Sample records for high al stress

  1. Phosphorus Enhances Al Resistance in Al-resistant Lespedeza bicolor but not in Al-sensitive L. cuneata Under Relatively High Al Stress

    PubMed Central

    Sun, Qing Bin; Shen, Ren Fang; Zhao, Xue Qiang; Chen, Rong Fu; Dong, Xiao Ying

    2008-01-01

    Background and Aims Aluminium (Al) toxicity and phosphorus (P) deficiency often co-exist in acidic soils and limit crop production worldwide. Lespedeza bicolor is a leguminous forage species that grows very well in infertile, acidic soils. The objective of this study was to investigate the effects of Al and P interactions on growth of Lespedeza and the distributions of Al and P in two different Al-resistant species, and to explore whether P can ameliorate the toxic effect of Al in the two species. Methods Two species, Lespedeza bicolor and L. cuneata, were grown for 30 d with alternate Al and P treatments in a hydroponics system. Harvested roots were examined using a root-system scanner, and the contents of Al, P and other nutrient elements in the plants were determined using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Haematoxylin staining was used to observe the distribution of Al in the roots of seedlings. After pre-culture with or without P application, organic acids in the exudates of roots exposed to Al were held in an anion-exchange resin, eluted with 2 m HCl and then analysed using high-performance liquid chromatography (HPLC). Key Results Lespedeza bicolor exhibited a stronger Al resistance than did L. cuneata; Al exclusion mechanisms may mainly be responsible for resistance. P application alleviated the toxic effect of Al on root growth in L. bicolor, while no obvious effects were observed in L. cuneata. Much less Al was accumulated in roots of L. bicolor than in L. cuneata after P application, and the P contents in both roots and shoots increased much more for L. bicolor than for L. cuneata. Lespedeza bicolor showed a higher P/Al ratio in roots and shoots than did L. cuneata. P application decreased the Al accumulation in root tips of L. bicolor but not in L. cuneata. The amount of Al-induced organic acid (citrate and malate) exudation from roots pre-cultured with P was much less than from roots without P application; no malate and citrate exudation was detected in L. cuneata. Conclusions P enhanced Al resistance in the Al-resistant L. bicolor species but not in the Al-sensitive L. cuneata under relatively high Al stress, although P in L. cuneata might also possess an alleviative potential. Enhancement of Al resistance by P in the resistant species might be associated with its more efficient P accumulation and translocation to shoots and greater Al exclusion from root tips after P application, but not with an increased exudation of organic acids from roots. PMID:18757448

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

    E-print Network

    Azize, Mohamed

    We report the nanoscale characterization of the mechanical stress in InAlN/GaN nanoribbon-structured high electron mobility transistors (HEMTs) through the combined use of convergent beam electron diffraction (CBED) and ...

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

    E-print Network

    Li, Libing

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

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

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

  5. The impact of mechanical stress on the degradation of AlGaN/GaN high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Choi, Sukwon; Heller, Eric; Dorsey, Donald; Vetury, Ramakrishna; Graham, Samuel

    2013-10-01

    Coupled electro-thermo-mechanical simulation and Raman thermometry were utilized to analyze the evolution of mechanical stress in AlGaN/GaN high electron mobility transistors (HEMTs). This combined analysis was correlated with electrical step stress tests to determine the influence of mechanical stress on the degradation of actual devices under diverse bias conditions. It was found that the total stress as opposed to one dominant stress component correlated the best with the degradation of the HEMT devices. These results suggest that minimizing the total stress as opposed to the inverse piezoelectric stress in the device is necessary in order to avoid device degradation which can be accomplished through various growth methods.

  6. Reduction of Flicker Noise in AlGaN\\/GaN-Based HFETs After High Electric-Field Stress

    Microsoft Academic Search

    Congyong Zhu; Cemil Kayis; Mo Wu; Xing Li; Fan Zhang; Vitaliy Avrutin; Ümit Ozgur; Hadis Morkoc

    2011-01-01

    We report on the evolution of AlGaN\\/GaN-based het- erojunction field-effect transistor (HFET) operation under high- electric-field stress. Specifically, a 10 ? 15 dB decrease in the flicker noise is observed after stress in contrast with what has been nominally observed and reported in the literature in the realm of direct-current characteristics. Gate lag measurements revealed a trap state with an

  7. AlGaN/GaN High Electron Mobility Transistor degradation under on-and off-state stress

    E-print Network

    Florida, University of

    AlGaN/GaN High Electron Mobility Transistor degradation under on- and off-state stress E.A. Douglas of Materials Science & Engineering, University of Florida, Gainesville, FL 32611, United States b Department degradation of the submi- cron HEMTs as compared to the excellent stability of the TLM patterns under the same

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

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

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

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

    SciTech Connect

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

    2011-04-01

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

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

    SciTech Connect

    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

    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.

  11. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: High-electric-field-stress-induced degradation of SiN passivated AlGaN\\/GaN high electron mobility transistors

    Microsoft Academic Search

    Wen-Ping Gu; Huan-Tao Duan; Jin-Yu Ni; Yue Hao; Jin-Cheng Zhang; Qian Feng; Xiao-Hua Ma

    2009-01-01

    AlGaN\\/GaN high electron mobility transistors (HEMTs) are fabricated by employing SiN passivation, this paper investigates the degradation due to the high-electric-field stress. After the stress, a recoverable degradation has been found, consisting of the decrease of saturation drain current IDsat, maximal transconductance gm, and the positive shift of threshold voltage VTH at high drain-source voltage VDS. The high-electric-field stress degrades

  12. High mobility AlGaN/GaN heterostructures grown on Si substrates using a large lattice-mismatch induced stress control technology

    NASA Astrophysics Data System (ADS)

    Cheng, Jianpeng; Yang, Xuelin; Sang, Ling; Guo, Lei; Hu, Anqi; Xu, Fujun; Tang, Ning; Wang, Xinqiang; Shen, Bo

    2015-04-01

    A large lattice-mismatch induced stress control technology with a low Al content AlGaN layer has been used to grow high quality GaN layers on 4-in. Si substrates. The use of this technology allows for high mobility AlGaN/GaN heterostructures with electron mobility of 2040 cm2/(V.s) at sheet charge density of 8.4 × 1012 cm-2. Strain relaxation and dislocation evolution mechanisms have been investigated. It is demonstrated that the large lattice mismatch between the low Al content AlGaN layer and AlN buffer layer could effectively promote the edge dislocation inclination with relatively large bend angles and therefore significantly reduce the dislocation density in the GaN epilayer. Our results show a great potential for fabrication of low-cost and high performance GaN-on-Si power devices.

  13. Recovery in dc and rf performance of off-state step-stressed AlGaN/GaN high electron mobility transistors with thermal annealing

    NASA Astrophysics Data System (ADS)

    Kim, Byung-Jae; Hwang, Ya-Hsi; Ahn, Shihyun; Zhu, Weidi; Dong, Chen; Lu, Liu; Ren, Fan; Holzworth, M. R.; Jones, Kevin S.; Pearton, Stephen J.; Smith, David J.; Kim, Jihyun; Zhang, Ming-Lan

    2015-04-01

    The recovery effects of thermal annealing on dc and rf performance of off-state step-stressed AlGaN/GaN high electron mobility transistors were investigated. After stress, reverse gate leakage current and sub-threshold swing increased and drain current on-off ratio decreased. However, these degradations were completely recovered after thermal annealing at 450 °C for 10 mins for devices stressed either once or twice. The trap densities, which were estimated by temperature-dependent drain-current sub-threshold swing measurements, increased after off-state step-stress and were reduced after subsequent thermal annealing. In addition, the small signal rf characteristics of stressed devices were completely recovered after thermal annealing.

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

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

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

    Microsoft Academic Search

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

    2008-01-01

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

  16. Electron velocity of 6 × 107 cm/s at 300 K in stress engineered InAlN/GaN nano-channel high-electron-mobility transistors

    NASA Astrophysics Data System (ADS)

    Arulkumaran, S.; Ng, G. I.; Manoj Kumar, C. M.; Ranjan, K.; Teo, K. L.; Shoron, O. F.; Rajan, S.; Bin Dolmanan, S.; Tripathy, S.

    2015-02-01

    A stress engineered three dimensional (3D) Triple T-gate (TT-gate) on lattice matched In0.17Al0.83N/GaN nano-channel (NC) Fin-High-Electron-Mobility Transistor (Fin-HEMT) with significantly enhanced device performance was achieved that is promising for high-speed device applications. The Fin-HEMT with 200-nm effective fin-width (Weff) exhibited a very high IDmax of 3940 mA/mm and a highest gm of 1417 mS/mm. This dramatic increase of ID and gm in the 3D TT-gate In0.17Al0.83N/GaN NC Fin-HEMT translated to an extracted highest electron velocity (ve) of 6.0 × 107 cm/s, which is ˜1.89× higher than that of the conventional In0.17Al0.83N/GaN HEMT (3.17 × 107 cm/s). The ve in the conventional III-nitride transistors are typically limited by highly efficient optical-phonon emission. However, the unusually high ve at 300 K in the 3D TT-gate In0.17Al0.83N/GaN NC Fin-HEMT is attributed to the increase of in-plane tensile stress component by SiN passivation in the formed NC which is also verified by micro-photoluminescence (0.47 ± 0.02 GPa) and micro-Raman spectroscopy (0.39 ± 0.12 GPa) measurements. The ability to reach the ve = 6 × 107 cm/s at 300 K by a stress engineered 3D TT-gate lattice-matched In0.17Al0.83N/GaN NC Fin-HEMTs shows they are promising for next-generation ultra-scaled high-speed device applications.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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.

  18. Progressive failure site generation in AlGaN/GaN high electron mobility transistors under OFF-state stress: Weibull statistics and temperature dependence

    NASA Astrophysics Data System (ADS)

    Sun, Huarui; Bajo, Miguel Montes; Uren, Michael J.; Kuball, Martin

    2015-01-01

    Gate leakage degradation of AlGaN/GaN high electron mobility transistors under OFF-state stress is investigated using a combination of electrical, optical, and surface morphology characterizations. The generation of leakage "hot spots" at the edge of the gate is found to be strongly temperature accelerated. The time for the formation of each failure site follows a Weibull distribution with a shape parameter in the range of 0.7-0.9 from room temperature up to 120 °C. The average leakage per failure site is only weakly temperature dependent. The stress-induced structural degradation at the leakage sites exhibits a temperature dependence in the surface morphology, which is consistent with a surface defect generation process involving temperature-associated changes in the breakdown sites.

  19. Stress-corrosion resistance of high-strength Al-Zn-Mg-Cu alloys with and without silver additions

    Microsoft Academic Search

    H. Y. Hunsicker; J. T. Staley; R. H. Brown

    1972-01-01

    The separate and combined effects of adding silver, substituting other elements for chromium, increasing zinc, or varying\\u000a the copper content on the tensile properties and resistance to stress-corrosion cracking of 7075-type alloys were investigated.\\u000a Adding silver produced no increase in strength and marginal increases in the resistance to stress-corrosion cracking. Substituting\\u000a either zirconium or manganese for chromium increased strength and

  20. ALS and Oxidative Stress: The Neurovascular Scenario

    PubMed Central

    Thakur, Keshav; Gupta, Pawan Kumar

    2013-01-01

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

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

    SciTech Connect

    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

    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.

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

    SciTech Connect

    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

    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.

  3. Stress measurements in thermal loaded (Ti,Al)N hard coatings

    Microsoft Academic Search

    Th. Göbel; S. Menzel; M. Hecker; W. Brückner; K. Wetzig; Ch. Genzel

    2001-01-01

    Extreme thermal load of (Ti,Al)N coated WC–Co tools during the dry high-speed cutting process results in large thermal stresses superimposing the residual stresses in the films. This can cause layer damage by cracking and delamination. Therefore a stress determination in (Ti,Al)N coatings can help to understand these damaging processes. Fine crystalline (Ti,Al)N hard coatings with an Al\\/Ti ratio of 1.33

  4. Stress granules as crucibles of ALS pathogenesis

    PubMed Central

    King, Oliver D.

    2013-01-01

    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

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

    SciTech Connect

    Chouchane, F.; Almuneau, G., E-mail: almuneau@laas.fr; Arnoult, A.; Lacoste, G.; Fontaine, C. [CNRS, LAAS, 7 avenue du colonel Roche, F-31400 Toulouse (France); Univ de Toulouse, UPS, LAAS, F-31400 Toulouse (France); Cherkashin, N. [Univ de Toulouse, UPS, LAAS, F-31400 Toulouse (France); CNRS, CEMES, 29 Rue Jeanne Marvig, 31055 Toulouse Cedex 4 (France)

    2014-07-28

    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 Al{sub x}Ga{sub 1?x}As/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.

  6. Stress corrosion of high strength aluminum alloys.

    NASA Technical Reports Server (NTRS)

    Cocks, F. H.; Brummer, S. B.

    1972-01-01

    An investigation has been carried out to examine the relationship of the observed chemical and mechanical properties of Al-Cu and Al-Zn-Mg alloys to the stress corrosion mechanisms which dominate in each case. Two high purity alloys and analogous commercial alloys were selected. Fundamental differences between the behavior of Al-Cu and of Al-Zn-Mg alloys were observed. These differences in the corrosion behavior of the two types of alloys are augmented by substantial differences in their mechanical behavior. The relative cleavage energy of the grain boundaries is of particular importance.

  7. High temperature deformation of 6061 Al

    SciTech Connect

    Kyungtae Park; Lavernia, E.J.; Mohamed, F.A. (Univ. of California, Irvine (United States). Dept. of Mechanical and Aerospace Engineering)

    1994-03-01

    The creep behavior of powder metallurgy (PM) 6061 Al, which has been used as a metal matrix alloy in the development of discontinuous silicon carbide reinforced aluminum (SiC-Al) composites, has been studied over six orders of magnitude of strain rate. The experimental data show that the steady-state stage of the creep curve is of short duration; that the stress dependence of creep rate is high and variable; and that the temperature dependence of creep rate is much higher than that for self-diffusion in aluminum. The above creep characteristics are different from those documented for aluminum based solid-solution alloys but are similar to those reported for discontinuous SiC-Al composites and dispersion-strengthened (DS) alloys. Analysis of the experimental data shows that while the high stress dependence of creep rate in 6061 Al, like that in DS alloys, can be explained in terms of a threshold stress for creep, the strong temperature dependence of creep rate in the alloy is incompatible with the predictions of available threshold stress models and theoretical treatments proposed for DS alloys.

  8. On the effect of deep-rolling and laser-peening on the stress-controlled low- and high-cycle fatigue behavior of Ti-6Al-4V at elevated temperatures up to 550?C

    SciTech Connect

    Ritchie, IAltenberger, RKNalla, YSano LWagner, RO

    2012-04-01

    The effect of surface treatment on the stress/life fatigue behavior of a titanium Ti-6Al-4V turbine fan blade alloy is investigated in the regime of 102 to 106 cycles to failure under fully reversed stress-controlled isothermal push-pull loading between 25? and 550?C at a frequency of 5 Hz. Specifically, the fatigue behavior was examined in specimens in the deep-rolled and laser-shock peened surface conditions, and compared to results on samples in the untreated (machined and stress annealed) condition. Although the fatigue resistance of the Ti-6Al-4V alloy declined with increasing test temperature regardless of surface condition, deep-rolling and laser-shock peening surface treatments were found to extend the fatigue lives by factors of more than 30 and 5-10, respectively, in the high-cycle and low-cycle fatigue regimes at temperatures as high as 550?C. At these temperatures, compressive residual stresses are essentially relaxed; however, it is the presence of near-surface work hardened layers, with a nanocystalline structure in the case of deep-rolling and dense dislocation tangles in the case of laser-shock peening, which remain fairly stable even after cycling at 450?-550?C, that provide the basis for the beneficial role of mechanical surface treatments on the fatigue strength of Ti-6Al-4V at elevated temperatures.

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

    SciTech Connect

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

    2004-12-01

    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.

  10. 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)

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

    2012-09-01

    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.

  11. Residual stresses in continuous graphite fiber Al metal matrix composites

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    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.

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

    SciTech Connect

    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

    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.

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

    SciTech Connect

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

    2005-04-20

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

  14. Stress and Western Kansas High School Students.

    ERIC Educational Resources Information Center

    Walker, Janet K.

    Research on adolescent stress indicates that most high school students have experienced stress. This study was conducted to learn more about stress in western Kansas high school students. The sample was from 1A schools, defined as having less than 75 students enrolled in grades 10 to 12. Three-hundred twenty-two students participated. Stress was…

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  16. High Temperature Mechanical Characterization and Analysis of Al2O3 /Al2O3 Composition

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, John Z.; Jaskowiak, Martha H.

    1999-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    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

    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.

  18. Thermal Relaxation of Residual Stresses in Shot Peened Surface Layer of SiCw/Al Composite

    NASA Astrophysics Data System (ADS)

    Huang, Junjie; Wang, Zhou; Bian, Kai; Jiang, Chuanhai

    2012-06-01

    The residual stress relaxation of the shot peened layer on the SiCw/Al composite during isothermal annealing was investigated. The results showed that the residual stresses relaxed in the whole deformation layer especially when the annealing temperature was higher than 200 °C. The relaxation process during isothermal annealing could be described precisely using Zener-Wert-Avrami function. Because of high intensity dislocation around reinforcements producing a large amount of stored energy, the residual stress relaxation activation enthalpy of shot peened SiCw/Al was smaller than self-diffusion activation enthalpy of pure aluminum. According to the analysis of full-width at half-maximum (FWHM) of the shot peened composite in different annealing temperatures, it can be concluded the recovery and recrystallization behavior became intensely when anneal temperature was larger than 200 °C. The small relaxation of residual stress in low annealing temperature was mainly due to partly recovery and recrystallization in a very low level.

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

    ERIC Educational Resources Information Center

    Belsky, Jay

    2014-01-01

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

  20. Relationship between electrical conductivity and stress corrosion cracking susceptibility of Al 7075 and Al 7475 alloys

    SciTech Connect

    Tsai, T.C.; Chuang, T.H. [National Taiwan Univ., Taipei (Taiwan, Province of China). Inst. of Materials Science and Engineering

    1996-06-01

    A relationship between electrical conductivity and stress corrosion cracking (SCC) resistance of the 7,000-series Al-Zn-Mg alloys has been established, although only from the near-peak strength T6 temper to the overaged T73 tempered condition. The present work investigated whether this relationship exists for all periods of aging and for Al alloys with different compositions and grain structures. The materials studied were commercial 2-mm thick Al 7075 (Al-5.76% Zn-2.46% Mg-1.70% Cu-0.20% Cr-0.12% Fe-0.09% Si-0.06% Mn-0.04% Ti) and Al 7475 (Al-5.80% Zn-2.24% Mg-1.53% Cu-0.19% Cr-0.08% Fe-0.02% Si-0.01% Mn-0.02% Ti) alloy plates.

  1. High temperature deformation of 6061 Al

    Microsoft Academic Search

    Kyungtae Park; E. J. Lavernia; F. A. Mohamed

    1994-01-01

    The creep behavior of powder metallurgy (PM) 6061 Al, which has been used as a metal matrix alloy in the development of discontinuous silicon carbide reinforced aluminum (SiC-Al) composites, has been studied over six orders of magnitude of strain rate. The experimental data show that the steady-state stage of the creep curve is of short duration; that the stress dependence

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

    NASA Astrophysics Data System (ADS)

    Waki, Hiroyuki; Fujioka, Hidenori; Kobayashi, Akira

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

  3. In situ stress evolution during and after sputter deposition of Al thin films

    NASA Astrophysics Data System (ADS)

    Pletea, M.; Koch, R.; Wendrock, H.; Kaltofen, R.; Schmidt, O. G.

    2009-06-01

    The stress, growth, and morphology evolution of Al thin films up to 300 nm thick, sputter deposited at a constant rate of 0.04 nm s-1 onto thermally oxidized Si(100) substrates have been investigated for various sputter pressures in the range from 0.05 to 6 Pa. The stress evolution has been studied during and after the film deposition by means of in situ substrate curvature measurements using an optical two-beam deflection method. In order to obtain insight into the mechanisms of stress generation and relaxation, the microstructure of the films was investigated by scanning electron microscopy, focused-ion-beam microscopy, and atomic force microscopy. The stress evolution during the early stage of deposition of films is consistent with the Volmer-Weber growth mode known for metals with high adatom mobility. For thicker films, the compressive stress increases in the sputter pressure range of 0.05-0.5 Pa, whereas at even higher sputter pressures a transition from compressive to tensile stress takes place. This transition is correlated with a change from a relatively dense to a more porous microstructure characterized by decreasing mass density and increasing electrical resistivity with increasing sputter pressure. The dependence of the stress and microstructure on the sputter pressure can be consistently understood through a combination of the stress mechanisms for vapor and sputter deposited films proposed in the literature.

  4. Optical characterization of AlN films: measurement of stress

    Microsoft Academic Search

    K. Chakrabarti; K. K. Chattopadhyay; S. Chaudhuri; A. K. Pal

    1997-01-01

    AlN films were deposited on quartz and silicon substrates by d.c. magnetron sputtering of an Al target in argon + nitrogen plasma (20–100 vol.% nitrogen). Transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies indicated the films to be polycrystalline for higher nitrogen (>30 vol.%) and amorphous for lower nitrogen in the sputtering gas. Direct optical transition with high band

  5. Investigation for Different Peening Techniques on Residual Stress Field of SiCw/Al Composite

    NASA Astrophysics Data System (ADS)

    Huang, Junjie; Wang, Zhou; Bian, Kai; Jiang, Chuanhai

    2013-03-01

    In order to improve the residual stress field of SiCw/Al composite after conventional shot peening, modified warm peening, stress peening, and compound peening were carried out on SiCw/Al composite specimens and residual stress fields of those specimens were investigated via x-ray measurement. Results show conventional peening can improve residual stress field of SiCw/Al composite but the improvement has a limit. Compared with conventional peening, modified warm peening can increase the maximum residual stress, the depth of compressive residual stress layer and improve stability of residual stress field whereas stress peening can increase all characteristic parameters of residual stress field efficiently. Compound peening combines the positive effects of modified warm peening and stress peening, and has the most strengthening effects.

  6. Degradation characteristics of AlGaN-GaN high electron mobility transistors

    Microsoft Academic Search

    Hyungtak Kim; V. Tilak; B. M. Green; Ho-young Cha; J. A. Smart; J. R. Shealy; L. F. Eastman

    2001-01-01

    AlGaN-GaN high electron mobility transistors (HEMTs) have shown great potential for high temperature\\/high power electronics. However, the study on the reliability of GaN-based devices is still at the initial stages. In this work, we report the degradation characteristics of AlGaN HEMTs under various stress conditions such as DC stress (gate current extraction and hot electron cycles) and RF input drive

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

    Microsoft Academic Search

    P. Dong; J. K. Hong; P. Rogers

    1998-01-01

    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

  8. Correlation of mechanical stress and Doppler broadening of the positron annihilation line in Al and Al alloys

    NASA Astrophysics Data System (ADS)

    Hugenschmidt, C.; Qi, N.; Stadlbauer, M.; Schreckenbach, K.

    2009-12-01

    The plastic deformation of Al samples, of the technical alloys AlMgSi0.5, and AlMg3 was studied by Doppler-broadening spectroscopy (DBS) of the positron annihilation line. First, the defect sensitive line-shape parameter S was measured after the application of axial tensile stress, and the corresponding stress-strain curves were recorded that allowed us to correlate the strain, the mechanical stress and the S -parameter values after mechanical load quantitatively. In a next step, asymmetrically deformed Al samples were investigated with a monoenergetic positron beam by DBS in order to obtain the laterally resolved information of the stress-induced defects. It is demonstrated that the resulting two-dimensional S -parameter map (scan area 14×14mm2 , step width 1 mm) can be expressed quantitatively in terms of the locally acting stress which is responsible for the creation of the lattice defects.

  9. Stress evolution during and after sputter deposition of thin Cu Al alloy films

    NASA Astrophysics Data System (ADS)

    Pletea, M.; Wendrock, H.; Kaltofen, R.; Schmidt, O. G.; Koch, R.

    2008-06-01

    The stress evolution during and after sputter deposition of thin Cu-Al alloy films containing 1 and 2 at.% Al onto oxidized Si(100) substrates has been studied up to thicknesses of 300 nm by means of in situ substrate curvature measurements. In order to correlate stress and morphology, the microstructure was investigated by focused ion beam microscopy, scanning electron microscopy, and atomic force microscopy. The evolution of the stress and microstructure of the Cu-Al alloy films is similar to that for sputtered pure Cu films. Film growth proceeds in the Volmer-Weber mode, typical for high mobility metals. It is characterized by nucleation, island, percolation, and channel stages before the films become continuous, as well as lateral grain growth in the compact films. With increasing Al content the overall atom mobility and, thus, the average grain size of the alloy films are reduced. Increase of the sputter pressure from 0.5 to 2 Pa leads to films with larger grain size, rougher surface morphology and higher electrical resistivity.

  10. On Core Structure Properties and Peierls Stress of Dissociated Superdislocations in Aluminides: NiAl and FeAl

    Microsoft Academic Search

    Xiaozhi Wu; Shaofeng Wang; Congbo Li

    2010-01-01

    The study of dislocation properties in B2 structure intermetallics NiAl and FeAl is crucial to understand their mechanical behaviors. In this paper, the core structure and Peierls stress of collinear dissociated (111}{110} edge superdislocations in NiAl and FeAl are investigated with the modified P-N dislocation equation. The generalized stacking fault energy curve along (111) direction in {110} slip plane contains

  11. Modelling Of Residual Stresses Induced By High Speed Milling Process

    NASA Astrophysics Data System (ADS)

    Desmaison, Olivier; Mocellin, Katia; Jardin, Nicolas

    2011-05-01

    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.

  12. Stress management in high-field dipoles

    Microsoft Academic Search

    N. Diaczenko; T. Elliott; A. Jaisle; D. Latypov; P. McIntyre; P. McJunkins; L. Richards; W. Shen; R. Soika; D. Wendt; R. Gaedke

    1997-01-01

    The management of Lorentz stress and preload forces is the biggest single challenge in the effort to develop collider dipoles with ever greater field strength. Were the Lorentz forces permitted to accumulate through a coil, they would exceed the limit for strain degradation for the A15 and high-temperature superconductors which are capable of sustaining such field strength. A strategy has

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

    SciTech Connect

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

    2012-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

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

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

    SciTech Connect

    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

    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.

  16. Residual Stress Characterization of Al/SiC Nanoscale Multilayers using X-ray

    SciTech Connect

    D Singh X Deng; N Chawla; J Bai; C Hubbard; G Tang; Y Shen

    2011-12-31

    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.

  17. The strengthening effect of Al{sub 3}Ti in high temperature deformation of Al-Al{sub 3}Ti composites

    SciTech Connect

    Wang, S.H.; Kao, P.W. [National Sun Yat-Sen Univ., Kaohsiung (Taiwan, Province of China). Inst. of Materials Science and Engineering] [National Sun Yat-Sen Univ., Kaohsiung (Taiwan, Province of China). Inst. of Materials Science and Engineering

    1998-05-01

    A series of Al-Al{sub 3}Ti composites with systematic variation of Al{sub 3}Ti content were prepared by mechanical alloying. Microstructural observations have indicated that among these composites, the only distinct variable is the Al{sub 3}Ti content, while the other microstructural variables are essentially the same. The high temperature (623--773 K) deformation behavior of these composites was found to be similar to that of dispersion-hardened aluminum. By considering the presence of a threshold stress, the plastic flow in these composites can be described by lattice-diffusion controlled dislocation creep in the aluminum matrix with a constant structure. The presence of Al{sub 3}Ti particles can increase the creep strength of these alloys significantly. By considering the load-sharing effect of Al{sub 3}Ti, an analysis based on continuum mechanics approach has been conducted, which can successfully account for the creep rate of these Al-Al{sub 3}Ti composites. The threshold stress for creep in these composites was found to increase with increasing Al{sub 3}Ti content, which could be attributed to the load-shearing effect of Al{sub 3}Ti particles.

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

    PubMed

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

    2015-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  20. Intrinsic stress evolution during amorphous oxide film growth on Al surfaces

    SciTech Connect

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

    2014-03-03

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

  1. Student Stress in High-Pressure College Preparatory Schools

    Microsoft Academic Search

    Lauren Deborah Feld

    2011-01-01

    Purpose: To enhance understanding of academic stress in the lives of high-achieving students enrolled in college-preparatory high schools. The three main goals of this study were to explore: 1) the effects of stress, 2) student coping behaviors and support network, and 3) sources of stress in these high-achieving environments.

  2. Characterisation of stress corrosion cracking (SCC) of Mg–Al alloys

    Microsoft Academic Search

    N. Winzer; A. Atrens; W. Dietzel; V. S. Raja; G. Song; K. U. Kainer

    2008-01-01

    Stress corrosion cracking (SCC) of the Mg–Al alloys AZ91, AZ31 and AM30 in distilled water has been characterised using constant extension rate tests (CERTs) and linearly increasing stress tests (LISTs). AZ91 consists of an ?-matrix with extensive ?-particles, whereas AZ31 and AM30 consist only of an ?-matrix with an Al-concentration similar to that in AZ91. The presence of ?-particles in

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Herzog, J. A.

    1981-01-01

    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.

  5. Stress Wave attenuation in SiC3D/Al Composite

    NASA Astrophysics Data System (ADS)

    Chunyuan, Yuan; Yangwei, Wang; Guoju, Li; Xu, Zhang; Jubin, Gao

    2013-03-01

    SiC3D/Al composite is a kind of special composite with interpenetrating network microstructure. The attenuation properties of stress wave propagation along the SiC3D/Al composite are studied by a Split Hopkinson Pressure Bar system & FEM simulations, and the attenuation mechanism is discussed in this paper. Results show that the attenuation rate of the stress wave in the composite is up to 1.73MPa·mm-1. The reduction of the amplitude of waves is caused by that plenty of interfaces between SiC and Al within the composite acting with stress waves. When the incident plane wave reaches the SiC3D/Al interface, reflection wave and transmission wave propagates in different directions along the irregular interface between SiC phase and aluminium phase due to the impedance mismatch of them, which leads to the divergence of stress wave. At the same time, some stress micro-focuses occurs in the aluminium phase for the complex wave superimposition, and some plastic deformation may take place within such micro-regions, which results in the consumption of stress wave energy. In conclusion, the stress wave attenuation is derived from divergence and consumption of stress wave.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  7. Effect of high substrate temperature on Al-doped ZnO thin films grown by pulsed laser deposition

    Microsoft Academic Search

    J Mass; P Bhattacharya; R. S Katiyar

    2003-01-01

    Thin films of Al-doped ZnO were grown on Al2O3 at high substrate temperature of 750°C by pulsed laser deposition technique with different Al concentrations. Highly c-axis oriented and transparent (80%) thin films were obtained at 1 mTorr of O2 pressure. Increase of Al doping changes the stress in the ZnO films from tensile to compressive as measured from c-parameter. The

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

    E-print Network

    Makaram, Prashanth

    We have investigated the surface morphology of electrically stressed AlGaN/GaN high electron mobility transistors using atomic force microscopy and scanning electron microscopy after removing the gate metallization by ...

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

    PubMed

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

    2013-03-01

    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

  10. Minimization of Residual Stress in an Al-Cu Alloy Forged Plate by Different Heat Treatments

    NASA Astrophysics Data System (ADS)

    Dong, Ya-Bo; Shao, Wen-Zhu; Jiang, Jian-Tang; Zhang, Bao-You; Zhen, Liang

    2015-06-01

    In order to improve the balance of mechanical properties and residual stress, various quenching and aging treatments were applied to Al-Cu alloy forged plate. Residual stresses determined by the x-ray diffraction method and slitting method were compared. The surface residual stress measured by x-ray diffraction method was consistent with that measured by slitting method. The residual stress distribution of samples quenched in water with different temperatures (20, 60, 80, and 100 °C) was measured, and the results showed that the boiling water quenching results in a 91.4% reduction in residual stress magnitudes compared with cold water quenching (20 °C), but the tensile properties of samples quenched in boiling water were unacceptably low. Quenching in 80 °C water results in 75% reduction of residual stress, and the reduction of yield strength is 12.7%. The residual stress and yield strength level are considerable for the dimensional stability of aluminum alloy. Quenching samples into 30% polyalkylene glycol quenchants produced 52.2% reduction in the maximum compressive residual stress, and the reduction in yield strength is 19.7%. Moreover, the effects of uphill quenching and thermal-cold cycling on the residual stress were also investigated. Uphill quenching and thermal-cold cycling produced approximately 25-40% reduction in residual stress, while the effect on tensile properties is quite slight.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  12. Thermal residual strains and stresses in Al{sub 2}O{sub 3}/Al composites with interpenetrating networks

    SciTech Connect

    Hoffman, M. [Univ. of Technology, Darmstadt (Germany). Dept. of Materials Science] [Univ. of Technology, Darmstadt (Germany). Dept. of Materials Science; [Univ. of New South Wales, Sydney, New South Wales (Australia). School of Materials Science and Engineering; Skirl, S.; Roedel, J. [Univ. of Technology, Darmstadt (Germany). Dept. of Materials Science] [Univ. of Technology, Darmstadt (Germany). Dept. of Materials Science; Pompe, W. [Technical Univ. Dresden (Germany). Dept. of Materials Science] [Technical Univ. Dresden (Germany). Dept. of Materials Science

    1999-01-15

    Thermal expansion data for Al{sub 2}O{sub 3}/Al interpenetrating network composites, obtained using a dilatometer, are analyzed to determine the residual stress during, and after, thermal cycling between room temperature and 600 C. A rigorous technique, using the effective medium approximation method, is applied, utilizing unconstrained thermal strains of the individual phases which are determined experimentally. Coefficients of thermal expansion are predicted as a function of metal content and temperature. Residual stresses are calculated using two approaches: (1) a macroscopic approach which considers total composite strain and (2) a micromechanical approach which considers time dependent effects in the metal phase. Predictions agree well with experimental data and neutron diffraction measurements, and provide a mechanistic understanding of the thermo-mechanical behavior of the material.

  13. High School Seniors Tell Why They Are "Stressed Out."

    ERIC Educational Resources Information Center

    Amen, John; Reglin, Gary

    1992-01-01

    Determines through the analysis of data collected from students the primary causes of stress among high school seniors. Presents research findings based on 348 responses to open-ended questions regarding stress. Lists stresses in six categories: school, family, employment, intimate relationships, friends/peers, and worrying about college. (HB)

  14. The microstructure, mechanical stress, texture, and electromigration behavior of Al-Pd alloys

    NASA Astrophysics Data System (ADS)

    Rodbell, K. P.; Knorr, D. B.; Mis, J. D.

    1993-06-01

    As the minimum feature size of interconnect lines decreases below 0.5 urn, the need to control the line microstructure becomes increasingly important. The alloy content, deposition process, fabrication method, and thermal history all determine the microstructure of an interconnect, which, in turn, affects its performance and reliability. The motivation for this work was to characterize the microstructure of various sputtered Al-Pd alloys (Al-0.3wt.%Pd, Al-2Cu-0.3Pd, and Al-0.3Nb-0.3Pd) vs sputtered Al-Cu control samples (Al-0.5Cu and Al-2Cu) and to assess the role of grain size, mechanical stress, and crystallographic texture on the electromigration behavior of submicrometer wide lines. The grain size, mechanical stress, and texture of blanket films were measured as a function of annealing. The as-deposited film stress was tensile and followed a similar stress history on heating for all of the films; on cooling, however, significant differences were observed between the Al-Pd and Al-Cu films in the shape of their stress-temperature-curves. A strong (111) crystallographic texture was typically found for Al-Cu films deposited on SiO2. A stronger (111) texture resulted when Al-Cu was deposited on 25 nm titanium. Al-0.3Pd films, however, exhibited either a weak (111) or (220) texture when deposited on SiO2, which reverted to a strong (111) texture when deposited on 25 nm titanium. The electromigration lifetimes of passivated, ?0.7 ?m wide lines at 250°C and 2.5 × 106 A/cm2 for both single and multi-level samples (separated with W studs) are reported. The electromigration behavior of Al-0.3Pd was found to be less dependent on film microstructure than on the annealing atmosphere used, i.e. forming gas (90% N2-10%H2) annealed Al-0.3Pd films were superior to all of the alloys investigated, while annealing in only N2 resulted in poor lifetimes.

  15. Coping with the Stress of High Stakes Testing

    ERIC Educational Resources Information Center

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

    2007-01-01

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

  16. Stacking fault energy, yield stress anomaly, and twinnability of Ni3Al: A first principles study

    NASA Astrophysics Data System (ADS)

    Liu, Li-Li; Wu, Xiao-Zhi; Wang, Rui; Li, Wei-Guo; Liu, Qing

    2015-07-01

    Using first principles calculations combined with the quasiharmonic approach, we study the effects of temperature on the elastic constants, generalized stacking fault energies, and generalized planar fault energies of Ni3Al. The antiphase boundary energies, complex stacking fault energies, superlattice intrinsic stacking fault energies, and twinning energies decrease slightly with temperature. Temperature dependent anomalous yield stress of Ni3Al is predicted by the energy-based criterion based on elastic anisotropy and antiphase boundary energies. It is found that p increases with temperature and this can give a more accurate description of the anomalous yield stress in Ni3Al. Furthermore, the predicted twinnablity of Ni3Al is also decreasing with temperature. Project supported by the National Natural Science Foundation of China (Grant Nos. 11104361 and 11304403) and the Fundamental Research Funds for the Central Universities, China (Grant Nos. CQDXWL2014003 and CDJZR14328801).

  17. AlGaN\\/AlN\\/GaN high-power microwave HEMT

    Microsoft Academic Search

    L. Shen; S. Heikman; B. Moran; R. Coffie; N.-Q. Zhang; D. Buttari; I. P. Smorchkova; S. Keller; S. P. DenBaars; U. K. Mishra

    2001-01-01

    In this letter, a novel heterojunction AlGaN\\/AlN\\/GaN high-electron mobility transistor (HEMT) is discussed. Contrary to normal HEMTs, the insertion of the very thin AlN interfacial layer (~1 nm) maintains high mobility at high sheet charge densities by increasing the effective ?EC and decreasing alloy scattering. Devices based on this structure exhibited good DC and RF performance. A high peak current

  18. ZERODUR® glass ceramics for high stress applications

    NASA Astrophysics Data System (ADS)

    Hartmann, Peter; Nattermann, Kurt; Döhring, Thorsten; Jedamzik, Ralf; Kuhr, Markus; Thomas, Peter; Kling, Guenther; Lucarelli, Stefano

    2009-08-01

    Recently SCHOTT has shown in a series of investigations the suitability of the zero expansion glass ceramic material ZERODUR® for applications like mirrors and support structures of complicated design used at high mechanical loads. Examples are vibrations during rocket launches, bonded elements to support single mirrors or mirrors of a large array, or controlled deformations for optical image correction, i.e. adaptive mirrors. Additional measurements have been performed on the behavior of ZERODUR® with respect to the etching process, which is capable of increasing strength significantly. It has been determined, which minimum layer thickness has to be removed in order to achieve the strength increase reliably. New data for the strength of the material variant ZERODUR K20® prepared with a diamond grain tool D151 are available and compared with the data of ZERODUR® specimens prepared in the same way. Data for the stress corrosion coefficient n of ZERODUR® for dry and normal humid environment have been measured already in the 1980s. It has been remeasured with the alternative double cleavage drilled compression (DCDC) method.

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

    NASA Astrophysics Data System (ADS)

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

    2013-11-01

    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.

  20. Oxidative stress in ALS: A mechanism of neurodegeneration and a therapeutic target

    Microsoft Academic Search

    Siân C. Barber; Richard J. Mead; Pamela J. Shaw

    2006-01-01

    The cause(s) of amyotrophic lateral sclerosis (ALS) is not fully understood in the vast majority of cases and the mechanisms involved in motor neuron degeneration are multi-factorial and complex. There is substantial evidence to support the hypothesis that oxidative stress is one mechanism by which motor neuron death occurs. This theory becomes more persuasive with the discovery that mutation of

  1. Effects of SiN passivation and high-electric field on AlGaN-GaN HFET degradation

    Microsoft Academic Search

    Hyungtak Kim; Richard M. Thompson; Vinayak Tilak; Thomas R. Prunty; James R. Shealy; Lester F. Eastman

    2003-01-01

    The authors report on the effects of silicon nitride (SiN) surface passivation and high-electric field stress (hot electron stress) on the degradation of undoped AlGaN-GaN power HFETs. Stressed devices demonstrated a decrease in the drain current and maximum transconductance and an increase in the parasitic drain series resistance, gate leakage, and subthreshold current. The unpassivated devices showed more significant degradation

  2. Observation of morphology and stress distribution around dislocation in Ni3Al on the atomic scale

    NASA Astrophysics Data System (ADS)

    Ma, S. Y.; Ren, N. N.; Zhang, J. X.

    2015-06-01

    Dislocation is very important for the properties of materials. In this work, morphology and stress distribution around dislocation in Ni3Al are observed in atomic scale by the molecular dynamics. We obtained the dislocation morphology by the simulation and found that the atom distribution around the dislocation core is irregular. Layers of atoms on both the left and right sides of the dislocation core leans to the core, and about six layers of atoms are fractured due to the missing of the half plane of atoms. Along the [1 1 1] direction, there are about eight layers of atoms deviating from its equilibrium position. These results demonstrated that influenced area of dislocation is pipe-like. The stress distribution agrees with the results from the formula. Both normal stress and shear stress components exist in the edge dislocation stress field, normal stress mainly concentrating on two sides of the dislocation line, while the shear stress exist several angstrom away from the dislocation line.

  3. Piezospectroscopic Study of Residual Stresses in Al2O3-ZrO2 Directionally Solidified Eutectics

    Microsoft Academic Search

    Rosa I. Merino; Victor M. Orera; Javier LLorca

    2000-01-01

    The residual thermoelastic stresses were studied in Al2O3- ZrO2 (monoclinic zirconia, m-ZrO2) and Al2O3-ZrO2(Y2O3) (tetragonal zirconia, t-ZrO2) fibrous eutectics that were pro- duced via the laser floating zone method, using different piezospectrosocopic probes. The luminescence of the R-lines of ruby (Cr31 in Al2O3 phase) was used to determine the stresses in the Al2O3 matrix, assuming that the stress state in

  4. Microstructure and stress—strain responses of Al Mg Si alloy matrix composites reinforced with 10 vol.% Al 2O 3 particulates

    Microsoft Academic Search

    S. I. Hong; G GRAYIII; Z. Wang

    1996-01-01

    In this study, the microstructures and mechanical properties of underaged and peak-aged 6061 AlAl2O3 particulate composites were investigated. In the underaged composites, small spherical zones were observed and, in the peak-aged composites, needle-shaped Mg2Si precipitates were observed throughout the matrix. The stress-strain responses of the 6061 Al matrix composites were observed to be similar to those of commercially pure Al

  5. Weibull analysis of ceramics under high stress gradients

    Microsoft Academic Search

    T. Fett; E. Ernst; D. Munz; D. Badenheim; R. Oberacker

    2003-01-01

    The Weibull parameter m of the strength distribution of ceramics under high stress gradients differs from that for moderate stress gradients. This is shown for contact loading. Bars were loaded by oppositely concentrated forcers via rollers. For most investigated materials, measured contact strengths showed strongly reduced Weibull exponents compared with those from 4-point bending tests. This was the reason for

  6. Stress Manifestation in High School Students: An Australian Sample.

    ERIC Educational Resources Information Center

    Moulds, John D.

    2003-01-01

    Assesses stress symptoms associated with main daily hassles among grades 7, 9 and 11 students in all-female, all-male, and coeducational Catholic high schools in Western Sydney, Australia. Factor analysis identified the stress manifestation domains of anxiety, anger, and physiological arousal. Differences in these are examined and a conceptual…

  7. ZERODUR glass ceramics: design of structures with high mechanical stresses

    Microsoft Academic Search

    Kurt Nattermann; Peter Hartmann; Guenther Kling; Peter Gath; Stefano Lucarelli; Boris Messerschmidt

    2008-01-01

    Designing highly mechanically loaded structures made of the zero expansion glass ceramic material ZERODUR® means to analyze the stress for the whole loaded surface, considering changes of the stress state occurring over the total lifetime. Strength data are obtained from specimens with small size and relatively short loading duration, making them not directly applicable to the much larger areas that

  8. Through-thickness determination of phase composition and residual stresses in thermall barrier coatings using high- energy x-rays.

    SciTech Connect

    Weyant, , C. M.; Almer, J. D.; Faber, K. T.; Stony Brook Univ.

    2009-01-01

    High-energy X-rays were used to determine the local phase composition and residual stresses through the thickness of as-sprayed and heat-treated plasma-sprayed thermal barrier coatings consisting of a NiCoCrAlY bond coat and an yttria-stabilized zirconia (YSZ) topcoat produced with through-thickness segmentation cracks. The as-sprayed residual stresses reflected the combined influence of quenching stresses from the plasma spray process, thermal expansion mismatch between the topcoat, bond coat and substrate, and stress relief from the segmentation cracks. Heat treatments led to the formation of a thermally grown oxide (TGO) which was in compression in the plane, as well as relief of quenching stresses and development of a stress gradient in the YSZ topcoat. The high-energy X-ray technique used in this study revealed the effects that TGO and segmentation cracks have on the in-plane stress state of the entire coating.

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

    Microsoft Academic Search

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

    1998-01-01

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

  10. Magnetic properties and high frequency characteristics of FeCoAlON alloy films

    NASA Astrophysics Data System (ADS)

    Zheng, Kuohai; Yang, Shengsheng; Zheng, Fu; Luo, Feilong; Bai, Jianmin; Cao, Jiangwei; Wei, Fulin

    2015-06-01

    In this work, we report the magnetic properties, domain structures and high frequency properties of FeCoAlON alloy films prepared by reactive magnetron sputtering. With increasing N addition content, the films transfer from in-plane anisotropic properties to isotropic behavior. The obvious stripe domain structure is observed in the films with high N content, and the domain parameters depend on the thickness of the films. The XRD analysis indicates that the stripe domain may origin from the stress-induced perpendicular anisotropy by Al, O and N addition. Meanwhile, a double-peak resonance behavior is observed in the permeability spectra of the films with stripe domain structure.

  11. Stress corrosion cracking of sensitized AA5083 (Al4.5Mg1.0Mn)

    Microsoft Academic Search

    J. L. Searles; P. I. Gouma; R. G. Buchheit

    2001-01-01

    The AA5083 (Al-4.4Mg-0.7Mn-0.15Cr) alloy is a nonheat-treatable aluminum alloy known for its excellent corrosion resistance.\\u000a However, it can become susceptible to intergranular stress corrosion cracking (IGSCC) when exposed to temperatures ranging\\u000a from 50 °C to 200 °C for sufficient lengths of time. This IGSCC is widely believed to be associated with dissolution of the\\u000a electrochemically active ? phase, Al3Mg2, which

  12. Stress corrosion cracking and hydrogen embrittlement of an Al–Zn–Mg–Cu alloy

    Microsoft Academic Search

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

    2004-01-01

    The age hardening, stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of an Al–Zn–Mg–Cu 7175 alloy were investigated experimentally. There were two peak-aged states during ageing. For ageing at 413 K, the strength of the second peak-aged state was slightly higher than that of the first one, whereas the SCC susceptibility was lower, indicating that it is possible to heat

  13. Stress corrosion crack velocity and grain boundary precipitates in an Al-Zn-Mg alloy

    Microsoft Academic Search

    P. K. Poulose; J. E. Morral; A. J. McEvily

    1974-01-01

    The fracture kinetics of Al-5.5 Zn-2.5 Mg alloys submersed in 3 pct NaCl-H2O solutions were varied by heat treatment. The steady state velocity, on a plot of velocity vs stress intensity, was compared\\u000a with microstructure and it was found to be inversely proportional to the volume of MgZn2 in the grain boundary. This behavior suggests that grain boundary precipitates can

  14. Effect of microstructure on stress corrosion cracking of an Al-Zn-Mg-Cu alloy

    Microsoft Academic Search

    M. Puiggali; A. Zielinski; J. M. Olive; E. Renauld; D. Desjardins; M. Cid

    1998-01-01

    The susceptibility to stress corrosion cracking (SCC) of the Al-Zn-Mg-Cu French 7010 alloy of different temper has been investigated by Slow Strain Rate Testing. The tests have been carried out at strain rate ranged between 10?5 and 10?7s?1, at corrosion potential and at cathodic polarisation, in NaCl and NaCl + As2O3 solution. The lowest susceptibility to SCC of overaged alloy

  15. Stress distribution and mechanical properties of free and assembled Ni3Al nanoclusters

    Microsoft Academic Search

    E. E. Zhurkin; G. Hautier; M. Hou

    2006-01-01

    Classical molecular dynamics with a semiempirical N -body potential is used to study the distribution of local stress in bimetallic Ni3Al nanoparticles and in cluster-assembled materials. The materials considered are synthesized with these particles by low-energy deposition at 0.5eV per atom and by compaction with an external pressure of 2GPa , thus featuring different nanostructures. Both are nanoporous, the lowest

  16. High Performance AlInGaAs/AlGaAs Photocathode

    SciTech Connect

    Mamaev, Yu. A.; Gerchikov, L. G.; Yashin, Yu. P.; Vasiliev, D. A.; Kuzmichev, V. V. [State Polytechnic University, 195251, St. Petersburg (Russian Federation); Ustinov, V. M.; Zhukov, A. E. [St. Petersburg Scientific-Educational Center RAS, 195251, St. Petersburg (Russian Federation); Mikhrin, V. S. [Ioffe Physico-Technical Institute, RAS, 194021, St. Petersburg (Russian Federation)

    2008-02-06

    New photocathode for highly polarized electron emission has been developed, fabricated and studied. Polarized electron source is based on short-period strained AlInGaAs/AlGaAs superlattice grown by MBE method. Deformation of AlInGaAs quantum well results in 85 meV energy splitting between heavy hole and light hole minibands. Electron emission from the developed photocathode demonstrates maximal polarization of 92% with quantum efficiency of 0.85%.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    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.

  18. Elevated temperature neutron measurements of thermal residual stresses in a SiC fiber reinforced Al alloy

    SciTech Connect

    Ceretti, M. [CE Saclay, Gif sur Yvette (France). Lab. Leon Brillouin; Kocsis, M. [European Synchrotron Radiation Facility, Grenoble (France); Lodini, A. [Univ. de Reims Champagne Ardenne (France)

    1995-12-31

    The main objective of the present investigation is to determine the evolution of residual stresses by neutron powder diffraction in an Al/SiC composite (Al 7075 reinforced by 27 vol.% SiC whiskers), originating from thermal treatment and mechanical loading. The results show that residual stresses in the matrix and in the reinforcement decrease in magnitude with increasing temperature and they reach the stress free state at the equivalent temperature. As the temperature further increases, these stresses increase numerically in a reverse sense for both phases. The data obtained are analyzed in terms of a simple model based on Eshelby`s equivalent inclusion method.

  19. Nonuniform magnetic stresses in high temperature superconducting thin films

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  20. Influence of Pre-Heated Al 6061 Substrate Temperature on the Residual Stresses of Multipass Al Coatings Deposited by Cold Spray

    NASA Astrophysics Data System (ADS)

    Rech, Silvano; Trentin, Andrea; Vezzù, Simone; Legoux, Jean-Gabriel; Irissou, Eric; Guagliano, Mario

    2011-01-01

    In this work, the influence of the substrate temperature on the deposition efficiency, on the coating properties and residual stress was investigated. Pure Al coatings were deposited on Al 6061 alloy substrates using a CGT Kinetics 3000 cold spray system. The substrate temperature was in a range between 20 (room temperature) and 375 °C and was kept nearly constant during a given deposition while all the other deposition parameters were unchanged. The deposited coatings were quenched in water (within 1 min from the deposition) and then characterized. The residual stress was determined by Almen gage method, Modified Layer Removal Method, and XRD in order to identify both the mean coating stress and the stress profile through the coating thickness from the surface to the coating-substrate interface. The residual stress results obtained by these three methods were compared and discussed. The coating morphology and porosity were investigated using optical and scanning electron microscopy.

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

    PubMed

    Carradó, Adele

    2010-02-01

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

  2. Characteristics of MCrAlY coatings sprayed by high velocity oxygen-fuel spraying system

    SciTech Connect

    Itoh, Y.; Saitoh, M.; Tamura, M.

    2000-01-01

    High velocity oxygen-fuel (HVOF) spraying system in open air has been established for producing the coatings that are extremely clean and dense. It is thought that the HVOF sprayed MCrAlY (M is Fe, Ni and/or Co) coatings can be applied to provide resistance against oxidation and corrosion to the hot parts of gas turbines. Also, it is well known that the thicker coating can be sprayed in comparison with any other thermal spraying systems due to improved residual stresses. However, thermal and mechanical properties of HVOF coatings have not been clarified. Especially, the characteristics of residual stress, that are the most important property from the view point of production technique, have not been made clear. In this paper, the mechanical properties of HVOF sprayed MCrAlY coatings were measured in both the case of as-sprayed and heat-treated coatings in comparison with a vacuum plasma sprayed MCrAlY coatings. It was confirmed that the mechanical properties of HVOF sprayed MCrAlY coatings could be improved by a diffusion heat treatment to equate the vacuum plasma sprayed MCrAlY coatings. Also, the residual stress characteristics were analyzed using a deflection measurement technique and a X-ray technique. The residual stress of HVOF coating was reduced by the shot-peening effect comparable to that of a plasma spray system in open air. This phenomena could be explained by the reason that the HVOF sprayed MCrAlY coating was built up by poorly melted particles.

  3. High occupational stress and low career satisfaction of Korean surgeons.

    PubMed

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

    2015-02-01

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

  4. High quality heteroepitaxial AlN films on diamond

    NASA Astrophysics Data System (ADS)

    Vogg, G.; Miskys, C. R.; Garrido, J. A.; Hermann, M.; Eickhoff, M.; Stutzmann, M.

    2004-07-01

    Heteroepitaxial AlN films grown on (100)- and (111)-oriented diamond (C?) substrates by plasma-induced molecular beam epitaxy have been investigated by x-ray diffraction (XRD) and atomic force microscopy (AFM). High quality epitaxial growth of almost strain-free wurtzite AlN is observed for both orientations. For the AlN/C?(111) heterostructures, the epitaxial orientation relationship (0001)[101¯0] AlN?(111)[011¯]C? is obtained. However, a significant fraction of up to 20% of the epitaxial layer is oriented differently with (101¯1) AlN?(111)C?. In case of AlN on C?(100), a double-domain structure with either (0001)[101¯0] AlNI?(100)[011]C? or (0001)[1¯21¯0] AlNII?(100)[011]C? is found. The linewidths of the XRD ? and 2?/? scans of the symmetric AlN 002 reflection have been determined as 1.4 and 0.17° for AlN/C?(100), 0.55° and 0.11° for AlN/C?(111), as well as 0.51 and 0.05° for an AlN/sapphire (0001) reference sample grown under similar conditions. Thus, the crystal quality of AlN on C?(111) is close to that of AlN on sapphire. The corresponding AlN rms roughness values found by AFM are 1.9 nm on C?(100), 1.7 nm on C?(111), and 3.2 nm on sapphire (0001), respectively.

  5. High voltage bushing having weathershed and surrounding stress relief collar

    DOEpatents

    Cookson, Alan H. (Pittsburgh, PA)

    1981-01-01

    A high voltage electric bushing comprises a hollow elongated dielectric weathershed which encloses a high voltage conductor. A collar formed of high voltage dielectric material is positioned over the weathershed and is bonded thereto by an interface material which precludes moisture-like contaminants from entering between the bonded portions. The collar is substantially thicker than the adjacent weathershed which it surrounds, providing relief of the electric stresses which would otherwise appear on the outer surface of the weathershed. The collar may include a conductive ring or capacitive foil to further relieve electric stresses experienced by the bushing.

  6. Uncertainties in obtaining high reliability from stress-strength models

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  7. High-energy magnetic excitations in UCoAl

    NASA Astrophysics Data System (ADS)

    Javorský, P.; Havela, L.; Bewley, R.; Adroja, D.; Boulet, P.

    2004-05-01

    The results of an inelastic neutron scattering experiment on UCoAl are presented. We map the magnetic excitations especially at moderate and high energies. In comparison to isostructural URhAl, we observed a relatively narrow and weak quasielastic response without any strong temperature dependence. The high-energy spectra revealed a very broad magnetic excitations in the 100-200meV energy range. We did not find any traces of an intermultiplet transition.

  8. Stress relaxation behavior of shot-peened Ti–6Al–4V under fretting fatigue at elevated temperature

    Microsoft Academic Search

    Hyukjae Lee; Shankar Mall

    2004-01-01

    Relaxation behavior of residual stress in a shot-peened titanium alloy, Ti–6Al–4V subjected to fretting fatigue was investigated at room and elevated temperatures. Constant amplitude fretting fatigue tests were conducted at several maximum stress levels, ?max ranging from 333 to 666MPa with a stress ratio of 0.1. Two heaters, placed at the front and back of specimen, were used to heat

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

    SciTech Connect

    Tyler, C.; Bourne, N. K. [University of Manchester, Sackville Street, Manchester, M60 1QD (United Kingdom); Millett, J. C. F. [Defence Academy of the United Kingdom, Cranfield University, Shrivenham, Swindon, SN6 8LA (United Kingdom)

    2006-07-28

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

  10. Incorporation of Residual Stresses in the Fatigue Performance Design of Ti6Al4V

    Microsoft Academic Search

    P. S. Prevéy; N. Jayaraman; R. Ravindranath

    The high cycle fatigue (HCF) performance of turbine engine components has long been improved by the introduction of a surface layer of compressive residual stress, usually by shot peening. However, credit has not been taken for the improved fatigue performance in component design; rather shot peening is used primarily as an additional safe guard against fatigue failure. Recently, laser shock

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

    PubMed Central

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

    2012-01-01

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

  12. ZERODUR® glass ceramics for high stress applications

    Microsoft Academic Search

    Peter Hartmann; Kurt Nattermann; Thorsten Döhring; Ralf Jedamzik; Markus Kuhr; Peter Thomas; Guenther Kling; Stefano Lucarelli

    2009-01-01

    Recently SCHOTT has shown in a series of investigations the suitability of the zero expansion glass ceramic material ZERODUR® for applications like mirrors and support structures of complicated design used at high mechanical loads. Examples are vibrations during rocket launches, bonded elements to support single mirrors or mirrors of a large array, or controlled deformations for optical image correction, i.e.

  13. High noise suppression using magnetically isotropic (CoFe-AlN)/(AlN) multilayer films

    NASA Astrophysics Data System (ADS)

    Kijima, Hanae; Ohnuma, Shigehiro; Masumoto, Hiroshi; Shimada, Yutaka; Endo, Yasushi; Yamaguchi, Masahiro

    2015-05-01

    Magnetically isotropic (CoFe-AlN)n/(AlN)n+1 multilayer films, in which the number of CoFe-AlN magnetic layers n ranged from 1 to 27, were prepared by radio frequency sputtering to achieve noise suppression at gigahertz frequencies. The soft CoFe-AlN magnetic layers consisted of nanometer-sized CoFe ferromagnetic grains embedded in an insulating AlN amorphous matrix, while the insulating AlN layers comprised AlN columnar crystals. All films showed a similar frequency dependence of permeability and ferromagnetic resonance of 1.7 GHz. Noise suppression was evaluated using a microstrip line as a noise source by determining the in-line conductive loss and the near-field intensity picked up by magnetic field detective probes. High noise suppression effects were observed in every direction in the film plane. Maximum noise suppression values amounted to 60% for the in-line conductive loss and -20 dB for the magnetic near-field intensity at around 1.7 GHz in the 27-layer film. These high-frequency noise suppression levels may be attributed to eddy current losses and ferromagnetic resonance.

  14. High temperature stress-strain analysis

    NASA Technical Reports Server (NTRS)

    Thompson, Robert L.

    1985-01-01

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

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

    Microsoft Academic Search

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

    2007-01-01

    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

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

    SciTech Connect

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

    1995-09-28

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

  17. Performance of Nb3Sn Quadrupole Under High Stress

    SciTech Connect

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

    2010-08-01

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

  18. Very small critical current spreads in Nb\\/Al-AlOx\\/Nb integrated circuits using low-temperature and low-stress ECR PECVD silicon oxide films

    Microsoft Academic Search

    Xiaofan Meng; Anupama Bhat; Theodore Van Duzer

    1999-01-01

    We have developed a new Nb\\/Al-AlOx\\/Nb IC process with very small critical current spread. Low-temperature and low-stress ECR (Electron Cyclotron Resonance) PECVD (Plasma Enhanced Chemical Vapor Deposition) silicon oxide films have been used in the Nb IC process for all dielectric insulating layers to replace e-beam evaporated silicon monooxide films and RF reactive sputtered silicon oxide. Since ECR PECVD silicon

  19. Influence of Pre-Heated Al 6061 Substrate Temperature on the Residual Stresses of Multipass Al Coatings Deposited by Cold Spray

    Microsoft Academic Search

    Silvano Rech; Andrea Trentin; Simone Vezzù; Jean-Gabriel Legoux; Eric Irissou; Mario Guagliano

    2011-01-01

    In this work, the influence of the substrate temperature on the deposition efficiency, on the coating properties and residual\\u000a stress was investigated. Pure Al coatings were deposited on Al 6061 alloy substrates using a CGT Kinetics 3000 cold spray\\u000a system. The substrate temperature was in a range between 20 (room temperature) and 375 °C and was kept nearly constant during\\u000a a

  20. LIQUEFACTION OF DEEP SATURATED SANDS UNDER HIGH EFFECTIVE CONFINING STRESS

    Microsoft Academic Search

    R Scott Steedman; Michael Sharp

    This paper describes the findings of an ongoing experimental study supported by the U.S. Army Centrifuge Research Center and Engineer Earthquake Engineering Research Program (EQEN) into the behavior of saturated sands under high initial effective confining stresses subjected to strong ground shaking. The research was conducted using the Army Centrifuge at the U.S. Army Engineering Research and Development Center (ERDC),

  1. Stress curves and mechanical properties of high performance concrete

    Microsoft Academic Search

    2004-01-01

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

  2. Protective role of antioxidant enzymes under high temperature stress

    Microsoft Academic Search

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

    2006-01-01

    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

  3. Piezoelectric Energy Harvesting under High PreStressed Cyclic Vibrations

    Microsoft Academic Search

    Hyeoung Woo Kim; Shashank Priya; Kenji Uchino; Robert E. Newnham

    2005-01-01

    Cymbal transducers have been found as a promising structure for piezoelectric energy harvesting under high force (? 100 N) at cyclic conditions (? 100–200 Hz). The thicker steel cap enhances the endurance of the ceramic to sustain higher ac loads along with stress amplification. This study reports the performance of the cymbal transducer under ac force of 70 N with

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

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

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

  6. ZERODUR glass ceramics: design of structures with high mechanical stresses

    NASA Astrophysics Data System (ADS)

    Nattermann, Kurt; Hartmann, Peter; Kling, Guenther; Gath, Peter; Lucarelli, Stefano; Messerschmidt, Boris

    2008-07-01

    Designing highly mechanically loaded structures made of the zero expansion glass ceramic material ZERODUR® means to analyze the stress for the whole loaded surface, considering changes of the stress state occurring over the total lifetime. Strength data are obtained from specimens with small size and relatively short loading duration, making them not directly applicable to the much larger areas that occur in practical cases. This publication gives guidelines for calculating a fracture probability for mirrors and structures on the basis of existing strength data.

  7. Synchrotron XRD study of residual stress in a shot peened Al\\/SiC p composite

    Microsoft Academic Search

    Fabio Rotundo; Alexander M. Korsunsky

    2009-01-01

    In the present study, residual strain profiles in shot peened specimens of 2124-T4 aluminium alloy matrix composite reinforced with 17vol% particulate silicon carbide (SiCp) were measured by means of synchrotron-based diffraction using monochromatic, high energy X-ray beams. The stress state was considered in relation with the microstructural and morphological modifications induced in the material by shot peening. Strain-induced changes in

  8. Resilience in highly stressed urban children: concepts and findings.

    PubMed

    Cowen, E L; Wyman, P A; Work, W C

    1996-01-01

    The Rochester Child Resilience Project is a coordinated set of studies of the correlates and antecedents of outcomes relating to resilience among profoundly stressed urban children. The studies have been conducted over the course of the past decade. Based on child test data, parent, teacher, and self ratings of child adjustment, and in-depth individual interviews with parents and children, a cohesive picture has developed of child and family milieu variables that consistently differentiate children with resilient versus stress-affected outcomes within this highly stressed sample. Resilient children are characterized by an easy temperament and higher IQ; sound parent/child relationships; a parent's sense of efficacy; the parent's own wellness, especially mental health; and the child's perceived competence, realistic control, empathy, and social problem-solving. PMID:8982521

  9. Dislocation loop models for the high temperature creep of Al-5.5 at.% Mg alloy

    SciTech Connect

    An, S.U. [Korea Inst. of Science and Technology, Seoul (Korea, Republic of). Advanced Analysis Center] [Korea Inst. of Science and Technology, Seoul (Korea, Republic of). Advanced Analysis Center; Blum, W. [Univ. Erlangen-Nuernberg, Erlangen (Germany). Inst. I Fuer Werkstoffwissenschaften] [Univ. Erlangen-Nuernberg, Erlangen (Germany). Inst. I Fuer Werkstoffwissenschaften

    1995-04-15

    The Al-5.5 at.% Mg alloy is a typical class I type solution hardened material. The dislocation loop models proposed by Orlova and Cadek and by Mills et al., respectively are widely applied models in describing the high temperature creep behavior of the Al-5.5 at.% Mg alloy. These models, however, are in conflict in explaining dislocation loop theory. Orlova and Cadek suggest that in class I solution hardened alloys screw dislocations are relatively easier to migrate because they are subject to a smaller resistance in motion than edge dislocations. Consequently, the migration rate of screw dislocations is higher than that of edge dislocations. However, since dislocation loops are composed of both screw and edge components, the overall migration rate of screw dislocations are reduced by that of the edge component. Mills et al. on the contrary, used a different dislocation loop model. As the loop grows while it moves, it takes on the shape of an ellipsoid due to the unbalance in growth rate, the score segment moving much easier than the edge. Therefore, as shown in the results of the stress reduction tests, rapid elastic ({Delta} {var_epsilon}{sub el}) and anelastic contraction ({Delta} {var_epsilon}{sub an}) occur simultaneously directly after stress reduction. During the movement of the dislocation loop, the screw component hence becomes severely curved, while the edge component retains a straight line. This has been proved through dislocation structure observations by TEM.

  10. High-Temperature Thick Al Wire Bonding Technology for High-Power Modules

    NASA Astrophysics Data System (ADS)

    Komiyama, Takao; Chonan, Yasunori; Onuki, Jin; Koizumi, Masahiko; Shigemura, Tatsuya

    2002-08-01

    In order to enhance the strength of thick Al wire bonds while eliminating damage, we have developed a new high-temperature thick Al wire bonding technology. The 300-?m-diameter Al wires were bonded to Al pads on an insulated gate bipolar transistor (IGBT) chip at varying substrate temperatures and ultrasonic powers. Al wire bonds joined at 423 K with 2.0 W ultrasonic power exhibited high bonding strength compared to those joined at room temperature with 5.0 W power. The main reason for the high bonding strength exhibited by the high-temperature bonding process with low ultrasonic power may be the ease of deformation of Al wires and Al electrode films which results in the enhancement of the true bonded area between Al wires and Al electrode films. We also confirmed that Si damage did not occur during this high temperature bonding process using low ultrasonic power. High-temperature thick Al wire bonding technology is considered to be a promising candidate for the production of reliable IGBT modules.

  11. Life expectancy of modular Ti6Al4V hip implants: influence of stress and environment.

    PubMed

    Chandra, A; Ryu, J J; Karra, P; Shrotriya, P; Tvergaard, V; Gaisser, M; Weik, T

    2011-11-01

    Stress dependent electrochemical dissolution is identified as one of the key mechanisms governing surface degradation in fretting and crevice corrosion of biomedical implants. The present study focuses on delineating the roles of mechanical stress and chemical conditions on the life expectancy of modular hip implants. First, material removal on a stressed surface of Ti6Al4V subjected to single asperity contact is investigated experimentally to identify the influence of contact load, in-plane stress and chemical environment on mean wear rates. A range of known stress levels are applied to the specimen while its surface is mechanically stimulated in different non-reactive to oxidizing aqueous environments. Evolution of surface degradation is monitored, and its mechanism is elucidated. This phase allows estimation of Preston Constant which is later used in the analysis. Second phase of the work is semi-analytical and computational, where, based on the estimated Preston constant and other material and process parameters, the scratch propensity (consisting of magnitude of scratch depth and their frequency per unit area) due to micro-motion in modular hip implants is estimated. The third phase views these scratches as initial notches and utilizes a mixed-mode fatigue crack propagation model to estimate the critical crack length for onset of instability. The number of loading cycles needed to reach this critical crack length is then labeled as the expected life of the implant under given mechanical and chemical conditions. Implications of different material and process conditions to life expectancy of orthopedic implants are discussed. It is observed that transverse micro-motion, compared to longitudinal micro-motion, plays a far more critical role in determining the implant life. Patient body weight, as well as proximity of the joint fluid to its iso-electric point play key roles in determining wear rates and associated life expectancies of modular hip implants. Sustained aeration of joint fluid, as well as proper tolerancing of mating surfaces, along with a proper choice of material microstructure may be utilized to extend implant life. PMID:22098898

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

    PubMed Central

    Sama, Reddy Ranjith Kumar; Ward, Catherine L.

    2014-01-01

    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

  13. Studies of deep level transient spectroscopy of DX centers in GaAlAs: Te under uniaxial stress

    SciTech Connect

    Li, Ming-Fu [California Univ., Berkeley, CA (United States). Dept. of Physics]|[California Univ., Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering; Yu, Y.P. [California Univ., Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley Lab., CA (United States); Weber, E.R.; Haller, E.E. [California Univ., Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering]|[Lawrence Berkeley Lab., CA (United States); Hansen, W.L. [Lawrence Berkeley Lab., CA (United States); Bauser, E. [Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany)

    1991-11-01

    DX centers in Al{sub 0.38}Ga{sub 0.62}As doped with Te have been studied by Deep Level Transient Spectroscopy (DLTS) as a function of uniaxial stress. No splitting nor broadening of the DLTS peaks were observed. However, the peak positions and heights depend on the stress and its directions. The results have been analyzed by comparison with existing models and hydrostatic pressure measurements.

  14. Eect of load ratio and maximum stress intensity on the fatigue threshold in Ti6Al4V

    E-print Network

    Ritchie, Robert

    Eect of load ratio and maximum stress intensity on the fatigue threshold in Ti±6Al±4V B.L. Boyce, R¯uence of the load ratio, R, and the maximum stress intensity, Kmax, on the threshold for fatigue-crack growth, DKth range of loading frequencies (m 50±1000 Hz) and load ratios (R 0X10±0X95) on fatigue-crack propagation

  15. Effects of fretting fatigue on the residual stress of shot peened Ti–6Al–4V samples

    Microsoft Academic Search

    S. A. Martinez; S. Sathish; M. P. Blodgett; S. Mall; S. Namjoshi

    2005-01-01

    X-ray diffraction residual stress measurement has been utilized as nondestructive tool for the characterization of fretting fatigue damage in shot peened samples of Ti–6Al–4V. Prior to fretting fatigue damage, compressive residual stresses were found to be uniform over the entire face of the sample and independent of the measurement direction. After fretting fatigue, inside and in the vicinity of the

  16. Fatigue properties of high Nb TiAl alloy

    NASA Astrophysics Data System (ADS)

    Kruml, T.; Dlouhý, A.; Petrenec, M.; Obrtlík, K.; Polák, J.

    2010-07-01

    Fatigue properties of the new generation of TiAl alloys with high Nb content are studied. Comparison with the previous alloy with 2at% Nb shows that the new alloy resists better to cyclic deformation at high temperatures. The microstructural observation proved that at 750 °C, the easiest deformation mode is the glide of ordinary dislocations followed by superdislocation glide and twinning. Nevertheless, all three modes seem to be active.

  17. Interfacial shear stress measurement using high spatial resolution multiphase PIV

    NASA Astrophysics Data System (ADS)

    André, Matthieu A.; Bardet, Philippe M.

    2015-06-01

    In multiphase flows, form drag and viscous shear stress transfer momentum between phases. For numerous environmental and man-made flows, it is of primary importance to predict this transfer at a liquid-gas interface. In its general expression, interfacial shear stress involves local velocity gradients as well as surface velocity, curvature, and surface tension gradients. It is therefore a challenging quantity to measure experimentally or compute numerically. In fact, no experimental work to date has been able to directly resolve all the terms contributing to the shear stress in the case of curved and moving surfaces. In an attempt to fully resolve the interface shear stress when surface tension gradients are negligible, high-resolution particle image velocimetry (PIV) data are acquired simultaneously on both sides of a water-air interface. The flow consists of a well-conditioned uniform and homogeneous water jet discharging in quiescent air, which exhibits two-dimensional surface waves as a result of a shear layer instability below the surface. PIV provides velocity fields in both phases, while planar laser-induced fluorescence is used to track the interface and obtain its curvature. To compute the interfacial shear stress from the data, several processing schemes are proposed and compared, using liquid and/or gas phase data. Vorticity at the surface, which relates to the shear stress through the dynamic boundary condition at the surface, is also computed and provides additional strategies for estimating the shear. The various schemes are in agreement within the experimental uncertainties, validating the methodology for experimentally resolving this demanding quantity.

  18. Finite element stress analysis of polymers at high strains

    NASA Technical Reports Server (NTRS)

    Durand, M.; Jankovich, E.

    1973-01-01

    A numerical analysis is presented for the problem of a flat rectangular rubber membrane with a circular rigid inclusion undergoing high strains due to the action of an axial load. The neo-hookean constitutive equations are introduced into the general purpose TITUS program by means of equivalent hookean constants and initial strains. The convergence is achieved after a few iterations. The method is not limited to any specific program. The results are in good agreement with those of a company sponsored photoelastic stress analysis. The theoretical and experimental deformed shapes also agree very closely with one another. For high strains it is demonstrated that using the conventional HOOKE law the stress concentration factor obtained is unreliable in the case of rubberlike material.

  19. High temperature deformation behavior of Al–Cu–Mg alloys micro-alloyed with Sn

    Microsoft Academic Search

    Sanjib Banerjee; P. S. Robi; A. Srinivasan; Lakavath Praveen Kumar

    2010-01-01

    Deformation behavior of Al–6.2%Cu–0.6%Mg alloy and Al–6.2%Cu–0.6%Mg alloy containing 0.06wt.% of Sn was studied by hot compression tests conducted at various temperatures and strain rates. During the deformation process, the flow stress of the Al–Cu–Mg alloy increased due to trace addition of Sn. The peak flow stress for both the alloys increased with increase in strain rate and decrease in

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

    NASA Astrophysics Data System (ADS)

    Fouad, Yasser; Metwally, Mostafa El

    2013-12-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    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.

  2. Stress analysis and microstructure of PVD monolayer TiN and multilayer TiN\\/(Ti,Al)N coatings

    Microsoft Academic Search

    N. J. M. Carvalho; E. Zoestbergen; B. J. Kooi; J. Th. M. De Hosson

    2003-01-01

    Two PVD titanium nitride based coatings; monolayer TiN and multilayer resulting from the stacking of TiN and (Ti,Al)N layers were evaluated with respect to their stress state and microstructure. The TiN was deposited by triode evaporation ion plating, whereas the TiN\\/(Ti,Al)N was deposited using a reactive hybrid deposition process consisting of a combination of electron beam evaporation of Ti and

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

    NASA Astrophysics Data System (ADS)

    Jiang, Xiuping

    2007-12-01

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

  4. Structural analysis of highly porous ?-Al2O3

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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.

  5. [Clinical trials of ultra-high-dose methylcobalamin in ALS].

    PubMed

    Izumi, Yuishin; Kaji, Ryuji

    2007-10-01

    Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder affecting both upper and lower motor neurons. Weakness may begin in the legs, hands, proximal arms, or pharynx. The course is relentless and progressive without remissions, relapses, or even stable plateaus. There is no effective drug therapy for ALS, although riluzole has been shown to prolong life in sufferers, without tracheostomy. A vitamin B12 analog, methylcobalamin, has a protective effect on cultured cortical neurons against glutamate-induced cytotoxicity. We have shown the ultra-high-dose methylcobalamin (25 mg/day i.m.) slows down the progressive reduction of the CMAP (compound muscle action potential) amplitudes in ALS in the short term (4 weeks). The latencies of SSR (sympathetic skin response) were shorter after treatment (50 mg/day i.v., 2 weeks). In the long-term effect of methylcobalamin (50 mg/day i.m., twice a week), the survival time (or the period to become respirator-bound) was significantly longer in the treated group than in the untreated. Larger-scale randomized double blind trial was started in Japan in order to evaluate the long-term efficacy and the safety of ultra-high-dose methylcobalamin for sporadic or familial cases of ALS. PMID:17969354

  6. Yield Strength of Transparent MgAl2O4 Nano-Ceramic at High Pressure and Temperature.

    PubMed

    Zhang, Jie; Lu, Tiecheng; Chang, Xianghui; Jiang, Shengli; Wei, Nian; Qi, Jianqi

    2010-01-01

    We report here experimental results of yield strength and stress relaxation measurements of transparent MgAl2O4 nano-ceramics at high pressure and temperature. During compression at ambient temperature, the differential strain deduced from peak broadening increased significantly with pressure up to 2 GPa, with no clear indication of strain saturation. However, by then, warming the sample above 400°C under 4 GPa, stress relaxation was obviously observed, and all subsequent plastic deformation cycles are characterized again by peak broadening. Our results reveal a remarkable reduction in yield strength as the sintering temperature increases from 400 to 900°C. The low temperature for the onset of stress relaxation has attracted attention regarding the performance of transparent MgAl2O4 nano-ceramics as an engineering material. PMID:20676198

  7. Finite-element analysis of residual stresses in Al 2O 3–TiC\\/W18Cr4V diffusion bonded joints

    Microsoft Academic Search

    Xiaoqin Shen; Yajiang Li; U. A. Putchkov; Juan Wang; Wanqun Huang

    2009-01-01

    The residual stress distribution in Al2O3–TiC\\/W18Cr4V diffusion bonded joints was calculated using finite element method (FEM). The effects of pressure and interlayer on the axial stress and shear stress were also studied. The results show that the gradients of the axial stress and shear stress are great near the joint edge and are flat near the center of the joint.

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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.

  10. 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

    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

    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.

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

    SciTech Connect

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

    1992-06-01

    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.

  12. High mobility two-dimensional electron gases in nitride heterostructures with high Al composition AlGaN alloy barriers

    SciTech Connect

    Li Guowang; Cao Yu; Xing Huili Grace; Jena, Debdeep [Department of Electrical Engineering, University of Notre Dame, Indiana 46556 (United States)

    2010-11-29

    We report high-electron mobility nitride heterostructures with >70% Al composition AlGaN alloy barriers grown by molecular beam epitaxy. Direct growth of such AlGaN layers on GaN resulted in hexagonal trenches and a low mobility polarization-induced charge. By applying growth interruption at the heterojunction, the surface morphology improved dramatically and the room temperature two-dimensional electron gas (2DEG) mobility increased by an order of magnitude, exceeding 1300 cm{sup 2}/V s. The 2DEG density was tunable at 0.4-3.7x10{sup 13}/cm{sup 2} by varying the total barrier thickness (t). Surface barrier heights of the heterostructures were extracted and exhibited dependence on t.

  13. High temperature, oxidation resistant noble metal-Al alloy thermocouple

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  14. Gate length scaling effect on high-electron mobility transistors devices using AlGaN/GaN and AlInN/AlN/GaN heterostructures.

    PubMed

    Liao, S Y; Lu, C C; Chang, T; Huang, C F; Cheng, C H; Chang, L B

    2014-08-01

    Compared to AlGaN/GaN HEMT with 0.15 ?m T-gate length, the AlInN/AlN/GaN one exhibits much higher current density and transconductance of 1558 mA/mm at Vd = 2 V and 330 mS/mm, respectively. The high extrinsic ft and fmax of 82 GHz and 70 GHz are extracted from AlInN/AlN/GaN HEMT. Besides, we find that the transconductance roll-off is significant in AlGaN/GaN, but largely improved in AlInN/AlN/GaN HEMT, suggesting that the high carrier density and lattice-matched epitaxial heterostructure is important to reach both large RF output power and high operation frequency, especially for an aggressively gate length scaling. PMID:25936096

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

    NASA Astrophysics Data System (ADS)

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

    2007-08-01

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

  16. High Performance Polarized Electron Photocathodes Based on InGaAlAs/AlGaAs Superlattices

    SciTech Connect

    Mamaev, Yu.

    2004-12-10

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

  17. AlN nanowires for Al-based composites with high strength and low thermal expansion

    Microsoft Academic Search

    Y. B. Tang; Y. Q. Liu; C. H. Sun; H. T. Conga

    2007-01-01

    Based on the synthesis of a sufficient amount of AlN nanowires (AlN-NWs), AlN-NWs\\/Al composites with homogenously distributed AlN-NWs were fabricated. Microstructural observations reveal that the interface between AlN-NWs and Al matrix is clean and bonded well, and no interfacial reaction product was formed at the nanowire-matrix boundary. Mechanical properties including yield and tensile strength of the composites were improved with

  18. High temperature phase equilibria near Ti–50 at% Al composition in Ti–Al system studied by directional solidification

    Microsoft Academic Search

    In-Soo Jung; Min-Chul Kim; Je-Hyun Lee; Myung-Hoon Oh; Dang-Moon Wee

    1999-01-01

    High temperature phase diagram near the stoichiometric composition of TiAl has been established by the directional solidification and quenching technique. The quenched dendrite morphologies showed that the first solidified phase was the ? phase in Ti–44, 46, 48 at% Al alloys and the ? phase in Ti–50, 52 at% Al alloys. From the EDS analysis of the quenched dendrite tips

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

    Microsoft Academic Search

    B. Atzori; P. Lazzarin; R. Tovo

    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

  20. STRESS

    NSDL National Science Digital Library

    Ms. Hancey

    2010-04-27

    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 ...

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

    PubMed

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

    2014-02-01

    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

  2. High depth nondestructive stress measurements on thick steel alloys

    SciTech Connect

    Selim, F.A.; Wells, D.P.; Harmon, J.F.; Williams, J. [Department of Physics, Idaho State University, Pocatello, Idaho 83209 (United States)

    2005-06-01

    Stress measurements were performed using accelerator-based {gamma}-ray induced positron annihilation spectroscopy technique, which allows probing of defects at high depths in thick materials up to several centimeters. Induced stresses due to tensile, fatigue, cold work, and bending tests were investigated in steel alloys of about 1-cm thickness. The measurements showed the dependence of the line-shape parameter of the annihilation peak S on the induced deformation in the four tests. They also revealed an interesting behavior for the change of S parameter with tensile deformation, related to the engineering stress-strain curve of the material. Transmission electron microscopy measurements of dislocation density in cold work deformation suggested that the saturation of positron annihilation parameters often observed in cold work data is not due to compete positron trapping at defects. It was also shown that the S parameter has a weak sensitivity and quickly saturates in fatigue test when compared with the other mechanical tests, which was interpreted as being due to the brittle nature of fatigue failure and the very little plastic deformation associated with it.

  3. The temperature and strain rate dependence of the flow stress of single crystal NiAl deformed along <110>

    SciTech Connect

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

    1995-12-31

    Single crystal NiAl and Ni-49.75Al-0.25Fe have been deformed along <110> at temperatures of 77, 298 and 773K and strain rates of 0.001/s, and 2000/s. The flow stress of <110> NiAl is rate and temperature sensitive. The 0.25 at.% Fe addition resulted in a small increase in flow stress at strain rates of 0.001 and 0.1/s at 298 and 77K. A significant decrease in the work hardening rate is observed after deformation at 77K and a strain rate of 2000/s. Coarse [110] slip traces are observed after deformation at a strain rate of 2000/s at 77K, while no slip traces were observed after deformation under all other conditions. TEM observations reveal distinct [110] slip bands after deformation at 77K and a strain rate of 2000/s.

  4. High-rate sputter deposition and heat treatment of thick Nb-Al-Ge and Nb-Al superconductors

    Microsoft Academic Search

    S. D. Dahlgren

    1976-01-01

    Crystal structures, microstructures and critical temperatures were determined for Nb-Al-Ge and Nb-Al sputter-deposits in order\\u000a to evaluate their dependence on sputter-deposition conditions, heat treatment procedures and composition. High-rate sputter\\u000a deposition techniques were used to make the deposits at rates up to 1 ?m\\/min. Compositions studied were Nb3(Al0.6Ge0.4), Nb3(Al0.75Ge0.25), Nb3Al, Nb2.52(Al0.84)Ge0.16), Nb2.33Al, Nb3.07(Al0.75Ge0.25), and Nb4.15(Al0.71Ge0.29). The investigation indicated it is feasible

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  6. Structure, stress, and magnetic properties of high saturation magnetization films of FeCo

    Microsoft Academic Search

    V. A. Vas'ko; James O. Rantschler; Mark T. Kief

    2004-01-01

    Thin (?2000 Å) films of Fe60Co40 have been prepared by sputtering on Si\\/SiO2, Si\\/AlOx, AlTiC\\/AlOx, AlTiC\\/AlOx\\/NiFe, and AlTiC\\/AlOx\\/NiFeCr substrates using an alloy Fe60Co40 target. The structure of the films was characterized by means of X-ray diffraction and transmission electron microscopy (TEM). Surface roughness was characterized by atomic force microscopy (AFM). Stress, transport, and magnetic measurements were conducted. We observed correlation

  7. Elastic incompatibility stresses across planar and nonplanar grain boundaries applied to ductile fracture criteria under high triaxial stress

    Microsoft Academic Search

    R. Roehnelt; M. E. Kassner; T. C. Kennedy; R. S. Rosen

    1997-01-01

    Grain boundary interfaces in a polycrystal under load can develop elastic incompatibilities that, in turn, can lead to stress states in the vicinity of the interface that are different from the macroscopic or applied stresses because the single crystal elastic properties are anisotropic. The focus of the present study is the unstable growth of cavities as a result of high

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  9. Processing and mechanical properties of high temperature/high performance composites. Book 7. In-situ measurements of stress and damage. Annual report, March 1993-April 1994

    SciTech Connect

    Evans, A.G.; Leckie, F.A.

    1994-04-01

    Partial Contents: Residual Stress Measurement in Sapphire Fiber Composites: Through-Focus and Transmission Fluorescence Spectroscopy; Measurement of Residual Stresses in Sapphire Fiber Composites Using Optical Fluorescence; Luminescence Sensing of Stress in Ti/A2lO3 Fiber Reinforced Composites; Optical Fluorescence from Chromium Ions in Sapphire: A Probe of the Image Stress; Residual Stresses in Al12O3-ZrO2 Composites: A Test and Stochastic Stress Models; Stress Measurement Using Optical Fluorescence.

  10. 52 Richardson et al.: Drought Stress and Paper Birch (Betula papyrifera) Seedlings To improve the health of urban and ornamental trees, it is

    E-print Network

    Richardson, Andrew D.

    52 Richardson et al.: Drought Stress and Paper Birch (Betula papyrifera) Seedlings To improve, and leaf reflectance) to assess the level of drought stress in paper birch (Betula papyrifera) seedlings by DROUGHT STRESS AND PAPER BIRCH (BETULA PAPYRIFERA) SEEDLINGS: EFFECTS OF AN ORGANIC BIOSTIMULANT ON PLANT

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

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

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

    SciTech Connect

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

    2012-01-01

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

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

    SciTech Connect

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

    2014-06-23

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

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

    Microsoft Academic Search

    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

    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

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

    ERIC Educational Resources Information Center

    Falls, Leigh; Nichter, Mary

    2007-01-01

    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…

  16. Preparation of TiAl3-Al Composite Coating by Cold Spray and Its High Temperature Oxidation Behavior

    NASA Astrophysics Data System (ADS)

    Kong, L. Y.; Shen, L.; Lu, B.; Yang, R.; Cui, X. Y.; Li, T. F.; Xiong, T. Y.

    2010-12-01

    A novel TiAl3-Al coating was prepared by cold spray for high temperature protection of titanium aluminum-based alloy. The substrate alloy was orthorhombic-Ti-22Al-26Nb (at.%). The composite coating was mainly composed of TiAl3 embedded in the matrix of residual aluminum. An interlayer about 10 ?m was formed between the coating and the substrate. The oxidation test indicated that this composite coating was very effective in improving the high-temperature oxidation resistance of the substrate alloy at 950 °C in the tested 150 cycles without any sign of degradation. The microstructure analysis of the oxidized composite coating showed that an Al2O3 scale with a complex structure can be formed outside the interlayer during oxidation and no oxides beneath the interlayer were detected, which indicated that the complex continuous Al2O3 and the interlayer provide the protection of the substrate at high-temperature oxidation condition.

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

    SciTech Connect

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

    2014-01-20

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

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

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

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

  20. Highly stressed: stressful and traumatic experiences among individuals with HIV/AIDS in the Deep South.

    PubMed

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

    2011-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-11-01

    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.

  2. Effect of stress ratio on long life fatigue behavior of Ti-Al alloy under flexural loading

    Microsoft Academic Search

    Hong-qian XUE; Hua TAO; Ren-ping SHAO; B. CLAUDE

    2008-01-01

    A new ultrasonic three-point bending fatigue test device was introduced to investigate fatigue life ranging up to 1010 cycles and associated fracture behavior of Ti-Al alloy. Tests were performed at a frequency of 20 kHz with stress ratio R=0.5 and R=0.7 at ambient temperature in air. Three groups of specimens with different surface roughness were applied to investigate the effect

  3. The relationship between dealloying and transgranular stress-corrosion cracking of Cu-Zn and Cu-Al alloys

    Microsoft Academic Search

    K. Sieradzki; J. S. Kim; A. T. Cole; R. C. Newman

    1987-01-01

    Single crystals of various ..cap alpha..-phase Cu-Zn and Cu-Al alloys have been tested for dealloying and stress-corrosion cracking (SCC) in cuprous ammonia solutions. All tests were done at the equilibrium potential of a copper electrode. The dealloying tests were done by scratching coated specimens and measuring the consequent anodic current transients, and the SCC tests used a constant extension rate.

  4. Thermal stresses in a macroscopic graphite particulates reinforced CuAlMn shape memory alloy studied by internal friction

    Microsoft Academic Search

    Q. Z. Wang; F. S. Han; J. Wu; G. L. Hao

    2005-01-01

    In the present study, a novel metal matrix composite (MMC) has been fabricated with a Cu–11.9Al–2.5Mn (wt%) shape memory alloy (SMA) and macroscopic graphite particulates with the objective of damping enhancement. The functional properties of such MMC are directly related to the constraining behavior that the composite reinforcement has on the SMA. Following temperature changes large internal stress can be

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

    ERIC Educational Resources Information Center

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

    2008-01-01

    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…

  6. Stress-induced high-field gate leakage current in ultra-thin gate oxide

    Microsoft Academic Search

    Jianlin Wei; Lingfeng Mao; Mingzhen Xu; Changhua Tan; Xiaorong Duan

    2000-01-01

    A number of groups have reported that the low-field stress-induced leakage current (SILC) in thin oxides increased after the oxides had been subjected to high voltage stresses. In this study, we observed that high-field SILC increased after the oxides had been subjected to high voltage stresses. The experimental results suggest strongly that SILC must be considered at a high-field region,

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

    SciTech Connect

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

    2014-08-14

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

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

    PubMed

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

    2014-12-01

    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

  9. Deposition of Si-DLC films with high hardness, low stress and high deposition rates

    Microsoft Academic Search

    J. C Damasceno; S. S Camargo; F. L Freire; R Carius

    2000-01-01

    In this work silicon-incorporated diamond-like carbon (Si-DLC) films were produced by plasma enhanced chemical vapor deposition (PECVD) from gaseous mixtures of CH4 and SiH4. A study of the influence of self-bias and gas composition on the mechanical and structural properties of the films was carried out. Results show that films deposited at high self-bias present high deposition rates, low stress

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  11. Stress

    NSDL National Science Digital Library

    Mrs. Deaton

    2011-06-10

    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 ...

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

    SciTech Connect

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

    2013-06-15

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

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

    E-print Network

    Wang, Gwo-Ching

    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

  14. Straight-sided, buckling-driven delamination of thin films at high stress levels

    Microsoft Academic Search

    Henrik Myhre Jensen; Izhak Sheinman

    2001-01-01

    The fracture mechanics of a straight-sided, thin film delamination at stress levels, which are high compared to the stress required to initiate the delamination is investigated. Buckling at a bifurcation point of the delaminated region, resulting from incompletely relieved stresses in this region, is analysed by a semi- analytical approach for delaminations of infinite extent. The results are compared to

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

    ERIC Educational Resources Information Center

    McDaniel, Sheneatha Lashelle Alexander

    2012-01-01

    The purpose of this research was to examine the relationship between high-stakes tests and stress with secondary teachers. Furthermore, this study investigated whether veteran teachers experience more stress than novice teachers and whether or not self-efficacy, gender, accountability status, and years of experience influence teacher stress as it…

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

    Microsoft Academic Search

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

    1995-01-01

    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

  17. Raman spectroscopy of sputtered AlN films: E{sub 2}(high) biaxial strain dependence

    SciTech Connect

    Trodahl, H. J.; Martin, F.; Muralt, P.; Setter, N. [Laboratoire de Ceramique, Ecole Polytechnique Federal de Lausanne, 1015 Lausanne, Switzerland and MacDiarmid Institute, Victoria University of Wellington, 6015 Wellington (New Zealand); Laboratoire de Ceramique, Ecole Polytechnique Federal de Lausanne, 1015 Lausanne (Switzerland)

    2006-08-07

    Sputtered [0001] AlN films with directly measured biaxial strain have been investigated by Raman spectroscopy to determine the strain dependence of the zone-center mode frequencies. The E{sub 2}(high) feature near 655 cm{sup -1} is found to vary linearly with stress, and we determine the strain derivative of the line as -2.9{+-}0.3 cm{sup -1}/GPa, confirming the lowest previously reported derivative and a factor of 2 smaller than the largest. The result is 13% larger than has been predicted by ab initio calculations. The other zone-center lines accessible under normally incident geometry from a c-axis film are shown to be unsuitable as strain gauges.

  18. High temperature creep deformation of directionally solidified Al 2O 3\\/Er 3Al 5O 12

    Microsoft Academic Search

    J. Martinez Fernandez; A. Sayir; S. C. Farmer

    2003-01-01

    The microstructure of directionally solidified Al2O3\\/Er3Al5O12 (19.5 mol% Er2O3) is analyzed and high temperature creep deformation studied using fibers in tension between 1400° C and 1550° C. The directionally solidified Al2O3\\/Er3Al5O12 system is an in situ composite and has a fine eutectic- microstructure with sub-micron phase spacing. The microstructure is elongated in the direction of growth. Transmission electron microscopy observations

  19. Preparation of TiAl 3 Al Composite Coating by Cold Spray and Its High Temperature Oxidation Behavior

    Microsoft Academic Search

    L. Y. Kong; L. Shen; B. Lu; R. Yang; X. Y. Cui; T. F. Li; T. Y. Xiong

    2010-01-01

    A novel TiAl3-Al coating was prepared by cold spray for high temperature protection of titanium aluminum-based alloy. The substrate alloy\\u000a was orthorhombic-Ti-22Al-26Nb (at.%). The composite coating was mainly composed of TiAl3 embedded in the matrix of residual aluminum. An interlayer about 10 ?m was formed between the coating and the substrate.\\u000a The oxidation test indicated that this composite coating was very

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

    PubMed

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

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

  2. High radiation tolerance of InAs/AlSb high-electron-mobility transistors

    SciTech Connect

    Weaver, B.D.; Boos, J.B.; Papanicolaou, N.A.; Bennett, B.R.; Park, D.; Bass, R. [Naval Research Laboratory, Code 6818, Washington, DC 20375 (United States)

    2005-10-24

    InAs/AlSb-based high-electron-mobility transistors (HEMTs) were irradiated with 2 MeV protons. Radiation damage caused the source-drain current I{sub ds} to decrease nearly linearly with fluence {phi} at a rate of {delta}[I{sub ds}({phi})/I{sub ds}(0)]/{delta}{phi}{approx_equal}7x10{sup -16} cm{sup 2}. Radiation-induced decreases in I{sub ds} have been observed for other HEMT material systems, and have been attributed to high-efficiency defect-induced scattering of carriers out of the two-dimensional electron gas. However, in the InAs/AlSb system the rate of decrease of I{sub ds} is about 140 times less than that for typical GaAs/AlGaAs HEMTs. An explanation is presented in which the high radiation tolerance of InAs/AlSb HEMTs is related to carrier reinjection and the unusually large energy offset between the AlSb barriers and the InAs quantum well.

  3. Guided visualization interventions on perceived stress, dyadic satisfaction and psychological symptoms in highly stressed couples.

    PubMed

    Rogers, Kim R; Hertlein, Katherine; Rogers, Donna; Cross, Chad L

    2012-05-01

    This study focused on the effect of a brief CBT-based relaxation/guided visualization intervention on perceived stress, dyadic satisfaction and psychological symptoms. This study also tested the hypothesis that indicators of global orientation including Sense of Coherence and Differentiation of Self would mediate between perceived stress and symptoms of physical, psychological and relational distress. A three session intervention used guided visualization scripts which incorporated relaxation and controlled breathing techniques as well as a CBT approach that focused on stress management and internal locus of control. Results indicated that after the intervention, participants showed lower levels of perceived stress and lower levels of dyadic distress, as well as lower psychological and physical complaints as reported with the Symptom Checklist-90-R. Both Sense of Coherence and Differentiation of Self were mediators for the effect of perceived stress on the number of endorsed symptoms. PMID:22500848

  4. Static and kinetic friction of granite at high normal stress

    USGS Publications Warehouse

    Byerlee, J.D.

    1970-01-01

    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.

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

    ERIC Educational Resources Information Center

    Liu, Yangyang; Lu, Zuhong

    2011-01-01

    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…

  6. Correlations between mechanical stress, electrical conductivity and nanostructure in Al films on a polymer substrate

    Microsoft Academic Search

    J. R. Bautista; F. Avilés; A. I. Oliva; O. Ceh; J. E. Corona

    2010-01-01

    The relation between mechanical stress, electrical resistivity and film nanostructure is investigated here for 100nm thick aluminum films deposited on micrometer-thick polysulfone. It is observed that film electrical resistivity increases significantly before mechanical failure occurs, because of the formation of micro-cracks on the film surface. The applied tensile stress also influences the film nanostructure in an irreversible manner, causing plastic

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

    SciTech Connect

    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

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  9. Processing and mechanical properties of high temperature/high performance composites. Stress redistribution and notch properties. Book 2. Annual report, 1 March 1992-28 February 1994

    SciTech Connect

    Evans, A.G.; Leckie, F.A.

    1994-03-01

    Topics discussed in this document include: (1) Cracking and stress redistribution in ceramic layered composites; (2) Notch sensitivity and stress redistribution in CMCs; (3) Notch-sensitivity and shear bands in brittle matrix composites; (4) On large scale sliding in fiber-reinforced composites; (5) On the tensile strength of a fiber-reinforced ceramic composite containing a crack-like flaw; (6) SiC/CAS: a notch insensitive ceramic matrix composite; (7) On the tensile properties of a fiber reinforced titanium matrix composite; (8) Localization due to damage in two directions for fiber reinforced composites; (9) An elliptical inclusion embedded in an anisotropic body; (10) On the strength of fiber reinforced ceramic composites containing an elliptic hole; (11) On the theoretical toughness and strength of ceramic composites; (12) Microlaminated high temperature intermetallic composites; and (13) Fracture toughness of Al-4%Mg/Al2O3P composites.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    SciTech Connect

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

    2010-05-21

    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).

  12. Stress

    MedlinePLUS

    ... blood glucose elevation in response to mental stress. Learning to Relax For some people with diabetes, controlling ... uncross your legs and arms. Take in a deep breath. Then push out as much air as ...

  13. Stress

    MedlinePLUS

    ... Some changes are major, such as marriage or divorce, serious illness, or a car accident. Other changes ... sudden negative change, such as losing a job, divorce, or illness. Traumatic stress, experienced in an event ...

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

    PubMed

    Liu, Yangyang; Lu, Zuhong

    2012-10-01

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

  15. Introduction Endothelial cells develop and function in a highly stressed

    E-print Network

    Zaidel-Bar, Ronen

    et al., 2004). This alignment depends on intact microfilament and microtubule systems, tyrosine for endothelial cell alignment under flow (Civelekoglu-Scholey et al., 2005; Dieterich et al., 2000; Galbraith et resonance energy transfer experiments, and by the capacity of constitutively active Rac1 to abolish flow

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

    Microsoft Academic Search

    Yangjian Xu; Daihui Tu; Wei Wei

    2009-01-01

    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

  17. Eddy current measurement of residual stresses induced by shot peening in titanium Ti-6Al-4V

    SciTech Connect

    Schoenig, F.C. Jr.; Soules, J.A.; Chang, H.; DiCillo, J.J. (Cleveland State Univ., OH (United States). Advanced Manufacturing Center)

    1995-01-01

    An experimental investigation of the feasibility of using eddy current technology to nondestructively determine the residual stresses induced by shot peening in Ti-6Al-4V plate was undertaken. Because of the extremely small magnitude of the shot peening-induced conductivity changes, strict noise control was vital and was achieved by mechanical and thermal isolation of the apparatus. This was accomplished by modifying the instrument to improve temperature isolation of several key internal components and also by physically and electronically isolating the experimental apparatus. Results indicate that residual stress can be clearly determined for material shot peened to a depth of 0.3 mm (0.012 in.) or more with an experimental variation of less than 3 ppm.

  18. Stress-strain data obtained at high rates using an expanding ring

    Microsoft Academic Search

    C. R. Hoggatt; R. F. Recht

    1969-01-01

    Dynamic uniaxial tensile stress-strain data are obtained at high strain rates by measuring the kinematics of thin-ring specimens\\u000a expanding symmetrically by virtue of their own inertia. Impulsively loaded to produce high initial radial velocities, expanding\\u000a rings are decelerated by the radial component of the hoop stresses. Differential equations of motion are evaluated experimentally\\u000a to obtain the stress-strain (constitutive) relationships which

  19. Stress corrosion cracking of several high strength ferrous and nickel alloys

    NASA Technical Reports Server (NTRS)

    Nelson, E. E.

    1971-01-01

    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.

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

    E-print Network

    Wehrli, Bernhard

    -established coagulant in water treatment with high removal efficiency for arsenic. A high content of Al30 nanoclusters Coagulationeflocculatione sedimentation Water treatment Aggregation a b s t r a c t Polyaluminum chloride (PACl) is a well with 75% Al30 nanoclusters (PAClAl30) for the treatment of arsenic-contaminated well water by laboratory

  1. Deep ultraviolet emitting AlGaN quantum wells with high internal quantum efficiency

    E-print Network

    Deep ultraviolet emitting AlGaN quantum wells with high internal quantum efficiency A 2009 We report the development of Al0.7Ga0.3N/AlN quantum wells with high internal quantum efficiency. All samples had identical well and barrier thickness but the III/V flux ratio was varied during growth

  2. Stress-induced high-field gate leakage current in ultra-thin gate oxide

    NASA Astrophysics Data System (ADS)

    Wei, Jianlin; Mao, Lingfeng; Xu, Mingzhen; Tan, Changhua; Duan, Xiaorong

    2000-06-01

    A number of groups have reported that the low-field stress-induced leakage current (SILC) in thin oxides increased after the oxides had been subjected to high voltage stresses. In this study, we observed that high-field SILC increased after the oxides had been subjected to high voltage stresses. The experimental results suggest strongly that SILC must be considered at a high-field region, and the dependence of the high-field SILC on the measurement field Eox is proportional to exp (cE ox) , as compared to the exp (-c/E ox) , at a low field which was reported by some researchers. The high-field SILC increases and saturates after a long stress time, when the stress time increases, which is similar to the low-field SILC. Using the method of proportional difference operator, the trap generation/capture time constant can be obtained.

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

    SciTech Connect

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

    2014-06-02

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

  4. Effects of High Mean Stress on High-cycle Fatigue Behavior of PWA 1480

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    PWA 1480 is a potential candidate material for use in the high-pressure fuel turbine blade of the space shuttle main engine. As an engine material it will be subjected to high-cycle fatigue loading superimposed on a high mean stress due to combined centrifugal and thermal loadings. The present paper describes the results obtained in an ongoing program at the Argonne National Laboratory, sponsored by NASA Lewis, to determine the effects of a high mean stress on the high-cycle fatigue behavior of this material. Straight-gauge high-cycle fatigue specimens, 0.2 inch in diameter and with the specimen axis in the 001 direction, were supplied by NASA Lewis. The nominal room temperature yield and ultimate strength of the material were 146 and 154 ksi, respectively. Each specimen was polished with 1-micron diamond paste prior to testing. However, the surface of each specimen contained many pores, some of which were as large as 50 micron. In the initial tests, specimens were subjected to axial-strain-controlled cycles. However, very little cyclic plasticity was observed.

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

    PubMed

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

    2006-07-01

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

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

    E-print Network

    Joh, Jungwoo

    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 ...

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

    ERIC Educational Resources Information Center

    Peach, Larry

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

  8. Physiology and growth response of roughstalk bluegrass and creeping bentgrass to high temperature stress

    Microsoft Academic Search

    James Marable Rutledge

    2010-01-01

    Roughstalk bluegrass (Poa trivialis L.) (RBG) is a problematic weed in creeping bentgrass fairways (Agrostis stolonifera L.) (CBG) due to its susceptibility to high temperature stress. Our objective was to describe morphological and physiological characteristics of RBG and CBG under high temperature stress to ultimately improve management and control strategies of RBG. Laser (heat-tolerant) and Pulsar (heatsensitive) RBG performed statistically

  9. TEM investigation of age-hardenable Al 2519 alloy subjected to stress corrosion cracking tests

    Microsoft Academic Search

    Stanis?aw Dymek; Marek Dollar

    2003-01-01

    The influence of changes in chemical composition and pre-aging deformation on the resistance to stress corrosion cracking in the age-hardenable aluminum alloy 2519 was investigated by transmission electron microscopy. The improvement of this resistance may be accomplished by keeping the Cu concentration on the lower side of the allowed limit for the 2519 alloy. Also, plastic deformation prior to aging,

  10. Phase diagram of a highly diluted, disordered Ising system: The Al-rich, Al-Fe system

    Microsoft Academic Search

    J. Restrepo; G. A. Pérez Alcázar; J. M. González

    1998-01-01

    Disordered solid solutions containing a highly diluted magnetic element in which competitive exchange interactions are present can allow the observation of magnetic ordering (ferromagnetism, antiferromagnetism, and spin-glass behavior) at dilutor element contents different from those corresponding to ordered alloys. In this work we present a simulational study of the magnetic properties of the Al-rich, Al-Fe disordered alloy system, which meets

  11. Phase diagram of a highly diluted, disordered Ising system: The Al-rich, Al–Fe system

    Microsoft Academic Search

    J. Restrepo; G. A. Pe´rez Alca´zar; J. M. Gonza´lez

    1998-01-01

    Disordered solid solutions containing a highly diluted magnetic element in which competitive exchange interactions are present can allow the observation of magnetic ordering (ferromagnetism, antiferromagnetism, and spin-glass behavior) at dilutor element contents different from those corresponding to ordered alloys. In this work we present a simulational study of the magnetic properties of the Al-rich, Al–Fe disordered alloy system, which meets

  12. High Sensitivity Stress Sensor Based on Hybrid Materials

    NASA Technical Reports Server (NTRS)

    Cao, Xian-An (Inventor)

    2014-01-01

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

  13. High-brightness AlGaInN light-emitting diodes

    Microsoft Academic Search

    Michael R. Krames; G. Christenson; D. Collins; L. W. Cook; George M. Craford; A. Edwards; Robert M. Fletcher; Nathan F. Gardner; Werner K. Goetz; William R. Imler; E. Johnson; R. Scott Kern; Reena Khare; Frederick A. Kish; C. Lowery; Mike J. Ludowise; R. Mann; M. Maranowski; Steven A. Maranowski; Paul S. Martin; J. O'Shea; S. L. Rudaz; Dan A. Steigerwald; J. Thompson; Jonathan J. Wierer; J. G. Yu; David Basile; Ying-Lan Chang; Ghulam Hasnain; M. Heuschen; Kevin P. Killeen; Christophe P. Kocot; Steven Lester; Jeffrey N. Miller; Gerd O. Mueller; Regina Mueller-Mach; S. Jeffrey Rosner; Richard P. Schneider; Tetsuya Takeuchi; T. S. Tan

    2000-01-01

    Currently, commercial LEDs based on AlGaInN emit light efficiently from the ultraviolet-blue to the green portion of the visible wavelength spectrum. Data are presented on AlGaInN LEDs grown by organometallic vapor phase epitaxy (OMVPE). Designs for high-power AlGaInN LEDs are presented along with their performance in terms of output power and efficiency. Finally, present and potential applications for high-power AlGaInN

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

    ERIC Educational Resources Information Center

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

    2010-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

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

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

    PubMed

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

    2014-01-01

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

  17. Effect of Al2O3 on the Crystallization of Mold Flux for Casting High Al Steel

    NASA Astrophysics Data System (ADS)

    Zhou, Lejun; Wang, Wanlin; Zhou, Kechao

    2015-06-01

    In order to lower the weight of automotive bodies for better fuel-efficiency and occupant safety, the demand for high Al-containing advanced high strength steel, such as transformation-induced plasticity and twinning-induced plasticity steel, is increasing. However, high aluminum content in steels would tend to significantly affect the properties of mold flux during the continuous casting process. In this paper, a kinetic study of the effect of Al2O3 content on the crystallization behavior of mold flux was conducted by using the single hot thermocouple technique and the Johnson-Mehl-Avrami model combined with the Arrhenius Equation. The results suggested that Al2O3 behaves as an amphoteric oxide in the crystallization process of mold flux. The precipitated phases of mold flux change from cuspidine (Ca4Si2O7F2) into nepheline (NaAlSiO4) and CaF2, and then into gehlenite (Ca2Al2SiO7) with the increase of Al2O3 content. The kinetics study of the isothermal crystallization process indicated that the effective crystallization rate ( k) and Avrami exponent ( n) also first increased and then decreased with the increase of Al2O3 content. The values for the crystallization activation energy of mold flux with different Al2O3 contents were E R0.8A7 = 150.76 ± 17.89 kJ/mol, E R0.8A20 = 136.43 ± 6.48 kJ/mol, E R0.8A30 = 108.63 ± 12.25 kJ/mol and E R0.8A40 = 116.15 ± 8.17 kJ/mol.

  18. Effect of Al2O3 on the Crystallization of Mold Flux for Casting High Al Steel

    NASA Astrophysics Data System (ADS)

    Zhou, Lejun; Wang, Wanlin; Zhou, Kechao

    2015-03-01

    In order to lower the weight of automotive bodies for better fuel-efficiency and occupant safety, the demand for high Al-containing advanced high strength steel, such as transformation-induced plasticity and twinning-induced plasticity steel, is increasing. However, high aluminum content in steels would tend to significantly affect the properties of mold flux during the continuous casting process. In this paper, a kinetic study of the effect of Al2O3 content on the crystallization behavior of mold flux was conducted by using the single hot thermocouple technique and the Johnson-Mehl-Avrami model combined with the Arrhenius Equation. The results suggested that Al2O3 behaves as an amphoteric oxide in the crystallization process of mold flux. The precipitated phases of mold flux change from cuspidine (Ca4Si2O7F2) into nepheline (NaAlSiO4) and CaF2, and then into gehlenite (Ca2Al2SiO7) with the increase of Al2O3 content. The kinetics study of the isothermal crystallization process indicated that the effective crystallization rate (k) and Avrami exponent (n) also first increased and then decreased with the increase of Al2O3 content. The values for the crystallization activation energy of mold flux with different Al2O3 contents were E R0.8A7 = 150.76 ± 17.89 kJ/mol, E R0.8A20 = 136.43 ± 6.48 kJ/mol, E R0.8A30 = 108.63 ± 12.25 kJ/mol and E R0.8A40 = 116.15 ± 8.17 kJ/mol.

  19. Self-stressing test structures used for high-frequency electromigration

    SciTech Connect

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

    1994-02-01

    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.

  20. ALS mutant FUS proteins are recruited into stress granules in induced pluripotent stem cell-derived motoneurons

    PubMed Central

    Lenzi, Jessica; De Santis, Riccardo; de Turris, Valeria; Morlando, Mariangela; Laneve, Pietro; Calvo, Andrea; Caliendo, Virginia; Chiò, Adriano; Rosa, Alessandro; Bozzoni, Irene

    2015-01-01

    ABSTRACT Patient-derived induced pluripotent stem cells (iPSCs) provide an opportunity to study human diseases mainly in those cases for which no suitable model systems are available. Here, we have taken advantage of in vitro iPSCs derived from patients affected by amyotrophic lateral sclerosis (ALS) and carrying mutations in the RNA-binding protein FUS to study the cellular behavior of the mutant proteins in the appropriate genetic background. Moreover, the ability to differentiate iPSCs into spinal cord neural cells provides an in vitro model mimicking the physiological conditions. iPSCs were derived from FUSR514S and FUSR521C patient fibroblasts, whereas in the case of the severe FUSP525L mutation, in which fibroblasts were not available, a heterozygous and a homozygous iPSC line were raised by TALEN-directed mutagenesis. We show that aberrant localization and recruitment of FUS into stress granules (SGs) is a prerogative of the FUS mutant proteins and occurs only upon induction of stress in both undifferentiated iPSCs and spinal cord neural cells. Moreover, we show that the incorporation into SGs is proportional to the amount of cytoplasmic FUS, strongly correlating with the cytoplasmic delocalization phenotype of the different mutants. Therefore, the available iPSCs represent a very powerful system for understanding the correlation between FUS mutations, the molecular mechanisms of SG formation and ALS ethiopathogenesis. PMID:26035390

  1. ALS mutant FUS proteins are recruited into stress granules in induced pluripotent stem cell-derived motoneurons.

    PubMed

    Lenzi, Jessica; De Santis, Riccardo; de Turris, Valeria; Morlando, Mariangela; Laneve, Pietro; Calvo, Andrea; Caliendo, Virginia; Chiò, Adriano; Rosa, Alessandro; Bozzoni, Irene

    2015-07-01

    Patient-derived induced pluripotent stem cells (iPSCs) provide an opportunity to study human diseases mainly in those cases for which no suitable model systems are available. Here, we have taken advantage of in vitro iPSCs derived from patients affected by amyotrophic lateral sclerosis (ALS) and carrying mutations in the RNA-binding protein FUS to study the cellular behavior of the mutant proteins in the appropriate genetic background. Moreover, the ability to differentiate iPSCs into spinal cord neural cells provides an in vitro model mimicking the physiological conditions. iPSCs were derived from FUS(R514S) and FUS(R521C) patient fibroblasts, whereas in the case of the severe FUS(P525L) mutation, in which fibroblasts were not available, a heterozygous and a homozygous iPSC line were raised by TALEN-directed mutagenesis. We show that aberrant localization and recruitment of FUS into stress granules (SGs) is a prerogative of the FUS mutant proteins and occurs only upon induction of stress in both undifferentiated iPSCs and spinal cord neural cells. Moreover, we show that the incorporation into SGs is proportional to the amount of cytoplasmic FUS, strongly correlating with the cytoplasmic delocalization phenotype of the different mutants. Therefore, the available iPSCs represent a very powerful system for understanding the correlation between FUS mutations, the molecular mechanisms of SG formation and ALS ethiopathogenesis. PMID:26035390

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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.

  3. Achieving reversibility of ultra-high mechanical stress by hydrogen loading of thin films

    NASA Astrophysics Data System (ADS)

    Hamm, M.; Burlaka, V.; Wagner, S.; Pundt, A.

    2015-06-01

    Nano-materials are commonly stabilized by supports to maintain their desired shape and size. When these nano-materials take up interstitial atoms, this attachment to the support induces mechanical stresses. These stresses can be high when the support is rigid. High stress in the nano-material is typically released by delamination from the support or by the generation of defects, e.g., dislocations. As high mechanical stress can be beneficial for tuning the nano-materials properties, it is of general interest to deduce how real high mechanical stress can be gained. Here, we show that below a threshold nano-material size, dislocation formation can be completely suppressed and, when delamination is inhibited, even the ultrahigh stress values of the linear elastic limit can be reached. Specifically, for hydrogen solved in epitaxial niobium films on sapphire substrate supports a threshold film thickness of 6 nm was found and mechanical stress of up to (-10 ± 1) GPa was reached. This finding is of basic interest for hydrogen energy applications, as the hydride stability in metals itself is affected by mechanical stress. Thus, tuning of the mechanical stress-state in nano-materials may lead to improved storage properties of nano-sized materials.

  4. Internal friction in [gamma]-TiAl at high temperatures

    SciTech Connect

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

    1999-06-22

    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.

  5. Lamellar orientation control of TiAl alloys under high temperature gradient with a Ti-43Al-3Si seed

    NASA Astrophysics Data System (ADS)

    Luo, Wenzhong; Shen, Jun; Min, Zhixian; Fu, Hengzhi

    2008-12-01

    Microstructural evolution during directional solidification of TiAl alloys grown from Ti-43Al-3Si (at%) seeds was studied. By using an appropriately oriented seed, the TiAl/Ti 3Al lamellar microstructure was aligned parallel to the growth direction at growth rates of 36 and 54 mm/h. When the growth rate reached 90 mm/h, the lamellae could not remain parallel to the growth direction after a certain solidification length. It was found that new ? grains nucleate among the original ? columnar crystals, and the lamellar orientation changes to an angle of 45° to the growth direction beyond the transition point. Based on the equilibrium binary TiAl phase diagram, the solidification behavior of hypo-peritectic and hyper-peritectic alloys was analyzed. The results suggest that hyper-peritectic alloys should be used as master ingots to obtain a successful seeding of TiAl alloys. Using the nucleation and constitutional undercooling criteria, the nucleation undercooling for the ? phase in the Ti-47Al alloy during the seeding procedure was calculated to be 5.74 K at the given temperature gradient of 400 K/cm. Therefore, a high temperature gradient and a low growth rate were required to keep the ? phase growing in a stable way and to prevent nucleation of the ? phase.

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

    SciTech Connect

    Shimazu, T. [Graduate School of Environmental Studies Tohoku University, Sendai, Miyagi, 980-8579 (Japan); General Research Institute of Technology, INAX Corp., Minatomachi, Tokoname, Aichi, 479-8588 (Japan); Miura, M.; Isu, N. [General Research Institute of Technology, INAX Corp., Minatomachi, Tokoname, Aichi, 479-8588 (Japan); Ogawa, T. [Acoh Ceramic Corporation, Oroshicho, Toki, Gifu, 509-5202 (Japan); Ichikawa, A. [Sanwa Yuka Kogyo Corporation, Ichiriyamacho, Kariya, Aichi, 448-0002 (Japan); Ishida, E. H. [Graduate School of Environmental Studies Tohoku University, Sendai, Miyagi, 980-8579 (Japan)

    2006-05-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

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

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

    NASA Astrophysics Data System (ADS)

    Chen, Ying

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

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

    SciTech Connect

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

    2000-07-01

    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.

  10. Internal stress and dislocation structure of aluminum in high-temperature creep

    Microsoft Academic Search

    A. Orlová; Z. Tobolová; J. Cadek

    1972-01-01

    The dislocation structure formed in high-temperature creep of aluminum has been investigated in the transmission electron microscope. The effect of applied stress and temperature on the quantitative characteristics—dislocation density in sub-grains, subgrain size and misorientation—has been discussed. The correlation of the steady-state substructure characteristics with the macroscopic mean internal stress shows the main contribution of the internal stress field of

  11. Stress Evaluation in a Bulk High-Temperature Superconductor during Field-Cooling Magnetization

    NASA Astrophysics Data System (ADS)

    Takashima, Hideyoshi; Tsuchimoto, Masanori; Onishi, Toshitada

    2001-05-01

    Stresses in a bulk high-temperature superconductor are numerically evaluated during the magnetization process by field cooling. Shielding current distributions are obtained through a macroscopic numerical simulation with the Maxwell equations and the critical state model. The stress distributions are obtained through numerical analysis with the finite-difference method. Two numerical codes are combined in the iterative calculation. Peak values of the maximum hoop, radial and shear stresses are obtained under different conditions during the magnetization.

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

    PubMed Central

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

    2014-01-01

    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

  13. Defects and stresses in MBE-grown GaN and Al0.3Ga0.7N layers doped by silicon using silane

    NASA Astrophysics Data System (ADS)

    Ratnikov, V. V.; Kyutt, R. N.; Smirnov, A. N.; Davydov, V. Yu.; Shcheglov, M. P.; Malin, T. V.; Zhuravlev, K. S.

    2013-12-01

    The electric and structural characteristics of silicon-doped GaN and Al0.3Ga0.7N layers grown by molecular beam epitaxy (MBE) using silane have been analyzed by the Hall effect, Raman spectroscopy, and high-resolution X-ray diffractometry. It is established that the electron concentration linearly increases up to n = 4 × 1020 cm-3 with an increase in the silane flow rate for GaN:Si, whereas the corresponding dependence for Al0.3Ga0.7N:Si is sublinear and the maximum electron concentration is found to be n = 4 × 1019 cm-3. X-ray measurements of sample macrobending indicate a decrease in biaxial compressive stress with an increase in the electron concentration in both GaN:Si and Al0.3Ga0.7N:Si layers. The parameters of the dislocation structure, estimated from the measured broadenings of X-ray reflections, are analyzed.

  14. Fibular stress fracture in a high school athlete.

    PubMed

    Greenberg, Elliot M; Gohn, Nicholas; Grady, Matthew

    2013-01-01

    The patient was a 15-year-old adolescent male who was referred to a physical therapist for a chief complaint of bilateral posterolateral lower-leg pain, which was worse in the right lower extremity than in the left. Due to findings that were concerning for a stress fracture, the patient was referred to a pediatric sports medicine physician. Subsequent radiographs revealed findings that were concerning for a stress fracture along the medial aspect of the midshaft of the right fibula. PMID:23277163

  15. Proppant Fracture Conductivity with High Proppant Loading and High Closure Stress

    E-print Network

    Rivers, Matthew Charles

    2011-08-08

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

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

    E-print Network

    Aytür, Orhan

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  18. High temperature oxidation resistant coatings for the directionally solidified Ni-Nb-Cr-Al eutectic superalloy

    NASA Technical Reports Server (NTRS)

    Strangman, T. E.; Ulion, N. E.; Felten, E. J.

    1977-01-01

    Protective coatings required for the Ni-Nb-Cr-Al directionally solidified eutectic superalloy were developed and evaluated on the basis of oxidation resistance, diffusional stability, thermal fatigue, and creep resistance. NiCrAlY+Pt and NiCrAlY physical vapor-deposition coating systems exhibited the best combination of properties. Burner-rig testing indicated that the useful life of a 127-micron-thick NiCrAlY+Pt coating exceeds 1000 h at 1366 K. Eutectic-alloy creep lives at 1311 K and a stress of 151.7 MN/sq m were greater for NiCrAlY+Pt-coated specimens than for uncoated specimens by a factor of two.

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  20. Altered coordination of the neuroendocrine response during psychosocial stress in subjects with high trait anxiety

    Microsoft Academic Search

    Roman Duncko; Aikaterini Makatsori; Emilia Fickova; Dusan Selko; Daniela Jezova

    2006-01-01

    Contradicting data are available on stress responsiveness in subjects with high anxiety. In the present study we tested the hypothesis that high trait anxiety is associated with impaired coordination of the stress response, rather than global hypo- or hyper-responsiveness. The sample consisted of subjects with high (n=15) and with low (n=12) trait anxiety. Subjects with middle-range levels of anxiety were

  1. Residual stress in hydroxyapatite coating: nonlinear analysis and high-energy synchrotron measurements

    Microsoft Academic Search

    Paul Fogarassy; Bruno Cofino; Pierre Millet; Alain Lodini

    2005-01-01

    The thermal deposition of hydroxyapatite (HA) on titanium alloy substrate (Ti-6Al-4V) leads to a structure that has very good osseointegration properties. However, clinical failures have been occasionally reported at the interface between substrate and coating. Lifetime is the main parameter in such prostheses; therefore, in order to improve their quality, it is necessary to evaluate the level of stresses near

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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.

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

    E-print Network

    Dao, Ming

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

  4. Metal stress consequences on frost hardiness of plants at northern high latitudes: a review and hypothesis

    Microsoft Academic Search

    Kari Taulavuori; M. N. V. Prasad; Erja Taulavuori; Kari Laine

    2005-01-01

    This paper reviews the potential of trace\\/heavy metal-induced stress to reduce plant frost hardiness at northern high latitudes. The scientific questions are first outlined prior to a brief summary of heavy metal tolerance. The concepts of plant capacity and survival adaptation were used to formulate a hypothesis, according to which heavy metal stress may reduce plant frost hardiness for the

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

    E-print Network

    von Andrian, Ulrich H.

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

  6. Cataract formation in a strain of rats selected for high oxidative stress Stefania Marsilia

    E-print Network

    Johnsen, Sönke

    of oxidative damage may in part be a response to elevated levels of glucose. Because oxidative stressCataract formation in a strain of rats selected for high oxidative stress Stefania Marsilia-specific alterations in both fiber cell cytoplasmic protein matrix and membrane structure. The outer adult nuclear

  7. Stress analysis for the high-temperature gaseous corrosion of metal tubes

    Microsoft Academic Search

    V. Rosenband; A. Gany

    1995-01-01

    Stress analysis for the high-temperature gaseous corrosion of metal tubes is presented. The mechanical stresses arising from the difference in thermal expansion coefficients and volumes of a metal and its oxide can result in cracking of the oxide scale and in an increase of the oxidation rate. The model interprets the different behavior of oxide scale growths on outer versus

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  9. Anomalous strain rate dependence of the flow stress in TiAl intermetallic compounds

    Microsoft Academic Search

    Dong Zhu; Liming Wang; Dunxu Zou; Mei Yao; Qigong Cai

    1992-01-01

    The anomalous increase in yield and flow strength with increasing temperature in certain intermetallic compounds is one of the outstanding issues in materials science. This anomaly was well explained for the L12 structure [1]. Yoo et al. [2] studied the plastic deformation of Ni3A1 and\\/3-CuZn alloys with L12 and B2 structures, respectively. In the medium temperature region the shear fault

  10. High-Performance Laser Peening for Effective Mitigation of Stress Corrosion Cracking

    SciTech Connect

    Hackel, L; Hao-Lin, C; Wong, F; Hill, M

    2002-10-02

    Stress corrosion cracking (SCC) in the Yucca Mountain waste package closure welds is believed to be the greatest threat to long-term containment. Use of stress mitigation to eliminate tensile stresses resulting from welding can prevent SCC. A laser technology with sufficient average power to achieve high throughput has been developed and commercially deployed with high peak power and sufficiently high average power to be an effective laser peening system. An appropriately applied version of this process could be applied to eliminate SCC in the waste package closure welds.

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

    SciTech Connect

    L Li; D Weidner

    2011-12-31

    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.

  12. Mean stress effects on high-cycle fatigue of Alloy 718

    SciTech Connect

    Korth, G E

    1980-07-01

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

  13. Boechera Species Exhibit Species-Specific Responses to Combined Heat and High Light Stress

    PubMed Central

    Gallas, Genna; Waters, Elizabeth R.

    2015-01-01

    As sessile organisms, plants must be able to complete their life cycle in place and therefore tolerance to abiotic stress has had a major role in shaping biogeographical patterns. However, much of what we know about plant tolerance to abiotic stresses is based on studies of just a few plant species, most notably the model species Arabidopsis thaliana. In this study we examine natural variation in the stress responses of five diverse Boechera (Brassicaceae) species. Boechera plants were exposed to basal and acquired combined heat and high light stress. Plant response to these stresses was evaluated based on chlorophyll fluorescence measurements, induction of leaf chlorosis, and gene expression. Many of the Boechera species were more tolerant to heat and high light stress than A. thaliana. Gene expression data indicates that two important marker genes for stress responses: APX2 (Ascorbate peroxidase 2) and HsfA2 (Heat shock transcription factor A2) have distinct species-specific expression patterns. The findings of species-specific responses and tolerance to stress indicate that stress pathways are evolutionarily labile even among closely related species. PMID:26030823

  14. High-power InAlGaAs\\/GaAs and AlGaAs\\/GaAs semiconductor laser arrays emitting at 808 nm

    Microsoft Academic Search

    Y. Qu; Shu Yuan; Chong Yang Liu; Baoxue Bo; Guojun Liu; Huilin Jiang

    2004-01-01

    Molecular beam epitaxy (MBE) growth, device fabrication, and reliable operation of high-power InAlGaAs\\/GaAs and GaAlAs\\/GaAs laser arrays are described. Both InAlGaAs\\/GaAs and AlGaAs\\/GaAs laser arrays reached maximum continuous wave output powers of 40 W at room temperature. The external quantum efficiency was 50% and 45% for the InAlGaAs\\/GaAs and AlGaAs\\/GaAs laser arrays, respectively. Threshold current density for InAlGaAs\\/GaAs and AlGaAs\\/GaAs

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

    DOEpatents

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

    1995-07-04

    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.

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

    DOEpatents

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

    1995-01-01

    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.

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

    PubMed Central

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-06-01

    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.

  19. Cyclically-Induced Pore Pressure at High Confining Stress

    Microsoft Academic Search

    Michael K. Sharp; R. Scott Steedman

    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

  20. Ezetimibe Treatment Lowers Indicators of Oxidative Stress in Hypercholesterolemic Subjects with High Oxidative Stress

    Microsoft Academic Search

    Michael S. Kostapanos; Athanasia T. Spyrou; Constantinos C. Tellis; Irene F. Gazi; Alexandros D. Tselepis; Moses Elisaf; Evangelos N. Liberopoulos

    2011-01-01

    Ezetimibe effectively reduces low-density lipoprotein cholesterol (LDL-C). In this study, we tested the hypothesis that ezetimibe\\u000a monotherapy may also decrease markers of oxidative stress in subjects with hypercholesterolemia. Subjects with hypercholesterolemia\\u000a and no evidence of cardiovascular disease were randomly allocated to open-label ezetimibe monotherapy 10 mg\\/day (EZT group)\\u000a or therapeutic lifestyle changes (TLC group). At baseline and 12 weeks post-treatment serum lipoprotein

  1. Thermal properties of Al at high pressures and temperatures

    Microsoft Academic Search

    Shikai Xiang; Lingcang Cai; Fuqian Jing; Shunjin Wang

    2004-01-01

    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

  2. Passivity of high corrosion resistant Cu-Al-Sn alloys

    Microsoft Academic Search

    S. Virtanen; H. Wojtas; P. Schmuki; H. Boehni

    1993-01-01

    In a work studying the corrosion and tarnishing properties of a variety of copper alloys, the alloy Cu-Al10-Sn5 was found to show an excellent corrosion resistance in neutral solutions, where copper and most conventional Cu alloys are covered by thick nonprotective surface layers. The passive films formed on this alloy were characterized with electrochemical and photoelectrochemical methods. The pH dependence

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  4. 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)

    Bjorklund, R. A.

    1983-01-01

    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.

  5. AlGaN/AlN/GaN High-Electron-Mobility Transistors Fabricated with Au-Free Technology

    NASA Astrophysics Data System (ADS)

    Liu, Zhihong; Sun, Min; Lee, Hyung-Seok; Heuken, Michael; Palacios, Tomás

    2013-09-01

    A Au-free technology was developed to fabricate AlGaN/AlN/GaN high-electron-mobility transistors (HEMTs) on Si substrates. Ohmic contact resistance of ˜0.6 ? mm was achieved through a Ti/Al/Ni/Pt metal scheme annealed at 975 °C for 30 s in N2 atmosphere. The ohmic metal surface after annealing was very smooth, with a root-mean-square roughness of only 4.6 nm. The fabricated GaN HEMTs show an off-state breakdown voltage of 540 V with a gate-to-drain distance of 8 µm. These results demonstrate the potential of this Au-free GaN HEMT technology in power electronics and GaN-Si CMOS integration applications.

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

    E-print Network

    Holik, Eddie Frank

    2014-06-03

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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  8. Effect of stressed pre-exposure on the creep strengthening of a 2009 Al-SiC{sub w} composite

    SciTech Connect

    Mishra, R.S.; Lu, R.H.; Grishaber, R.B.; Mukherjee, A.K. [Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering and Materials Science] [Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering and Materials Science

    1998-05-12

    Clearly the present approach of analyzing the steady state or minimum creep data on the basis on a threshold stress is not likely to produce an unambiguous interpretation of the steady state creep mechanism in aluminum alloy matrix composites. In the authors` opinion it is important to (a) establish the existence of a true steady state creep regime in tension over a large enough strain rate range (e.g. a typical creep rate range for experimental verification would be 10{sup {minus}9}--10{sup {minus}5} s{sup {minus}1}), (b) establish a criterion for the lack of a true steady state creep regime (in at least some composites), and (c) look for some other creep parameter to understand the differences in the creep behavior of composites and unreinforced matrices. In this paper the authors report the creep behavior of a 2009Al-SiC{sub w} composite (w denotes whisker). They note that no steady state creep regime was observed at higher creep rates. Specimens pre-exposed at a prior stress (and only in a critical range) show an unusual creep strengthening. This observation hints at the role of matrix composition on overall creep behavior of composites. The primary creep strain and anelastic strain values are reported to highlight the role of SiC{sub w} reinforcement on the overall dislocation activities during creep.

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

    Microsoft Academic Search

    Liu Chuan; Zhang Jianxun; Niu Jing

    2009-01-01

    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

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

    PubMed Central

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

    2014-01-01

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

  11. Buffer-Related Degradation Aspects of Single and Double-Heterostructure Quantum Well InAlN/GaN High-Electron-Mobility Transistors

    NASA Astrophysics Data System (ADS)

    Kuzmik, Jan; Vitanov, Stanislav; Dua, Christian; Carlin, Jean-Francois; Ostermaier, Clemens; Alexewicz, Alexander; Strasser, Gottfried; Pogany, Dionyz; Gornik, Erich; Grandjean, Nicolas; Delage, Sylvain; Palankovski, Vassil

    2012-05-01

    We experimentally prove the viability of the concept of the double-heterostructure quantum well InAlN/GaN high-electron-mobility transistor (HEMT) for the device higher robustness and reliability. In the single quantum well InAlN/GaN HEMTs, the intrinsic channel resistance increases by 300% after 1 h off-state stress; much less degradation is observed in the double-heterostructure device with an AlGaN back barrier. Physics-based device simulation proves that the back barrier blocks the rate of carrier injection into the device buffer. However, whatever the quantum well design is, the energy of the injected electrons in the buffer of InAlN/GaN-based HEMTs is higher than that in the buffer of AlGaN/GaN HEMTs. This energy may be sufficient for releasing hydrogen from GaN point defects.

  12. An inducer of VGF protects cells against ER stress-induced cell death and prolongs survival in the mutant SOD1 animal models of familial ALS.

    PubMed

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

    2010-01-01

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

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

    PubMed Central

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

    2010-01-01

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

  14. The influence of low concentrations of chromium and yttrium on the oxidation behaviour, residual stress and corrosion performance of TiAlN hard coatings on steel substrates

    Microsoft Academic Search

    L. A Donohue; D. B Lewis; W-D Münz; M. M Stack; S. B Lyon; H-W Wang; D Rafaja

    1999-01-01

    Ti0.43Al0.52Cr0.03Y0.02N films, which have been shown to exhibit a fine grain near equiaxed microstructure were found to exhibit a compressive residual stress of ?6.5GPa in contrast to conventional columnar Ti0.44Al0.53Cr0.03N coatings which demonstrated ?3.8GPa compressive stress. Novel coatings with this modified microstructure were also found to possess improved resistance to both dry oxidation and wet aqueous corrosion. Glancing angle parallel

  15. Influence of Aging Treatments on Alterations of Microstructural Features and Stress Corrosion Cracking Behavior of an Al-Zn-Mg Alloy

    NASA Astrophysics Data System (ADS)

    Rout, Prasanta Kumar; Ghosh, M. M.; Ghosh, K. S.

    2015-05-01

    7xxx series Al-Zn-Mg-(Cu) alloys have higher strength in their peak-aged (T6) states compared with other age-hardenable aluminum alloys; however, the maximum strength peak-aged state is more susceptible to stress corrosion cracking (SCC) which leads to catastrophic failure. The over-aged (T7) temper with 10-15% lower strength has higher resistance to SCC requiring oversized structural aerospace component applications. The medium-strength AA7017 Al-Zn-Mg weldable alloy without Cu is also prone to SCC under certain environmental conditions. In the present investigation, the SCC behaviors of an AA7017 Al-Zn-Mg alloys of different tempers have been assessed. Specific aging schedules have been adapted to an AA7017 alloy to produce various tempers, e.g., under-, peak-(T6), over-(T7), and highly over-aged tempers. Artificial aging behavior of the AA7017 alloy has been characterized by hardness, electrical conductivity measurements, x-ray diffraction, differential scanning calorimetry, and electrochemical studies. Slow strain rate test technique was used to assess the SCC behaviors of the AA7017 alloys of under-, T6, T7, and highly over-aged tempers in 3.5 wt.% NaCl solution at free corrosion potential (FCP) and at applied anodic potential, as well. Results revealed that the AA7017 alloy tempers are not susceptible to SCC in 3.5 wt.% NaCl solution at FCP, but severely damaging to SCC at applied anodic potentials. Microstructural features, showing a non-recrystallized grain structure and the presence of discrete, widely spaced, not-interconnected ? precipitates at the grain boundaries, are the contributive factors by virtue of which the alloy tempers at FCP did not exhibit SCC. However, the applied anodic potential resulted in rapid metal dissolution from the grain boundary region and led to SCC. The local anodic dissolution (LAD) is believed to be the associated SCC mechanism.

  16. Effect of Al on High-Temperature Oxidation of Cr–W Alloys

    SciTech Connect

    Ö. N. Do?an

    2008-02-01

    Abstract The effect of Al on the high temperature oxidation behavior of Cr–10 wt.%W alloy was investigated using a cyclical oxidation test at 1,000 °C in dry air. First, Al was added into the Cr–W alloy as an alloying element up to 8 weight percent. Although alloying with Al reduced the spalling, it did not eliminate it. Secondly, Al was applied to the surface using an aluminizing process. Forming an Al–Cr layer on the Cr–W alloy reduced oxidation rate significantly and eliminated spalling completely.

  17. Degradation mechanisms in high-power multi-mode InGaAs-AlGaAs strained quantum well lasers for high-reliability applications

    NASA Astrophysics Data System (ADS)

    Sin, Yongkun; Presser, Nathan; Brodie, Miles; Lingley, Zachary; Foran, Brendan; Moss, Steven C.

    2015-03-01

    Laser diode manufacturers perform accelerated multi-cell lifetests to estimate lifetimes of lasers using an empirical model. Since state-of-the-art laser diodes typically require a long period of latency before they degrade, significant amount of stress is applied to the lasers to generate failures in relatively short test durations. A drawback of this approach is the lack of mean-time-to-failure data under intermediate and low stress conditions, leading to uncertainty in model parameters (especially optical power and current exponent) and potential overestimation of lifetimes at usage conditions. This approach is a concern especially for satellite communication systems where high reliability is required of lasers for long-term duration in the space environment. A number of groups have studied reliability and degradation processes in GaAs-based lasers, but none of these studies have yielded a reliability model based on the physics of failure. The lack of such a model is also a concern for space applications where complete understanding of degradation mechanisms is necessary. Our present study addresses the aforementioned issues by performing long-term lifetests under low stress conditions followed by failure mode analysis (FMA) and physics of failure investigation. We performed low-stress lifetests on both MBE- and MOCVD-grown broad-area InGaAs- AlGaAs strained QW lasers under ACC (automatic current control) mode to study low-stress degradation mechanisms. Our lifetests have accumulated over 36,000 test hours and FMA is performed on failures using our angle polishing technique followed by EL. This technique allows us to identify failure types by observing dark line defects through a window introduced in backside metal contacts. We also investigated degradation mechanisms in MOCVD-grown broad-area InGaAs-AlGaAs strained QW lasers using various FMA techniques. Since it is a challenge to control defect densities during the growth of laser structures, we chose to control defect densities by introducing extrinsic point defects to the laser via proton irradiation with different energies and fluences. These lasers were subsequently lifetested to study degradation processes in the lasers with different defect densities and also to study precursor signatures of failures - traps and non-radiative recombination centers (NRCs) in pre- and post-stressed lasers. Lastly, we employed focused ion beam (FIB), electron beam induced current (EBIC), and highresolution TEM (HR-TEM) techniques to further study dark line defects and dislocations in both post-aged and postproton irradiated lasers. We report on our long-term low-stress lifetest results and physics of failure investigation results.

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

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

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

  19. High-brightness AlGaInN light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Krames, Michael R.; Christenson, G.; Collins, Dave; Cook, Lou W.; Craford, M. G.; Edwards, A.; Fletcher, Robert M.; Gardner, Nathan F.; Goetz, Werner K.; Imler, William R.; Johnson, Eric; Kern, R. Scott; Khare, Reena; Kish, Frederick A.; Lowery, Chris; Ludowise, Mike J.; Mann, Richard; Maranowski, M.; Maranowski, Steven A.; Martin, Paul S.; O'Shea, J.; Rudaz, S. L.; Steigerwald, Dan A.; Thompson, J.; Wierer, Jonathan J.; Yu, Jingxi; Basile, David; Chang, Ying-Lan; Hasnain, Ghulam; Heuschen, M.; Killeen, Kevin P.; Kocot, Christophe P.; Lester, Steven; Miller, Jeffrey N.; Mueller, Gerd O.; Mueller-Mach, Regina; Rosner, S. Jeffrey; Schneider, Richard P., Jr.; Takeuchi, Tetsuya; Tan, Tun S.

    2000-04-01

    Currently, commercial LEDs based on AlGaInN emit light efficiently from the ultraviolet-blue to the green portion of the visible wavelength spectrum. Data are presented on AlGaInN LEDs grown by organometallic vapor phase epitaxy (OMVPE). Designs for high-power AlGaInN LEDs are presented along with their performance in terms of output power and efficiency. Finally, present and potential applications for high-power AlGaInN LEDs, including traffic signals and contour lighting, are discussed.

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

    Microsoft Academic Search

    M. A. Daeubler; G. Luetjering

    2008-01-01

    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

  1. Demonstration of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes on High-Quality AlN Templates

    Microsoft Academic Search

    Yusuke Sakai; Youhua Zhu; Shigeaki Sumiya; Makoto Miyoshi; Mitsuhiro Tanaka; Takashi Egawa

    2010-01-01

    The authors demonstrate AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) on high-quality AlN\\/sapphire template (AlN template) by evaluating its characteristics. LED structures can be grown directly on 2-in.-diameter AlN template by metal-organic chemical vapor deposition. AlGaN epilayers are confirmed to have high crystal quality on AlN template through X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM). The fabricated LEDs exhibit a

  2. Overcoming Si3N4 film stress limitations for High Quality factor ring resonators

    E-print Network

    Lipson, Michal

    . R. Dalton, "Polymer micro-ring filters and modulators," J. Light. Technol. 20, 1968­1975 (2002). #12­13556 (2011). 14. A. Gondarenko, J. S. Levy, and M. Lipson, "High confinement micron-scale silicon nitride­3], frequency combs [4­7], and high precision sensing [8­11], however the intrinsically high film stress

  3. The effect of the built-in stress level of AlN layers on the properties of piezoelectric vibration energy harvesters

    Microsoft Academic Search

    K. Karakaya; M. Renaud; M. Goedbloed; R. van Schaijk

    2008-01-01

    In this paper we investigated the effects of built-in stress on the dielectric and piezoelectric properties of sputtered AlN layers, meant to be implemented in micromachined piezoelectric vibration energy harvesters. Test structures including cantilevers, 4-point bending beams and metal-insulator-metal capacitors were manufactured with reactive sputtered AlN layers in a thickness range of 400-1200 nm. Various bias conditions during the deposition

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

    USGS Publications Warehouse

    Hardebeck, Jeanne L.

    2010-01-01

    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.

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

    PubMed

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

    2013-01-15

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

  6. Formation of V-grooves on the (Al,Ga)N surface as means of tensile stress relaxation

    NASA Astrophysics Data System (ADS)

    Cheng, Kai; Leys, M.; Degroote, S.; Bender, H.; Favia, P.; Borghs, G.; Germain, M.

    2012-08-01

    In this paper we present a study of the relaxation mechanism of the top Al0.30Ga0.70N layer grown on GaN, as used in High Electron Mobility Transistor (HEMT) structures. We show that the initial mechanism for relaxation of strain is by means of formation of V-grooves on the surface of the Al0.30Ga0.70N. It is also demonstrated that a thin Si3N4 layer, grown in-situ, immediately after the AlxGa1-xN can "freeze-in" the surface structure. Using tapping mode Atomic Force Microscopy (AFM) it can be observed that immediately after termination of the growth of the thin Al0.30Ga0.70N layer, the steps on the surface show round shape and spiral-like features. After about 1 min of annealing time under NH3 flow the surface structures become straighter. Upon prolonged annealing a V-groove pattern is observed. These V-grooves run along the <-1-120> directions. Although some other facets can be observed, from cross-sectional Transmission Electron Microscopy (TEM) images we can infer that the side walls of the grooves are {1-101} planes and that the grooves do not penetrate till the Al0.30Ga0.70N/GaN interface. Therefore, we come to the conclusion that the initial relaxation of a thin Al0.30Ga0.70N layer does not occur via a dislocation glide mechanism leading to the formation of an array of misfit dislocations at the Al0.30Gas.70N/GaN interface. Instead, we propose that the mechanism is by surface instability leading to V-groove formation.

  7. Response of propellants to high dynamic stresses: the uses of gun launch techniques

    SciTech Connect

    Lee, E.L.; James, E.; Green, L.; Von Holle, W.; Tarver, C.; Curran, D.; Murri, W.; Seaman, D.

    1984-02-28

    High energy propellants subjected to sufficiently high stresses and high stress rates will ignite and begin to release chemical energy. The ensuing response can vary from mild reaction to high order detonation. Considerable experimental and calculational effort has been spent over the past decade to understand, to predict, and to modify this response. It is our purpose here to review this work with emphasis on the more recent work. Particular emphasis will be given to experimental work using guns to impact flat plates on oriented propellant samples. Such experiments offer special advantages from both an experimentalist's and analyst's point of view because of accessibility of diagnostics and because of simpler geometry.

  8. Relation between coda Q, S-wave velocity and seismicity around the Nobi fault zone, central Japan: High stressing rate below the brittle-ductile transition zone

    NASA Astrophysics Data System (ADS)

    Hiramatsu, Y.; tsuji, S.

    2013-12-01

    Monitoring of the state of stress in the crust is important to understand crustal dynamics, such as the occurrence of a large earthquake. The stress field controls the distribution of cracks and/or fractures in the crust, causing scattering of seismic wave. Coda Q as the reference of scattering character is considered to be a good indicator of the state of stress in the crust (Aki, 1980; Hiramatsu et al., 2000). A dense GPS network revealed a high strain rate zone with many historical damaged earthquakes in central Japan (Sagiya et al., 2000). The strength of stress-induced shear wave polarization anisotropy and coda Q at lower frequencies show a good spatial correlation with the strain rate in/around the high strain rate zone (Hiramatsu et al., 2010; 2013). A spatial variation in stressing rate estimated from the spatial variation in coda Q is larger than those estimated from shear wave splitting. This difference is interpreted by high deformation rate below the brittle-ductile transition zone that causes high stressing rate in the lower crust, resulting the high strain rate zone at the surface (Hiramatsu et al., 2010; 2013). In this study, we investigate a spatial variation in coda Q around the Nobi fault zone in a high strain zone, central Japan, to examine relation between coda Q, shear wave velocity, and seismicity. We analyzed waveform data of 178 events during May 2009-August 2012 obtained by a dense seismic observation operated mainly by the Joint observation group in the Nobi-earthquake region. We apply the single back scattering model (Aki and Chouet, 1975) for waveforms of five frequency bands from 1-32 Hz to obtain the value of coda Q. Relatively low coda Q that is coincident with the high strain rate zone is distinct at the lowest frequency band 1-2 Hz. On the other hand, at higher frequencies, a spatial pattern of coda Q that characterizes the high strain rate zone is not recognized, showing consistency with the results of Jin and Aki (2005) and Hiramatsu et al. (2013). We recognize a good positive correlation between coda Q at 1-2 Hz frequency band and the velocity perturbation of S wave at 25 km depth reported by Matsubara et al. (2008). This suggests that the coda Q reflects the ductile deformation below the brittle-ductile transition zone. Furthermore, coda Q at 1-2 Hz frequency band correlates negatively with seismicity at 10-15 km depth, implying a high stressing rate in low coda Q area. These facts support a high deformation rate below the brittle-ductile transition zone, that is high stressing rate, and resulting high seismicity suggested by Hiramatsu et al. (2010; 2013).

  9. High-dose implantations of Al into Si(111) and Si(100)

    SciTech Connect

    Daley, R.S.; Musket, R.G.

    1992-12-14

    High dose implants of Al (0.5 [times] 10[sup 18] to 2.0 [times] 10[sup 18]/cm[sup 2]) at 200 keV into silicon substrates at 375C were performed in an attempt to form a pure, monocrystalline buried layer of Al in silicon upon post-implant annealing. Nuclear reaction analysis (NRA) and Auger electron spectroscopy (AES) were used to determine the Al concentration and morphology as a function of depth. Results show a peak Al concentration of 83 at.% at a depth of [approx]350 run for the highest dose, and the morphology of the Al is of an interconnected network of 100 at.% Al. Failure to form a continuous elemental layer is explained by the as-implanted morphology resulting thermally induced precipitate coarsening rate at 375C. Formation of large, stable, individual Al precipitates was thermodynamically favored for the implant conditions and effectively precluded coalescence into a continuous layer.

  10. High-dose implantations of Al into Si(111) and Si(100)

    SciTech Connect

    Daley, R.S.; Musket, R.G.

    1992-12-14

    High dose implants of Al (0.5 {times} 10{sup 18} to 2.0 {times} 10{sup 18}/cm{sup 2}) at 200 keV into silicon substrates at 375C were performed in an attempt to form a pure, monocrystalline buried layer of Al in silicon upon post-implant annealing. Nuclear reaction analysis (NRA) and Auger electron spectroscopy (AES) were used to determine the Al concentration and morphology as a function of depth. Results show a peak Al concentration of 83 at.% at a depth of {approx}350 run for the highest dose, and the morphology of the Al is of an interconnected network of 100 at.% Al. Failure to form a continuous elemental layer is explained by the as-implanted morphology resulting thermally induced precipitate coarsening rate at 375C. Formation of large, stable, individual Al precipitates was thermodynamically favored for the implant conditions and effectively precluded coalescence into a continuous layer.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  12. Stress management as an enabling technology for high-field superconducting dipole magnets

    NASA Astrophysics Data System (ADS)

    Holik, Eddie Frank, III

    This dissertation examines stress management and other construction techniques as means to meet future accelerator requirement demands by planning, fabricating, and analyzing a high-field, Nb3Sn dipole. In order to enable future fundamental research and discovery in high energy accelerator physics, bending magnets must access the highest fields possible. Stress management is a novel, propitious path to attain higher fields and preserve the maximum current capacity of advanced superconductors by managing the Lorentz stress so that strain induced current degradation is mitigated. Stress management is accomplished through several innovative design features. A block-coil geometry enables an Inconel pier and beam matrix to be incorporated in the windings for Lorentz Stress support and reduced AC loss. A laminar spring between windings and mica paper surrounding each winding inhibit any stress transferral through the support structure and has been simulated with ALGORRTM. Wood's metal filled, stainless steel bladders apply isostatic, surface-conforming preload to the pier and beam support structure. Sufficient preload along with mica paper sheer release reduces magnet training by inhibiting stick-slip motion. The effectiveness of stress management is tested with high-precision capacitive stress transducers and strain gauges. In addition to stress management, there are several technologies developed to assist in the successful construction of a high-field dipole. Quench protection has been designed and simulated along with full 3D magnetic simulation with OPERARTM. Rutherford cable was constructed, and cable thermal expansion data was analysed after heat treatment. Pre-impregnation analysis techniques were developed due to elemental tin leakage in varying quantities during heat treatment from each coil. Robust splicing techniques were developed with measured resistivites consistent with nO joints. Stress management has not been incorporated by any other high field dipole research laboratory and has not yet been put to a definitive high-field test. The TAMU Physics Accelerator Research Laboratory has constructed a Nb 3Sn dipole, TAMU3, that is specially designed to provide a test bed for high-field stress management.

  13. Microstructure of stress-induced martensite in a TiNiHf high temperature shape memory alloy

    E-print Network

    Zheng, Yufeng

    with the stress-induced martensitic transformation in the TiNi based shape memory alloys (SMAs) [1­3]. For TiMicrostructure of stress-induced martensite in a Ti­Ni­Hf high temperature shape memory alloy X rights reserved. Keywords: High temperature shape memory alloy; TiNiHf alloy; Microstructure; Stress

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

    Microsoft Academic Search

    P. K. Ghosh; Aritra K. Ghosh

    2004-01-01

    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

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

    PubMed

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

    2014-02-01

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

  16. Corrosion Properties of Lightweight and High-strength 2195 Al-Li Alloy

    Microsoft Academic Search

    Yue XU; Xiaojing WANG; Zhaotong YAN; Jiaxue LI

    2011-01-01

    The intergranular corrosion and exfoliation corrosion of 2195 Al-Li alloy treated by multi-step heating-rate controlled aging (MSRC) are studied. The corrosion features of 2195 Al-Li alloys which are respectively treated by high-temperature nucleation MSRC (H-M) and low-temperature nucleation MSRC (L-M) are contrasted. And the corrosion mechanism of 2195 Al-Li alloy is also discussed from the viewpoint of microstructure (types, distribution,

  17. Skin solidification during high pressure die casting of Al–11Si–2Cu–1Fe alloy

    Microsoft Academic Search

    Z. W. Chen

    2003-01-01

    Surface regions of Al–11Si–2Cu–1Fe alloy castings produced by high pressure die casting (HPDC) were examined and three microstructural features were observed. In locations of direct melt impingement, there was not an ?-Al rich layer. In most surface locations, a porosity-free ?-Al rich layer was observed. However, in surface locations of low impact of melt, a porosity-free layer being a mixture

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

    SciTech Connect

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

    2014-03-15

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

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

    SciTech Connect

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

    1992-06-01

    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.

  20. In-situ Stress Measurement of MOVPE Growth of High Efficiency Lattice-Mismatched Solar Cells

    SciTech Connect

    Geisz, J. F.; Levander, A. X.; Norman, A. G.; Jones, K. M.; Romero, M. J.

    2007-04-01

    We have recently reported high efficiencies in a monolithic III-V triple-junction solar cell design that is grown inverted with a metamorphic 1.0 eV bottom In{sub .27}Ga{sub .73}As junction. The biaxial stress and strain grown into this highly lattice-mismatched junction can be controlled by varying the design of a step-graded Ga{sub x}In{sub 1-x}P buffer layer, in which most, but not all, of the 1.9% misfit strain is relieved. A multi-beam optical stress sensor (MOSS) is a convenient tool for in situ measurement of stress during metal-organic vapor phase epitaxy (MOVPE) for the optimization of solar cell performance. The analysis of stress from curvature data is complicated by significant temperature effects due to relatively small thermal gradients in our atmospheric-pressure MOVPE reactor. These temperature effects are discussed and approximations made to allow practical analysis of the data. The results show excellent performance of inverted In{sub .27}Ga{sub .73}. As solar cells grown with slight compressive stress, but degradation under tensile stress. The best devices had a V{sub oc} of 0.54 V and a dislocation density in the low 10{sup 6} cm{sup -2}. The in situ stress data is also compared with ex situ strain data derived from X-ray diffraction measurements.

  1. Electroluminescence of hot electrons in AlGaN/GaN high-electron-mobility transistors under radio frequency operation

    NASA Astrophysics Data System (ADS)

    Brazzini, Tommaso; Casbon, Michael A.; Sun, Huarui; Uren, Michael J.; Lees, Jonathan; Tasker, Paul J.; Jung, Helmut; Blanck, Hervé; Kuball, Martin

    2015-05-01

    Hot electrons in AlGaN/GaN high electron mobility transistors are studied during radio frequency (RF) and DC operation by means of electroluminescence (EL) microscopy and spectroscopy. The measured EL intensity is decreased under RF operation compared to DC at the same average current, indicating a lower hot electron density. This is explained by averaging the DC EL intensity over the measured load line used in RF measurements, giving reasonable agreement. In addition, the hot electron temperature is lower by up to 15% under RF compared to DC, again at least partially explainable by the weighted averaging along the specific load line. However, peak electron temperature under RF occurs at high VDS and low IDS where EL is insignificant suggesting that any wear-out differences between RF and DC stress of the devices will depend on the balance between hot-carrier and field driven degradation mechanisms.

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

    SciTech Connect

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

    2010-11-18

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

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    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.

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

    SciTech Connect

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

    2010-08-09

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  6. High-reflectivity mirrors by Al2O3, LaF3 and AlF3 for 193 nm application

    NASA Astrophysics Data System (ADS)

    Sun, Jian; Li, Xu; Zhang, Weili; Yi, Kui; Shao, Jianda

    2014-03-01

    As important components in deep-ultraviolet (DUV) optics, especially 193 nm lithographic systems, high-reflectivity (HR) mirrors with excellent optical properties and long lifetimes are needed urgently. In this study, we designed and produced three HR coatings for 193 nm on fused quartz substrates: Al2O3/AlF3 coating, LaF3/AlF3 coating and a double stack mirror with combined Al2O3/AlF3 and LaF3/AlF3. The reflectance of the Al2O3/AlF3 coating with 14 layer pairs reached 98.0% at 193 nm. However, the absorption of Al2O3 prevented the reflectance to increase further. The maximum reflectance of the LaF3/AlF3 coating with 15 layer pairs reached 98.1%, with initial micro-cracks formation. The reflectance decreased as the number of layer pairs increased to 16 because of numerous micro-cracks. The mirror with combined Al2O3/AlF3 and LaF3/AlF3 coatings which combined their advantages obtained a reflectance of 98.8% at 193 nm after deposition. This value could still reach 98.5% at 4 months after deposition and remain stable thereafter. Therefore, the combined coating of Al2O3/AlF3 and LaF3/AlF3 is an excellent candidate for practical application.

  7. High efficiency InAlN-based solar cells

    Microsoft Academic Search

    R. E. Jones; R. Broesler; K. M. Yu; J. W. Ager; E. E. Haller; W. Walukiewicz; X. Chen; W. J. Schaff

    2008-01-01

    The band gap energies of the In1?xAlxN alloys are continuously tunable across the solar spectrum, making them good candidates for high efficiency solar cells. In particular, multijunction solar cells could be fabricated entirely from different compositions of this one alloy system. From modeling experimental measurements of the optical absorption coefficient in alloys with 0 ? × ? 0.6, a band

  8. HIGH TEMPERATURE SULFIDATION BEHAVIOR OF LOW Al IRON-ALUMINUM COMPOSITIONS

    E-print Network

    DuPont, John N.

    . Experimental Procedure Cast Fe-Al alloys, with 5, 7.5, and 10 wt% aluminum, were produced by arc-melting high-Al alloys were cast to produce nominal aluminum contents of 5, 7.5, and 10 wt% for testing in moderately, the application of iron-aluminum alloys is currently limited due to hydrogen cracking susceptibility subsequent

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  10. Stress relaxation behavior of nanocluster-strengthened ferritic alloy at high temperatures

    Microsoft Academic Search

    Jeoung Han Kim; Thak Sang Byun; D. T. Hoelzer

    Stress relaxation behavior was investigated for the nanoclusters\\/dispersoids-strengthened steels including the nanostructured ferritic alloy 14YWT (SM10), oxide-dispersion strengthened (ODS) Eurofer97, and commercial ODS steel PM2000. The stress relaxation tests were carried out at high temperatures ranging from 600 to 1000°C. Overall, the relaxation rates of 14YWT and ODS-Eurofer97 were lower than that of PM2000. To analyze the strain rate sensitivity

  11. [Ecophysiological responses of Festuca arundinacea to high temperature stress].

    PubMed

    Xu, Sheng; He, Xing-Yuan; Chen, Wei; Li, Jian-Long

    2007-10-01

    The measurement of leaf relative water content (RWC), chlorophyll content, cell membrane lipid peroxidation, anti-oxidative system, and photosynthesis of two F. arundinacea cultivars (Barlexas and Crossfire II) and Cynodon dactylon under high temperature (38 degrees C / 30 degrees C, day/ night) showed that with the increasing time of exposure to high temperature, the leaf RWC, chlorophyll content, net photosynthetic rate (P(n)) and photochemical efficiency (F(v)/F(m)) of two F. arundinacea cultivars had a decreasing trend, and the average decrement was smaller for Barlexas than for Crossfire II. After exposed to high temperature for 9 days, the average activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in Barlexas leaves were 19.7%, 17.9% and 17.7% higher than those in Crossfire II leaves, and the P(n) of Barlexas and Crossfire II was decreased by 60.7% and 81.9%, respectively. Under high temperature, the F(v)/F(m) of Barlexas leaves was higher than that of Crossfire II leaves, which could be helpful to mitigate the damage of high temperature to the photosynthetic apparatus of Barlexas. No significant change was observed for each test physiological parameter of C. dactylon leaves with the increase of exposure time under high temperature. The adaptation ability to high temperature was in the order of C. dactylon > Barlexas > Crossfire II. PMID:18163301

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

    SciTech Connect

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

    2013-05-10

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

  13. Hoop stress test on new high strength alloy laminated Bi-2223 conductor

    NASA Astrophysics Data System (ADS)

    Miyoshi, Y.; Nishijima, G.; Kitaguchi, H.; Chaud, X.

    2015-07-01

    Bi-2223, despite its high field transport performance, lacks mechanical strength and relies on lamination technology for applications where both current density and mechanical strength are important. The hoop stress limits of a newly available high-strength Bi-2223 has been measured by two different methods at LNCMI-Grenoble and Tsukuba Magnet Laboratory. The measurements confirm the new conductor’s high tensile strength up to 400 MPa. We discuss briefly the role of bending strain with the aid of a supplementary hoop stress measurement with reduced winding diameter.

  14. Financial stress, parent functioning and adolescent problem behavior: an actor-partner interdependence approach to family stress processes in low-, middle-, and high-income families.

    PubMed

    Ponnet, Koen

    2014-10-01

    The family stress model proposes that financial stress experienced by parents is associated with problem behavior in adolescents. The present study applied an actor-partner interdependence approach to the family stress model and focused on low-, middle-, and high-income families to broaden our understanding of the pathways by which the financial stress of mothers and fathers are related to adolescent outcomes. The study uses dyadic data (N = 798 heterosexual couples) from the Relationship between Mothers, Fathers and Children study in which two-parent families with an adolescent between 11 and 17 years of age participated. Path-analytic results indicated that in each of the families the association between parents' financial stress and problem behavior in adolescents is mediated through parents' depressive symptoms, interparental conflict, and positive parenting. Family stress processes also appear to operate in different ways for low-, middle-, and high-income families. In addition to a higher absolute level of financial stress in low-income families, financial stress experienced by mothers and fathers in these families had significant direct and indirect effects on problem behavior in adolescents, while in middle- and high-income families only significant indirect effects were found. The financial stress of a low-income mother also had a more detrimental impact on her level of depressive feelings than it had on mothers in middle-income families. Furthermore, the study revealed gender differences in the pathways of mothers and fathers. Implications for research, clinical practice, and policy are also discussed. PMID:25053382

  15. Can InAlN\\/GaN be an alternative to high power \\/ high temperature AlGaN\\/GaN devices?

    Microsoft Academic Search

    F. Medjdoub; J.-F. Carlin; M. Gonschorek; E. Feltin; M. A. Py; D. Ducatteau; C. Gaquiere; N. Grandjean; E. Kohn

    2006-01-01

    The performance of novel AlInN\\/GaN HEMTs for high power \\/ high temperature applications is discussed. With 0.25 mum gate length the highest maximum output current density of more than 2 A\\/mm at room temperature and more than 3 A\\/mm at 77 K have been obtained even with sapphire substrates. Cut-off frequencies were fT = 50 GHz and fMAX = 60

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

    E-print Network

    Jiang, Hongxing

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

  17. Self-Propagating High-Temperature Synthesis of AlN Nanostructures and Their Sintering Properties

    Microsoft Academic Search

    RADWAN Mohamed; MIYAMOTO Yoshinari

    This investigation describes novel growth of quasi-aligned aluminum nitride (AlN) nanofibers by the self-propagating high-temperature synthesis (SHS) under low nitrogen pressure. The starting charge consists of Al and AlN diluent (40\\/60 mole%) with a mixture of Y2O3 and NH4Cl additives (5 wt% each). The combustion reaction was performed under 0.25 MPa N2 pressure. The microstructure of as-synthesized AlN powder consists

  18. Experimental studies on optimization of process parameters and finite element analysis of temperature and stress distribution on joining of Al–Al and Al–Al 2 O 3 using ultrasonic welding

    Microsoft Academic Search

    Elangovan Sooriyamoorthy; Shenton Ponnayya John Henry; Prakasan Kalakkath

    2011-01-01

    This study is carried out to optimize the process parameters like weld time, weld pressure, and amplitude of vibration to\\u000a maximize the weld strength in Al–Al welding using Taguchi’s design of experiments methodology. Experiments are conducted using\\u000a 0.3-mm thick pieces of aluminum, and the temperature generated at the weld interface and the weld strength for all the specimens\\u000a are measured.

  19. MOCVD growth of high-quality AlGaAs on Si substrates for high-efficiency solar cells

    NASA Astrophysics Data System (ADS)

    Soga, T.; Kato, T.; Baskar, K.; Shao, C. L.; Jimbo, T.; Umeno, M.

    1997-01-01

    The crystallinity and solar cell efficiency of Al 0.22Ga 0.78As layers grown on Si substrates have been studied by varying the thermal cycle annealing (TCA) temperature. The optimum TCA temperature to obtain an Al 0.22Ga 0.78As layer with long minority carrier lifetime and high conversion efficiency has been presented. The active-area conversion efficiency of an Al 0.22Ga 0.78As solar cell on a Si substrate as high as 10.2% has been obtained under AM0 and 1 sun conditions.

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

    Microsoft Academic Search

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

    2002-01-01

    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

  1. High stress late Maastrichtian paleoenvironment: inference from planktonic foraminifera in Tunisia

    E-print Network

    Keller, Gerta

    High stress late Maastrichtian paleoenvironment: inference from planktonic foraminifera in Tunisia, USA Received 10 July 1999; accepted 9 August 2001 Abstract High resolution (V5^10 kyr) planktonic) relatively stable environmental conditions and cool temperatures are indicated by diverse planktonic

  2. Fluid shear stress in trabecular bone marrow due to low-magnitude high-frequency vibration.

    PubMed

    Coughlin, Thomas R; Niebur, Glen L

    2012-08-31

    Low-magnitude high-frequency (LMHF) loading has recently received attention for its anabolic effect on bone. The mechanism of transmission of the anabolic signal is not fully understood, but evidence indicates that it is not dependent on bone matrix strain. One possible source of signaling is mechanostimulation of the cells in the bone marrow. We hypothesized that the magnitude of the fluid shear stress in the marrow during LMHF loading is in the mechanostimulatory range. As such, the goal of this study was to determine the range of shear stress in the marrow during LMHF vibration. The shear stress was estimated from computational models, and its dependence on bone density, architecture, permeability, marrow viscosity, vibration amplitude and vibration frequency were examined. Three-dimensional finite element models of five trabecular bone samples from different anatomic sites were constructed, and a sinusoidal velocity profile was applied to the models. In human bone models during axial vibration at an amplitude of 1 g, more than 75% of the marrow experienced shear stress greater than 0.5Pa. In comparison, in vitro studies indicate that fluid induced shear stress in the range of 0.5 to 2.0Pa is anabolic to a variety of cells in the marrow. Shear stress at the bone-marrow interface was as high as 5.0Pa. Thus, osteoblasts and bone lining cells that are thought to reside on the endosteal surfaces may experience very high shear stress during LMHF loading. However, a more complete understanding of the location of the various cell populations in the marrow is needed to quantify the effects on specific cell types. This study suggests the shear stress within bone marrow in real trabecular architecture during LMHF vibration could provide the mechanical signal to marrow cells that leads to bone anabolism. PMID:22784651

  3. High quality AlN grown on double layer AlN buffers on SiC substrate for deep ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Al tahtamouni, T. M.; Lin, J. Y.; Jiang, H. X.

    2012-11-01

    High quality AlN epilayers were grown on SiC substrates using double layer AlN buffers growth method by metal organic chemical vapor deposition and exploited as active deep ultraviolet optoelectronic materials through the demonstration of AlN Schottky barrier photodetectors. The grown AlN epilayers have smooth surfaces, low etch-pit density, narrow width of x-ray rocking curves, and strong band edge photoluminescence emission with low impurity emissions. AlN Schottky photodetectors are shown to possess outstanding features including extremely low dark current and high breakdown voltage.

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

    SciTech Connect

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

    2014-01-15

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

  5. Nucleation Enhancement of Al Alloys by High Intensity Ultrasound

    NASA Astrophysics Data System (ADS)

    Youn, Jeong Il; Jig Kim, Young

    2009-07-01

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

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

    Microsoft Academic Search

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

    2007-01-01

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

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

    Microsoft Academic Search

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

    2001-01-01

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

  8. Highly precise quantification of protein molecules per cell during stress and starvation responses in Bacillus subtilis.

    PubMed

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

    2014-09-01

    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

  9. Highly transparent and conductive ZnO:Al thin films prepared by vacuum arc plasma evaporation

    NASA Astrophysics Data System (ADS)

    Miyata, Toshihiro; Minamino, Youhei; Ida, Satoshi; Minami, Tadatsugu

    2004-07-01

    A vacuum arc plasma evaporation (VAPE) method using both oxide fragments and gas sources as the source materials is demonstrated to be very effective for the preparation of multicomponent oxide thin films. Highly transparent and conductive Al-doped ZnO (AZO) thin films were prepared by the VAPE method using a ZnO fragment target and a gas source Al dopant, aluminum acethylacetonate (Al(C5H7O2)3) contained in a stainless steel vessel. The Al content in the AZO films was altered by controlling the partial pressure (or flow rate) of the Al dopant gas. High deposition rates as well as uniform distributions of resistivity and thickness on the substrate surface were obtained on large area glass substrates. A low resistivity on the order of 10-4 ? cm and an average transmittance above 80% in the visible range were obtained in AZO thin films deposited on glass substrates. .

  10. Optical floating zone growth of high-quality Cu2MnAl single crystals

    E-print Network

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

    2012-01-01

    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.

  11. High-performance AlGaInP light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Maranowski, Steven A.; Camras, Michael D.; Chen, Changhua; Cook, Lou W.; Craford, M. G.; DeFevere, Dennis C.; Fletcher, Robert M.; Hofler, Gloria E.; Kish, Frederick A.; Kuo, Chihping; Moll, A. J.; Osentowski, Tim; Park, K. G.; Peanasky, Michael J.; Rudaz, S. L.; Steigerwald, Dan A.; Steranka, Frank M.; Stockman, Steve A.; Tan, I. H.; Tarn, J.; Yu, Jingxi; Ludowise, Mike J.; Robbins, Virginia M.

    1997-04-01

    A new class of LEDs based on the AlGaInP material system first became commercially available in the early 1990's. These devices benefit from a direct bandgap from the red to the yellow-green portion of the spectrum. The high efficiencies possible in AlGaInP across this spectrum have enabled new applications for LEDs including automotive lighting, outdoor variable message signs, outdoor large screen video displays, and traffic signal lights. A review of high-brightness AlGaInP LED technology will be presented.

  12. High quality Nb-AlO sub x junctions for microwave receivers and SFQ logic device

    SciTech Connect

    Koshelets, V.P.; Kovtonyuk, S.A.; Serpuchenko, I.L.; Filippenko, L.V.; Shchukin, A.V. (Institute of Radio Engineering and Electronics, USSR Academy of Sciences, Marx Avenue 18, Moscow GSP-3, 103907 (SU))

    1991-03-01

    This paper reports on the high quality Nb--AlO{sub x}--Nb tunnel junctions used for the creation of the low noise SIS mixer and elaboration of the SQUIDs and SFQ logic devices. In this work the specific capcitance of high quality (V{sub m} {gt} 50 mV) Nb--AlO{sub x}--Nb tunnel junctions has been determined by the following methods: the measurement of Zero Field Step resonances in specially prepared long Josephson junctions; the definition of the resonant voltages in two-junctions interferometers based on Nb--AlO{sub x}--Nb junctions.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  14. Interfacial Characterization of Dissimilar Joints Between Al/Mg/Al-Trilayered Clad Sheet to High-Strength Low-Alloy Steel

    NASA Astrophysics Data System (ADS)

    Macwan, A.; Jiang, X. Q.; Chen, D. L.

    2015-06-01

    Magnesium (Mg) alloys are increasingly used in the automotive and aerospace sectors to reduce vehicle weight. Al/Mg/Al tri-layered clad sheets are deemed as a promising alternative to improve the corrosion resistance and formability of Mg alloys. The structural application of Al/Mg/Al tri-layered clad sheets inevitably involves welding and joining in the multi-material vehicle body manufacturing. This study aimed to characterize the bonding interface microstructure of the Al/Mg/Al-clad sheet to high-strength low-alloy steel with and without Zn coating using ultrasonic spot welding at different levels of welding energy. It was observed that the presence of Zn coating improved the bonding at the interface due to the formation of Al-Zn eutectic structure via enhanced diffusion. At a higher level of welding energy, characteristic flow patterns of Zn into Al-clad layer were observed with an extensive penetration mainly along some high angle grain boundaries. The dissimilar joints without Zn coating made at a high welding energy of 800 J failed partially from the Al/Fe weld interface and partially from the Al/Mg clad interface, while the joints with Zn coating failed from the Al/Mg clad interface due to the presence of brittle Al12Mg17 phase.

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

    PubMed Central

    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

    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

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

    PubMed Central

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

    2013-01-01

    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.

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

    PubMed

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

    2014-10-28

    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

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

    DOEpatents

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

    2001-01-01

    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.

  19. High reflectance-low stress Mo-Si multilayer reflective coatings

    DOEpatents

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

    2000-01-01

    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.

  20. Friction Stir Processing of a High Entropy Alloy Al0.1CoCrFeNi

    NASA Astrophysics Data System (ADS)

    Kumar, N.; Komarasamy, M.; Nelaturu, P.; Tang, Z.; Liaw, P. K.; Mishra, R. S.

    2015-05-01

    High entropy alloys are a new class of metallic materials with a potential for use in structural applications. However, most of the studies have focused on microhardness and compressive strength measurements for mechanical properties determination. This study presents the tensile deformation behavior of a single-phase, face-centered cubic Al0.1CoCrFeNi high entropy alloy (HEA). Friction stir processing was carried out to refine the grain size. Scanning electron microscopy and electron backscatter diffraction were carried out for microstructural examination. The grain size of the alloy was on the order of millimeters in the as-received condition. The average grain size after friction stir processing of the alloy was 14 ± 10 micrometers. The mechanical properties were determined through microhardness measurement and mini-tensile tests. The friction stir processed alloy showed a total elongation of ~75% for the mini-tensile sample used and yield strength of 315 MPa. It is an exceptional combination of strength and ductility. Friction stress was determined to be 174 MPa and the Hall-Petch coefficient was 371 MPa ( µm)1/2. Such a high value of Hall-Petch coefficient suggests that grain boundary strengthening can be a very effective strengthening mechanism for the HEA Al0.1CoCrFeNi.

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

    PubMed

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

    2014-09-01

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

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

    PubMed

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

    2015-02-01

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

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

    E-print Network

    Hamza, Iqbal

    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

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

    E-print Network

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

  5. High efficiency AlGaN deep ultraviolet light emitting diodes on silicon

    NASA Astrophysics Data System (ADS)

    Mi, Zetian; Zhao, Songrui; Connie, Ashfiqua; Tavakoli Dastjerdi, Mohammad Hadi

    2015-02-01

    The performance of conventional Al(Ga)N planar devices decays drastically with increasing Al content, leading to low internal quantum efficiencies (IQEs) and high device operation voltages. In this paper, we show that these challenges can be addressed by utilizing epitaxially grown nitrogen polar (N-polar) Al(Ga)N nanowires. With a careful control of the growth conditions, a strong AlN band edge emission at 210 nm can be observed at room temperature, and an IQE of 80% was derived. Furthermore, the Mg incorporation can be drastically enhanced by controlling the growth rate. The hole concentrations of AlN:Mg nanowires were estimated to be on the order of 1016 cm-3, or higher at room temperature. 210 nm emitting AlN nanowire LEDs were achieved, which exhibit excellent electrical performance (at a forward current of 20 mA, the forward bias is about 8 V for a standard 300×300 ?m2 device.). This can be ascribed to both efficient Mg doping and N-polarity induced internal electrical field that enhances hole injection. In the end, high performance AlGaN nanowire LEDs were demonstrated. This work provides a practical path for high efficiency DUV light sources with nanotechnology.

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

    Microsoft Academic Search

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

    2007-01-01

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

  7. The role of oxidative stress in pro-inflammatory activation of human endothelial cells on Ti6Al4V alloy.

    PubMed

    Tsaryk, Roman; Peters, Kirsten; Barth, Susanne; Unger, Ronald E; Scharnweber, Dieter; Kirkpatrick, C James

    2013-11-01

    Inflammation is an important step in the early phase of tissue regeneration around an implanted metallic orthopaedic device. However, prolonged inflammation, which can be induced by metallic corrosion products, can lead to aseptic loosening and implant failure. Cells in peri-implant tissue as well as metal corrosion can induce reactive oxygen species (ROS) formation, thus contributing to an oxidative microenvironment around an implant. Understanding cellular reactions to implant-induced oxidative stress and inflammatory activation is important to help prevent an adverse response to metallic materials. In an earlier study we have shown that endothelial cells grown on Ti6Al4V alloy are subjected to oxidative stress. Since endothelial cells play a critical role in inflammation, in this study we examined the role of oxidative stress in their response to pro-inflammatory activation. Therefore, we stimulated endothelial cells in contact with Ti6Al4V with tumour necrosis factor-? (TNF-?) and monitored the expression of inflammation-associated molecules, such as E-selectin, intercellular adhesion molecule-1 (ICAM-1) and interleukin-8 (IL-8). The induction of these proteins was lower in endothelial cells on Ti6Al4V compared to control tissue culture conditions. There was, however, a discrepancy in pro-inflammatory activation at protein compared to mRNA level in the cells on Ti6Al4V. To examine the role of oxidative stress in this response we utilized different ROS scavengers and showed that ROS depletion improved cellular response to TNF-? on Ti6Al4V. These results could contribute to developing strategies to improve tissue response to metal implants. PMID:23891083

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

    Microsoft Academic Search

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

    2009-01-01

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

  9. High-resolution electron microscope observation of interface microstructure of a cast Al-Mg-Si-Bi-Pb(6262)/Al2O3p composite.

    PubMed

    Zhou, Z.; Fan, Z.; Peng, H. X.; Li, D. X.

    2001-02-01

    High-resolution electron microscopy was employed to characterize the interface structure of a cast Al-Mg-Si-Bi-Pb aluminium(6262)-based composite reinforced by alpha alumina particles with a trace of beta alumina in order to investigate the behaviour of alloying elements in cast composites. Except for a few primary Mg2Si particles, few reaction products were detected at the interface of Al/alpha-Al2O3 due to the unfavourable reaction kinetics during the squeeze-casting process. The Mg2Si particle has an orientation relationship with alpha-Al2O3 of [011]Mg2Si//[1210]alpha-Al2O3 (111)Mg2Si//(0006)alpha-Al2O3. A significant amount of MgAl2O4 was found on the surface of the beta-Al2O3 particles, which is in contrast to the small degree of reaction found on alpha-Al2O3 particles. MgAl2O4 and beta-Al2O3 particles have the following orientation relationship: [011]MgAl2O4//[1210]beta-Al2O3 (111) MgAl2O4//(0006)beta-Al2O3. The similar crystal structure of beta-Al2O3 to MgAl2O4 favours MgAl2O4 nucleation and growth on the surface of beta-Al2O3. Interfacial energy minimization dominates the atomic structure of the interface with the result that close packed planes and directions in the Al2O3 reinforcement and reaction products are parallel to the interfaces. Bi and Pb were found in the form of metallic nanometre particles between Al2O3 particles, or between the MgAl2O4 and Al2O3 particles, or in the open channels of beta-Al2O3 filled by the Al matrix. PMID:11207916

  10. Photosynthetic Decline from High Temperature Stress during Maturation of Wheat 1

    PubMed Central

    Harding, Scott A.; Guikema, James A.; Paulsen, Gary M.

    1990-01-01

    High temperature stress reduces grain growth in wheat (Triticum aestivum L.) by altering source activity and sink capacity. The impact of stress on source and sink interactions in two wheat cultivars of differing source thermotolerance was monitored by analysis of chlorophyll fluorescence transients, Fv (variable fluorescence) and PSM (peak, stationary, maximum), of attached flag leaves on intact and decapitated tillers grown at optimum (20°C) and stress (35°C) temperatures after anthesis. The thermotolerant cultivar Waverly had reduced Fv and PS quenching and a large increase of SM during heat stress. The less thermotolerant cultivar, Len, exhibited increased Fv and PS quenching and a small increase of SM. Fluorescence induction was similar in intact and decapitated tillers of Len, indicating diminished sinksource interaction during heat stress. The present results and previous observations of photosynthetic activities indicate that cyclic electron transport and photophosphorylation in flag leaves of the thermotolerant cultivar were stimulated by sink demand (increased SM in intact plants). Reduced grain development in the thermolabile cultivar resulted from limited capacity to support cyclic electron transport and photophosphorylation (slight increase in SM of intact plants and large reduction of Cytochrome f/b6-mediated electron transport capacity). It was concluded that heat stress injures the photosynthetic apparatus during reproductive growth of wheat and that diminished source activity and sink capacity may be equally important in reducing productivity. PMID:16667330

  11. Tyrosine nitration provokes inhibition of sunflower carbonic anhydrase (?-CA) activity under high temperature stress.

    PubMed

    Chaki, Mounira; Carreras, Alfonso; López-Jaramillo, Javier; Begara-Morales, Juan C; Sánchez-Calvo, Beatriz; Valderrama, Raquel; Corpas, Francisco J; Barroso, Juan B

    2013-02-28

    Protein tyrosine nitration is a post-translational modification (PTM) mediated by reactive nitrogen species (RNS) and it is a new area of research in higher plants. Previously, it was demonstrated that the exposition of sunflower (Helianthus annuus L.) seedlings to high temperature (HT) caused both oxidative and nitrosative stress. The nitroproteome analysis under this stress condition showed the induction of 13 tyrosine-nitrated proteins being the carbonic anhydrase (CA) one of these proteins. The analysis of CA activity under high temperature showed that this stress inhibited the CA activity by a 43%. To evaluate the effect of nitration on the CA activity in sunflower it was used 3-morpholinosydnonimine (SIN-1) (peroxynitrite donor) as the nitrating agent. Thus the CA activity was inhibited by 41%. In silico analysis of the pea CA protein sequence suggests that Tyr(205) is the most likely potential target for nitration. PMID:23266784

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

    SciTech Connect

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

    2010-01-07

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

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

    Microsoft Academic Search

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

    2011-01-01

    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

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

    Microsoft Academic Search

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

    2012-01-01

    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

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

    SciTech Connect

    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

    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.

  16. 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)

    Terrell, J.

    1973-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Lee, Jonathan A.

    2009-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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 ?.

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

    PubMed

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

    2014-10-01

    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

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

    E-print Network

    Piner, Edwin L.

    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 ...

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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.

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

    PubMed

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

    2013-04-01

    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

  4. Highly Resistive Iron-Doped AlInAs Layers Grown by Metalorganic Chemical Vapor Deposition

    Microsoft Academic Search

    Hideto Ishikawa; Mikio Kamada; Hiroji Kawai; Kunio Kaneko

    1992-01-01

    We report for the first time highly resistive iron-doped AlInAs layers grown by metalorganic chemical vapor deposition (MOCVD) using a popular iron doping source, (C5H5)2Fe. The linear relationship between Fe atom concentration of Fe-doped AlInAs layers, which was measured by SIMS analysis, and (C5H5)2Fe flow rate was obtained. To evaluate the effect of Fe doping quantitatively, samples of Si-doped n-AlInAs

  5. Microstructure, wear and high temperature oxidation resistance of nitrided TiAl based alloys

    Microsoft Academic Search

    J. Sun; J. S. Wu; B. Zhao; F. Wang

    2002-01-01

    Gas nitridation of the TiAl based alloys in ammonia atmosphere was investigated in the present work. The scales of the nitrided alloys were characterized by X-ray diffraction (XRD) and electron probe microanalysis (EPMA). The evaluation of the surface hardness, wear and high-temperature oxidation resistance of the nitrided TiAl alloy was performed to compare with those of non-nitrided alloys. The results

  6. AlGaAs/GaAs photovoltaic converters for high power narrowband radiation

    SciTech Connect

    Khvostikov, Vladimir; Kalyuzhnyy, Nikolay; Mintairov, Sergey; Potapovich, Nataliia; Shvarts, Maxim; Sorokina, Svetlana; Andreev, Viacheslav [Ioffe Physical-Technical Institute, 26 Polytechnicheskaya, St. Petersburg, 194021 (Russian Federation); Luque, Antonio [Ioffe Physical-Technical Institute, 26 Polytechnicheskaya, St. Petersburg, 194021, Russia and Instituto de Energia Solar, Universidad Politecnica de Madrid, Madrid (Spain)

    2014-09-26

    AlGaAs/GaAs-based laser power PV converters intended for operation with high-power (up to 100 W/cm{sup 2}) radiation were fabricated by LPE and MOCVD techniques. Monochromatic (? = 809 nm) conversion efficiency up to 60% was measured at cells with back surface field and low (x = 0.2) Al concentration 'window'. Modules with a voltage of 4 V and the efficiency of 56% were designed and fabricated.

  7. Surface hardening of Al by high current Fe-ion implantation

    Microsoft Academic Search

    K. Y. Gao; B. X. Liu

    1997-01-01

    Surface modification of Al was studied by high current Fe-ion implantation using a metal vapor vacuum arc ion source. In the implantation process, two parameters were adjusted, that is, current density and ion dose, corresponding to varying the temperature and time for growing surface Fe-aluminide compound. The major hardening phase was identified to be Al13Fe4 and its depth profile was

  8. Invited Paper AlGaN-based high-performance metal-semiconductor-metal photodetectors

    Microsoft Academic Search

    Mutlu Gokkavas; Serkan Butun; Turgut Tut; Necmi Biyikli; Ekmel Ozbay

    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 1010 A\\/cm2 at a 50 V bias, which is four orders of magnitude lower compared to control devices. A 229 nm cut-off wavelength, a peak

  9. High-Temperature Oxidation Behavior of ODS–Fe3Al

    Microsoft Academic Search

    I. G. Wright; B. A. Pint; P. F. Tortorelli

    2001-01-01

    The high-temperature oxidation behavior of an oxide dispersion-strengthened (ODS) Fe3Al alloy has been studied during isothermal and cyclic exposures in oxygen and air over the temperature range 1000 to 1300°C. Compared to commercially available ODS–FeCrAl alloys, it exhibited very similar short-term rates of oxidation at 1000 and 1100°C, but at higher temperatures the oxidation rate increased because of increased scale

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

    ERIC Educational Resources Information Center

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

    2006-01-01

    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…

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

    E-print Network

    Keller, Gerta

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

  12. The Effects of Mindfulness Meditation Training on Multitasking in a High-Stress Information Environment

    E-print Network

    Wobbrock, Jacob O.

    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 of training in body relaxation. We found that only those trained in meditation stayed on tasks longer and made

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

    Microsoft Academic Search

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

    1979-01-01

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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

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

  15. OFDR DISTRIBUTED STRAIN MEASUREMENTS FOR SHM OF HYDROSTATIC STRESSED STRUCTURES: AN APPLICATION TO HIGH

    E-print Network

    Paris-Sud XI, Université de

    hydrogen storage, based on embedded optical fibres and Rayleigh OFDR. Fibre Bragg Gratings in situ strain on high resolution distributed strain profiles analysis along singlemode optical fibres embeddedOFDR DISTRIBUTED STRAIN MEASUREMENTS FOR SHM OF HYDROSTATIC STRESSED STRUCTURES: AN APPLICATION

  16. The effect of thermal stress on high density packaging integrated circuits

    Microsoft Academic Search

    Bin Yao; Ping Lai; Jian Liu; Xiaosi Liang

    2011-01-01

    The trend of electronics industry is toward advanced high density packaging technologies. The reliability of integrated circuits (ICs) which is significantly affected by thermal stress has become more essential as the packaging density increases. In this paper, an accelerated thermal reliability test method for evaluating the packaging reliability of ICs which includes hot step, cold step and rapid thermal cycling

  17. Sealing of large leaks in high-vacuum systems subject to mechanical and thermal stresses

    NASA Technical Reports Server (NTRS)

    Christian, J. D.; Gilbreath, W. P.

    1974-01-01

    The use of silicone rubber adhesive (particularly, G.E. RTV-108) for sealing large leaks in high vacuum systems subject to mechanical and thermal stresses is shown to be more effective than that of epoxy cements. The sealant is applied externally to the leak while the system is partially evacuated so that it is drawn into the hole.

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

    ERIC Educational Resources Information Center

    Christian, Sonya Colman

    2010-01-01

    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…

  19. Analysis of Residual Stresses in High-Pressure Sheet Metal Forming

    Microsoft Academic Search

    M. Kleiner; R. Krux; W. Homberg

    2004-01-01

    The further development of innovative forming processes like sheet metal hydroforming is only possible with the help of detailed knowledge about the workpiece properties and their formation depending on the particular process strategy. Up to now, the detailed understanding regarding the formation of residual stresses in hydroforming processes like the high-pressure sheet metal forming (HBU) is insufficient. Therefore, numerical (FEM)

  20. Stress Management with Adolescents at the Junior High Transition: An Outcome Evaluation of Coping Skills Intervention

    Microsoft Academic Search

    Steven P. Schinke; Robert F. Schilling; William H. Snow

    1987-01-01

    This paper reports an outcome study of coping skills intervention to help adolescents manage stress associated with the transition from elementary school to junior high. In a randomized design, sixth grade students from four elementary schools were pretested, then two schools each were assigned to an intervention condition and to a control condition. Intervention condition subjects received eight sessions of

  1. The meaning of high stress abrasion and its application in white cast irons

    Microsoft Academic Search

    J. D. Gates; G. J. Gore; M. J. P. Hermand; M. J. P. Guerineau; P. B. Martin; J. Saad

    2007-01-01

    White cast irons perform much less favourably in industrial service environments such as ball mills than would be predicted by standard laboratory abrasion tests. Pin abrasive tests are widely thought to simulate high stress abrasion, but in reality they grossly over-estimate service lives of white iron mill liners compared to pearlitic steel liners. The ‘impact-abrasion’ hypothesis has suggested that the

  2. Mechanical behavior and constitutive modeling during high temperature deformation of Al laminated metal composites

    SciTech Connect

    Grishaber, R.B.; Mishra, R.S.; Mukherjee, A.K. [Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering and Material Science

    1996-12-31

    A constitutive model for deformation of a novel laminated metal composite (LMC) which is comprised of 21 alternating layers of Al 5182 alloy and Al 6090/SiC/25p metal matrix composite (MMC) has been proposed. The LMC as well as the constituent or neat structures have been deformed in uniaxial tension within a broad range of strain-rates (i.e., 10{sup {minus}5} to 10{sup 0}s{sup {minus}1}) and homologous temperatures (i.e., 0.8 {ge} 0.95 T{sub m}). The results of these experiments have led to a thorough characterization of the mechanical behavior and a subsequent semiempirical constitutive rate equation for both the Al 5182 and Al 6090/SiC/25p when tested monolithically. These predictive relations have been coupled with a proposed model which takes into account the dynamic load sharing between the elastically stiffer and softer layers when loaded axially during isostrain deformation of the LMC. This model has led to the development of a constitutive relationship between flow stress and applied strain-rate for the laminated structure.

  3. Study of Residual Stress and Surface Morphology Changes in Al 2 O 3 Induced by Nd:YAG Laser Irradiation

    Microsoft Academic Search

    Sunmog Yeo; Sung-Ki Hong; Sung-Jun Lee; Changhwan Lim; Jae-Won Park

    2010-01-01

    In this study, the residual stress and surface morphology changes in alumina plates by the irradiation of a Q-switched Nd:YAG\\u000a laser were investigated. The results of x-ray diffraction using the sin2? technique show that laser irradiation induces tensile residual stresses on the surface of the plates, which increase with\\u000a the increasing energy density of the laser beam. Residual stress and

  4. Oxidative stress plays a role in high glucose-induced activation of pancreatic stellate cells

    SciTech Connect

    Ryu, Gyeong Ryul; Lee, Esder; Chun, Hyun-Ji; Yoon, Kun-Ho; Ko, Seung-Hyun; Ahn, Yu-Bae; Song, Ki-Ho, E-mail: kihos@catholic.ac.kr

    2013-09-20

    Highlights: •High glucose increased production of reactive oxygen species in cultured pancreatic stellate cells. •High glucose facilitated the activation of these cells. •Antioxidant treatment attenuated high glucose-induced activation of these cells. -- Abstract: The activation of pancreatic stellate cells (PSCs) is thought to be a potential mechanism underlying islet fibrosis, which may contribute to progressive ?-cell failure in type 2 diabetes. Recently, we demonstrated that antioxidants reduced islet fibrosis in an animal model of type 2 diabetes. However, there is no in vitro study demonstrating that high glucose itself can induce oxidative stress in PSCs. Thus, PSCs were isolated and cultured from Sprague Dawley rats, and treated with high glucose for 72 h. High glucose increased the production of reactive oxygen species. When treated with high glucose, freshly isolated PSCs exhibited myofibroblastic transformation. During early culture (passage 1), PSCs treated with high glucose contained an increased number of ?-smooth muscle actin-positive cells. During late culture (passages 2–5), PSCs treated with high glucose exhibited increases in cell proliferation, the expression of fibronectin and connective tissue growth factor, release of interleukin-6, transforming growth factor-? and collagen, and cell migration. Finally, the treatment of PSCs with high glucose and antioxidants attenuated these changes. In conclusion, we demonstrated that high glucose increased oxidative stress in primary rat PSCs, thereby facilitating the activation of these cells, while antioxidant treatment attenuated high glucose-induced PSC activation.

  5. Corrosion behavior of 2195 and 1420 Al-Li alloys in neutral 3.5% NaCl solution under tensile stress

    Microsoft Academic Search

    Jin-feng LI; Wen-jing CHEN; Xu-shan ZHAO; Wen-da REN; Zi-qiao ZHENG

    2006-01-01

    The corrosion behaviors of 1420 and 2195 Al-Li alloys under 308 and 490 MPa tensile stress respectively in neutral 3.5% NaCl solution were investigated using electrochemical impedance spectroscopy(EIS) and scanning electron microscope(SEM). It is found that the unstressed 1420 alloy is featured with large and discrete pits, while general corrosion and localized corrosion including intergranular corrosion and pitting corrosion occur

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

    NASA Astrophysics Data System (ADS)

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

    1997-05-01

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

  7. Long-Term High Protein Intake Does Not Increase Oxidative Stress in Rats

    Microsoft Academic Search

    Klaus J. Petzke; Angelika Elsner; Jurgen Proll; Frank Thielecke; Cornelia C. Metges

    The maximum dietary protein intake that does not cause adverse effects in a healthy population is uncertain. We tested whether a high protein intake enhances oxidative stress. Adult rats were adapted to different casein-based diets containing either an adequate (13.8%; AP), medium (25.7%; MP), or high (51.3%; HP) level of crude protein; a fourth group received a HP diet but

  8. Compact analytical model for single gate AlInSb/InSb high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Chandra, S. Theodore; Balamurugan, N. B.; Subalakshmi, G.; Shalini, T.; Lakshmi Priya, G.

    2014-11-01

    We have developed a 2D analytical model for the single gate AlInSb/InSb HEMT device by solving the Poisson equation using the parabolic approximation method. The developed model analyses the device performance by calculating the parameters such as surface potential, electric field distribution and drain current. The high mobility of the AlInSb/InSb quantum makes this HEMT ideal for high frequency, high power applications. The working of the single gate AlInSb/InSb HEMT device is studied by considering the variation of gate source voltage, drain source voltage, and channel length under the gate region and temperature. The carrier transport efficiency is improved by uniform electric field along the channel and the peak values near the source and drain regions. The results from the analytical model are compared with that of numerical simulations (TCAD) and a good agreement between them is achieved.

  9. High breakdown voltage AlGaN-GaN HEMTs achieved by multiple field plates

    Microsoft Academic Search

    Huili Xing; Y. Dora; A. Chini; S. Heikman; S. Keller; U. K. Mishra

    2004-01-01

    High-voltage Al0.22Ga0.78N-GaN high-electron mobility transistors have been fabricated using multiple field plates over dielectric passivation layers. The device breakdown voltage was found to increase with the addition of the field plates. With two field plates, the device showed a breakdown voltage as high as 900 V. This technique is easy to apply, based on the standard planar transistor fabrication, and

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

    Microsoft Academic Search

    Omair I. Saadat; Jinwook W. Chung; Edwin L. Piner; TomÁs Palacios

    2009-01-01

    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 it is optimized to stand the 870degC ohmic contact annealing. The deposition of the W\\/high-k dielectric protects the intrinsic transistor early in the fabrication process. Three different gate stacks

  11. Ultrasonic elastic wave velocity measurements of polycrystalline MgAl2O4 spinel at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Irifune, T.; Zou, Y.; Greaux, S.; Zhou, C.; Whitaker, M. L.; Higo, Y.; Li, B.

    2012-12-01

    Magnesium aluminate (MgAl2O4) spinel is considered an important functional/structural material widely used at extreme conditions, due to its good mechanical strength, high resistance to chemical attack, good stability, and excellent optical and dielectric properties. Moreover, MgAl2O4 spinel also plays a significant role in geophysics as an important rock-forming mineral, which constitutes peridotites from the uppermost of the Earth's mantle. Therefore, understanding the elasticity and sound velocities of MgAl2O4 spinel are of great interest in the fields ranging from materials physics to geophysics by various experimental techniques. Previous experimental studies on MgAl2O4 spinel were carried out either at high temperature or high temperature. To date, there are no direct measurements of the elastic wave velocities of MgAl2O4 spinel at simultaneous high-pressure and high-temperature conditions. Recently, elasticity and sound velocities of polycrystalline MgAl2O4 spinel have been firstly measured up to 14 GPa and 900 K using ultrasonic interferometry in conjunction with energy-dispersive synchrotron X-ray diffraction. It is found that compressional wave velocity (VP) increases with pressure and decreases with temperature, whereas the shear wave velocity (VS) decreases with both pressure and temperature. Two-dimensional linear fittings of the present data give: KS0 =195 (1) GPa, dKs/dP = 4.4(1), dKs/dT = -0.023(1) GPa/K, G0 = 108(1) GPa, dG/dP = 0.38(1), dG/dT = -0.014(1) GPa/K. Moreover, the bulk modulus (KS) exhibits obvious increase with pressure, while the shear modulus (G) shows a weak variation with pressure, which may be due to the shear deformation relaxation by the coupling between atomic displacements and shear strains.

  12. Stress corrosion crack detection in alloy 600 in high temperature caustic. Master`s thesis

    SciTech Connect

    Brisson, B.W.

    1996-06-01

    Alloy 600, the material used for pressurized water reactor steam generator tubing, is susceptible to environmentally assisted stress corrosion cracking. Intergranular stress corrosion cracking (IGSCC) attacks the tubes in areas of high residual stress, and in crevice regions. No method has been successfully developed to monitor steam generator tubing in-situ for crack initiation and growth. Essentially all available published IGSCC crack growth data for alloy 600 is based on non-tubing material. Although it is very likely that the current data base is applicable to tubing processing, differences between tube and other geometries make a comparison between tubing and other data important for verification purposes. However, obtaining crack initiation and growth data from tubing is difficult due to the geometry and the thin wall thickness.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Nakano, Takuma; Chiba, Masahito; Akazawa, Masamichi

    2014-04-01

    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.

  15. Creep of carbon-yarn and carbon-carbon composites at high temperatures and high stresses. Technical report

    SciTech Connect

    Sines, G.; Yang, Z.; Vickers, B.D.

    1988-05-01

    To better understand the creep-behavior of carbon yarn and carbon-carbon composites, creep experiments were developed that permitted testing at high temperatures (up to 2500 C) and at high stresses (up to 850 MPa) on specially prepared, uniaxial specimens that had a known gage length. Using a Dorn-type power-law relation to model steady-state creep, the apparent activation energy for the carbon-yarn and carbon-composite specimens was determined to be 1082 kj/mol. This value represents a single thermally activated process, vacancy diffusion, that compares favorably with the various types of graphitizable carbon. The value determined for the stress exponent was 7.5. It too was found to be independent of the carbon-matrix's presence and independent of the specimens' loading history. Values of the pre-exponential constant for the carbon yarn and carbon composites were also calculated. The carbon matrix greatly improves the creep resistance of the carbon composite. This improvement was attributed to the matrix's microstructure. It distributes applied loads more evenly and it may also impose a triaxial stress state in the yarns's filaments. It is proposed that such a stress state may inhibit the flux of vacancies, thus accounting in part for this increase in creep resistance.

  16. High intake of heterocyclic amines from meat is associated with oxidative stress.

    PubMed

    Carvalho, A M; Miranda, A M; Santos, F A; Loureiro, A P M; Fisberg, R M; Marchioni, D M

    2015-04-28

    High meat intake has been related to chronic diseases such as cancer and CVD. One hypothesis is that heterocyclic amines (HCA), which are formed during the cooking process of meat, can generate reactive species. These compounds can cause oxidation of lipids, proteins and DNA, resulting in oxidative stress, cell damage and loss of biological function. This association has been seen in vitro; however, it remains unclear in vivo. The aim of the present study was to investigate the association between oxidative stress and HCA intake, and oxidative stress and meat intake. Data were from the Health Survey for Sao Paulo--ISA-Capital (561 adult and elderly). Food intake was estimated by one 24-h dietary recall (24HR) complemented by a detailed FFQ with preferences of cooking methods and level of doneness for meat. HCA intake was estimated linking the meat from the 24HR to a database of HCA. Oxidative stress was estimated by malondialdehyde (MDA) concentration in the plasma, after derivatisation with thiobarbituric acid and quantification by HPLC/diode array. Analyses were performed using multivariate logistic regressions adjusted for smoking, sex, age, BMI, skin colour, energy intake, fruit and vegetable intake, and physical activity. A positive association between HCA intake and MDA concentration (OR 1·17; 95% CI 1·01, 1·38) was observed, showing that HCA from meat may contribute to increase oxidative stress, and may consequently increase the risk of chronic diseases. PMID:25812604

  17. The High Molecular Weight Stress Proteins: Identification, Cloning, and Utilization in Cancer Immunotherapy*

    PubMed Central

    Wang, Xiang-Yang; Subjeck, John R.

    2013-01-01

    Although the large stress/heat shock proteins (HSPs), i.e., Hsp110 and Grp170, were identified over 30 years ago, these abundant and highly conserved molecules have received much less attention compared to other conventional HSPs. Large stress proteins act as molecular chaperones with exceptional protein-holding capability and prevent the aggregation of proteins induced by thermal stress. The chaperoning properties of Hsp110 and Grp170 are integral to the ability of these molecules to modulate immune functions and are essential for developing large chaperone complex vaccines for cancer immunotherapy. The potent antitumor activity of the Hsp110/Grp170-tumor protein antigen complexes, demonstrated in preclinical studies, has led to a phase I clinical trial through the National Cancer Institute's RAID Program that is presently underway. Here we review aspects of the structure and function of these large stress proteins, their roles as molecular chaperones in the biology of cell stress, and prospects for their use in immune regulation and cancer immunotherapy. Lastly, we will discuss the recently revealed immunosuppressive activity of scavenger receptor A that binds to Hsp110 and Grp170, as well as the feasibility of targeting this receptor to promote T-cell activation and antitumor immunity induced by large HSP vaccines and other immunotherapies. PMID:23829534

  18. Static and dynamic stress analyses of the prototype high head Francis runner based on site measurement

    NASA Astrophysics Data System (ADS)

    Huang, X.; Oram, C.; Sick, M.

    2014-03-01

    More efforts are put on hydro-power to balance voltage and frequency within seconds for primary control in modern smart grids. This requires hydraulic turbines to run at off-design conditions. especially at low load or speed-no load. Besides. the tendency of increasing power output and decreasing weight of the turbine runners has also led to the high level vibration problem of the runners. especially high head Francis runners. Therefore. it is important to carry out the static and dynamic stress analyses of prototype high head Francis runners. This paper investigates the static and dynamic stresses on the prototype high head Francis runner based on site measurements and numerical simulations. The site measurements are performed with pressure transducers and strain gauges. Based on the measured results. computational fluid dynamics (CFD) simulations for the flow channel from stay vane to draft tube cone are performed. Static pressure distributions and dynamic pressure pulsations caused by rotor-stator interaction (RSI) are obtained under various operating conditions. With the CFD results. static and dynamic stresses on the runner at different operating points are calculated by means of the finite element method (FEM). The agreement between simulation and measurement is analysed with linear regression method. which indicates that the numerical result agrees well with that of measurement. Furthermore. the maximum static and dynamic stresses on the runner blade are obtained at various operating points. The relations of the maximum stresses and the power output are discussed in detail. The influences of the boundary conditions on the structural behaviour of the runner are also discussed.

  19. MOCVD growth of high efficiency current-matched {AlGaAs}/{Si} tandem solar cell

    NASA Astrophysics Data System (ADS)

    Soga, T.; Baskar, K.; Kato, T.; Jimbo, T.; Umeno, M.

    1997-04-01

    The improvements of the AlGaAs crystal quality grown on Si substrate and the {AlGaAs}/{Si} tandem solar cell have been studied by varying the growth conditions and solar cell structure. The crystal quality of the AlGaAs layer was evaluated by time resolved photoluminescence and double crystal X-ray diffraction while varying the thermal cycle annealing temperature. The optimum thermal cycle annealing temperature and the buffer layer thickness for the growth of high efficiency {AlGaAs}/{Si} tandem solar cells have been presented. The active-area conversion efficiency of 21.2 and 21.4% (AM 0 and 1 sun at 27°C) has been demonstrated with two-terminal and four-terminal configurations, respectively, by perfect photocurrent matching between the top cell and the bottom cell.

  20. Trap states in AlGaN channel high-electron-mobility transistors

    SciTech Connect

    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

    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.

  1. Preliminary study of the characteristics of a high Mg containing Al-Mg-Si alloy

    NASA Astrophysics Data System (ADS)

    Yan, F.; McKay, B. J.; Fan, Z.; Chen, M. F.

    2012-01-01

    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.

  2. Al{sub 2}O{sub 3}-Ni composites with high strength and fracture toughness

    SciTech Connect

    Fahrenholtz, W.G.; Ellerby, D.T.; Loehman, R.E.

    2000-05-01

    Al{sub 2}O{sub 3}-Ni composites were prepared by the reactive hot pressing of Al and NiO. The composites had a two-phase, interpenetrating microstructure and contained {approximately}35 vol% Ni. They exhibited an impressively high combination of strength and toughness at room temperature; the four-point bending strength was in excess of 600 MPa with a fracture toughness of more than 12 MPa{sm_bullet}m{sup 1/2}. Examination of fracture surfaces showed that Ni ligaments underwent ductile deformation during fracture. SEM analysis revealed knife-edged Ni ligaments with a limited amount of debonding around their periphery (i.e., at the Ni-Al{sub 2}O{sub 3} interface), indicating a strong Ni-Al{sub 2}O{sub 3} bond.

  3. StressChip as a high-throughput tool for assessing microbial community responses to environmental stresses.

    PubMed

    Zhou, Aifen; He, Zhili; Qin, Yujia; Lu, Zhenmei; Deng, Ye; Tu, Qichao; Hemme, Christopher L; Van Nostrand, Joy D; Wu, Liyou; Hazen, Terry C; Arkin, Adam P; Zhou, Jizhong

    2013-09-01

    Microbial community responses to environmental stresses are critical for microbial growth, survival, and adaptation. To fill major gaps in our ability to discern the influence of environmental changes on microbial communities from engineered and natural environments, a functional gene-based microarray, termed StressChip, has been developed. First, 46 functional genes involved in microbial responses to environmental stresses such as changes to temperature, osmolarity, oxidative status, nutrient limitation, or general stress response were selected and curated. A total of 22,855 probes were designed, covering 79,628 coding sequences from 985 bacterial, 76 archaeal, and 59 eukaryotic species/strains. Probe specificity was computationally verified. Second, the usefulness of functional genes as indicators of stress response was examined by surveying their distribution in metagenome data sets. The abundance of individual stress response genes is consistent with expected distributions based on respective habitats. Third, the StressChip was used to analyze marine microbial communities from the Deepwater Horizon oil spill. That functional stress response genes were detected in higher abundance (p < 0.05) in oil plume compared to nonplume samples indicated shifts in community composition and structure, consistent with previous results. In summary, StressChip provides a new tool for accessing microbial community functional structure and responses to environmental changes. PMID:23889170

  4. Mean-stress dependence of the thermoelastic parameter for three high-strength alloys. Aircraft structures report

    SciTech Connect

    Dunn, S.A.; Wong, A.K.; Sparrow, J.G.

    1988-07-01

    Experimental verification for the theoretical basis of the mean stress dependence of the thermoelastic parameter is presented here for 4340 steel and collated with previous results for 2024 aluminum and 6 Al-4V titanium alloys. Various experimental techniques are described and their relationship with the theory is discussed in detail. Finally, the means by which the thermoelastic effect may be used to determine residual stresses in practice is discussed.

  5. Secondary Al-Si-Mg High-pressure Die Casting Alloys with Enhanced Ductility

    NASA Astrophysics Data System (ADS)

    Bösch, Dominik; Pogatscher, Stefan; Hummel, Marc; Fragner, Werner; Uggowitzer, Peter J.; Göken, Mathias; Höppel, Heinz Werner

    2015-03-01

    Al-Si-Mg-based secondary cast alloys are attractive candidates for thin-walled high-pressure die castings for applications in the transport industry. The present study investigates the effect of manganese additions at high cooling rates on microstructure, mechanical properties, and on the dominating fracture mechanisms of alloy AlSi10Mg with an elevated iron concentration. Systematic variations of the Mn content from 0.20 to 0.85 wt pct at a constant Fe content of 0.55 wt pct illustrate the key changes in type, phase fraction, and shape of the Fe-containing intermetallic phases, and the corresponding influence on the alloy's ductility. For high-pressure die casting (HPDC), an optimal range of the Mn content between 0.40 and 0.60 wt pct, equivalent to a Mn/Fe ratio of approximately 1, has been identified. At these Mn and Fe contents, the high cooling rates obtained in HPDC result in the formation of fine and homogeneously distributed ?-Al15(Fe,Mn)3Si2 phase, and crack initiation is transferred from AlFeSi intermetallics to eutectic silicon. The study interprets the microstructure-property relationship in the light of thermodynamic calculations which reveal a significant increase in undercooling of the ?-Al15(Fe,Mn)3Si2 phase with increased Mn content. It concludes that the interdependence of the well-defined Mn/Fe ratio and the high cooling rate in HPDC can generate superior ductility in secondary AlSi10Mg cast alloys.

  6. Role of High-Fat Diet in Stress Response of Drosophila

    PubMed Central

    Heinrichsen, Erilynn T.; Haddad, Gabriel G.

    2012-01-01

    Obesity is associated with many diseases, one of the most common being obstructive sleep apnea (OSA), which in turn leads to blood gas disturbances, including intermittent hypoxia (IH). Obesity, OSA and IH are associated with metabolic changes, and while much mammalian work has been done, mechanisms underlying the response to IH, the role of obesity and the interaction of obesity and hypoxia remain unknown. As a model organism, Drosophila offers tremendous power to study a specific phenotype and, at a subsequent stage, to uncover and study fundamental mechanisms, given the conservation of molecular pathways. Herein, we characterize the phenotype of Drosophila on a high-fat diet in normoxia, IH and constant hypoxia (CH) using triglyceride and glucose levels, response to stress and lifespan. We found that female flies on a high-fat diet show increased triglyceride levels (p<0.001) and a shortened lifespan in normoxia, IH and CH. Furthermore, flies on a high-fat diet in normoxia and CH show diminished tolerance to stress, with decreased survival after exposure to extreme cold or anoxia (p<0.001). Of interest, IH seems to rescue this decreased cold tolerance, as flies on a high-fat diet almost completely recovered from cold stress following IH. We conclude that the cross talk between hypoxia and a high-fat diet can be either deleterious or compensatory, depending on the nature of the hypoxic treatment. PMID:22870336

  7. Faceted growth of primary Al{sub 2}Cu crystals during directional solidification in high magnetic field

    SciTech Connect

    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

    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)

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

    SciTech Connect

    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

    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.

  9. Surface modification of Al-20Si alloy by high current pulsed electron beam

    NASA Astrophysics Data System (ADS)

    Hao, Y.; Gao, B.; Tu, G. F.; Li, S. W.; Hao, S. Z.; Dong, C.

    2011-02-01

    Hypereutectic Al-20Si (Si 20 wt.%, Al balance)alloy surface was treated with high current pulsed electron beam (HCPEB) under different pulse numbers. The results indicate that HCPEB irradiation induces the formation of metastable structures on the treated surface. The coarse primary Si particle melts, producing a "halo" microstructure with primary Si as the center on the melted surface. A supersaturated solid solution of Al is formed in the melted layer caused by Si atoms dissolving into the Al matrix. Cross-section structure analysis shows that a 4 ?m remelted layer is formed underneath the top surface of the HCEPB-treated sample. Compared with the matrix, the Al and Si elements in the remelted layer are distributed uniformly. In addition, the grains of the Al-20Si alloy surface are refined after HCPEB treatment, as shown by TEM observation. Nano-silicon particles are dispersed on the surface of remelted layer. Polygonal subgrains, approximately 50-100 nm in size, are formed in the Al matrix. The hardness test results show that the microhardness of the ?(Al) and eutectic structure is increased with increasing pulse number. The hardness of the "halo" microstructure presents a gradient change after 15 pulse treatment due to the diffusion of Si atoms. Furthermore, hardness tests of the cross-section at different depths show that the microhardness of the remelted layer is higher than that of the matrix. Therefore, HCPEB technology is a good surface modification method for enhancing the surface hardness of hypereutectic Al-20Si alloy.

  10. Investigation of trap states under Schottky contact in GaN/AlGaN/AlN/GaN high electron mobility transistors

    SciTech Connect

    Ma, Xiao-Hua, E-mail: xhma@xidian.edu.cn, E-mail: yhao@xidian.edu.cn; Chen, Wei-Wei; Hou, Bin; Zhu, Jie-Jie [School of Advanced Materials and Nanotechnology, Xidian University, Xi'an 710071 (China); Key Lab of Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071 (China); Zhang, Kai; Zhang, Jin-Cheng; Zheng, Xue-Feng; Hao, Yue, E-mail: xhma@xidian.edu.cn, E-mail: yhao@xidian.edu.cn [Key Lab of Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071 (China)

    2014-03-03

    Forward gate-bias stress experiments are performed to investigate the variation of trap states under Schottky contact in GaN-based high electron mobility transistors. Traps with activation energy E{sub T} ranging from 0.22?eV to 0.31?eV are detected at the gate-semiconductor interface by dynamic conductance technique. Trap density decreases prominently after stressing, particularly for traps with E{sub T}?>?0.24?eV. X-ray photoelectron spectroscopy measurements reveal a weaker Ga-O peak on the stressed semiconductor surface. It is postulated that oxygen is stripped by Ni to form NiO upon electrical stress, contributing to the decrease in O{sub N} donor sates under the gate contact.

  11. Internal stress-induced melting below melting temperature at high-rate laser heating

    SciTech Connect

    Hwang, Yong Seok, E-mail: yshwang@iastate.edu [Department of Aerospace Engineering, Iowa State University, Ames, Iowa 50011 (United States); Levitas, Valery I., E-mail: vlevitas@iastate.edu [Departments of Aerospace Engineering, Mechanical Engineering, and Material Science and Engineering, Iowa State University, Ames, Iowa 50011 (United States)

    2014-06-30

    In this Letter, continuum thermodynamic and phase field approaches (PFAs) predicted internal stress-induced reduction in melting temperature for laser-irradiated heating of a nanolayer. Internal stresses appear due to thermal strain under constrained conditions and completely relax during melting, producing an additional thermodynamic driving force for melting. Thermodynamic melting temperature for Al reduces from 933.67?K for a stress-free condition down to 898.1?K for uniaxial strain and to 920.8?K for plane strain. Our PFA simulations demonstrated barrierless surface-induced melt nucleation below these temperatures and propagation of two solid-melt interfaces toward each other at the temperatures very close to the corresponding predicted thermodynamic equilibrium temperatures for the heating rate Q?1.51×10{sup 10}K/s. At higher heating rates, kinetic superheating competes with a reduction in melting temperature and melting under uniaxial strain occurs at 902.1?K for Q?=?1.51?×?10{sup 11?}K/s and 936.9?K for Q?=?1.46?×?10{sup 12?}K/s.

  12. Internal stress-induced melting below melting temperature at high-rate laser heating

    NASA Astrophysics Data System (ADS)

    Hwang, Yong Seok; Levitas, Valery I.

    2014-06-01

    In this Letter, continuum thermodynamic and phase field approaches (PFAs) predicted internal stress-induced reduction in melting temperature for laser-irradiated heating of a nanolayer. Internal stresses appear due to thermal strain under constrained conditions and completely relax during melting, producing an additional thermodynamic driving force for melting. Thermodynamic melting temperature for Al reduces from 933.67 K for a stress-free condition down to 898.1 K for uniaxial strain and to 920.8 K for plane strain. Our PFA simulations demonstrated barrierless surface-induced melt nucleation below these temperatures and propagation of two solid-melt interfaces toward each other at the temperatures very close to the corresponding predicted thermodynamic equilibrium temperatures for the heating rate Q ?1.51×1010K/s. At higher heating rates, kinetic superheating competes with a reduction in melting temperature and melting under uniaxial strain occurs at 902.1 K for Q = 1.51 × 1011 K/s and 936.9 K for Q = 1.46 × 1012 K/s.

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

    SciTech Connect

    Neuville, Daniel R.; Roux, Jacques [Physique des Mineraux et des Magmas, IPGP-CNRS, 4 place Jussieu, 75005 Paris (France); Cormier, Laurent [IMPMC, Universite Pierre et Marie Curie, Universite Denis Diderot, CNRS UMR 7590, 140 rue de Lourmel, 75015 Paris (France); Henderson, Grant S. [Dept of Geology, University of Toronto, 22 Russell St, Toronto (Canada); Ligny, Dominique de [LPCML, UCBL, 12 rue Ampere, 69622 Villeurbanne (France); Flank, Anne-Marie; Lagarde, Pierre [CNRS- UR1 SOLEIL, BP 48, 91192 Gif sur Yvette (France); SLS, 5232 Villigen-PSI (Switzerland)

    2007-02-02

    Using X-ray absorption at the Al K-edge at high temperature, structural information was determined on Al2O3, CaAl2O4 (CA), Ca3Al2O6 (C3A) and CaAl2Si2O8 (anorthite) in the crystalline and liquid states (2380 K). Important changes are observed for Al2O3 where all oscillation in the XANES spectra disappear above the liquidus temperature. For the three other compositions some modifications of the XANES spectra can be attributed to changes in the Al coordination.

  14. Stress and Strain Distributions during Machining of Ti-6Al-4V at Ambient and Cryogenic Temperatures

    NASA Astrophysics Data System (ADS)

    Rahman, Md. Fahim

    Dry and liquid nitrogen pre-cooled Ti-6Al-4V samples were machined at a cutting speed of 43.2 m/min and at low (0.1 mm/rev) to high (0.4 mm/rev) feed rates for understanding the effects of temperature and strain rate on chip microstructures. During cryogenic machining, it was observed that between feed rates of 0.10 and 0.30 mm/rev, a 25% pressure reduction on tool occurred. Smaller number of chips and low tool/chip contact time and temperature were observed (compared to dry machining under ambient conditions). An in-situ set-up that consisted of a microscope and a lathe was constructed and helped to propose a novel serrated chip formation mechanism when microstructures (strain localization) and surface roughness were considered. Dimpled fracture surfaces observed in high-speed-machined chips were formed due to stable crack propagation that was also recorded during in-situ machining. An instability criterion was developed that showed easier strain localization within the 0.10-0.30mm/rev feed rate range.

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    This paper presents an analytical approach used to develop a novel fatigue crack growth coupon for a highly plastic 3-D stress field condition. The flight hardware investigated in this paper is a large separation bolt that fractures using pyrotechnics at the appointed time during the flight sequence. The separation bolt has a deep notch that produces a severe stress concentration and a large plastic zone when highly loaded. For this geometry, linear-elastic fracture mechanics (LEFM) techniques are not valid due to the large nonlinear stress field. Unfortunately, industry codes that are generally available for fracture mechanics analysis and fatigue crack growth (e.g. NASGRO (11) are limited to LEFM and are available for only a limited number of geometries. The results of LEFM based codes are questionable when used on geometries with significant plasticity. Therefore elastic-plastic fracture mechanics (EPFM) techniques using the finite element method (FEM) were used to analyze the bolt and test coupons. scale flight hardware is very costly in t e r n of assets, laboratory resources, and schedule. Therefore to alleviate some of these problems, a series of novel test coupons were developed to simulate the elastic-plastic stress field present in the bolt.

  16. The flavoprotein Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells

    SciTech Connect

    Nishimura, Akira; Kawahara, Nobuhiro [Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan)] [Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan); Takagi, Hiroshi, E-mail: hiro@bs.naist.jp [Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan)] [Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan)

    2013-01-04

    Highlights: Black-Right-Pointing-Pointer NO is produced from L-arginine in response to elevated temperature in yeast. Black-Right-Pointing-Pointer Tah18 was first identified as the yeast protein involved in NO synthesis. Black-Right-Pointing-Pointer Tah18-dependent NO synthesis confers tolerance to high-temperature on yeast cells. -- Abstract: Nitric oxide (NO) is a ubiquitous signaling molecule involved in the regulation of a large number of cellular functions. In the unicellular eukaryote yeast, NO may be involved in stress response pathways, but its role is poorly understood due to the lack of mammalian NO synthase (NOS) orthologues. Previously, we have proposed the oxidative stress-induced L-arginine synthesis and its physiological role under stress conditions in yeast Saccharomyces cerevisiae. Here, our experimental results indicated that increased conversion of L-proline into L-arginine led to NO production in response to elevated temperature. We also showed that the flavoprotein Tah18, which was previously reported to transfer electrons to the Fe-S cluster protein Dre2, was involved in NO synthesis in yeast. Gene knockdown analysis demonstrated that Tah18-dependent NO synthesis confers high-temperature stress tolerance on yeast cells. As it appears that such a unique cell protection mechanism is specific to yeasts and fungi, it represents a promising target for antifungal activity.

  17. Figures of merit for high-energy laser-window materials: thermal lensing and thermal stresses

    NASA Astrophysics Data System (ADS)

    Klein, Claude A.

    2007-01-01

    The selection of a suitable laser-window material involves considerations relating to "thermal lensing," that is, the process of beam distrotion caused by thermally induced phase-aberrations, in addition to issues relating to the stress field generated by beam-induced temperature gradients. The purpose of this paper is to obtain improved figures of merit (FoM) for ranking high-energy laser-window materials in regard to thermal lensing and thermal stresses. We address this task in the following manner: (a) We provide proper analytical expressions for describing how beam-induced optical distortions and beam-induced hoop stresses control the allowable beam fluence; (b) We re-evaluate the role of axial stresses, which may lead to failure through compressive yielding or thermal shock, and derive appropriate FoMs based on allowable irradiances; (c) We illustrate the procedure through FoM evaluations of six window-material candidates for operation at the chemical oxygen-iodine laser wavelength (1.315 µm). This methodology confirms that low-absorption, impurity-free fused silica is the window material of choice for contemplated high-energy laser systems operating in the near-infrared.

  18. Measurement and interpretation of threshold stress intensity factors for steels in high-pressure hydrogen gas.

    SciTech Connect

    Dadfarnia, Mohsen (University of Illinois at Urbana-Champaign, Urbana, IL); Nibur, Kevin A.; San Marchi, Christopher W.; Sofronis, Petros (University of Illinois at Urbana-Champaign, Urbana, IL); Somerday, Brian P.; Foulk, James W., III; Hayden, Gary A. (CP Industries, McKeesport, PA)

    2010-07-01

    Threshold stress intensity factors were measured in high-pressure hydrogen gas for a variety of low alloy ferritic steels using both constant crack opening displacement and rising crack opening displacement procedures. The sustained load cracking procedures are generally consistent with those in ASME Article KD-10 of Section VIII Division 3 of the Boiler and Pressure Vessel Code, which was recently published to guide design of high-pressure hydrogen vessels. Three definitions of threshold were established for the two test methods: K{sub THi}* is the maximum applied stress intensity factor for which no crack extension was observed under constant displacement; K{sub THa} is the stress intensity factor at the arrest position for a crack that extended under constant displacement; and K{sub JH} is the stress intensity factor at the onset of crack extension under rising displacement. The apparent crack initiation threshold under constant displacement, K{sub THi}*, and the crack arrest threshold, K{sub THa}, were both found to be non-conservative due to the hydrogen exposure and crack-tip deformation histories associated with typical procedures for sustained-load cracking tests under constant displacement. In contrast, K{sub JH}, which is measured under concurrent rising displacement and hydrogen gas exposure, provides a more conservative hydrogen-assisted fracture threshold that is relevant to structural components in which sub-critical crack extension is driven by internal hydrogen gas pressure.

  19. Stress Corrosion Cracking Model for High Level Radioactive-Waste Packages

    SciTech Connect

    P. Andresen; G. Gordon; S. Lu

    2004-10-05

    A stress corrosion cracking (SCC) model has been adapted for performance prediction of high level radioactive-waste packages to be emplaced in the proposed Yucca Mountain repository. For waste packages of the proposed Yucca Mountain repository, the outer barrier material is the highly corrosion-resistant Alloy UNS-N06022 (Alloy 22), the environment is represented by aqueous brine films present on the surface of the waste package from dripping or deliquescence of soluble salts present in any surface deposits, and the tensile stress is principally from weld induced residual stress. SCC has historically been separated into ''initiation'' and ''propagation'' phases. Initiation of SCC will not occur on a smooth surface if the surface stress is below a threshold value defined as the threshold stress. Cracks can also initiate at and propagate from flaws (or defects) resulting from manufacturing processes (such as welding); or that develop from corrosion processes such as pitting or dissolution of inclusions. To account for crack propagation, the slip dissolution/film rupture (SDFR) model is adopted to provide mathematical formulae for prediction of the crack growth rate. Once the crack growth rate at an initiated SCC is determined, it can be used by the performance assessment to determine the time to through-wall penetration for the waste package. This paper presents the development of the SDFR crack growth rate model based on technical information in the literature as well as experimentally determined crack growth rates developed specifically for Alloy UNS-N06022 in environments relevant to high level radioactive-waste packages of the proposed Yucca Mountain radioactive-waste repository. In addition, a seismic damage related SCC crack opening area density model is briefly described.

  20. Structural characterization by high-resolution electron microscopy of an Al–Mg alloy processed by high-pressure torsion

    Microsoft Academic Search

    Manping Liu; Hans J. Roven; Maxim Murashkin; Ruslan Z. Valiev

    2009-01-01

    Defects and deformation structures including 0° and 60° full dislocations, 30° Shockley partials, stacking faults and deformation twins in a nanostructured Al–Mg alloy processed by high-pressure torsion were identified using high-resolution transmission electron microscopy. The twinning mechanism previously predicted by the molecular dynamics simulation, i.e., the homogeneous mechanism involving dynamic overlapping of the stacking faults inside grains, was directly verified.

  1. High breakdown voltage AlGaN-GaN power-HEMT design and high current density switching behavior

    Microsoft Academic Search

    Wataru Saito; Yoshiharu Takada; Masahiko Kuraguchi; Kunio Tsuda; Ichiro Omura; Tsuneo Ogura; Hiromichi Ohashi

    2003-01-01

    AlGaN-GaN power high-electron mobility transistors (HEMTs) with 600-V breakdown voltage are fabricated and demonstrated as switching power devices for motor drive and power supply applications. The fabricated power HEMT realized the high breakdown voltage by optimized field plate technique and the low on-state resistance of 3.3 m?cm2, which is 20 times lower than that or silicon MOSFETs, thanks to the

  2. High temperature properties of equiatomic FeAl with ternary additions

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Chang, Yu-Chi; Wang, Yeong-Her

    2015-03-01

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

  4. N-Polarity InN/GaN/InAlN High-Electron-Mobility Transistors

    NASA Astrophysics Data System (ADS)

    Kuzmík, Ján

    2012-04-01

    Using a coupled Schrödinger-Poisson equation solver, we propose an N-polarity InN-channel quantum well high-electron-mobility transistors. The structure comprises from the bottom, a relaxed InAlN buffer with Al mole fraction between 0.1 and 0.3, GaN spacer with thickness less than 1 nm, 5 nm strained InN, and 5 nm ZrO2 or HfO2 to insulate a gate. Depending on the Al mole fraction, calculations indicate highly confined electrons in the channel with a two-dimensional density ranging from 1.6×1013 to 3.5×1013 cm-2. The polarity of the structure provides a possibility to grow InN as the last III-N layer with a relatively low polarization charge at the surface.

  5. Amorphous and nanocrystalline phase formation in highly-driven Al-based binary alloys

    SciTech Connect

    Kalay, Yunus Eren

    2008-10-15

    Remarkable advances have been made since rapid solidification was first introduced to the field of materials science and technology. New types of materials such as amorphous alloys and nanostructure materials have been developed as a result of rapid solidification techniques. While these advances are, in many respects, ground breaking, much remains to be discerned concerning the fundamental relationships that exist between a liquid and a rapidly solidified solid. The scope of the current dissertation involves an extensive set of experimental, analytical, and computational studies designed to increase the overall understanding of morphological selection, phase competition, and structural hierarchy that occurs under far-from equilibrium conditions. High pressure gas atomization and Cu-block melt-spinning are the two different rapid solidification techniques applied in this study. The research is mainly focused on Al-Si and Al-Sm alloy systems. Silicon and samarium produce different, yet favorable, systems for exploration when alloyed with aluminum under far-from equilibrium conditions. One of the main differences comes from the positions of their respective T{sub 0} curves, which makes Al-Si a good candidate for solubility extension while the plunging T{sub 0} line in Al-Sm promotes glass formation. The rapidly solidified gas-atomized Al-Si powders within a composition range of 15 to 50 wt% Si are examined using scanning and transmission electron microscopy. The non-equilibrium partitioning and morphological selection observed by examining powders at different size classes are described via a microstructure map. The interface velocities and the amount of undercooling present in the powders are estimated from measured eutectic spacings based on Jackson-Hunt (JH) and Trivedi-Magnin-Kurz (TMK) models, which permit a direct comparison of theoretical predictions. For an average particle size of 10 {micro}m with a Peclet number of {approx}0.2, JH and TMK deviate from each other. This deviation indicates an adiabatic type solidification path where heat of fusion is reabsorbed. It is interesting that this particle size range is also consistent with the appearance of a microcellular growth. While no glass formation is observed within this system, the smallest size powders appear to consist of a mixture of nanocrystalline Si and Al. Al-Sm alloys have been investigated within a composition range of 34 to 42 wt% Sm. Gas atomized powders of Al-Sm are investigated to explore the morphological and structural hierarchy that correlates with different degrees of departure from full equilibrium conditions. The resultant powders show a variety of structural selection with respect to amount of undercooling, with an amorphous structure appearing at the highest cooling rates. Because of the chaotic nature of gas atomization, Cu-block melt-spinning is used to produce a homogeneous amorphous structure. The as-quenched structure within Al-34 to 42 wt% Sm consists of nanocrystalline fcc-Al (on the order of 5 nm) embedded in an amorphous matrix. The nucleation density of fcc-Al after initial crystallization is on the order of 10{sup 22}-10{sup 23} m{sup -3}, which is 10{sup 5}-10{sup 6} orders of magnitude higher than what classical nucleation theory predicts. Detailed analysis of liquid and as-quenched structures using high energy synchrotron X-ray diffraction, high energy transmission electron microscopy, and atom probe tomography techniques revealed an Al-Sm network similar in appearance to a medium range order (MRO) structure. A model whereby these MRO clusters promote the observed high nucleation density of fcc-Al nanocrystals is proposed. The devitrification path was identified using high temperature, in-situ, high energy synchrotron X-ray diffraction techniques and the crystallization kinetics were described using an analytical Johnson-Mehl-Avrami (JMA) approach.

  6. High-Resolution Characterization of Intergranular Attack and Stress Corrosion Cracking of Alloy 600 in High-Temperature Primary Water

    Microsoft Academic Search

    Larry E. Thomas; Stephen M. Bruemmer

    2000-01-01

    Intergranular (IG) attack regions and stress-corrosion cracks in alloy 600 U-bend samples tested in 330C, pressurized-water-reactor water have been characterized by analytical transmission electron microscopy (ATEM). Observations of cross-sectional samples revealed short oxidized zones preceding crack tips and narrow (10-nm wide), deeply penetrated, oxidized zones along grain boundaries exposed along open cracks. High-resolution TEM imaging and fine-probe analysis were used

  7. The role of stress waves in thoracic visceral injury from blast loading: modification of stress transmission by foams and high-density materials.

    PubMed

    Cooper, G J; Townend, D J; Cater, S R; Pearce, B P

    1991-01-01

    Materials have been applied to the thoracic wall of anaesthetised experimental animals exposed to blast overpressure to investigate the coupling of direct stress waves into the thorax and the relative contribution of compressive stress waves and gross thoracic compression to lung injury. The ultimate purpose of the work is to develop effective personal protection from the primary effects of blast overpressure--efficient protection can only be achieved if the injury mechanism is identified and characterized. Foam materials acted as acoustic couplers and resulted in a significant augmentation of the visceral injury; decoupling and elimination of injury were achieved by application of a high acoustic impedance layer on top of the foam. In vitro experiments studying stress wave transmission from air through various layers into an anechoic water chamber showed a significant increase in power transmitted by the foams, principally at high frequencies. Material such as copper or resin bonded Kevlar incorporated as a facing upon the foam achieved substantial decoupling at high frequencies--low frequency transmission was largely unaffected. An acoustic transmission model replicated the coupling of the blast waves into the anechoic water chamber. The studies suggest that direct transmission of stress waves plays a dominant role in lung parenchymal injury from blast loading and that gross thoracic compression is not the primary injury mechanism. Acoustic decoupling principles may therefore be employed to reduce the direct stress coupled into the body and thus reduce the severity of lung injury--the most simple decoupler is a high acoustic impedance material as a facing upon a foam, but decoupling layers may be optimized using acoustic transmission models. Conventional impacts producing high body wall velocities will also lead to stress wave generation and transmission--stress wave effects may dominate the visceral response to the impact with direct compression and shear contributing little to the aetiology of the injury. PMID:2050704

  8. Enhanced performance of an AlGaN/GaN high electron mobility transistor on Si by means of improved adatom diffusion length during MOCVD epitaxy

    NASA Astrophysics Data System (ADS)

    Shahedipour-Sandvik, F.; Leathersich, J.; Tompkins, R. P.; Suvarna, P.; Tungare, M.; Walsh, T. A.; Kirchner, K. W.; Zhou, S.; Jones, K. A.

    2013-07-01

    Four types of AlGaN/GaN high electron mobility transistor (HEMT) structures have been epitaxially grown on Si substrates by metalorganic chemical vapor deposition (MOCVD) and fabricated into devices. To achieve crack-free device structures, various stress-engineering methods have been employed including the use of AlGaN/AlGaN-graded layers, insertion of low-temperature AlN layers and ion implantation of the AlN/Si substrate. To improve material quality, pulsed MOCVD is used to enhance adatom diffusion length during (Al) GaN epitaxy of various layers in the HEMT structure. A comparison between structural and morphological characteristics of the HEMTs shows improvement in the (0 0 0 2) symmetric rocking curve value to 837.9 s-1 and the surface roughness of 0.21 nm for HEMT structures grown using pulsed epitaxy. An OFF-state breakdown voltage of 217 V at a drain current of 1 mA mm-1 at Vg = -8 V was measured for the structure with enhanced material quality.

  9. Modeling of high homologous temperature deformation behavior for stress and life-time analyses

    SciTech Connect

    Krempl, E. [Rensselaer Polytechnic Institute, Troy, NY (United States)

    1997-12-31

    Stress and lifetime analyses need realistic and accurate constitutive models for the inelastic deformation behavior of engineering alloys at low and high temperatures. Conventional creep and plasticity models have fundamental difficulties in reproducing high homologous temperature behavior. To improve the modeling capabilities {open_quotes}unified{close_quotes} state variable theories were conceived. They consider all inelastic deformation rate-dependent and do not have separate repositories for creep and plasticity. The viscoplasticity theory based on overstress (VBO), one of the unified theories, is introduced and its properties are delineated. At high homologous temperature where secondary and tertiary creep are observed modeling is primarily accomplished by a static recovery term and a softening isotropic stress. At low temperatures creep is merely a manifestation of rate dependence. The primary creep modeled at low homologous temperature is due to the rate dependence of the flow law. The model is unaltered in the transition from low to high temperature except that the softening of the isotropic stress and the influence of the static recovery term increase with an increase of the temperature.

  10. New insulating materials and their use to achieve high operating stresses in electrostatic machines

    NASA Astrophysics Data System (ADS)

    Cooke, Chathan M.

    1986-02-01

    Compressed gas insulation has provided the main insulation for sustaining terminal voltages of electrostatic accelerators. Essentially coaxial geometry is used with mechanical support of the terminal achieved by long columns which also support the acceleration tubes. Because of the vacuum insulation in the acceleration tubes, the electric gradient along the columns is typically 10-20 kV/cm, whereas the radial gas gap can operate at stresses about ten times larger. Until now, the terminal support has always been located in the low stress axial direction along the column and not in the radial high stress region. This paper is concerned with support insulation to be used in the radial direction. Advantages of radial supports include: simpler, more compact column structures, higher total voltages, and support of discrete stress redistribution electrodes such as vivitron. Important factors to the design of radial support insulators include the insulation constraints imposed by the gas gap, mechanical contact to the solid insulator, and basic limits of gas-solid dielectric interfaces. The gas gap insulation strength is shown to be limited by surface microirregularities and this accounts for electrode area and pressure effects. Based on the gas gap requirements, a design strategy for the insulators is developed. Epoxy is employed as the dielectric to allow the use of cast-in metal inserts at the ends. The inserts provide mechanical contact, shielding of the triple junction, and redistribution of the interface electric stresses. By careful design, the electric stress on the interface is made lower than that in the plain coaxial electrode gap. Practical experience shows that voltage increases linearly with insulator length and that designs achieve more than 10 MV/m into the multimegavolt region.

  11. Investigation of thermoelastic stresses induced at high altitudes on aircraft external fuel tanks

    NASA Astrophysics Data System (ADS)

    Mousseau, Stephanie Lynn Steber

    As composite technology has grown over the past several decades, the use of composite materials in military applications has become more feasible and widely accepted. Although composite materials provide many benefits, including strength optimization and reduced weight, damage and repair of these materials creates an additional challenge, especially when operating in a marine environment, such as on a carrier deck. This is evident within the Navy, as excessive damage often leads to the scrapping of F/A-18 External Fuel Tanks. This damage comes in many forms, the most elusive of which is delamination. Often the delamination found on the tanks is beyond repairable limits and the cause unknown, making it difficult to predict and prevent. The purpose of this investigation was to study the structure of the Navy's 330 gallon External Fuel Tanks and investigate one potential cause of delamination, stresses induced at high altitudes by cold temperatures. A stress analysis was completed using finite element software, and validation of the model was accomplished through testing of a scale model specimen. Due to the difficulties in modeling and predicting delamination, such as unknown presence of voids and understanding failure criteria, delamination was not modeled in Abaqus, rather stresses were observed and characteristics were studied to understand the potential for delamination within the layup. In addition, studies were performed to understand the effect of material properties and layup sequence on the stress distribution within the tank. Alternative design solutions are presented which could reduce the radial stresses within the tank, and recommendations are made for further study to understand the trade-offs between stress, cost, and manufacturability.

  12. Optical properties of AlGaN\\/GaN multiple quantum well structure by using a high-temperature AlN buffer on sapphire substrate

    Microsoft Academic Search

    J. Bai; T. Wang; P. Comming; P. J. Parbrook; J. P. R. David; A. G. Cullis

    2006-01-01

    We demonstrated highly improved optical properties of the AlGaN\\/GaN multiple quantum well (MQW) structure grown on a GaN layer with significant reduction of dislocations achieved using an AlN buffer directly grown on a sapphire substrate at high temperature, in comparison with the MQW grown using a conventional two-step technique. An enhancement of room-temperature photoluminescence intensity by up to one order

  13. Reversed polarized emission in highly strained a -plane GaN\\/AlN multiple quantum wells

    Microsoft Academic Search

    R. Mata; A. Cros; J. A. Budagosky; A. Molina-Sánchez; N. Garro; A. García-Cristóbal; J. Renard; S. Founta; B. Gayral; E. Bellet-Amalric; C. Bougerol; B. Daudin

    2010-01-01

    The polarization of the emission from a set of highly strained a -plane GaN\\/AlN multiple quantum wells of varying well widths has been studied. A single photoluminescence peak is observed that shifts to higher energies as the quantum well thickness decreases due to quantum confinement. The emitted light is linearly polarized. For the thinnest samples the preferential polarization direction is

  14. AlN thin film transducers for high temperature non-destructive testing applications

    NASA Astrophysics Data System (ADS)

    Hou, Ruozhou; Hutson, David; Kirk, Katherine J.; Qing Fu, Yong

    2012-04-01

    AlN thin film ultrasonic transducers are being developed for non-destructive testing (NDT) applications in detection and monitoring in a high temperature environment. The ultrasonic transducers were fabricated by RF sputter deposition of c-axis oriented AlN films on aluminum alloy and carbon steel substrates. High temperature performance and durability of the transducers were investigated using pulse-echo experiments at elevated temperatures, and the transducer failure mode was characterized. Results showed that the sputtered AlN films maintained a stable crystalline structure and orientation at elevated temperatures up to 600 °C. The high temperature performance of the ultrasonic transducers, however, was limited by the deterioration of substrate properties. The high temperature limit for the films on aluminum alloy was found to be the melting temperature of the substrate. The AlN films deposited on the carbon steel substrate operated up to 500 °C, but if the temperature was increased further, rapid surface oxidation of the carbon steel caused the transducer to fail.

  15. Neutron radiation effects in high electron mobility transistors [AlGaAs\\/GaAs

    Microsoft Academic Search

    M. Papastamatiou; Nikos Arpatzanis; G. J. Papaioannou; C. Papastergiou; A. Christou

    1997-01-01

    The effect of fast neutron radiation has been investigated in High Electron Mobility Transistors (HEMT's). Devices with different layer structures have been employed for the better understanding of failure mechanism sources. The deep traps introduced by neutron irradiation in the AlGaAs donor layer have been, for the first time, studied. The application of charge control model allowed the determination of

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

    E-print Network

    Lu, Bin

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

  17. ANN constitutive model for high strain-rate deformation of Al 7075-T6

    Microsoft Academic Search

    Jamal Sheikh-Ahmad; Janet Twomey

    2007-01-01

    An artificial neural network (ANN) constitutive model was developed for Al 7075-T6 based on flow data found in the literature and orthogonal machining tests. The use of orthogonal machining data allowed the ANN network to be trained and tested at high strain-rates of deformation common in machining operations. A new ANN method of network construction (training and validation) was successfully

  18. Conducting High Cycle Fatigue Strength Step Tests on Gamma TiAl

    NASA Technical Reports Server (NTRS)

    Lerch, Brad; Draper, Sue; Pereira, J. Mike

    2002-01-01

    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.

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

    E-print Network

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

    2014-05-12

    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...

  20. Low noise and high gain-bandwidth product AlInAs avalanche photodiodes

    Microsoft Academic Search

    Anne Rouvie; Daniele Carpentier; Jean Decobert; Nadine Lagay; Frederic Pommereau; Mohand Achouche

    2008-01-01

    We demonstrate a planar junction AlInAs APD using Carbon as p-doping impurity of the charge layer allowing to achieve simultaneously a high primary sensitivity of 0.9 A\\/W, a low dark current (Idark(M=10)=17 nA at ambient temperature), a low excess noise factor (f(M=10)=3.5) and high gaintimesbandwidth product over 140 GHz.

  1. Reliability of high-power AlGaAs\\/GaAs QW laser diodes

    Microsoft Academic Search

    F. P. Dabkowski; D. R. Pendse; R. J. Barrett; Aland K. Chin; Richard Jollay; Edward M. Clausen; L. C. Hughes; N. B. Sanders

    1996-01-01

    High power laser diodes have been continuously gaining more practical applications. In the majority of these applications, device performance is a determining factor. However, device reliability determines whether a laser diode can be successfully introduced in a commercial product. We review some device reliability problems and their solutions found through customer experience while supplying packaged high power AlGaAs\\/GaAs quantum well

  2. High-brightness tapered lasers with an Al-free active region at 1060 nm

    Microsoft Academic Search

    M. Ruiz; H. Odriozola; C. H. Kwok; N. Michel; M. Calligaro; M. Lecomte; O. Parillaud; M. Krakowski; J. M. G. Tijero; I. Esquivias; R. V. Penty; I. H. White

    2009-01-01

    High-brightness diode lasers at 1060 nm are useful in display applications (to provide green light by frequency doubling) and in free-space optical communications. On Al-free active region laser structures, we have obtained low optical losses of 0.9 cm-1, a high internal quantum efficiency of 98% and a low transparency current density of 64 A\\/cm2. On uncoated broad-area lasers (2 mm

  3. Performance of AlGaN/GaN high electron mobility transistors at nanoscale gate lengths.

    PubMed

    Johnson, J W; Ren, F; Pearton, S J; Baca, A G; Han, J; Dabiran, A M; Chow, P P

    2002-01-01

    The DC and RF performance of AlGaN/GaN high electron mobility transistors with nanoscale gate lengths is presented. The layer structures were grown by either metal organic chemical vapor deposition or rf plasma-assisted molecular beam epitaxy. Excellent scaling properties were observed as a function of both gate length and width and confirm that these devices are well suited to both high speed switching and power microwave applications. PMID:12908259

  4. High-power AlGaN\\/GaN HEMTs for Ka-band applications

    Microsoft Academic Search

    T. Palacios; A. Chakraborty; S. Rajan; C. Poblenz; S. Keller; S. P. DenBaars; J. S. Speck; U. K. Mishra

    2005-01-01

    We report on the fabrication and high-frequency characterization of AlGaN\\/GaN high-electron mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). In devices with a gate length of 160 nm, a record power density of 10.5 W\\/mm with 34% power added efficiency (PAE) has been measured at 40 GHz in MOCVD-grown HEMTs biased at VDS=30

  5. High-performance E-mode AlGaN\\/GaN HEMTs

    Microsoft Academic Search

    T. Palacios; C.-S. Suh; A. Chakraborty; S. Keller; S. P. DenBaars; U. K. Mishra

    2006-01-01

    Enhancement-mode AlGaN\\/GaN high electron-mobility transistors have been fabricated with a gate length of 160 nm. The use of gate recess combined with a fluorine-based surface treatment under the gate produced devices with a threshold voltage of +0.1 V. The combination of very high transconductance (> 400 mS\\/mm) and low gate leakage allows unprecedented output current levels in excess of 1.2

  6. Effects of Low-Oxygen-Content Metalorganic Precursors on AlInAs and High Electron Mobility Transistor Structures with the Thick AlInAs Buffer Layer

    Microsoft Academic Search

    Tsuyoshi Tanaka; Kohichi Tokudome; Yasuyuki Miyamoto

    2003-01-01

    We investigated the effects of low-oxygen-content metalorganic precursors on oxygen impurities and Hall mobility. The oxygen concentration in the AlInAs layer was less than 2× 1017 cm-3 under all growth conditions. We confirmed the high mobility of the AlInAs\\/InP high electron mobility transistors (HEMT) structure with the AlInAs buffer layer (5,500 cm2\\/V\\\\cdots at 300 K, and 110,000 cm2\\/V\\\\cdots at 77

  7. A high-throughput virus-induced gene silencing protocol identifies genes involved in multi-stress tolerance

    PubMed Central

    2013-01-01

    Background Understanding the function of a particular gene under various stresses is important for engineering plants for broad-spectrum stress tolerance. Although virus-induced gene silencing (VIGS) has been used to characterize genes involved in abiotic stress tolerance, currently available gene silencing and stress imposition methodology at the whole plant level is not suitable for high-throughput functional analyses of genes. This demands a robust and reliable methodology for characterizing genes involved in abiotic and multi-stress tolerance. Results Our methodology employs VIGS-based gene silencing in leaf disks combined with simple stress imposition and effect quantification methodologies for easy and faster characterization of genes involved in abiotic and multi-stress tolerance. By subjecting leaf disks from gene-silenced plants to various abiotic stresses and inoculating silenced plants with various pathogens, we show the involvement of several genes for multi-stress tolerance. In addition, we demonstrate that VIGS can be used to characterize genes involved in thermotolerance. Our results also showed the functional relevance of NtEDS1 in abiotic stress, NbRBX1 and NbCTR1 in oxidative stress; NtRAR1 and NtNPR1 in salinity stress; NbSOS1 and NbHSP101 in biotic stress; and NtEDS1, NbETR1, NbWRKY2 and NbMYC2 in thermotolerance. Conclusions In addition to widening the application of VIGS, we developed a robust, easy and high-throughput methodology for functional characterization of genes involved in multi-stress tolerance. PMID:24289810

  8. High Glucose–Induced Oxidative Stress Increases Transient Receptor Potential Channel Expression in Human Monocytes

    PubMed Central

    Wuensch, Tilo; Thilo, Florian; Krueger, Katharina; Scholze, Alexandra; Ristow, Michael; Tepel, Martin

    2010-01-01

    OBJECTIVE Transient receptor potential (TRP) channel–induced cation influx activates human monocytes, which play an important role in the pathogenesis of atherosclerosis. In the present study, we investigated the effects of high glucose–induced oxidative stress on TRP channel expression in human monocytes. RESEARCH DESIGN AND METHODS Human monocytes were exposed to control conditions (5.6 mmol/l d-glucose), high glucose (30 mmol/l d-glucose or l-glucose), 100 ?mol/l peroxynitrite, or high glucose in the presence of the superoxide dismutase mimetic tempol (100 ?mol/l). TRP mRNA and TRP protein expression was measured using quantitative real-time RT-PCR and quantitative in-cell Western assay, respectively. Calcium influx and intracellular reactive oxygen species were measured using fluorescent dyes. RESULTS Administration of high d-glucose significantly increased reactive oxygen species. High d-glucose or peroxynitrite significantly increased the expression of TRP canonical type 1 (TRPC1), TRPC3, TRPC5, TRPC6, TRP melastatin type 6 (TRPM6), and TRPM7 mRNA and TRPC3 and TRPC6 proteins. High d-glucose plus tempol or high l-glucose did not affect TRP expression. Increased oxidative stress by lipopolysaccharide or tumor necrosis factor-? increased TRP mRNA expression, whereas the reduction of superoxide radicals using diphenylene iodonium significantly reduced TRP mRNA expression. Increased TRPC3 and TRPC6 protein expression was accompanied by increased 1-oleoyl-2-acetyl-sn-glycerol–induced calcium influx, which was blocked by the TRPC inhibitor 2-aminoethoxydiphenylborane. TRPC6 mRNA was significantly higher in monocytes from 18 patients with type 2 diabetes compared with 28 control subjects (P < 0.05). CONCLUSIONS High d-glucose–induced oxidative stress increases TRP expression and calcium influx in human monocytes, pointing to a novel pathway for increased activation of monocytes and hence atherosclerosis in patients with diabetes. PMID:20068131

  9. Content analysis to detect high stress in oral interviews and text documents

    NASA Technical Reports Server (NTRS)

    Thirumalainambi, Rajkumar (Inventor); Jorgensen, Charles C. (Inventor)

    2012-01-01

    A system of interrogation to estimate whether a subject of interrogation is likely experiencing high stress, emotional volatility and/or internal conflict in the subject's responses to an interviewer's questions. The system applies one or more of four procedures, a first statistical analysis, a second statistical analysis, a third analysis and a heat map analysis, to identify one or more documents containing the subject's responses for which further examination is recommended. Words in the documents are characterized in terms of dimensions representing different classes of emotions and states of mind, in which the subject's responses that manifest high stress, emotional volatility and/or internal conflict are identified. A heat map visually displays the dimensions manifested by the subject's responses in different colors, textures, geometric shapes or other visually distinguishable indicia.

  10. Antioxidant responses of Propylaea japonica (Coleoptera: Coccinellidae) exposed to high temperature stress.

    PubMed

    Zhang, Shize; Fu, Wenyan; Li, Ning; Zhang, Fan; Liu, Tong-Xian

    2015-02-01

    Temperature is one of the most important environmental factors, and is responsible for a variety of physiological stress responses in organisms. Induced thermal stress is associated with elevated reactive oxygen species (ROS) generation leading to oxidative damage. The ladybeetle, Propylaea japonica (Thunberg) (Coleoptera: Coccinellidae), is considered a successful natural enemy because of its tolerance to high temperatures in arid and semi-arid areas in China. In this study, we investigated the effect of high temperatures (35, 37, 39, 41 and 43 °C) on the survival and activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), peroxidases (POD), glutathione-S-transferases (GST), and total antioxidant capacity (TAC) as well as malondialdehyde (MDA) concentrations in P. japonica adults. The results indicated that P. japonica adults could not survive at 43 °C. CAT, GST and TAC were significantly increased when compared to the control (25 °C), and this played an important role in the process of antioxidant response to thermal stress. SOD and POD activity, as well as MDA, did not differ significantly at 35 and 37 °C compared to the control; however, there were increased levels of SOD, POD and MDA when the temperature was above 37 °C. These results suggest that thermal stress leads to oxidative stress and antioxidant enzymes play important roles in reducing oxidative damage in P. japonica adults. This study represents the first comprehensive report on the antioxidant defense system in predaceous coccinellids (the third trophic level). The findings provide useful information for predicting population dynamics and understanding the potential for P. japonica as a natural enemy to control pest insects under varied environmental conditions. PMID:25614965

  11. Transcriptomic Analysis of Petunia hybrida in Response to Salt Stress Using High Throughput RNA Sequencing

    PubMed Central

    Villarino, Gonzalo H.; Bombarely, Aureliano; Giovannoni, James J.; Scanlon, Michael J.; Mattson, Neil S.

    2014-01-01

    Salinity and drought stress are the primary cause of crop losses worldwide. In sodic saline soils sodium chloride (NaCl) disrupts normal plant growth and development. The complex interactions of plant systems with abiotic stress have made RNA sequencing a more holistic and appealing approach to study transcriptome level responses in a single cell and/or tissue. In this work, we determined the Petunia transcriptome response to NaCl stress by sequencing leaf samples and assembling 196 million Illumina reads with Trinity software. Using our reference transcriptome we identified more than 7,000 genes that were differentially expressed within 24 h of acute NaCl stress. The proposed transcriptome can also be used as an excellent tool for biological and bioinformatics in the absence of an available Petunia genome and it is available at the SOL Genomics Network (SGN) http://solgenomics.net. Genes related to regulation of reactive oxygen species, transport, and signal transductions as well as novel and undescribed transcripts were among those differentially expressed in response to salt stress. The candidate genes identified in this study can be applied as markers for breeding or to genetically engineer plants to enhance salt tolerance. Gene Ontology analyses indicated that most of the NaCl damage happened at 24 h inducing genotoxicity, affecting transport and organelles due to the high concentration of Na+ ions. Finally, we report a modification to the library preparation protocol whereby cDNA samples were bar-coded with non-HPLC purified primers, without affecting the quality and quantity of the RNA-seq data. The methodological improvement presented here could substantially reduce the cost of sample preparation for future high-throughput RNA sequencing experiments. PMID:24722556

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

    SciTech Connect

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

    1999-10-22

    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.

  13. Dissection of Oxidative Stress Tolerance Using Transgenic Plants

    Microsoft Academic Search

    Randy D. Allen

    1995-01-01

    Environmental stress is the major limiting factor in plant productivity. Much of the injury to plants caused by stress exposure is associated with oxidative damage at the cellu- lar level. Widespread losses of forests and crops due to ozone pollution provide a highly visible example of oxida- tive stress (see Tingey et al., 1993, for a review), but less obvious

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

    SciTech Connect

    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

    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.

  15. Worksite Stress Management with High-Risk Maintenance Workers: A Controlled Study

    Microsoft Academic Search

    Kathleen K. Peters; John G. Carlson

    1999-01-01

    This study evaluated effects of a worksite stress management\\/health promotion program with primarily minority blue-collar employees showing a number of high-risk health behaviors. In a biopsychosocial approach, participants were assessed with a standardized health risk appraisal that included physical and behavioral variables, plus measures of self-control, health attitudes\\/satisfaction, and other factors. A controlled group design was employed with pretreatment, treatment,

  16. Modeling high-temperature stress-strain behavior of cast aluminum alloys

    Microsoft Academic Search

    Tracy J. Smith; Huseyin Sehitoglu; Eric Fleury; Hans J. Maier; John Allison

    1999-01-01

    A modified two-state-variable unified constitutive model is presented to model the high-temperature stress-strain behavior\\u000a of a 319 cast aluminum alloy with a T7 heat treatment. A systematic method is outlined, with which one can determine the material\\u000a parameters used in the experimentally based model. The microstructural processes affecting the material behavior were identified\\u000a using transmission electron microscopy and were consequently

  17. Determination of tensile flow stress beyond necking at very high strain rate

    Microsoft Academic Search

    A. M. Rajendran; S. J. Bless

    1986-01-01

    The objective of this effort was to extend the Bridgman analysis of tensile necking to obtain stress-strain data beyond the\\u000a point of onset of necking from a split Hopkinson bar. For this purpose, combined analytical and experimental techniques were\\u000a considered. The analytical efforts were focused on validating the use of Bridgman solutions for high rate of deformation through\\u000a a finite-element

  18. Effects of arbuscular mycorrhizal fungus on photosynthesis and water status of maize under high temperature stress

    Microsoft Academic Search

    Xian-Can Zhu; Feng-Bin Song; Sheng-Qun Liu; Tie-Dong Liu

    The purpose of this study was to investigate the effects of arbuscular mycorrhizal (AM) symbiosis on gas exchange, chlorophyll\\u000a fluorescence, pigment concentration and water status of maize plants in pot culture under high temperature stress. Zea mays L. genotype Zhengdan 958 were cultivated in soil at 26\\/22°C for 6 weeks, and later subjected to 25, 35 and 40°C for 1 week.\\u000a The

  19. Stress Mechanism about Field Lightning Surge of High Voltage BJT Based Line Driver for ADSL System

    Microsoft Academic Search

    Jae-seong Jeong; Jae-hyun Lee; Jong-shin Ha; Sang-deuk Park

    2005-01-01

    In this paper, we have verified stress root caused by lightning surge in High voltage BJT based line driver of ADSL telecommunication and created failure mechanism. To reproduce damages in Line driver, we have applied STD surge waveform in operating condition, which is specified in IEC-6000-4-5, to component and board level. Visual isolation for Damage root was conducted with Real-time

  20. Mechanisms of Stress Corrosion Cracking for Iron-Based Alloys in High-Temperature Water

    Microsoft Academic Search

    X. Y. Zhou; A. Y. Bahraloloom; J. Y. Congleton

    1998-01-01

    Stress corrosion cracking (SCC) susceptibilities of a series of iron-based alloys (IBA), including some high-purity irons, were evaluated in lithiated water at temperatures up to 300 C. Inclusion distributions in each material were established using quantitative metallography and energy dispersive x-ray analysis (EDX). Electrochemical measurements were performed to investigate film formation kinetics. Results showed the minimum potential for SCC was

  1. The influence of biaxial stresses on high-cycle fatigue-crack propagation

    Microsoft Academic Search

    G. G. Garrett; P. R. G. Anderson; I. M. H. Charvat

    1980-01-01

    Arising from a design study, an examination has been made of the problems associated with evaluating the fatigue behavior of an I-beam section joined to a transverse stiffener, loaded in biaxial bending. A laboratory test rig has been designed to study high-frequency (40–230 Hz) fatigue-crack propagation in the tensile flange of a composite aluminum I-section, for a range of stress

  2. Stress Analysis of a High Temperature Superconductor Coil Wound With Bi-2223/Ag Tapes for High Field HTS/LTS NMR Magnet Application

    E-print Network

    Kiyoshi, Tsukasa

    The electromagnetic stress distribution inside a HTS insert is one of the key issues for construction of a high field high/low temperature superconductor (HTS/LTS) magnet. The rmiddotJmiddotB formulae is widely used for ...

  3. Growth and characterization of highly oriented AlN films by DC reactive sputtering

    NASA Astrophysics Data System (ADS)

    Panda, Padmalochan; Sravani, Bulusu; Ramaseshan, R.; Ravi, N.; Jose, Feby; Dash, S.; Tyagi, A. K.

    2015-06-01

    Wurtzite type AlN thin films were grown on Si (100) substrates at substrate temperatures (S.T.) varying from RT to 600 °C using DC reactive magnetron sputtering by keeping the parameters such as Ar/N2, power and target to substrate distance (TSD) constant. Evolution of preferred orientation of the deposited films was studied by GIXRD and a-axis orientation was observed at 400 °C. The residual stress measurement of these films was carried out by sin2? technique and they varied from tensile to compressive (R.T. to 600 °C). Highest hardness (HIT) was observed for 400 °C as 20 GPa, whereas highest modulus was observed for 600 °C as 264 GPa.

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

    SciTech Connect

    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

    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}.

  5. AlGaN-based high-performance metal–semiconductor–metal photodetectors

    Microsoft Academic Search

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

    2007-01-01

    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?10A\\/cm2 at a 50V bias, which is four orders of magnitude lower compared to control devices. A 229nm cut-off wavelength, a peak responsivity of 0.53A\\/W at

  6. A high-power AlGaN\\/GaN heterojunction field-effect transistor

    Microsoft Academic Search

    Seikoh Yoshida; Hirotatsu Ishii; Jiang Li; Deliang Wang; Masakazu Ichikawa

    2003-01-01

    We fabricated an AlGaN\\/GaN heterojunction field effect transistor (HFET) with a very low on-state resistance. An undoped Al0.2Ga0.8N(30 nm)\\/GaN(2 ?m) heterostructure was grown on a sapphire substrate using gas-source molecular-beam epitaxy. The undoped GaN layer had a high resistivity (above 10 M?) and the breakdown field of the undoped layer was about 2 MV\\/cm. Si-doped GaN with a carrier concentration

  7. Investigation of the dynamic mechanical behavior of polyetheretherketone (PEEK) in the high stress tensile regime

    NASA Astrophysics Data System (ADS)

    Berer, M.; Major, Z.; Pinter, G.; Constantinescu, D. M.; Marsavina, L.

    2014-11-01

    Due to its outstanding mechanical performance both in static and dynamic loading and its resistance up to very high temperatures, Polyetheretherketone (PEEK) has attracted many practical applications. The loaded contact state for the application of PEEK rolls as bearing elements was recently analyzed by the corresponding author. High irreversible deformations on the mantle side were caused by the rolling contact and thus the rolling performance is supposed to be strongly affected by the dynamic mechanical properties of this irreversibly deformed material. Tensile fatigue tests at various stress levels up to the thermally dominated fatigue regime were conducted in order to get information regarding the dynamic mechanical material behavior at high stress regimes. Two types of PEEK (annealed and untreated) were investigated and two load ratios, R, were used (0.1 and 0.5). During the fatigue tests extensometer strain, load and surface temperature were recorded and a quantitative hysteresis loop analysis with calculated secant modulus and dynamic modulus was performed. Furthermore, the concept of isocyclic stress-strain diagrams was applied to enlarge and confirm the results obtained from the hysteresis loop analysis. A sharp transition between thermally dominated and mechanically dominated fatigue regimes was found for both PEEK types (annealed and untreated) and for both load ratios. Moreover, the annealed PEEK was stiffer in the tensile fatigue tests than the untreated material. Both examined PEEK types showed distinct hardening throughout the fatigue tests which made them "more elastic" (higher stiffness and less damping).

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

    NASA Astrophysics Data System (ADS)

    Li, Xinghua; Vaddi, Butchi R.

    2011-03-01

    Chemically strengthened glass is finding increasing use in handheld, IT and TV cover glass applications. Chemically strengthened glass, particularly with high (>600MPa) compressive stress (CS) and deeper depth of layer (DOL), enable to retain higher strength after damage than non-strengthened glass when its surface is abraded. Corning Gorilla® Glass has particularly proven to be advantageous over competition in this attribute. However, due to high compressive stress (CS) and Central Tension (CT) cutting ion-exchanged glass is extremely difficult and often unmanageable where ever the applications require dicing the chemically strengthened mother glass into smaller parts. We at Corning have developed a CO2 laser scribe and break method (LSB) to separate a single chemically strengthened glass sheet into plurality of devices. Furthermore, CO2 laser scribe and break method enables debris-free separation of glass with high edge strength due to its mirror-like edge finish. We have investigated laser scribe and break of chemically strengthened glass with surface compressive stress greater than 600 MPa. In this paper we present the results of CO2 scribe and break method and underlying laser scribing mechanisms. We demonstrated cross-scribe repetitively on GEN 2 size chemically strengthened glass substrates. Specimens for edge strength measurements of different thickness and CS/DOL glass were prepared using the laser scribe and break technique. The specimens were tested using the standard 4-point bend method and the results are presented.

  9. Subcellular proteomic characterization of the high-temperature stress response of the cyanobacterium Spirulina platensis

    PubMed Central

    Hongsthong, Apiradee; Sirijuntarut, Matura; Yutthanasirikul, Rayakorn; Senachak, Jittisak; Kurdrid, Pavinee; Cheevadhanarak, Supapon; Tanticharoen, Morakot

    2009-01-01

    The present study examined the changes in protein expression in Spirulina platensis upon exposure to high temperature, with the changes in expression analyzed at the subcellular level. In addition, the transcriptional expression level of some differentially expressed proteins, the expression pattern clustering, and the protein-protein interaction network were analyzed. The results obtained from differential expression analysis revealed up-regulation of proteins involved in two-component response systems, DNA damage and repair systems, molecular chaperones, known stress-related proteins, and proteins involved in other biological processes, such as capsule formation and unsaturated fatty acid biosynthesis. The clustering of all differentially expressed proteins in the three cellular compartments showed: (i) the majority of the proteins in all fractions were sustained tolerance proteins, suggesting the roles of these proteins in the tolerance to high temperature stress, (ii) the level of resistance proteins in the photosynthetic membrane was 2-fold higher than the level in two other fractions, correlating with the rapid inactivation of the photosynthetic system in response to high temperature. Subcellular communication among the three cellular compartments via protein-protein interactions was clearly shown by the PPI network analysis. Furthermore, this analysis also showed a connection between temperature stress and nitrogen and ammonia assimilation. PMID:19723342

  10. Chronic stress of rainbow trout Oncorhynchus mykiss at high altitude: a field study.

    PubMed

    Hunt von Herbing, I; Pan, T-C F; Méndez-Sánchez, F; Garduño-Paz, M; Hernández-Gallegos, O; Ruiz-Gómez, M L; Rodríguez-Vargas, G

    2015-07-01

    The stress response of Oncorhynchus mykiss in high-altitude farms in central Mexico was investigated over two seasons: the cool (9·1-13·7° C) dry winter season, and the warmer (14·7-15·9° C), wetter summer season. Fish were subjected to an acute stress test followed by sampling of six physiological variables: blood cortisol, glucose, lactate, total antioxidant capacity, haemoglobin concentration and per cent packed cell volume (VPC %). Multivariate analyses revealed that lactate and total antioxidant capacity were significantly higher in the summer, when water temperatures were warmer and moderate hypoxia (4·9-5·3 mg l(-1) ) prevailed. In contrast, plasma cortisol was significantly higher in the winter (mean ± s.e.: 76·7 ± 4·0 ng ml(-1) ) when temperatures were cooler and dissolved oxygen levels higher (6·05-7·9 mg l(-1) ), than in the summer (22·7 ± 3·8 ng ml(-1) ). Haemoglobin concentrations (mg dl(-1) ) were not significantly different between seasons, but VPC % was significantly higher in the summer (50%) than in the winter (35%). These results suggest that in summer, effects of high altitude on farmed fish are exacerbated by stresses of high temperatures and hypoxia, resulting in higher blood lactate, increased total antioxidant capacity and elevated VPC % levels. PMID:26148653

  11. Physiological and biochemical responses of Prorocentrum minimum to high light stress

    NASA Astrophysics Data System (ADS)

    Park, So Yun; Choi, Eun Seok; Hwang, Jinik; Kim, Donggiun; Ryu, Tae Kwon; Lee, Taek-Kyun

    2009-12-01

    Prorocentrum minimum is a common bloomforming photosynthetic dinoflagellate found along the southern coast of Korea. To investigate the adaptive responses of P. minimum to high light stress, we measured growth rate, and generation of reactive oxidative species (ROS), superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) in cultures exposed to normal (NL) and high light levels (HL). The results showed that HL (800 ?mol m-2 s-1) inhibited growth of P. minimum, with maximal inhibition after 7-9 days. HL also increased the amount of ROS and MDA, suggesting that HL stress leads to oxidative damage and lipid peroxidation in this species. Under HL, we first detected superoxide on day 4 and H2O2 on day 5. We also detected SOD activity on day 5 and CAT activity on day 6. The level of lipid peroxidation, an indicator of cell death, was high on day 8. Addition of diphenyleneiodonium (DPI), an NAD(P)H inhibitor, decreased the levels of superoxide generation and lipid peroxidation. Our results indicate that the production of ROS which results from HL stress in P. minimum also induces antioxidative enzymes that counteract oxidative damage and allow P. minimum to survive.

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

    SciTech Connect

    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

    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.

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

    NASA Astrophysics Data System (ADS)

    Killat, N.; Montes Bajo, M.; Paskova, T.; Evans, K. R.; Leach, J.; Li, X.; Özgür, Ü.; Morkoç, H.; Chabak, K. D.; Crespo, A.; Gillespie, J. K.; Fitch, R.; Kossler, M.; Walker, D. E.; Trejo, M.; Via, G. D.; Blevins, J. D.; Kuball, M.

    2013-11-01

    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.

  14. Stress relaxation behavior of nanocluster-strengthened ferritic alloy at high temperatures

    SciTech Connect

    Kim, Jeoung H [ORNL; Byun, Thak Sang [ORNL; Hoelzer, David T [ORNL

    2012-01-01

    Stress relaxation behavior was investigated for the nanoclusters/dispersoids-strengthened steels including the nanostructured ferritic alloy 14YWT (SM10), oxide-dispersion strengthened (ODS) Eurofer97, and commercial ODS steel PM2000. The stress relaxation tests were carried out at high temperatures ranging from 600 to 1000 degrees C. Overall, the relaxation rates of 14YWT and ODS-Eurofer97 were lower than that of PM2000. To analyze the strain rate sensitivity of the alloys, the load drop-time curves were converted to the stress-strain rate curves. In the log-log plots of these curves, no significant change in slope was observed in the strain rate range of 2 x 10(-5)-1 x 10(-3)s(-1). At 600 degrees C, 14YWT and ODS-Eurofer97 have similar activation values of similar to 50b(3) while PM2000 has similar to 100b(3). Above 700 degrees C, the differences of the activation energy among alloys become more noticeable with increasing temperature. The activation energies of the three alloys were derived and compared. The rate-controlling mechanisms in the stress relaxation of the three nanoclusters/dispersoids-hardened alloys include dislocation glide and climb, and further study is necessary to clarify detailed contributing mechanisms.

  15. Stress relaxation behavior of nanocluster-strengthened ferritic alloy at high temperatures

    NASA Astrophysics Data System (ADS)

    Han Kim, Jeoung; Sang Byun, Thak; Hoelzer, D. T.

    2012-06-01

    Stress relaxation behavior was investigated for the nanoclusters/dispersoids-strengthened steels including the nanostructured ferritic alloy 14YWT (SM10), oxide-dispersion strengthened (ODS) Eurofer97, and commercial ODS steel PM2000. The stress relaxation tests were carried out at high temperatures ranging from 600 to 1000 °C. Overall, the relaxation rates of 14YWT and ODS-Eurofer97 were lower than that of PM2000. To analyze the strain rate sensitivity of the alloys, the load drop-time curves were converted to the stress-strain rate curves. In the log-log plots of these curves, no significant change in slope was observed in the strain rate range of 2 × 10-5-1 × 10-3s-1. At 600 °C, 14YWT and ODS-Eurofer97 have similar activation values of ˜50b3 while PM2000 has ˜100b3. Above 700 °C, the differences of the activation energy among alloys become more noticeable with increasing temperature. The activation energies of the three alloys were derived and compared. The rate-controlling mechanisms in the stress relaxation of the three nanoclusters/dispersoids-hardened alloys include dislocation glide and climb, and further study is necessary to clarify detailed contributing mechanisms.

  16. Compression of dispersions to high stress under electric fields: effects of concentration and dispersing oil.

    PubMed

    Lynch, Rachel; Meng, Y; Filisko, F E

    2006-05-01

    Dispersions of various concentrations (15-35%) were prepared in silicone oils of vastly different viscosities (40, 1000, 10,000, and 30,000 mPa s) and compressed to high values of stress while under an electric field of 2 kV/mm. A purpose of this study was to observe the effect of compression and E field simultaneously on these dispersions and assess predictions of most common and relevant theories. As shown, static stresses of over 1000 kPa could readily be obtained although the data presented here were held below 300 kPa to protect the load cell and equipment. The results are compared to and discussed in terms of a power law fit for stress vs gap since most theories predict such a dependence. The PL exponents fall around 3 ranges: (-2), (-3), and much less than (-3). The PL coefficients however reflect in systematic way the viscosities of the dispersing oils. The compressive stress vs strain behavior is studied with regard to particle concentration and dispersing oil viscosity. PMID:16309696

  17. AlN/3C-SiC composite plate enabling high-frequency and high-Q micromechanical resonators.

    PubMed

    Lin, Chih-Ming; Chen, Yung-Yu; Felmetsger, Valery V; Senesky, Debbie G; Pisano, Albert P

    2012-05-22

    An AlN/3C-SiC composite layer enables the third-order quasi-symmetric (QS(3)) Lamb wave mode with a high quality factor (Q) characteristic and an ultra-high phase velocity up to 32395 ms(-1). A Lamb wave resonator utilizing the QS(3) mode exhibits a low motional impedance of 91 ? and a high Q of 5510 at a series resonance frequency (f(s)) of 2.92 GHz, resulting in the highest f(s)·Q product of 1.61 × 10(13) Hz among the suspended piezoelectric thin film resonators reported to date. PMID:22495881

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

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

    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.

  20. Microstructure evolution of Al12SiCuNiMg alloy under high temperature low cycle fatigue

    E-print Network

    Volinsky, Alex A.

    behavior of cast Al­Si alloys. Numerous studies show a decrease in fatigue life with increase in the size of cast Al­Si alloys in cyclic loading at high temperature. Due to the disadvantages of high thermal of aluminum alloys as piston materials is severely limited in harsh environments. It is well known that high