively weak dependency of ?E with ?.p up to strain rates of ˜107 s-1. Our Fe data, reveals a sharp increase in ?E at ?.p>5×106s-1. This is consistent with a transition in plastic flow to a phonon drag regime.

Smith, R. F.; Eggert, J. H.; Rudd, R. E.; Swift, D. C.; Bolme, C. A.; Collins, G. W.

2011-12-01

75

ALS-associated peripherin spliced transcripts form distinct protein inclusions that are neuroprotective against oxidative stress.  

PubMed

Intracellular proteinaceous inclusions are well-documented hallmarks of the fatal motor neuron disorder amyotrophic lateral sclerosis (ALS). The pathological significance of these inclusions remains unknown. Peripherin, a type III intermediate filament protein, is upregulated in ALS and identified as a component within different types of ALS inclusions. The formation of these inclusions may be associated with abnormal peripherin splicing, whereby an increase in mRNA retaining introns 3 and 4 (Per-3,4) leads to the generation of an aggregation-prone isoform, Per-28. During the course of evaluating peripherin filament assembly in SW-13 cells, we identified that expression of both Per-3,4 and Per-28 transcripts formed inclusions with categorically distinct morphology: Per-3,4 was associated with cytoplasmic condensed/bundled filaments, small inclusions (<10?M), or large inclusions (?10?M); while Per-28 was associated with punctate inclusions in the nucleus and/or cytoplasm. We found temporal and spatial changes in inclusion morphology between 12 and 48h post-transfected cells, which were accompanied by unique immunofluorescent and biochemical changes of other ALS-relevant proteins, including TDP-43 and ubiquitin. Despite mild cytotoxicity associated with peripherin transfection, Per-3,4 and Per-28 expression increased cell viability during H2O2-mediated oxidative stress in BE(2)-M17 neuroblastoma cells. Taken together, this study shows that ALS-associated peripherin isoforms form dynamic cytoplasmic and intranuclear inclusions, effect changes in local endogenous protein expression, and afford cytoprotection against oxidative stress. These findings may have important relevance to understanding the pathophysiological role of inclusions in ALS. PMID:24907400

McLean, Jesse R; Smith, Gaynor A; Rocha, Emily M; Osborn, Teresia M; Dib, Samar; Hayes, Melissa A; Beagan, Jonathan A; Brown, Tana B; Lawson, Tristan F S; Hallett, Penelope J; Robertson, Janice; Isacson, Ole

2014-11-01

76

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

77

Ab initio investigation of thermoelectric properties of AlN nanowires under axial stress  

NASA Astrophysics Data System (ADS)

Small diameter nanowires, down to a few lattice constants, are structurally and electronically different from bulk, due to the large surface-to-volume ratio and the effects of the surface states, which has consequences in the optical absorption and in the electrical/thermal transport. It has been recently established that AlN nanowires can suffer a stress induced phase transition from a wurtzite to a graphite-like phase [1]. The thermopower of atomic-sized wurtzite AlN wires coupled to Al(111) bulk contacts is investigated at low temperatures using Green-Keldysh formalism. We ?nd that the conduction of the wide bandgap semiconductor wire is essentially enhanced by the presence of surface states. We show that the evanescent coupling to the surface states is strong enough to render thermopower of a few tens of micro-V/K, which may be enhanced by controlling the position of the surface states. [2]. We also investigate the changes in the thermopower under applied axial stress, comparatively analyzing the nanowires in the wurtzite and graphite-like configurations. [1] T.L. Mitran, Adela Nicolaev, G.A. Nemnes, L. Ion, S. Antohe, Comput. Mat. Sci. 50, 2955 (2011) [2] G.A. Nemnes, C. Visan, S. Antohe, Physica E 44, 1092 (2012)

Alexandru Nemnes, George; Mitran, Tudor Luca; Nicolaev, Adela; Visan, Camelia; Ion, Lucian; Antohe, Stefan

2013-03-01

78

Time Evolution of Electrical Degradation under High-Voltage Stress  

E-print Network

Time Evolution of Electrical Degradation under High-Voltage Stress in GaN High Electron Mobility the time evolution of electrical degradation of GaN high electron mobility transistors under high voltage in current collapse and eventually permanent degradation in ID. We also found that the time evolution of gate

del Alamo, Jesús A.

79

Prediction of internal cracking in a direct-chill cast, high strength, Al–Mg–Si alloy  

Microsoft Academic Search

In order to develop a new method for predicting the internal cracking in direct-chill (DC) cast billets, tensile tests of the mushy zone of high-strength Al–Mg–Si alloys were undertaken, and solidification and thermal stress simulations of the DC casting process were performed. In this study, the solidification process was calculated using a commercial solidification package, CAPFLOW and the thermal stress

Hiromi Nagaumi; Takateru Umeda

2002-01-01

80

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

PubMed

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

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

2013-07-31

81

Influence of Al2O3/YSZ micro-laminated coatings on high temperature oxidation and spallation resistance of MCrAlY alloys  

NASA Astrophysics Data System (ADS)

Al2O3/YSZ micro-laminated coatings with different layers were prepared on MCrAlY alloys by magnetron sputtering and characterized by high-resolution field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). Results indicated that the laminated structures of Al2O3 and YSZ layers were observed with compact microstructure and the thickness at sub-micron level each layer. High-temperature cyclic oxidation test at 1000°C in air was performed to investigate the oxidation and spallation resistance of the coatings on MCrAlY substrates. Result shows that the coatings exhibit more excellent oxidation and spallation resistance with the increase of the layers, which can be attributed to the increase of stress tolerance and fracture toughness in the laminated coatings by the thinner layers and crack deflection toughening.

Yao, Junqi; He, Yedong; Wang, Deren

2013-03-01

82

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

83

Simulation of distortion and residual stress in high pressure die casting - modelling and experiments  

NASA Astrophysics Data System (ADS)

Two individual high-pressure die-casting geometries were developed in order to study the influence of process parameters and different alloys on the distortion behaviour of castings. These geometries were a stress lattice and a V-shaped sample tending to form residual stress due to different wall thickness respectively by a deliberate massive gating system. In the experimental castings the influence of the most important process parameters such as die temperature and die opening time and the cooling regime was examined. The time evolution of process temperatures was measured using thermal imaging. The heat transfer coefficients were adapted to the observed temperature distributions. Castings were produced from the two alloys AlSi12 and AlSi10MnMg. The distortion of the castings was measured by means of a tactile measuring device. For the alloy AlSi10MnMg thermo-physical and thermo-mechanical data were obtained using differential scanning calorimetry, laser flash technique, dilatometry and tensile testing at elevated temperatures. These data were used for modelling the material behaviour of the AlSi10MnMg alloy in the numerical model while for the alloy AlSi12(Fe) literature data were used. Process and stress simulation were conducted using the commercial FEM software ANSYS Workbench. A survey on the results of the comparison between simulation and experiment is given for both alloys.

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

2012-07-01

84

Neutron-diffraction measurement of residual stresses in Al-Cu cold-cut welding  

NASA Astrophysics Data System (ADS)

Usually, when it is necessary to join different materials with a large difference in their melting points, welding should be avoided. To overcome this problem we designed and built a device to obtain cold-cut welding, which is able to strongly decrease oxidation problems of the surfaces to be welded. Thanks to this device it is possible to achieve good joining between different pairs of materials (Al-Ti, Cu-Al, Cu-Al alloys) without reaching the material melting point. The mechanical and microstructural characterisation of the joining and the validation of its quality were obtained using several experimental methods. In particular, in this work neutron-diffraction experiments for the evaluation of residual stresses in Cu-Al junctions are described, carried out at the G5.2 diffractometer of LLB, Saclay. Neutron-diffraction results are presented and related to other experimental tests such as microstructural characterisation (through optical and scanning electron microscopy) and mechanical characterisation (tensile-strength tests) of the welded interface.

Fiori, F.; Marcantoni, M.

85

High-Temperature Stress Relaxation Cracking and Stress Rupture Observed in a Coke Gasifier Failure  

Microsoft Academic Search

This article discusses the high-temperature metal degradation mechanisms that occurred in the failure of a nine-story tall\\u000a coke gasifier, located in a refinery power plant. Cracking of gasifier internals, bulging and stress rupture of the vessel\\u000a shell, and escape of hot syngas resulted in an external fire. The failure mechanisms include stress relaxation cracking of\\u000a a large diameter Incoloy Alloy

Daniel J. BenacDouglas; Douglas B. Olson; Michael Urzendowski

2011-01-01

86

Adolescents’ sleep in low-stress and high-stress (exam) times: A prospective quasi-experiment  

Microsoft Academic Search

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

J. F. Dewald; A. M. Meijer; F. J. Oort; G. A. Kerkhof; S. M. Bögels

2012-01-01

87

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

88

High temperature nitrogen implantation of Ti6Al4V  

Microsoft Academic Search

Titanium alloys offer desirable properties that make them attractive candidates for tribological applications. Their surface-related properties, however, such as coefficient of friction and wear rate, are less than optimum and must be improved by surface modification. To increase the tribological properties of Ti-6Al-4V, a high temperature ion implantation method, employing a high current density beam (e.g., 500 μA\\/cm²) of nitrogen

F. M. Kustas; M. S. Misra; R. Wei; P. J. Wilbur; J. A. Knapp

1991-01-01

89

Stress, Coping, and High-Risk Sexual Behavior  

Microsoft Academic Search

We examined the relation between stress, coping, and a high-risk sexual behavior (unprotected anal intercourse) in 398 nonmonogamous gay and bisexual men from the AIDS Behavioral Research Project in San Francisco. Unprotected anal intercourse during the previous month, the amount of stress experienced during the previous month in each of 10 domains, six types of coping (self-controlling coping, escape-avoidance, distancing,

Susan Folkman; Margaret A. Chesney; Lance Pollack; Connie Phillips

1992-01-01

90

High flux isotope reactor redesigned beryllium reflector thermal stress calculations  

SciTech Connect

The Beryllium reflector of the High Flux Isotope Reactor is currently redesigned for upgrading the capability of the reactor. The original design criteria are adopted in the redesign analysis. Both nuclear heating and thermal stress calculations are revised. The results show that more margin of safety have been achieved and the updated design assures more precise design estimates for the reflector thermal stress conditions. 1 ref., 2 figs., 2 tabs.

Chang, S.J.

1996-06-01

91

The ALS -- A high-brightness XUV synchrotron radiation source  

SciTech Connect

The Advanced Light Source (ALS) at the Lawrence Berkeley Laboratory is scheduled to be operational in the spring of 1993 as a US Department of Energy national user facility. The ALS will be a next-generation source of soft x-ray and ultraviolet (XUV) synchrotron radiation. Undulators will provide high-brightness radiation oat photon energies from below 10 eV to above 2 keV; wiggler and bend-magnet radiation will extend the spectral coverage with high fluxes approaching 20 keV. The ALS will support an extensive research program in which XUV radiation is used to study matter in all its varied gaseous, liquid, and solid forms. the high brightness will open new areas of research from the materials sciences, such as spatially resolved spectroscopy, to the life sciences, such as x-ray microscopy with element-specific sensitivity. Experimental facilities (insertion devices, beamlines, and end stations) will be developed and operated by participating research teams working with the ALS staff. 6 refs., 2 figs., 2 tabs.

Robinson, A.L.; Schlachter, A.S.

1991-05-01

92

Degradation of AlGaN/GaN high electron mobility transistors related to hot electrons  

NASA Astrophysics Data System (ADS)

This paper reports on an extensive analysis of the degradation of AlGaN/GaN high electron mobility transistors (HEMTs) submitted to on-state and off-state stresses. The results of this study indicate that: (i) the analyzed devices do not show any degradation when submitted to off-state stress tests up to 100 V; (ii) during on-state stress, devices show a significant decrease in drain current and in the electroluminescence (EL) signal; (iii) degradation rate is strongly dependent on the intensity of the EL signal measured during stress on the devices, which is related to the concentration of hot electrons in the channel. Based on the experimental evidence collected within this paper, the on-state degradation of HEMTs is ascribed to the trapping of negative charge in the gate-drain access region, triggered by hot electrons. By considering the intensity of the EL signal as a measure of the stress acceleration factor, we have derived an acceleration law for the hot-electron induced degradation.

Meneghini, Matteo; Stocco, Antonio; Silvestri, Riccardo; Meneghesso, Gaudenzio; Zanoni, Enrico

2012-06-01

93

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

94

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

95

Evolution of Grain Boundary Precipitates in Al 7075 Upon Aging and Correlation with Stress Corrosion Cracking Behavior  

NASA Astrophysics Data System (ADS)

Transmission electron microscopy (TEM) was employed to investigate the microchemistry and microstructure of grain boundary precipitates in Al 7075 aged at room temperature for several hours, at 393 K (120 °C) for 12 hours (under aged), at peak aged (T651) and over aged (T73) conditions. High resolution TEM analysis of precipitates at grain boundaries and fine probe energy dispersive spectrometry showed that the grain boundary precipitates at peak and over aged conditions are hexagonal ? phase with stoichiometry Mg(Cu x Zn1- x )2. Considerable increase in Cu content in the grain boundary ? in the over aged condition compared to the peak aged condition was observed. The average Cu content in the over aged condition was found to be 20 at. pct. The higher Cu content of the precipitate is associated with a lower stress corrosion cracking plateau velocity.

Goswami, Ramasis; Lynch, Stanley; Holroyd, N. J. Henry; Knight, Steven P.; Holtz, Ronald L.

2013-03-01

96

The effect of Fe-addition to Al-10Ti alloy on superplasticity at high strain rates  

SciTech Connect

Ultra-fine microstructure consisting of equiaxed Al-grains and aluminide particulate was produced by powder metallurgy process using gas-atomized powders of Al-10wt%Ti-2wt%Fe alloy. High strain rate superplasticity (HSRS) has been investigated at 873--923 K and strain rates higher than 10{sup {minus}3} s{sup {minus}1} in tension, and total elongation up to 500% was observed at the strain-rate of 10{sup {minus}1} s{sup {minus}1}. The strain rate vs. flow stress behavior exhibits the typical aspect of HSRS such as the increase of strain-rate sensitivity exponent with increase in strain-rate and an apparent activation energy higher than that for lattice diffusion in aluminum. The concept of threshold stress has been incorporated to illustrate the HSRS behavior, where the stress exponent of 3 describes the experimental data. The determined threshold stress showed strong temperature dependence as in the case of a similarly processed Al-10wt%Ti alloy, which exhibited the stress exponent of 2 in the same testing conditions. Solute drag mechanism has been postulated for the Al-Ti-Fe alloy.

Kum, D.; Kim, W.J.

2000-07-01

97

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

98

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

99

Deformation of FeAl single crystals at high temperatures  

Microsoft Academic Search

Single crystals of the intermetallic compound FeAl with the CsCl structure have been deformed in compression at temperatures between 470 and 1000 K to study the slip geometry and the dislocation arrangements in this material at high temperatures. At temperatures below 0·44 of the melting temperature, Tm, slip occurs on the {110}?111? systems, while at 0·44Tm, the transitions in the

Y. Umakoshi; M. Yamaguchi

1980-01-01

100

First-principles characterization of the anisotropy of theoretical strength and the stress-strain relation for a TiAl intermetallic compound.  

PubMed

We perform first-principles computational tensile and compressive tests (FPCTT and FPCCT) to investigate the intrinsic bonding and mechanical properties of a ?-TiAl intermetallic compound (L 1(0) structure) using a first-principles total energy method. We found that the stress-strain relations and the corresponding theoretical tensile strengths exhibit strong anisotropy in the [001], [100] and [110] crystalline directions, originating from the structural anisotropy of ?-TiAl. Thus, ?-TiAl is a representative intermetallic compound that includes three totally different stress-strain modes. We demonstrate that all the structure transitions in the FPCTT and FPCCT result from the breakage or formation of bonds, and this can be generalized to all the structural transitions. Furthermore, based on the calculations we qualitatively show that the Ti-Al bond should be stronger than the Ti-Ti bond in ?-TiAl. Our results provide a useful reference for understanding the intrinsic bonding and mechanical properties of ?-TiAl as a high-temperature structural material. PMID:21825422

Zhou, Hong-Bo; Zhang, Ying; Liu, Yue-Lin; Kohyama, Masanori; Yin, Peng-Gang; Lu, Guang-Hong

2009-04-29

101

Effect of multiaxial stresses on the high-temperature behavior and rupture of advanced alloys  

NASA Astrophysics Data System (ADS)

The evolution and effect of multiaxial stress states on the high temperature deformation and rupture behavior of materials with non-uniform microstructures has been investigated. Through a detailed description of the role that multiaxial stresses play on damage evolution and rupture, the abundant existing data for uniaxial rupture can be used to more successfully design for the life of high temperature components. Three dimensional finite element calculations of primary creep deformation were performed for particulate reinforced metal matrix composites under a variety of multiaxial loading conditions. A quasi-steady state stress distribution develops during primary creep for each of the conditions considered. The results indicate that higher stresses exist in regions above and below the particles and accommodate the development of creep damage. The nature of the stress state within these regions is not significantly altered by the presence of the particles. The strain fields show a distribution similar to the stress fields. Despite significantly large regions of enhanced stress, the overall creep strain rates for all models are decreased by the presence of the particles. The applied effective stress does not have a unique relationship with overall effective strain rate for particulate reinforced composites under different applied stress states. The failure of sections of turbine rotor disks formed from the superalloy V-57 which operate under highly multiaxial stresses has been investigated. Optical microscopy of a turbine rotor disk removed from service after 30,000 hrs showed an intergranular crack that initiated at the root of a fir-tree turbine rotor blade attachment. Transmission electron microscopy studies showed heavy grain boundary oxidation that could account for the cracking and failure of the rotor disks. Heat treatments of a TiAl alloy have been established for producing a microstructure suitable for high temperature multiaxial rupture testing. The morphology of tested material has a fully lamellar microstructure with interlocking colony boundaries. Despite the interlocked boundaries, rupture time data correlates well with the principal facet stress, which indicates that a localized deformation mechanism controls the rupture process. Possible deformation mechanisms include lath boundary sliding and fast creep within the softer alphasb2 laths.

Johnson, Nancy Louise

1998-05-01

102

Effect of internal stresses on the fracture toughness of a TiAl-based alloy with duplex microstructures  

Microsoft Academic Search

A series of fine duplex microstructures with different volume ratios of equiaxed ? and lath colonies (?2+?) were achieved from an isothermally forged Ti–46.5Al–2Cr–2Nb alloy. The internal stress determination using X-ray diffraction techniques and plane-strain fracture toughness tests were carried out at room temperature, and the effects of the internal stresses on the fracture toughness were investigated. It was found

F. A Guo; V Ji; M Francois; Y. G Zhang

2003-01-01

103

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

104

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

SciTech Connect

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

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

2008-06-26

105

Protective role of antioxidant enzymes under high temperature stress  

Microsoft Academic Search

An experiment was conducted to study the effect of high temperature stress on the antioxidant enzyme activity in five wheat genotypes viz., PBW 343, PBW 175, HDR-77, HD 2815 and HD 2865. There was significant increase in the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) in the late and very late planting and at all stages

Moaed Almeselmani; P. S. Deshmukh; R. K. Sairam; S. R. Kushwaha; T. P. Singh

2006-01-01

106

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

107

Effects of laser peening on residual stresses and fatigue crack growth properties of Ti-6Al-4V titanium alloy  

NASA Astrophysics Data System (ADS)

The effects of laser peening (LP) with different laser peening coverage rates on residual stresses and fatigue crack growth (FCG) properties of Ti-6Al-4V titanium alloy were investigated. Residual stresses after LP and micro-structure with different fatigue striation patterns on fracture cross-sections were analyzed. Compressive residual stresses and dense dislocation arrangements can be obtained in the superficial layer after LP. The influence of compressive residual stresses induced under different LP coverage rates on FCG properties was revealed. LP coverage rate had an apparent influence on FCG properties as confirmed by the fatigue striation spacing on fracture cross-sections. Moreover, FCG rate decreased with the increase of compressive residual stresses perpendicular to the crack growth direction, which indicated that LP had an obvious inhibitory effects on FCG.

Zhou, J. Z.; Huang, S.; Zuo, L. D.; Meng, X. K.; Sheng, J.; Tian, Q.; Han, Y. H.; Zhu, W. L.

2014-01-01

108

Cryogenic Treatment of Al-Li Alloys for Improved Weldability, Repairability, and Reduction of Residual Stresses  

NASA Technical Reports Server (NTRS)

Service performance has shown that cryogenic treatment of some metals provides improved strength, fatigue life, and wear resistance to the processed material. Effects such as these were initially discovered by NASA engineers while evaluating spacecraft that had returned from the cold vacuum of space. Factors such as high cost, poor repairability, and poor machinability are currently prohibitive for wide range use of some aerospace aluminum alloys. Application of a cryogenic treatment process to these alloys is expected provide improvements in weldability and weld properties coupled with a reduction in repairs resulting in a significant reduction in the cost to manufacture and life cycle cost of aerospace hardware. The primary purpose of this effort was to evaluate the effects of deep cryogenic treatment of some aluminum alloy plate products, welds, and weld repairs, and optimize a process for the treatment of these materials. The optimized process is being evaluated for improvements in properties of plate and welds, improvements in weldability and repairability of treated materials, and as an alternative technique for the reduction of residual stresses in repaired welds. This paper will present the results of testing and evaluation conducted in this effort. These results will include assessments of changes in strength, toughness, stress corrosion susceptability, weldability, repairability, and reduction in residual stresses of repaired welds.

Malone, Tina W.; Graham, Benny F.; Gentz, Steven J. (Technical Monitor)

2001-01-01

109

High temperature stability of multicomponent TiAlSiN and CrAlSiN coatings.  

PubMed

The high temperature oxidation behavior of TiAlSiN and CrAlSiN coatings was studied. These coatings were deposited on silicon substrates by using a cathodic-arc deposition system with lateral rotating arc cathodes. Titanium, chromium and Al88Si12 cathodes were used for the deposition of TiAlSiN and CrAlSiN coatings. All the deposited Ti(0.49)Al(0.44)Si(0.07)N, Ti(0.41)Al(0.51)Si(0.08)N and Cr(0.50)Al(0.440Si(0.06)N coatings showed B1-NaCl crystal structure and possessed nano-grain sizes of 6-8 nm. For the high temperature oxidation test, the coated samples were annealed at 900 degrees C in air for 2 hours. The Ti(0.41)Al(0.51)Si(0.08)N with higher Al and Si contents possessed lower oxidation rate than that of Ti(0.49)Al(0.44)Si(0.07)N. The oxide layer formed on the Ti(0.49)Al(0.44)Si(0.07)N coatings consisted of large TiO2 and TiAlSiN grains at the oxide-coating interface, followed by a layer of Al2O3 in the near-surface region. The oxidation rate of the Cr(0.50)Al(0.44)Si(0.06)N coated sample was much lower than that of the Ti(0.49)Al(0.44)Si(0.07)N and Ti(0.41)Al(0.51)Si(0.08)N. The dense Al2O3 with amorphous top layer at the oxide-coating interface retarded the diffusion of oxygen into the Cr(0.50)Al(0.44)Si(0.06)N. The deposited Cr(0.50)Al(0.44)Si(0.06)N showed a high temperature performance superior to those of the Ti(0.49)Al(0.44)Si(0.07)N and Ti(0.41)Al(0.51)Si(0.08)N. PMID:21128495

Chang, Yin-Yu; Chang, Chi-Pang

2010-07-01

110

Stress-dependent band gap shift and quenching of defects in Al-doped ZnO films  

NASA Astrophysics Data System (ADS)

Al-doped ZnO (AZO) films were deposited on quartz substrates by the ultrasonically assisted chemical vapour deposition technique. The undoped ZnO film was found to be subjected to a stress which increases initially up to 3% Al doping, and then a slight decrease was observed for 5% Al doping. The band gap of AZO shows a blue shift up to 3% of Al doping as compared with the undoped ZnO. The blue shift in the band gap of the AZO films cannot be understood in the framework of Burstein-Moss shift and has been attributed to an increase in the stress present in the film. The photoluminescence spectrum of the undoped ZnO film shows a wide peak in the visible region which is suppressed with a small red shift after Al doping in the ZnO film. A detailed analysis of photoluminescence of ZnO and AZO films indicates suppression of zinc interstitials (Zni) and oxygen vacancies (VO) and creation of oxygen interstitial (Oi) defects after Al doping in ZnO films. X-ray photoelectron spectroscopy study also reveals suppression of oxygen vacancy related defects after Al doping in the ZnO film. The presence of Al in the ZnO matrix seems to change the defect equilibria leading to a suppression of Zni and VO and enhancement of Oi defects. The suppression of Zni defects is correlated with the increase in stress in Al-doped ZnO films.

Sharma, Bhupendra K.; Khare, Neeraj

2010-11-01

111

High Temperature Deformation Behavior of As-Cast Al-3Mg-0.25Sc Alloy  

NASA Astrophysics Data System (ADS)

High temperature deformation behavior of as-cast Al-3Mg-0.25Sc alloy was characterized in a wide range of temperatures 573 K to 773 K (300 °C to 500 °C) and strain rates (0.001 to 10 s-1). A threshold stress behavior is observed in the temperature range of 573 K to 673 K (300 °C to 400 °C) due to interaction of dislocations with precipitates. In the temperature range of 573 K to 623 K (300 °C to 350 °C), the dislocations are pinned by precipitates, following Orowan-bowing mechanism. At 673 K (400 °C), the dislocations bypass the particles by climb process. At high temperature and low strain rate of 723 K (450 °C), and 0.001 s-1, respectively, the alloy exhibited high efficiency of power dissipation for optimal hot working process.

Suresh Kumar, M.; Ambresha; Venkateswarlu, K.; Ranganath, V. R.

2014-07-01

112

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

113

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

114

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

PubMed Central

ABSTRACT 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.

2014-01-01

115

Residual stresses in welded joints of high-strength steels  

Microsoft Academic Search

By using a “GLEEBLE-3800” complex, we perform the experimental investigations of the dynamics of changes in the yield strength\\u000a of the metal of the heat-affected zone (HAZ) in low-carbon high-strength steels for various rates of cooling of the welded\\u000a joints. The influence of the rate of energy input and thermal welding cycles on the formation of residual stresses in welded

L. Lobanov; V. Poznyakov; V. Pivtorak; O. Mikhodui; V. Orlovs’kyi

2009-01-01

116

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

117

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

2014-11-01

118

High-amplitude dynamics of nanoelectromechanical systems fabricated on the basis of GaAs/AlGaAs heterostructures  

NASA Astrophysics Data System (ADS)

Nonlinear vibrations of nanoelectromechanical beam fabricated from the GaAs/AlGaAs heterostructure containing two-dimensional electron gas are investigated. The measurement of time-averaged conductance is shown to be a sensitive method for the nanomechanical motion detection. The possibilities to excite high-amplitude (up to 20 nm) mechanical vibrations and to effectively detect them using the simple conductance measurement make such systems promising for practical applications. High-amplitude vibrations of the beam are shown to demonstrate softening nonlinearity. This can be attributed to the bending of the beam due to Euler buckling instability caused by the compressive stress though GaAs/AlGaAs heterostructures are typically considered as stress-free.

Shevyrin, A. A.; Pogosov, A. G.; Budantsev, M. V.; Bakarov, A. K.; Toropov, A. I.; Ishutkin, S. V.; Shesterikov, E. V.; Arakcheev, A. S.

2013-09-01

119

A New High-Pressure, High-Shear Stress Viscometer and Results for Lubricants  

Microsoft Academic Search

A new high-pressure, high-shear stress viscometer has been developed with a pressure capability of 300 MPa and shear stress of 26 MPa for shear which is essentially isothermal in the context of the Theological characterization of shear-thinning lubricants. Four liquid lubricants have been investigated. Newtonian and rate-independent behavior were observed, and it appears that molecular weight may have a role

Scott Bair; Ward O. Winer

1993-01-01

120

High velocity impact characterization of Al alloys for oblique impacts  

NASA Astrophysics Data System (ADS)

This paper describes the experimental and computational analyses of a high velocity aluminum projectile impact on an Al6061-T6 spacecraft inner wall at different oblique angles. Al2017-T4 spherical projectiles of 5.56 mm in diameter and 0.25 g in weight were chosen within the velocity range of 1000±200 m/s due to the limitation of the light gas gun. The energy absorbed was calculated by measuring the velocities before and after impact on the inner wall. The energy absorbed by the wall and the remaining energy carried by the projectile helped to estimate the severity of further damage to inner components. Afterwards, validation was done by using the commercially available software LS-DYNA with a dedicated SPH. On average, a 10% energy absorption difference between experimentation and simulation was found. By using C-SCAN, the damage area proportion of the total inner wall to impact penetration hole area was found to be on average 6%, 26% and 53% greater than the projectile cross sectional area for the oblique angle impacts of 30°, 45°, and 60°, respectively. These findings helped to understand the relationship between the oblique impact event and the damage area on a spacecraft inner wall along with space debris cloud propagation and comparison with experimental results using LS-DYNA.

Baluch, Abrar. H.; Park, Yurim; Kim, C. G.

2014-12-01

121

Effects of Nb and Al on the microstructures and mechanical properties of high Nb containing TiAl base alloys  

Microsoft Academic Search

The influence of Nb and Al contents on the microstructure and yield strength of high Nb containing TiAl base alloys was investigated. The experimental results show that the yield strength at 900 °C of the alloys with the same type of microstructure, such as fully lamellar (FL), nearly lamellar (NL) and degraded fully lamellar (DFL), increases with increasing Nb content and

Z. C. Liu; J. P. Lin; S. J. Li; G. L. Chen

2002-01-01

122

Electrorheological fluid with an extraordinarily high yield stress  

NASA Astrophysics Data System (ADS)

Surface modified complex strontium titanate microparticles are synthesized by means of a modified sol-gel technique. A suspension composed of these particles immersed in a silicone oil exhibits excellent electrorheological properties attractive to industry and technology applications: a yield stress as high as 27 kPa in an applied electric field of 3 kV/mm, a low leakage current, wide dynamic ranges in temperature and shear rate, and a long-term stability against sedimentation. In addition to the high dielectric constant of strontium titanate, surfactant and water-free character of the particles may be responsible for the dramatic improvement of the electrorheological properties of the suspension.

Zhang, Yuling; Lu, Kunquan; Rao, Guanghui; Tian, Yu; Zhang, Shaohua; Liang, Jingkui

2002-02-01

123

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

124

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

125

High-temperature mechanical properties and deformation behavior of high Nb containing TiAl alloys fabricated by spark plasma sintering  

NASA Astrophysics Data System (ADS)

A high Nb containing TiAl alloy was prepared from the pre-alloyed powder of Ti-45Al-8.5Nb-0.2B-0.2W-0.02Y (at%) by spark plasma sintering (SPS). Its high-temperature mechanical properties and compressive deformation behavior were investigated in a temperature range of 700 to 1050°C and a strain rate range of 0.002 to 0.2 s-1. The results show that the high-temperature mechanical properties of the high Nb containing TiAl alloy are sensitive to deformation temperature and strain rate, and the sensitivity to strain rate tends to rise with the deformation temperature increasing. The hot workability of the alloy is good at temperatures higher than 900°C, while fracture occurs at lower temperatures. The flow curves of the samples compressed at or above 900°C exhibit obvious flow softening after the peak stress. Under the deformation condition of 900-1050°C and 0.002-0.2 s-1, the interrelations of peak flow stress, strain rate, and deformation temperature follow the Arrhenius' equation modified by a hyperbolic sine function with a stress exponent of 5.99 and an apparent activation energy of 441.2 kJ·mol-1.

Lu, Xin; Zhao, Li-hua; Zhu, Lang-ping; Zhang, Bin; Qu, Xuan-hui

2012-04-01

126

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

127

Severely affected ALS patients have broad and high expectations for brain-machine interfaces.  

PubMed

Abstract Brain-machine interfaces (BMIs) may provide new communication channels and motor function to individuals with severe neurodegenerative diseases, but little is known about their interests in such devices. We investigated the interests of severely affected ALS patients in BMIs, and examined factors that might influence these interests. We conducted an anonymous, mail-back questionnaire survey of severely disabled ALS patients diagnosed using the revised El Escorial criteria. Thirty-seven patients responded to the questionnaire. Twenty-nine (78.4%) had undergone tracheostomy positive pressure ventilation. More than 80% of the patients were interested in communication support. Thirty-three (89.2%) felt stressed during communication. Among those using assistive communication devices (17 patients), 15 (88.2%) were not satisfied with them. More than 50% of the patients expressed an interest in BMIs. Their expectations of BMIs ranged widely from emergency alarm to postural change. The frequent use of personal computers tended to be correlated with an interest in invasive BMIs (p = 0.07). In conclusion, this was the first questionnaire survey demonstrating that severely affected ALS patients have broad and high expectations for BMIs. Communication was the most desired support from BMIs for such patients. We need to meet their widely ranging expectations of BMIs. PMID:25204774

Kageyama, Yu; Hirata, Masayuki; Yanagisawa, Takufumi; Shimokawa, Toshio; Sawada, Jinichi; Morris, Shayne; Mizushima, Nozomi; Kishima, Haruhiko; Sakura, Osamu; Yoshimine, Toshiki

2014-12-01

128

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

NASA Astrophysics Data System (ADS)

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

Kawasaki, Megumi; Langdon, Terence G.

2014-08-01

129

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

E-print Network

ns up to any arbitrary length of time over many decades. We find that HP-stress results in much this technique, we study here the impact of high-power (HP) stress on dynamic RON. We find that HP-stress results. Our results point out the importance of characterizing electrically stress- induced dynamic RON

del Alamo, Jesús A.

130

High temperature nitrogen implantation of Ti-6Al-4V  

SciTech Connect

Titanium alloys offer desirable properties that make them attractive candidates for tribological applications. Their surface-related properties, however, such as coefficient of friction and wear rate, are less than optimum and must be improved by surface modification. To increase the tribological properties of Ti-6Al-4V, a high temperature ion implantation method, employing a high current density beam (e.g., 500 {mu}A/cm{sup 2}) of nitrogen (N) ions is being developed, where surface temperatures greater than 1000{degrees}C can be obtained. A systematic study was performed with N implantation at temperatures from 400{degrees} to >1000{degrees}C, and to a range of doses from 0.1--1.0{times}10{sup 18} N{sub 2}{sup +}--N{sup +}/cm{sup 2}. Microstructure characterization by Rutherford Backscattering Spectroscopy (RBS) and Glancing Incidence X-ray Diffraction (GID) was performed to determine N distribution and compound formation. RBS analysis showed enhanced N penetrations (i.e., greater than 0.3 {mu}m) for the 800{degrees} and 1000{degrees}C implantations, with the deepest penetration (about 3.5 atomic percent N remaining at 0.75 {mu}m) for the 1000{degrees}C treatment. GID indicated TiN and Ti{sub 2}N concentrations were the greatest for the 800{degrees}C implantation treatment. 11 refs., 4 figs.

Kustas, F.M.; Misra, M.S. (Martin Marietta Aerospace, Denver, CO (United States). Astronautics Group); Wei, R.; Wilbur, P.J. (Colorado State Univ., Fort Collins, CO (United States)); Knapp, J.A. (Sandia National Labs., Albuquerque, NM (United States))

1991-01-01

131

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

132

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

133

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

134

Preparation and Thermal Stress Analysis of Al O Insulation Coatings on SS304 Tape  

Microsoft Academic Search

Al2O3 insulation coatings are grown on long-length stainless steel (SS) tapes using reel-to-reel sol-gel method for applications of HTS\\/LTS coils and magnets. Various ceramic solutions are prepared from Al based precursors, solvent and chelating agent, the coating are fabricated on SS substrates. Al2O3 solution was successfully obtained using Al-sec-butoxide precursor, and isopropanol and acetylacetone as solvent and chelating agents, respectively.

S. Ataoglu; L. Arda; N. Kadioglu; O. Cakiroglu; O. Bulut; A. N. Gulluoglu; I. Belenli

2009-01-01

135

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

136

HIGH CYCLE FATIGUE BEHAVIOUR OF WELDED JOINTS BASED ON NOTCH STRESS INTENSITY FACTORS  

Microsoft Academic Search

The present paper summarises the application of NSIF approach to stress analysis and high cycle fatigue assessment of welded joints. This approach is based on linear elastic stress analysis of the open sharp corner defined at the weld toe; in that corner the NSIFs evaluate the intensity of the stress singularity similarly to the evaluation of the stress field ahead

B. Atzori; P. Lazzarin; R. Tovo

137

The Chinese high school student’s stress in the school and academic achievement  

Microsoft Academic Search

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 the students. In this class, the students’ stress negatively

Yangyang Liu; Zuhong Lu

2011-01-01

138

Inversion of stresses from polyphase fault/slip data with high or low diversity: An updated version of INVSFS  

NASA Astrophysics Data System (ADS)

Fault/slip data with low diversity show limited range in orientation, and their equations, according to the Wallace-Bott hypothesis often give rise to an unstable stress solution. It is necessary in this case to introduce some auxiliary constraint(s), so as to make a stable stress solution from these equations. A new method for inverting stress from polyphase fault/slip data with low diversity but having all or a majority of newly formed faults in each subset is developed in this paper. It combines a weak criterion that favors the newly formed faults, together with the Wallace-Bott hypothesis or the strong criterion. Both criteria are solved for stresses using the Fuzzy C-lines clustering analysis technique. This permits the updating of the INVSFS code ( Li et al., 2005). Two artificial sets of polyphase fault/slip data with high and low diversity are chosen to demonstrate the performance of the updated version.

Shan, Yehua; Tian, Ye; Xiao, Wenjiao

2011-08-01

139

STRESS  

NSDL National Science Digital Library

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

Hancey, Ms.

2010-04-27

140

Dislocations and extended defects in AlN deformed at high temperatures  

Microsoft Academic Search

Polycrystalline AlN could be deformed up to 10% strain in compression at elevated temperatures (1820–1920 K) under constant stress in the range 150–250 MPa or at a fixed strain rate of 5.6 × 10?6 s?1. Stress-strain curves show a marked temperature dependence. TEM investigations point to cavitation at grain boundaries as the main source of damage. Intragranular plasticity is achieved

Virginia Feregotto; Amand George; Jean-Pierre Michel

1997-01-01

141

Fatigue Life and Short Crack Behavior in Ti-6Al-4V Alloy; Interactions of Foreign Object Damage, Stress, and Temperature  

NASA Astrophysics Data System (ADS)

High-cycle fatigue (HCF) failures associated with foreign object damage (FOD) in turbine engines of military aircrafts have been of major concern for the aeronautic industry in recent years. The present work is focused on characterizing the effects of FOD on crack initiation and small crack growth of a Ti-6Al-4V alloy at ambient and also elevated temperatures. Results show that the preferred crack initiation site depends on applied stress and temperature as maximum fractions of cracks emanating from the simulated damage site, and naturally initiated cracks are observed at 25 °C under the maximum stress of 700 MPa and at 300 °C under the maximum stress of 300 MPa. The fatigue crack growth rate is influenced by increasing temperature, and the FCG rate at 300 °C is higher than that at room temperature under the same ? K, whereas this effect for FOD-site initiated cracks is not so remarkable. This observation seems to be due to the effect of stress relaxation at 300 °C. Results also indicate that fatigue crack initiation life ( N i ) and fatigue life ( N f ) are expressed by three-parameter Weibull distribution function.

Majidi, Behzad

2008-04-01

142

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

NASA Astrophysics Data System (ADS)

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

Jin, J. F.; Xiao, W. L.; Chen, H. B.

2010-05-01

143

The Flow Stress of High Purity Alkali Metals  

NASA Astrophysics Data System (ADS)

Among the b.c.c. alkali metals there are striking differences in the deformation behaviour between potassium on the one hand, which retains the b.c.c. structure down to the lowest temperatures investigated, and lithium and sodium, on the other hand, which undergo martensitic transformations to close-packed structures at low temperatures. The deformation behaviour of potassium is very similar to that of the b.c.c. refractory metals. Recent measurements show that in potassium there exist three different temperature and stress regimes within the flow-stress-versus-temperature curves, too. Hence this appears to be an intrinsic property of all b.c.c. metals. The deformation behaviour of lithium and sodium is characterized by a very strong orientation dependence and asymmetry of the flow stress with respect to the deformation direction in a temperature range which is by far too high for an intrinsic lattice mechanism to be the rate-controlling process. A model is presented which ascribes this behaviour to precursor phenomena of the martensitic transformation. Im Deformationsverhalten der Alkalimetalle bestehen wesentliche Unterschiede zwischen Kalium einerseits, welches im gesamten Temperaturbereich die kubisch-raumzentrierte Struktur besitzt, und Lithium und Natrium andererseits, welche martensitische Umwandlungen bei tiefen Temperaturen aufweisen. Das Verformungsverhalten von Kalium zeigt starke Ähnlichkeiten zu den kubisch-raumzentrierten Übergangsmetallen. Kürzlich wurde gezeigt, daß auch in Kalium drei verschiedene Temperatur- und Spannungsbereiche in der Temperaturabhängigkeit der Fließspannung bestehen. Dies scheint daher eine intrinsische Eigenschaft aller kubisch-raumzentrierten Metalle zu sein. Lithium und Natrium zeigen eine ungewöhnlich starke Orientierungsabhängigkeit und Zug-Druck-Asymmetrie in einem Temperaturbereich, in welchem ein intrinsischer Gittermechanismus mit Sicherheit ausgeschlossen werden kann. Es wird ein Modell präsentiert, welches dieses Verhalten auf Vorläufererscheinungen der martensitischen Transformation zurückführt.

Pichl, W.; Krystian, M.

1997-04-01

144

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

145

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

146

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

ERIC Educational Resources Information Center

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

Falls, Leigh; Nichter, Mary

2007-01-01

147

The Effects of a High School Stress Management Unit on Student's Heart Rate and Muscle Tension.  

ERIC Educational Resources Information Center

Attempted to determine effectiveness of three-week stress management unit for high school students. Measures of heart rate and muscle tension were used to determine the amount of control demonstrated during a period of relaxation and a period of induced stress. Results of the study indicate that a stress management unit for high school students…

Richardson, Glenn E.; And Others

1982-01-01

148

Blood Pressure and Heart Rate Responses to Anticipated High-stress Dental Treatment  

Microsoft Academic Search

Twenty-four healthy adults participated in a study to determine the effects of anticipated high-stress dental treatment on blood pressure and heart rate. Blood pressure, heart rate, and state anxiety were assessed prior to four consecutive dental appointments. Appointments 1, 2, and 4 were of relatively low stress and appointment 3 was of relatively high stress. Blood pressure was unaffected while

Frank M. Beck; Joël M. Weaver

1981-01-01

149

Measurement of in-shoe plantar triaxial stresses in high-heeled shoes  

Microsoft Academic Search

Foot problems such as pain and calluses are common for high-heeled shoe wearers. These problems may be related to the excessive local plantar loading, including pressure and shear stress. The shear stress is important on such a declined support surface of high-heeled shoe. The purpose of this study was to investigate the distribution of contact pressures and shear stresses simultaneously

Yan Cong; Ming Zhang

2010-01-01

150

Stress effects on rats chronically receiving a highly palatable diet are sex-specific  

Microsoft Academic Search

The stress response is known to lead to behavioral and metabolic changes. Exposure to chronic stress can promote the development of physiological and behavioral dysfunctions, including alterations in feeding behavior. The aim of this study was to verify whether chronic restraint stress alters the consumption of a highly palatable, highly caloric diet (chocolate), chronically offered to the animals. Male rats

Andrelisa Fachin; Rachel Krolow S. Silva; Cristie G. Noschang; Leticia Pettenuzzo; Liane Bertinetti; Mauro Nör Billodre; William Peres; Fernanda Busnello; Carla Dalmaz

2008-01-01

151

Inhibition of photosynthesis and energy dissipation induced by water and high light stresses in rice  

Microsoft Academic Search

Photoprotection mechanisms of rice plants were stu- died when its seedlings were subjected to the com- bined stress of water and high light. The imposition of water stress, induced by PEG 6000 which was applied to roots, resulted in substantial inhibition of stomatal conductance and net photosynthesis under all irradiance treatments. Under high light stress, the rapid decline of photosynthesis

Yanhong Zhou; Hon Ming Lam; Jianhua Zhang

2007-01-01

152

New stress and velocity fields for highly frictional granular materials  

NASA Astrophysics Data System (ADS)

The idealized theory for the quasi-static flow of granular materials which satisfy the Coulomb-Mohr hypothesis is considered. This theory arises in the limit as the angle of internal friction approaches {pi}/2, and accordingly these materials may be referred to as being highly frictional'. In this limit, the stress field for both two-dimensional and axially symmetric flows may be formulated in terms of a single nonlinear second-order partial differential equation for the stress angle. To obtain an accompanying velocity field, a flow rule must be employed. Assuming the non-dilatant double-shearing flow rule, a further partial differential equation may be derived in each case, this time for the streamfunction. Using Lie symmetry methods, a complete set of group-invariant solutions is derived for both systems, and through this process new exact solutions are constructed. Only a limited number of exact solutions for gravity-driven granular flows are known, so these results are potentially important in many practical applications. The problem of mass flow through a two-dimensional wedge hopper is examined as an illustration.

McCue, Scott W.; Johnpillai, I. Kenneth; Hill, James M.

2005-02-01

153

High level compressive residual stresses produced in aluminum alloys by laser shock processing  

NASA Astrophysics Data System (ADS)

Laser shock processing (LSP) has been proposed as a competitive alternative technology to classical treatments for improving fatigue and wear resistance of metals. We present a configuration and results for metal surface treatments in underwater laser irradiation at 1064 nm. A convergent lens is used to deliver 1.2 J/cm 2 in a 8 ns laser FWHM pulse produced by 10 Hz Q-switched Nd:YAG, two laser spot diameters were used: 0.8 and 1.5 mm. Results using pulse densities of 2500 pulses/cm 2 in 6061-T6 aluminum samples and 5000 pulses/cm 2 in 2024 aluminum samples are presented. High level of compressive residual stresses are produced -1600 MPa for 6061-T6 Al alloy, and -1400 MPa for 2024 Al alloy. It has been shown that surface residual stress level is higher than that achieved by conventional shot peening and with greater depths. This method can be applied to surface treatment of final metal products.

Gomez-Rosas, G.; Rubio-Gonzalez, C.; Ocaña, J. L.; Molpeceres, C.; Porro, J. A.; Chi-Moreno, W.; Morales, M.

2005-11-01

154

High-strain-rate superplasticity in ultrahigh-carbon steel containing 10 wt.% Al (UHCS-10Al)  

SciTech Connect

The present study represents a new processing route by which high-strain-rate superplasticity can be obtained in a two-phase, Fe-base alloy. For this study, an ultrahigh-carbon steel containing 10 wt.% Al (UHCS-10Al) was processed by a powder-metallurgy technique. Mechanical attrition was used to introduce a large degree of cold work into pre-alloyed powders, creating the very fine microstructural features necessary for high-strain-rate superplasticity. Because this material contains two phases, {alpha}-Fe and {kappa}-carbide (Fe{sub 3}AlC{sub x} where x = 0.5 to 1), in the range of processing temperatures, a fine grain size was produced upon consolidation and retained during deformation. It is this fine grain size which is responsible for the high-strain-rate superplastic behavior observed.

Taleff, E.M. [Univ. of Texas, Austin, TX (United States). Dept. of Aerospace Engineering and Engineering Mechanics] [Univ. of Texas, Austin, TX (United States). Dept. of Aerospace Engineering and Engineering Mechanics; Nagao, Mamoru [Kobe Steel, Ltd., Hyogo (Japan)] [Kobe Steel, Ltd., Hyogo (Japan); Higashi, Kenji [Univ. of Osaka Prefecture, Sakai (Japan)] [Univ. of Osaka Prefecture, Sakai (Japan); Sherby, O.D. [Stanford Univ., CA (United States). Dept. of Materials Science and Engineering] [Stanford Univ., CA (United States). Dept. of Materials Science and Engineering

1996-06-15

155

Stress Management Model for the Elementary/Middle/High School.  

ERIC Educational Resources Information Center

The Matthews Stress Management formula is a stress management model for use in schools. This effective, practical, and inexpensive model entails the awareness of the physiology of stress, perception of tangible bases of motivation for children, appropriate and simplified techniques, applicability to other areas, and full recognition of the…

Matthews, Doris B.

156

A Thermal-Stress Model of a High Pressure Diamond-Anvil Cell  

NASA Astrophysics Data System (ADS)

A time-dependent mathematical model to describe both thermal and stress propagation in a material compressed to high pressures in a diamond-anvil cell has been formulated. The cell is treated as an axisymmetric composite solid with temperature-dependent thermal conductivity. The effects of various boundary conditions on the interior temperature have been modeled and investigated. A finite-element code (FlexPDE) is utilized to solve the heat-conduction equation and the associated stress propagation equations. The model is utilized to interpret recent experiments* that investigate the transport of thermal and elastic waves in compressed media. The mathematical analysis and experimental data reveal that both thermal and stress propagation simultaneously occurs over two distinct time scales. The thermal propagation model utilizes the familiar parabolic heat-conduction equation, which implies that the effects of the thermal disturbance are instantaneously felt throughout the computational domain. The validity of the parabolic heat-conduction model is examined and compared with available experimental data. A one-dimensional transient analytic approximation for the temperature is also discussed. * Ladouceur, et.al., 1999 AIRAPT Proc.

Ladouceur, H. D.; Pangilinan, G. I.; Russell, T. P.

2000-03-01

157

Virtual melting as a new mechanism of stress relaxation under high strain rate loading  

PubMed Central

Generation and motion of dislocations and twinning are the main mechanisms of plastic deformation. A new mechanism of plastic deformation and stress relaxation at high strain rates (109–1012 s-1) is proposed, under which virtual melting occurs at temperatures much below the melting temperature. Virtual melting is predicted using a developed, advanced thermodynamic approach and confirmed by large-scale molecular dynamics simulations of shockwave propagation and quasi-isentropic compression in both single and defective crystals. The work and energy of nonhydrostatic stresses at the shock front drastically increase the driving force for melting from the uniaxially compressed solid state, reducing the melting temperature by 80% or 4,000 K. After melting, the relaxation of nonhydrostatic stresses leads to an undercooled and unstable liquid, which recrystallizes in picosecond time scales to a hydrostatically loaded crystal. Characteristic parameters for virtual melting are determined from molecular dynamics simulations of Cu shocked/compressed along the and directions and Al shocked/compressed along the direction. PMID:22847409

Levitas, Valery I.; Ravelo, Ramon

2012-01-01

158

Virtual melting as a new mechanism of stress relaxation under high strain rate loading.  

PubMed

Generation and motion of dislocations and twinning are the main mechanisms of plastic deformation. A new mechanism of plastic deformation and stress relaxation at high strain rates (10(9)-10(12) s(-1)) is proposed, under which virtual melting occurs at temperatures much below the melting temperature. Virtual melting is predicted using a developed, advanced thermodynamic approach and confirmed by large-scale molecular dynamics simulations of shockwave propagation and quasi-isentropic compression in both single and defective crystals. The work and energy of nonhydrostatic stresses at the shock front drastically increase the driving force for melting from the uniaxially compressed solid state, reducing the melting temperature by 80% or 4,000 K. After melting, the relaxation of nonhydrostatic stresses leads to an undercooled and unstable liquid, which recrystallizes in picosecond time scales to a hydrostatically loaded crystal. Characteristic parameters for virtual melting are determined from molecular dynamics simulations of Cu shocked/compressed along the ?110? and ?111? directions and Al shocked/compressed along the ?110? direction. PMID:22847409

Levitas, Valery I; Ravelo, Ramon

2012-08-14

159

Relationships among Stress, Coping, and Mental Health in High-Achieving High School Students  

ERIC Educational Resources Information Center

This study investigates the relationships among stress, coping, and mental health in 139 students participating in an International Baccalaureate (IB) high school diploma program. Mental health was assessed using both positive indicators (life satisfaction, academic achievement, academic self-efficacy) and negative indicators (psychopathology) of…

Suldo, Shannon M.; Shaunessy, Elizabeth; Hardesty, Robin

2008-01-01

160

INTERNATIONAL CONFERENCE ON SEMICONDUCTOR INJECTION LASERS SELCO-87: Thermally induced stresses in stripe GaAs/GaAlAs laser diodes  

NASA Astrophysics Data System (ADS)

Heating of the active region of stripe GaAlAs/GaAs double-heterostructure laser diodes by an injection current has a strong influence on the stresses in this region. An increase in the temperature of the region by 10 K can alter a shear stress by 5-10 MPa. In the case of lasers with a large thermal resistance the strong heating of the active region can induce mechanical stresses exceeding technological stresses (10 MPa) or even critical shear stresses for dislocation motion (20 MPa).

Rimpler, R.; Both, W.

1988-11-01

161

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

162

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

163

Proppant Fracture Conductivity with High Proppant Loading and High Closure Stress  

E-print Network

was measured by pumping oil to simulate reservoir conditions. Proppant performance and fracture fluids, which carry the proppant into the fracture, and their subsequent clean-up during production, were studied. High strength proppant is ideal for deep..., laboratory tests will be carried out using different concentrations and types of high-strength proppant to study the effects of increasing proppant pack closure stress and its effect on fracture conductivity. An experimental apparatus will be developed...

Rivers, Matthew Charles

2011-08-08

164

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

165

High Performance Polycrystalline SiGe Thin Film Transistors Using Al2O3 Gate Insulator  

E-print Network

1 High Performance Polycrystalline SiGe Thin Film Transistors Using Al2O3 Gate Insulator Zhonghe TFTs [6], its applicability in poly-SiGe is investigated in this work. Experimental The Al2O3 thin was used to generate the plasma. Al2O3 was sputtered reactively using an N2O plasma, with the wafer

166

Convective Heat Transfer Steady Thermal Stress and Effect Factors in a ZrO2\\/FGM\\/Ti6Al4V Composite EFBF Plate  

Microsoft Academic Search

A finite element model is constructed to analyze the steady thermal stress and effect factors in a ZrO2\\/FGM\\/Ti-6Al-4V composite EFBF plate under convective heat transfer boundary. From numerical calculation, when hmacra=hmacrb=1, T0=Ta =300 K and Tb=1 800 K, the stress distributions in the plate were obtained. The numerical results show that compared with h2= 2 mm the tensile stress of

Yangjian Xu; Daihui Tu; Wei Wei

2009-01-01

167

Characterization of the reliability and uniformity of an anodization-free fabrication process for high-quality Nb/Al-AlOx/Nb Josephson junctions  

NASA Astrophysics Data System (ADS)

We have developed a reliable and reproducible fabrication process for high-quality Nb/Al-AlOx/Nb Josephson junctions that completely avoids anodization techniques, that are typically used to define the junction area, to electrically insulate the base electrode as well as the sidewalls of the counter-electrode and to protect the tunnel barrier. Hence, this process is well suited for the fabrication of electrically floating junction-based devices such as non-hysteretic rf-SQUIDs. Josephson junctions of various sizes have been produced and characterized at 4.2 K. We found that our junctions have a high quality, which is confirmed by measured gap voltages Vg and Ic Rn products up to 2.9 and 1.8 mV and on-wafer average values of the resistance ratio Rsg/Rn above 30 in most cases. Here, Rsg and Rn denote the subgap and the normal state resistance of a Josephson junction. Although the uniformity of the properties of the Josephson junctions across a wafer is high, we observe some systematic variations of the critical current density and the gap voltage over an entire wafer. These variations are most likely to be attributed to residual stress in the Nb films as well as the surface roughness of the Nb base electrode.

Kempf, S.; Ferring, A.; Fleischmann, A.; Gastaldo, L.; Enss, C.

2013-06-01

168

Internal stress and degradation in short-wavelength AlGaAs double-heterojunction devices  

NASA Technical Reports Server (NTRS)

Aging tests of incoherently operated zinc-doped double-heterojunction (DH) lasers designed for short-wavelength (0.71-0.72 micron) operation show that the introduction of buffer layers between the substrate and the DH structure leads to a drastic reduction in gradual degradation. This is attributed to a decrease in lattice mismatch stress.

Ladany, I.; Furman, T. R.; Marinelli, D. P.

1979-01-01

169

The Effect of Prenatal Stress on Birth Weight: Evidence from the al-Aqsa Intifada  

Microsoft Academic Search

No previous study has attempted to estimate the effect of intrauterine exposure to armed conflict, a potential source of stress, on pregnancy outcomes. Drawing on data from the 2004 Palestinian Demographic and Health Survey, we examine the relationship between fatalities caused by Israeli security forces (a measure of conflict intensity) and birth weight. Our estimates suggest that first-trimester fatalities are

Hani Mansour; Daniel I. Rees

2011-01-01

170

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

171

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

172

High Glucose-Mediated Oxidative Stress Impairs Cell Migration  

PubMed Central

Deficient wound healing in diabetic patients is very frequent, but the cellular and molecular causes are poorly defined. In this study, we evaluate the hypothesis that high glucose concentrations inhibit cell migration. Using CHO.K1 cells, NIH-3T3 fibroblasts, mouse embryonic fibroblasts and primary skin fibroblasts from control and diabetic rats cultured in 5 mM D-glucose (low glucose, LG), 25 mM D-glucose (high glucose, HG) or 25 mM L-glucose medium (osmotic control - OC), we analyzed the migration speed, protrusion stability, cell polarity, adhesion maturation and the activity of the small Rho GTPase Rac1. We also analyzed the effects of reactive oxygen species by incubating cells with the antioxidant N-Acetyl-Cysteine (NAC). We observed that HG conditions inhibited cell migration when compared to LG or OC. This inhibition resulted from impaired cell polarity, protrusion destabilization and inhibition of adhesion maturation. Conversely, Rac1 activity, which promotes protrusion and blocks adhesion maturation, was increased in HG conditions, thus providing a mechanistic basis for the HG phenotype. Most of the HG effects were partially or completely rescued by treatment with NAC. These findings demonstrate that HG impairs cell migration due to an increase in oxidative stress that causes polarity loss, deficient adhesion and protrusion. These alterations arise, in large part, from increased Rac1 activity and may contribute to the poor wound healing observed in diabetic patients. PMID:21826213

Lamers, Marcelo L.; Almeida, Maira E. S.; Vicente-Manzanares, Miguel; Horwitz, Alan F.; Santos, Marinilce F.

2011-01-01

173

Extrusion Processing of High-Strength Al Alloy 7055  

Microsoft Academic Search

The effects of a combination of extrusion processing parameters and aging schedules on the microstructure and mechanical properties of the 7055 Al alloy were investigated. A safe extrusion processing zone is determined through a limit diagram constructed over the experimental initial billet temperature ranging from 380° to 420°C, extrusion ratio from 10:1 to 40:1, and the ram speed ranging from

Chandan Mondal; A. K. Mukhopadhyay; T. Raghu; K. S. Prasad

2007-01-01

174

Evolution of stress failure resulting from high-temperature stress-corrosion cracking in a hot isostatically pressed silicon nitride  

Microsoft Academic Search

Stress-corrosion cracking in a commercially available, hot isostatically pressed (HIPed), yttria-fluxed, silicon nitride was the prevalent mode of failure in specimens creep-ruptured at 1,370 C. High-temperature diffusional processes associated with oxygen were responsible for the creation of an advancing stress-corrosion front that had formed at the specimen surface and advanced radially inward. The volume of material in the wake of

Andrew A. Wereszczak; Mattison K. Ferber; Timothy P. Kirkland; Karren L. More; Michael R. Foley; Russell L. Yeckley

1995-01-01

175

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

176

Stress  

NSDL National Science Digital Library

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

Deaton, Mrs.

2011-06-10

177

Creep rupture mechanisms in annealed and overheated 7075 Al under multiaxial stress states  

Microsoft Academic Search

The creep deformation and rupture behavior of annealed and overheated 7075 A1 was investigated under uniaxial, biaxial, and\\u000a triaxial stress states. Examinations of samples prior to and after testing using optical microscopy, scanning electron microscopy\\u000a (SEM), and transmission electron microscopy (TEM) were also performed to develop a better understanding of the microstructural\\u000a mechanisms governing this behavior. These observations combined with

AHMADALI YOUSEFIANI; Farghalli A. Mohamed; James C. Earthman

2000-01-01

178

Stress corrosion cracking behavior of friction-stir-welded Al 6061-T651  

Microsoft Academic Search

In the present study, the stress corrosion cracking (SCC) behavior of friction-stir-welded AI 6061-T651 alloy was examined\\u000a of ?650 mV vs Ag\\/AgCl using a slow strain rate testing technique. The resistance to SCC was correlated to the percent change in tensile\\u000a elongation with exposure to 3.5 pct NaCl aqueous solution with respect to the reference environment. It was demonstrated the

Sunggon Lim; Sangshik Kim; Chang-Gil Lee; Sungjoon Kim

2005-01-01

179

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

180

Notch size effects on high cycle fatigue limit stress of Udimet 720  

Microsoft Academic Search

Notch size effects on the high cycle fatigue (HCF) limit stress of Ni-base superalloy Udimet 720 were investigated on cylindrical specimens with three notch sizes of the same stress concentration factor Kt=2.74. The HCF limit stress corresponding to a life of 106 cycles was experimentally determined at a stress ratio of 0.1 and a frequency of 25 Hz at room

Weiju Ren; Theodore Nicholas

2003-01-01

181

Cavity Optomechanics with High-Stress Silicon Nitride Films  

NASA Astrophysics Data System (ADS)

There has been a barrage of interest in recent years to marry the fields of nanomechanics and quantum optics. Mechanical systems provide sensitive and scalable architectures for sensing applications ranging from atomic force microscopy to gravity wave interferometry. Optical resonators driven by low noise lasers provide a quiet and well-understood means to read-out and manipulate mechanical motion, by way of the radiation pressure force. Taken to an extreme, a device consisting of a high-Q nanomechanical oscillator coupled to a high-finesse optical cavity may enable ground-state preparation of the mechanical element, thus paving the way for a new class of quantum technology based on chip-scale phononic devices coupled to optical photons. By way of mutual coupling to the optical field, this architecture may enable coupling of single phonons to real or artificial atoms, an enticing prospect because of the vast "quantum optics toolbox" already developed for cavity quantum electrodynamics. The first step towards these goals --- ground-state cooling of the mechanical element in a "cavity optomechanical" system --- has very recently been realized in a cryogenic setup. The work presented in this thesis describes an effort to extend this capability to a room temperature apparatus, so that the usual panoply of table-top optical/atomic physics tools can be brought to bear. This requires a mechanical oscillator with exceptionally low dissipation, as well as careful attention to extraneous sources of noise in both the optical and mechanical componentry. Our particular system is based on a high- Q, high-stress silicon nitride membrane coupled to a high-finesse Fabry-Perot cavity. The purpose of this thesis is to record in detail the procedure for characterizing/modeling the physical properties of the membrane resonator, the optical cavity, and their mutual interaction, as well as extraneous sources of noise related to multimode thermal motion of the oscillator, thermal motion of the cavity apparatus, optical absorption, and laser phase fluctuations. Our principle experimental result is the radiation pressure-based cooling of a high order, ? 4.8 MHz drum mode of the membrane from room temperature to ? 100 mK (? 500 phonons). Secondary results include an investigation of the Q-factor of membrane oscillators with various geometries, some of which exhibit state-of-the-art Qxfrequency products of 3 x 1013 Hz, and a novel technique to suppress extraneous radiation pressure noise using electro-optic feedback.

Wilson, Dalziel Joseph

182

The effect of residual stress on the fatigue crack growth behavior of Al-Si-Mg cast alloys—Mechanisms and corrective mathematical models  

NASA Astrophysics Data System (ADS)

The fatigue crack growth (FCG) behavior of various types of alloys is significantly affected by the presence of residual stress induced by manufacturing and post-manufacturing processes. There is a qualitative understanding of the effects of residual stress on fatigue behavior, but the effects are not comprehensively quantified or accounted for. The difficulty in quantifying these effects is largely due to the complexity of residual-stress measurements (especially considering that parts produced in similar conditions can have different residual-stress levels) and the lack of mathematical models able to convert experimental data with residual stress into residual-stress-free data. This article provides experimental, testing, and mathematical techniques to account for residual-stress effects on crack growth rate data, together with two methods for eliminating residual stresses in crack growth test specimens. Fracture-mechanics concepts are used to calculate, in simple and convenient ways, stress-intensity factors caused by residual stresses. The method is advantageous, considering that stress-intensity factors are determined before the actual test is conducted. Further on, residual-stress-intensity factors are used to predict the residual-stress distribution in compact tension (CT) specimens prior to testing. Five cast Al-Si-Mg alloys with three Si levels (in unmodified (UM) as well as Sr-modified (M) conditions) were analyzed both with and without residual stress. Fatigue cracks are grown under both constant stress ratio, R=0.1, and constant maximum stress-intensity factor, K max = const., conditions. The mechanisms involved in crack growth through residual-stress fields are presented.

Lados, Diana A.; Apelian, Diran

2006-01-01

183

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

184

Stress  

MedlinePLUS

... daily responsibilities Stress brought about by a sudden negative change, such as losing a job, divorce, or illness Traumatic stress, which happens when you are in danger of being seriously hurt or killed. Examples include a major accident, war, assault, or a natural disaster. This type of ...

185

Mg-doped AlGaInP laser diodes with high characteristic temperature  

Microsoft Academic Search

In this paper, we demonstrate Mg-doped AlGalnP LDs with high characteristic temperature. We found that abrupt Mg profiles can be obtained in quaternary alloys like AlGalnP, although significant memory effects are observed in GaAs. Based on this effect, we fabricated AlGalnP LDs with a highly Mg-doped cladding layer. As a result, reliable 650-nm-band LDs with characteristic temperature over 133 K

T. Onishi; K. Inoue; T. Takayama; M. Yuri; K. Onozawa; D. Ueda

2003-01-01

186

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

187

Combination of high fat diet and chronic stress retracts hippocampal dendrites  

PubMed Central

Adult male rats were fed a low or high fat diet and given psychosocial stress (crowded and unstable housing with daily predator exposure) for 3 weeks. Neither stress nor high fat diet, alone, produced dendritic atrophy; only the group given the combination of stress and high fat diet developed a reduction of the length and number of branch points of apical dendrites of CA3 neurons. These findings indicate that a synergy between high fat diet and stress caused a retraction of CA3 dendrites. The findings are consistent with work on peripheral (e.g., cardiovascular) systems demonstrating a synergy between stress and high fat diet, and are relevant toward understanding how diet and stress interact to adversely a¡ectbrain and memory processing. PMID:15618887

Baran, Sarah E.; Campbell, Adam M.; Kleen, Jonathan K.; Foltz, Cainan H.; Wright, Ryan L.; Diamond, David M.; Conrad, Cheryl D.

2006-01-01

188

The role of dislocations in high-strain-rate superplasticity of an Al-Ni-misch metal alloy  

SciTech Connect

Plastic deformation, microstructure and deformation substructure in an Al-14 wt% Ni-14 wt% Mm (misch metal) alloy produced from amorphous powders were examined focusing on the effects of the initial average grain size d{sub 0}, the grain boundary sliding and the motion of dislocations on the superplasticity. The as-received and annealed specimens with d{sub 0} = 0.8, 1.6 and 1.5 {micro}m deformed at 873 K at an initial strain rate of 1/s. The specimen with d{sub 0} = 0.8 {micro}m showed high-strain-rate superplasticity accompanied by low flow stress and 350% elongation, while the flow stress increased and elongation deceased with greater grain size. Grain refinement occurred and the frequency of small angle boundaries showed a complicated change during superplastic deformation. On the other hand, in the specimen with d{sub 0} = 1.6 {micro}m, the grains coarsened rapidly. A large number of dislocations were observed in grains even in the superplastically deformed specimen. The high-strain-rate superplasticity of Al-14 wt% Ni-14 wt% Mm alloy is controlled by the grain boundary sliding but the motion of dislocations also plays an important role in accommodating the highly strained region near triple junctions of the grain boundaries.

Umakoshi, Y.; Fujitani, W.; Nakano, T. [Osaka Univ., Suita, Osaka (Japan)] [Osaka Univ., Suita, Osaka (Japan); Inoue, A. [Tohoku Univ., Sendai (Japan). Inst. of Materials Research] [Tohoku Univ., Sendai (Japan). Inst. of Materials Research; Ohtera, K. [Y.K.K. Kurobe, Toyama (Japan). Technical Research Labs.] [Y.K.K. Kurobe, Toyama (Japan). Technical Research Labs.; Mukai, T. [Osaka Municipal Technical Research Inst. (Japan)] [Osaka Municipal Technical Research Inst. (Japan); Higashi, K. [Osaka Prefecture Univ., Sakai, Osaka (Japan)] [Osaka Prefecture Univ., Sakai, Osaka (Japan)

1998-08-10

189

OXIDATION MECHANISMS OF LOW ENERGY-HIGH FLUX NITRIDED ODS FeAl INTERMETALLIC ALLOY  

E-print Network

an argon atmosphere. Then, an artificial air (80% N2-20% O2) flow was let in the oxidising chamber for 24 h.- INTRODUCTION Upon the high temperature oxidation in air of TiAl intermetallic alloys, nitridation is observed diffusion layer containing AlN and a segregation of - Fe. The high temperature isothermal oxidation

Paris-Sud XI, Université de

190

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

191

Ti 2AlC coatings deposited by High Velocity Oxy-Fuel spraying  

Microsoft Academic Search

High Velocity Oxy-Fuel has been utilized to spray coatings from Ti2AlC (MAXTHAL 211®) powders. X-ray diffraction showed that the coatings consist predominantly of Ti2AlC with inclusions of the phases Ti3AlC2, TiC, and Al–Ti alloys. The fraction of Ti2AlC in coatings sprayed with a powder size of 38 ?m was found to increase with decreasing power of the spraying flame as controlled

Jenny Frodelius; Marie Sonestedt; Stefan Björklund; Jens-Petter Palmquist; Krystyna Stiller; Hans Högberg; Lars Hultman

2008-01-01

192

Cation disorder determined by MAS {sup 27}Al NMR in high dose neutron irradiated spinel  

SciTech Connect

Spinel (MgAl{sub 2}O{sub 4}) single crystals which had been neutron irradiated to high doses (53-250 dpa) were examined using {sup 27}Al magic angle spinning (MAS) nuclear magnetic resonance (NMR). The sensitivity of this procedure to a specific cation (Al) residing in different crystallographic environments allowed one to determine the distribution of the Al between the two cation sites in the spinel structure. The samples were irradiated at two different temperatures (400 and 750{degrees}C) and various doses. These results indicate that the Al was nearly fully disordered over the two lattice sites after irradiation.

Cooper, E.A.; Sickafus, K.E.; Hughes, C.D.; Earl, W.L. [Los Alamos National Lab., NM (United States); Hollenberg, G.W.; Garner, F.A. [Pacific Northwest Labs., Richland, WA (United States); Bradt, R.C. [Univ. of Alabama, Tuscaloosa, AL (United States). Dept. of Metallurgical and Materials Engineering

1995-12-31

193

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

PubMed Central

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. In order 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 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 of the compounds, we tested compounds by Western Blot analysis and in a 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

Zauur, Nava; Liu, Min; Concannon, John; Ebata, Atsushi; Wolozin, Benjamin; Glicksman, Marcie A.

2014-01-01

194

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

195

Improvement in electrical characteristics of high-k Al2O3 gate dielectric by field-assisted nitric oxidation  

NASA Astrophysics Data System (ADS)

The authors perform a simple technique for the improvements in both current density reliability of high-k Al2O3 gate dielectrics. An Al2O3 was prepared by chemical oxidation at an appropriate electrical field in nitric acid at room temperature then furnace annealed at 650°C in N2. The interface trap-induced capacitance was used to investigate the interfacial property between the gate dielectric Si substrate. On the other hand the stress induced leakage current (SILC) was measured for characterizing the property of bulk oxide. It was found that the electrical characteristics of bulk oxide including leakage breakdown field SILC, were much improved without sacrificing interfacial property. The improvement can be ascribed to the compensation oxidation process.

Chuang, Kai-Chieh; Hwu, Jenn-Gwo

2006-12-01

196

Thermal properties of Al at high pressures and temperatures  

NASA Astrophysics Data System (ADS)

Thermal properties of the face-centered-cubic (fcc) aluminum (Al) crystal including the linear thermal expansion coefficient, specific heat at constant volume, Hugoniot in the P-V plane, thermodynamic Grüneisen parameter and elastic constants at pressures up to 120GPa and temperatures to 3300K have been evaluated by using the full-potential linear muffin-tin orbital (FPLMTO) total-energy method combining with a mean-field model of the vibrational partition function. The mean-field is constructed from the sum of all the pair potentials between the reference atom and the others of the system. The calculated properties are in good agreement with available static and shock-wave experimental measurements.

Xiang, Shikai; Cai, Lingcang; Jing, Fuqian; Wang, Shunjin

2004-11-01

197

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

198

Growth of highly oriented ?- and ?-Al2O3 thin films by pulsed laser deposition  

NASA Astrophysics Data System (ADS)

Highly oriented aluminum oxide (Al2O3) thin films were grown on SrTiO3 (100), ?-Al2O3 (11¯02), ?-Al2O3 (0001) and MgO (100) single crystal substrates at an optimized oxygen partial pressure of 3.5×10-3 mbar and 700 °C by pulsed laser deposition. The films were characterized by X-ray diffraction and atomic force microscopy. The X-ray diffraction studies indicated the highly oriented growth of ?-Al2O3 (400) ? SrTiO3 (100), ?-Al2O3 (024) ? ?-Al2O3 (11¯02), ?-Al2O3 (006) ? ?-Al2O3 (0001) and ?-Al2O3 (006) ? MgO (100). Formation of nanostructures with dense and smooth surface morphology was observed using atomic force microscopy. The root mean square surface roughness of the films were 0.2 nm, 0.5 nm, 0.7 nm and 0.3 nm on SrTiO3 (100), ?-Al2O3 (11¯02), ?-Al2O3 (0001) and MgO (100) substrates, respectively.

Balakrishnan, G.; Babu, R. Venkatesh; Shin, K. S.; Song, J. I.

2014-03-01

199

Preparation of Nb3Al by high-energy ball milling and superconductivity  

NASA Astrophysics Data System (ADS)

The A15 phase superconductor Nb3Al has been considered as an alternative to Nb3Sn for high field and large scale applications. However, to prepare a stoichiometric Nb3Al with fine grain structures is very difficult. High-energy ball milling is a solid state powder processing technique and is a very useful for preparing Nb-Al alloys (Nb3Al). The effects of ball milling time and annealing temperature on the formation of Nb3Al superconducting phase have been studied. Pure Nb and Al powders with stoichiometric ratio of Nb3Al were mixed and milled, and the charging and milling were performed in an inert atmosphere. Phase formation and structural evolution during high-energy ball milling have been examined by X-ray diffraction. Al disappeared and Nb peaks broadened after about one hour of milling. With increasing milling time, the peaks of Nb became considerably broader and intensities decreased, the Nb-Al solid solution phase was extensive when milled about 3 hours. In order to obtain Nb3Al superconducting phase, a subsequent anneal was required. We have annealed the as-milled powders at 800-900°C for different times to prepared Nb3Al superconducting alloy. The results indicated that Nb3Al with small amount of impurity phase can be obtained on annealing the Nb-Al solid solution phase and the superconducting transition temperature was about 15K, but it is difficult to obtain a homogeneous Nb3Al phase by annealing the amorphous powder.

Chen, Yongliang; Liu, Zhao; Li, Pingyuan; Zhang, Xiaolan; Yang, Suhua; Yang, Dawei; Du, Lupeng; Cui, Yajing; Pan, Xifeng; Yan, Guo; Zhao, Yong

2014-05-01

200

Development of a high-performance TiAl exhaust valve  

SciTech Connect

A new high-performance and lightweight TiAl intermetallic compound exhaust valve has been developed. The TiAl valve can improve power output and fuel economy by contributing higher engine speeds and a reduction in valve train friction. It was achieved by developing A Ti-33.5Al-0.5Si-1Nb-0.5Cr (mass %) intermetallic compound, a precision casting method for TiAl that provides a low-cost, high-quality process, and a plasma carburizing technique for assuring good wear resistance on the valve stem end, stem and face.

Maki, Kunio; Ehira, Atsushi; Sayashi, Mamoru; Sasaki, Toru; Noda, Toshiharu; Okabe, Michio; Isobe, Susumu

1996-09-01

201

High damping Al-Fe-Mo-Si/Zn-Al composites produced by rapidly solidified powder metallurgy process  

SciTech Connect

The metallic materials commonly used in aircraft and aerospace fields, such as aluminum and titanium alloys, steels, etc., show extremely low damping capacity (usually of the order of or less than 10{sup {minus}3}). Thus, some problems related to vibration may emerge and influence the reliability, safety and life of airplanes, satellites, etc. It has been reported that almost two thirds of errors for rockets and satellites are related to vibration and noise. One effective way to solve these vibration-related problems is to adopt high damping metallic materials. Conventional high damping alloys exhibit damping capacity above 10{sup {minus}2}, however, their densities are usually great than 5 x 10{sup 3} kg m{sup {minus}3}, or their strengths are less than 200 MPa (for alloys based on dislocation damping), making them impossible to be applied to aircraft and aerospace areas. Recently, some low-density high-damping metal/metal composites based on aluminum and high damping alloys have been developed in Beijing Institute of Aeronautical Materials (BIAM) by the rapidly solidified power metallurgy process. This paper aims to report the properties of the composites based on a high temperature Al-Fe-Mo-Si alloy and a high damping Zn-Al alloy, and compare them with that of 2618-T61 alloy produced by the ingot metallurgy process.

Li, P.Y.; Dai, S.L.; Chai, S.C.; Li, Y.R.

2000-05-10

202

Stress  

MedlinePLUS

... blood glucose elevation in response to mental stress. Learning to Relax For some people with diabetes, controlling ... care issues can also help. Think about the aspects of life with diabetes that are the most ...

203

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

204

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

205

Fatigue behavior of high strength titanium alloys at elevated temperatures. [Ti8. 6Al, Ti6Al4V, IMI 685, and Ti6242  

Microsoft Academic Search

The influence of microstructure on mechanical properties at elevated temperatures in vacuum (10⁻⁴ Pa) has been investigated. Four different titanium alloys were tested: Ti-8.6 Al, Ti-6 Al-4V, IMI 685 and Ti-6242. The tensile tests showed the predicted decrease in yield stress Ï{sub 0.2} and increase in fracture strain ε{sub F} with increased temperature from 350 C to 500 C. For

M. A. Daeubler; G. Luetjering

2008-01-01

206

Time evolution of electrical degradation under high-voltage stress in GaN high electron mobility transistors  

E-print Network

In this work, we investigate the time evolution of electrical degradation of GaN high electron mobility transistors under high voltage stress in the OFF state. We found that the gate current starts to degrade first, followed ...

Joh, Jungwoo

207

High strain rate superplasticity of an ultrafine grained Al-Ti-Fe alloy  

SciTech Connect

Transition metals have limited solubility in aluminum, and alloying content higher than the solubility limit results in high melting point aluminides. When Fe is added into a hyper peritectic Al-Ti alloy, Al{sub x}Fe(X = 3 or 6) aluminide forms by an eutectic reaction at 655 C, and thus the Al{sub x}Fe phase could be an additional reinforcement to the Al-Ti system. The presence of the secondary Al{sub x}Fe particles is expected to enhance superplasticity by promoting finer grain size during PM processing and by retarding grain growth during deformation at elevated temperatures. The purpose of this study is to investigate HSRS behavior of an Fe-added Al-10wt%Ti alloy prepared by powder metallurgy and to compare it with that of similarly processed Al-10wt%Ti alloy.

Kum, D.W. [Korea Inst. of Science and Technology, Seoul (Korea, Republic of)] [Korea Inst. of Science and Technology, Seoul (Korea, Republic of); Kim, W.J. [Hong-ik Univ., Seoul (Korea, Republic of)] [Hong-ik Univ., Seoul (Korea, Republic of); Frommeyer, G. [Max-Plank-Inst. fuer Eisenforschung GmbH, Dusseldorf (Germany)] [Max-Plank-Inst. fuer Eisenforschung GmbH, Dusseldorf (Germany)

1998-12-18

208

Mechanical characteristics of a Zn–22% Al alloy processed to very high strains by ECAP  

Microsoft Academic Search

A Zn–22% Al eutectoid alloy was processed by equal-channel angular pressing for various numbers of passes up to a maximum of 24. Observations show the as-pressed grain size remains constant between 4 and 24 passes and the stress–strain behavior at room temperature is essentially independent of the number of imposed passes when using strain rates of 1.0×10?3 and 1.0×10?2s?1. The

Praveen Kumar; Cheng Xu; Terence G. Langdon

2006-01-01

209

Workability of Ti–6Al–4V alloy at high temperatures and strain rates  

Microsoft Academic Search

Hot workability of Ti–6Al–4V has been investigated by means of hot compression tests carried out in the 880–950 °C temperature range and 1–50 s?1 strain rate range. The effect of microstructural characteristics of the deformed specimens have been studied and correlated with the test temperature, total strain and strain rate. A constitutive equation for the flow stress has been defined

S. Bruschi; S. Poggio; F. Quadrini; M. E. Tata

2004-01-01

210

Design properties of a high-strength titanium alloy, Ti10V-2Fe3Al  

Microsoft Academic Search

The new titanium alloy Ti-10V-2Fe-3Al is shown to have adequate fracture toughness and stress corrosion resistance at the 180 ksi tensile strength level. This alloy has higher strength and fatigue resistance than other commercially available titanium alloys, and a considerable strength-to-weight advantage over comparable-strength steels. Detailed fracture toughness and fatigue data are presented and compared to commercially available titanium alloys.

1980-01-01

211

Effect of multiaxial stresses on the high-temperature behavior and rupture of advanced alloys  

Microsoft Academic Search

The evolution and effect of multiaxial stress states on the high temperature deformation and rupture behavior of materials with non-uniform microstructures has been investigated. Through a detailed description of the role that multiaxial stresses play on damage evolution and rupture, the abundant existing data for uniaxial rupture can be used to more successfully design for the life of high temperature

Nancy Louise Johnson

1998-01-01

212

Efficacy of Abbreviated Progressive Muscle Relaxation in a High-Stress College Sample  

Microsoft Academic Search

This study's purpose was to examine the efficacy of abbreviated progressive muscle relaxation (APMR) to enhance physiological and psychological functioning among high-stress college students. Participants (N = 128) were undergraduates, 19 years old on average, predominantly female and White, with high Perceived Stress Scale scores. After random assignment, for 20 min, 66 experimental group participants underwent APMR lying down and

Christyn L. Dolbier; Taylor E. Rush

2012-01-01

213

Preparation and characterization of high-performance direct current magnetron sputtered ZnO:Al films  

Microsoft Academic Search

High-performance aluminium-doped zinc oxide (ZnO:Al) thin films were deposited on glass substrate by direct current reactive magnetron sputtering from a Zn–Al metallic target (Al 3 wt.%). Films with a tangly string-like surface morphology, an average thickness of 837 nm, an optical transmittance up to 85% in the visible range and electrical resistivity down to 1.80×10?4 ? cm were obtained. The

W. W. Wang; X. G. Diao; Z. Wang; M. Yang; T. M. Wang; Z. Wu

2005-01-01

214

High power 625-nm AlGaInP laser diode  

Microsoft Academic Search

This paper presents high power AlGalnP LD with lasing wavelength of 625 nm. High power 625-nm AlGalnP laser diode was fabricated and evaluated. Remarkable short wavelength lasing at 624.9 nm was achieved on the condition of Tc = 25°C and 50 mW output under CW operation. At injection current of 800 mA, a high output power of 220 mW was

Naoyuki Shimada; Akihito Ohno; Shinji Abe; Motoharu Miyashita; Tetsuya Yagi

2010-01-01

215

High-resolution /sup 27/Al NMR study of calcium aluminate catalysts  

SciTech Connect

The high-resolution /sup 27/Al NMR spectra of calcium aluminates, calcium hydroaluminates, and calcium alumina supports and catalysts have been studied. The structures of the anhydrous calcium aluminates (CaAl/sub 2/O/sub 3/, CaAl/sub 4/O/sub 7/, 3CaO x Al/sub 2/O/sub 3/, 12CaO x 7Al/sub 2/O/sub 3/, talyum) consist of aluminum-oxygen tetrahedra and contain various types of aluminum atoms, the nonequivalence of which increases in going from strongly basic to weakly basic aluminates. In the NMR spectrum the signal of octahedrally coordinated aluminum is due to disordered aluminum-oxygen structures. During the forming of the calcium-alumina catalysts and supports the process (AlO/sub 4/) ..-->.. (AlO/sub 6/) takes place during hydration, and (AlO/sub 6/) ..-->.. (AlO/sub 4/) during thermolysis; the nonequivalence of the tetrahedrally coordinated aluminum atoms decreases, while the (AlO/sub 4/):(AlO/sub 6/) ratio decreases as the degree of hydration increases.

Yakerson, V.I.; Nissenbaum, V.D.; Golosman, E.Z.; Mastikhin, V.M.

1987-06-01

216

The 2002 M5 Au Sable Forks, NY, Earthquake Sequence: Evidence for High Stress Drops in an Intraplate Setting  

NASA Astrophysics Data System (ADS)

We find invariant high stress drops and high radiated energy for the intraplate earthquake sequence near Au Sable Forks, NY, in 2002. The M5 mainshock is the largest earthquake to occur in Eastern North America (ENA) since 1988 and the sequence is the best recorded in the region, by regional broadband stations, and a local aftershock deployment. Well recorded earthquakes are rare in low-seismicity, intraplate regions, but knowledge of the earthquake source characteristics impacts earthquake physics, seismic hazard and nuclear monitoring. There is controversy regarding (1) the invariance of stress drop with earthquake size in ENA, and (2) whether earthquakes in intraplate regions have higher stress drops than those in more tectonically active regions. We use both regional and local recordings of the direct waves to calculate source parameters for the mainshock and 21 aftershocks in 4 clusters. We use the Empirical Green's Function (EGF) approach and a multitaper method that includes complex spectral division with minimum frequency leakage, and allows transformation back to the time domain to check the validity of the EGF event (German et al., 2008). We define a set of criteria for the selection of EGF earthquake pairs and quality verification of the obtained EGF spectral ratio. The earthquakes have high stress drops (median 104 MPa), significantly larger than interplate earthquakes. The longer fault healing times in intraplate environments may lead to stronger faults and hence be responsible for the higher average stress drops. We find constant stress drop between M1 and M5, up to the bandwidth resolution limit (80 Hz). The previously reported breakdown of self-similarity in the region is most likely an artifact of the data limitations. We calculate radiated seismic energy (ES) for the best recorded earthquakes and find that it is consistently high. We obtain high radiated energy to seismic moment ratios (ES /M0, median of 9×10-5), significantly larger than estimates for interplate earthquakes (~2×10-5), consistent with the high stress drops. We find a slight dependence of apparent stress with earthquake size, but it becomes unclear and within the uncertainties if we consider local and regional data separately.

Viegas, G.; Abercrombie, R.; Kim, W.

2008-12-01

217

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

218

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

219

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 pressure and temperature. We predict asymmetric hydrogen bonding in the stishovite^N-AlOOH solid solution symmetric hydrogen bonding in N-AlOOH, and indicate that symmetric hydrogen bonding may be stable at ambient

Stixrude, Lars

220

Self-stressing test structures used for high-frequency electromigration  

SciTech Connect

We demonstrate for the first time high frequency (500 mhz) electromigration at the wafer-level using on-chip, self-stressing test structures. Since the stress temperature, frequency, duty cycle and current are controlled by DC signals in these structures, we used conventional DC test equipment without any special modifications (such as high frequency cabling, high temperature probe cards, etc.). This structure significantly reduces the cost of performing realistic high frequency electromigration experiments.

Snyder, E.S.; Pierce, D.G.; Campbell, D.V.; Swanson, S.E.

1994-02-01

221

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

222

Numerical and Experimental Analysis of Residual Stresses in Full-Penetration Laser Beam Welding of Ti6Al4V Alloy  

Microsoft Academic Search

A 3D thermal elastic-plastic finite element model to predict welding residual stresses induced by full-penetration laser welding of Ti6Al4V alloy was described in detail. The welding experiments and residual stresses measurements by through-thickness hole-drilling method were also performed to validate the simulated results. A uniform conical heat source model with parameters taken from the actual weld seam dimensions was developed

Liu Chuan; Zhang Jianxun; Niu Jing

2009-01-01

223

Reduction in the operating current of high-power 660-nm AlGaInP laser diodes with an AlInP current blocking layer  

Microsoft Academic Search

Summary form only given. High-power 660-nm AlGaInP laser diodes with a stable transverse mode are indispensable as the light source of recordable or rewritable DVD systems. The window-mirror structure is effective for obtaining a high COD (catastrophic optical damage) level. We report on high-power 660 nm AlGaInP laser diodes with Zn-diffused window-mirrors and an AlInP current blocking layer. These laser

R. Hiroyama; D. Inoue; Y. Nomura; M. Shono; M. Sawada

2001-01-01

224

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

E-print Network

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

Jiang, Hongxing

225

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

226

High-intensity acoustic tests of a thermally stressed plate  

Microsoft Academic Search

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

Chung Fai Ng; Sherman A. Clevenson

1991-01-01

227

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

228

High-Cycle Fatigue Behavior of Microarc Oxidation Coatings Deposited on a 6061-T6 Al Alloy  

NASA Astrophysics Data System (ADS)

The objective of this article is to evaluate the influence of microarc oxidation (MAO) coatings on the high-cycle rotating bending fatigue behavior of the 6061-T6 aluminum alloy. Toward this purpose, the influence of the MAO coating process parameter (current density) and coating thickness on the fatigue life of the 6061-T6 Al alloy has been evaluated in the present study. In addition, the influence of the coating roughness on the fatigue life of the MAO-coated 6061-T6 Al-alloy sample has also been investigated. The results indicate that the high-cycle fatigue life of the 6061-T6 Al alloy is substantially degraded due to the presence of MAO coatings, especially at lower alternating stress values and for thicker coatings. Surface roughness, altered by polishing, does not have any effect on fatigue life. An examination of coated samples interrupted at various fractions of fatigue life leads to the conclusion that the crack propagates from the coating surface to the coating-substrate interface very rapidly and thus fatigue life is largely controlled by the propagation of the crack into the substrate.

Wasekar, Nitin P.; Ravi, N.; Suresh Babu, P.; Rama Krishna, L.; Sundararajan, G.

2010-01-01

229

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 stress – stress-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

230

High novelty-seeking rats are resilient to negative physiological effects of the early life stress.  

PubMed

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 stress - stress-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

231

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

232

Microstructure of high velocity oxy-fuel sprayed Ti 2 AlC coatings  

Microsoft Academic Search

The microstructure formation and phase transformations in Ti2AlC-rich coatings deposited by High Velocity Oxy-fuel spraying of Maxthal 211® powders is presented. High resolution electron microscopy analysis, using both scanning and transmission electron microscopy\\u000a with energy dispersive spectrometry and energy filtering, combined with X-ray diffraction reveals that the coatings consist\\u000a of Ti2AlC grains surrounded by regions of very small TiC grains

Marie Sonestedt; Jenny Frodelius; Jens-Petter Palmquist; Hans Högberg; Lars Hultman; Krystyna Stiller

2010-01-01

233

Theoretical study of thermally stable SiO2/AlN/SiO2 Lamb wave resonators at high temperatures  

NASA Astrophysics Data System (ADS)

Aluminum nitride (AlN) and silicon dioxide (SiO2) bilayer structure has been widely utilized in temperature-compensated micromechanical resonators as SiO2 has unique positive temperature coefficients of elasticity. However, the thermal expansion mismatch would cause large bending deformation and stress distribution in the resonant plate. In this study, a symmetrical SiO2/AlN/SiO2 sandwiched structure is proposed to reduce the temperature-induced deformation in the asymmetrical AlN/SiO2 bilayer plate. The thermal compensation at high temperatures for the Lamb wave resonators utilizing the lowest-order symmetric (S0) mode in the SiO2/AlN/SiO2 sandwiched structure is theoretically investigated herein. While operation temperature rises from room temperature to 600 °C, the temperature-induced bending deformation in the symmetrical SiO2/AlN/SiO2 composite plate is much less than that in the AlN/SiO2 composite plate conventionally used for temperature compensation. Furthermore, the different material properties of the AlN and SiO2 layers make the displacements of the S0 mode not purely symmetric with respect to the neutral axis, whereas the symmetrical SiO2/AlN/SiO2 sandwiched membrane still can enable a pure S0 mode which shows higher phase velocity and larger electromechanical coupling coefficient than the lowest-order quasi-symmetric (QS0) mode traveling in the AlN/SiO2 bilayer membrane. With proper thickness selection of AlN and SiO2, the S0 mode in the symmetrical SiO2/AlN/SiO2 sandwiched membrane can simultaneously offer excellent thermal compensation, high phase velocity, large electromechanical coupling coefficient, and small thermally induced deformation at high temperatures.

Zou, Jie; Lin, Chih-Ming; Chen, Yung-Yu; Pisano, Albert P.

2014-03-01

234

Fabrication of High TCR TaAl-N Thin Film by Reactive Sputtering Method  

NASA Astrophysics Data System (ADS)

The electric characteristics of TaAl-N thin film were investigated. The resistivity of the TaAl-N thin films, having been prepared by DC reactive sputtering of Ta and Al (8:2 area ratio) target in a gas mixture of argon and nitrogen, showed pressure-ratio dependence of nitrogen (PN2/Ptotal). The condition of high PN2/Ptotal was effective for fabricating the films, having a high TCR (the temperature coefficient of the resistivity). As a result, in the condition of PN2/Ptotal=75%, the TCR values were (-)35000 ppm/°C (at 100°C) and (-)25000 ppm/°C (at 200°C, resistivity).

Okano, Yukiko; Tajiri, Shuichi; Aozono, Takashi; Okamoto, Akio; Ogawa, Soichi; Mima, Hiroshi

235

Zn–Al-based metal–matrix composites with high stiffness and high viscoelastic damping  

Microsoft Academic Search

A maximal product of stiffness and viscoelastic damping (E tan ?), a figure of merit for damping layers, is desirable for structural damping applications. Particulate-reinforced metal–matrix composites were prepared by ultrasonic agitation of the melt and composed of the zinc–aluminum (ZnAl) alloy Zn80Al20 (in wt%) as the lossy matrix and SiC or BaTiO3 as the particulate reinforcements. ZnAl–SiC composites were

T Jaglinski; RS Lakes

2012-01-01

236

Cyclically-Induced Pore Pressure at High Confining Stress  

Microsoft Academic Search

Experiments were conducted by the ERDC Centrifuge Research Team to investigate effective confining stress effects on liquefaction potential of fine, clean, Nevada sand, under the boundary and loading conditions of a centrifuge model. For this test series, twenty-six level ground models with either a dense layer over a loose layer or homogeneous profile were tested in an equivalent-shear-beam box. Some

Michael K. Sharp; R. Scott Steedman

237

High-Cycle Fatigue Properties and Fatigue Crack Initiation Behavior of Ti5%Al2.5%Sn Eli Alloy at Cryogenic Temperatures  

Microsoft Academic Search

Tensile tests and uni-axial loading fatigue tests were performed at 4 K, 77 K and 293 K for Ti-5%Al-2.5%Sn extra low interstitial (ELI) forged alloy. The 0.2% proof stress and the tensile strength of this alloy increased with a decrease of temperature. However, high-cycle fatigue strength at cryogenic temperatures was relatively low compared to that at 293 K. In the

Y. Ono; M. Demura; T. Yuri; T. Ogata; S. Matsuoka; S. Hori

2008-01-01

238

Finite element analysis for uniaxial time-dependent ratcheting of SiC P\\/6061Al composites at room and high temperatures  

Microsoft Academic Search

The cyclic deformation, especially the time-dependent ratcheting behaviors of SiC particulate reinforced 6061Al alloy composites in uniaxial cyclic straining and cyclic stressing at room and high temperatures (573K) were analyzed by finite element code ABAQUS, respectively, using the single particulate model of the composites and employing axi-symmetrical 2-D 6-node elements. The ratcheting behaviors of un-reinforced matrix metals occurred in uniaxial

Guozheng Kang; Cheng Dong; Sujuan Guo

2007-01-01

239

Optical floating zone growth of high-quality Cu2MnAl single crystals  

E-print Network

We report the growth of large single-crystals of Cu2MnAl, a ferromagnetic Heusler compound suitable for polarizing neutron monochromators, by means of optical floating zone under ultra-high vacuum compatible conditions. Unlike Bridgman or Czochralsky grown Cu2MnAl, our floating zone grown single-crystals show highly reproducible magnetic properties and an excellent crystal quality with a narrow and homogeneous mosaic spread as examined by neutron diffraction. An investigation of the polarizing properties in neutron scattering suggests a high polarization efficiency, limited by the relatively small sample dimensions studied. Our study identifies optical floating zone under ultra-high vacuum compatible conditions as a highly reproducible method to grow high-quality single-crystals of Cu2MnAl.

Neubauer, Andreas; Meven, Martin; Georgii, Robert; Brandl, Georg; Behr, Gunther; Böni, Peter; Pfleiderer, Christian; 10.1016/j.nima.2012.06.012

2012-01-01

240

High-Density Pulse Current-Induced Unsteady Stress-Strain State in a Long Rod  

Microsoft Academic Search

The results of experimental investigations and numerical calculations of the unsteady stress-strain state in a thin steel rod (wire length) prestressed statically below the yield strength upon the passage of a high-density current pulse are presented. The current pulse gives rise to oscillations of axial stresses with a period corresponding to the period of natural longitudinal oscillations of the rod.

G. V. Stepanov; A. I. Babutskii; I. A. Mameev

2004-01-01

241

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

242

Residual stresses in structures coated by a high velocity oxy-fuel technique  

Microsoft Academic Search

The high-velocity oxy-fuel thermal spray-coating technique is investigated with regard to the residual stresses that can develop in the coating and in the coated material. The hole-drilling strain-gauge method is used to measure the stresses. Different pre-heating temperatures of the specimen surface and the influence of the coating thickness are explored.

M. S. J Hashmi; C Pappalettere; F Ventola

1998-01-01

243

Effect of Hf-Rich Particles on the Creep Life of a High-Strength NiAl Single Crystal Alloy  

NASA Technical Reports Server (NTRS)

Additions of small amounts of Hf and Si to NiAl single crystals significantly improve their high-temperature strength and creep properties. However, if large Hf-rich dendritic particles formed during casting of the alloyed single crystals are not dissolved completely during homogenization heat treatment, a large variation in creep rupture life can occur. This behavior, observed in five samples of a Hf containing NiAl single crystal alloy tested at 1144 K under an initial stress of 241.4 MPa, is described in detail highlighting the role of interdendritic Hf-rich particles in limiting creep rupture life.

Garg, A.; Raj, S. V.; Darolia, R.

1995-01-01

244

Synchronized Stress-strain Measurements in Dynamic Loading at High Pressure using D-DIA  

SciTech Connect

A new data collection protocol for forced oscillation experiments using a multianvil high pressure device is reported. We derive the stress of the sample at high pressure and temperature from synchrotron x-ray diffraction that is synchronized with sample strain measurements from x-ray radiographs. This method yields stress directly from the sample rather than a stress proxy. Furthermore, the diffraction pattern yields useful information concerning time evolution of structurally related phenomena. Here we illustrate some of these possibilities with high pressure experimental data.

L Li; D Weidner

2011-12-31

245

High-efficiency AlGaN-based UV light-emitting diode on laterally overgrown AlN  

Microsoft Academic Search

Ultraviolet light-emitting diodes (UV-LEDs) with a peak wavelength of 335nm were fabricated on AlN\\/sapphire templates. As templates for the fabrication of UV-LEDs, planar AlN and epitaxial laterally overgrown (ELO) AlN on sapphire (0001) substrates were compared. The output power of UV-LEDs grown on ELO-AlN was 27 times higher than that of UV-LEDs on the planar AlN template.

Kentaro Nagamatsu; Narihito Okada; Hiroki Sugimura; Hirotoshi Tsuzuki; Fumiaki Mori; Kazuyoshi Iida; Akira Bando; Motoaki Iwaya; Satoshi Kamiyama; Hiroshi Amano; Isamu Akasaki

2008-01-01

246

Fabrication of high wear resistant Al\\/Al 3Ti metal matrix composite by in situ hot press method  

Microsoft Academic Search

In this study, hot press method has been used to fabricate Al\\/Al3Ti composite. In situ reacted Al3Ti compound is formed through Al and TiO2 powder blend in order to enhance mechanical properties and mainly wear resistance. After homogeneous blending of Al and TiO2, hot pressing was performed at 580°C at different durations and pressures. Scanning electron microscopy was used for

M. Nofar; H. R. Madaah Hosseini; N. Kolagar-Daroonkolaie

2009-01-01

247

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

NASA Astrophysics Data System (ADS)

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

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

2010-06-01

248

Quaternary InAlGaN-based high-efficiency ultraviolet light-emitting diodes  

Microsoft Academic Search

In order to realize 250-350-nm-band high-efficiency deep ultraviolet (UV) emitting devices using group-III-nitride materials, it is necessary to obtain high-efficiency UV emission from wide-band-gap (In)AlGaN. The use of the In-segregation effect, which has already been used for InGaN blue emitting devices, is quite effective for achieving high-efficiency deep UV emission. We have demonstrated high-efficiency UV emission from quaternary InAlGaN-based quantum

Hideki Hirayama

2005-01-01

249

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

Microsoft Academic Search

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

Toshiyuki Obata; Hideki Hirayama; Yoshinobu Aoyagi; Koji Ishibashi

2004-01-01

250

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

251

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

252

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

SciTech Connect

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

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

1998-11-02

253

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

254

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.

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

2014-01-01

255

Correlates of high perceived stress among pregnant Hispanic women in Western Massachusetts.  

PubMed

Prenatal psychosocial stress has been associated with adverse pregnancy outcomes, even after controlling for known risk factors. This paper aims to evaluate correlates of high perceived stress among Hispanic women, a group with elevated rates of stress during pregnancy. We conducted this analysis among 1,426 pregnant Hispanic women using data from Proyecto Buena Salud, a prospective cohort study conducted in Western Massachusetts. Cohen's Perceived Stress Scale (PSS-14) validated in English and Spanish was administered in early (mean = 12.4 weeks gestation), mid (mean = 21.3 weeks gestation) and late (mean = 30.8 weeks gestation) pregnancy at which time bilingual interviewers collected data on socio-demographic, acculturation, behavioral, and psychosocial factors. High perceived stress was defined as a PSS score >30. Young maternal age (odds ratio (OR) = 0.6; 95 % confidence interval (CI) 0.4-0.9 for <19 vs. 19-23 years), pre-pregnancy consumption of alcohol (OR = 2.2; 95 % CI 1.4-3.5 for >12 drinks/month vs. none) and smoking (OR = 2.2; 95 % CI 1.3-3.7 for >10 cigarettes/day vs. none) were associated with high perceived stress during early pregnancy. Furthermore, higher annual household income (OR = 0.4; 95 % CI 0.1-0.9 for >$30,000 vs. <$15,000), greater number of adults in the household (OR = 1.8; 95 % CI 1.1-3.0 for ?3 vs. 1) and language preference (OR = 0.6; 95 % CI 0.4-0.9 for Spanish vs. English) were associated with high stress during mid-pregnancy. Likewise, annual household income was inversely associated with high stress during late pregnancy. Our results have important implications for incorporation of routine screening for psychosocial stress during prenatal visits and implementation of psychosocial counseling services for women at high risk. PMID:23010861

Silveira, Marushka Leanne; Pekow, Penelope S; Dole, Nancy; Markenson, Glenn; Chasan-Taber, Lisa

2013-08-01

256

Radiation response behaviour of Al codoped germano-silicate SM fiber at high radiation dose  

NASA Astrophysics Data System (ADS)

Radiation response behaviour of Ge + Al doped SM fiber fabricated by the solution doping process has been studied at room temperature with respect to 1310 nm transmission wavelength under three different dose rates of 200, 400 and 600 Rad/min to compare with that of standard Er doped as well as Ge doped SM fibers. Their radiation sensitivity has been observed with variation of dose rates, transmission wavelength along with their recovery nature. Radiation response behaviour of Al doped SM fiber is found to be slightly non-linear in nature with very low dose rate dependency. No saturation level was found upto 13 Krad cumulative dose. Thermobleaching as well as photobleaching phenomena have also been studied. Gamma irradiated Al doped preform shows an absorption peak at around 300 nm due to generation of Al (E') defect center and gets annihilated after thermobleaching process. Gamma irradiated Al doped SM fiber shows prominent photobleaching effect on their optical attenuation with respect to the 850 nm transmission wavelength. From ESR study resonance signals for Al 3+ related radiation-induced defect centers are not clearly observed in this study. A very weak hyperfine pattern has been observed for gamma irradiated Al doped preform sample. The high radiation sensitivity along with linear response behaviour, low recovery and almost dose rate independence behaviour of the material system of Ge + Al codoped SM core optical fiber under gamma radiation shows their potential for application as fiber optic radiation sensor in comparison to the universal standard erbium doped SM fiber.

Paul, M. C.; Sen, R.; Bhadra, S. K.; Dasgupta, K.

2009-03-01

257

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

258

Optical and electronic properties of highly stable and textured hydrogenated ZnO:Al thin films  

SciTech Connect

Highlights: ? We investigate the impact of hydrogen treatment at high temperature of ZnO:Al film. ? Electrical properties of the ZnO:Al films improved due to hydrogen annealing. ? Optical properties of the ZnO:Al films enhanced due to hydrogen annealing. ? ZnO:Al film properties strongly depend on the hydrogen treatment temperature. -- Abstract: We have experimentally investigated the effects of hydrogen-annealing on the structural, electrical, and optical properties of Al-doped ZnO (ZnO:Al) thin films prepared by RF magnetron sputtering at room temperature. From the X-ray diffraction observations, the orientation of ZnO:Al films was found to be a c-axis in the hexagonal structure. We found that intentionally incorporated hydrogen plays an important role in n-type conduction as a donor, improving free carrier concentration and electrical stability. We simultaneously obtained improved optical transmission and enhanced absorption edge of the ZnO:Al film due to hydrogen-annealing. Our experimental data suggest the hydrogen-annealing process as an important role in the enhancement of electrical and optical properties, which is promising as a back reflector material for thin-film solar cells.

Hwang, Younghun, E-mail: younghh@ulsan.ac.kr [Basic Science Research Institute, University of Ulsan, Ulsan 680-749 (Korea, Republic of)] [Basic Science Research Institute, University of Ulsan, Ulsan 680-749 (Korea, Republic of); Kim, Hyungmin [Department of Physics, University of Ulsan, Ulsan 680-749 (Korea, Republic of)] [Department of Physics, University of Ulsan, Ulsan 680-749 (Korea, Republic of); Um, Youngho, E-mail: yhum@ulsan.ac.kr [Department of Physics, University of Ulsan, Ulsan 680-749 (Korea, Republic of)] [Department of Physics, University of Ulsan, Ulsan 680-749 (Korea, Republic of); Park, Hyoyeol [Semiconductor Applications, Ulsan College, Ulsan 680-749 (Korea, Republic of)] [Semiconductor Applications, Ulsan College, Ulsan 680-749 (Korea, Republic of)

2012-09-15

259

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

PubMed

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

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

2014-10-01

260

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

261

Investigation of stress-corrosion cracking of high-strength steels in certain media  

Microsoft Academic Search

One of the factors limiting the range of industrial applications of high-strength steels is their relatively high susceptibility to stress-corrosion cracking, especially in hydrogen-chargin g media. When a stressed metal undergoes corrosion in a medium with hydrogen depolarization, the adsorption of hydrogen ions on cathodic surface regions leads to hydrogen charging of the metal and produces a sharp reduction in

M. G. Khitarishvili; I. I. Dikii; A. I. Zyubrik; I. I. Vasilenko

1974-01-01

262

The fast initial threshold voltage shift: NBTI or high-field stress  

Microsoft Academic Search

Recent negative bias temperature instability (NBTI) studies have come to involve very high electric fields, yet these same studies are used to criticize the lower field ldquoNBTIrdquo models. This study examines both high- and low-field degradation phenomena by monitoring the initial threshold voltage shift (DeltaVTH) as a function of stress time and stress voltage. We demonstrate that the initial DeltaVTH

J. P. Campbell; K. P. Cheung; J. S. Suehle; A. Oates

2008-01-01

263

Characterization of interface states in Al{sub 2}O{sub 3}/AlGaN/GaN structures for improved performance of high-electron-mobility transistors  

SciTech Connect

We have investigated the relationship between improved electrical properties of Al{sub 2}O{sub 3}/AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) and electronic state densities at the Al{sub 2}O{sub 3}/AlGaN interface evaluated from the same structures as the MOS-HEMTs. To evaluate Al{sub 2}O{sub 3}/AlGaN interface state densities of the MOS-HEMTs, two types of capacitance-voltage (C-V) measurement techniques were employed: the photo-assisted C-V measurement for the near-midgap states and the frequency dependent C-V characteristics for the states near the conduction-band edge. To reduce the interface states, an N{sub 2}O-radical treatment was applied to the AlGaN surface just prior to the deposition of the Al{sub 2}O{sub 3} insulator. As compared to the sample without the treatment, the N{sub 2}O-radical treated Al{sub 2}O{sub 3}/AlGaN/GaN structure showed smaller frequency dispersion of the C-V curves in the positive gate bias range. The state densities at the Al{sub 2}O{sub 3}/AlGaN interface were estimated to be 1?×?10{sup 12}?cm{sup ?2}?eV{sup ?1} or less around the midgap and 8?×?10{sup 12}?cm{sup ?2}?eV{sup ?1} near the conduction-band edge. In addition, we observed higher maximum drain current at the positive gate bias and suppressed threshold voltage instability under the negative gate bias stress even at 150?°C. Results presented in this paper indicated that the N{sub 2}O-radical treatment is effective both in reducing the interface states and improving the electrical properties of the Al{sub 2}O{sub 3}/AlGaN/GaN MOS-HEMTs.

Hori, Y.; Yatabe, Z. [Research Center for Integrated Quantum Electronics (RCIQE) and Graduate School of Information Science and Technology, Hokkaido University, North 13 West 8, Sapporo, 060-8628 Hokkaido (Japan); Hashizume, T., E-mail: hashi@rciqe.hokudai.ac.jp [Research Center for Integrated Quantum Electronics (RCIQE) and Graduate School of Information Science and Technology, Hokkaido University, North 13 West 8, Sapporo, 060-8628 Hokkaido (Japan); Japan Science and Technology Agency (JST), CREST, Tokyo 102-0075 (Japan)

2013-12-28

264

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

265

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

266

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

267

Straight through cold-applied shrinkable EPDM cable joints designed for high stress medium voltage EPR cables  

Microsoft Academic Search

The introduction of high electrical stress EPR insulated medium voltage cables leads to the development of new cable joints suitable for installation. This paper presents the joint design considerations and test data. The test program is based on IEEE Standard 404-1993. Test samples include joints for high stress EPR cables and transition joints from high stress EPR cables to PILC

Y. Wen; A. Shocket; P. L. Cinquemani; U. Vallauri; G. Lencot

1998-01-01

268

Al NMR study of molten aluminum oxide compounds and mixtures, measured at ultra high temperatures  

Microsoft Academic Search

The technique of ultra high-temperature nuclear magnetic resonance (NMR) has provided insight into the chemical structure and properties of molten aluminum-bearing refractory ceramics, at temperatures in excess of 2000 ^oC. Through application of standard NMR measurements we have studied molten aluminum-bearing ceramics via ^27Al NMR. We have measured spin-lattice (T_1) and spin-spin (T_2) relaxation times, have studied Al-O-P chemical bonding

J. Piwowarczyk; R. F. Marzke; G. H. Wolf; W. T. Petuskey; B. Takulapalli

2002-01-01

269

Magnesium and Calcium Aluminate Liquids: In Situ High-Temperature 27Al NMR Spectroscopy  

Microsoft Academic Search

The use of high-temperature nuclear magnetic resonance (NMR) spectroscopy provides a means of investigating the structure of refractory aluminate liquids at temperatures up to 2500 K. Time-averaged structural information indicates that the average aluminum coordination for magnesium aluminate (MgAl_2O_4) liquid is slightly greater than for calcium aluminate (CaAl_2O_4) liquid and that in both liquids it is close to four. Ion

B. T. Poe; P. F. McMillan; B. Cote; D. Massiot; J. P. Coutures

1993-01-01

270

Defect engineering for 650 nm high-power AlGaInP laser diodes  

Microsoft Academic Search

To find the optimal growth and annealing conditions for high-power 650 nm band AlGaInP laser diodes, we carried out defect engineering, in which the distribution and density of deep level defects of the laser structure was analyzed. For this purpose, deep level transient spectroscopy (DLTS) measurements were carried out for each layer of the 650 nm band AlGaInP laser. By

D. S. Kim; K. C. Kim; Y. C. Shin; D. H. Kang; B. J. Kim; Y. M. Kim; T. G. Kim

2006-01-01

271

Defect engineering for 650 nm high-power AlGaInP laser diodes  

Microsoft Academic Search

To find the optimal growth and annealing conditions for high-power 650nm band AlGaInP laser diodes, we carried out defect engineering, in which the distribution and density of deep level defects of the laser structure was analyzed. For this purpose, deep level transient spectroscopy (DLTS) measurements were carried out for each layer of the 650nm band AlGaInP laser. By layer optimization

D. S. Kim; K. C. Kim; Y. C. Shin; D. H. Kang; B. J. Kim; Y. M. Kim; T. G. Kim

2006-01-01

272

AlGaAs/GaAs photovoltaic converters for high power narrowband radiation  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

273

High velocity oxy-fuel thermal spraying of a NiCoCrAlY alloy  

Microsoft Academic Search

During the last few years third-generation high velocity oxy-fuel (HVOF) spray systems have gained interest concerning the deposition of sensitive metal alloys such as MCrAlYs. This work deals with the HVOF thermal spraying of a NiCoCrAlY alloy and its isothermal oxidation behaviour. Two HVOF systems were investigated, DJ 2600 and JP 5000. For both spray systems, the influence of the

Lidong Zhao; Maria Parco; Erich Lugscheider

2004-01-01

274

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

275

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

276

High-power continuous wave 690 nm AlGaInP laser-diode arrays  

Microsoft Academic Search

High-power diode laser arrays emitting at 690 nm have been developed for solid-state laser pumping. The laser diode bars (fill factor ≊0.7) have been fabricated from single quantum well AlGaInP-based heterostructures. Using silicon microchannel heatsinks, a record high 360 W\\/cm2 per emitting aperture is achieved under continuous wave operation.

J. A. Skidmore; M. A. Emanuel; R. J. Beach; W. J. Benett; B. L. Freitas; N. W. Carlson; R. W. Solarz

1995-01-01

277

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.

278

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

279

A New High-Pressure Phase With Mg2Al2O5 Composition  

NASA Astrophysics Data System (ADS)

As MgAl2O4 is one of major components of both spinel phase and calcium ferrite phase in the Earth"fs mantle, many researchers have studied its high-pressure phase relations. However, the high- pressure high-temperature phase relation has been unclear at temperature higher than 2000 °C. By performing high-pressure experiments, we found that MgAl2O4 spinel decomposes to Mg2Al2O5 and Al2O3 at 20-25 GPa and temperature higher than 2000 °C. This is the first report of a compound with the composition of Mg2Al2O5. The powder X-ray diffraction pattern can not be explained by crystal structures of already known high-pressure phases like brownmillerite-type Ca2Al2O5. In this study, we tried to construct a crystal structure model of the new Mg2Al2O5 phase. The obtained structure model was used for structure refinement by the Rietveld analysis. The Mg2Al2O5 phase for a powder XRD measurement was synthesized using a Kawai-type multi-anvil high-pressure apparatus at Gakushuin University. The starting material of a mixture of MgO:Al2O3 = 2:1 (in molar ratio) was hold at 23 GPa and 2500 °C for 10 min. After quenching, the sample was recoverd to ambient pressure. The sintered polycrystalline sample was crushed by a die and ground into powder. The powder X-ray diffraction profile was measured using Rigaku RINT2500V (Cr K?, 45 kV, 250 mA) with the step size of 0.02°. The Rietveld analysis was made using RIETAN-2000 program. The XRD profile showed that symmetry of the Mg2Al2O5 phase is orthorhombic. The extinction rules of the powder XRD peaks suggested the space group of Pba2 or Pbam. Since it was found that the XRD pattern is close to that of (Mg, Fe2+)2(Fe3+, Al)(BO3)O2 ludwigite, a structure model of the Mg2Al2O5 phase was constructed based on it. It should be noted that planner three coordinated sites in ludwigite in which boron places were moved by 0.5 in atomic coordinate along c-axis, because interatomic distances between cation and oxygen in the planner three coordinated sites are too short for Mg2+ and Al3+. In this structure model, (Mg, Al)O6 octahedra connected by edge-sharing and corner-sharing form triangular tunnels along c-axis. Cation sites occupied by only Mg are placed in the tunnels. The sites have a coordination environment of trigonal prism- type MgO6. By the Rietveld analysis, lattice parameters were determined as a = 9.3710(6) Å, b = 12.1952(6) Å, c = 2.7916(2) Å. The calculated density of 3.801(1) g/cm3 is consistent with the high-pressure phase relations. R factor by adopting the space group of Pbam is smaller than that by Pba2. Therefore, it is suggested that the space group of the Mg2Al2O5 phase is Pbam

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

2008-12-01

280

Optimizing amorphous indium zinc oxide film growth for low residual stress and high electrical conductivity  

NASA Astrophysics Data System (ADS)

With recent advances in flexible electronics, there is a growing need for transparent conductors with optimum conductivity tailored to the application and nearly zero residual stress to ensure mechanical reliability. Within amorphous transparent conducting oxide (TCO) systems, a variety of sputter growth parameters have been shown to separately impact film stress and optoelectronic properties due to the complex nature of the deposition process. We apply a statistical design of experiments (DOE) approach to identify growth parameter-material property relationships in amorphous indium zinc oxide (a-IZO) thin films and observed large, compressive residual stresses in films grown under conditions typically used for the deposition of highly conductive samples. Power, growth pressure, oxygen partial pressure, and RF power ratio (RF/(RF + DC)) were varied according to a full-factorial test matrix and each film was characterized. The resulting regression model and analysis of variance (ANOVA) revealed significant contributions to the residual stress from individual growth parameters as well as interactions of different growth parameters, but no conditions were found within the initial growth space that simultaneously produced low residual stress and high electrical conductivity. Extrapolation of the model results to lower oxygen partial pressures, combined with prior knowledge of conductivity-growth parameter relationships in the IZO system, allowed the selection of two promising growth conditions that were both empirically verified to achieve nearly zero residual stress and electrical conductivities >1480 S/cm. This work shows that a-IZO can be simultaneously optimized for high conductivity and low residual stress.

Kumar, Mukesh; Sigdel, A. K.; Gennett, T.; Berry, J. J.; Perkins, J. D.; Ginley, D. S.; Packard, C. E.

2013-10-01

281

27Al NMR and Raman spectroscopic studies of alkaline aluminate solutions with extremely high caustic content – Does the octahedral species Al(OH) 6 3? exist in solution?  

Microsoft Academic Search

27Al NMR and Raman spectra of alkaline aluminate solutions with 0.005M?[Al(III)]T?3M in various M?OH solutions (M?+=Na+, K+ and Li+) were recorded and analysed. Caustic concentrations up to 20M were used to explore whether higher aluminium hydroxo complexes are formed at extremely high concentrations of hydroxide. A single peak was observed on the 27Al NMR spectrum of each solution. The chemical

Pál Sipos; Glenn Hefter; Peter M. May

2006-01-01

282

High velocity oxy-fuel spraying of a NiCoCrAlY and an intermetallic NiAl?TaCr alloy  

Microsoft Academic Search

The high velocity oxy-fuel (HVOF) spray systems of the third generation can be used to process some oxidation sensitive materials such as MCrAlYs, due to possible lower melting degrees and higher kinetic energies of the powder particles. In the study presented here, a NiCoCrAlY and an intermetallic NiAl?TaCr were sprayed using the HVOF process. The influence of the spray parameters

Lidong Zhao; Erich Lugscheider

2002-01-01

283

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

284

ALS-Associated Ataxin 2 PolyQ Expansions Enhance Stress-Induced Caspase 3 Activation and Increase TDP-43 Pathological Modifications  

PubMed Central

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease caused by the loss of motor neurons. The degenerating motor neurons of ALS patients are characterized by the accumulation of cytoplasmic inclusions containing phosphorylated and truncated forms of the RNA-binding protein TDP-43. Ataxin 2 intermediate-length polyglutamine (polyQ) expansions were recently identified as a risk factor for ALS; however, the mechanism by which they contribute to disease is unknown. Here, we show that intermediate-length ataxin 2 polyQ expansions enhance stress-induced TDP-43 C-terminal cleavage and phosphorylation in human cells. We also connect intermediate-length ataxin 2 polyQ expansions to the stress-dependent activation of multiple caspases, including caspase 3. Caspase activation is upstream of TDP-43 cleavage and phosphorylation since caspase inhibitors block these pathological modifications. Analysis of the accumulation of activated caspase 3 in motor neurons revealed a striking association with ALS cases harboring ataxin 2 polyQ expansions. These findings indicate that activated caspase 3 defines a new pathological feature of ALS with intermediate-length ataxin 2 polyQ expansions. These results provide mechanistic insight into how ataxin 2 intermediate-length polyQ expansions could contribute to ALS—by enhancing stress-induced TDP-43 pathological modifications via caspase activation. Because longer ataxin 2 polyQ expansions are associated with a different disease, spinocerebellar ataxia 2, these findings help explain how different polyQ expansions in the same protein can have distinct cellular consequences, ultimately resulting in different clinical features. Finally, since caspase inhibitors are effective at reducing TDP-43 pathological modifications, this pathway could be pursued as a therapeutic target in ALS. PMID:22764223

Hart, Michael P.; Gitler, Aaron D.

2012-01-01

285

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

286

Mechanical alloying and high pressure processing of a TiAl-V intermetallic alloy.  

PubMed

An alloy with a chemical composition of Ti-45Al-5V (at.%) was synthesized by mechanical alloying in a Szegvari-type attritor from elemental powders of high purity. Before compaction, the powders were characterized by X-ray diffraction and scanning as well as transmission electron microscopy. The compaction of powders was carried out by hot isostatic pressing and hot isostatic extrusion. The resulting material was subjected to microstructural and mechanical characterization. The microstructure investigated by transmission and scanning electron microscopy supplemented by X-ray diffraction revealed that the bulk material was composed of a mixture of TiAl- and Ti(3)Al-based phases, however, the typical lamellar microstructure for such alloys was not observed. The materials exhibited exceptionally high yield strength together with satisfactory ductility and fracture toughness. The high strength was unequivocally due to grain refinement and the presence of oxide dispersoid. PMID:20500422

Dymek, S; Wróbel, M; Witczak, Z; Blicharski, M

2010-03-01

287

Complexity of physiological responses decreases in high-stress musical performance.  

PubMed

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

2013-12-01

288

Control of residual stresses affecting fatigue life of pulsed current gas-metal-arc weld of high-strength aluminum alloy  

Microsoft Academic Search

The influence of pulse parameters on residual stresses of the gas-metal-arc (GMA) weld of a 10-mm-thick extruded section of\\u000a high-strength Al-Zn-Mg alloy has been analyzed. The role of pulse parameters affecting the residual stresses of the weld joint\\u000a has been studied by considering a summarized influence of pulse parameters defined by a dimensionless factor ?=[(I\\u000a \\u000a b\\u000a \\/I\\u000a \\u000a p\\u000a ) ft

P. K. Ghosh; Aritra K. Ghosh

2004-01-01

289

High Temperature Hall sensors using AlGaN/GaN HEMT Structures  

NASA Astrophysics Data System (ADS)

Hall effect sensors are the most widely used magnetic sensors, and are commonly fabricated using narrow band-gap semiconductors such as InSb and GaAs. However, the operation of InSb and GaAs-based Hall sensors is unstable at elevated temperatures. Here, we exploited the fact that gallium nitride- (GaN) based wide band-gap (3.4eV) semiconductors have high breakdown electric field strength and are robust at elevated temperatures and tested the high temperature electrical characteristics of AlGaN/GaN heterostructure micro-Hall effect sensors with a two-dimensional electron gas (2DEG). The AlGaN/GaN heterostructures had an electron mobility of 1360 cm2/Vs and a 2DEG density of 1.0 × 1013 cm-2. The supply-current-related sensitivity (SCRS) was 77VA-1T-1 at room temperature. Notably, the temperature coefficient of the Hall voltage was +0.05 %/°C near room temperature, and SCRS was 67 VA-1T-1 at 400°C. The results for AlGaN/GaN were compared with those for AlGaAs/GaAs and AlInSb/InAsSb/AlInSb QW Hall effect sensors.

Koide, S.; Takahashi, H.; Abderrahmane, A.; Shibasaki, I.; Sandhu, A.

2012-03-01

290

Microstructure, mechanical properties, and high-temperature oxidation resistance of boronized {gamma}-TiAl(Mn)  

SciTech Connect

Titanium aluminide (TiAl) based intermetallic compounds are considered as potential materials for high-performance automobile and aircraft engine components and airframe applications because of their low density (3.8 g/cm{sup 3}), high melting temperature (1,480 C), and good elevated temperature strength retention. To improve the wear and high-temperature oxidation resistance of reactively sintered {gamma}-TiAl(Mn) intermetallic compounds, they were boronized in the temperature range of 900 to 1,100 C for 5 to 11 hours with powder mixtures of B{sub 4}C and Na{sub 2}B{sub 4}O{sub 7}. It was found that the coating layer consisted of three sublayers, i.e., outer, middle, and inner sublayers. The outer, middle, and inner sublayers were identified as a mixture of TiB{sub 2} and TiO{sub 2}, a mixture of Al{sub 2}O{sub 3} and TiO{sub 2}, and Ti-rich TiAl based compounds, respectively. The coating layer significantly improved the surface hardness and the wear and high-temperature oxidation resistances. The highest surface hardness (Hv {approx} 2,720) was obtained at 900 C for 11 hours. This surface hardness is much higher than that of TiAl(Mn) (Hv {approx} 400). In addition, the specimens boronized at both 1,000 and 1,050 C for 9 hours showed an excellent high-temperature oxidation resistance. It is believed that the boronizing on the TiAl(Mn) intermetallics is very effective to improve the wear and high-temperature oxidation resistances.

Kim, S.; Yoon, Y. [Inha Univ., Inchon (Korea, Republic of). Dept. of Metallurgical Engineering; Kim, H. [Inha Technical Coll., Inchon (Korea, Republic of). Dept. of Metallurgical Engineering; Park, K. [Chung-ju National Univ., Chungbuk (Korea, Republic of). Dept. of Materials Engineering

1997-12-31

291

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

292

Trap states in AlGaN channel high-electron-mobility transistors  

SciTech Connect

Frequency dependent capacitance and conductance measurements were performed to analyze the trap states in the AlGaN channel high-electron-mobility transistors (HEMTs). The trap state density in the AlGaN channel HEMTs decreases from 1.26?×?10{sup 13}?cm{sup ?2}eV{sup ?1} at the energy of 0.33?eV to 4.35?×?10{sup 11}?cm{sup ?2}eV{sup ?1} at 0.40?eV. Compared with GaN channel HEMTs, the trap states in the AlGaN channel HEMTs have deeper energy levels. The trap with deeper energy levels in the AlGaN channel HEMTs is another reason for the reduction of the reverse gate leakage current besides the higher Schottky barrier height.

Zhao, ShengLei; Zhang, Kai; Ha, Wei; Chen, YongHe; Zhang, Peng; Zhang, JinCheng; Hao, Yue, E-mail: yhao@xidian.edu.cn [Key Laboratory of Wide Band Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071 (China)] [Key Laboratory of Wide Band Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071 (China); Ma, XiaoHua, E-mail: xhma@xidian.edu.cn [Key Laboratory of Wide Band Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071 (China) [Key Laboratory of Wide Band Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071 (China); School of Advanced Materials and Nanotechnology, Xidian University, Xi'an 710071 (China)

2013-11-18

293

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

294

High temperature deformation behavior and mechanism of spray deposited Al-Fe-V-Si alloy  

Microsoft Academic Search

Al-8.5Fe-1.3V-1.7Si alloy was prepared by spray deposition and hot extrusion. The high temperature plastic deformation behavior of the spray deposited Al-8.5Fe-1.3V-1.7Si alloy was investigated in the strain rate range of 2.77 × 10?4?2.77 × 10?2s?1 and temperature range of 350–550 °C by Gleebe-1500 thermomechanical simulator. The mechanism of the high temperature plastic deformation of the alloys was studied by TEM

Yu-de XIAO; Wei WANG; Wen-xian LI

2007-01-01

295

Osmium Metal Studied under High Pressure and Nonhydrostatic Stress  

SciTech Connect

Interest in osmium as an ultra-incompressible material and as an analog for the behavior of iron at high pressure has inspired recent studies of its mechanical properties. We have measured elastic and plastic deformation of Os metal at high pressures using in situ high pressure x-ray diffraction in the radial geometry. We show that Os has the highest yield strength observed for any pure metal, supporting up to 10 GPa at a pressure of 26 GPa. Furthermore, our data indicate changes in the nonhydrostatic apparent c/a ratio and clear lattice preferred orientation effects at pressures above 15 GPa.

Weinberger,M.; Tolbert, S.; Kavner, A.

2008-01-01

296

High-temperature stability of {alpha}-Ta{sub 4}AlC{sub 3}  

SciTech Connect

Graphical abstract: In this study, stability of {alpha}-Ta{sub 4}AlC{sub 3} is investigated to test a hypothesized thermodynamically driven {alpha}-{beta} phase transformation. It is found that the {alpha} phase is stable up to 1600 {sup o}C, with impurities and point defects most likely increasing the stability of the {alpha}-Ta{sub 4}AlC{sub 3}. Highlights: {yields} Cold-pressed {alpha}-Ta{sub 4}AlC{sub 3} powders are annealed up to 1750 {sup o}C to test first-principles predictions of {alpha}-{beta} phase-stability reversal at 1600 {sup o}C. {yields} The {alpha}-Ta{sub 4}AlC{sub 3} samples are stable up to 1600 {sup o}C, with no indications of any {alpha}-{beta} transformation. {yields} Transmission electron microscopy shows zig-zag stacking sequence characteristic of {alpha}-Ta{sub 4}AlC{sub 3}, as well as tantalum oxide impurities. {yields} The XRD patterns suggest that defects such as vacancies or antisites may increase the stability of {alpha}-Ta{sub 4}AlC{sub 3}. -- Abstract: Cold-pressed {alpha}-Ta4AlC3 powders were annealed up to 1750 {sup o}C to test first-principles predictions of {alpha}-{beta} phase-stability reversal at 1600 {sup o}C. Up to 1600 {sup o}C, the {alpha}-Ta{sub 4}AlC{sub 3} samples were stable with no indications of any {alpha}-{beta} transformation, as shown by the strong characteristic X-ray diffraction peaks of {alpha}-Ta{sub 4}AlC{sub 3} and the zigzag stacking observed by transmission electron microscopy. These results show that, in this experimental situation, high temperature alone is not sufficient to cause the {alpha}-{beta} transformation.

Lane, Nina J., E-mail: lane@drexel.edu [Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104 (United States); Eklund, Per; Lu, Jun [Department of Physics, Chemistry and Biology (IFM), Linkoeping University, SE-581 83 Linkoeping (Sweden)] [Department of Physics, Chemistry and Biology (IFM), Linkoeping University, SE-581 83 Linkoeping (Sweden); Spencer, Charles B. [Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104 (United States)] [Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104 (United States); Hultman, Lars [Department of Physics, Chemistry and Biology (IFM), Linkoeping University, SE-581 83 Linkoeping (Sweden)] [Department of Physics, Chemistry and Biology (IFM), Linkoeping University, SE-581 83 Linkoeping (Sweden); Barsoum, Michel W. [Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104 (United States)] [Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104 (United States)

2011-07-15

297

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

298

Dislocation mechanism of high-temperature plastic deformation of Al–Cu–Fe and Al–Pd–Mn icosahedral quasicrystals  

Microsoft Academic Search

Microstructures in hot-impacted Al62.5Cu25Fe12.5 and Al70.4Pd21.2Mn8.4 icosahedral quasicrystals (IQCs) were studied by transmission electron microscopy (TEM). Densely distributed dislocations and stacking fault (SF) type contrast were observed for the first time in Al–Cu–Fe IQC. This result confirms that dislocation motion is an important deformation mechanism for Al–Cu–Fe IQC. Moving dislocations in quasicrystalline materials leave phason-type SFs behind. In situ TEM

Renhui Wang; Wenge Yang; Jianian Gui; Knut Urban

2000-01-01

299

Relation between the residual stresses and the high-temperature oxidation resistance of superalloys protected by plasma-sprayed coatings. II  

Microsoft Academic Search

Previous studies on the oxidation behavior of two superalloys, IN100 and CMSX2, protected by LPPS MCrAlYTa coatings, were the basis to relate the high-temperature oxidation resistance to the oxidation stresses. Details are given on the choice of the X-ray diffraction conditions and on the calculations of the crystallographic elastic constants of each phase studied. Dilatometric tests were used to determine

A. M. Huntz; J. L. Lebrun; A. Boumaza

1990-01-01

300

Perturbed angular correlation studies of uniaxial compressive stressed zinc, titanium, rutile, Ti2AlN, and Nb2AlC.  

PubMed

We use the perturbed angular correlation method with (111)In-(111)Cd probe atoms to in situ study the changes in the electric field gradient at room temperature of polycrystalline Ti(2)AlN and Nb(2)AlC, titanium and zinc, and rutile samples, as a function of cyclic uniaxial compressive loads. The load dependence of the quadrupole coupling constant ?Q was found to be large in titanium and zinc but small in Ti(2)AlN, Nb(2)AlC and rutile. Reversible and irreversible increases in the electric field gradient distribution widths were found under load and after releasing the load, respectively. Annihilation of dislocations, as well as elastic deformation, are considered to contribute to the reversible behavior. The irreversible response must be caused by a permanent increase in dislocation and point defect densities. The deformation induced broadening of the electric field gradient can be recovered by post-annealing of the deformed sample. PMID:24957211

Brüsewitz, C; Vetter, U; Hofsäss, H; Barsoum, M W

2014-07-23

301

Perturbed angular correlation studies of uniaxial compressive stressed zinc, titanium, rutile, Ti2AlN, and Nb2AlC  

NASA Astrophysics Data System (ADS)

We use the perturbed angular correlation method with 111In-111Cd probe atoms to in situ study the changes in the electric field gradient at room temperature of polycrystalline Ti2AlN and Nb2AlC, titanium and zinc, and rutile samples, as a function of cyclic uniaxial compressive loads. The load dependence of the quadrupole coupling constant ?Q was found to be large in titanium and zinc but small in Ti2AlN, Nb2AlC and rutile. Reversible and irreversible increases in the electric field gradient distribution widths were found under load and after releasing the load, respectively. Annihilation of dislocations, as well as elastic deformation, are considered to contribute to the reversible behavior. The irreversible response must be caused by a permanent increase in dislocation and point defect densities. The deformation induced broadening of the electric field gradient can be recovered by post-annealing of the deformed sample.

Brüsewitz, C.; Vetter, U.; Hofsäss, H.; Barsoum, M. W.

2014-07-01

302

Sulfide stress cracking of high-strength steels in laboratory and oilfield environments  

Microsoft Academic Search

The results of laboratory and field tests indicate that high-strength steels are resistant to sulfide stress cracking (SSC) under specified conditions of temperature and HâS concentration. The field behavior of these materials can be predicted, based on information gained from laboratory SSC tests. Stressed specimens of J-55, C-75, N-80, MOD N-80 SOO-95 P-100, SOO-125 SOO-140 V-150, and 410 stainless steel

R. D. Kane; J. B. Greer

1976-01-01

303

Optimal bound on high stresses occurring between stiff fibers with arbitrary shaped cross-sections  

Microsoft Academic Search

We consider high stresses in stiff-fiber reinforced materials, which increase rapidly as fibers approximate to one another. This paper presents the optimal blow-up rate of the stresses with respect to the distance between a pair of stiff fibers in R3. The blow-up result plays an important role in our understanding of low strengths of fiber-reinforced composites. Referring to a problem

KiHyun Yun

2009-01-01

304

A stress-induced, developmentally regulated, highly polymorphic protein family in Pisum sativum L  

Microsoft Academic Search

The expression of members of two closely related abscisic acid (ABA)-responsive pea protein families, ABR17 and ABR18 (ABA-responsive 17200-Mr and 18100-Mr, respectively), is developmentally, tissueand stress-specifically regulated. Two-dimensional polyacrylamide gel electrophoresis revealed a number of ABR polypeptides on fluorographs of immunoprecipitated translation products of mRNAs, depending on the tissue, stage of development or type of stress. High endogenous ABA, or

D. H. P. Barratt; J. A. Clark

1993-01-01

305

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

Microsoft Academic Search

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

George Boukouvalas; Kyriaki Gerozissis; Eirini Markaki; Efthimia Kitraki

2010-01-01

306

High School Students Whose Parents Did Not Attend College: Do Stressful Circumstances Relate to their Academic Success?  

E-print Network

Stress Do high school students with and without college-students with and without college-educated parents, stresscollege attainment between students with and without college-educated parents in this subsample, does stress

Morazes, Jennifer Lynne

2011-01-01

307

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

308

High temperature oxidation of Ni{sub 50}(Al,Be){sub 50}  

SciTech Connect

Effect of Be on high-temperature oxidation of NiAl was investigated. From 1 to 10% Be was substituted for Al on a 1 to 1 atomic basis. Oxidation experiments were conducted in pure oxygen. Exposure temperatures ranged from 800 to 1200 C for 16 hours. In addition to thermogravimetry, postexposure analysis involved SEM of intact scales, XRD, XPS, and Rutherford backscattering spectroscopy. At every temperature tested, the Be modified NiAl containing 1, 2, or 5 at.% Be exhibited lower weight gain and comparable or slower oxidation rates than the pure binary material. The surfaces of the Be modified specimens showed minimal topography, with no evidence of the usual transient alumina phases grown on binary NiAl in this temperature range. XRD and surface analysis showed the presence of layers of Al{sub 2}O{sub 3} and ternary oxide phases, primarily BeO*Al{sub 2}O{sub 3}. The growth of this complex scale apparently prevents growth of the transient alumina phases.

Hanrahan, R.J. Jr.; Butt, D.P.; Thoma, D.J.; Taylor, T.N.; Maggiore, C.J.

1996-12-31

309

Comparative study of etching high crystalline quality AlN and GaN  

NASA Astrophysics Data System (ADS)

High-quality AlN and GaN bulk crystals were etched in a KOH aqueous solution or a KOH/H2O2 mixture. As etched surfaces were characterized by scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray photoelectron spectroscopy (XPS). It was found that the N-polar surfaces had approximately 900 and 20 times higher etch rate than the III-polar surface for AlN and GaN, respectively. AlN had a higher total etch rate than GaN at the same condition. Hexagonal hillocks were observed on N-polar face with {10-1-1} boundary planes for both AlN and GaN, while metal polar surfaces remained smooth. Formation of aluminum oxide/hydroxide AlOx(OH)y was confirmed by XPS on as etched N polar AlN surface; the addition of H2O2 resulted in a higher total surface oxygen concentration. The smoothening effect by adding H2O2 oxidizer was explained by the formation and dissolution of aluminum oxide/hydroxide.

Guo, W.; Xie, J.; Akouala, C.; Mita, S.; Rice, A.; Tweedie, J.; Bryan, I.; Collazo, R.; Sitar, Z.

2013-03-01

310

Chronic unpredictable mild stress combined with a high-fat diets aggravates atherosclerosis in rats  

PubMed Central

Background Depression and high-fat diet are both known as independent risk factors for atherosclerosis and other cardiovascular diseases, suggesting the interaction of psychological and physiological factors in the development of these diseases. The liver is a crucial organ that facilitate lipid metabolism especially in reverse cholesterol transport (RCT), while according to the theory of Traditional Chinese Medicine, depression as a kind of psychological stress has an influence on hepatic function. So there seem to be some links between depression and lipid metabolic disorders. Methods To investigate these links, we separately treated rats with chronic unpredictable mild stress (CMS) and/or a high-fat diet (HD) to evaluate the development of atherosclerosis and the expression of hepatic ABCG8, ABCG5, SR-BI, CYP7A1, LXR?, and LCAT which were associated with reverse cholesterol transport. Results This study provided evidence that high-fat diet greatly decreased these genes expression related to RCT while chronic stress alone tended to promote RCT. Chronic unpredictable mild stress combined with a high-fat diet attenuated RCT and aggravated atherogenesis. Conclusions These observations suggested that chronic psychological stress alone is virtually propitious to lipid metabolism, however when under a condition of high-fat diet, it deteriorated atherosclerotic plague and did harm to RCT. PMID:24885743

2014-01-01

311

Report on the Workshop Fornax, Virgo, Coma et al.: Stellar Systems in High Density Environments  

NASA Astrophysics Data System (ADS)

The workshop focused on recent observational progress in the understanding of stellar systems in the nearby clusters Fornax, Virgo, Coma et al. and provided a forum for comparing the results from theory and observations on galaxy evolution in high density environments at redshift zero.

Arnaboldi, M.

2011-12-01

312

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

313

High-Strength Weldable Alloy 1970 Based on the Al - Zn - Mg System  

Microsoft Academic Search

In the 1980s researchers of the All-Russia Institute of Light Alloys and the “Komposit” Research and Production Association developed a high-strength weldable corrosion-resistant alloy based on the Al - Zn - Mg - Cu - Sc - Zr system. The alloy was graded 1970 and used for fabricating pilot batches of sheets, plates, sections, and pressed preforms. Results of studies

V. V. Zakharov; T. D. Rostova

2005-01-01

314

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

315

High-performance AlGaN/GaN High-electron-mobility transistors employing H2O annealing  

NASA Astrophysics Data System (ADS)

We have proposed and fabricated high performance AlGaN/GaN high-electron-mobility transistors (HEMTs), of which the breakdown voltage is considerably high and the leakage current is efficiently suppressed employing H2O annealing. We also investigated the effects of H2O annealing on the formation of GaOx film on the surface of AlGaN/GaN HEMT as well as reverse blocking characteristics including the breakdown voltage and the leakage current. We compared the reverse blocking characteristics of the AlGaN/GaN HEMTs fabricated by the proposed H2O annealing treatment with those of the HEMT by widely used O2 annealing method. Also, we investigated the reverse blocking characteristics of HEMT fabricated without any annealing treatment. We used the smaller molecular size, higher permeation probability, and the lower activation energy of H2O than O2. The breakdown voltage of AlGaN/GaN HEMT with the LGD of 20 ?m employing H2O and O2 annealing was 1674 and 1512 V, respectively. The drain leakage current of these devices using H2O and O2 annealing was 13.1 and 60.1 nA/mm under VDS of 100 V and VGS of -10 V, respectively. A conventional device without any annealing process exhibited the breakdown voltage of 598 V and the leakage current of 666.0 ?A/mm. In order to investigate the amounts of deep traps in the interface of AlGaN/GaN HEMT, we measured the pulsed I-V. A low drain current of the device under pulsed bias indicated that the GaOx, which was formed by H2O annealing, induced the deeper level and longer emission time of traps compared to the shallow ones. These may be related to the surface leakage current in the AlGaN/GaN HEMTs.

Ahn, Woojin; Seok, Ogyun; Song, Seung Min; Han, Min-Koo; Ha, Min-Woo

2013-09-01

316

High-performance AlGaInP tunneling heterostructure-emitter bipolar transistor  

NASA Astrophysics Data System (ADS)

In this paper, a high-performance heterostructure-emitter bipolar transistor employing an AlGaInP quaternary compound tunneling layer is fabricated and demonstrated. In the studied device, a 50 Å n-AlGaInP tunneling emitter layer together with a 200 Å n-GaAs layer forms the heterostructure emitter to decrease the collector-emitter offset voltage. On the other hand, due to the relatively large valence band discontinuity (?0.4 eV) at AlGaInP/GaAs heterojunction and the small hole transmission coefficient across the AlGaInP tunneling layer, most of holes injecting from base to emitter will be blocked at AlGaInP/GaAs heterojunction and then high collector current and current gain are achieved. The experimental results exhibit a large collector current of 92 mA, a large current gain of 446, and a relatively low offset voltage of only 45 mV, respectively. Furthermore, a large current-gain cutoff frequency ft up to 63.7 GHz is obtained for the device with a thin tunneling layer.

Tsai, Jung-Hui

2014-11-01

317

AlGaN Ultraviolet A and Ultraviolet C Photodetectors with Very High Specific Detectivity D*  

NASA Astrophysics Data System (ADS)

The development of AlGaN pin photodetectors sensitive in the UV range with different narrow band active regions is reported in this paper. Structures were grown by metalorganic vapor phase epitaxy on (0001) sapphire substrates using three-dimensional GaN as well as high temperature AlN nucleation. Very high specific detectivities of 1×1014 cm Hz0.5 W-1 can be achieved based on optimized growth conditions of undoped and doped AlGaN layers with an Al-content ranging from 0% up to 100%. The crack-free AlGaN layers have edge dislocation densities in the range of 5×109 cm-2. Based on the two different nucleation types, pin layer structures were grown and fabricated to UV-A (320 to 365 nm) and UV-C (< 280 nm) photodetectors. The electro-optical performance of these photodetectors measured on-wafer will be presented in this paper, supplemented by the data of a single photodetector chip mounted in a TO 18 package.

Albrecht, Björn; Kopta, Susanne; John, Oliver; Kirste, Lutz; Driad, Rachid; Köhler, Klaus; Walther, Martin; Ambacher, Oliver

2013-08-01

318

AlGaN-based high-performance metal semiconductor metal photodetectors  

NASA Astrophysics Data System (ADS)

Design, structure growth, fabrication, and characterization of high performance AlGaN-based metal-semiconductor-metal (MSM) photodetectors (PD) are reported. By incorporating AlN nucleation and buffer layers, the leakage current density of GaN MSM PD was reduced to 1.96 × 10 -10 A/cm 2 at a 50 V bias, which is four orders of magnitude lower compared to control devices. A 229 nm cut-off wavelength, a peak responsivity of 0.53 A/W at 222 nm, and seven orders of magnitude visible rejection was obtained from Al 0.75Ga 0.25N MSM PD. Two-color monolithic AlGaN MSM PD with excellent dark current characteristics were demonstrated, where both detectors reject the other detector spectral band with more than three orders of magnitude. High-speed measurements of Al 0.38Ga 0.62N MSM PD resulted in fast responses with greater than gigahertz bandwidths, where the fastest devices had a 3-dB bandwidth of 5.4 GHz.

Gökkavas, Mutlu; Butun, Serkan; Tut, Turgut; Biyikli, Necmi; Ozbay, Ekmel

2007-10-01

319

High performance AlScN thin film based surface acoustic wave devices with large electromechanical coupling coefficient  

NASA Astrophysics Data System (ADS)

AlN and AlScN thin films with 27% scandium (Sc) were synthesized by DC magnetron sputtering deposition and used to fabricate surface acoustic wave (SAW) devices. Compared with AlN-based devices, the AlScN SAW devices exhibit much better transmission properties. Scandium doping results in electromechanical coupling coefficient, K2, in the range of 2.0% ˜ 2.2% for a wide normalized thickness range, more than a 300% increase compared to that of AlN-based SAW devices, thus demonstrating the potential applications of AlScN in high frequency resonators, sensors, and high efficiency energy harvesting devices. The coupling coefficients of the present AlScN based SAW devices are much higher than that of the theoretical calculation based on some assumptions for AlScN piezoelectric material properties, implying there is a need for in-depth investigations on the material properties of AlScN.

Wang, Wenbo; Mayrhofer, Patrick M.; He, Xingli; Gillinger, Manuel; Ye, Zhi; Wang, Xiaozhi; Bittner, Achim; Schmid, Ulrich; Luo, J. K.

2014-09-01

320

Acute Stress Induces Hyperacusis in Women with High Levels of Emotional Exhaustion  

PubMed Central

Background Hearing problems is one of the top ten public health disorders in the general population and there is a well-established relationship between stress and hearing problems. The aim of the present study was to explore if an acute stress will increase auditory sensitivity (hyperacusis) in individuals with high levels of emotional exhaustion (EE). Methods Hyperacusis was assessed using uncomfortable loudness levels (ULL) in 348 individuals (140 men; 208 women; age 23–71 years). Multivariate analyses (ordered logistic regression), were used to calculate odds ratios, including interacting or confounding effects of age, gender, ear wax and hearing loss (PTA). Two-way ANCOVAs were used to assess possible differences in mean ULLs between EE groups pre- and post-acute stress task (a combination of cold pressor, emotional Stroop and Social stress/video recording). Results There were no baseline differences in mean ULLs between the three EE groups (one-way ANOVA). However, after the acute stress exposure there were significant differences in ULL means between the EE-groups in women. Post-hoc analyses showed that the differences in mean ULLs were between those with high vs. low EE (range 5.5–6.5 dB). Similar results were found for frequencies 0.5 and 1 kHz. The results demonstrate that women with high EE-levels display hyperacusis after an acute stress task. The odds of having hyperacusis were 2.5 (2 kHz, right ear; left ns) and 2.2 (4 kHz, right ear; left ns) times higher among those with high EE compared to those with low levels. All these results are adjusted for age, hearing loss and ear wax. Conclusion Women with high levels of emotional exhaustion become more sensitive to sound after an acute stress task. This novel finding highlights the importance of including emotional exhaustion in the diagnosis and treatment of hearing problems. PMID:23301005

Hasson, Dan; Theorell, Tores; Bergquist, Jonas; Canlon, Barbara

2013-01-01

321

High temperature performance of low stress electrically conductive adhesives in electronic applications  

Microsoft Academic Search

The electronics industry has shown an increased interest in low stress, flexible, electrically conductive adhesives for harsh environment applications. These include the assembly of materials with large CTE mismatches or high peel strength requirements for 3D-MID and flexible substrate technologies. Depending on the application requirements different flexible conductive adhesives can be considered. Recent product development has focused on highly conductive,

G. Dreezen; L. Theunissen; G. Luyckx; P. Dooling; A. Borak

2008-01-01

322

Fabrication of highly conductive stressed-metal springs and their use as sliding-contact interconnects  

Microsoft Academic Search

Stressed-metal springs with small dimensions and high compliance have been demonstrated as alternative to wire bonds and flip-chip solder bumps. For higher spring conductivity and increased wear resistance, additional spring coatings are highly desired. Therefore, we have developed plating procedures which allow us to coat springs with thick and uniform metal films. This paper presents springs plated with gold, copper

T. Hantschel; L. Wong; C. L. Chua; D. K. Fork

2003-01-01

323

Osmium Metal Studied under High Pressure and Nonhydrostatic Stress Michelle B. Weinberger,1,  

E-print Network

Osmium Metal Studied under High Pressure and Nonhydrostatic Stress Michelle B. Weinberger,1, Sarah) Interest in osmium as an ultra-incompressible material and as an analog for the behavior of iron at high with other mechanical properties, particularly bulk modulus, have resulted in significant interest in osmium

Tolbert, Sarah

324

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

Microsoft Academic Search

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

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

2002-01-01

325

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

326

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

327

Highly Precise Quantification of Protein Molecules per Cell During Stress and Starvation Responses in Bacillus subtilis.  

PubMed

Systems biology based on high quality absolute quantification data, which are mandatory for the simulation of biological processes, successively becomes important for life sciences. We provide protein concentrations on the level of molecules per cell for more than 700 cytosolic proteins of the Gram-positive model bacterium Bacillus subtilis during adaptation to changing growth conditions. As glucose starvation and heat stress are typical challenges in B. subtilis' natural environment and induce both, specific and general stress and starvation proteins, these conditions were selected as models for starvation and stress responses. Analyzing samples from numerous time points along the bacterial growth curve yielded reliable and physiologically relevant data suitable for modeling of cellular regulation under altered growth conditions. The analysis of the adaptational processes based on protein molecules per cell revealed stress-specific modulation of general adaptive responses in terms of protein amount and proteome composition. Furthermore, analysis of protein repartition during glucose starvation showed that biomass seems to be redistributed from proteins involved in amino acid biosynthesis to enzymes of the central carbon metabolism. In contrast, during heat stress most resources of the cell, namely those from amino acid synthetic pathways, are used to increase the amount of chaperones and proteases. Analysis of dynamical aspects of protein synthesis during heat stress adaptation revealed, that these proteins make up almost 30% of the protein mass accumulated during early phases of this stress. PMID:24878497

Maa?, Sandra; Wachlin, Gerhild; Bernhardt, Jörg; Eymann, Christine; Fromion, Vincent; Riedel, Katharina; Becher, Dörte; Hecker, Michael

2014-09-01

328

Residual Stresses in High-Velocity Oxy-Fuel Metallic Coatings  

SciTech Connect

X-ray based residual stress measurements were made on type 316 stainless steel and Fe3A1 coatings that were high-velocity oxy-fuel (HVOF) sprayed onto low-carbon and stainless steel substrates. Nominal coating thicknesses varied from 250 to 1500 mm. 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. Difference in thermal expansion coefficient between low-carbon and stainless steels led to a 180 MPa difference in residual stress for Fe3A1 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.

Terry C. Totemeier; Richard N. Wright; W. David Swank

2004-06-01

329

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

Microsoft Academic Search

A ring-cutting test and an elastic theory were applied to evaluate the macroscopic residual stress in a thick-walled ring\\u000a made of Al-SiC functionally graded material (FGM). The FGM ring specimens, with outer diameter 90 mm, radial thickness approximately\\u000a 8.4 to 10 mm, and width 30 mm, were fabricated by the centrifugal casting method from an ingot of Duralcan F3D.20S of

Yasuyoshi Fukui; Yoshimi Watanabe

1996-01-01

330

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

331

Combined effects of weld-induced residual stresses and flaws on the fracture strength of Ti-5Al-2.5Sn  

NASA Technical Reports Server (NTRS)

The combined effects of weld-induced residual stresses and flaws on fracture strength were experimentally evaluated by testing Ti-5Al-2.5Sn surface flawed specimens at -320F (-195C) in liquid nitrogen. Flaws were located in weld metal with crack planes either parallel to or perpendicular to gas tungsten arc weld centerlines, and in base metal with the crack plane perpendicular to the rolling direction. Tests were conducted using two different flaw sizes to effect fracture stresses at two different levels including one level either at or near, and one level well below the tensile yield strength. Three different residual stress levels were generated, measured, and tested. Results were evaluated using modified linear elastic fracture mechanics theory.

Hall, L. R.

1973-01-01

332

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

333

High-Power 625-nm AlGaInP Laser Diode  

Microsoft Academic Search

Highly efficient quantum well laser diode is promising as a red light source for laser display. In the wavelength range of red light, short lasing wavelength is preferred because spectral luminous efficiency increases sharply as wavelength shortens. In this paper, we present high-power AlGaInP laser diode with remarkably short lasing wavelength of 625 nm. The fabricated device showed 220 mW

Naoyuki Shimada; Akihito Ohno; Shinji Abe; Motoharu Miyashita; Tetsuya Yagi

2011-01-01

334

Short-red-wavelength, high-power, AlGaInP laser diodes  

Microsoft Academic Search

AlGaInP-based, high power laser diodes operating at wavelengths of 630 to 645 nm have been designed, fabricated, and characterized. Cw output powers approaching 1 Watt and thresholds below 400 A\\/cm2 have been achieved. Measurement of internal laser parameters indicates low internal loss and transparency current, high gain, and moderate internal quantum efficiency. Characteristic temperature data suggest that the lowest practical

Harvey B. Serreze; Ying-Chih Chen

1993-01-01

335

High-power continuous wave 690 nm AlGaInP laser-diode arrays  

Microsoft Academic Search

High-power diode laser arrays emitting at 690 nm have been developed for solid-state laser pumping. The laser diode bars (fill factor [approx]0.7) have been fabricated from single quantum well AlGaInP-based heterostructures. Using silicon microchannel heatsinks, a record high 360 W\\/cm[sup 2] per emitting aperture is achieved under continuous wave operation.

J. A. Skidmore; M. A. Emanuel; R. J. Beach; W. J. Benett; B. L. Freitas; N. W. Carlson; R. W. Solarz

1995-01-01

336

Drain resistance degradation under high fields in AlInAs\\/GaInAs MODFETs  

Microsoft Academic Search

Lattice-matched AlInAs\\/GaInAs modulation-doped FETs (MODFETs) demonstrate excellent high-frequency, small-signal performance. However, high-power, large-signal applications of these devices may be limited. Impact ionization and tunneling reduce the breakdown voltage, which limits the upper end of the output voltage swing, thus reducing the output power. Our results indicate that the lower end of the voltage swing (knee voltage) is also degraded by

A. S. Wakita; H. Rohdin; C.-Y. Su; N. Moll; A. Nagy; V. M. Robbins

1997-01-01

337

Feasibility study of Nb3Al Rutherford cable for high field accelerator magnet application  

SciTech Connect

Feasibility study of Cu stabilized Nb{sub 3}Al strand and Rutherford cable for the application to high field accelerator magnets are being done at Fermilab in collaboration with NIMS. The Nb{sub 3}Al strand, which was developed and manufactured at NIMS in Japan, has a non-copper Jc of about 844 A/mm{sup 2} at 15 Tesla at 4.2 K, a copper content of 50%, and filament size of about 50 microns. Rutherford cables with 27 Nb{sub 3}Al strands of 1.03 mm diameter were fabricated and tested. Quench tests on a short cable were done to study its stability with only its self field, utilizing a high current transformer. A pair of 2 meter long Nb{sub 3}Al cables was tested extensively at CERN at 4.3 and 1.9 K up to 11 Tesla including its self field with a high transport current of 20.2 kA. In the low field test we observed instability near splices and in the central region. This is related to the flux-jump like behavior, because of excessive amount of Nb in the Nb{sub 3}Al strand. There is possibility that the Nb in Nb{sub 3}Al can cause instability below 2 Tesla field regions. We need further investigation on this problem. Above 8 Tesla, we observed quenches near the critical surface at fast ramp rate from 1000 to 3000 A/sec, with quench velocity over 100 m/sec. A small racetrack magnet was made using a 14 m of Rutherford cable and successfully tested up to 21.8 kA, corresponding to 8.7 T.

Yamada, R.; /Fermilab; Kikuchi, A.; /Tsukuba Magnet Lab.; Ambrosio, G.; Andreev, N.; Barzi, E.; Cooper, C.; Feher, S.; Kashikhin, V.V.; Lamm, M.; Novitski, I.; /Fermilab; Takeuchi, T.; /Tsukuba Magnet Lab.; Tartaglia, M.; Turrioni, D.; /Fermilab; Verweij, A.P.; /CERN; Wake, M.; Willering, G; /Tsukuba Magnet Lab.; Zlobin, A.V.; /Fermilab

2006-08-01

338

Water Transport Properties of Roots and Root Cortical Cells in Proton- and Al-Stressed Maize Varieties.  

PubMed Central

Root and root cell pressure-probe techniques were used to investigate the possible relationship between Al- or H+-induced alterations of the hydraulic conductivity of root cells (LPc) and whole-root water conductivity (LPr) in maize (Zea mays L.) plants. To distinguish between H+ and Al effects two varieties that differ in H+ and Al tolerance were assayed. Based on root elongation rates after 24 h in nutrient solution of pH 6.0, pH 4.5, or pH 4.5 plus 50 [mu]M Al, the variety Adour 250 was found to be H+-sensitive and Al-tolerant, whereas the variety BR 201 F was found to be H+-tolerant but Al-sensitive. No Al-induced decrease of root pressure and root cell turgor was observed in Al-sensitive BR 201 F, indicating that Al toxicity did not cause a general breakdown of membrane integrity and that ion pumping to the stele was maintained. Al reduced LPc more than LPr in Al-sensitive BR 201 F. Proton toxicity in Adour 250 affected LPr more than LPc. In this Al-tolerant variety LPc was increased by Al. Nevertheless, this positive effect on LPc did not render higher LPr values. In conclusion, there were no direct relationships between Al- or H+-induced decreases of LPr and the effects on LPc. To our knowledge, this is the first time that the influence of H+ and Al on root and root cell water relations has been directly measured by pressure-probe techniques. PMID:12223628

Gunse, B.; Poschenrieder, C.; Barcelo, J.

1997-01-01

339

227-261 nm AlGaN-based Deep Ultraviolet Light-emitting Diodes Fabricated on High-quality AlN Buffer on Sapphire  

NASA Astrophysics Data System (ADS)

We demonstrated AlGaN multi-quantum well (MQW) deep ultraviolet (UV) light-emitting diodes (LEDs) with wavelength in the range of 227-261 nm fabricated on high-quality AlN buffers on sapphire substrates. We achieved crack-free, thick AlN buffer on sapphire with low threading dislocation density (TDD) and atomically flat surface by introducing an ammonia (NH3) pulse-flow multi-layer (ML) growth method through metal-organic chemical vapor deposition (MOCVD). The edge- and screw-type dislocation densities of AlGaN layer on AlN buffer were reduced to 7.5×108 and 3.8×107 cm-2, respectively, by using a ML-AlN buffer. We achieved single-peaked high-brightness operations of AlGaN deep-UV LEDs by fabricating them on the ML-AlN buffers on sapphire substrates. The maximum output power and external quantum efficiency (EQE) of the 261 nm and 227.5 nm LEDs were 1.65 mW and 0.23% under room-temperature (RT) CW operation, and 0.15 mW and 0.2%, under RT pulsed operation, respectively.

Hirayama, Hideki; Yatabe, Tohru; Noguchi, Norimichi; Kamata, Norihiko

340

Solid state amorphization in the Al-Fe binary system during high energy milling  

NASA Astrophysics Data System (ADS)

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 Al5Fe2.

Urban, P.; Cuevas, F. G.; Montes, J. M.; Cintas, J.

2013-12-01

341

B2 structure of high-entropy alloys with addition of Al  

SciTech Connect

A series of AlCrCoNiFe based alloys with equal percentage of principal components (high-entropy alloys or HE alloys) is fabricated. The related crystalline structures of the alloys are measured and calculated. Results show that the formed bcc phase is a compound based B2 structure where there is partial ionic bonding between Al and other transition metals. Thus, the bcc structure of the alloys should be a B2 instead of an A2 due to the large difference in electronegativities among the components consisting of the HE alloys.

Li, C.; Zhao, M.; Li, J. C.; Jiang, Q. [Key Laboratory of Automobile Materials, Jilin University, Changchun 130022 (China); Ministry of Education (China) and Department of Materials Science and Engineering, Jilin University, Changchun 130022 (China)

2008-12-01

342

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

343

Bacillus pumilus reveals a remarkably high resistance to hydrogen peroxide provoked oxidative stress.  

PubMed

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

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

2014-01-01

344

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

PubMed Central

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

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

2014-01-01

345

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

346

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

PubMed

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. PMID:24494239

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

2013-10-01

347

Highly cooperative stress relaxation in two-dimensional soft colloidal crystals.  

PubMed

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

2014-10-28

348

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

PubMed

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

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

2011-04-01

349

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

PubMed

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

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

2014-04-10

350

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

PubMed

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

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

2014-04-01

351

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

352

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

353

Effect of chronic mild stress on hippocampal transcriptome in mice selected for high and low stress-induced analgesia and displaying different emotional behaviors  

Microsoft Academic Search

There is increasing evidence that mood disorders may derive from the impact of environmental pressure on genetically susceptible individuals. Stress-induced hippocampal plasticity has been implicated in depression. We studied hippocampal transcriptomes in strains of mice that display high (HA) and low (LA) swim stress-induced analgesia and that differ in emotional behaviors and responses to different classes of antidepressants. Chronic mild

Pawel Lisowski; Grzegorz R. Juszczak; Joanna Goscik; Marek Wieczorek; Lech Zwierzchowski; Artur H. Swiergiel

2011-01-01

354

High Temperature Oxidation and Microstructural Evolution of Modified MCrAlY Coatings  

NASA Astrophysics Data System (ADS)

Thermal sprayed MCrAlY coatings are widely used as a bond coat in thermal barrier systems to protect the substrate from corrosion and high temperature oxidation and to improve the compatibility between the ceramic top coat and metallic substrate. In this paper, the high temperature oxidation resistance of MCrAlY coatings with modified compositions was evaluated; in particular, the effect of the addition of reactive and refractory elements (Ta, Re, Si, and Hf) was investigated. MCrAlY coatings were obtained by high velocity oxygen fuel spray and vacuum plasma spray techniques; samples were exposed to air at 1423 K (1150 °C) and the oxidation kinetics were evaluated by measuring the thickness of the thermally grown oxide (TGO) scale at several exposure times. Experimental data confirmed that the oxidation resistance of MCrAlY coatings is strictly related to the amount of the reactive and refractory elements in the starting powders and that a thorough understanding of the microstructural modifications taking place during oxidation is essential for controlling TGO growth and thermal barriers' durability.

Pulci, Giovanni; Tirillò, Jacopo; Marra, Francesco; Sarasini, Fabrizio; Bellucci, Alessandra; Valente, Teodoro; Bartuli, Cecilia

2013-11-01

355

Starbursts and high-redshift galaxies are radioactive: high abundances of 26Al and other short-lived radionuclides  

NASA Astrophysics Data System (ADS)

Short-lived radionuclides (SLRs) like 26Al are synthesized by massive stars and are a byproduct of star formation. The abundances of SLRs in the gas of a star-forming galaxy are inversely proportional to the gas consumption time. The rapid evolution of specific star formation rate (SSFR) of normal galaxies implies they had mean SLR abundances ˜3-10 times higher at z = 2. During the epoch of Solar system formation, the background SLR abundances of the Galaxy were up to twice as high as at present, if SLR yields from massive stars do not depend on metallicity. If SLRs are homogenized in the gas of galaxies, the high SSFRs of normal galaxies can partly explain the elevated abundance of SLRs like 60Fe and 26Al in the early Solar system. Starburst galaxies have much higher SSFRs still, and have enormous mean abundances of 26Al (26Al/27Al ?10-3 for solar metallicity gas). The main uncertainty is whether the SLRs are mixed with the star-forming molecular gas: they could be trapped in hot gas and decay before entering the colder phases, or be blown out by starburst winds. I consider how variability in star formation rate affects the SLR abundances, and I discuss how SLR transport may differ in these galaxies. The enhanced 26Al of starbursts might maintain moderate ionization rates (10-18-10-17 s-1), possibly dominating ionization in dense clouds not penetrated by cosmic rays. Similar ionization rates would be maintained in protoplanetary discs of starbursts, if the SLRs are well mixed, and the radiogenic heating of planetesimals would likewise be much higher. In this way, galaxy evolution can affect the geological history of planetary systems.

Lacki, Brian C.

2014-06-01

356

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

357

High Density Hydrogen Storage System Demonstration Using NaAlH4 Based Complex Compound Hydrides  

SciTech Connect

This final report describes the motivations, activities and results of the hydrogen storage independent project "High Density Hydrogen Storage System Demonstration Using NaAlH4 Based Complex Compound Hydrides" performed by the United Technologies Research Center under the Department of Energy Hydrogen Program, contract # DE-FC36-02AL67610. The objectives of the project were to identify and address the key systems technologies associated with applying complex hydride materials, particularly ones which differ from those for conventional metal hydride based storage. This involved the design, fabrication and testing of two prototype systems based on the hydrogen storage material NaAlH4. Safety testing, catalysis studies, heat exchanger optimization, reaction kinetics modeling, thermochemical finite element analysis, powder densification development and material neutralization were elements included in the effort.

Daniel A. Mosher; Xia Tang; Ronald J. Brown; Sarah Arsenault; Salvatore Saitta; Bruce L. Laube; Robert H. Dold; Donald L. Anton

2007-07-27

358

The triclinic high temperature modification of the {alpha} phase of the Zn-Al system  

SciTech Connect

The structure of the {beta} phase of the Zn-Al system was reinvestigated. The X-ray diffraction (XRD) pattern of the Zn-21.0wt%Al after 9 h at 350 C clearly showed the splitting of some Bragg peaks. The triclinic structure permits a description of the spectra with a = 285.857, b = 285.283, c = 285.847 pm, {alpha} = 59.602{degree}, {beta} = 59.869{degree}, {gamma} = 59,716{degree}. This structure corresponds to a small distortion of the primitive R cell of the high temperature fcc solid solution {alpha}-(Al) when the Zn content reaches about 69.5 wt% at 350 C.

Sandoval-Jimenez, A.; Negrete, J.; Torres-Villasenor, G.

1999-12-01

359

Botulinum toxin detection using AlGaN /GaN high electron mobility transistors  

NASA Astrophysics Data System (ADS)

Antibody-functionalized, Au-gated AlGaN /GaN high electron mobility transistors (HEMTs) were used to detect botulinum toxin. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN /GaN HEMT drain-source current showed a rapid response of less than 5s when the target toxin in a buffer was added to the antibody-immobilized surface. We could detect a range of concentrations from 1to10ng/ml. These results clearly demonstrate the promise of field-deployable electronic biological sensors based on AlGaN /GaN HEMTs for botulinum toxin detection.

Wang, Yu-Lin; Chu, B. H.; Chen, K. H.; Chang, C. Y.; Lele, T. P.; Tseng, Y.; Pearton, S. J.; Ramage, J.; Hooten, D.; Dabiran, A.; Chow, P. P.; Ren, F.

2008-12-01

360

A new type of Cu-Al-Ta shape memory alloy with high martensitic transformation temperature  

NASA Astrophysics Data System (ADS)

In this study, a new type of Cu-Al-Ta (Cu86Al12Ta2 wt%) shape memory alloy with high martensitic transformation temperature is explored. The microstructure, reversible martensitic transformation and shape memory properties are investigated by means of optical microscopy, back-scattered electron, electron probe microanalysis, x-ray diffraction, differential scanning calorimetry and tensile tests. It is proposed that Cu86Al12Ta2 alloy consists of a mixture of primarily {\\beta }_{1}^{\\prime} martensite and a little {\\gamma }_{1}^{\\prime} martensite and some different precipitates. The tiny thin-striped Ta2(Al,Cu)3 precipitate is predominant in the as-quenched condition, whereas the particle-shaped Cu(Al, Ta) precipitate is dominant after hot-rolling. Additionally, the dendritic-shaped ?1(Cu9Al4) phase begins to appear after hot-rolling, but it disappears when the sample is re-quenched. All studied samples have reversible martensitic transformation temperatures higher than 450?° C. The results show that two-step martensitic transformation behavior is observed for Cu86Al12Ta2 alloy in all three different conditions due to the transformations between ({\\beta }_{1}^{\\prime}+{\\gamma }_{1}^{\\prime}) martensites and the austenite parent phase. The results further show that the recovery ratios are almost 100% when the pre-strains are ?2.5%, then they gradually decrease with further increase of the pre-strains. The shape memory effects clearly increase as a result of increase of the pre-strains, up to a maximum value of 3.2%.

Wang, C. P.; Su, Y.; Y Yang, S.; Shi, Z.; Liu, X. J.

2014-02-01

361

Reactive wetting of molten Al on different oriented ?-Al 2O 3 single crystals at high temperatures  

Microsoft Academic Search

The reactive wetting of molten Al on three different oriented ?-Al2O3 single crystals, R(011?2), A(112?0) and C(0001), was investigated by an improved sessile drop method at temperatures between 1350 and 1500 °C in a reduced Ar–3%H2 atmosphere. The wettability is in the order of R>A>C. The spreading is reaction-limited and the rate is dominated by the change in the solid–liquid

Ping Shen; Hidetoshi Fujii; Taihei Matsumoto; Kiyoshi Nogi

2003-01-01

362

Phase Diagrams of High-Entropy Alloy System Al-Co-Cr-Fe-Mo-Ni  

NASA Astrophysics Data System (ADS)

The high-entropy alloy system Al-Co-Cr-Fe-Mo-Ni has been previously designed based on the Al x CoCrCuFeNi system and was demonstrated to have great improvements in toughness at high hardness level and in softening resistance at elevated temperatures. For this promising system, it is important to have phase diagrams for further efficient alloy design and research. The current study combines the results from scanning electron microscopy, transmission electron microscopy, room-temperature and high-temperature x-ray diffractometry, and differential thermal analysis to construct approximate phase diagrams by varying the content of each composing element. Thermodynamic calculation in considering both mixing enthalpy and entropy was also used to justify the simple phase fields in these phase diagrams.

Hsu, Chin-You; Juan, Chien-Chang; Chen, Shin-Tsung; Sheu, Tsing-Shien; Yeh, Jien-Wei; Chen, Swe-Kai

2013-12-01

363

Low Cost Al-Si Casting Alloy As In-Situ Composite for High Temperature Applications  

NASA Technical Reports Server (NTRS)

A new aluminum-silicon (Al-Si) alloy has been successfully developed at NASA- Marshall Space Flight Center (MSFC) that has significant improvement in tensile and fatigue strength at elevated temperatures (500 F-700 F). The alloy offers a number of benefits such as light weight, high hardness, low thermal expansion and high surface wear resistance. In hypereutectic form, this alloy is considered as an in-situ Al-Si composite with tensile strength of about 90% higher than the auto industry 390 alloy at 600 F. This composite is very economically produced by using either conventional permanent steel molds or die casting. The projected material cost is less than $0.90 per pound, and automotive components such as pistons can be cast for high production rate using conventional casting techniques with a low and fully accounted cost. Key Words: Metal matrix composites, In-situ composite, aluminum-silicon alloy, hypereutectic alloy, permanent mold casting, die casting.

Lee, Jonathan A.

2000-01-01

364

Surface modification by oil jet peening in Al alloys, AA6063-T6 and AA6061-T4: Residual stress and hardness  

NASA Astrophysics Data System (ADS)

The life of structural members that experience cyclic loading is improved by the introduction of surface compressive residual stresses. A high-pressure oil jet is used for the introduction of surface compressive residual stresses in aluminum alloys, AA6063-T6 and AA6061-T4. The peening machine designed and developed in the laboratory is capable of generating high pressures using hydraulic oil. The magnitude of residual stress developed depends upon the stand-off distance and yield strength of the material. A hardened layer up to a depth of about 350 ?m was developed in the materials investigated. The residual stresses and surface hardening induced are comparable to that produced by other peening processes. An analytical model is proposed to predict the impact pressure.

Grinspan, A. Sahaya; Gnanamoorthy, R.

2006-11-01

365

Method for improving performance of highly stressed electrical insulating structures  

DOEpatents

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

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

2002-01-01

366

Stress analysis at the interface between Ni-P coating and SiC p/Al substrate of space mirror  

NASA Astrophysics Data System (ADS)

This paper investigates the mechanical properties at the interface of the coating-substrate system, which comprises the electroless nickel-phosphorus (Ni-P) coating and the aluminum matrix composite substrate reinforced by the silicon carbide particles (SiC p/Al), and is used for the space mirror. To estimate the adhesion of Ni-P coating on SiC p/Al substrate, the scratch adhesion testing has been performed by drawing a spherically tipped diamond indenter with a radius of 200 ?m over the coated surface. The influence of the coating thickness on the interfacial stress induced by the inertial accelerations, temperature gradients and thermal soaks has been evaluated by simulation analysis based on the finite element method. The results of the scratch testing indicate that the adhesion strength of Ni-P coating to SiC p/Al composite is more than 3.0 GPa. Compared the maximum value of the interfacial stress obtained by simulation analysis with results of the scratch testing, it is can be seen that the mirror has enough safety margin. Furthermore, the most significant conclusion that can be drawn from this work is that the coating thickness should not exceed 45 ?m in order to ensure the performance and reliability of Ni-P coating and SiC p/Al substrate system for space applications.

Guo, Shaowen; Li, Libo; Zhang, Guangyu; Wang, Wuyi; Zhao, Xuezeng

2009-01-01

367

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

368

Structural properties of Al/Mo/SiC multilayers with high reflectivity for extreme ultraviolet light.  

PubMed

We present the results of an optical and chemical, depth and surface study of Al/Mo/SiC periodic multilayers, designed as high reflectivity coatings for the extreme ultra-violet (EUV) range. In comparison to the previously studied Al/SiC system, the introduction of Mo as a third material in the multilayer structure allows us to decrease In comparison to the previously studied Al/SiC system with a reflectance of 37% at near normal incidence around 17 nm, the introduction of Mo as a third material in the multilayer structure allows us to decrease the interfacial roughness and achieve an EUV reflectivity of 53.4%, measured with synchrotron radiation. This is the first report of a reflectivity higher than 50% around 17 nm. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and x-ray photoelectron spectroscopy (XPS) measurements are performed on the Al/Mo/SiC system in order to analyze the individual layers within the stack. ToF-SIMS and XPS results give evidence that the first SiC layer is partially oxidized, but the O atoms do not reach the first Mo and Al layers. We use these results to properly describe the multilayer stack and discuss the possible reasons for the difference between the measured and simulated EUV reflectivity values. PMID:20940893

Hu, Min-Hui; Le Guen, Karine; André, Jean-Michel; Jonnard, Philippe; Meltchakov, Evgueni; Delmotte, Franck; Galtayries, Anouk

2010-09-13

369

High-resolution imagery of active faulting offshore Al Hoceima, Northern Morocco  

NASA Astrophysics Data System (ADS)

Two recent destructive earthquakes in 1994 and 2004 near Al Hoceima highlight that the northern Moroccan margin is one of the most seismically active regions of the Western Mediterranean area. Despite onshore geodetic, seismological and tectonic field studies, the onshore-offshore location and extent of the main active faults remain poorly constrained. Offshore Al Hoceima, high-resolution seismic reflection and swath-bathymetry have been recently acquired during the Marlboro-2 cruise. These data at shallow water depth, close to the coast, allow us to describe the location, continuity and geometry of three active faults bounding the offshore Nekor basin. The well-expressed normal-left-lateral onshore Trougout fault can be followed offshore during several kilometers with a N171°E ± 3° trend. Westward, the Bousekkour-Aghbal normal-left-lateral onshore fault is expressed offshore with a N020°E ± 4° trending fault. The N030°E ± 2° Bokkoya fault corresponds to the western boundary of the Plio-Quaternary offshore Nekor basin in the Al Hoceima bay and seems to define an en échelon tectonic pattern with the Bousekkour-Aghbal fault. We propose that these three faults are part of the complex transtensional system between the Nekor fault and the Al-Idrissi fault zone. Our characterization of the offshore expression of active faulting in the Al Hoceima region is consistent with the geometry and nature of the active fault planes deduced from onshore geomorphological and morphotectonic analyses, as well as seismological, geodetic and geodynamic data.

d'Acremont, E.; Gutscher, M.-A.; Rabaute, A.; Mercier de Lépinay, B.; Lafosse, M.; Poort, J.; Ammar, A.; Tahayt, A.; Le Roy, P.; Smit, J.; Do Couto, D.; Cancouët, R.; Prunier, C.; Ercilla, G.; Gorini, C.

2014-09-01

370

Microwave Annealing of High Dose Al+-implanted 4H-SiC: Towards Device Fabrication  

NASA Astrophysics Data System (ADS)

High-purity semi-insulating 8° off-axis <0001> 4H-SiC was implanted with Al+ at different doses and energies to obtain a dopant concentration in the range of 5 × 1019-5 × 1020 cm-3. A custom-made microwave heating system was employed for post-implantation annealing at 2,000 °C for 30 s. Sheet resistance and Hall-effect measurements were performed in the temperature range of 150-700 K. At room temperature, for the highest Al concentration, a minimum resistivity of 3 × 10-2 ? cm was obtained, whereas for the lowest Al concentration, the measured resistivity value was 4 × 10-1 ? cm. The onset of impurity band conduction was observed at around room temperature for the samples implanted with Al concentrations ?3 × 1020 cm-3. Vertical p +- i- n diodes whose anodes were made by 1.5 × 1020 cm-3 Al+ implantation and 2,000 °C/30 s microwave annealing showed exponential forward current-voltage characteristics with two different ideality factors under low current injection. A crossover point of the temperature coefficient of the diode resistance, from negative to positive values, was observed when the forward current entered the ohmic regime.

Nath, A.; Rao, Mulpuri V.; Tian, Y.-L.; Parisini, A.; Nipoti, R.

2014-04-01

371

High-field 19.6T 27Al solid-state MAS NMR of in vitro aluminated brain tissue  

Microsoft Academic Search

The combination of 27Al high-field solid-state NMR (19.6T) with rapid spinning speeds (17.8kHz) is used to acquire 27Al NMR spectra of total RNA human brain temporal lobe tissues exposed to 0.10mM Al3+ (as AlCl3) and of human retinal pigment epithelial cells (ARPE-19), grown in 0.10mM AlCl3. The spectra of these model systems show multiple Al3+ binding sites, good signal\\/noise ratios

Pamela L. Bryant; Walter J. Lukiw; Zhehong Gan; Randall W. Hall; Leslie G. Butler

2004-01-01

372

High-field 19.6 T 27Al solid-state MAS NMR of in vitro aluminated brain tissue  

Microsoft Academic Search

The combination of 27Al high-field solid-state NMR (19.6T) with rapid spinning speeds (17.8kHz) is used to acquire 27Al NMR spectra of total RNA human brain temporal lobe tissues exposed to 0.10mM Al3+ (as AlCl3) and of human retinal pigment epithelial cells (ARPE-19), grown in 0.10mM AlCl3. The spectra of these model systems show multiple Al3+ binding sites, good signal\\/noise ratios

Pamela L. Bryant; Walter J. Lukiw; Zhehong Gan; Randall W. Hall; Leslie G. Butler

2004-01-01

373

The growth and optical properties of large, high-quality AlN single crystals Martin Strassburg,a)  

E-print Network

The growth and optical properties of large, high-quality AlN single crystals Martin Strassburg and thermal mismatch.5­7 Therefore, the growth of bulk AlN crystals is of primary importance of an ap- propriate growth procedure to achieve sufficiently large AlN single crystals with reproducible

Nabben, Reinhard

374

HIGH-TEMPERATURE FRACTURE AND FATIGUE RESISTANCE OF A DUCTILE b-TiNb REINFORCED g-TiAl  

E-print Network

HIGH-TEMPERATURE FRACTURE AND FATIGUE RESISTANCE OF A DUCTILE b-TiNb REINFORCED g-TiAl) AbstractÐThe high-temperature fatigue-crack propagation and fracture resistance of a model g-TiAl inter the fracture toughness of g-TiAl, even at high temperatures, from about 12 to H40 MPa m1/2 , although

Ritchie, Robert

375

Electrical properties of Al-In-Sn alloys directionally solidified in high and low gravitational fields  

NASA Technical Reports Server (NTRS)

The Al-In-Sn alloys were directionally solidified in the NASA KC-135 aircraft which flies a series of parabolas to generate high (high-g) and low (low-g) gravity forces parallel to the longitudinal growth axis. Thus, for a given sample, successive sections can be identified which were solidified in high-g and low-g. Measurements of the electronic properties of the samples reveal that: the resistivity of the low-g sections is larger (about a factor of 10) than that of the high-g sections; the low-g sections behave conductively like a semi-metal, while the high-g sections are essentially metallic; and both high-g and low-g sections are superconducting but the superconducting transition temperature of the low-g sections is 1 K higher than that of the high-g sections.

Wu, M. K.; Ashburn, J. R.; Kaukler, W. F.; Curreri, P. A.

1987-01-01

376

Electrical properties of Al-In-Sn alloys directionally solidified in high and low gravitational fields  

NASA Technical Reports Server (NTRS)

The Al-In-Sn alloys were directionally solidified in the NASA KC-135 aircraft which flies a series of parabolas to generate high (high-g) and low (low-g) gravity forces parallel to the longitudinal growth axis. Thus, for a given sample, successive sections can be identified which were solidified in high-g and low-g. Measurements of the electronic properties of the samples reveal that: the resistivity of the low-g sections is larger (about a factor of 10) than that of the high-g sections; the low-g sections behave conductively like a semi-metal, while the high-g sections are essentially metallic; and both high-g and low-g sections are superconducting but the superconducting transition temperature of the low-g sections is 1 K higher than that of the high-g sections.

Curreri, P. A.; Wu, M. K.; Ashburn, J. R.; Kaukler, W. F.

1986-01-01

377

Mechanical properties of Al and Al alloys and their relationship to interconnection reliability  

NASA Astrophysics Data System (ADS)

Pure Al, Al-3 wt %Si, and Al-15 at. % C films are characterized macroscopically in terms of yield stress and hardness and microscopically in terms of a grain structure to investigate the effects of Si and carbon additives to modify mechanical properties of the Al matrix. A theory is presented to estimate the yield stress of metal films. The experimental method is based on laser interferometer measurements of the varied substrate curvature involved with thermal treatment of a film-substrate composite. It is shown that carbon addition increases yield stress and hardness of Al, whereas Si addition decreases these properties. Carbon addition suppresses grain growth by 450 °C annealing as small as about 0.04 ?m. Reliability tests on Al and Al-alloy interconnects revealed that increased yield stress improves resistance against failures due to the stress at high temperatures and high current densities, but degrades resistance against cycled thermal shock. The double layered Al-C/Al structure was highly resistant against both thermal and current stress.

Ozawa, Kiyoshi

1993-01-01

378

A comparative proteomic analysis of rice seedlings under various high-temperature stresses  

Microsoft Academic Search

To understand the responses of rice seedlings to different high-temperature stresses, seven-day-old rice seedlings were exposed to different high temperatures for 48 h, and the maximal quantum yield of PS II photochemistry measurements, ascorbate peroxidase activity assays and proteomic analyses in leaf tissue were performed. The results showed that when rice seedlings were exposed to high temperatures at 35 °C, 40 °C and

Feng Han; Hui Chen; Xiao-Juan Li; Ming-Feng Yang; Gong-She Liu; Shi-Hua Shen

2009-01-01

379

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 environments as to· potential stresses to beef cattle Characterization of phenotypes/· genotypes

380

The effects of stress on androgen production, spermiation response and sperm quality in high and low cortisol  

E-print Network

and low cortisol responsive domesticated male striped bass Daniel A. Castranovaa , William King V1 , L December 2004 Abstract Domesticated male striped bass were selected as high cortisol stress responders (HCR) or low cortisol stress responders (LCR) by ranking mean 1-h post-stress plasma cortisol levels following

Hamza, Iqbal

381

Stress and fatigue life monitoring of high temperature bearing elements based on the solution of inverse conduction problem  

Microsoft Academic Search

The stress and fatigue life monitoring of high temperature bearing elements is of great significance for the safe and economic operation of thermal power plant. The calculation of temperature distribution is the fundamental of the stress and fatigue life analysis. In order to improve the precision of the temperature distribution, a method for stress and fatigue life analysis of boiler

Li Bin; Wang Song-ling; Yang Dong

2008-01-01

382

Highly conductive and transparent laser ablated nanostructured Al: ZnO thin films  

NASA Astrophysics Data System (ADS)

Al doped ZnO thin films are prepared by pulsed laser deposition on quartz substrate at substrate temperature 873 K under a background oxygen pressure of 0.02 mbar. The films are systematically analyzed using X-ray diffraction, atomic force microscopy, micro-Raman spectroscopy, UV-vis spectroscopy, photoluminescence spectroscopy, z-scan and temperature-dependent electrical resistivity measurements in the temperature range 70-300 K. XRD patterns show that all the films are well crystallized with hexagonal wurtzite structure with preferred orientation along (0 0 2) plane. Particle size calculations based on XRD analysis show that all the films are nanocrystalline in nature with the size of the quantum dots ranging from 8 to 17 nm. The presence of high frequency E2 mode and longitudinal optical A1 (LO) modes in the Raman spectra suggest a hexagonal wurtzite structure for the films. AFM analysis reveals the agglomerated growth mode in the doped films and it reduces the nucleation barrier of ZnO by Al doping. The 1% Al doped ZnO film presents high transmittance of ˜75% in the visible and near infrared region and low dc electrical resistivity of 5.94 × 10 -6 ? m. PL spectra show emissions corresponding to the near band edge (NBE) ultra violet emission and deep level emission in the visible region. Nonlinear optical measurements using the z-scan technique shows optical limiting behavior for the 5% Al doped ZnO film.

Vinodkumar, R.; Navas, I.; Chalana, S. R.; Gopchandran, K. G.; Ganesan, V.; Philip, Reji; Sudheer, S. K.; Mahadevan Pillai, V. P.

2010-11-01

383

Optimal microelectromechanical systems (MEMS) device for achieving high pyroelectric response of AlN  

NASA Astrophysics Data System (ADS)

This paper discusses research being conducted on aluminum nitride (AlN) as a pyroelectric material for use in detecting applications. AlN is being investigated because of its high pyroelectric coefficient, thermal stability, and high Curie temperature. In order to determine suitability of the pyroelectric properties of AlN for use as a detector, testing of several devices was conducted. These devices were fabricated using microelectromechanical systems (MEMS) fabrication processes; the devices were also designed to allow for voltage and current measurements. The deposited AlN films used were 150 nm - 300 nm in thickness. Thin-films were used to rapidly increase the temperature response after the thermal stimulus was applied to the pyroelectric material. This is important because the pyroelectric effect is directly proportional to the rate of temperature change. The design used was a face-electrode bridge that provides thermal isolation which minimizes heat loss to the substrate, thereby increasing operation frequency of the pyroelectric device. A thermal stimulus was applied to the pyroelectric material and the response was measured across the electrodes. A thermal imaging camera was used to monitor the changes in temperature. Throughout the testing process, the annealing temperatures, type of layers, and thicknesses were also varied. These changes resulted in improved MEMS designs, which were fabricated to obtain an optimal design configuration for achieving a high pyroelectric response. A pyroelectric voltage response of 38.9 mVp-p was measured without filtering, 12.45 mVp-p was measured in the infrared (IR) region using a Si filter, and 6.38 mVp-p was measured in the short wavelength IR region using a long pass filter. The results showed that AlN's pyroelectric properties can be used in detecting applications.

Kebede, Bemnnet; Coutu, Ronald A.; Starman, LaVern

2014-03-01

384

Mixed-mode fatigue-crack growth thresholds in Ti-6Al-4V at high frequency  

SciTech Connect

Multiaxial loading conditions exist at fatigue-critical locations within turbine engine components, particularly in association with fretting fatigue in the blade dovetail/disk contact section. For fatigue-crack growth in such situations, the resultant crack-driving force is a combination of the influence of a mode I (tensile opening) stress-intensity range, {Delta}K{sub I}, as well as mode II (in-plane shear) and/or mode III (anti-plane shear) stress-intensity ranges, {Delta}K{sub II} and {Delta}K{sub III}, respectively. For the case of the high-cycle fatigue of turbine-engine alloys, it is critical to quantify such behavior, as the extremely high cyclic loading frequencies ({approximately}1--2 kHz) and correspondingly short times to failure may necessitate a design approached based on the fatigue-crack growth threshold. Moreover, knowledge of such thresholds is required for accurate prediction of fretting fatigue failures. Accordingly, this paper presents the mixed-mode fatigue crack growth thresholds for mode I + II loading (phase angles from 0{degree} to 82{degree}) in a Ti-6Al-4V blade alloy. These results indicate that when fatigue-crack growth in this alloy is characterized in terms of the crack-driving force {Delta}G, which incorporates both the applied tensile and shear loading, the mode 1 fatigue-crack growth threshold is a lower bound (worst case) with respect to mixed-mode (I + II) crack-growth behavior.

Campbell, J.P.; Ritchie, R.O.

1999-10-22

385

MCrAlY Bondcoats by High-Velocity Atmospheric Plasma Spraying  

NASA Astrophysics Data System (ADS)

MCrAlY bondcoats (M = Co, Ni) are used to protect metallic substrates from oxidation and to improve adhesion of ceramic thermal barrier coatings for high temperature applications, such as in land-based and aviation turbines. Since MCrAlYs are prone to take up oxygen during thermal spraying, bondcoats often are manufactured under inert gas conditions at low pressure. Plasma spraying at atmospheric conditions is a cost-effective alternative if it would be possible to limit the oxygen uptake as well as to obtain sufficiently dense microstructures. In the present work, high-velocity spray parameters were developed for the TriplexPro 210 three-cathode plasma torch using MCrAlY powders of different particle size fractions to achieve these objectives. The aims are conflictive since the former requires cold conditions, whereas the latter is obtained by more elevated particle temperatures. High particle velocities can solve this divergence as they imply shorter time for oxidation during flight and contribute to coating densification by kinetic rather than thermal energy. Further aims of the experimental work were high deposition efficiencies as well as sufficient surface roughness. The oxidation behavior of the sprayed coatings was characterized by thermal gravimetric analyses and isothermal heat treatments.

Mauer, G.; Sebold, D.; Vaßen, R.

2014-01-01

386

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

387

Stress redistribution in individual ultrathin strained silicon nanowires: a high-resolution polarized Raman study  

NASA Astrophysics Data System (ADS)

Strain nano-engineering provides valuable opportunities to create high-performance nanodevices by a precise tailoring of semiconductor band structure. Achieving these enhanced capabilities has sparked a surge of interest in controlling strain on the nanoscale. In this work, the stress behavior in ultrathin strained silicon nanowires directly on oxide is elucidated using background-free, high-resolution polarized Raman spectroscopy. We established a theoretical framework to quantify the stress from Raman shifts taking into account the anisotropy associated with the nanowire quasi-one-dimensional morphology. The investigated nanowires have lateral dimensions of 30, 50 and 80 nm and a length of 1 ?m top-down fabricated by patterning and etching 15 nm thick biaxially tensile strained silicon nanomembranes generated using heteroepitaxy and ultrathin layer transfer. The concern over the contribution of Raman scattering at the nanowire <110> oriented sidewalls is circumvented by precisely selecting the incident polarization relative to the sidewalls of the nanowire, thus enabling an accurate and rigorous analysis of stress profiles in individual nanowires. Unlike suspended nanowires, which become uniaxially strained as a result of free surface-induced relaxation, we demonstrated that stress profiles in single nanowires are rather complex and non-uniform along different directions due to the oxide-nanowire interface. As a general trend, higher stresses are observed at the center of the nanowire and found to decrease linearly as a function of the nanowire width. Using multi-wavelength high-resolution Raman spectroscopy, we also extracted the stress profiles at different depths in the nanowire. The residual stress in the top ˜10 nm of the nanowire was found to be nearly uniaxial and increase from the edge toward the center, which remains highly strained. In contrast, the average stress profiles measured over the whole nanowire thickness exhibit different behavior characterized by a plateau in the region ˜200 nm away from the edges. Our observations indicate that the lattice near the newly formed free surface moves inwards and drags the underlying substrate leading to a complex redistribution of stress. This nanoscale patterning-induced relaxation has direct implications for electrical and mechanical properties of strained silicon nanowires and provides myriad opportunities to create entirely new strained-engineered nanoscale devices.

Tarun, Alvarado; Hayazawa, Norihiko; Balois, Maria Vanessa; Kawata, Satoshi; Reiche, Manfred; Moutanabbir, Oussama

2013-05-01

388

Effect of electrode force condition on nugget diameter and residual stress in resistance spot welded high-strength steel sheets  

NASA Astrophysics Data System (ADS)

This study examines the effect of the electrode force condition on the nugget diameter and residual stress in spot welded high-strength steel sheets. Numerical simulations of spot welding were performed to examine the nugget diameter and residual stress. The results indicate that adjusting the force profile changes the current density and stress state at the spot welds. Therefore, choosing an appropriate force profile extends the nugget diameter and reduces the residual stress.

Iyota, M.; Mikami, Y.; Hashimoto, T.; Taniguchi, K.; Ikeda, R.; Mochizuki, M.

2012-08-01

389

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

390

Repetitive Ultra-low Stress Induced Nanocrystallization in Amorphous Cu?Zr?Al Alloy Evidenced by in situ Nanoindentation  

E-print Network

Stress driven nucleation of nanocrystals in amorphous alloys has been a subject of intensive debate in the past decade. It has long been postulated that nanocrystals form succeeding the occurrence of shear bands in deformed amorphous alloys...

Liu, Y.; Jian, J.; Lee, J. H.; Wang, C.; Cao, Q. P.; Gutierrez, C.; Wang, H.; Jiang, J. Z.; Zhang, X.

2014-05-12

391

Complex borides based on AlLiB14 as high-temperature thermoelectric compounds.  

PubMed

AlLiB14 is examined as a potential high-temperature thermoelectric material. First-principles methods are used to investigate the thermoelectric behavior and it is found to have a band gap of 2.13 eV, and an electronic dispersion with characteristic indicative of having a high Seebeck coefficient. Semiclassical Boltzmann transport theory predicts that AlLiB14 will have a Seebeck coefficient greater than 200 ?V K(-1), at temperatures near 1000 K and carrier concentrations around 1 × 10(20) cm(-3). Using a elasticity based expression for the thermal conductivity, the thermoelectric figure of merit is approximated to be 0.45 × 10(-3) T at moderate doping levels. PMID:25337901

Wan, L F; Beckman, S P

2014-12-14

392

Magnesium and Calcium Aluminate Liquids: In Situ High-Temperature 27Al NMR Spectroscopy.  

PubMed

The use of high-temperature nuclear magnetic resonance (NMR) spectroscopy provides a means of investigating the structure of refractory aluminate liquids at temperatures up to 2500 K. Time-averaged structural information indicates that the average aluminum coordination for magnesium aluminate (MgAl(2)O(4)) liquid is slightly greater than for calcium aluminate (CaAl(2)O(4)) liquid and that in both liquids it is close to four. Ion dynamics simulations for these liquids suggest the presence of four-, five-, and six-coordinated aluminate species, in agreement with NMR experiments on fast-quenched glasses. These species undergo rapid chemical exchange in the high-temperature liquids, which is evidenced by a single Lorentzian NMR line. PMID:17809340

Poe, B T; McMillan, P F; Coté, B; Massiot, D; Coutures, J P

1993-02-01

393

Clustering and Vacancy Behavior in High- and Low-Solute Al-Mg-Si Alloys  

NASA Astrophysics Data System (ADS)

The precipitate microstructure and vacancy distribution in Al-Mg-Si alloys with different amounts of solute and different heat treatments were investigated by transmission electron microscopy and muon spin relaxation measurements. A high amount of vacancies is normally present in Al-Mg-Si alloys as these bind to atomic clusters. We observe these vacancies to leave the material not before over-aging at very high temperatures such as 623 K (350 °C), meaning that vacancies do not bind to incoherent over-aged precipitates. For samples only stored at room temperature after solution heat treatment, a reduction of muon trapping was found at a temperature of 140 K (-133 °C) when reducing the amount of solute in the alloy. This might be connected to a lower number density of Cluster (1), which contrary to Cluster (2) do not nucleate precipitates upon further aging of the material.

Wenner, Sigurd; Nishimura, Katsuhiko; Matsuda, Kenji; Matsuzaki, Teiichiro; Tomono, Dai; Pratt, Francis L.; Marioara, Calin D.; Holmestad, Randi

2014-11-01

394

Defect engineering for 650 nm high-power AlGaInP laser diodes  

NASA Astrophysics Data System (ADS)

To find the optimal growth and annealing conditions for high-power 650 nm band AlGaInP laser diodes, we carried out defect engineering, in which the distribution and density of deep level defects of the laser structure was analyzed. For this purpose, deep level transient spectroscopy (DLTS) measurements were carried out for each layer of the 650 nm band AlGaInP laser. By layer optimization at growth and annealing conditions, the laser diode was able operate stably and kink-free at high power over 220 mW at 70 °C. The characteristic temperatures ( T0) were 212 K for 25-60 °C and 106 K over 60 °C.

Kim, D. S.; Kim, K. C.; Shin, Y. C.; Kang, D. H.; Kim, B. J.; Kim, Y. M.; Park, Y.; Kim, T. G.

2006-04-01

395

Size effect of (Al2O3-Y2O3)/YSZ micro-laminated coating on high-temperature oxidation resistance  

NASA Astrophysics Data System (ADS)

The size effect of structure plays an important role in the high-temperature oxidation and spallation resistance of micro-laminated coating on alloy substrate. In this study, (Al2O3-Y2O3)/YSZ micro-laminated coatings with different thickness ratios and layer numbers were prepared on MCrAlY alloy by electrolytic deposition and microwave sintering under pressure. The oxidation and spallation resistance of the micro-laminated coatings were investigated by cyclic oxidation tests in air at 1050 °C for 200 h. Results indicate that both oxidation resistance and spallation resistance of the coating have been improved significantly, by increasing the thickness ratio of YSZ layer to Al2O3-Y2O3 layer and layer number in a specific range. In such micro-laminated coating, increasing the thickness ratio of YSZ layer to Al2O3-Y2O3 layer can improve the apparent thermal expansion coefficient of coating and decrease the thermal stresses. While, increasing the layer number can extend the crack propagation paths and improve the plasticity and fracture toughness. They can improve the mechanical properties of micro-laminated coating and exhibit excellent cracking and spallation resistance. This would give rise to the beneficial effects on suppressing the oxygen inward diffusion and consequently improve the high-temperature oxidation resistance of micro-laminated coating. Such size effect would provide reference values in the structural design of micro-laminated coating in high-temperature application.

Yao, Junqi; Lv, Lili; He, Yedong; Wang, Deren

2013-08-01

396

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

PubMed

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

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

2013-04-01

397

High-power and high-brightness laser diode structures using Al-free active region  

Microsoft Academic Search

High bit-rate, WDM, networks are reliant on Er or Er\\/Yb doped fiber amplifiers. Reliable, high power laser diodes at 980nm and 1480nm are key devices for pumping these amplifiers. We have developed several 980 nm laser diode structures at 980 nm, using an Aluminum free active region and standard AR\\/HR coatings on the facets. Our laser show low optical losses,

Sophie-Charlotte Auzanneau; Michel M. Krakowski; Francois Berlie; Michel Calligaro; Yannick Robert; Olivier Parillaud; Michel Lecomte; B. Boulant; Thierry Fillardet

2003-01-01

398

Reliability of AlGaN/GaN high electron mobility transistors on low dislocation density bulk GaN substrate: Implications of surface step edges  

SciTech Connect

To enable gaining insight into degradation mechanisms of AlGaN/GaN high electron mobility transistors, devices grown on a low-dislocation-density bulk-GaN substrate were studied. Gate leakage current and electroluminescence (EL) monitoring revealed a progressive appearance of EL spots during off-state stress which signify the generation of gate current leakage paths. Atomic force microscopy evidenced the formation of semiconductor surface pits at the failure location, which corresponds to the interaction region of the gate contact edge and the edges of surface steps.

Killat, N., E-mail: Nicole.Killat@bristol.ac.uk, E-mail: Martin.Kuball@bristol.ac.uk; Montes Bajo, M.; Kuball, M., E-mail: Nicole.Killat@bristol.ac.uk, E-mail: Martin.Kuball@bristol.ac.uk [Center for Device Thermography and Reliability (CDTR), H.H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL (United Kingdom); Paskova, T. [Kyma Technologies, Inc., Raleigh, North Carolina 27617 (United States) [Kyma Technologies, Inc., Raleigh, North Carolina 27617 (United States); Materials Science and Engineering Department, North Carolina State University, Raleigh, North Carolina 27695 (United States); Evans, K. R. [Kyma Technologies, Inc., Raleigh, North Carolina 27617 (United States)] [Kyma Technologies, Inc., Raleigh, North Carolina 27617 (United States); Leach, J. [Kyma Technologies, Inc., Raleigh, North Carolina 27617 (United States) [Kyma Technologies, Inc., Raleigh, North Carolina 27617 (United States); Electrical and Computer Engineering Department, Virginia Commonwealth University, Richmond, Virginia 23284 (United States); Li, X.; Özgür, Ü.; Morkoç, H. [Electrical and Computer Engineering Department, Virginia Commonwealth University, Richmond, Virginia 23284 (United States)] [Electrical and Computer Engineering Department, Virginia Commonwealth University, Richmond, Virginia 23284 (United States); Chabak, K. D.; Crespo, A.; Gillespie, J. K.; Fitch, R.; Kossler, M.; Walker, D. E.; Trejo, M.; Via, G. D.; Blevins, J. D. [Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio 45433 (United States)] [Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio 45433 (United States)

2013-11-04

399

Operating limits of AL-alloyed high-low junctions for BSF solar cells  

Microsoft Academic Search

Experimental estimations of the effective surface recombination velocity of the high-low junction and of the base diffusion length are carried out for Al-alloyed n(plus)pp(plus) bifacial cells and the results are presented in form of histograms. These results agree with calculated values of the effective surface recombination velocity when the characteristics of the recrystallized Si layer and heavy doping effects are

J. del Alamo; J. Eguren; A. Luque

1981-01-01

400

Electrical conductivity of aluminum hydride AlH3 at high pressure and temperature  

Microsoft Academic Search

A study of electrophysical and thermodynamic properties of alane AlH3 under multi shock compression has been carried out. The increase in specific electroconductivity of alane at shock compression up to pressure 100 GPa have been measured. High pressures and temperatures were obtained with explosive device, which accelerates the stainless impactor up to 3 km\\/sec. The impact shock is split into

Denis Shakhray; Alexander Molodets; Vladimir Fortov; Aleksei Khrapak

2009-01-01

401

Parameter studies on high-velocity oxy-fuel spraying of MCrAlY coatings  

Microsoft Academic Search

Todays thermally sprayed MCrAlY coatings are commonly manufactured by the vacuum plasma spraying (VPS) process. This technique provides dense and oxide-free coatings. However, mainly due to the vacuum procedures this production is cost intensive and time consuming. The third generation of high-velocity oxy-fuel (HVOF) systems nowadays offer processing of materials that are sensitive to oxidation even in atmosphere. This is

Erich Lugscheider; Christian Herbst; Lidong Zhao

1998-01-01

402

Development of high strength austenitic stainless steel for conduit of Nb{sub 3}Al conductor  

SciTech Connect

Japan Atomic Energy Research Institute (JAERI) started developing new austenitic stainless steel for a conduit (1 - 2 mm) of a Nb{sub 3}Al conductor in collaboration with Nippon Steel Corporation (NSC). A high strength austenitic stainless steel is required for a conduit of a Nb{sub 3}Al conductor to make the best use of superconducting properties of a Nb{sub 3}Al conductor. JAERI and NSC successfully developed the high strength austenitic stainless steel, JN1 (YS {ge} 1,300 MPa, KIc {ge} 200 MPa{radical}m at 4K) for magnet structures having thick section. However, JN1 is not suitable for a conduit material because elongation of JN1 decreases to less than 10 % due to sensitization during reaction heat treatment for Nb{sub 3}Al. Therefore, modification of JN1 was performed as a first step to develop a new conduit material which withstands Nb{sub 3}Al reaction heating. Small trial lots heat-treated at 973 - 1173 K for 2 - 200 hours were prepared and evaluated by Charpy impact test and tensile test at 77 K and 4K. A material having yield strength of 1,390 MPa and elongation of 34 % after aging at 973 K x 200 h are developed up to now. This paper describes requirements on the mechanical properties and status of the development work. In addition, empirical equations to predict 4K yield strength, elongation, and Charpy absorbed energy from 77K data are proposed in this paper.

Nakajima, H.; Nunoya, Y.; Nozawa, M. [Japan Atomic Energy Research Institute, Naka, Ibaraki (Japan)] [and others

1997-06-01

403

Characteristics of High-Temperature Deformation Behavior of Ti-45Al-2Cr-3Ta-0.5W Alloy  

NASA Astrophysics Data System (ADS)

High-temperature deformation behavior tests of as-cast Ti-45Al-2Cr-3Ta-0.5W alloy were conducted over a wide range of strain rates (0.001-1.0 s-1) and temperatures (1150-1300 °C). The flow curves for the current alloy exhibited sharp peaks at low strain levels, followed by pronounced work hardening and flow localization at high strain levels. Phenomenological analysis of the strain rate and temperature dependence of peak stress data yielded an average value of the strain rate sensitivity equal to 0.25 and an apparent activation energy of ~420 kJ/mol. Processing maps were established under different deformation conditions, and the optimal condition for hot work on this material was determined to be 1250 °C/0.001 s-1. The stable deformation region was also found to decrease with increasing strain. Dynamic recrystallization (DRX) was the major softening mechanism controlling the growth of grains at the grain boundary. Meanwhile, local globularization and dynamic recovery (DR) were the main softening mechanisms in the lamellar colony. When deformed at higher temperatures (~1300 °C), the cyclic DRX and DR appeared to dominate the deformation. Moreover, the evolution of the ? phase during hot deformation played an important role in the dynamic softening of the alloy.

Luo, Y. Y.; Xi, Z. P.; Zeng, W. D.; Mao, X. N.; Yang, Y. L.; Niu, H. Z.

2014-07-01

404

Characteristics of High-Temperature Deformation Behavior of Ti-45Al-2Cr-3Ta-0.5W Alloy  

NASA Astrophysics Data System (ADS)

High-temperature deformation behavior tests of as-cast Ti-45Al-2Cr-3Ta-0.5W alloy were conducted over a wide range of strain rates (0.001-1.0 s-1) and temperatures (1150-1300 °C). The flow curves for the current alloy exhibited sharp peaks at low strain levels, followed by pronounced work hardening and flow localization at high strain levels. Phenomenological analysis of the strain rate and temperature dependence of peak stress data yielded an average value of the strain rate sensitivity equal to 0.25 and an apparent activation energy of ~420 kJ/mol. Processing maps were established under different deformation conditions, and the optimal condition for hot work on this material was determined to be 1250 °C/0.001 s-1. The stable deformation region was also found to decrease with increasing strain. Dynamic recrystallization (DRX) was the major softening mechanism controlling the growth of grains at the grain boundary. Meanwhile, local globularization and dynamic recovery (DR) were the main softening mechanisms in the lamellar colony. When deformed at higher temperatures (~1300 °C), the cyclic DRX and DR appeared to dominate the deformation. Moreover, the evolution of the ? phase during hot deformation played an important role in the dynamic softening of the alloy.

Luo, Y. Y.; Xi, Z. P.; Zeng, W. D.; Mao, X. N.; Yang, Y. L.; Niu, H. Z.

2014-10-01

405

Fiber Bragg grating sensor for the simultaneous measurement of stress and temperature in high temperature environment  

Microsoft Academic Search

A novel fiber Bragg grating sensor operating in the environment of high temperature is studied. And the sensor can realize the simultaneous measurement of stress and temperature. The sensing head is comprised of one metal strip, one adiabatic strip and two FBGs with the same specification. The metal strip converts the measured temperature into the strain of the FBG2, and

Fang Li; Yuesong Jiang

2008-01-01

406

Micromechanical Modelling of Time-Dependent Stress-Corrosion Behaviour of High-Strength Steel  

Microsoft Academic Search

This paper provides micromechanical bases to explain the time-dependent stress corrosion behaviour of high-strength prestressing steel wires. To this end, two eutectoid steels in the form of hot rolled bar and cold drawn wire were subjected to slow strain rate tests in aqueous environments in corrosive conditions corresponding to localized anodic dissolution and hydrogen assisted cracking. While a tensile crack

J. Toribio

1998-01-01

407

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

408

Investigation of the Effects of Stress Corrosion on High-Strength Steel Alloys.  

National Technical Information Service (NTIS)

The stress corrosion susceptibility of several high strength steels has been evaluated by alternate-immersion laboratory testing in a 3.5-percent sodium chloride solution. The steels evaluated were the stainless steels AFC 77, AM 350, AM 355, and 17-4PH; ...

G. A. Dreyer, W. C. Gallaugher

1964-01-01

409

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

E-print Network

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

Paris-Sud XI, Université de

410

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.

411

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

412

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

413

A study on the yield stress of perlite-filled high-density polyethylenes  

Microsoft Academic Search

Four different types of high-density polyethylenes were blended with expanded perlite at different compositions. ?-aminopropyltriethoxysilane was applied to perlite (2 wt%) from ether and water solutions to enhance the interfacial adhesion between the polymer and the filler. It was shown that silane treatment advances the yield stress with improving dispersion and increasing the interfacial adhesion of the filler with the

G. Akin Öktem; T. Tincer

1993-01-01

414

Cohesion and dilatation of powder compacts containing hard phase particles under highly deviatoric stress states  

Microsoft Academic Search

The effect of hard particles in compacted powders is studied under highly deviatoric stress states. The soft matrix powder is pure aluminum while the hard particles are W2C particles. The behavior of compacts with volume fractions of hard particles up to 60% is investigated. Diametral compression and simple compression tests are carried out both at room temperature and at 450?C.

C. L. Martin; O. Lame; D. Bouvard

2000-01-01

415

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

Microsoft Academic Search

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

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

2006-01-01

416

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

ERIC Educational Resources Information Center

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

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

2006-01-01

417

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

418

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

419

XRD and XAS structural study of CuAlO2 under high pressure  

NASA Astrophysics Data System (ADS)

We present the results of x-ray diffraction and x-ray absorption spectroscopy experiments in CuAlO2 under high pressure. We discuss the polarization dependence of the x-ray absorption near-edge structure at the Cu K-edge. XRD under high pressure evidences anisotropic compression, the a-axis being more compressible than the c-axis. EXAFS yields the copper-oxygen bond length, from which the only internal parameter of the delafossite structure is deduced. The combination of anisotropic compression and the internal parameter decrease results in a regularization of the AlO6 octahedra. The anisotropic compression is related to the chemical trends observed in the lattice parameters when Al is substituted by other trivalent cations. Both experiments evidence the existence of an irreversible phase transition that clearly manifests at 35 ± 2 GPa. The structure of the high-pressure polymorph could not be determined, but it implies a change of the Cu environment, which remains anisotropic. Precursor effects are observed from the lowest pressures, which are possibly related to crystal breaking at a submicroscopic scale with partial reorientation of the crystallites.

Pellicer-Porres, J.; Segura, A.; Ferrer-Roca, Ch; Polian, A.; Munsch, P.; Kim, D.

2013-03-01

420

XRD and XAS structural study of CuAlO2 under high pressure.  

PubMed

We present the results of x-ray diffraction and x-ray absorption spectroscopy experiments in CuAlO(2) under high pressure. We discuss the polarization dependence of the x-ray absorption near-edge structure at the Cu K-edge. XRD under high pressure evidences anisotropic compression, the a-axis being more compressible than the c-axis. EXAFS yields the copper-oxygen bond length, from which the only internal parameter of the delafossite structure is deduced. The combination of anisotropic compression and the internal parameter decrease results in a regularization of the AlO(6) octahedra. The anisotropic compression is related to the chemical trends observed in the lattice parameters when Al is substituted by other trivalent cations. Both experiments evidence the existence of an irreversible phase transition that clearly manifests at 35 ± 2 GPa. The structure of the high-pressure polymorph could not be determined, but it implies a change of the Cu environment, which remains anisotropic. Precursor effects are observed from the lowest pressures, which are possibly related to crystal breaking at a submicroscopic scale with partial reorientation of the crystallites. PMID:23423689

Pellicer-Porres, J; Segura, A; Ferrer-Roca, Ch; Polian, A; Munsch, P; Kim, D

2013-03-20

421

Observations of Glide and Decomposition of a<101> Dislocations at High Temperatures in Ni-Al Single Crystals Deformed along the Hard Orientation  

NASA Technical Reports Server (NTRS)

Ni-44at.% Al and Ni-50at.% single crystals were tested in compression in the hard (001) orientations. The dislocation processes and deformation behavior were studied as a function of temperature, strain and strain rate. A slip transition in NiAl occurs from alpha(111) slip to non-alphaaaaaaaaaaa9111) slip at intermediate temperatures. In Ni-50at.% Al single crystal, only alpha(010) dislocations are observed above the slip transition temperature. In contrast, alpha(101)(101) glide has been observed to control deformation beyond the slip transition temperature in Ni-44at.%Al. alpha(101) dislocations are observed primarily along both (111) directions in the glide plane. High-resolution transmission electron microscopy observations show that the core of the alpha(101) dislocations along these directions is decomposed into two alpha(010) dislocations, separated by a distance of approximately 2nm. The temperature window of stability for these alpha(101) dislocations depends upon the strain rate. At a strain rate of 1.4 x 10(exp -4)/s, lpha(101) dislocations are observed between 800 and 1000K. Complete decomposition of a alpha(101) dislocations into alpha(010) dislocations occurs beyond 1000K, leading to alpha(010) climb as the deformation mode at higher temperature. At lower strain rates, decomposition of a alpha(101) dislocations has been observed to occur along the edge orientation at temperatures below 1000K. Embedded-atom method calculations and experimental results indicate that alpha(101) dislocation have a large Peieris stress at low temperature. Based on the present microstructural observations and a survey of the literature with respect to vacancy content and diffusion in NiAl, a model is proposed for alpha(101)(101) glide in Ni-44at.%Al, and for the observed yield strength versus temperature behavior of Ni-Al alloys at intermediate and high temperatures.

Srinivasan, R.; Daw, M. S.; Noebe, R. D.; Mills, M. J.

2003-01-01

422

High strain rate superplasticity of AlN particulate reinforced aluminium alloy composites  

SciTech Connect

Ceramic whisker or particulate reinforced aluminium alloy composites have a great potential for automobile engineering components, aerospace structures, semi-conductor packaging and so on, because of the composites ability to exhibit a high specific elastic modulus and specific tensile strength, excellent wear resistance and heat resistance, low thermal expansion and good dimensional stability. A serious problem involving practical application of ceramic whisker or particulate reinforced aluminium alloy composites is due to the low tensile ductility, fracture toughness at room temperature and, also, their hardness qualities that make it difficult to deform by conventional forming processing and machining by ordinary tools. It has been found, however, that aluminium alloy composites reinforced by SiC or Si[sub 3]N[sub 4] whiskers or particulates produce superplasticity at a high strain rate of about 0.1s[sup [minus]1]. Superplastic deformation mechanisms of the ceramic whisker or particulate reinforced aluminium alloy composites are fine grain boundary sliding, interfacial sliding at a liquid phase and dynamic recrystallization. An AlN particulate reinforced aluminium alloy composite exhibits a high elastic modulus and a high thermal conductivity, and their thermal expansion is similar to silicon in that the AlN particulate reinforced aluminum alloy composite is expected to apply to semi-conductor packaging in the aerospace structure. In addition, if the composite could produce superplasticity at high strain rates, the market of aerospace application for superplastic composites could be expanded. The purpose of this study is to make clear if an AlN particulate reinforced aluminium alloy composite can produce superplasticity at high strain rate and the superplastic characteristics.

Imai, T. (National Industrial Research Inst. of Nagoya (Japan)); L'Esperance, G.; Hong, B.D. (Ecole Polytechnique de Montreal, Quebec (Canada))

1994-08-01

423

Notch effects on high-cycle fatigue properties of Ti–6Al–4V ELI alloy at cryogenic temperatures  

Microsoft Academic Search

Notch effects on the high-cycle fatigue properties of the forged Ti–6Al–4V ELI alloy at cryogenic temperatures were investigated. Also, the high-cycle fatigue data were compared with the rolled Ti–5Al–2.5Sn ELI alloy. The one million cycles fatigue strength (FS) of the smooth specimen for the forged Ti–6Al–4V ELI alloy increased with a decrease of test temperature. However, the FS of each

T. Yuri; Y. Ono; T. Ogata

2006-01-01